Handbook of Petrochemical Processes

HANDBOOK OF PETROCHEMICAL PROCESSES JAMES G SPEIGHT CRC Press Taylor Francis Group Handbook of Petrochemical Processes Chemical Industries Founding Editor Heinz Heinemann Series Editor James G Speight The Chemical Industries Series offers indepth texts related to all aspects of the chemical indus tries from experts and leaders in academia and industry The titles explore recent developments and best practices that facilitate successful process control and commercialization of industrial processes and products to help meet changing market demands and match the stringent emission standards The series focuses on technologies process development improvements and new appli cations to ensure proper performance in industrial units and evaluation of novel process designs that will result in production of valuable products from efficient and economical processes Modeling of Processes and Reactors for Upgrading of Heavy Petroleum Jorge Ancheyta Synthetics Mineral Oils and BioBased Lubricants Chemistry and Technology Second Edition Leslie R Rudnick Transport Phenomena Fundamentals Third Edition Joel Plawsky The Chemistry and Technology of Petroleum Fifth Edition James G Speight Refining Used Lubricating Oils James Speight and Douglas I Exall Petroleum and Gas Field Processing Second Edition Hussein K AbdelAal Mohamed A Aggour and Mohamed A Fahim Handbook of Refinery Desulfurization Nour Shafik ElGendy and James G Speight Handbook of Petroleum Refining James G Speight Advances in Refining Catalysis Deniz Uner Lubricant Additives Chemistry and Applications Third Edition Leslie R Rudnick Handbook of Petrochemical Processes James G Speight For more information about this series please visit httpswwwcrcpresscomChemicalIndustries bookseriesCRCCHEMINDUS Handbook of Petrochemical Processes James G Speight CRC Press Taylor Francis Group 6000 Broken Sound Parkway NW Suite 300 Boca Raton FL 334872742 2019 by Taylor Francis Group LLC CRC Press is an imprint of Taylor Francis Group an Informa business No claim to original US Government works Printed on acidfree paper International Standard Book Number13 9781498729703 Hardback This book contains information obtained from authentic and highly regarded sources Reasonable efforts have been made to publish reliable data and information but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint Except as permitted under US Copyright Law no part of this book may be reprinted reproduced transmitted or utilized in any form by any electronic mechanical or other means now known or hereafter invented including photocopying microfilming and recording or in any information storage or retrieval system without written per mission from the publishers For permission to photocopy or use material electronically from this work please access wwwcopyrightcom http wwwcopyrightcom or contact the Copyright Clearance Center Inc CCC 222 Rosewood Drive Danvers MA 01923 9787508400 CCC is a notforprofit organization that provides licenses and registration for a variety of users For organizations that have been granted a photocopy license by the CCC a separate system of payment has been arranged Trademark Notice Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe Library of Congress CataloginginPublication Data Names Speight James G author Title Handbook of petrochemical processes James G Speight Description Boca Raton FL CRC PressTaylor Francis Group 2019 Series Chemical industries Identifiers LCCN 2019003675 ISBN 9781498729703 hardback acidfree paper Subjects LCSH PetroleumRefining Petroleum chemicals Chemical processes Classification LCC TP6903 S64 2019 DDC 66553dc23 LC record available at httpslccnlocgov2019003675 Visit the Taylor Francis Website at httpwwwtaylorandfranciscom and the CRC Press Web site at httpwwwcrcpresscom v Contents Prefacexv About the Author xvii Chapter 1 The Petrochemical Industry 1 11 Introduction 1 12 Historical Aspects and Overview 10 13 The Petrochemical Industry 11 14 Petrochemicals 17 141 Primary Petrochemicals 19 142 Products and End Use 19 15 Production of Petrochemicals 20 16 The Future 24 References 29 Chapter 2 Feedstock Composition and Properties 31 21 Introduction 31 22 Natural Gas 31 221 Composition and Properties 33 222 Natural Gas Liquids 42 223 Gas Condensate 43 224 Gas Hydrates 44 225 Other Types of Gases 46 2251 Biogas 47 2252 Coalbed Methane 48 2253 Coal Gas 49 2254 Geopressurized Gas 51 2255 Landfill Gas 51 2256 Refinery Gas 53 2257 Synthesis Gas 57 2258 Tight Gas58 23 Petroleum 59 231 Composition and Properties 59 2311 Opportunity Crude Oil 61 2312 High Acid Crude Oil 61 2313 Foamy Oil 62 2314 Tight Oil 62 232 Other PetroleumDerived Feedstocks 63 2321 Naphtha 63 2322 Kerosene 64 2323 Fuel Oil 65 2324 Gas Oil 67 2325 Residua 67 2326 Used Lubricating Oil 68 24 Heavy Oil Extra Heavy Oil and Tar Sand Bitumen 68 241 Heavy Oil 69 vi Contents 242 Extra Heavy Oil 69 243 Tar sand Bitumen 71 References 74 Chapter 3 Other FeedstocksCoal Oil Shale and Biomass 79 31 Introduction 79 32 Coal 81 321 Coal Feedstocks 82 322 Properties and Composition 83 323 Conversion 83 324 Coal Tar Chemicals 85 33 Oil Shale 90 331 Shale Oil Production 90 332 Shale Oil Properties 91 3321 Hydrocarbon Products 92 3322 NitrogenContaining Compounds 93 3323 OxygenContaining Compounds 94 3324 SulfurContaining Compounds 94 34 Biomass94 341 Biomass Feedstocks 97 3411 Carbohydrates 99 3412 Vegetable Oils 99 3413 Plant Fibers 99 342 Biorefining 100 3421 Pyrolysis 103 3422 Gasification 103 3423 Anaerobic Digestion 107 3424 Fermentation 110 343 Chemicals from Biomass 111 3431 Gaseous Products 111 3432 Liquid Products 112 3433 Solid Products 114 35 Waste 114 References 115 Chapter 4 Feedstock Preparation 119 41 Introduction 119 42 Gas Streams 120 421 Sources 121 4211 Gas Streams from Natural Gas 121 4212 Natural Gas Liquids and Liquefied Petroleum Gas 123 4213 Gas Streams from Crude Oil 124 422 Gas Processing 127 4221 Acid Gas Removal 128 4222 Recovery of Condensable Hydrocarbon Derivatives 137 4223 Water Removal 142 4224 Nitrogen Removal 145 4225 The Claus Process 145 43 Petroleum Streams 147 vii Contents 431 Refinery Configuration 149 432 Cracking Processes 150 4321 Thermal Cracking Processes 150 4322 Catalytic Cracking Processes 153 433 Dehydrogenation Processes 155 434 Dehydrocyclization Processes 157 44 Streams from Coal Oil Shale and Biomass 158 441 Coal 158 4411 Coal Gas 158 4412 Coal Liquids 158 442 Oil Shale 159 4421 Oil Shale Gas 159 4422 Shale Oil 160 443 Biomass 161 4431 Biogas 161 4432 Bioliquids 161 References 162 Chapter 5 Feedstock Preparation by Gasification 165 51 Introduction 165 52 Gasification Chemistry 168 521 General Aspects 169 522 Pretreatment 170 523 Reactions 171 5231 Primary Gasification 174 5232 Secondary Gasification 174 5233 WaterGas Shift Reaction 176 5234 Carbon Dioxide Gasification 177 5235 Hydrogasification 178 5236 Methanation 178 53 Gasification Processes 179 531 Gasifiers 180 532 FT Synthesis 181 533 Feedstocks 183 5331 Heavy Feedstocks 183 5332 Solvent Deasphalter Bottoms 184 5333 Asphalt Tar and Pitch 184 5334 Petroleum Coke 186 5335 Coal 188 5336 Biomass 189 5337 Solid Waste 191 5338 Black Liquor 193 54 Gasification in a Refinery 193 541 Gasification of Heavy Feedstocks 195 542 Gasification of Heavy Feedstocks with Coal 195 543 Gasification of Heavy Feedstocks with Biomass 196 544 Gasification of Heavy Feedstocks with Waste 198 55 Gas Production and Other Products 198 551 Gaseous Products 199 5511 Synthesis Gas 199 viii Contents 5512 Low Btu Gas 200 5513 Medium Btu Gas 200 5514 High Btu Gas 201 552 Liquid Products 201 553 Solid Products 202 56 The Future 202 References 204 Chapter 6 Chemicals from Paraffin Hydrocarbons 209 61 Introduction 209 62 Methane 211 621 Physical Properties 212 622 Chemical Properties 213 623 Chemicals from Methane 215 6231 Carbon Disulfide 216 6232 Ethylene 217 6233 Hydrogen Cyanide 218 6234 Chloromethane Derivatives 218 6235 Synthesis Gas 220 6236 Urea 223 6237 Methyl Alcohol 223 6238 Formaldehyde 226 6239 Aldehyde Derivatives 229 62310 Ethylene Glycol 229 62311 Nitration 230 62312 Oxidation 230 62313 Carboxylic Acids 231 62314 Alkylation 231 62315 Thermolysis 232 624 Oxidative Coupling 233 63 Ethane 235 631 Physical Properties 235 632 Chemical Properties 236 633 Chemicals from Ethane 237 64 Propane 238 641 Physical Properties 238 642 Chemical Properties 239 643 Chemicals from Propane 240 6431 Oxidation 240 6432 Chlorination 240 6433 Dehydrogenation 241 6434 Nitration 247 65 Butane Isomers 247 651 Physical Properties 249 652 Chemical Properties 249 653 Chemicals from Butane 250 6531 Oxidation 250 6532 Production of Aromatics 252 6533 Isomerization 252 654 Chemicals from Isobutane 252 ix Contents 66 Liquid Petroleum Fractions and Residues 252 661 Naphtha 254 6611 Physical Properties 254 6612 Chemical Properties 255 6613 Chemicals from Naphtha 256 662 Kerosene 257 6621 Physical Properties 257 6622 Chemical Properties 257 6623 Chemicals from Kerosene 258 663 Gas Oil 258 6631 Physical Properties 258 6632 Chemical Properties 259 6633 Chemicals from Gas Oil 259 664 Fuel Oil 260 6641 Physical Properties 261 6642 Chemical Properties 261 6643 Chemicals from Fuel Oil 262 665 Resids 262 6651 Physical Properties 263 666 Used Lubricating Oil 263 667 Naphthenic Acids 263 668 Chemicals from Liquid Petroleum Fractions and Residues 264 6681 Oxidation 265 6682 Chlorination 265 6683 Sulfonation 265 6684 Other Products 266 References 266 Chapter 7 Chemicals from Olefin Hydrocarbons 269 71 Introduction 269 72 Chemicals from Ethylene 271 721 Alcohols273 722 Alkylation 275 723 Halogen Derivatives 276 724 Oxygen Derivatives 277 7241 Ethylene Glycol 279 7242 Ethoxylates 281 7243 Ethanolamines 282 7244 13Propanediol 282 7245 Acetaldehyde283 725 Carbonylation 285 726 Chlorination286 7261 Vinyl Chloride 286 7262 Perchloroethylene and Trichloroethylene 287 727 Hydration 287 728 Oligomerization 288 729 Polymerization 289 7210 1 Butylene 290 7211 Polymerization 290 73 Chemicals from Propylene 291 x Contents 731 Oxidation 294 732 Ammoxidation 296 733 Oxyacylation 299 734 Chlorination300 735 Hydration 300 736 Addition of Organic Acids 302 737 Hydroformylation 302 738 Disproportionation 303 739 Alkylation 303 74 Chemicals from C4 Olefins 303 741 Butylene 304 7411 Oxidation 306 7412 Hydration 308 7413 Isomerization 309 7414 Metathesis 309 7415 Oligomerization 310 742 Isobutylene 310 7421 Oxidation 311 7422 Epoxidation 311 7423 Addition of Alcohols 312 7424 Hydration 312 7425 Carbonylation 312 7426 Dimerization 312 75 Chemicals from Diolefins 313 751 Chemicals from Butadiene 313 7511 Adiponitrile 314 7512 Hexamethylenediamine 314 7513 Adipic Acid 314 7514 Butanediol 315 7515 Chloroprene 315 7516 Cyclic Oligomers 316 752 Isoprene 316 76 Chemicals from Acetylene 316 References 321 Chapter 8 Chemicals from Aromatic Hydrocarbons 323 81 Introduction 323 82 Chemicals from Benzene 331 821 Alkylation 334 822 Chlorination 339 823 Hydrogenation 340 824 Nitration342 825 Oxidation 343 83 Chemicals from Toluene 343 831 Carbonylation 345 832 Chlorination345 833 Dealkylation 347 834 Disproportionation 348 835 Nitration348 836 Oxidation 350 xi Contents 84 Chemicals from Xylene Isomers 352 85 Chemicals from Ethylbenzene 355 References 357 Chapter 9 Chemicals from Nonhydrocarbons 359 91 Introduction 359 92 Ammonia 360 921 Production 361 922 Properties and Uses 362 93 Carbon Black 363 931 Production 363 932 Properties and Uses 364 94 Carbon Dioxide and Carbon Monoxide 364 941 Production 365 942 Properties and Uses 365 95 Hydrazine 366 951 Production 366 952 Properties and Uses 367 96 Hydrogen 368 961 Production 368 962 Properties and Uses 370 97 Nitric Acid 371 971 Production 372 972 Properties and Uses 372 98 Sulfur 373 981 Production 373 982 Properties and Uses 375 99 Sulfuric Acid 376 991 Production 376 992 Properties and Uses 379 910 Synthesis Gas 380 9101 Production 381 9102 Properties and Uses 382 References 383 Chapter 10 Chemicals from the FischerTropsch Process 385 101 Introduction 385 102 History and Development of the FischerTropsch Process 388 103 Synthesis Gas 390 104 Production of Synthesis Gas 392 1041 Feedstocks 393 1042 Processes 395 10421 Steam Reforming 395 10422 Autothermal Reforming 398 10423 Combined Reforming 399 10424 Partial Oxidation400 1043 Product Distribution 401 105 Process Parameters 401 106 Reactors and Catalysts 403 xii Contents 1061 Reactors 403 1062 Catalysts 405 107 Products and Product Quality 409 1071 Products 409 1072 Product Quality 410 108 FischerTropsch Chemistry 412 1081 Chemical Principles 412 1082 Refining FischerTropsch Products 416 References 417 Chapter 11 Monomers Polymers and Plastics 421 111 Introduction 421 112 Processes and Process Chemistry 425 1121 Addition Polymerization 426 1122 Free Radical Polymerization 427 1123 Cationic Polymerization 427 1124 Anionic Polymerization 428 1125 Coordination Polymerization 428 1126 Condensation Polymerization 429 1127 RingOpening Polymerization 430 113 Polymer Types 431 1131 Polyethylene 435 11311 LowDensity Polyethylene 435 11312 HighDensity Polyethylene 436 11313 Linear LowDensity Polyethylene 436 11314 Properties and Uses 436 1132 Polypropylene 437 1133 Polyvinyl Chloride 438 1134 Polystyrene 439 1135 Nylon Resins 440 1136 Polyesters 441 1137 Polycarbonates 441 1138 Polyether Sulfones 442 1139 Polyphenylene Oxide 444 11310 Polyacetal 444 11311 Butadiene Polymers and Copolymers 445 114 Plastics and Thermoplastics 446 1141 Classification 449 1142 Chemical Structure 450 1143 Properties 451 11431 Mechanical Properties 451 11432 Chemical Properties 452 11433 Electrical Properties 453 11434 Optical Properties 453 115 Thermosetting Plastics 453 1151 Polyurethanes 453 1152 Epoxy Resins 455 1153 Unsaturated Polyesters 455 1154 PhenolFormaldehyde Resins 455 1155 Amino Resins 456 xiii Contents 1156 Polycyanurates 457 116 Synthetic Fibers 457 1161 Polyester Fibers 458 1162 Polyamides 459 11621 Nylon 66 460 11622 Nylon 6 460 11623 Nylon 12460 11624 Nylon 4 460 11625 Nylon 11 461 11626 Other Nylon Polymers 461 1163 Acrylic and Modacrylic Fibers 461 1164 Graphite Fibers 462 1165 Polypropylene Fibers 462 117 Synthetic Rubber 462 1171 StyreneButadiene Rubber 463 1172 Nitrile Rubber 464 1173 Polyisoprene 464 1174 Polychloroprene 465 1175 Butyl Rubber 465 1176 EthylenePropylene Rubber 465 References 465 Chapter 12 Pharmaceuticals 467 121 Introduction 467 122 Medicinal Oils from Petroleum 470 1221 Mineral OilWhite Oil 471 1222 Petroleum Jelly 472 1223 Paraffin Wax 474 1224 Bitumen 475 1225 Solvents 476 123 Pharmaceutical Products 478 124 Production of Pharmaceuticals 479 1241 Acetaminophen 480 1242 Aleve 480 1243 Aspirin 481 1244 Cepacol 482 1245 Excedrin 482 1246 Gaviscon 482 1247 Ibuprofen 483 1248 Kaopectate 483 1249 LMenthol 484 12410 Orajel 485 12411 Tylenol 485 12412 Zantac 485 References 486 Conversion Tables 489 Glossary 493 Index 557 Taylor Francis Taylor Francis Group httptaylorandfranciscom xv Preface The petrochemical industry had its modern origins in the later years of the 19th century However the production of products from naturally occurring bitumen is a much older industry There is evi dence that the ancient Bronze Age towns of Tuttul Syria and Hit also spelled Heet Iraq used bitu men from seepages as a caulking material and mastic Also Arabian scientists knew that attempts to distill the bitumen caused it to decompose into a variety of products By the time that the 19th century had dawned it was known that kerosene a fuel for heating and cooking was the primary product of the petroleum industry in the 1800s Rockefeller and other refinery owners considered gasoline a useless byproduct of the distillation process But all of that changed around 1900 when electric lights began to replace kerosene lamps and automobiles came in the scene New petroleum fuels were also needed to power the ships and airplanes used in World War I After the war an increasing number of farmers began to operate tractors and other equip ment powered by oil The growing demand for petrochemicals and the availability of petroleum and natural gas caused the industry to quickly expand in the 1920s and 1930s During World War II vast amounts of oil were produced and made into fuels and lubricants The United States supplied more than 80 of the aviation gasoline used by the allies during the war American oil refineries also manufactured synthetic rubber toluene an ingredient in TNT medicinal oils and other key military supplies The term petrochemicals represents a large group of chemicals manufactured from petroleum and natural gas as distinct from fuels and other products that are also derived from petroleum and natural gas by a variety of processes and used for a variety of commercial purposes Petrochemical products include such items as plastics soaps and detergents solvents drugs fertilizers pesticides explosives synthetic fibers and rubbers paints epoxy resins and flooring and insulating materials Petrochemicals are found in products as diverse as aspirin luggage boats automobiles aircraft polyester clothes and recording discs and tapes It is the changes in product demand that have been largely responsible for the evolution of the petroleum industry from the demand for asphalt mastic used in ancient times to the current high demand for gasoline other liquid fuels an products as well increasing demand for as a wide variety of petrochemicals As a result the petrochemical industry is a huge field that encompasses many commercial chemi cals and polymers The organic chemicals produced in the largest volumes are methanol ethylene propylene butadiene benzene toluene and xylenes Ethylene propylene and butadiene along with butylenes are collectively called olefins which belong to a class of unsaturated aliphatic hydrocar bons having the general formula CnH2n Olefins contain one or more double bonds which make them chemically reactive Benzene toluene and xylenes commonly referred to as aromatics are unsaturated cyclic hydrocarbons containing one or more rings Olefins aromatics and methanol are precursors to a variety of chemical products and are generally referred to as primary petrochemi cals Given the number of organic chemicals and the variety and multitude of ways by which they are converted to consumer and industrial products this report focuses primarily on these seven petrochemicals their feedstock sources and their end uses Furthermore because ethylene and propylene are the major building blocks for petrochemicals alternative ways for their production have always been sought The main route for producing ethyl ene and propylene is steam cracking which is an energyextensive process Fluid catalytic cracking FCC is also used to supplement the demand for these low molecular weight olefins Basic chemicals and plastics are the key building blocks for manufacture of a wide variety of durable and nondurable consumer goods Considering the items we encounter every daythe clothes we wear construction materials used to build our homes and offices a variety of household appliances and electronic equipment food and beverage packaging and many products used in various modes of transportationchemical and plastic materials provide the fundamental building xvi Preface blocks that enable the manufacture of the vast majority of these goods Demand for chemicals and plastics is driven by global economic conditions which are directly linked to demand for consumer goods The search for alternative ways to produce monomers and chemicals from sources other than crude oil In fact FisherTropsch technology which produces in addition to fuels low molecular weight olefins could enable nonpetroleum feedstocks such as extra heavy oil tar sand bitumen coal oil shale and biomass to be used as feedstocks for petrochemicals In the book the reactions and processes involved in transforming petroleumbased hydrocar bons into the chemicals that form the basis of the multibillion dollar petrochemical industry are reviewed and described In addition the book includes information on new process developments for the production of raw materials and intermediates for petrochemicals This book will provide the readers with a valuable source of information containing insights into petrochemical reactions and products process technology and polymer synthesis The book will also provide the reader with descriptions of role of nonpetroleum sources in the production of chemicals and present to the reader alternate routes to chemicals Dr James G Speight CDW Inc Laramie Wyoming 82070 USA xvii About the Author Dr James G Speight has doctorate degrees in Chemistry Geological Sciences and Petroleum Engineering and is the author of more than 80 books in petroleum science petroleum engineering and environmen tal sciences Dr Speight has more than 50 years of experience in areas associated with i the properties recovery and refining of reservoir fluids conven tional petroleum heavy oil and tar sand bitumen ii the properties and refining of natural gas gaseous fuels iii the production and properties of petrochemicals iv the properties and refining of biomass biofuels biogas and the generation of bioenergy and v the environmental and toxicological effects of fuels His work has also focused on safety issues environmental effects remediation and safety issues as well as reactors associated with the pro duction and use of fuels and biofuels He is the author of more than 70 books in petroleum science petroleum engineering biomass and biofuels and environmental sciences Although he has always worked in private industry which focused on contractbased work he has served as a Visiting Professor in the College of Science University of Mosul Iraq and has also been a Visiting Professor in Chemical Engineering at the following universities University of Missouri Columbia the Technical University of Denmark and the University of Trinidad and Tobago In 1996 Dr Speight was elected to the Russian Academy of Sciences and awarded the Gold Medal of Honor that same year for outstanding contributions to the field of petroleum sciences In 2001 he received the Scientists without Borders Medal of Honor of the Russian Academy of Sciences and was also awarded the Einstein Medal for outstanding contributions and service in the field of Geological Sciences In 2005 the Academy awarded Dr Speight the Gold MedalScientists without Frontiers Russian Academy of Sciences in recognition of Continuous Encouragement of Scientists to Work Together Across International Borders In 2007 Dr Speight received the Methanex Distinguished Professor award at the University of Trinidad and Tobago in recognition of excellence in research Taylor Francis 1 1 The Petrochemical Industry 11 INTRODUCTION The constant demand for hydrocarbon products such as liquid fuels is one of the major driving forces behind the petroleum industry However the other driving force is a major group of hydrocar bon products petrochemicals that are the basis of a major industry There is a myriad of products that have evolved through the short life of the petroleum industry either as bulk fractions or as single hydrocarbon products Tables 11 and 12 And the complexities of product composition have matched the evolution of the products In fact it is the complexity of product composition that has served the industry well and at the same time had an adverse effect on product use A petrochemical is a chemical product developed from petroleum that has become an essen tial part of the modern chemical industry Table 13 Speight 1987 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The chemical industry is in fact the chemical process industry by which a variety of chemicals are manufactured The chemical process industry is in fact subdivided into other categories that are i the chemicals and allied product industries in which chemicals are manufactured from a variety of feedstocks and may then be put to further use ii the rubber and miscellaneous product industries which focus on the manufacture of rubber and plastic materials and iii petroleum refining and related industries which on the basis of the following chapters in this text is now selfexplanatory Thus the petrochemical industry falls under the subcategory of petroleum and related industries In the context of this book the definition of petrochemicals excludes fuel products lubricants asphalt and petroleum coke but does include chemicals produced from other feedstocks such as coal oil shale and biomass which could well be the sources of chemicals in the future Thus pet rochemicals are in the strictest sense different to petroleum products insofar as the petrochemicals are the basic building blocks of the chemical industry Petrochemicals are found in products as diverse as plastics polymers synthetic rubber synthetic fibers detergents industrial chemicals and fertilizers Table 13 Petrochemicals are used for production of several feedstocks and monomers and monomer precursors The monomers after polymerization process create several polymers which ultimately are used to produce gels lubricants elastomers plastics and fibers By way of definition and clarification as it applies to the petrochemical and chemical industry primary raw materials are naturally occurring substances that have not been subjected to chemical TABLE 11 The Various Distillation Fractions of Petroleum Product Lower Carbon Numbera Upper Carbon Numbera Lower bp Ca Upper bp Ca Lower bp Fa Upper bp Fa Liquefied petroleum gas C3 C4 42 1 44 31 Naphtha C5 C17 36 302 97 575 Kerosene C8 C18 126 258 302 575 Light gas oil C12 C20 216 421 345 650 Heavy gas oil C20 345 650 Residuum C20 345 660 a The carbon number and boiling point difficult to assess accurately because of variations in production parameters from refinerytorefinery and are inserted for illustrative purposes only 2 Handbook of Petrochemical Processes changes after being recovered Currently through a variety of intermediates petroleum and natural gas are the main sources of the raw materials because they are the least expensive most readily available and can be processed most easily into the primary petrochemicals An aromatic petro chemical is also an organic chemical compound but one that contains or is derived from the basic benzene ring system Primary petrochemicals include i olefin derivatives such as ethylene propylene and butadiene ii aromatic derivatives such as benzene toluene and the isomers of xylene BTX and iii meth anol However although petroleum contains different types of hydrocarbon derivatives not all hydrocarbon derivatives are used in producing petrochemicals Petrochemical analysis has made it possible to identify some major hydrocarbon derivatives used in producing petrochemicals Speight 2015 From the multitude of hydrocarbon derivatives those hydrocarbon derivatives serving as major raw materials used by petrochemical industries in the production of petrochemicals are i the raw materials obtained from natural gas processing such as methane ethane propane and TABLE 12 Properties of Hydrocarbon Products from Petroleum Molecular Weight Specific Gravity Boiling Point F Ignition Temperature F Flash Point F Flammability Limits in Air vv Benzene 781 0879 1762 1040 12 135665 nButane 581 0601 311 761 76 186841 isobutane 581 109 864 117 180844 nButene 561 0595 212 829 Gas 198965 isobutene 561 196 869 Gas 1890 Diesel fuel 170198 0875 100130 Ethane 301 0572 1275 959 Gas 30125 Ethylene 280 1547 914 Gas 28286 Fuel oil No 1 0875 304574 410 100162 0750 Fuel oil No 2 0920 494 126204 Fuel oil No 4 1980 0959 505 142240 Fuel oil No 5 0960 156336 Fuel oil No 6 0960 150 Gasoline 1130 0720 100400 536 45 1476 nHexane 862 0659 1557 437 7 12570 nHeptane 1002 0668 4190 419 25 100600 Kerosene 1540 0800 304574 410 100162 0750 Methane 160 0553 2587 9001170 Gas 50150 Naphthalene 1282 4244 959 174 090590 Neohexane 862 0649 1215 797 54 119758 Neopentane 721 491 841 Gas 138711 nOctane 1142 0707 2583 428 56 09532 isooctane 1142 0702 2439 837 10 079594 nPentane 721 0626 970 500 40 140780 isopentane 721 0621 822 788 60 131916 nPentene 701 0641 860 569 165770 Propane 441 438 842 Gas 21101 Propylene 421 539 856 Gas 200111 Toluene 921 0867 3211 992 40 127675 Xylene 1062 0861 2811 867 63 100600 3 The Petrochemical Industry butane ii the raw materials obtained from petroleum refineries such as naphtha and gas oil and iii the raw materials such as benzene toluene and the xylene isomers obtained when extracted from reformate the product of reforming processes through catalysts called catalytic reformers in petroleum refineries Parkash 2003 Gary et al 2007 Speight 2008 2014 Hsu and Robinson 2017 Speight 2017 Thus petrochemicals are chemicals derived from petroleum and natural gas and for conve nience of identification petrochemicals can be divided into two groups i primary petrochemicals and ii intermediates and derivatives Figure 11 Primary petrochemicals include olefins ethylene propylene and butadiene aromatics benzene toluene and xylenes and methanol Petrochemical intermediates are generally pro duced by chemical conversion of primary petrochemicals to form more complicated derivative products Petrochemical derivatives can be made in a variety of ways i directly from pri mary petrochemicals ii through intermediate products which still contain only carbon and hydrogen and iii through intermediates which incorporate chlorine nitrogen or oxygen in the TABLE 13 Examples of Products from the Petrochemical Industry Group Areas of Use Plastics and polymers Agricultural water management Packaging Automobiles Telecommunications Health and hygiene Transportation Synthetic rubber Transportation industry Electronics Adhesives Sealants Coatings Synthetic fibers Textile Transportation Industrial fabrics Detergents Health and hygiene Industrial chemicals Pharmaceuticals Pesticides Explosives Surface coating Dyes Lubricating oil additives Adhesives Oil field chemicals Antioxidants Printing ink Paints Corrosion inhibitors Solvents Perfumes Food additives Fertilizers Agriculture 4 Handbook of Petrochemical Processes finished derivative In some cases they are finished products in others more steps are needed to be arrived at the desired composition Moreover petrochemical feedstocks can be classified into several general groups olefins aro matics and methanol a fourth group includes inorganic compounds and synthesis gas mixtures of carbon monoxide and hydrogen In many instances a specific chemical included among the petrochemicals may also be obtained from other sources such as coal coke or vegetable products For example materials such as benzene and naphthalene can be made from either petroleum or coal while ethyl alcohol may be of petrochemical or vegetable origin Thus primary petrochemicals are not end products but are the chemical building blocks for a wide range of chemical and manufactured materials For example petrochemical intermedi ates are generally produced by chemical conversion of primary petrochemicals to form more complicated derivative products Parkash 2003 Gary et al 2007 Speight 2008 2014 Hsu and Robinson 2017 Speight 2017 Petrochemical derivative products can be made in a variety of ways i directly from primary petrochemicals ii through intermediate products which still con tain only carbon and hydrogen and iii through intermediates which incorporate chlorine nitro gen or oxygen in the finished derivative In some cases they are finished products in others more steps are needed to arrive at the desired composition Some typical petrochemical intermediates are i vinyl acetate CH3CO2CHCH2 for paint paper and textile coatings ii vinyl chloride CH2CHCl for polyvinyl chloride PVC iii ethylene glycol HOCH2CH2OH for polyester textile fibers and iv styrene C6H5CHCH2 which is important in rubber and plastic manufac turing Of all the processes used one of the most important is polymerization Chapter 11 It is used in the production of plastics fibers and synthetic rubber the main finished petrochemical derivatives Following from this secondary raw materials or intermediate chemicals Chapters 5 and 6 are obtained from a primary raw material through a variety of different processing schemes The inter mediate chemicals may be lowboiling hydrocarbon compounds such as methane ethane propane and butane or higherboiling hydrocarbon mixtures such as naphtha kerosene or gas oil In the latter cases naphtha kerosene and gas oil these fractions are used in addition to the production of fuels as feedstocks for cracking processes to produce a variety of petrochemical products eg ethylene propylene benzene toluene and the xylene isomers which are identified by the relative placement of the two methyl groups on the aromatic ring FIGURE 11 Raw materials and primary petrochemicals Speight JG 2007 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Figure 273 p 784 5 The Petrochemical Industry Also by way of definition petrochemistry is a branch of chemistry in which the transforma tion of petroleum crude oil and natural gas into useful products or feedstock for other process is studied A petrochemical plant is a plant that uses chemicals from petroleum as a raw material the feedstock are usually located adjacent to or within the precinct of a petroleum refinery in order to minimize the need for transportation of the feedstocks produced by the refinery Figure 12 On the other hand specialty chemical plants and fine chemical plants are usually much smaller than a petrochemical plant and are not as sensitive to location Furthermore a paraffinic petrochemical is an organic chemical compound but one that does not contain any ring systems such as a cycloalkane naphthene ring or an aromatic ring A naphthenic petrochemical is an organic chemical compound that contains one or more cycloalkane ring sys tems An aromatic petrochemical is also an organic chemical compound but one that contains or is derived from the basic benzene ring system FIGURE 12 Schematic diagram of a refinery showing the production of products during the distillation and during thermal processing eg visbreaking coking and catalytic cracking 6 Handbook of Petrochemical Processes Petroleum products in contrast to petrochemicals are those hydrocarbon fractions that are derived from petroleum and have commercial value as a bulk product Tables 11 and 12 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 These products are generally not accounted for in petrochemical production or used in statistics Thus in the context of this definition of petrochemicals this book focuses on chemicals that are produced from petro leum as distinct from petroleum products which are organic compounds typically hydrocarbon compounds that are burned as a fuel In the strictest sense of the definition a petrochemical is any chemical that is manufactured from petroleum and natural gas as distinct from fuels and other products which are derived from petroleum and natural gas by a variety of processes and used for a variety of commercial purposes Chenier 2002 Meyers 2005 Naderpour 2008 Speight 2014 Petrochemical products include such items as plastics soaps and detergents solvents drugs fertil izers pesticides explosives synthetic fibers and rubbers paints epoxy resins and flooring and insulating materials Moreover the classification of materials as petrochemicals is used to indicate the source of the chemical compounds but it should be remembered that many common petrochemicals can be made from other sources and the terminology is therefore a matter of source identification However in the setting of modern industry the term petrochemicals is often used in an expanded form to include chemicals produced from other fossil fuels such as coal or natural gas oil shale and renew able sources such as corn or sugar cane as well as other forms of biomass Chapter 3 It is in the expanded form of the definition that the term petrochemical is used in this book In fact in the early days of the chemical industry coal was the major source of chemicals it was not then called the petrochemical industry and it was only after the discovery of petroleum and the recognition that petroleum could produce a variety of products other than fuels that the petrochemi cal industry came into being Spitz 1988 Speight 2013 2014 2017 For several decades both coal and petroleum served as the primary raw materials for the manufacture of chemicals Then during the time of World War II petroleum began to outpace coal as a source of chemicalsthe exception being the manufacture of synthetic fuels from coal because of the lack of access to petroleum by German industry To complete this series of definitions and to reduce the potential for any confusion that might occur later in this text specialty chemicals also called specialties or effect chemicals are par ticular chemical products which provide a wide variety of effects on which many other industry sectors rely Specialty chemicals are materials used on the basis of their performance or function Consequently in addition to effect chemicals they are sometimes referred to as performance chemi cals or formulation chemicals The physical and chemical characteristics of the single molecules or the formulated mixtures of molecules and the composition of the mixtures influence the perfor mance of the end product On the other hand the term fine chemicals is used in distinction to heavy chemicals which are produced and handled in large lots and are often in a crude state Since their inception in the late 1970s fine chemicals have become an important part of the chemical industry Fine chemicals are typically single but often complex pure chemical substances produced in limited quantities in multipurpose plants by multistep batch chemical or biotechnological processes and are described by specifications to which the chemical producers must strictly adhere Fine chemicals are used as starting materials for specialty chemicals particularly pharmaceutical chemicals biopharmaceuti cal chemicals and agricultural chemicals To return to the subject of petrochemicals a petroleum refinery converts raw crude oil into useful products such as liquefied petroleum gas LPG naphtha from which gasoline is manu factured kerosene from which diesel fuel is manufactured and a variety of gas oil fractionsof particular interest is the production of naphtha that serves as a feedstock for several processes that produce petrochemical feedstocks Table 14 However each refinery has its own specific arrange ment and combination of refining processes largely determined by the market demand Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The most common 7 The Petrochemical Industry petrochemical precursors are various hydrocarbon derivatives olefin derivatives aromatic deriva tives including benzene toluene and xylene isomers and synthesis gas also called syngasa mixture of carbon monoxide and hydrogen A typical crude oil refinery produces a variety of hydrocarbon derivatives olefin derivatives and aromatic derivatives by processes such as coking and fluid catalytic cracking of various feed stocks Chemical plants produce olefin derivatives by steam cracking natural gas liquids such as ethane CH3CH3 and propane CH3CH2CH3 to produce ethylene CH2CH2 and propylene CH3CHCH2 respectively A steam cracking unit Figure 13 is in theory one of the simplest operations in a refineryessentially a hot reactor into which steam and the feedstock are intro duced but in reality the steam cracking is one of the most technically complex and energyintensive plants in the refining industry and in the petrochemical industry The equipment typically oper ates over the range 175C1125C 345F2055F and from a near vacuum ie 147 psi to high pressure 1500 psi While the fundamentals of the process have not changed in recent decades improvements continue to be made to the energy efficiency of the furnace ensuring that the cost of production is continually reduced In more general terms steam cracking units use a variety of feedstocks for example i ethane propane and butane from natural gas ii naphtha a mixture of C5C8 or C5C10 hydrocarbon TABLE 14 Naphtha Production Primary Process Primary Product Secondary Process Secondary Product Atmospheric distillation Naphtha Light naphtha Heavy naphtha Gas oil Catalytic cracking Naphtha Gas oil Hydrocracking Naphtha Vacuum distillation Gas oil Catalytic cracking Naphtha Hydrocracking Naphtha Residuum Coking Naphtha Hydrocracking Naphtha FIGURE 13 Representation of a steam cracking operations 8 Handbook of Petrochemical Processes derivatives from the distillation of crude oil iii gas oil and iv residsalso called residue or residuafrom the primary distillation of crude oil In the steam cracking process a gaseous or liquid hydrocarbon feedstock is diluted with steam and then briefly heated in a furnace obviously without the presence of oxygen Typically the reaction temperature is high up to 1125C 2055F but the reaction is only allowed to take place very briefly short residence time The residence time is even reduced to milliseconds resulting in gas velocities reaching speeds beyond the speed of sound in order to improve the yield of desired products After the cracking temperature has been reached the gas is quickly quenched to stop the reaction in a transfer line exchanger The product type and product yield produced in the cracking unit depend on i the composition of the feed ii the hydrocarbon to steam ratio iii the cracking temperature and iv the residence time of the feedstock in the hot zone The advantages of steam cracking are that the process reduced the need for repeated product distillation that produces a wider range of products However the disadvantage is that the process may not produce the product that is needed in high enough yield In fact aromatic derivatives such as benzene C6H6 toluene C6H5CH3 and the xylenes ortho meta and paraisomers H3CC6H4CH3 are produced by reforming naphtha which is a lowboiling liquid product obtained by distillation from crude oil Tables 11 and 14 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 With higher molecular weight higherboiling feedstocks such as gas oil it is important to ensure that the feedstock does not crack to form carbon which is normally formed at this temperature This is avoided by passing the gaseous feedstock very quickly and at very low pressure through the pipes which run through the furnace On the basis of chemical structure petrochemicals are categorized into a variety of petrochemi cal products which are named according to the chemical character of the constituents Paraffin derivatives such as methane CH4 ethane C2H6 propane C3H8 the butane isomers C4H10 and higher molecular weight hydrocarbon derivatives up to and including lowboiling mixtures such as naphtha Olefin derivatives such as ethylene CH2CH2 and propylene CH3CHCH2 which are important sources of industrial chemicals and plastics the diolefin derivative butadiene CH2CHCHCH2 is used in making synthetic rubber Aromatic derivatives such as benzene C6H6 toluene C6H5CH3 and the xylene isomers CH3C6H4CH3which are identified by the relative placement of the two methyl groups on the aromatic ring 12CH3C6H4CH3 13CH3C6H4CH3 and 14CH3C6H4CH3 and which have a variety of usesbenzene is a raw material for dyes and synthetic detergents and benzene and toluene for isocyanates while the xylene isomers are used in the manufacture of plastics and synthetic fibers Synthesis gas a mixture of carbon monoxide CO and hydrogen H2 that is sent to a FischerTropsch reactor to produce naphtharange and kerosenerange hydrocarbon deriv ative as well as methanol CH3OH and dimethyl ether CH3OCH3 Ethylene and propylene the major part of olefins are the basic source in preparation of several industrial chemicals and plastic products whereas butadiene is used to prepare synthetic rubber Benzene toluene and the xylene isomers are major components of aromatic chemicals These aro matic petrochemicals are used in the manufacturing of secondary products like synthetic deter gents polyurethanes plastic and synthetic fibers Synthesis gas comprises carbon monoxide and hydrogen which are basically used to produce ammonia and methanol which are further used to produce other chemical and synthetic substances Lowboiling olefins light olefinsethylene and propyleneare the most important interme diates in the production of plastics and other chemical products The current end use of ethylene worldwide is for i the manufacture of polyethylene which is used in plastics ii the manufac ture of ethylene oxideglycol which is used in fibers and plastic iii the manufacture of ethylene 9 The Petrochemical Industry dichloride which is used in polyvinyl chloride polymers and iv the manufacture of ethylbenzene which is used in styrene polymers The current end use of propylene worldwide is in i the manu facture of polypropylene which is used in plastics ii the manufacture of acrylonitrile iii the manufacture of cumene which is used in phenolic resin iv the manufacture of propylene oxide and v the manufacture of 8 oxoalcohol derivatives Also nonolefin petrochemicals are typically aromatic derivatives benzene toluene and the xylene isomers or simply BTX Most of the benzene is used to make i styrene which is used in the manufacture of polymers and plastics ii phenol which is used in the manufacture of res ins and adhesives by way of cumene and iii cyclohexane which is used in the manufacture of nylon Chapters 8 and 11 Benzene is also used in the manufacture of rubber lubricants dyes detergents drugs explosives and pesticides Toluene is used as a solvent for making paint rub ber and adhesives a gasoline additive or for making toluene isocyanate toluene isocyanate is used for making polyurethane foam phenol and trinitrotoluene generally known as TNT Xylene is used as a solvent and as an additive for making fuels rubber leather and terephthalic acid 14HO2CC6H4CO2H also written as 14CO2HC6H4CO2H or 14C6H4CO2H2 which is used in the manufacture of polymers The primary focus of this book is on chemical products derived from petroleum and natural gas but chemicals from sources such as coal and biomass are also included as alternate feedstocks Tables 15 and 16 However petrochemicals in the strictest sense are chemical products derived from petroleum although many of the same chemical compounds are also obtained from other Terephthalic acid TABLE 15 Alternative Feedstocks for the Production of Petrochemicals Chemicals PetroleumNatural Gas Feedstock Alternate Feedstock Methane Natural gas Coal as byproduct of separation of coke gases Refinery gas Coal hydrogenation Ammonia Methane From coal via water gas Methyl alcohol Methane From coal via watergas reaction Ethylene Pyrolysis of lowboiling hydrocarbon derivatives Dehydration of ethyl alcohol Acetylene Ethylene Calcium carbide Ethylene glycol Ethylene From coal via carbon monoxide and formaldehyde Acetaldehyde Paraffin gas oxidation Fermentation of ethyl alcohol Oxidation of ethylene Acetylene Acetone Propylene Destructive distillation of wood Pyrolysis of acetic acid Acetylenesteam reaction Glycerol Propylene Byproduct of soap manufacture Butadiene 1 and 2Butenes Ethyl alcohol acetaldehyde via 13butanediol Butane Acetylene and formaldehyde from coal Aromatic hydrocarbons Aromaticrich fractions by catalytic reforming Byproducts of coal tar distillation Naphthenerich fractions by catalytic reforming 10 Handbook of Petrochemical Processes fossil fuels such as coal and natural gas or from renewable sources such as corn sugar cane and other types of biomass Matar and Hatch 2001 Meyers 2005 Speight 2008 2013 2014 Clark and Deswarte 2015 But first there is the need to understand the origins of the industry and above all the continuing need for the petrochemical industry 12 HISTORICAL ASPECTS AND OVERVIEW When coal came to prominence as a fuel during the Industrial Revolution there was a parallel development relating to the use of coal for the production of chemicals Byproduct liquids and gases from coal carbonization processes became the basic raw materials for the organic chemical indus try and the production of metallurgical coke from coal was essential to the development of steel manufacture Speight 2013 Coal tar constituents were used for the industrial syntheses of dyes perfumes explosives flavorings and medicines Processes were also developed for the conversion of coal to fuel gas and to liquid fuels By the time that the decade of the 1930s had dawned the direct and indirect liquefaction tech nologies became available for the substantial conversion of coals to liquid fuels and chemicals Subsequently the advent of readily available petroleum and natural gas and the decline of the steel industry reduced dependence on coal as a resource for the production of chemicals and materials For the last several decades as the 20th century came to a close and the 21st century dawned the availability of coal tar chemicals has depended on the production of metallurgical coke which is in turn tied to the fortunes and future of the steel industry The petroleum era was ushered in by the discovery of petroleum at Titusville Pennsylvania in 1859 Although the petroleum era was ushered in by the discovery of petroleum at Titusville Pennsylvania in 1859 the production of chemicals from natural gas and petroleum has been a recognized industry only since the early 20th century Nevertheless the petrochemical industry has made quantum leaps in the production of a TABLE 16 Illustration of the Production of Petrochemical Starting Materials from Petroleum and Natural Gas Feedstock Process Product Petroleum Distillation Light ends Methane Ethane Propane Butane Catalytic cracking Ethylene Propylene Butylenes Higher olefins Catalytic reforming Benzene Toluene Xylenes Coking Ethylene Propylene Butylenes Higher olefins Natural gas Refining Methane Ethane Propane Butane 11 The Petrochemical Industry wide variety of chemicals Chenier 2002 which being based on starting feedstocks from petro leum is termed petrochemicals Following from this the production of chemicals from natural gas and petroleum has been a rec ognized industry since the early decades of the 20th century Nevertheless the lead up and onset of World War II led to the development and expansion of the petrochemical industry which since that time has made quantum leaps in terms of the production of a wide variety of chemicals Chenier 2002 Meyers 2005 Naderpour 2008 Speight 2014 EPCA 2016 Hsu and Robinson 2017 At this time coal alone could no longer satisfy the demand for basic chemicals that had increased by the demands of World War II and the production of chemicals from coal tar or some agricultural prod ucts was not sufficient and led to the major development of chemicals production from petroleum During the 1950s and 1960s the increased demand for liquid fuels increased phenomenally and paralleling the demand for fuels the onset of the age of plastics which also included demand for rubber fibers surfactants pesticides fertilizers pharmaceuticals dyes solvents lubricating oils and food additives caused an increase in the demand for chemicals from petroleum and natural gas This trend has continued until the present decade and demand for the manufacture of chemicals will continue for the foreseeable future 13 THE PETROCHEMICAL INDUSTRY The petrochemical industry as the name implies is based upon the production of chemicals from petroleum However there is more to the industry than just petroleum products The petrochemical industry also deals with chemicals manufactured from the byproducts of petroleum refining such as natural gas natural gas liquids and in the context of this book other feedstocks such as coal oil shale and biomass The structure of the industry is extremely complex involving thousands of chemicals and processes and there are many interrelationships within the industry with products of one process being the feedstocks of many others For most chemicals the production route from feedstock to final products is not unique but includes many possible alternatives As complicated as it may seem however this structure is comprehensible at least in general form At the beginning of the production chain are the raw feedstocks petroleum natural gas and alternate carbonaceous feedstocks tar From these are produced a relatively small number of impor tant building blocks which include primarily but not exclusively the lowerboiling olefins and aromatic derivatives such as ethylene propylene butylenes butadiene benzene toluene and the xylene isomers These building blocks are then converted into a complex array of thousands of intermediate chemicals Some of these intermediates have commercial value in and of themselves and others are purely intermediate compounds in the production chains The final products of the petrochemical industry are generally not consumed directly by the public but are used by other industries to manufacture consumer goods Thus on a scientific basis as might be expected the petrochemical industry is concerned with the production and trade of petrochemicals that have a wide influence on lifestyles through the pro duction of commodity chemicals and specialty chemicals that have a marked influence on lifestyles Petroleumnaturalgas bulkchemicals commoditychemicals specialtychemicals The basis of the petrochemical industry and therefore petrochemicals production consists of two steps i feedstock production from primary energy sources to feedstocks and ii and petrochemi cals production from feedstocks Petroleumnaturalgas feedstockproduction petrochemicalproducts This simplified equation encompasses the multitude of production routes available for most chemi cals In the actual industry many chemicals are products of more than one method depending 12 Handbook of Petrochemical Processes upon local conditions corporate polices and desired byproducts There are also additional methods available which have either become obsolete and are no longer used or which have never been used commercially but could become important as technology supplies and other factors change Such versatility adaptability and dynamic nature are three of the important features of the modern petrochemical industry Thus the petrochemical industry began as suitable byproducts became available through improvements in the refining processes As the decades of the 1920s and 1930s closed the indus try developed in parallel with the crude oil industry and has continued to expand rapidly since the 1940s as the crude oil refining industry was able to provide relatively cheap and plentiful raw materials Speight 2002 Gary et al 2007 Lee et al 2007 Speight 2011 2014 Hsu and Robinson 2017 Speight 2017 The supplydemand scenario as well as the introduction of many innovations has resulted in basic chemicals and plastics becoming the key building blocks for manufacture of a wide variety of durable and nondurable consumer goods Chemicals and plastic materials provide the fundamental building blocks that enable the manufacture of the vast majority of consumer goods Moreover the demand for chemicals and plastics is driven by global economic conditions which are directly linked to demand for consumer goods At the start of the production chain is the selection and preparation of the feedstock from which the petrochemicals will be produced Typically the feedstock is a primary energy source such as crude oil natural gas coal and biomass are extracted and then converted into feedstocks such as naphtha gas oil andor methanol In the production of petrochemicals the feedstocks are con verted into basic petrochemicals such as ethylene CH2CH2 and aromatic derivatives which are then separated from each other Thus petrochemicals or products derived from these feedstocks along with other raw materials are converted to a wide range of products Table 13 Therefore the history of the industry has always been strongly influenced by the supply of pri mary energy sources and feedstocks Thus the petrochemical industry directly interfaces with the petroleum industry and the natural gas industry which proves the feedstocks Chapter 2 and espe cially the downstream sector as well as the potential for the introduction and use of nonconven tional feedstocks Chapter 3 A major part of the petrochemical industry is made up of the polymer plastics industry Chapter 11 The petrochemical industry is currently the biggest of the industrial chemical sectors and petrochemicals represent the majority of all chemicals shipped between the continents of the world EPCA 2016 Petrochemicals have a history that began in the 19th century that has experienced many changes However from the beginning there have been underlying trends which shaped the evolution of the industry to modern times From the start it was an industry that was destined to become a global sector because of the contribution the product makes to raise the standards of living of much of the population of the world These same influences have also shaped the rate and nature of the expansion and the structure of the industry as it exist in the 21st century In the petrochemical industry the organic chemicals produced in the largest volumes are methanol methyl alcohol CH3OH ethylene CH2CH2 propylene CH3CHCH2 butadiene CH2CHCHCH2 benzene C6H6 toluene C6H5CH3 and the xylene isomers H3CC6H4CH3 Ethylene propylene and butadiene along with butylenes are collectively called olefins which belong to a class of unsaturated aliphatic hydrocarbon derivatives having the general formula CnH2n Olefin derivatives contain one or more double bonds CC which make them chemically reac tive and hence the starting materials for many products Benzene toluene and xylenes commonly referred to as aromatics are unsaturated cyclic hydrocarbon derivatives containing one or more rings As stated above some of the chemicals and compounds produced in a refinery are destined for further processing and as raw material feedstocks for the fast growing petrochemical industry Such nonfuel uses of crude oil products are sometimes referred to as its nonenergy uses Petroleum prod ucts and natural gas provide two of the basic starting points for this industry methane Figure 14 naphtha including benzene toluene and the xylene isomers Figure 15 and refinery gases which 13 The Petrochemical Industry contain olefin derivatives such as ethylene Figure 16 propylene Figure 17 and potentially all of the butylene isomers Figures 17 and 18 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Petrochemical intermediates are generally produced by chemical conversion of primary petro chemicals to form more complicated derivative products Petrochemical derivative products can be made in a variety of ways directly from primary petrochemicals through intermediate prod ucts which still contain only carbon and hydrogen and through intermediates which incorporate chlorine nitrogen or oxygen in the finished derivative In some cases they are finished products in others more steps are needed to arrive at the desired composition The end products number in the thousands some going on as inputs into the chemical industry for further processing The more common products made from petrochemicals include adhesives plastics soaps detergents solvents paints drugs fertilizers pesticides insecticides explosives synthetic fibers synthetic rubber and flooring and insulating materials Petrochemical products include such items as plastics soaps and detergents solvents drugs fertilizers pesticides explosives synthetic fibers and rubbers paints epoxy resins and flooring and insulating materials Petrochemicals are found in products as diverse as aspirin luggage boats automobiles aircraft polyester clothes and recording discs and tapes The petrochemical industry has grown with the petroleum industry Goldstein 1949 Steiner 1961 Hahn 1970 and is considered by some to be a mature industry However as is the case with the latest trends in changing crude oil types it must also evolve to meet changing technological needs The manufacture of chemicals or chemical intermediates from a variety of raw materials is well established Wittcoff and Reuben 1996 And the use of petroleum and natural gas is an excellent example of the conversion of such raw materials to more valuable products The individual chemicals made from petroleum and natural gas are numerous and include industrial chemicals FIGURE 14 Chemicals from methane Speight JG 2007 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Figure 278 p 800 14 Handbook of Petrochemical Processes household chemicals fertilizers and paints as well as intermediates for the manufacture of prod ucts such as synthetic rubber and plastics Petrochemicals are generally considered chemical compounds derived from petroleum either by direct manufacture or indirect manufacture as byproducts from the variety of processes that are used during the refining of petroleum Gasoline kerosene fuel oil lubricating oil wax asphalt and the like are excluded from the definition of petrochemicals since they are not in the true sense chemical compounds but are in fact intimate mixtures of hydrocarbon derivatives The classification of materials as petrochemicals is used to indicate the source of the chemical compounds but it should be remembered that many common petrochemicals can be made from other sources and the terminology is therefore a matter of source identification The starting materials for the petrochemical industry are obtained from crude petroleum in one of two general ways They may be present in the raw crude oil and as such are isolated by physi cal methods such as distillation or solvent extraction Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 On the other hand they may be present if at all in trace amounts and are synthesized during the refining operations In fact unsaturated olefin hydro carbon derivatives which are not usually present in crude oil are nearly always manufactured as FIGURE 15 Chemicals from benzene toluene and the xylene isomers Speight JG 2007 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Figure 277 p 798 15 The Petrochemical Industry intermediates during the various refining sequences Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The manufacture of chemicals from petroleum is based on the ready response of the various com pound types to basic chemical reactions such as oxidation halogenation nitration dehydrogenation addition polymerization and alkylation The low molecular weight paraffins and olefins as found in natural gas and refinery gases and the simple aromatic hydrocarbon derivatives have so far been of the most interest because it is individual species that can be readily be isolated and dealt with A wide range of compounds is possible many are being manufactured and we are now progressing to the stage in which a sizable group of products is being prepared from the heavier fractions of petro leum For example the various reactions of asphaltene constituents Chapter 2 Speight 1994 2014 indicate that these materials may be regarded as containing chemical functions and are therefore different and are able to participate in numerous chemical or physical conversions to perhaps more useful materials The overall effect of these modifications is the production of materials that either affords goodgrade aromatic cokes comparatively easily or the formation of products bearing func tional groups that may be employed as a nonfuel material For example the sulfonated and sulfomethylated materials and their derivatives have satisfacto rily undergone tests as drilling mud thinners and the results are comparable to those obtained with commercial mud thinners Here there is the potential slowrelease soil conditioners that only release the nitrogen or phos phorus after considerable weathering or bacteriological action One may proceed a step further and suggest that the carbonaceous residue remaining after release of the heteroelements may be a benefit to humusdepleted soils such as the graywooded and solonetzic soils It is also feasible that coating a conventional quickrelease inorganic fertilizer with a watersoluble or waterdispersible FIGURE 16 Chemicals from ethylene Speight JG 2007 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Figure 275 p 788 16 Handbook of Petrochemical Processes derivative will provide a slowerrelease fertilizer and an organic humuslike residue In fact varia tions on this theme are multiple Nevertheless the main objective in producing chemicals from petroleum is the formation of a variety of welldefined chemical compounds that are the basis of the petrochemical industry It must be remembered however that ease of separation of a particular compound from petroleum does not guarantee its use as a petrochemical building block Other parameters particularly the economics of the reaction sequences including the costs of the reactant equipment must be taken into consideration Petrochemicals are made or recovered from the entire range of petroleum fractions but the bulk of petrochemical products are formed from the lighter C1C4 hydrocarbon gases as raw materials These materials generally occur as natural gas but they are also recovered from the gas streams produced during refining especially cracking operations Refinery gases are also particularly valu able because they contain substantial amounts of olefins that because of the double bonds are much FIGURE 17 Chemicals from propylene and butylene Speight JG 2007 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Figure 276 p 789 17 The Petrochemical Industry more reactive then the saturated paraffin hydrocarbon derivatives Also important as raw materi als are the aromatic hydrocarbon derivatives benzene toluene and xylene that are obtained in rare cases from crude oil and more likely from the various product streams By means of the catalytic reforming process nonaromatic hydrocarbon derivatives can be converted to aromatics by dehydro genation and cyclization Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 A highly significant proportion of these basic petrochemicals is converted into plastics syn thetic rubbers and synthetic fibers Together these materials are known as polymers because their molecules are high molecular weight compounds made up of repeated structural units that have combined chemically The major products are polyethylene polyvinyl chloride and polystyrene all derived from ethylene and polypropylene derived from monomer propylene Major raw materials for synthetic rubbers include butadiene ethylene benzene and propylene Among synthetic fibers the polyesters which are a combination of ethylene glycol and terephthalic acid made from xylene are the most widely used They account for about onehalf of all synthetic fibers The second major synthetic fiber is nylon it is the most important raw material being benzene Acrylic fibers in which the major raw material is the propylene derivative acrylonitrile make up most of the remainder of the synthetic fibers 14 PETROCHEMICALS For the purposes of this text there are four general types of petrochemicals i aliphatic com pounds ii aromatic compounds iii inorganic compounds and iv synthesis gas carbon monoxide and hydrogen Synthesis gas is used to make ammonia NH3 and methanol methyl alcohol CH3OH as well as a variety of other chemicals Figure 19 Ammonia is used primarily to form ammonium nitrate NH4NO3 a source of fertilizer Much of the methanol produced is used in making formaldehyde HCHO The rest is used to make polyester fibers plastics and silicone rubber An aliphatic petrochemical compound is an organic compound that has an open chain of carbon atoms be it normal straight eg npentane CH3CH2CH2CH2CH3 or branched eg isopentane 2 methylbutane CH3CH2CHCH3CH3 The unsaturated compounds olefins include important IUPAC name Common name Structure Skeletal formula But1ene 1butylene cisBut2ene cis2butylene cisBut2ene trans3butylene 2methylprop1ene Isobutylene FIGURE 18 Representation of the various isomers of butylene C4H8 18 Handbook of Petrochemical Processes starting materials such as ethylene CH2CH2 propylene CH3CHCH2 butene1 CH3CH2CH2CH2 isobutene 2methylpropene CH3CH3CCH2 and butadiene CH2CHCHCH2 As already defined a petrochemical is any chemical as distinct from fuels and petroleum products manufactured from petroleum and natural gas as well as other carbonaceous sources and used for a variety of commercial purposes Chenier 2002 The definition however has been broadened to include the whole range of aliphatic aromatic and naphthenic organic chemi cals as well as carbon black and such inorganic materials as sulfur and ammonia Gasoline kerosene fuel oil lubricating oil wax asphalt and the like are excluded from the definition of petrochemicals since they are not in the true sense chemical compounds but are in fact inti mate mixtures of hydrocarbon derivatives The classification of materials as petrochemicals is used to indicate the source of the chemical compounds but it should be remembered that many common petrochemicals can be made from other sources and the terminology is therefore a matter of source identification Petroleum and natural gas are made up of predominantly hydrocarbon constituents which are comprised of one or more carbon atoms to which hydrogen atoms are attachedin some cases petroleum contains a considerable proportion of nonhydrocarbon constituents such as organic compounds containing one or more heteroatoms such as nitrogen oxygen sulfur and metals Currently through a variety of intermediates petroleum and natural gas are the main sources of the raw materials because they are the least expensive most readily available and can be processed most easily into the primary petrochemicals An aromatic petrochemical is also an organic chemi cal compound but one that contains or is derived from the basic benzene ring system Furthermore petrochemicals are often made in clusters of plants in the same area These plants are often operated by separate companies and this concept is known as integrated manufacturing Groups of related materials are often used in adjacent manufacturing plants to use common infrastructure and mini mize transport FIGURE 19 Production of chemicals from synthesis gas Speight JG 2007 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Figure 279 p 802 19 The Petrochemical Industry 141 Primary Petrochemicals The primary petrochemicals are not the raw materials for the petrochemical industry Primary raw materials are naturally occurring substances that have not been subjected to chemical changes after being recovered Natural gas and crude oil are the basic raw materials for the manufacture of petro chemicals Secondary raw materials or intermediates are obtained from natural gas and crude oils through different processing schemes The intermediate chemicals may be lowboiling hydrocarbon compounds such as methane and ethane or heavier hydrocarbon mixtures such as naphtha or gas oil Both naphtha and gas oil are crude oil fractions with different boiling ranges Coal oil shale and biomass are complex carbonaceous raw materials and possible future energy and chemical sources However they must undergo lengthy and extensive processing before they yield fuels and chemicals similar to those produced from crude oils substitute natural gas SNG and synthetic crudes from coal oil shale and biooil The term primary petrochemical is more specific and includes olefins ethylene propylene and butadiene aromatics benzene toluene and the isomers of xylene and methanol from which petrochemical products are manufactured The two most common petrochemical classes are olefin derivatives including ethylene CH2CH2 and propylene CH3CHCH2 and aromatic derivatives such as benzene C6H6 toluene C6H5CH3 and the xylene isomers H3CC6H4CH3 Olefin derivatives and aromatic derivatives are typically produced in a crude oil refinery by fluid catalytic cracking of the various crude oil distillate fractions Speight 1987 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Olefins are also produced by steam cracking of methane CH4 ethane CH3CH3 and propane CH3CH2CH3 and aromatic derivatives are produced by steam reforming of naphtha Speight 1987 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Olefin derivatives and aromatic derivatives are the intermediate chemicals that lead to a sub stantial number some observers would say an innumerable number of products such as solvents detergents plastics fibers and elastomers In many instances a specific chemical included among the petrochemicals may also be obtained from other sources such as coal coke or vegetable products For example materials such as ben zene and naphthalene can be made from either petroleum or coal while ethyl alcohol may be of pet rochemical or vegetable origin Matar and Hatch 2001 Meyers 2005 Speight 2008 2013 2014 142 Products and end use Petrochemical products include such items as plastics soaps and detergents solvents drugs fertil izers pesticides explosives synthetic fibers and rubbers paints epoxy resins and flooring and insulating materials Table 13 Petrochemicals use is also found in products as diverse as aspirin luggage boats automobiles aircraft polyester clothes and recording discs and tapes Although the petrochemical industry was showing steady growth some observers would say rapid growth the onset of World War II increased the demand for synthetic materials to replace costly and sometimes less efficient products was a catalyst for the development of petrochemicals Before the 1940s it was an experimental sector starting with basic materials i synthetic rubber in the 1900s ii Bakelite the first petrochemicalderived plastic in 1907 iii the first petrochemi cal solvents in the 1920s and iv polystyrene in the 1930s After this the industry moved into a variety of areasfrom household goods kitchen appliances textile furniture to medicine heart pacemakers transfusion bags from leisure such as running shoes computersto highly specialized fields like archaeology or crime detection Thus the petrochemical industry has grown with the petroleum industry Goldstein 1949 Steiner 1961 Hahn 1970 Chenier 2002 and is considered by some to be a mature industry However as is the case with the latest trends in changing crude oil types the refining industry must also evolve to meet changing technological needs Speight 2011 2014 2017 The manufacture of chemicals or chemical intermediates from a variety of raw materials is well established Wittcoff and Reuben 20 Handbook of Petrochemical Processes 1996 Speight 2014the use of petroleum and natural gas is an excellent example of the conversion of such raw materials to more valuable products The individual chemicals made from petroleum and natural gas are numerous and include industrial chemicals household chemicals fertilizers and paints as well as intermediates for the manufacture of products such as synthetic rubber and plastics The petroleum and petrochemical industries have revolutionized modern life by providing the major basic needs of a rapidly growing expanding and highly technical civilization They provide a source of products such as fertilizers synthetic fibers synthetic rubbers polymers intermediates explosives agrochemicals dyes and paints The petrochemical industry fulfills a large number of requirements which includes uses in the fields such as automobile manufacture telecommunica tion pesticides fertilizers textiles dyes pharmaceuticals and explosives Table 13 15 PRODUCTION OF PETROCHEMICALS For approximately 100 years chemicals obtained as byproducts in the primary processing of coal to metallurgical coke have been the main source of a multitude of chemicals used as intermediates in the synthesis of dyes drugs antiseptics and solvents Historically producing chemicals from coal through gasification has been used since the 1950s and as such dominated a large share of the chemicals industry Because the slate of chemical products that can be made via coal gasification the chemical industry tends to use whatever feedstocks are most costeffective Therefore interest in using coal tends to increase when oil and natural gas prices are higher and during periods of high global eco nomic growth that may strain oil and gas production Also production of chemicals from coal is of much higher interest in countries like South Africa China India and the United States where there are abundant coal resources However in recent decades largely due to the supply of relatively cheap natural gas and crude oil the use of coal as a source of chemicals has been superseded by the production of the chemicals from petroleumrelated sources The use of coal has also decreased because of environmental concerns without any acknowledgement that with the installation of mod ern process controls coal can be a clean fuel Speight 2013 Nevertheless considering the case of natural gas and crude oil the production of petrochemicals begins at the time the natural gas andor the crude petroleum enters the refinery natural gas Katz 1959 Kohl and Riesenfeld 1985 Maddox et al 1985 Newman 1985 Kohl and Nielsen 1997 Mokhatab et al 2006 leading to the separation of contaminants from the hydrocarbon constituents Petroleum refining Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 begins with the distillation or fractionation of crude oils into separate fractions of hydrocarbon groups The resultant products are directly related to the characteristics of the natural gas and crude oil being processed Most of these products of distillation are further converted into more useable products by changing their physical and molecular structures through cracking reforming and other conversion processes These products are subsequently subjected to various treatment and separation processes such as extraction hydrotreating and sweetening in order to produce finished products While the simplest refineries are usually limited to atmospheric and vacuum distillation integrated refineries incorporate fractionation conversion treatment and blending with lubricant heavy fuels and asphalt manufacturing they may also include petrochemical processing It is during the refining process that other products are also produced These products include the gaseous constituent dis solved in the crude oil that are released during the distillation processes as well as the gases produced during the various refining processes and both of these gaseous streams provide feedstocks for the petrochemical industry The gas often referred to as refinery gas or process gas varies in composition and volume depending on the origin of the crude oil and on any additions ie other crude oils blended into the refinery feedstock to the crude oil made at the loading point It is not uncommon to reinject light hydrocarbon derivatives such as propane and butane into the crude oil before dispatch by tanker or 21 The Petrochemical Industry pipeline This results in a higher vapor pressure of the crude but it allows one to increase the quan tity of light products obtained at the refinery Since light ends in most petroleum markets command a premium while in the oil field itself propane and butane may have to be reinjected or flared the practice of spiking crude oil with liquefied petroleum gas is becoming fairly common These gases are recovered by distillation Figure 12 In addition to distillation gases are also produced in the various thermal cracking processes Figure 12 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Thus in processes such as coking or visbreaking processes a variety of gases is produced Another group of refining operations that contributes to gas production is that of the catalytic crack ing processes Both catalytic and thermal cracking processes result in the formation of unsatu rated hydrocarbon derivatives particularly ethylene CH2CH2 but also propylene propene CH3CHCH2 isobutylene isobutene CH32CCH2 and the nbutenes CH3CH2CHCH2 and CH3CHCHCH3 in addition to hydrogen H2 methane CH4 and smaller quantities of ethane CH3CH3 propane CH3CH2CH3 and butanes CH3CH2CH2CH3 CH33CH Diolefins such as butadiene CH2CHCHCH2 are also present A further source of refinery gas is hydrocracking a catalytic highpressure pyrolysis process in the presence of fresh and recycled hydrogen The feed stock is again heavy gas oil or residual fuel oil and the process is mainly directed at the production of additional middle distillates and gasoline Since hydrogen is to be recycled the gases produced in this process again have to be separated into lighter and heavier streams any surplus recycled gas and the liquefied petroleum gas from the hydrocracking process are both saturated Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 In a series of reforming processes Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 commercialized under names such as Platforming paraffin and naphthene cyclic nonaromatic hydrocarbon derivatives are converted in the presence of hydrogen and a catalyst is converted into aromatics or isomerized to more highly branched hydrocarbon derivatives Catalytic reforming processes thus not only result in the formation of a liquid product of higher octane number but also produce substantial quantities of gases The latter are not only rich in hydrogen but also contain hydrocarbon derivatives from methane to butane isomers with a preponderance of propane CH3CH2CH3 nbutane CH3CH2CH2CH3 and isobutane CH33CH As might be expected the composition of the process gas varies in accordance with reforming severity and reformer feedstock All catalytic reforming processes require substantial recycling of a hydrogen stream Therefore it is normal to separate reformer gas into a propane CH3CH2CH3 and or a butane stream CH3CH2CH2CH3 plus CH33CH which becomes part of the refinery liquefied petroleum gas production and a lighter gas fraction part of which is recycled In view of the excess of hydrogen in the gas all products of catalytic reforming are saturated and there are usually no olefin gases present in either gas stream In many refineries naphtha in addition to other refinery gases is also used as the source of petrochemical feedstocks In the process naphtha crackers convert naphtha feedstock produced by various process Table 14 into ethylene propylene benzene toluene and xylenes as well as other byproducts in a twostep process of cracking and separating In some cases a combination of naphtha gas oil and liquefied petroleum gas may be used The feedstock typically naphtha is introduced into the pyrolysis section of the naphtha where it is cracked in the presence of steam The naphtha is converted into lowerboiling fractions primarily ethylene and propylene The hot gas effluent from the furnace is then quenched to inhibit further cracking and to condense higher molecular weight products The higher molecular weight products are subsequently processed into fuel oil light cycle oil and pyrolysis gas byproducts The pyrolysis gas stream can then be fed to the aromatics plants for benzene and toluene production In addition to recovery of gases in the distillation section of a refinery distillation gases are also produced in the various thermal processes thermal cracking processes and catalytic cracking processes Figure 12 and are also available in processes such as visbreaking and coking Speight 1987 Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 22 Handbook of Petrochemical Processes Thermal cracking processes were first developed for crude oil refining starting in 1913 and continuing the next two decades and were focused primarily on increasing the quantity and qual ity of gasoline components Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 As a byproduct of this process gases were produced that included a sig nificant proportion of lower molecular weight olefins particularly ethylene CH2CH2 propylene CH3CHCH2 and butylenes butenes CH3CHCHCH3 and CH3CH2CHCH2 Catalytic crack ing introduced in 1937 is also a valuable source of propylene and butylene but it does not account for a very significant yield of ethylene the most important of the petrochemical building blocks Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Ethylene is polymerized to produce polyethylene or in combination with propylene to produce copolymers that are used extensively in foodpackaging wraps plastic household goods or building materials Prior to the use of petroleum and natural gas as sources of chemicals coal was the main source of chemicals Speight 2013 Once produced and separated from other product streams the cooled gases are then compressed treated to remove acid gases dried over a desiccant and fractionated into separate components at low temperature through a series of refrigeration processes Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Hydrogen and methane are removed by way of a compression expansion process after which the methane is distributed to other processes as deemed appropriate for fuel gas Hydrogen is collected and further purified in a pressure swing unit for use in the hydrogenation hydrotreating and hydrocracking processes Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Polymer grade ethylene and propylene are separated in the cold section after which the ethane and propane streams are recycled back to the furnace for further cracking while the mixed butane C4 stream is hydrogenated prior to recycling back to the furnace for further cracking In many refineries naphtha in addition to other refinery gases is also used as the source of petro chemical feedstocks In the process naphtha crackers convert naphtha as well as gas oil feedstocks produced by various process Table 14 into ethylene propylene benzene toluene and xylenes as well as into other byproducts in a twostep process of cracking and separating In some cases a combination of naphtha gas oil and liquefied petroleum gas may be used The feedstock typically naphtha is introduced into the pyrolysis section of the naphtha where it is cracked in the presence of steam The naphtha is converted into lowerboiling fractions primarily ethylene and propylene The hot gas effluent from the furnace is then quenched to inhibit further cracking and to condense higher molecular weight products The higher molecular weight products are subsequently processed into fuel oil light cycle oil and pyrolysis gas byproducts The pyrolysis gas stream can then be fed to the aromatics plants for benzene and toluene production The cooled gases are then compressed treated to remove acid gases dried over a desiccant and fractionated into separate components at low temperature through a series of refrigeration processes Parkash 2003 Gary et al 2007 Hsu and Robinson 2017 Speight 2017 Hydrogen and methane are removed by way of a compression expansion process after which the methane is distributed to other process as deemed appropriate or fuel gas Hydrogen is collected and further purified in a pressure swing unit for use in the hydrogenation process Polymer grade ethylene and propylene are separated in the cold section after which the ethane and propane streams are recycled back to the furnace for further cracking while the mixed butane C4 stream is hydrogenated prior to recycling back to the furnace for further cracking The refinery gas or the process gas stream and the products of naphtha cracking are the source of a variety of petrochemicals For example thermal cracking processes Parkash 2003 Gary et al 2007 Hsu and Robinson 2017 Speight 2017 developed for crude oil refining starting in 1913 and continuing the next two decades were focused primarily on increasing the quantity and quality of gasoline components As a byproduct of this process gases were produced that included a significant proportion of lower molecular weight olefins particularly ethylene CH2CH2 propylene CH3CHCH2 and butylenes butenes CH3CHCHCH3 and CH3CH2CHCH2 23 The Petrochemical Industry Catalytic cracking Parkash 2003 Gary et al 2007 Hsu and Robinson 2017 Speight 2017 introduced in 1937 is also a valuable source of propylene and butylene but it does not account for a very significant yield of ethylene the most important of the petrochemical building blocks Ethylene is polymerized to produce polyethylene or in combination with propylene to produce copolymers that are used extensively in foodpackaging wraps plastic household goods or building materials Prior to the use of petroleum and natural gas as sources of chemicals coal was the main source of chemicals Speight 2013 The petrochemical industry has grown with the petroleum industry Goldstein 1949 Steiner 1961 Hahn 1970 and is considered by some to be a mature industry However as is the case with the latest trends in changing crude oil types it must also evolve to meet changing technological needs The manufacture of chemicals or chemical intermediates from a variety of raw materials is well established Wittcoff and Reuben 1996 And the use of petroleum and natural gas is an excellent example of the conversion of such raw materials to more valuable products The individual chemicals made from petroleum and natural gas are numerous and include industrial chemicals household chemicals fertilizers and paints as well as intermediates for the manufacture of prod ucts such as synthetic rubber and plastics The manufacture of chemicals from petroleum is based on the ready response of the various compound types to basic chemical reactions such as oxidation halogenation nitration dehydro genation addition polymerization and alkylation The low molecular weight paraffins and olefins as found in natural gas and refinery gases and the simple aromatic hydrocarbon derivatives have so far been of the most interest because it is individual species that can be readily be isolated and dealt with A wide range of compounds is possible many are being manufactured and we are now progressing to the stage in which a sizable group of products is being prepared from the higher molecular weight fractions of petroleum The various reactions of asphaltene constituents indicate that these materials may be regarded as containing chemical functions and are therefore different and are able to participate in numer ous chemical or physical conversions to perhaps more useful materials The overall effect of these modifications is the production of materials that either affords goodgrade aromatic cokes com paratively easily or the formation of products bearing functional groups that may be employed as a nonfuel material For example the sulfonated and sulfomethylated materials and their derivatives have satisfacto rily undergone tests as drilling mud thinners and the results are comparable to those obtained with commercial mud thinners Moschopedis and Speight 1971 1974 1976a 1978 In addition these compounds may also find use as emulsifiers for the in situ recovery of heavy oils These are also indi cations that these materials and other similar derivatives of the asphaltene constituents especially those containing such functions as carboxylic or hydroxyl readily exchange cations and could well compete with synthetic zeolites Other uses of the hydroxyl derivatives andor the chloroasphaltenes include hightemperature packing or heat transfer media Moschopedis and Speight 1976b Reactions incorporating nitrogen and phosphorus into the asphaltene constituents are particularly significant at a time when the effects on the environment of many materials containing these ele ments are receiving considerable attention In this case there are potential slowrelease soil condi tioners that only release the nitrogen or phosphorus after considerable weathering or bacteriological action One may proceed a step further and suggest that the carbonaceous residue remaining after release of the heteroelements may be a benefit to humusdepleted soils such as the graywooded soils It is also feasible that coating a conventional quickrelease inorganic fertilizer with a water soluble or waterdispersible derivative will provide a slowerrelease fertilizer and an organic humus like residue In fact variations on this theme are multiple Moschopedis and Speight 1974 1976a Petrochemicals are made or recovered from the entire range of petroleum fractions but the bulk of petrochemical products are formed from the lighter C1C4 hydrocarbon gases as raw materials These materials generally occur as natural gas but they are also recovered from the gas streams produced during refining especially cracking operations Refinery gases are also particularly 24 Handbook of Petrochemical Processes valuable because they contain substantial amounts of olefins that because of the double bonds are much more reactive then the saturated paraffin hydrocarbon derivatives Also important as raw materials are the aromatic hydrocarbon derivatives benzene toluene and xylene that are obtained in rare cases from crude oil and more likely from the various product streams By means of the catalytic reforming process nonaromatic hydrocarbon derivatives can be converted to aromatics by dehydrogenation and cyclization A highly significant proportion of these basic petrochemicals are converted into plastics syn thetic rubbers and synthetic fibers Together these materials are known as polymers because their molecules are high molecular weight compounds made up of repeated structural units that have combined chemically The major products are polyethylene polyvinyl chloride and polystyrene all derived from ethylene and polypropylene derived from monomer propylene Major raw materials for synthetic rubbers include butadiene ethylene benzene and propylene Among synthetic fibers the polyesters which are a combination of ethylene glycol and terephthalic acid made from xylene are the most widely used Petrochemical production relies on multiphase processing of oil and associated petroleum gas Key raw materials in the petrochemical industry include products of petroleum oil refining pri marily gases and naphtha Petrochemical goods include ethylene propylene and benzene source monomers for synthetic rubbers and inputs for technical carbon The petrochemical industry has grown with the petroleum industry and is considered by some to be a mature industry However as is the case with the latest trends in changing crude oil types it must also evolve to meet changing technological needs The manufacture of chemicals or chemi cal intermediates from a variety of raw materials is well established And the use of petroleum and natural gas is an excellent example of the conversion of such raw materials to more valuable products The individual chemicals made from petroleum and natural gas are numerous and include industrial chemicals household chemicals fertilizers and paints as well as intermediates for the manufacture of products such as synthetic rubber and plastics The main objective in producing chemicals from petroleum is the formation of a variety of well defined chemical compounds that are the basis of the petrochemical industry 16 THE FUTURE The petrochemical industry is concerned with the production and trade of petrochemicals and has a direct relationship with the petroleum industry especially the downstream sector of the industry The petrochemical industries are specialized in the production of petrochemicals that have vari ous industrial applications The petrochemical industry can be considered to be a subsector of the crude oil industry since without the petroleum industry the petrochemical industry cannot exist Thus petroleum is the major prerequisite raw material for the production of petrochemicals either in qualities or quantities In addition the petrochemical industry is subject to the geopolitics of the petroleum industry with each industry being reliant upon the other for sustained survival In the 1970s as a result of various oil embargos coal liquefaction processes seemed on the point of commercialization and would have provided new sources of coal liquids for chemical use as well as fulfilling the principal intended function of producing alternate fuels Because of the varying price of petroleum this prospect is unlikely to come to fruition in the immediate future due to the question of economic viability rather than not technical feasibility The combination of these and other factors has contributed to sharpening the focus on the use of coal for the production of heat and power and lessening or eclipsing its possible use as a starting point for other processes The growth and development of petrochemical industries depends on a number of factors and also varies from one country to another either based on technical knowhow marketability and applicability of these petrochemicals for manufacture of petrochemical products through petro chemical processes which are made feasible by knowledge and application of petrochemistry Moreover petrochemistry is a branch of chemistry chemistry being a branch of natural science 25 The Petrochemical Industry concerned with the study of the composition and constitution of substances and the changes such substances undergo because of changes in the molecules that make up such substances that deals with petroleum natural gas and their derivatives However not all of the petrochemical or commodity chemical materials produced by the chemi cal industry are made in one single location but groups of related materials are often made in adja cent manufacturing plants to induce industrial symbiosis as well as material and utility efficiency and other economies of scale integrated manufacturing Specialty and fine chemical companies are sometimes found in similar manufacturing locations as petrochemicals but in most cases they do not need the same level of largescale infrastructure eg pipelines storage ports and power etc and therefore can be found in multisector business parks This will continue as long as the refining industry continues to exist in its present form Favennec 2001 Speight 2011 The petrochemical industry continues to be impacted by the globalization and integration of the world economy For example worldscale petrochemical plants built during the past several years are substantially larger than those built over two decades ago As a result smaller older and less efficient units are being shut down expanded or in some cases retrofitted to produce different chemical products In addition crude oil prices had been on the rise during the past decade and petrochemical markets are impacted during sharp price fluctuations creating a cloud of uncertainty in upstream and downstream investments Also increasing concerns over fossil fuel supply and consumption with respect to their impact on health and the environment have led to the passage of legislation globally that will affect chemical and energy production and processing for the foresee able future The recent shift from local markets to a large global market led to an increase in the competi tive pressures on petrochemical industries Further because of fluctuations in products price and high price of feedstocks economical attractiveness of petrochemical plants can be considered as a main challenge The everincreasing cost of energy and more stringent environmental regulations impacted the operational costs When cheap feedstocks are not available the best method of profit ability is to apply integration and optimization in petrochemical complexes with adjacent refineries This is valid for installed plants and plants under construction Petrochemicalrefinery integration is an important factor in reducing costs and increasing efficiencies because integration guarantees the supply of feedstock for petrochemical industries Also integrated schemes take the advantage of the economy of scale and an integrated complex can produce more diverse products Petrochemical refinery integration avoids selling crude oil optimizes products economizes costs and increases benefits On an innovation and technological basis Hassani et al 2017 manufacturing processes intro duced in recent years have resulted in raw material replacement shifts in the ratio of coproducts produced and cost This has led to a supplydemand imbalance particularly for smaller downstream petrochemical derivatives In addition growing environmental concerns and higher crude oil prices have expedited the development and commercialization of renewably derived chemical products and technologies previously considered economically impractical Among the various technologi cal advances the combination of vertical hydraulic fracturing fracking and horizontal drilling in multistage hydraulic fracturing resulted in a considerable rise in natural gas production in the United States This new potential has caused many countries to reexamine their natural gas reserves and pursue development of their own gas plays Currently crude oil and natural gas are the main sources of the raw materials for the production of petrochemicals because they crude oil and natural gas are the least expensive most readily available and can be processed most easily into the primary petrochemicals However as the cur rent century progresses and the changes in crude oil supply that might be anticipated during the next five decades Speight 2011 there is a continuing need to assess the potential of other sources of petrochemicals For example coal could well see a revitalization of use understanding that there is the need to adhere to the various environmental regulations that apply to the use of any fossil fuel Coal 26 Handbook of Petrochemical Processes carbonization was the earliest and most important method to produce chemicals For many years chemicals that have been used for the manufacture of such diverse materials as nylon styrene fer tilizers activated carbon drugs and medicine as well as many others have been made from coal These products will expand in the future as petroleum and natural gas resources become strained to supply petrochemical feedstocks and coal becomes a predominant chemical feedstock once more The ways in which coal may be converted to chemicals include carbonization hydrogenation oxi dation solvent extraction hydrolysis halogenation and gasification followed by conversion of the synthesis gas to chemical products Speight 2013 2014 In some cases such processing does not produce chemicals in the sense that the products are relatively pure and can be marketed as even industrial grade chemicals Thus although many traditional markets for coal tar chemicals have been taken over by the petrochemical industry the position can change suddenly as oil prices fluc tuate upwards Therefore the concept of using coal as a major source of chemicals can be very real indeed Compared to petroleum crude shale oils obtained by retorting of worlds oil shales in their multitude and dissimilarity are characterized by wide boiling range and by large concentrations of heteroelements and also by high content of oxygen nitrogen or sulfurcontaining compounds The chemical potential of oil shale as retort fuel to produce shale oil and from that liquid fuel and specialty chemicals has been used so far to a relatively small extent While the majority of countries are discovering the real practical value of shale oil in Estonia retorting of its national resource kukersite oil obtained for production of a variety of products is in use for 75 years already Using stepwise cracking motor fuels have been produced and even exported before World War II At the same time shale oils possess molecular structures of interest to the specialty chemicals industry and also a number of nonfuel specialty products have been marketed based on functional group broad range concentrate or even pure compound values Based on large quantity of oxygencontaining compounds in heavy fraction asphaltblending material road asphalt and road oils construction mastics anticorrosion oils and rubber softeners are produced Benzene and toluene for production of benzoic acid as well as solvent mixtures on pyrolysis of lighter fractions of shale oil are produced Middle shale oil fractions having antiseptic properties are used to produce effective oil for the impregnation of wood as a major shale oilderived specialty product Watersoluble phenols are selectively extracted from shale oil fractionated and crystallized for production of pure 5methylresorcinol and other alkyl resorcinol derivatives and highvalue intermediates to produce tanning agents epoxy resins and adhesives diphenyl ketone and phenolformaldehyde adhesive resins rubber modifiers chemicals and pesticides Some con ventional products such as coke and distillate boiler fuels are produced from shale oil as byproducts New market opportunities for shale oil and its fractions may be found improving the oil conversion and separation techniques In the petrochemical industry the organic chemicals produced in the largest volumes are metha nol ethylene propylene butadiene benzene toluene and xylenes Basic chemicals and plastics are the key building blocks for manufacture of a wide variety of durable and nondurable consumer goods The demand for chemicals and plastics is driven by global economic conditions which are directly linked to demand for consumer goods The petrochemical industry continues to be impacted by the globalization and integration of the world economy In the future manufacturing processes introduced in recent years will continue to result in the adaptation of the industry to new feedstocks which will chase shifts in the ratio of products produced This in turn will lead to the potential for a supplydemand imbalance particularly for smaller downstream petrochemical derivatives In addition growing environmental concerns and the variability of crude oil prices usually upward will expedite the development and commercialization of chemical prod ucts from sources other than crude oil and natural gas As a result feedstocks and technologies previously considered economically impractical will rise to meet the increasing demand There is however the everpresent political uncertainty that arise from the occurrence of natural gas and crude oil resources in countries provider countries other than user countries This has 27 The Petrochemical Industry serious global implications for the supply and demand of petrochemicals and raw materials In addi tion the overall expansion of the population and an increase in individual purchasing power has resulted in an increase in demand for finished goods and greater consumption of energy in China India and Latin America However the continued development of shale gas tight gas resources as well as crude oil from tight formation as well as the various technological advances to recover these resources such as the combination of vertical hydraulic fracturing and horizontal drilling will lead to a considerable rise in natural gas production and crude oil production This new potential will cause many countries to reexamine their natural gas reserves and crude oil reserves to pursue development of their own nationally occurring gas plays and crude oil plays The production of chemicals from biomass is becoming an attractive area of investment for industries in the framework of a more sustainable economy From a technical point of view a large fraction of industrial chemicals and materials from fossil resources can be replaced by their biobased counterparts Nevertheless fossilbased chemistry is still dominant because of optimized production processes and lower costs The best approach to maximize the valorization of biomass is the processing of biological feedstocks in integrated biorefineries where both biobased chemicals and energy carriers can be produced similar to a traditional petroleum refinery The challenge is to prove together with the technical and economic feasibility an environmental feasibility in terms of lower impact over the entire production chain Biomass is essentially a rich mixture of chemicals and materials and as such has a tremendous potential as feedstock for making a wide range of chemicals and materials with applications in industries from pharmaceuticals to furniture Various types of available biomass feedstocks includ ing waste and the different pretreatment and processing technologies being developed to turn these feedstocks into platform chemicals polymers materials and energy There are several viable biological and chemical transformation pathways from sugars to build ing blocks A large number of sugars to building block transformations can be done by aerobic fermentation employing fungi yeast or bacteria Chemical and enzymatic transformations are also important process options It should be noted however that pathways with more challenges and bar riers are less likely be considered as viable industrial processes In addition to gasification followed by FischerTropsch chemistry of the gaseous product synthesis gas chemical reduction oxida tion dehydration bond cleavage and direct polymerization are predominated Enzymatic biotrans formations comprise the largest group of biological conversions and some biological conversions can be accomplished without the need for an intermediate building block The 13Propanediol HOCH2CH2CH2OH is an example where a set of successive biological processes convert sugar directly to an end product Each pathway has its own set of advantages and disadvantages Biological conversions of course can be tailored to result in a specific molecular structure but the operating conditions must be relatively mild Chemical transformations can operate at high throughput but unfortunately less conversion specificity is achieved Biobased feedstocks may present a sustainable alternative to petrochemical sources to satisfy the everincreasing demand for chemicals However the conversion processes needed for these future biorefineries will likely differ from those currently used in the petrochemical industry Biotechnology and chemocatalysis offer routes for converting biomass into a variety of chemicals that can serve as startingpoint chemicals While a host of technologies can be leveraged for bio mass upgrading the outcome can be significant because there is the potential to upgrade the bio derived feedstocks while minimizing the loss of carbon and the generation of byproducts In fact biomass offers a source of carbon from the biosphere as an alternative to fossilized carbon laid down tens of millions of years ago Anything that grows and is available in nonfossil ized form can be classified as biomass including arable crops trees bushes animal byproducts human and animal waste waste food and any other waste stream that rots quickly and which can be replenished on a rolling time frame of years or decades One of the attractions of biomass is its versatility under the right circumstances it can be used to provide a sustainable supply of 28 Handbook of Petrochemical Processes electricity heat transport fuels or chemical feedstocks in addition to its many other uses One of the drawbacks of biomass especially in the face of so many potential end uses is its limited availability even though the precise limitation is the subject of debate Compared with the level of attention given to biomass as a source of electricity or heat relatively little attention has been paid to biomass as a chemical feedstock However in a world in which conventional feedstocks are becoming constrained and countries are endeavoring to meet targets for reducing carbon dioxide emissions there is a question as to whether biomass is too good to burn Developments in homogeneous and heterogeneous catalysis have led the way to effective approaches to utilizing renewable sources however further advances are needed to realize technol ogies that are competitive with established petrochemical processes Catalysis will play a key role with new reactions processes and concepts that leverage both traditional and emerging chemo and biocatalytic technologies Thus new knowledge and better technologies are needed in dealing with chemical transforma tions that involve milder oxidation conditions selective reduction and dehydration better control of bond cleavage and improvements to direct polymerization of multifunctional monomers For biological transformations better understanding of metabolic pathways and cell biology lower downstream recovery costs increased utility of mixed sugar streams and improved molecular thermal stability are necessary While it is possible to prepare a very large number of molecular structures from the top building blocks there is a scarcity of information about these behaviors of the molecular products and industrial processing properties A comprehensive database on biomo lecular performance characteristics would prove extremely useful to both the public sector and pri vate sector Nevertheless here is a significant market opportunity for the development of biobased products from the fourcarbon building blocks In order to be competitive with petrochemical derived products there is a significant technical challenge and should be undertaken with a long term perspective In summary the petrochemical industry which is based on crude oil and natural gas competes with the energy providing industry for the same fossil raw material Dwindling oil and gas reserves concern regarding the greenhouse effect carbon dioxide emissions and worldwide rising energy demand raise the question of the future availability of fossil raw materials Biotechnological chemi cal and engineering solutions are needed for utilization of this secondgeneration bio renewable based supply chain One approach consists of the concept of a biorefinery Also gasification followed by FischerTropsch chemistry is a promising pathway In the short term and in the medium term a feedstock mix with crude oil and natural gas dominating can most likely be expected In the long term due to the final limited availability of oil and gas biomass will prevail Prior to this change to occur great research and development efforts must be carried out to have the necessary technology available when needed In summary the petrochemical industry gives a series of valueadded products to the petroleum and natural gas industry but like any other business suffers from issues relating to maturity The reasons relating to the maturity of the industry are i expired patents ii varying demand iii matching demand with capacity and iv intense competition Actions to combat the aches and pains of maturity are to restructure capacity achieving mega sizes downstream and restructuring business practices Strategies followed by some companies to combat maturity include exit focus on core business and exploit a competitive advantage Nevertheless the petrochemical industry is and will remain a necessary industry for the support of modern and emerging lifestyles In order to maintain an established petrochemical industry strategic planning is the dominating practice to maintain the industry replace imports export new products alternate feedstocks such as the return to the chemicalsfromcoal concept and the acceptance of feedstocks such as oil shale and biomass including developing criteria for selecting productsprojects After the oil crises of the 1970s even though it is now four decades since these crises it is necessary to cope with the new environment of product demand through the response to new growth markets and security of feedstock supply Mergers alliances and acquisitions could 29 The Petrochemical Industry well be the dominating practice to combat industry maturity and increased market demand as one of the major activities Other strategies are the focus on core business the production of chemicals and last but not least the emergence or in the case of coal the reemergence of alternate feed stocks to ensure industry survival REFERENCES Chenier PJ 2002 Survey of Industrial Chemicals 3rd Edition Springer New York Clark JH and Deswarte F Editors 2015 Introduction to Chemicals from Biomass 2nd Edition John Wiley Sons Inc Hoboken NJ EPCA 2016 50 Years of Chemistry for You European Petrochemical Association Brussels Belgium https epcaeu Favennec JP Editor 2001 Petroleum Refining Refinery Operation 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Technologies CRC Press Boca Raton FL Maddox RN Bhairi A Mains GJ and Shariat A 1985 In Acid and Sour Gas Treating Processes SA Newman Editor Gulf Publishing Company Houston TX Chapter 8 Matar S and Hatch LF 2001 Chemistry of Petrochemical Processes 2nd Edition ButterworthHeinemann Woburn MA Meyers RA 2005 Handbook of Petrochemicals Production Processes McGrawHill New York Mokhatab S Poe WA and Speight JG 2006 Handbook of Natural Gas Transmission and Processing Elsevier Amsterdam Netherlands Moschopedis SE and Speight JG 1971 WaterSoluble Derivatives of Athabasca Asphaltenes Fuel 50 34 Moschopedis SE and Speight JG 1974 The Chemical Modification of Bitumen and Its NonFuel Uses Preprints Div Fuel Chem Am Chem Soc 192 291 Moschopedis SE and Speight JG 1976a The Chemical Modification of Bitumen Heavy Ends and Their NonFuel Uses In Shale Oil Tar Sands and Related Fuels Sources Adv in Chem Series No 151 Am Chem Soc TF Yen Editor p 144 Moschopedis SE and Speight JG 1976b The Chlorinolysis of Petroleum Asphaltenes Chemika Chronika 5 275 Moschopedis SE and Speight JG 1978 Sulfoxidation of Athabasca Bitumen Fuel 857 647 Naderpour N 2008 Petrochemical Production Processes SBS Publishers Delhi India Newman SA 1985 Acid and Sour Gas Treating Processes Gulf Publishing Company Houston TX Parkash S 2003 Refining Processes Handbook Gulf Professional Publishing Elsevier Amsterdam Netherlands Spitz PH 1988 Petrochemicals The Rise of an Industry John Wiley Sons Inc Hoboken NJ Speight JG 1987 Petrochemicals Encyclopedia of Science and Technology Vol 13 6th Edition McGrawHill New York p 251 Speight JG 1994 Chemical and Physical Studies of Petroleum Asphaltene Constituents In Asphaltene Constituents and Asphalts I Developments in Petroleum Science 40 TF Yen and GV Chilingarian Editors Elsevier Amsterdam Netherlands Chapter 2 Speight JG 2002 Chemical Process and Design Handbook McGrawHill New York 30 Handbook of Petrochemical Processes Speight JG 2008 Handbook of Synthetic Fuels Handbook Properties Processes and Performance McGrawHill New York Speight JG 2011 The Refinery of the Future Gulf Professional Publishing Elsevier Oxford UK Speight JG 2013 The Chemistry and Technology of Coal 3rd Edition CRC Press Boca Raton FL Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Speight JG 2015 Handbook of Petroleum Product Analysis 2nd Edition John Wiley Sons Inc Hoboken NJ Speight JG 2016 Handbook of Hydraulic Fracturing John Wiley Sons Inc Hoboken NJ Speight JG 2017 Handbook of Petroleum Refining CRC Press Boca Raton FL Steiner H 1961 Introduction to Petroleum Chemicals Pergamon Press New York Wittcoff HA and Reuben BG 1996 Industrial Organic Chemicals John Wiley Sons Inc New York 31 2 Feedstock Composition and Properties 21 INTRODUCTION In any text related to the various aspects of petrochemical technology it is necessary to consider the properties and behavior of the feedstocks first through the name or terminology andor the definition of the feedstock Because of the need for a thorough understanding of the petrochemical industry as well as crude oil and the associated feedstocks it is essential that the definitions and the terminology of petrochemical science and technology be given prime consideration Terminology is the means by which various subjects are named so that reference can be made in conversations and in writings and so that the meaning is passed on Definitions are the means by which scientists and engineers communicate the nature of a material to each other and to the world either through the spoken or the written word Thus the definition of a material can be extremely important and have a profound influence on how the technical community and the public perceive that material This part of the text attempts to alleviate much of the confusion that exists but it must be remembered that the terminology of crude oil is unfortunately still open to personal choice and historical use of the various names While there is standard terminology that is recommended for crude oil and crude oil prod ucts ASTM D4175 2018 there is little in the way of standard terminology for heavy oil extra heavy oil and tar sand bitumen Speight 2013a 2013b 2013c 2014a At best the terminology is illdefined and subject to changes from one governing body company to another The particu larly troublesome and more confusing terminologies are those terms that are applied to the more viscous feedstocks for example the use of the terms bitumen the naturally occurring carbona ceous material in tar sand deposits and asphalt refinery product produced from residua Another example of an irrelevant terminology is the term black oil which besides the color of the oil offers nothing in the way of explanation of the properties of the oil and certainly adds nothing to any scientific andor engineering understanding of the oil this term ie black oil is not used in this textThe feedstocks to be considered here are i natural gas ii conventional crude oil iii heavy oil iv extra heavy oil v tar sand bitumen vi coal vii oil shale and viii biomass including landfill gas and biogas All of these current and potential feedstocks could continue in the petro chemical industry for the foreseeable future as the reserves of natural gas and conventional crude oil become depleted to the point of exhaustion during the next 50 years Speight 2011a Speight and Islam 2016 However for the most part in view of the current sources of petrochemicals the major focus will be on petroleum with reference where appropriate to the other sources of petrochemicals 22 NATURAL GAS Natural gas predominantly methane occurs in underground reservoirs separately or in association with crude oil Chapter 2 Speight 2007 2008 2014a The principal types of hydrocarbon deriva tives produced from natural gas are methane CH4 and varying amounts of higher molecular weight hydrocarbon derivatives from ethane CH3CH3 to octane CH3CH26CH3 Generally the higher molecular weight liquid hydrocarbon derivatives from pentane to octane are collectively referred to as gas condensate 32 Handbook of Petrochemical Processes While natural gas is predominantly a mixture of combustible hydrocarbon derivatives Table 21 many natural gases also contain nitrogen N2 as well as carbon dioxide CO2 and hydrogen sulfide H2S Trace quantities of helium and other sulfur and nitrogen compounds may also be pres ent However raw natural gas varies greatly in composition and the constituents can be several of a group of saturated hydrocarbon derivatives from methane to higher molecular weight hydrocarbon derivatives especially natural gas that has been associated with crude oil in the reservoir and non hydrocarbon constituents Table 21 The treatment required to prepare natural gas for distribution as an industrial or household fuel is specified in terms of the use and environmental regulations Briefly natural gas contains hydrocarbon derivatives and nonhydrocarbon gases Hydrocarbon gases are methane CH4 ethane C2H6 propane C3H8 butanes C4H10 pentanes C5H12 hexane C6H14 heptane C7H16 and sometimes trace amounts of octane C8H18 and higher molecular weight hydrocarbon derivatives For example TABLE 21 Composition of Associated Natural Gas from a Petroleum Well Category Component Amount vv Paraffins Methane CH4 7098 Ethane C2H6 110 Propane C3H8 Trace5 Butane C4H10 Trace2 Pentane C5H12 Tracel Hexane C6H14 Trace05 Heptane and higher molecular weight C7 Trace Cycloparaffins Cyclohexane C6H12 Trace Aromatics Benzene C6H6 other aromatics Trace Nonhydrocarbons Nitrogen N2 Trace15 Carbon dioxide CO2 Trace1 Hydrogen sulfide H2S Trace1 Helium He Trace5 Other sulfur and nitrogen compounds Trace Water H2O Trace5 CH3CH2CH2CH3 nButane CH33CH or CH32CHCH3 isobutane CH3CH2CH2CH2CH3 nPentane CH32CHCH2CH3 isopentane 33 Feedstock Composition and Properties As illustrated above an isoparaffin is an isomer having a methyl group branching from carbon number 2 of the main chain The higherboiling hydrocarbon constituents than methane CH4 are often referred to as natural gas liquids NGLs and the natural gas may be referred to as rich gas The constituents of natu ral gas liquids are hydrocarbon derivatives such as ethane CH3CH3 propane CH3CH2CH3 butane CH3CH2CH2CH3 as well as isobutane pentane derivatives CH3CH2CH2CH2CH3 as well as isopentane and higher molecular weight hydrocarbon derivatives which have wide use in the petrochemical industry Chapter 6 Some aromatic derivatives BTXbenzene C6H6 toluene C6H5CH3 and the xylene isomers o m and pCH3C6H4CH3 can also be present raising safety issues due to their toxicity The nonhydrocarbon gas portion of the natural gas contains nitrogen N2 carbon dioxide CO2 helium He hydrogen sulfide H2S water vapor H2O and other sul fur compounds such as carbonyl sulfide COS and mercaptans eg methyl mercaptan CH3SH and trace amounts of other gases In addition the composition of a gas stream from a source or at a location can also vary over time which can cause difficulties in resolving the data from the applica tion of standard test methods Klimstra 1978 Liss and Thrasher 1992 Carbon dioxide and hydrogen sulfide are commonly referred to as acid gases since they form cor rosive compounds in the presence of water Nitrogen helium and carbon dioxide are also referred to as diluents since none of these burn and thus they have no heating value Mercury can also be present either as a metal in vapor phase or as an organometallic compound in liquid fractions Concentration levels are generally very small but even at very small concentration levels mercury can be detrimental due its toxicity and its corrosive properties reaction with aluminum alloys The higher molecular weight constituents ie the C5 product are also commonly referred to as gas condensate or natural gasoline or sometimes on occasion as casinghead gas because of the tendency of these constituents to condense at the top of the well casing When referring to natural gas liquids in the gas stream the term gallon per thousand cubic feet is used as a measure of high molecular weight hydrocarbon content On the other hand the composition of nonassociated gas sometimes called well gas is deficient in natural gas liquids The gas is produced from geological formations that typically do not contain much if any hydrocarbon liquids Furthermore within the natural gas family the composition of associated gas a byproduct of oil production and the oil recovery process is extremely variable even within the gas from a petroleum reservoir Speight 2014a 2018 After the production fluids are brought to the surface they are separated at a tank battery at or near the production lease into a hydrocarbon liquid stream crude oil or condensate a produced water stream brine or salty water and a gas stream The gaseous mixtures considered in this volume are mixtures of various constituents that may or may not vary over narrow limits The defining characteristics of the various gas streams in the context of this book are that the gases i exist in a gaseous state at room temperature ii may con tain hydrocarbon constituents with 14 carbons ie methane ethane propane and butane isomers iii may contain diluents and inert gases and iv may contain contaminants in the form of non hydrocarbon constituents Each constituent of the gas influences the properties Typically these gases fall into the general category of fuel gases and each gas is any one of sev eral fuels that at standard conditions of temperature and pressure are gaseous Before sale of the gas to the consumer actions it is essential to give consideration of the variability of the composition of gas streams before and after processing Table 22 and the properties of the individual constitu ents and their effects on gas behavior even when considering the hydrocarbon constituents only If not the properties of the gas may be unstable and the ability of the gas to be used for the desired purpose will be seriously affected 221 comPosition and ProPerties Natural gas is a naturally occurring gas mixture consisting mainly of methane that is found in porous formations beneath the surface of the earth often in association with crude oil but while the gas from 34 Handbook of Petrochemical Processes the various sources has a similar analysis it is not entirely the same In fact variation in composition varies from field to field and may even vary within a reservoir In addition the variation of gas streams from different sources Chapter 3 must also be considered when processing options are being assessed Thus because of the lower molecular weight constituents of these gases and their volatility gas chro matography has been the technique of choice for fixed gas and hydrocarbon speciation and mass spec trometry is also a method of choice for compositional analysis of low molecular weight hydrocarbon derivatives Speight 2015 ASTM 2018 Speight 2018 The vapor pressure and volatility specifica tions will often be met automatically if the hydrocarbon composition is in order with the specification As with crude oil natural gas from different wells varies widely in composition and analyses Mokhatab et al 2006 Speight 2014a and the proportion of nonhydrocarbon constituents can vary over a very wide range The nonhydrocarbon constituents of natural gas can be classified as two types of materials i diluents such as nitrogen carbon dioxide and water vapors and ii contaminants such as hydrogen sulfide andor other sulfur compounds Thus a particular natural gas field could require production processing and handling protocols different from those used for gas from another field Thus there is no single composition of components which might be termed typical natural gas Speight 2007 2014a 2018 Methane and ethane often constitute the bulk of the combustible com ponents carbon dioxide CO2 and nitrogen N2 are the major noncombustible inert components Thus sour gas is natural gas that occurs mixed with higher levels of sulfur compounds such as hydrogen sulfide H2S and mercaptan derivatives often called thiols RSH and which consti tute a corrosive gas Speight 2014b The sour gas requires additional processing for purification Mokhatab et al 2006 Speight 2014a Olefin derivatives are also present in the gas streams from various refinery processes and are not included in liquefied petroleum gas but are removed for use in petrochemical operations Crawford et al 1993 The composition and properties of any gas stream depends on the characterization and properties of the hydrocarbon derivatives that make up the stream and calculation of the properties of a mix ture depends on the properties of its constituents However calculation of the property of a mixture based on an average calculation neglects any interactions between the constituents This makes the issue of modeling of the properties of the gas mixture a difficult one because of the frequent lack of knowledge and omission of any chemical or physical interactions between the gas stream constitu ents Because of the lower molecular weight constituents of these gases and their volatility gas chro matography has been the technique of choice for hydrocarbon speciation and mass spectrometry is also a method of choice for compositional analysis of low molecular weight hydrocarbon derivatives Speight 2015 ASTM 2018 Speight 2018 The vapor pressure and volatility specifications will often be met automatically if the hydrocarbon composition is in order with the specification TABLE 22 General Properties of Unrefined Natural Gas and Refined Natural Gas Property Unrefined Gas Refined Gas Carbon ww 73 75 Hydrogen ww 27 25 Oxygen ww 04 0 Hydrogentohydrogen atomic ratio 35 40 Vapor density air 1 15C 15 06 Methane vv 80 1000 Ethane vv 5 0 Nitrogen vv 15 0 Carbon dioxide vv 5 0 Sulfur ppm ww 5 0 35 Feedstock Composition and Properties Natural gas is found in petroleum reservoirs as free gas associated gas or in solution with petroleum in the reservoir dissolved gas or in reservoirs that contain only gaseous constituents and no or little petroleum unassociated gas Speight 2014a The hydrocarbon content varies from mixtures of methane and ethane with very few other constituents dry gas to mixtures containing all the hydrocarbon derivatives from methane to pentane and even hexane C6H14 and heptane C7H16 wet gas In both cases some carbon dioxide CO2 and inert gases including helium He are present together with hydrogen sulfide H2S and a small quantity of organic sulfur The term petroleum gases in this context is also used to describe the gaseous phase and liquid phase mixtures comprised mainly of methane to butane C1C4 hydrocarbon derivatives that are dissolved in the crude oil and natural gas as well as gases produced during thermal processes in which the crude oil is converted to other products It is necessary however to acknowledge that in addition to the hydrocarbon derivatives gases such as carbon dioxide hydrogen sulfide and ammo nia are also produced during petroleum refining and will be constituents of refinery gas that must be removed Olefin derivatives are also present in the gas streams of various processes and are not included in liquefied petroleum gas but are removed for use in petrochemical operations Crawford et al 1993 Nonassociated natural gas which is found in reservoirs in which there is no or at best only minimal amounts of crude oil Chapter 1 Nonassociated gas is usually richer in methane but is markedly leaner in terms of the higher molecular weight hydrocarbon derivatives and condensate Conversely there is also associated natural gas dissolved natural gas that occurs either as free gas or as gas in solution in the petroleum Gas that occurs as a solution with the crude petroleum is dis solved gas whereas the gas that exists in contact with the crude petroleum gas cap is associated gas Chapter 1 Associated gas is usually leaner in methane than the nonassociated gas but is richer in the higher molecular weight constituents Thus the most preferred type of natural gas is the nonassociated gas Such gas can be produced at high pressure whereas associated or dissolved gas must be separated from petroleum at lower separator pressures which usually involves increased expenditure for compression Thus it is not surprising that such gas under conditions that are not economically favorable is often flared or vented Natural gas is a naturally occurring mixture of lowboiling hydrocarbon derivatives accom panied by some nonhydrocarbon compounds Nonassociated natural gas is found in reservoirs containing no oil dry wells Associated gas on the other hand is present in contact with andor dissolved in crude oil and is coproduced with it The principal component of most natural gases is methane Higher molecular weight paraffin hydrocarbon derivatives C2C7 even to C10 in some cases are usually present in smaller amounts with the natural gas mixture and their ratios vary considerably from one gas field to another Nonassociated gas normally contains a higher methane ratio than associated gas while the latter contains a higher ratio of higher molecular weight hydro carbon derivatives Table 21 Crude oilrelated gases including associated natural gas and refinery gases process gases as well as product gases produced from petroleum upgrading are a category of saturated and unsaturated gaseous hydrocarbon derivatives predominantly in the C1C6 carbon number range Some gases may also contain inorganic compounds such as hydrogen nitrogen hydrogen sulfide carbon monoxide and carbon dioxide As such petroleum and refinery gases unless produced as a salable product that must meet specifications prior to sale are often unknown or variable composition and toxic API 2009 ASTM 2018 The siterestricted petroleum and refinery gases ie those not produced for sale often serve as fuels consumed onsite as intermediates for puri fication and recovery of various gaseous products or as feedstocks for isomerization and alkyla tion processes within a facility Thus natural gas is a combustible mixture of hydrocarbon gases that in addition to methane also includes ethane propane butane and pentane The composition of natural gas can vary widely before it is refined Tables 21 and 22 Mokhatab et al 2006 Speight 2014a In its purest form such as the natural gas that is delivered to the consumer is almost pure methane 36 Handbook of Petrochemical Processes The principal constituent of most natural gases is methane with minor amounts of heavier hydro carbon derivatives and certain nonhydrocarbon gases such as nitrogen carbon dioxide hydrogen sulfide and helium Mokhatab et al 2006 Speight 2014a ASTM 2018 Speight 2018 Methane can be produced in the laboratory by heating sodium acetate with sodium hydroxide and by the reaction of aluminum carbide Al4C3 with water Al C 12H O 4Al OH 3CH 4 3 2 3 4 CH CO Na NaOH CH Na CO 3 2 4 2 3 The members of the hydrocarbon gases are predominantly alkane derivatives CnH2n2 where n is the number of carbon atoms When inorganic constituents are present in natural gas they consist of asphyxiant gases such as hydrogen Unlike other categories of crude oil products such as naphtha kerosene and the higherboiling products Speight 2014a ASTM 2018 Speight 2017 the constituents of the various gas streams can be evaluated and the results of the constituent evaluation can then be used to estimate the behavior of the gas ASTM 2018 Speight 2018 The constituents used to evaluate the behavior of the gas are i the C1C4 hydrocarbon derivatives ii the C5C6 hydrocarbon derivatives although in natural gas the C1C4 constituents predominate and iii the asphyxiant gases ie carbon diox ide nitrogen and hydrogen In general most gas streams used in this text are composed of predomi nantly the methane C1 to butane C4 hydrocarbon derivatives which have extremely low melting points and boiling points Each of these gases has a high vapor pressures and low octanolwater partition coefficientsthe octanolwater partition coefficient Kow is a valuable parameter that represents a measure of the tendency of a chemical to move from the aqueous phase to the organic octanol phase Thus K C C ow op w Cop and Cw are the concentrations of the chemical in gmL of the chemical in the octanolrich phase and in the waterrich phase respectively In the determination of the partition coefficient at 25C 77F the waterrich phase is essentially pure water 9999 mol water while the octanolrich phase is a mixture of octanol and water 793 mol octanol While not always required in the pro duction of petrochemicals such a property may be of some value during application of the synthetic method and as a means of product purification The aqueous solubility of the various constituents of gas streams varies but the solubility of most of the hydrocarbon derivatives typically falls within a range of 22 mgL to several hundred parts per million There are also a few gas streams that may contain heptane derivatives and octane deriva tive although such streams would necessarily be at elevated temperature andor reduced pressure to maintain the heptane derivatives and the octane derivatives in the gaseous state Hydrocarbon compounds containing pentane hexane heptane and octane derivatives occur predominantly in lowboiling crude oil naphtha and also occur in gas condensate and natural gas By way of recall in addition to methane natural gas contains other constituents that are vari ously referred to as i natural gas liquids ii natural gas condensate and iii natural gasoline Chapter 1 Also by way of a refresher definition natural gas liquids are hydrocarbon deriva tives that occur as gases at ambient conditions atmospheric pressure and temperature but as liq uids under higher pressure and which can also be liquefied by cooling The specific pressure and temperature at which the gases liquefy vary by the type of gas liquids and may be described as lowboiling light or highboiling heavy according to the number of carbon atoms and hydrogen atoms in the molecule In terms of the chemical reactions of natural gas the most common reaction is combustion pro cess which is represented as chemical reaction between methane and oxygen which results in the 37 Feedstock Composition and Properties production of carbon dioxide CO2 water H2O plus the exothermic liberation of energy heat Thus CH g 2O g CO g 2H Ol 4 2 2 2 Higher molecular weight hydrocarbon alkane constituents will also participate in the combustion reaction In an unlimited supply of oxygen and assuming that there may be traces of hydrocarbon derivatives up to octane in a natural gas stream the combustion reactions are C H 5O 3CO 4H O 3 8 2 2 2 2C H g 13O g 8CO g 10H Og 4 10 2 2 2 C H g 8O g 5CO g 6H Og 5 12 2 2 2 2C H l 19O g 12CO g 14H Og 6 14 2 2 2 C H l 11O g 7CO g 8H Og 7 16 2 2 2 2C H l 25O g 16CO g 18H Og 8 18 2 2 2 The balanced chemical equation for the complete combustion of a general hydrocarbon fuel CxHy is C H x y4 O xCO x2H O x y 2 2 2 To the purist chemical equations do not involve fractions and to balance this final equation the fractional numbers should be converted to whole numbers In an inadequate supply of air carbon monoxide and water vapor are formed using methane as the example 2CH 3O 2CO 4H O 4 2 2 In this context of combustion natural gas is the cleanest of all the fossil fuels Coal and crude oil are composed of much more complex molecules with a higher carbon ratio and as well as constitu ents containing nitrogen and sulfur contents Thus when combusted coal and oil release higher levels of harmful emissions including a higher ratio of carbon emissions nitrogen oxides NOx and sulfur dioxide SO2 which under the conditions of the atmosphere can be converted to sulfur trioxide SO3 Upon further reaction with the water in the atmosphere the oxides of nitrogen and the oxides of sulfur are converted to acids and thus the overall result is the production of acid rain Chapter 10 SO H O H SO 2 2 2 3 2SO O 2SO 2 2 3 SO H O H SO 3 2 2 4 2NO H O 2HNO 2 2 2NO O 2NO 2 2 NO H O HNO 2 2 3 38 Handbook of Petrochemical Processes Substitution reactions will also occur in which the hydrocarbon derivatives in natural gas will react with for example chlorine to produce a range of chloroderivatives CH Cl CH Cl HCl 4 2 3 CH Cl Cl CH Cl HCl 3 2 2 2 CH Cl Cl CHCl HCl 2 2 2 3 CHCl Cl CCl HCl 2 2 4 The reaction of chlorine with ethane may be written similar to C H Cl C H Cl HCl 2 6 2 2 5 C H Cl Cl C H Cl HCl 2 4 2 2 2 3 3 The ultimate product is hexachloroethane Both of these reactions may be used industrially As the hydrocarbon derivatives increase in molecular size to propane and butane the reaction becomes more complex In addition to gas streams particularly natural gas being used as fuel to produce heat as well as the production of hydrogen the steammethane reforming process and ammonia CH H O CO 3H steam methanereforming 4 2 2 CO H O CO H hydrogenproduction 2 2 2 3H N 2NH Haber Boschprocess 2 2 3 The steammethane reforming process is major source of hydrogen for refineries and other indus tries Speight 2016b The general feedstock for this process is natural gas which has a high content of methane 8595 vv Once the feedstock gas is obtained it is desulfurized and treated before being sent to the reformer The feedstock must be treated first to ensure that the sulfur is not released to the environment where it can cause significant damage In the endothermic process hightemperature steam 700C1100C 1290F2010F is used to produce hydrogen from a methane source such as natural gas at pressures in the order of 45370 psi Subsequently in what is called the watergas shift reaction the carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen In a final process step pressureswing adsorption carbon dioxide and other impurities are removed from the gas stream leaving essentially pure hydrogen CH H O CO 3H steam methanereforming 4 2 2 CO H O CO H water gasshiftreaction 2 2 2 In most plants this reaction will occur in two different stages a hightemperature shift reaction which is then followed by a lowtemperature shift reactor The purpose of including both reactors is to maximize the yield of hydrogen The byproduct passes through the hightemperature shift reactor first where due to the high temperature the reaction will be able to occur rapidly However due to the reaction being a slightly exothermic reaction when it shifts right it is possible to obtain a greater yield of hydrogen by passing the reformer byproducts through the lowtemperature shift reactor In both reactors a catalyst is employed to increase the hydrogen yield 39 Feedstock Composition and Properties The other low molecular weight hydrocarbon derivatives in the gasethane C2H6 propane C3H8 and the butane isomers C4H10 either in the gas phase or liquefied are also used for heat ing as well as for motor fuels and as feedstocks for chemical processing The pentane derivatives C5H12 are products of natural gas or crude oil fractionation or refinery operations ie reform ing and cracking that are removed for use as chemical feedstocks Table 23 It is only rarely that olefin derivatives occur in natural gas and they are not typically constituents of natural gas stream However olefin derivatives do occur in biogas produced by thermal methods Parkash 2003 Mokhatab et al 2006 Gary et al 2007 Speight 2011a 2011b 2014a Hsu and Robinson 2017 Speight 2017 Because of the wide range of chemical and physical properties a wide range of tests have been and continue to be developed to provide an indication of the means by which a particular gas should be processed although certain of these test methods are in more common use than others Speight 2015 ASTM 2018 Speight 2018 Initial inspection of the nature of the petroleum will provide deductions about the most logical means of refining or correlation of various properties to structural types present and hence attempted classification of the petroleum Proper interpretation of the data resulting from the inspection of crude oil requires an understanding of their significance Having decided what characteristics are necessary for a gas stream it then remains to describe the product in terms of a specification This entails selecting suitable test methods to determine the constituents and properties of the gas stream and setting appropriate limits for any variation of the proportion of the constituents and the limits of the variation in the properties The hydrocarbon component distribution of liquefied petroleum gases and propene mixtures is often required for end use sale of this material Applications such as chemical feedstocks or fuel require precise compositional data to ensure uniform quality Trace amounts of some hydrocarbon impurities in these materials can have adverse effects on their use and processing The component distribution data of liquefied petroleum gases and propene mixtures can be used to calculate physi cal properties such as relative density and vapor pressure Precision and accuracy of compositional data are extremely important when these data are used to calculate various properties An issue that arises during the characterization of liquefied petroleum gas relates to the accu rate determination of higherboiling residues ie higher molecular weight hydrocarbon deriva tives and even oils in the gas Test methods using procedures similar to those employed in gas TABLE 23 Possible Constituents of Natural Gas and Refinery Process Gas Streams Gas Molecular Weight Boiling Point 1 atm C F Density at 60F 156C 1 atm gL Relative to Air 1 Methane 16043 1615 2587 06786 05547 Ethylene 28054 1037 1547 11949 09768 Ethane 30068 886 1275 12795 10460 Propylene 42081 477 539 18052 14757 Propane 44097 421 438 18917 15464 12Butadiene 54088 109 516 23451 19172 13Butadiene 54088 44 241 23491 19203 1Butene 56108 63 207 24442 19981 cis2Butene 56108 37 387 24543 20063 trans2Butene 56108 09 336 24543 20063 isobutene 56104 69 196 24442 19981 nButane 58124 05 311 25320 20698 isobutane 58124 117 109 25268 20656 40 Handbook of Petrochemical Processes chromatographic simulated distillation are becoming available In fact the presence of any compo nent substantially less volatile than the main constituents of the liquefied petroleum gas will give rise to unsatisfactory performance It is difficult to set limits to the amount and nature of the residue which will make a product unsatisfactory For example liquefied petroleum gases that contain cer tain antiicing additives can give erroneous results by this test method Control over the residue content is of considerable importance in end use applications of lique fied petroleum gases In liquid feed systems residues can lead to troublesome deposits and in vapor withdrawal systems residues that are carried over can foul regulating equipment Any residue that remains in the vaporwithdrawal systems will accumulate can be corrosive and will contaminate subsequent product Water particularly if alkaline can cause failure of regulating equipment and corrosion of metals Obviously small amounts of oillike material can block regulators and valves In liquid vaporizer feed systems the gasolinetype material could cause difficulty Olefin derivatives ethylene CH2CH2 propylene CH3CHCH2 butylene derivatives such as CH3CH2CHCH2 and pentylene derivatives such as CH3CH2CH2CHCH2 that occur in refin ery gas process gas have specific characteristics and require specific testing protocols Speight 2015 ASTM 2018 Speight 2018 The amount of ethylene CH2CH2 in a gas stream is limited because it is necessary to restrict the number of unsaturated components to avoid the formation of deposits caused by the polymerization of the olefin constituents In addition ethylene boiling point 104C 155F is more volatile than ethane boiling point 88C 127F and therefore a product with a substantial proportion of ethylene will have a higher vapor pressure and volatility than one that is predominantly ethane Butadiene is also undesirable because it may also produce polymeric products that form deposits and cause blockage of lines As stated above the amount of ethylene and other olefin derivatives in the mixture is limited because not only it is necessary to restrict the amount of the unsaturated components olefin deriva tives so as to avoid the formation of deposits caused by the polymerization of the olefins but also to control the volatility of the sample Ethylene boiling point 104C 155F is more volatile than ethane boiling point 88C 127F and therefore a product with a substantial proportion of ethylene will have a higher vapor pressure and volatility than one that is predominantly ethane Butadiene is also undesirable because it may also produce polymeric products that form deposits and cause blockage of lines Ethylene is one of the highest volume chemicals produced in the world with global produc tion exceeding 100 million metric tons annually Ethylene is primarily used in the manufacture of polyethylene ethylene oxide and ethylene dichloride as well as many other lower volume products Most of these production processes use various catalysts to improve product quality and process yield Impurities in ethylene can damage the catalysts resulting in significant replacement costs reduced product quality process downtime and decreased yield Ethylene is typically manufactured through the use of steam cracking In this process gas eous or light liquid hydrocarbon derivatives are combined with steam and heated to 750C950C 1380F1740F in a pyrolysis furnace Numerous free radical reactions are initiated and larger hydrocarbon derivatives are converted cracked into smaller hydrocarbon derivatives In addition the high temperatures used in steam cracking promote the formation of unsaturated or olefin com pounds such as ethylene Ethylene feedstocks must be tested to ensure that only highpurity eth ylene is delivered for subsequent chemical processing Samples of highpurity ethylene typically contain only two minor impurities methane and ethane which can be detected in low ppm vv concentrations However steam cracking can also produce higher molecular weight hydrocarbon derivatives especially when propane butane or light liquid hydrocarbon derivatives are used as starting mate rials and the feedstock is a heavy oil where the coking tendency of the heavy feedstock is high Parkash 2003 Mokhatab et al 2006 Gary et al 2007 Van Geem et al 2008 Speight 2011a 2014a Hsu and Robinson 2017 Speight 2017 Although fractionation is used in the final produc tion stages to produce a highpurity ethylene product it is still important to be able to identify and 41 Feedstock Composition and Properties quantify any other hydrocarbon derivatives present in an ethylene sample Achieving sufficient resolution of all of these compounds can be challenging due to their similarities in boiling point and chemical structure Since the composition of the various gases can vary so widely no single set of specifications could cover all situations The requirements are usually based on performances in burners and equipment on minimum heat content and on maximum sulfur content Gas utilities in most states come under the supervision of state commissions or regulatory bodies and the utilities must provide a gas that is acceptable to all types of consumers and that will give satisfactory performance in all kinds of consuming equipment However particularly relevant are the heating values of the various fuel gases and their constituents For this reason measurement of the properties of fuel gases is an important aspect of fuel gas technology However the physical properties of unrefined natural gas are variable because the composi tion of natural gas is never constant Therefore the properties and behavior of natural gas are best understood by investigating the properties and behavior of the constituents Thus if the natural gas has been processed ie any constituents such as carbon dioxide and hydrogen sulfide have been removed and the only constituents remaining are hydrocarbon derivatives then the properties and behavior of natural gas becomes a study of the properties and behavior of the relevant constituents The composition of natural gas varies depending on the field the formation or the character of the reservoir from which the gas is extracted and that are an artifact of its formation Speight 2014a Also the properties of other gas streams Chapter 3 vary with the source from which the gas was produced and the process by which the gas was produced The different hydrocarbon derivatives that form the gas streams can be separated using their different physical properties as weight boiling point or vapor pressure Chapters 6 and 7 Depending on its content of higher molecular weight hydrocarbon components natural gas can be considered as rich five or six gal lons or more of recoverable hydrocarbon components per cubic feet or lean less than one gallon of recoverable hydrocarbon components per cubic feet In terms of chemical behavior hydrocarbon derivatives are simple organic chemicals that contain only carbon and hydrogen Thus in this sec tion the properties and behavior of hydrocarbon derivatives up to and include noctane C8H18 are presented On the other hand when natural gas is refined and any remaining hydrocarbon deriva tives are removed the gas that is sold to the consumer the sole component other than an odorizer is methane CH4 and the properties are constant There are two major technical aspects to which gas quality relates i the pipeline specification in which stringent specifications for water content and hydrocarbon dew point are stated along with limits for contaminants such as sulfurthe objective is to ensure pipeline material integrity for reliable gas transportation purpose and ii the interchangeability specification which may include analytical data such as calorific value and relative density that are specified to ensure satisfactory performance of end use equipment Gas interchangeability is a subset of the gas quality specification ensuring that gas supplied to domestic users will combust safely and efficiently The Wobbe number is a common but not uni versal measure of interchangeability and is used to compare the rate of combustion energy output of different composition fuel gases in combustion equipment For two fuels with identical Wobbe Indices the energy output will be the same for given pressure and valve settings Finally in terms of properties and any test methods that are applied to natural gas Speight 2015 ASTM 2018 Speight 2018 it is necessary to recognize the other constituents of a natural gas stream that is produced from a reservoir as well as any gas streams Chapter 3 that may be blended into the natural gas stream Briefly blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled Thus natural gas liquids are products other than methane from natural gas ethane butane isobutane and propane Test methods for gaseous fuels have been developed over many years extending back into the 1930s Bulk physical property tests such as density and heating value as well as some composi tional tests such as the Orsat analysis and the mercuric nitrate method for the determination of 42 Handbook of Petrochemical Processes unsaturation were widely used More recently mass spectrometry has become a popular method of choice for compositional analysis of low molecular weight and has replaced several older meth ods Also gas chromatography is another method of choice for hydrocarbon identification in gases Speight 2015 ASTM 2018 Speight 2018 The various gas streams Chapter 3 are generally amenable to analytical techniques and there has been the tendency and it remains for the determination of both major constituents and trace constituents than is the case with the heavier hydrocarbon derivatives The complexity of the mix tures that are evident as the boiling point of petroleum fractions and petroleum products increases make identification of many of the individual constituents difficult if not impossible In addition methods have been developed for the determination of physical characteristics such as calorific value specific gravity and enthalpy from the analyses of mixed hydrocarbon gases but the accu racy does suffer when compared to the data produced by methods for the direct determination of these properties The different methods for gas analysis include absorption distillation combustion mass spec troscopy infrared spectroscopy and gas chromatography Absorption methods involve absorbing individual constituents one at a time in suitable solvents and recording of contraction in volume measured Distillation methods depend on the separation of constituents by fractional distillation and measurement of the volumes distilled In combustion methods certain combustible elements are caused to burn carbon dioxide and water and the volume changes are used to calculate com position Infrared spectroscopy is a useful application and for the most accurate analyses mass spectroscopy and gas chromatography are the preferred methods However the choice of a particular test to determine any property remains as the decision of the analyst that then depends upon the nature of the gas under study For example judgment by the analyst is necessary whether or not a test that is applied to a gas stream is suitable for that gas stream insofar as inference from the nonhydrocarbon constituents will be minimal The following section presents a brief illustration of the properties of natural gas hydrocar bon derivatives from methane up to and including noctane C8H18 This will allow the reader to understand the folly of stating the properties of natural gas as average properties rather than allowing for the composition of the gas mixture and recognition of the properties of the individual constituents 222 natural Gas liquids Natural gas liquids lease condensate natural gasoline are components of natural gas that are liquid at surface in gas or oil field facilities or in gas processing plants The composition of the natural gas liquids is dependent upon the type of natural gas and the composition of the natural gas Natural gas liquids are the nonmethane constituents such as ethane propane butane and pen tanes and higher molecular weight hydrocarbon constituents which can be separated as liquids during gas processing Chapter 7 While natural gas liquids are gaseous at underground pressure the molecules condense at atmospheric pressure and turn into liquids The composition of natural gas can vary by geographic region the geological age of the deposit the depth of the gas and many other factors Natural gas that contains a lot of natural gas liquids and condensates is referred to as wet gas while gas that is primarily methane with little to no liquids in it when extracted is referred to as dry gas The higher molecular weight constituents of natural gas ie the C5 product are commonly referred to as gas condensate or natural gasoline Rich gas will have a high heating value and a high hydrocarbon dew point When referring to natural gas liquids in the gas stream the term gallon per thousand cubic feet is used as a measure of high molecular weight hydrocarbon content On the other hand the composition of nonassociated gas sometimes called well gas is deficient in natural gas liquids The gas is produced from geological formations that typically do not contain much if any hydrocarbon liquids 43 Feedstock Composition and Properties Generally the hydrocarbon derivatives having a higher molecular weight than methane as well as any acid gases carbon dioxide and hydrogen sulfide are removed from natural gas prior to use of the gas as a fuel However since the composition of natural gas is never constant there are standard test methods by which the composition and properties of natural gas can be determined and thus prepared for use It is not the intent to cover the standard test methods in any detail in this text since descriptions of the test methods are available elsewhere Speight 2015 ASTM 2018 Speight 2018 Natural gas liquids can be classified according to their vapor pressures as low condensate inter mediate natural gasoline and high liquefied petroleum gas vapor pressure Natural gas liquids include propane butane pentane hexane and heptane but not methane and not always ethane since these hydrocarbon derivatives need refrigeration to be liquefied A more general definition of natural gas liquids includes the nonmethane hydrocarbon deriva tives from natural gas that are separated from the gas as liquids through the process of absorption condensation adsorption or other methods in gas processing or cycling plants Generally under this definition such liquids consist of ethane propane butane and higher molecular weight hydro carbon derivatives For further use the hydrocarbon derivatives are fractionated using a system which after deethanization of the natural gas liquids produces propane butanes and naphtha C5 Mokhatab et al 2006 Speight 2007 223 Gas condensate Also by way of a further reminder natural gas condensate also called condensate or gas con densate or natural gasoline is a lowdensity mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields Mokhatab et al 2006 Speight 2007 2014a Some gas constituents within the raw unprocessed natural gas will condense to a liquid state if the temperature is reduced to below the hydrocarbon dew point temperature at a set pressure There are many condensate sources and each has its own unique gas condensate composition Natural gas condensate condensate gas condensate natural gasoline is a lowdensity mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields Gas condensate condenses out of the raw natural gas if the temperature is reduced to below the hydrocarbon dew point temperature of the raw gas The composition of the gas condensate liquids is dependent upon the type of natural gas and the composition of the natural gas Similarities exist between the composition of natural gas liquids and gas condensateto the point that the two names are often sometimes erroneously used interchangeably On a strictly comparative basis the constituents of gas condensate represent the higherboiling constituents of natural gas liquids The fraction known as pentanes plus is a mixture of pentane isomers and higher molecular weight constituents C5 that is a liquid at ambient temperature and pressure and consists mostly of pentanes and higher molecular weight higher carbon number hydrocarbon derivatives Pentanes plus includes but is not limited to normal pentane isopentane hexanesplus natural gasoline and condensate To separate the condensate from a natural gas feedstock from a gas well or a group of wells the stream is cooled to lower the gas temperature to below the hydrocarbon dew point at the feedstock pressure and that condenses a good part of the gas condensate hydrocarbon derivatives Mokhatab et al 2006 Speight 2007 2014a The feedstock mixture of gas liquid condensate and water is then routed to a high pressure separator vessel where the water and the raw natural gas are sepa rated and removed The raw natural gas from the high pressure separator is sent to the main gas compressor The gas condensate from the high pressure separator flows through a throttling control valve to a lowpressure separator The reduction in pressure across the control valve causes the condensate 44 Handbook of Petrochemical Processes to undergo a partial vaporization referred to as a flash vaporization The raw natural gas from the lowpressure separator is sent to a booster compressor which raises the gas pressure and sends it through a cooler and on to the main gas compressor The main gas compressor raises the pressure of the gases from the high and lowpressure separators to whatever pressure is required for the pipeline transportation of the gas to the raw natural gas processing plant The main gas compressor discharge pressure will depend upon the distance to the raw natural gas processing plant and it may require that a multistage compressor be used At the raw natural gas processing plant the gas will be dehydrated and acid gases and other impurities will be removed from the gas Then the ethane propane butanes and pentanes plus higher molecular weight hydrocarbon derivatives referred to as C5 will also be removed and recovered as byproducts The water removed from both the high and lowpressure separators will probably need to be processed to remove hydrogen sulfide before the water can be disposed or reused in some fashion 224 Gas hydrates The concept of natural gas production from methane hydrate also called gas hydrate methane clathrate natural has hydrate methane ice hydromethane methane ice fire ice is relatively new but does offer the potential to recover hitherto unknown reserves of methane that can be expected to extend the availability of natural gas Giavarini et al 2003 Giavarini and Maccioni 2004 Giavarini et al 2005 Makogon et al 2007 Makogon 2010 Wang and Economides 2012 Yang and Qin 2012 In terms of gas availability from this resource 1 L of solid methane hydrate can contain up to 168 L of methane gas Natural gas hydrates are an unconventional source of energy and occur abundantly in nature both in arctic regions and in marine sediments Bishnoi and Clarke 2006 The formation of gas hydrate occurs when water and natural gas are present at low temperature and high pressure Such conditions often exist in oil and gas wells and pipelines Gas hydrates offer a source of energy as well as a source of hydrocarbon derivatives for the future Gas hydrates are an icelike material which is made up of methane molecules contained in a cage of water molecules and held together by hydrogen bonds This material occurs in large underground deposits found beneath the ocean floor on continental margins and in places north of the Arctic Circle such as Siberia It is estimated that gas hydrate deposits contain twice as much carbon as all other fossil fuels on earth This source if proven feasible for recovery could be a future energy as well as chemical source for petrochemicals Due to its physical nature a solid material only under high pressure and low temperature it cannot be processed by conventional methods used for natural gas and crude oils One approach is by dissociating this cluster into methane and water by injecting a warmer fluid such as sea water Another approach is by drilling into the deposit This reduces the pressure and frees methane from water However the environmental effects of such drilling must still be evaluated The methane in gas hydrates is predominantly generated by bacterial degradation of organic matter in lowoxygen environments Organic matter in the uppermost few centimeters of sediments is first attacked by aerobic bacteria generating carbon dioxide which escapes from the sediments into the water column In this region of aerobic bacterial activity sulfate derivatives SO4 are reduced to sulfide derivatives S If the sedimentation rate is low 1 cm per 1000 years the organic carbon content is low 1 ww and oxygen is abundant and the aerobic bacteria use up all the organic matter in the sediments However when sedimentation rate is high and the organic carbon content of the sediment is high the pore waters in the sediments are anoxic at depths of less than one foot or so and methane is produced by anaerobic bacteria The two major conditions that promote hydrate formation are thus i high gas pressure and low gas temperature and ii the gas at or below its water dew point with free water present Sloan 1998b Collett et al 2009 The hydrates are believed to form by migration of gas from depth along 45 Feedstock Composition and Properties geological faults followed by precipitation or crystallization on contact of the rising gas stream with cold sea water At high pressures methane hydrates remain stable at temperatures up to 18C 64F and the typical methane hydrate contains one molecule of methane for every six molecules of water that forms the ice cage However the methane hydrocarbonwater ratio is dependent on the number of methane molecules that fit into the cage structure of the water lattice Chemically gas hydrates are nonstoichiometric compounds formed by a lattice of hydrogen bonded molecules host which engage low molecular weight gases or volatile liquids guest with specific properties that differentiate them from ice Bishnoi and Clarke 2006 No actual chemical bond exists between guest and host molecules Hydrate formation is favored by low tem perature and high pressure Makogon 1997 Sloan 1998a Lorenson and Collett 2000 Carrol 2003 Seo et al 2009 Most methane hydrate deposits also contain small amounts of other hydrocarbon hydrates these include ethane hydrate and propane hydrate In fact gas hydrates of current interest are composed of water and the following molecules methane ethane propane isobutane normal butane nitrogen carbon dioxide and hydrogen sulfide However other non polar components such as argon Ar and ethyl cyclohexane C6H11C2H5 can also form hydrates Typically gas hydrates form at temperatures in the order of 0C 32F and elevated pressures Sloan 1998a The composition of natural gas hydrates is determined by the composition of the gas and water and the pressure and temperature which existed at the time of their formation Over geologic time there will be changes in the thermodynamic conditions and the vertical and lateral migration of gas and water therefore the composition of hydrate can change both due to the absorption of free gas and the recrystallization of alreadyformed hydrate In the hydrate structure methane is trapped within a cagelike crystal structure composed of water molecules in a structure that resembles packed snow or ice Lorenson and Collett 2000 The hydrate usually consists of methane with small amounts higher molecular weight components However in a number of cases the hydrate contains a significant volume of higher molecular weight hydrocarbon derivatives Table 24 Taylor 2002 The presence of higher molecular weight hydro carbon other than methane in the hydrates may be an indicator of the presence of petroleum reser voirs in the formation below the gas hydrate deposit TABLE 24 Composition of Gas Produced from Various Gas Hydrates Gas Hydrate Deposit Gas Composition mol CH4 C2H6 C3H8 iC4H10 nC4H10 C5 CO2 N2 Haakon Mosby Mud volcano 995 01 01 01 01 01 Nankai Trough Japan 993 063 Bush Hill White 721 115 131 24 1 0 Bush Hill Yellow 735 115 116 2 1 03 01 Green Canyon White 665 89 158 72 14 02 Green Canyon Yellow 695 86 152 54 12 0 Bush Hill 297 153 366 97 4 48 Messoyakha Russia 987 003 05 077 Mallik Canada 997 003 027 Nankai Trough1 Japan 943 26 057 009 08 024 14 Blake Ridge United States 999 002 008 Source Taylor 2002 46 Handbook of Petrochemical Processes Under the appropriate pressure gas hydrates can exist at temperatures significantly above the freezing point of water but the stability of the hydrate derivatives depends on pressure and gas composition and is also sensitive to temperature changes Stern et al 2000 Stoll and Bryan 1979 Collett 2001 Belosludov et al 2007 Collett 2010 For example methane plus water at 600 psia forms hydrate at 5C 41F while at the same pressure methane with 1 vv propane forms a gas hydrate at 94C 49F Hydrate stability can also be influence by other factors such as salinity Methane hydrates are restricted to the shallow lithosphere ie at depths less than 6000 ft below the surface The necessary conditions for the formation of hydrates are found only either in polar continental sedimentary rocks where surface temperatures are less than 0C 32F or in oceanic sediment at water depths greater than 1000 ft where the bottom water temperature is in the order of 2C 35F Caution is advised when drawing generalities about the formation and the stability of gas hydrates Methane hydrates are also formed during natural gas production operations when liquid water is condensed in the presence of methane at high pressure Higher molecular weight hydro carbon derivatives such as ethane and propane can also form hydrates although larger molecules butane hydrocarbon derivatives and pentane hydrocarbon derivatives cannot fit into the water cage structure and therefore tend to destabilize the formation of hydrates Belosludov et al 2007 However for this text the emphasis is focused on methane hydrates 225 other tyPes of Gases The composition and properties of any gas stream depends on the characterization and properties of the hydrocarbon derivatives that make up the stream and calculation of the properties of a mixture depends on the properties of its constituents However calculation of the property of a mixture based on an average calculation neglects any interactions between the constituents This makes the issue of modeling properties a difficult one because of the frequent omission of any chemical or physical interactions between the gas stream constituents The defining characteristics of the various gas streams in the context of this book are that the gases i exist in a gaseous state at room temperature ii may contain hydrocarbon constituents with 14 carbons ie methane ethane propane and butane isomers iii may contain diluents and inert gases and iv may contain contaminants in the form of nonhydrocarbon constituents Each constituent of the gas influences the properties Thus Many hydrocarbon gases do contain C5 and C6 hydrocarbon derivatives and apart from gas streams produced as processed byproducts in a refinery the C5 constituents are typically found at lower concentrations vv in gases than the C1C4 constituents There are also a few category members that may contain C7 and even C8 hydrocarbon derivatives although such streams would necessarily be at elevated temperature andor pressure to maintain the heptane C7H16 and octane C8H18 constituents in the gaseous state Hydrocarbon compounds such as pentane C5H12 hexane C6H14 heptane C7H16 and octane C8H18 derivatives are typically found predominantly in naph tha derived from crude oil Typically natural gas produced from shale reservoirs and other tight reservoirs has been clas sified under the general title unconventional gas The production process requires stimulation by horizontal drilling coupled with hydraulic fracturing because of the pack of permeability in the gasbearing formation The boundary between conventional gas and unconventional gas resources is not well defined because they result from a continuum of geologic conditions Coal seam gas Hydrocarbons Provide the calorific value of natural gas when it is burned Diluentsinert gases Typical gases are carbon dioxide nitrogen helium and argon Contaminants Present in low concentrations will affect processing operations 47 Feedstock Composition and Properties more frequently called coalbed methane CBM is frequently referred to as unconventional gas Tight shale gas and gas hydrates are also placed into the category of unconventional gas In addition to gas hydrate derivatives there are several types of unconventional gas resources that arise from different sources andor are currently produced by methods other than those used for conventional gas production and require processing before sale to the consumer In this section it would be remiss not to mention prominent gases produced from biomass and waste materials viz biogas and landfill gas Both types of gas contain methane and carbon dioxide as well as various other constituents and are often amenable to gas processing methods that are applied to natural gas Chapter 4 The other types of gases are listed alphabetically rather than on the basis of current importance and are i biogas ii coalbed methane iii coal gas iv flue gas iv gas in geopressurized zones v gas in tight formations vii landfill gas viii refinery gas and ix shale gas Mokhatab et al 2006 Speight 2011a 2013b 2014a 2251 Biogas Biogas often called biogenic gas and sometimes incorrectly known as swamp gas typically refers to a biofuel gas produced by i anaerobic digestion by anaerobic organisms which digest material inside a closed system or ii fermentation of biodegradable organic matter including manure sewage sludge municipal solid waste biodegradable waste or any other biodegradable feedstock under anaerobic con ditions Speight 2011 Examples of biomass are i wood and wood processing wastes ii agricultural crops and waste materials iii food yard and wood waste in garbage and iv animal manure and human sewage which are all potential sources of biogas biogenic gas The process of biogas produc tion typically an anaerobic process is a multistep biological process where the originally complex and bigsized organic solid wastes are progressively transformed into simpler and smallersized organic compounds by different bacteria strains to have a final energetically worthwhile gaseous product and a semisolid material digestate that is rich in nutrients and thus suitable for its utilization in farming Biogas production typically an anaerobic process is a multistep process in which originally complex organic liquid or solid wastes are progressively transformed into low molecular weight products by different bacteria strains Esposito et al 2012 Biogas can also be produced by pyroly sis of biomass freshly harvested or as a biomass waste Thus the name biogas refers to a large vari ety of gases resulting from specific treatment processes starting from various organic wastes such as livestock manure food waste and sewage that are all potential sources of biogenic gas or biogas which is usually considered a form of renewable energy and is often categorized according to the source Table 25 In spite of the potential differences in composition biogas can be processed upgraded to the standards required for natural gas although the choice of the relevant processing sequence depends upon the composition of the gas Chapters 7 and 8 During the combustion of biomass various kinds of impurities are generated and some of them occur in the flue gas and most of the contaminants in the flue gas are related to the composition of the biomass If the combustion is incomplete ie carried out in a deficiency of oxygen then soot unburned matter toxic dioxin derivatives may also occur in the flue gas In addition metals Cui et al 2013 such as lead Pb also occur in the ash and may even evapo rate during combustion and react condense andor sublime during cooling in the boiler While upstream of the gas cleaning installation normally at a temperature 200C 390F all metals will occur as solid particles except mercury which evaporates during combustion and reacts in the 12Dioxin 14Dioxin 48 Handbook of Petrochemical Processes boiler but remains mainly in its gaseous form The impurities in the biogas are harmful if they are emitted to the atmosphere and gas cleaning units must be installed to eliminate or at least reduce this problem The extent of the gas cleaning depends on federal regional and local regulations but regional and local authorities organizations and individuals have often an opinion on an actual plant due to its size and location More generally contaminants aside in terms of composition biogas is primarily a mixture of methane CH4 and inert carbonic gas CO2 but variations in the composition of the source material lead to variations in the composition of the gas Table 21 Speight 2011 Water H2O hydrogen sulfide H2S and particulates are removed if present at high levels or if the gas is to be completely cleaned Carbon dioxide is less frequently removed but it must also be separated to achieve pipeline quality gas If the gas is to be used without extensive cleaning it is sometimes cofired with natural gas to improve combustion Biogas cleaned up to pipeline quality is called renewable natural gas Finally while natural gas is classified as a fossil fuel Speight 2014a and biomethane is defined as a nonfossil fuel Speight 2011 it is further characterized or described as a green energy source Noteworthy at this point is that methane whatever the source fossil fuel or nonfossil fuel and when released into the atmosphere is approximately 20 times more potent as a greenhouse gas than car bon dioxide Organic matter from which biomethane is produced would release the carbon dioxide into the atmosphere if simply left to decompose naturally while other gases that are produced dur ing the decomposition process for example nitrogen oxides would make an additional contribu tion to the greenhouse effect 2252 Coalbed Methane Just as natural gas is often located in the same reservoir as the crude oil a gas predominantly meth ane can also be found trapped within coal seams where it is often referred to as coalbed methane or coal bed methane CBM sometimes referred to as coalmine methane CMM The gas occurs in the pores and cracks in the coal seam and is held there by underground water pressure To extract the gas a well is drilled into the coal seam and the water is pumped out dewatering which allows the gas to be released from the coal and brought to the surface However the occurrence of methane in coal seams is not a new discovery and methane also called firedamp was known to coal miners for at least 150 years or more before it was rediscov ered and developed as coalbed methane Speight 2013b To the purist coalmine methane is the fraction of coalbed methane that is released during the mining operation referred to in the older literature as firedamp by miners because of its explosive nature In practice the terms coalbed methane and coalmine methane may usually refer to different sources of gasboth forms of gas whatever the name are equally dangerous to the miners TABLE 25 Examples of Biogas Composition Constituents Source1a Source2a Source3a Methane CH4 vv 5060 6075 6075 Carbon dioxide CO2 vv 3834 3319 3319 Nitrogen N2 vv 50 10 10 Oxygen O2 vv 10 05 05 Water H2O vv 6 40C 6 40C 6 40C Hydrogen sulfide H2S mgm3 100900 10004000 300010000 Ammonia NH3 mgm3 50100 a Source1 waste from domestic household sources Source2 sludge from a wastewater treatment plant Source3 agricultural waste 49 Feedstock Composition and Properties Coalbed methane is relatively pure compared to conventional natural gas containing only very small proportions of higher molecular weight hydrocarbon derivatives such as ethane and butane and other gases such as hydrogen sulfide and carbon dioxide Because coal is a solid very high carboncontent mineral there are usually no liquid hydrocarbon derivatives contained in the pro duced gas The coal bed coal seam must first be dewatered to allow the trapped gas to flow through the formation to produce the gas Consequently coalbed methane usually has a lower heating value and elevated levels of carbon dioxide oxygen and water that must be treated to an acceptable level given the potential to be corrosive Typically with some exceptions coalbed gas is typically in excess of 90 vv methane and as subject to gas composition data may be suitable for introduction into a commercial pipeline with little or no treatment Mokhatab et al 2006 Speight 2007 2013a Methane within coalbeds is not structurally trapped by overlying geologic strata as in the geologic environments typical of conven tional gas deposits Speight 2013a 2014a Only a small amount in the order of 510 vv of the coalbed methane is present as free gas within the joints and cleats of coalbeds Most of the coalbed methane is contained within the coal itself adsorbed to the sides of the small pores in the coal 2253 Coal Gas Typically coal gas is any gaseous product that is produced by carbonization of coaloccasionally the term coal gas is also applied to any gas produced by the gasification of coal Speight 2013b Coal carbonization is used for processing of coal to produce coke using metallurgical grade coal Speight 2013d The process involves heating coal in the absence of air to produce coke and is a multistep complex process in which a variety of solid liquids and gaseous products are produced which contain many valuable products The various products from coal carbonization in addition to coke are i coke oven gas ii coal tar iii lowboiling oil also called light oil and iv aqueous solution of ammonia and ammonium salts With the development of the steel industry there was a continuous development in coke oven plants during the later half of the 19th century to improve the process conditions and recovery of chemicals and this continued during the 20th century to adapt to environmental pollution control strategies and energy consumption measures The carbonization process can be carried out at various temperatures Table 26 Speight 2013d although low or high temperature is preferred Lowtemperature carbonization is used to produce liquid fuels while hightemperature carbonization is used to produce gaseous products Speight 2013d Lowtemperature carbonization approximately 450C750C 840F1380F is used to produce liquid fuels with smaller amounts of gaseous products while the hightemperature carbonization process approximately 900C 1650F is used to produce gaseous products The gaseous products from hightemperature carbonization process are less while liquid products are large and the production of tar is relatively low because of the cracking of the secondary liquid products and tar products Speight 2013d Gases of high calorific value are obtained by low temperature or mediumtemperature carbonization of coal The gases obtained by the carboniza tion of any given coal change in a progressive manner with increasing temperature Table 26 The composition of coal gas also changes during the course of carbonization at a given temperature and secondary reactions of the volatile products are important in determining gas composition Speight 2013d ASTM 2018 Low heatcontent gas lowBtu gas is produced during the gasification of when the oxygen is not separated from the air and thus the gas product invariably has a low heat content ca 150300 Btuft3 Low heatcontent gas is also the usual product of in situ gasification of coal which is used essentially as a technique for obtaining energy from coal without the necessity of mining the coal The process is a technique for utilization of coal which cannot be mined by other techniques The nitrogen content of low heatcontent gas ranges from somewhat less than 33 vv to slightly more than 50 vv and cannot be removed by any reasonable means the presence of nitrogen at these levels renders the product gas to be low heat content The nitrogen also strongly limits the applicability of the gas to chemical synthesis Two other noncombustible components water H2O 50 Handbook of Petrochemical Processes and carbon dioxide CO2 lower the heating value of the gas further Water can be removed by con densation and carbon dioxide by relatively straightforward chemical means Medium heatcontent gas mediumBtu gas has a heating value in the range 300550 Btuft3 and the composition is much like that of low heatcontent gas except that there is virtually no nitrogen The primary combustible gases in medium heatcontent gas are hydrogen and carbon monoxide Medium heatcontent gas is considerably more versatile than low heatcontent gas like low heat content gas medium heatcontent gas may be used directly as a fuel to raise steam or used through a combined power cycle to drive a gas turbine with the hot exhaust gases employed to raise steam Medium heatcontent gas is especially amenable to the production of i methane ii higher molecular weight hydrocarbon derivatives by the FischerTropsch synthesis iii methanol and iv a variety of synthetic chemicals Chadeesingh 2011 Speight 2013a The reactions used to pro duce medium heatcontent gas are the same as those employed for low heatcontent gas synthesis the major difference being the application of a nitrogen barrier such as the use of pure oxygen to keep diluent nitrogen out of the system In medium heatcontent gas the hydrogencarbon monoxide ratio varies from 23 to ca 31 and the increased heating value correlates with higher methane and hydrogen contents as well as with lower carbon dioxide contents In fact the nature of the gasification process used to produce the medium heatcontent gas has an effect on the ease of subsequent processing For example the carbon dioxideacceptor product is available for use in methane production because it has i the desired hydrogencarbon dioxide ratio just exceeding 31 ii an initially high methane content and iii relatively low carbon dioxide content and low water content High heatcontent gas highBtu gas is almost pure methane and often referred to as synthetic natural gas or substitute natural gas SNG However to qualify as substitute natural gas a product must contain at least 95 vv methane the energy content in the order of 9801080 Btuft3 The commonly accepted approach to the synthesis of high heatcontent gas is the catalytic reaction of hydrogen and carbon monoxide 3H CO CH H O 2 4 2 The water produced by the reaction is removed by condensation and recirculated as very pure water through the gasification system The hydrogen is usually present in slight excess to ensure that the toxic carbon monoxide is reacted The carbon monoxidehydrogen reaction is not the most efficient way to produce methane because of the exothermicity of the reaction Also the methanation catalyst is subject to poisoning TABLE 26 Effect of Carbonization Temperature on the Composition of Coal Gas Component Composition Temperature of carbonization 500 600 700 800 900 1000 C 930 1110 1290 1470 1650 1830 Fa Carbon dioxide 57 50 44 40 32 25 Unsaturated hydrocarbons 32 40 52 51 48 45 Carbon monoxide 58 64 75 85 95 110 Hydrogen 200 290 400 470 500 510 Methane 495 470 360 310 295 290 Ethane 140 53 45 30 10 05 Relative yield per ton 10 164 283 382 446 501 a Rounded to the nearest 5F 51 Feedstock Composition and Properties by sulfur compounds and the decomposition of metals can destroy the catalyst Hydrogasification may be employed to minimize the need for methanation C 2H CH coal 2 4 The product of this reaction is not pure methane and additional methanation is required after hydro gen sulfide and other impurities are removed 2254 Geopressurized Gas The term geopressure refers to a reservoir fluid including gas pressure that significantly exceeds hydrostatic pressure which is in the order of 0405 psi per foot of depth and may even approach overburden pressure in the order of 10 psi per foot of depth Thus geopressurized zones are natu ral underground formations that are under unusually high pressure for their depth The geopressur ized zones are formed by layers of clay that are deposited and compacted very quickly on top of more porous absorbent material such as sand or silt Water and natural gas that are present in this clay are squeezed out by the rapid compression of the clay and enter the more porous sand or silt deposits Geopressured reservoirs frequently are associated with substantial faulting and complex stratigraphy which can make correlation structural interpretation and volumetric mapping subject to considerable uncertainty Geopressurized zones are typically located at great depths usually 1000025000 ft below the surface of the earth The combination of all these factors makes the extraction of natural gas in geopressurized zones quite complicated However of all of the unconventional sources of natural gas geopressurized zones are estimated to hold the greatest amount of gas The amount of natural gas in these geopressurized zones is uncertain although unproven esti mates indicate that 500049000 trillion ft3 500049000 1012 ft3 of natural gas may exist in these areas Like gas hydrates the gas in the geopressurized zones offers an opportunity for future supplies of natural gas However the combination of the above factors makes the extraction of natu ral gas or crude oil located in geopressurized zones quite complicated Speight 2017 2255 Landfill Gas Landfill gas which is often included under the umbrella definition of biogas is also produced from the decay of organic wastes such as municipal solid waste that contains organic materials but these wastes may not be biomasstype materials Lohila et al 2007 Staley and Barlaz 2009 Speight 2011c Landfill sites offer another underutilized source of biogas When municipal waste is buried in a landfill bacteria break down the organic material contained in garbage such as news papers cardboard and food waste producing gases such as carbon dioxide and methane Rather than allowing these gases to go into the atmosphere where they contribute to global warming landfill gas facilities can capture them separate the methane and combust it to generate electricity heat or both Landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a bio gas In fact landfill gas is a product of three processes i evaporation of volatile organic compounds such as lowboiling solvents ii chemical reactions between waste components and iii microbial action especially methanogenesis The first two processes depend strongly on the nature of the wastethe most dominant process in most landfills is the third process whereby anaerobic bacteria decompose organic waste to produce biogas which consists of methane and carbon dioxide together with traces of other compounds Despite the heterogeneity of waste the evolution of gases follows welldefined kinetic pattern in which the formation of methane and carbon dioxide commences approximately 6 months after depositing the landfill material The evolution of landfill gases reaches a maximum at approximately 20 years then declines over the course of several decades As should be expected the amount of methane that is produced varies significantly based on composition of the waste Staley and Barlaz 2009 The efficiency of gas collection at landfills 52 Handbook of Petrochemical Processes directly impacts the amount of energy that can be recoveredclosed landfills those no longer accepting waste collect gas more efficiently than open landfills those that are still accepting waste The gas is a complex mix of different gases created by the action of microorganisms within a landfill Typically landfill gas is composed of 4560 vv methane 4060 vv carbon dioxide 010 vv hydrogen sulfide 002 vv hydrogen H2 trace amounts of nitrogen N2 low molec ular weight hydrocarbon derivatives dry volume basis and water vapor saturated The specific gravity of landfill gas is approximately 102106 Trace amounts of other volatile organic com pounds comprise the remainder typically 12 vv or less and these trace gases include a large array of species such as low molecular weight hydrocarbon derivatives Other minor components include hydrogen sulfide nitrogen oxides sulfur dioxide nonmethane volatile organic compounds polycyclic aromatic hydrocarbon derivatives polychlorinated dibenzodioxin derivatives and poly chlorinated dibenzofuran derivatives Brosseau 1994 Rasi et al 2007 All the aforementioned agents are harmful to human health at high doses Landfill gas collection is typically accomplished through the installation of wells installed verti cally andor horizontally in the waste mass Design heuristics for vertical wells call for about one well per acre of landfill surface whereas horizontal wells are normally spaced about 50200 ft apart on center Efficient gas collection can be accomplished at both open and closed landfills but closed landfills have systems that are more efficient owing to greater deployment of collection infrastructure since active filling is not occurring On average closed landfills have gas collection systems that capture approximately 84 vv of produced gas compared to approximately 67 vv for open landfills Landfill gas can also be extracted through horizontal trenches instead of vertical wells Both systems are effective at collecting Landfill gas is extracted and piped to a main collection header where it is sent to be treated or flared The main collection header can be connected to the leachate collection system to collect condensate forming in the pipes A blower is needed to pull the gas from the collection wells to the collection header and further downstream Landfill gas cannot be distributed through utility natural gas pipelines unless it is cleaned up to less than 3 carbon dioxide and a few parts per million of hydrogen sulfide because carbon dioxide and hydrogen sulfide corrode the pipelines Speight 2014b Thus landfill gas must be treated to remove impurities condensate and particulates hence the need for analysis to determine the com position of the gas However the treatment system depends on the end use i minimal treatment is needed for the direct use of gas in boiler furnaces or kilns and ii using the gas in electricity generation typically requires more indepth treatment Treatment systems are divided into primary and secondary treatment processing Primary pro cessing systems remove moisture and particulates Gas cooling and compression are common in primary processing Secondary treatment systems employ multiple cleanup processes physical and chemical depending on the specifications of the end use Two constituents that may need to be removed are siloxane derivatives and sulfurcontaining compounds which are damaging to equip ment and significantly increase maintenance cost Adsorption and absorption are the most common technologies used in secondary treatment processing Also landfill gas can be converted to high Btu gas by reducing the amount of carbon dioxide nitrogen and oxygen in the gas The highBtu gas can be piped into existing natural gas pipelines or in the form of compressed natural gas or liquid natural gas Compressed natural gas and liquid natural gas can be used onsite to power hauling trucks or equipment or sold commercially Three commonly used methods to extract the carbon dioxide from the gas are membrane separation molecular sieve and amine scrubbing Chapters 7 and 8 Oxygen and nitrogen are controlled by the design and operation of the landfill since the primary cause for oxygen or nitrogen in the gas is intrusion from outside into the landfill because of a difference in pressure Landfill gas condensate is a liquid that is produced in landfill gas collection systems and is removed as the gas is withdrawn from landfills Production of condensate may be through natu ral or artificial cooling of the gas or through physical processes such as volume expansion The 53 Feedstock Composition and Properties condensate is composed principally of water and organic compounds Often the organic compounds are not soluble in water and the condensate separates into a watery aqueous phase and a floating organic hydrocarbon phase which may constitute up to 5 vv of the liquid 2256 Refinery Gas In the context of the production of petrochemicals the most important gas streams are those pro duced during crude oil refining which are usually referred to as refinery gas or on some occasions petroleum gas However this latter term is not to be confused with liquefied petroleum gas The terms refinery gas or petroleum gas are often used to identify liquefied petroleum gas or even gas that emanates as light ends gases and volatile liquids from the atmospheric distillation unit or from any one of several other refinery processes For the purpose of this text refinery gas not only describes liquefied petroleum gas but also natural gas and refinery gas Mokhatab et al 2006 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 In this chapter each gas is in turn and referenced by its name rather than the generic term petroleum gas However the composi tion of each gas varies and recognition of this is essential before the relevant testing protocols are selected and applied Thus refinery gas fuel gas is the noncondensable gas that is obtained during distillation of crude oil or treatment cracking thermal decomposition of petroleum Table 27 Speight 2014a Refinery gas is produced in considerable quantities during the different refining processes and is used as fuel for the refinery itself and as an important feedstock for the production of petrochemi cals Chemically refinery gas consists mainly of hydrogen H2 methane CH4 ethane C2H6 pro pane C3H8 butane C4H10 and olefin derivatives RCHCHR1 where R and R1 can be hydrogen or a methyl group and may also include offgases from petrochemical processes Olefin derivatives such as ethylene CH2CH2 boiling point 104C 155F propene propylene CH3CHCH2 boiling point 47C 53F butene butene1 CH3CH2CHCH2 boiling point 5C 23F isobutylene CH32CCH2 boiling point 6C 21F cis and transbutene2 CH3CHCHCH3 boiling point ca 1C 30F and butadiene CH2CHCHCH2 boiling point 4C 24F as well as higherboiling olefin derivatives are produced by various refining processes As might be antici pated the composition of the offgas is variable depending on the type of crude oil the cracking severity and type of catalyst used for cracking Table 28 Still gas is broad terminology for lowboiling hydrocarbon mixtures and is the lowestboiling fraction isolated from a distillation still unit in the refinery Speight 2014a 2017 If the distil lation unit is separating light hydrocarbon fractions the still gas will be almost entirely methane TABLE 27 Origin of PetroleumRelated Gases Gas Origin Natural gas Occurs naturally with or without crude oil A varying mixture of lowboiling hydrocarbon constituents Predominantly C1 through C4 hydrocarbon derivatives some C5C8 hydrocarbon derivatives Gas condensate natural gasoline C5C8 hydrocarbon derivatives isolated from natural gas streams Refinery gas process gas A combination of gases produced by distillation Products from the thermal and catalytic cracking of crude oil or crude oil fraction such as gas oil Consists of C2C4 hydrocarbons including olefin CC gases Boiling range in the order of 51C to 1C 60F30F Tail gas A combination of hydrocarbon derivatives generated from cracking processes Predominantly C1C4 hydrocarbon derivatives 54 Handbook of Petrochemical Processes with only traces of ethane CH3CH3 If the distillation unit is handling higherboiling fractions the still gas might also contain propane CH3CH2CH3 butane CH3CH2CH2CH3 and their respective isomers Fuel gas and still gas are terms that are often used interchangeably but the term fuel gas is intended to denote the products destinationto be used as a fuel for boilers furnaces or heaters A group of refining operations that contributes to gas production are the thermal cracking and catalytic cracking processes The thermal cracking processes such as the coking processes pro duce a variety of gases some of which may contain olefin derivatives CC In the visbreaking process fuel oil is passed through externally fired tubes and undergoes liquid phase cracking reac tions which result in the formation of lowerboiling fuel oil components Substantial quantities of both gas and carbon are also formed in coking both fluid coking and delayed coking in addition to the middle distillate and naphtha When coking a residual fuel oil or heavy gas oil the feedstock is preheated and contacted with hot carbon coke which causes extensive cracking of the feedstock constituents of higher molecular weight to produce lower molecular weight products ranging from methane via liquefied petroleum gases and naphtha to gas oil and heating oil Products from cok ing processes tend to be unsaturated and olefintype components predominating in the tail gases from coking processes In various catalytic cracking processes higher boiling gas oil fractions are converted into lower boiling products by contacting the feedstock with the hot catalyst Thus both catalytic and thermal cracking processes the latter being now largely used to produce chemical raw materials result in the formation of unsaturated hydrocarbon derivatives particularly ethylene CH2CH2 but also propylene propene CH3CHCH2 isobutylene isobutene CH32CCH2 and the nbutenes CH3CH2CHCH2 and CH3CHCHCH3 in addition to hydrogen H2 methane CH4 and smaller quantities of ethane CH3CH3 propane CH3CH2CH3 and butane isomers CH3CH2CH2CH3 CH33CH Diolefin derivatives such as butadiene CH2CHCHCH2 are also present In a series of reforming processes distillation fractions which include paraffin derivatives and naphthene derivatives cyclic nonaromatic are treated in the presence of hydrogen and a catalyst to produce lower molecular weight products or are isomerized to more highly branched hydrocar bon derivatives Also the catalytic reforming process not only results in the formation of a liq uid product of higher octane number but also produces substantial quantities of gaseous products The composition of these gases varies in accordance with process severity and the properties of the feedstock The gaseous products are not only rich in hydrogen but also contain hydrocarbon derivatives from methane to butane derivatives with a preponderance of propane CH3CH2CH3 nbutane CH3CH2CH2CH3 and isobutane CH33CH Since all catalytic reforming processes TABLE 28 General Composition of Refinery Gas Component vv Hydrogen 1050 Carbon monoxide 011 Nitrogen 210 Methane 3055 Ethylene 518 Ethane 1520 Propylene 16 Propane 16 Butadiene 0015 Butylene 0105 Iso and nbutane 051 C5 022 55 Feedstock Composition and Properties require substantial recycling of a hydrogen stream it is normal to separate reformer gas into a pro pane CH3CH2CH3 andor a butane CH3CH2CH2CH3CH33CH stream which becomes part of the refinery liquefied petroleum gas production and a lowerboiling gaseous fraction part of which is recycled A further source of refinery gas is produced by the hydrocracking process which is a high pres sure pyrolysis process carried out in the presence of fresh and recycled hydrogen The feedstock is again heavy gas oil or residual fuel oil and the process is mainly directed at the production of additional middle distillates and gasoline Since hydrogen is to be recycled the gases produced in this process again must be separated into lighter and heavier streams any surplus recycle gas and the liquefied petroleum gas from the hydrocracking process are both saturated Both hydrocracker and catalytic reformer tail gases are commonly used in catalytic desulfuriza tion processes Speight 2014a 2017 In the latter feedstocks ranging from light to vacuum gas oils VGOs are passed at pressures in the order of 5001000 psi with hydrogen over a hydrofining catalyst This results mainly in the conversion of organic sulfur compounds to hydrogen sulfide S H H S hydrocarbonderivatives feedstock 2 2 The process also has the potential to produce lowerboiling hydrocarbon derivatives by hydrocracking Olefin derivatives are not typical constituents of natural gas but do occur in refinery gases which can be complex mixtures of hydrocarbon gases and nonhydrocarbon gas Speight 2014a 2017 Some gases may also contain inorganic compounds such as hydrogen nitrogen hydrogen sulfide carbon monoxide and carbon dioxide Many low molecular weight olefin derivatives such as eth ylene and propylene and diolefin derivatives such as butadiene which are produced in the refin ery are isolated for petrochemical use Speight 2014a The individual products are i ethylene ii propylene and iii butadiene Ethylene C2H4 is a normally gaseous olefinic compound having a boiling point of approxi mately 104C 155F which may be handled as a liquid at very high pressures and low tempera tures Ethylene is made normally by cracking an ethane or naphtha feedstock in a hightemperature furnace and subsequent isolation from other components by distillation The major uses of ethylene are in the production of ethylene oxide ethylene dichloride and the polyethylene polymers Other uses include the coloring of fruit rubber products ethyl alcohol and medicine anesthetic Propylene concentrates are mixtures of propylene and other hydrocarbon derivatives princi pally propane and trace quantities of ethylene butylenes and butanes Propylene concentrates may vary in propylene content from 70 mol up to over 95 mol and may be handled as a liquid at normal temperatures and moderate pressures Propylene concentrates are isolated from the furnace products mentioned in the preceding paragraph on ethylene Higher purity propylene streams are further purified by distillation and extractive techniques Propylene concentrates are used in the production of propylene oxide isopropyl alcohol polypropylene and the synthesis of isoprene As is the case for ethylene moisture in propylene is critical Butylene concentrates are mixtures of butene1 cis and transbutene2 and sometimes isobu tene 2methyl propylene C4H8 Butene1 cisButene2 56 Handbook of Petrochemical Processes These products are stored as liquids at ambient temperatures and moderate pressures Various impurities such as butane butadiene and the C5 hydrocarbon derivatives are generally found in butylene concentrates The majority of the butylene concentrates are used as a feedstock for either i an alkylation plant where isobutane and butylenes are reacted in the presence of either sulfuric acid or hydrofluoric acid to form a mixture of C7C9 paraffins used in gasoline or ii butylene dehy drogenation reactors for butadiene production Butadiene C4H6 CH2CHCHCH2 is a gaseous hydrocarbon at ambient temperature and pres sure having a boiling point of 438C 241F which may be handled as a liquid at moderate pres sure Ambient temperatures are generally used for longterm storage due to the easy formation of butadiene dimer 4vinyl cyclohexenel Butadiene is produced by two major methods the catalytic dehydrogenation of butane or butyl enes suing butylene1 as the example or both and as a byproduct from the production of ethylene CH CH CH CH CH CHCH CH 2H 3 2 2 3 2 2 2 CH CH CH CH CH CHCH CH H 3 2 2 2 2 2 2CH CH CH CHCH CH 3H 3 3 2 2 2 In each case the butadiene must be isolated from other components by extractive distillation tech niques and subsequent purification to polymerizationgrade specifications by fractional distilla tion The largest end use of butadiene is as a monomer for production of GRS synthetic rubber Butadiene is also chlorinated to produce 2chloro butadiene chloroprene CH2CHCClCH2 that is a feedstock used to produce neoprene a polychloroprene rubber The major quality criteria for butadiene are the various impurities that may affect the polymer ization reactions for which butadiene is used The gas chromatographic examination of butadiene ASTM 2018 can be employed to determine the gross purity as well as C3 C4 and C impurities transButene2 isobutene 2methylpropene 2methyl propylene 4vinyl cyclohexenel Chloroprene neoprene 57 Feedstock Composition and Properties Most of these hydrocarbon derivatives are innocuous to polymerization reactions but some such as butadiene12 and pentadiene14 are capable of polymer crosslinking CH2CCHCH3 CH2CCHCH2CH3 12butadiene 12pentadiene 2257 Synthesis Gas Synthesis gas also known as syngas is a mixture of carbon monoxide CO and hydrogen H2 that is used as a fuel gas but is produced from a wide range of carbonaceous feedstocks and is used to produce a wide range of chemicals The production of synthesis gas ie mixtures of carbon mon oxide and hydrogen has been known for several centuries and can be produced by gasification of carbonaceous fuels However it is only with the commercialization of the FischerTropsch reaction that the importance of synthesis gas has been realized Synthesis gas can be produced from any one of several carbonaceous feedstocks such as a crude oil residuum heavy oil tar sand bitumen and biomass by gasification partially oxidizing of the feedstock Speight 2011 2013a 2014a 2014b 2CH O 2CO H feedstock 2 2 The initial partial oxidation step consists of the reaction of the feedstock with a quantity of oxygen insufficient to burn it completely making a mixture consisting of carbon monoxide carbon dioxide hydrogen and steam Success in partially oxidizing heavy feedstocks such as heavy crude oil extra heavy crude oil and tar sand bitumen feedstocks depends mainly on the properties of the feedstock and the burner design The ratio of hydrogen to carbon monoxide in the product gas is a function of reaction temperature and stoichiometry and can be adjusted if desired by varying the ratio of the steam to the feedstock Synthesis gas can be produced from heavy oil by partially oxidizing the oil 2CH O 2CO H petroleum 2 2 Reactor temperatures vary from 1095C to 1490C 2000F2700F while pressures can vary from approximately atmospheric pressure to approximately 2000 psi 13790 kPa The process has the capability of producing highpurity hydrogen although the extent of the purification pro cedure depends upon the use to which the hydrogen is to be put For example carbon dioxide can be removed by scrubbing with various alkaline reagents while carbon monoxide can be removed by washing with liquid nitrogen or if nitrogen is undesirable in the product the carbon monoxide should be removed by washing with copperamine solutions The synthesis gas generation process is a noncatalytic process for producing synthesis gas prin cipally hydrogen and carbon monoxide for the ultimate production of highpurity hydrogen from gaseous or liquid hydrocarbon derivatives In this process a controlled mixture of preheated feed stock and oxygen is fed to the top of the generator where carbon monoxide and hydrogen emerge as the products Soot produced in this part of the operation is removed in a water scrubber from the product gas stream and is then extracted from the resulting carbon water slurry with naphtha and transferred to a fuel oil fraction The oilsoot mixture is burned in a boiler or recycled to the genera tor to extinction to eliminate carbon production soot formation as part of the process The soot free synthesis gas is then charged to a shift converter where the carbon monoxide reacts with steam to form additional hydrogen and carbon dioxide at the stoichiometric rate of 1 mole of hydrogen for every mole of carbon monoxide charged to the converter This particular partial oxidation technique has also been applied to a whole range of liquid feedstocks for hydrogen production There is now serious consideration being given to hydrogen production by the partial oxidation of solid feedstocks such as petroleum coke from both delayed 58 Handbook of Petrochemical Processes and fluidbed reactors lignite and coal as well as petroleum residua Although these reactions may be represented very simply using equations of this type the reactions can be complex and result in carbon deposition on parts of the equipment thereby requiring careful inspection of the reactor 2258 Tight Gas Gas from tight formations also called tight gas and shale gas is found in lowpermeability reservoir rocks such as shale which prohibit natural movement of the gas to a well The term tight formation refers to a formation consisting of extraordinarily impermeable hard rock Speight 2013a Tight for mations are relatively low permeability nonshale sedimentary formations that can contain oil and gas A tight reservoir tight sands is a lowpermeability sandstone reservoir that produce primarily dry natural gas A tight gas reservoir is one that cannot be produced at economic flow rates or recover economic volumes of gas unless the well is stimulated by a large hydraulic fracture treatment and or produced using horizontal wellbores This definition also applies to coalbed methane and tight carbonate reservoirsshale gas reservoirs are also included by some observers but not in this text By way of explanation and comparison in a conventional sandstone reservoir the pores are interconnected so that natural gas and crude oil can flow easily through the reservoir and to the production well Conventional gas typically is found in reservoirs with permeability greater than 1 milliDarcy mD and can be extracted via traditional techniques Figure 21 However in tight sandstone formations the pores are smaller and are poorly connected if at all by very narrow cap illaries which results in low permeability and immobility of the natural gas Such sediments typi cally have an effective permeability of less than 1 mD 1 mD In contrast unconventional gas is found in reservoirs with relatively low permeability less than 1 mD Figure 21 and hence cannot be extracted via conventional methods Shale is a sedimentary rock characterized by low permeability mainly compositing of mud silts and clay minerals but however this composition varies with burial depth and tectonic stresses Shale reservoirs have a permeability which is substantially lower than the permeability of other tight reservoirs Natural gas and lowviscosity crude oil also known as tight oil but sometimes erroneously referred to as shale oilby way of definition shale oil is the liquid product produced by the decomposition of the kerogen component of oil shale are confined in the pore spaces of these impermeable shale formations On the other hand oil shale is a kerogenrich petroleum source rock that was not buried under the correct maturation conditions to experience the temperatures required to generate oil and gas Speight 2014a The natural gas that is associated with shale formations and such gas is commonly referred to as shale gasto define the origin of the gas rather than the character and properties Speight 2013b Thus shale gas is natural gas produced from shale formations that typically function as both the reservoir and source rocks for the natural gas Speight 2013b The gas in a shale formation is pres ent as a free gas in the pore spaces or is adsorbed by clay minerals and organic matter Chemically shale gas is typically a dry gas composed primarily of methane 6095 vv but some formations do produce wet gasin the United States the Antrim and New Albany plays have typically pro duced water and gas Approximate scale Shale Tight Conventional 1 NanoDarcy 1 MicroDarcy 1 Darcy 1 MilliDarcy FIGURE 21 Representation of the differences in permeability of shale reservoirs tight reservoirs and con ventional reservoirs 59 Feedstock Composition and Properties 23 PETROLEUM Petroleum also called crude oil is a naturally occurring unrefined liquid which also may occur in gaseous andor sold form composed of hydrocarbon derivatives and other organic materials containing the socalled heteroatoms nitrogen oxygen sulfur and metals such as iron copper nickel and vanadium Petroleum is found in the microscopic pores of sedimentary rocks such as sandstone and limestone Niu and Hu 1999 Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Not all the pores in a rock contain crude oil and some pores will be filled with water or brine that is saturated with minerals Petroleum can be refined to produce usable products such as gasoline diesel fuel fuel oils lubri cating oil wax and various forms of petrochemicals Niu and Hu 1999 Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 However crude oil is a nonrenewable resource which cannot be replaced naturally at the rate that it is consumed it is therefore a limited resource but a current lifetime in the order of 50 years Speight 2011a 2011b 2011c Speight and Islam 2016 231 comPosition and ProPerties The molecular boundaries of crude oil cover a wide range of boiling points and carbon numbers of hydrocarbon compounds and other compounds containing nitrogen oxygen and sulfur as well as metalcontaining porphyrin constituents Speight 2012 However the actual boundaries of such a crude oil map can only be arbitrarily defined in terms of boiling point and carbon number In fact crude oil is so diverse that materials from different sources exhibit different boundary limits and for this reason alone it is not surprising that crude oil has been difficult to map in a precise manner In a very general sense crude oil is composed of the flowing chemical types i hydrocarbon compounds compounds composed of carbon and hydrogen only ii nonhydrocarbon compounds and iii organometallic compounds and inorganic salts metallic compounds Hydrocarbon com pounds are the principal constituents of most conventional crude oils and all hydrocarbon classes are present in the crude mixture except olefin derivatives and alkynes Alkanes paraffins are saturated hydrocarbon derivatives having the general formula CnH2n2 The simplest alkane methane CH4 is the principal constituent of natural gas Methane ethane CH3CH3 propane CH3CH2CH2 and butane CH3CH2CH2CH3 as well as other isobutane are gaseous hydrocarbon derivatives at ambient temperatures and atmospheric pressure They are usu ally found associated with crude oils in a dissolved state Normal alkanes nalkanes n paraffins are straightchain hydrocarbon derivatives having no branches Branched alkanes are saturated hydrocarbon derivatives with an alkyl substituent or a side branch from the main chain A branched alkane with the same number of carbons and hydrogens as an nalkane is called an isomer For example butane C4H10 has two isomers nbutane and 2methyl propane isobutane As the molecular weight of the hydrocarbon increases the number of isomers also increases Pentane C5H12 has three isomers hexane C6H14 has five isomers Example of the hexane isomers are 22 dimethylbutane and 23dimethylbutane Crude oils contain many short medium and longchain normal and branched paraffins A naph tha fraction obtained as a lowboiling liquid stream from crude fractionation with a narrow boiling range may contain a limited but still large number of isomers 22Dimethylbutane 23Dimethylbutane 60 Handbook of Petrochemical Processes Saturated cyclic hydrocarbon derivatives cycloparaffins also known as naphthenes are also part of the hydrocarbon constituents of crude oils The ratio however depends on the type of crude oil The lower molecular weight members of naphthenes are cyclopentane cyclohexane and their monosubstituted compounds They are normally present in the light and the heavy naphtha fractions Cyclohexane derivatives substituted cyclopentane derivatives and substituted cyclohex ane derivatives are important precursors for aromatic hydrocarbon derivatives The higherboiling petroleum fractions such as kerosene and gas oil may contain two or more cyclohexane rings fused through two vicinal carbon atoms Speight 2014a Lower molecular weight aromatic compounds are present in small amounts in crude oils and light petroleum fractions The simplest mononuclear aromatic compound is benzene C6H6 Toluene C6H5CH3 and xylene isomers H3CC6H4CH3 are also mononuclear aromatic compounds found in variable amounts in crude oils Benzene toluene and the xylene isomers BTX are important petrochemical intermediates as well as valuable gasoline components Separating the BTX aromatic derivatives from crude oil distillates is not feasible because they are present in low concentrations Enriching a naphtha fraction with these aromatic derivatives is possible through a catalytic reforming process Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Binuclear aromatic hydrocarbon derivatives occur in the higherboiling fractions than naphtha Trinuclear and polynuclear aromatic hydrocarbon derivatives in combination with heterocyclic compounds are major constituents of heavy crude oil and the distillation residua of crude oil The asphaltene fraction is a complex mixture of aromatic and heterocyclic compounds Speight 1994 2014a Various types of nonhydrocarbon compounds occur in crude oils and refinery streams The most important are the organic sulfur nitrogen and oxygen compounds Traces of metallic com pounds are also found in all crudes Sulfur in crude oil is mainly present in the form of organosulfur compounds Hydrogen sulfide is the only important inorganic sulfur compound found in crude oil but the presence of this gas is harmful because of its corrosive nature Organosulfur compounds may generally be classified as acidic and nonacidic Acidic sulfur compounds are the thiol derivatives mercaptan derivatives Thiophene derivatives sulfide derivatives and disulfide derivatives are examples of nonacidic sulfur compounds that occur in crude oil Most sulfur compounds can be removed from petroleum streams through hydrotreatment processes where hydrogen sulfide is produced and the corresponding hydro carbon released Hydrogen sulfide is then absorbed in a suitable absorbent and recovered as sulfur Organic nitrogen compounds occur in crude oils either in a simple heterocyclic form as in pyridine C5H5N derivatives and pyrrole C4H5N derivatives or in a complex structure as in porphyrin The nitrogen content in most crudes is very low and does not exceed 01 ww In some heavy crudes however the nitrogen content may reach up to 09 ww Nitrogen compounds are more thermally stable than sulfur compounds and accordingly are concentrated in higherboiling fractions and dis tillation residua Lowboiling streams may contain trace amounts of nitrogen compounds which should be removed because they poison many processing catalysts During hydrotreatment of petro leum fractions nitrogen compounds are hydrodenitrogenated to the corresponding hydrocarbon and ammonia For example using pyridine as the example the products are npentane and ammonia C H N 5H CH CH CH CH CH NH 5 5 2 3 2 2 2 3 3 Nitrogen compounds in crude oil may generally be classified into basic and nonbasic categories Basic nitrogen compounds are mainly those having a pyridine ring and the nonbasic compounds have a pyrrole structure Both pyridine and pyrrole are stable compounds due to their aromatic nature Porphyrin derivatives are nonbasic nitrogen compounds The porphyrin ring system is com posed of four pyrrole rings joined by methine CH groups and the entire ring system has aro matic character Many metal ions can replace the pyrrole hydrogens and form chelates The chelate is planar around the metal ion and resonance results in four equivalent bonds from the nitrogen atoms to the metal 61 Feedstock Composition and Properties Almost all crude oils and tar sand bitumen contain detectable amounts of vanadyl and nickel porphyrins Separation of nitrogen compounds is difficult and the compounds are susceptible to alteration and loss during handling However the basic low molecular weight compounds may be extracted with dilute mineral acids Oxygen compounds in crude oils are more complex than the sulfur types However their pres ence in petroleum streams is not poisonous to processing catalysts Many of the oxygen com pounds found in crude oils are weakly acidic They are carboxylic acids cresylic acid phenol and naphthenic acid Naphthenic acids are mainly cyclopentane and cyclohexane derivatives having a carboxyalkyl side chain Naphthenic acids in the naphtha fraction have a special commercial impor tance and can be extracted by using dilute caustic solutions The total acid content of most crudes is generally low but may reach as much as 3 ww Nonacidic oxygen compounds such as esters ketones and amides are less abundant than acidic compounds They are of no commercial value Many metals occur in crude oils Some of the more abundant are sodium calcium magnesium aluminum iron vanadium and nickel They are present either as inorganic salts such as sodium and magnesium chlorides or in the form of organometallic compounds such as those of nickel and vanadium as in porphyrin derivatives Calcium and magnesium can form salts or soaps with car boxylic acids These compounds act as emulsifiers and their presence is undesirable Although metals in crudes are found in trace amounts their presence is harmful and should be removed When crude oil is processed sodium and magnesium chlorides produce hydrochloric acid which is very corrosive Desalting crude oils is a necessary step to reduce these salts Vanadium and nickel are poisons to many catalysts and should be reduced to very low levels Most of the vanadium and nickel compounds are concentrated in the highboiling residua Solvent extraction processes are used to reduce the concentration of heavy metals in petroleum residues Before passing on to heavy oil as a feedstock for the production of petrochemicals there are three types of conventional crude oil that need to be addressed i opportunity crude oil ii high acid crude oil and iii foamy oil 2311 Opportunity Crude Oil Opportunity crude oils are either new crude oils with unknown or poorly understood properties relating to processing issues or are existing crude oils with wellknown properties and processing concerns Ohmes 2014 Speight 2014a 2014b Yeung 2014 Opportunity crude oils are often but not always heavy crude oils but in either case are more difficult to process due to high levels of solids and other contaminants produced with the oil high levels of acidity and high viscosity These crude oils may also be incompatible with other oils in the refinery feedstock blend and cause excessive equipment fouling when processed either in a blend or separately Speight 2015 There is also the need for a refinery to be configured to accommodate opportunity crude oils andor high acid crude oils which for many purposes are often included with heavy feedstocks 2312 High Acid Crude Oil High acid crude oils are crude oils that contain considerable proportions of naphthenic acids which as commonly used in the crude oil industry refers collectively to all of the organic acids present in the crude oil Shalaby 2005 Ghoshal and Sainik 2013 Speight 2014b By the original definition a naphthenic acid is a monobasic carboxyl group attached to a saturated cycloaliphatic structure However it has been a convention accepted in the oil industry that all organic Iron porphyrin 62 Handbook of Petrochemical Processes acids in crude oil are called naphthenic acids Naphthenic acids in crude oils are now known to be mixtures of low to high molecular weight acids and the naphthenic acid fraction also contains other acidic species Naphthenic acids which are not user friendly in terms of refining Kane and Cayard 2002 Ghoshal and Sainik 2013 Speight 2014c can be either or both watersoluble to oilsoluble depending on their molecular weight process temperatures salinity of waters and fluid pressures 2313 Foamy Oil Foamy oil is oilcontinuous foam that contains dispersed gas bubbles produced at the well head from heavy oil reservoirs under solution gas drive The nature of the gas dispersions in oil distin guishes foamy oil behavior from conventional heavy oil The gas that comes out of solution in the reservoir coalesces neither into large gas bubbles nor into a continuous flowing gas phase Instead it remains as small bubbles entrained in the crude oil keeping the effective oil viscosity low while providing expansive energy that helps drive the oil toward the production Foamy oil accounts for unusually high production in heavy oil reservoirs under solution gas drive Sun et al 2013 Foamy oil behavior is a unique phenomenon associated with production of heavy oils It is believed that this mechanism contributes significantly to the abnormally high production rate of heavy oils observed in the Orinoco Belt During production of heavy oil from solution gas drive res ervoirs the oil is pushed into the production wells by energy supplied by the dissolved gas As fluid is withdrawn from the production wells the pressure in the reservoir declines and the gas that was dissolved in the oil at high pressure starts to come out of solution hence foamy oil As pressure declines further with continued removal of fluids from the production wells more gas is released from solution and the gas already released expands in volume The expanding gas which at this point is in the form of isolated bubbles pushes the oil out of the pores and provides energy for the flow of oil into the production well This process is very efficient until the isolated gas bubbles link up and the gas itself starts flowing into the production well Once the gas flow starts the oil has to compete with the gas for available flow energy Thus in some heavy oil reservoirs due to the prop erties of the oil and the sand and also due to the production methods the released gas forms foam with the oil and remains subdivided in the form of dispersed bubbles much longer 2314 Tight Oil Tight oil is a lowviscosity crude oil sometimes erroneously referred to as shale oilby way of definition shale oil is the liquid product produced by the decomposition of the kerogen component of oil shale that is confined in the pore spaces of these impermeable shale formations On the other hand oil shale is a kerogenrich petroleum source rock that was not buried under the correct matu ration conditions to experience the temperatures required to generate oil and gas Speight 2014a Economic production from tight oil formations requires the same hydraulic fracturing and often uses the same horizontal well technology used in the production of tight gas Tight formations such as shale formations are heterogeneous and vary widely over relatively short distances Tight oil reservoirs subjected to fracking can be divided into four different groups i Type I has little matrix porosity and permeabilityleading to fractures dominating both storage capacity and fluid flow pathways ii Type II has low matrix porosity and permeability but here the matrix provides storage capacity while fractures provide fluidflow paths iii Type III are microporous reservoirs with high matrix porosity but low matrix permeability thus giving induced fractures dominance in fluid flow paths and iv Type IV is macroporous reservoirs with high matrix porosity and permeability thus the matrix provides both storage capacity and flow paths while fractures only enhance permeability Even in a single horizontal drill hole the amount recovered may vary as may recovery within a field or even between adjacent wells This makes evaluation of plays and decisions regarding the profitability of wells on a particular lease difficult Production of oil from tight formations requires a gas cap representing at least 1520 natural gas in the reservoir pore space to drive the oil toward the borehole tight reservoirs which contain only oil cannot be economically produced but such reserves may be limited Wachtmeister et al 2017 63 Feedstock Composition and Properties 232 other Petroleumderived feedstocks In the current context the term other petroleumderived feedstocks refers to the bulk petroleum products in contrast to petrochemicals which are the bulk fractions that are derived from petro leum and have commercial value as a bulk product Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 The fractions described below represent those that can be could be used for the production of petrochemicals remembering that the naphtha frac tion if it is highboiling naphthas might contain some kerosene constituent and the gas oil fraction again depending upon the boiling range might contain some kerosene and fuel oil constituents It must also be recognized that these named fractions as produced in a refinery will have simi lar boiling ranges but the boiling range is often refinery specific For example there may will be minor variations typically within 5C10C 9F18F in the boiling range of naphtha from one refinery as compared to the boiling range of naphtha from a different refinery Thus before using any of these fractions including naphtha for petrochemical production there should be an aware ness of the composition of the liquid by application of a relevant suite of analytical test methods Speight 2015 With this caveat in mind the following are the description of the crude oil fractions that can be used for the production of petrochemicals 2321 Naphtha Naphtha often referred to as naft in the older literature is actually a generic term applied to refined partly refined or an unrefined petroleum fraction In the strictest sense of the term not less than 10 vv of the material should distill below 175C 345F and not less than 95 vv of the mate rial should distill below 240C 465F under standardized distillation conditions ASTM D86 2018 ASTM D7213 2018 Generally but this can be refinery dependent naphtha is an unrefined petroleum that distills below 240C 465F and is after the gases constituents the most volatile fraction of the petroleum In fact in some specifications not less than 10 of material should distill below approximately 75C 167F It is typically used as a precursor to gasoline or to a variety of solvents Naphtha resembles gasoline in terms of boiling range and carbon number being a precur sor to gasoline 23211 Composition Naphtha contains varying amounts of paraffins olefin derivatives naphthene constituents and aro matic derivatives and olefin derivatives in different proportions in addition to potential isomers of paraffin that exist in naphtha boiling range As a result naphtha is divided predominantly into two main types i aliphatic naphtha and ii aromatic naphtha The two types differ in two ways first in the kind of hydrocarbon derivatives making up the solvent and second in the methods used for their manufacture Aliphatic solvents are composed of paraffinic hydrocarbon derivatives and cycloparaffins naphthenes and may be obtained directly from crude petroleum by distillation The second type of naphtha contains aromatic derivatives usually alkylsubstituted benzene and is very rarely if at all obtained from petroleum as straightrun materials In general naphtha may be prepared by any one of several methods which include i fractionation of straightrun cracked and reforming distillates or even fractionation of crude petroleum ii solvent extraction iii hydrogenation of cracked distillates iv polymerization of unsaturated compounds such as olefin derivatives and v alkylation processes In fact the naphtha may be a combination of product streams from more than one of these processes The more common method of naphtha preparation is distillation Depending on the design of the distillation unit either one or two naphtha steams may be produced i a single naphtha with an end point of approximately 205C 400F and similar to straightrun gasoline or ii this same fraction divided into a light naphtha and a heavy naphtha The end point of the light naphtha is varied to suit the subsequent subdivision of the naphtha into narrower boiling fractions and may be of the order of 120C 250F 64 Handbook of Petrochemical Processes Sulfur compounds are most commonly removed or converted to a harmless form by chemical treatment with lye doctor solution copper chloride or similar treating agents Hydrorefining pro cesses Parkash 2003 Gary et al 2007 Speight 2011 2014a Hsu and Robinson 2017 Speight 2017 are also often used in place of chemical treatment Solvent naphtha is solvents selected for low sulfur content and the usual treatment processes if required remove only sulfur compounds Naphtha with a small aromatic content has a slight odor but the aromatic constituents increase the solvent power of the naphtha and there is no need to remove aromatic derivatives unless an odorfree solvent is specified 23212 Properties and Uses Naphtha is required to have a low level of odor to meet the specifications for use which is related to the chemical compositiongenerally paraffin hydrocarbon derivatives possess the mildest odor and the aromatic hydrocarbon derivatives have a much stronger odor Naphtha containing higher proportions of aromatic constituents may be pale yellowusually naphtha is colorless water white and can be tested for the level of contaminants ASTM D156 2018 Naphtha is used as automo tive fuel engine fuel and jetB naphtha type Broadly naphtha is classified as light naphtha and heavy naphtha Light naphtha is used as rubber solvent lacquer diluent while heavy naphtha finds its application as varnish solvent dyers naphtha and cleaners naphtha More specifically naphtha is valuable as for solvents because of good dissolving power The wide range of naphtha available from the ordinary paraffin straightrun to the highly aromatic types and the varying degree of vola tility possible offer products suitable for many uses 2322 Kerosene Kerosene kerosine also called paraffin or paraffin oil is a flammable paleyellow or colorless oily liq uid with a characteristic odor It is obtained from petroleum and used for burning in lamps and domestic heaters or furnaces as a fuel or fuel component for jet engines and as a solvent for greases and insec ticides Kerosene is intermediate in volatility between naphtha and gas oil It is medium oil distilling between 150C and 300C 300F570F Kerosene has a flash point about 25C 77F and is suitable for use as an illuminant when burned in a wide lamp The term kerosene is also too often incorrectly applied to various fuel oils but a fuel oil is actually any liquid or liquid petroleum product that produces heat when burned in a suitable container or that produces power when burned in an engine Kerosene was the major refinery product before the onset of the automobile age but now kerosene can be termed one of several secondary petroleum products after the primary refinery productgasoline Kerosene originated as a straightrun petroleum fraction that boiled approxi mately between 205C and 260C 400F and 500F Some crude oils for example those from the Pennsylvania oil fields contain kerosene fractions of very high quality but other crude oils such as those having an asphalt base must be thoroughly refined to remove aromatic derivatives and sulfur compounds before a satisfactory kerosene fraction can be obtained 23221 Composition Chemically kerosene is a mixture of hydrocarbon derivatives the chemical composition depends on its source but it usually consists of about ten different hydrocarbon derivatives each containing from 10 to 16 carbon atoms per molecule the constituents include ndodecane nC12H26 alkyl ben zenes and naphthalene and its derivatives Kerosene is less volatile than gasoline it boils between 140C 285F and 320C 610F Kerosene because of its use as a burning oil must be free of aromatic and unsaturated hydrocar bon derivatives as well as free of the more obnoxious sulfur compounds The desirable constituents of kerosene are saturated hydrocarbon derivatives and it is for this reason that kerosene is manufac tured as a straightrun fraction not by a cracking process The criteria might apply when a kerosene fraction or a higherboiling fraction such as gas oil is used as a starting material for the production of petrochemical intermediates and for the direct production of petrochemical products 65 Feedstock Composition and Properties 23222 Properties and Uses Kerosene is by nature a fraction distilled from petroleum that has been used as a fuel oil from the beginning of the petroleumrefining industry As such low proportions of aromatic and unsatu rated hydrocarbon derivatives are desirable to maintain the lowest possible level of smoke during burning Although some aromatic derivatives may occur within the boiling range assigned to kerosene excessive amounts can be removed by extraction that kerosene is not usually pre pared from cracked products almost certainly excludes the presence of unsaturated hydrocarbon derivatives The essential properties of kerosene are flash point fire point distillation range burning sulfur content color and cloud point In the case of the flash point ASTM D56 2018 the mini mum flash temperature is generally placed above the prevailing ambient temperature the fire point ASTM D92 2018 determines the fire hazard associated with its handling and use The boiling range ASTM D86 2018 is of less importance for kerosene than for gasoline but it can be taken as an indication of the viscosity of the product for which there is no requirement for kerosene The ability of kerosene to burn steadily and cleanly over an extended period ASTM D187 2018 is an important property and gives some indication of the purity or composition of the product The significance of the total sulfur content of a fuel oil varies greatly with the type of oil and the use to which it is put Sulfur content is of great importance when the oil to be burned produces sulfur oxides that contaminate the surroundings The color of kerosene is of little significance but a product darker than usual may have resulted from contamination or aging and in fact a color darker than specified ASTM D156 2018 may be considered by some users as unsatisfactory Finally the cloud point of kerosene ASTM D2500 2018 gives an indication of the temperature at which the wick may become coated with wax particles thus lowering the burning qualities of the oil 2323 Fuel Oil Fuel oil is classified in several ways but was formally divided into two main types distillate fuel oil and residual fuel oil each of which was a blend of two or more refinery streams Parkash 2003 Gary et al 2007 Speight 2011 2014a Hsu and Robinson 2017 Speight 2017 Distillate fuel oil is vaporized and condensed during a distillation process and thus have a definite boiling range and do not contain highboiling constituents A fuel oil that contains any amount of the residue from crude distillation of thermal cracking is a residual fuel oil The terms distillate fuel oil and residual fuel oil are losing their significance since fuel oil is now made for specific uses and may be either distillates or residuals or mixtures of the two The terms domestic fuel oil diesel fuel oil and heavy fuel oil are more indicative of the uses of fuel oils 23231 Composition All of the fuel oil classes described here are refined from crude petroleum and may be categorized as either a distillate fuel or a residual fuel depending on the method of production Fuel oil no 1 and fuel oil no 2 are distillate fuels which consist of distilled process streams Residual fuel oil such as fuel oil no 4 is composed of the residuum remaining after distillation or cracking or blends of such residues with distillates Diesel fuel is approximately similar to fuel oil used for heating fuel oils no 1 fuel oil no 2 and fuel oil no 4 All fuel oils consist of complex mixtures of aliphatic and aromatic hydrocarbon derivatives the relative amounts depending on the source and grade of the fuel oil The aliphatic alkanes paraffins and cycloalkane constituents naphthene constituents are hydrogen saturated and compose as much as 90 vv of the fuel oil Aromatic constituents eg benzene and olefin constituents compose up to 20 and l vv respectively of the fuel oils Fuel oil no 1 straightrun kerosene is a distillate that consists primarily of hydrocarbon derivatives in the C9C16 range while fuel oil no 2 is a higher boiling usually blended distillate with hydrocarbon derivatives in the C11C20 range 66 Handbook of Petrochemical Processes Residual fuel oil andor heavy fuel oil is typically more complex in composition and impurities than distillate fuel oil Therefore a specific composition cannot always be determinedthe sulfur content in residual fuel oil has been reported to vary up to 5 ww Residual fuel oils are complex mixtures of high molecular weight compounds having a typical boiling range from 350C to 650C 660F1200F They consist of aromatic aliphatic and naphthenic hydrocarbon derivatives typi cally having carbon numbers from C20 to C50 together with asphaltene constituents and smaller amounts of heterocyclic compounds containing sulfur nitrogen and oxygen Residual fuel oil also contains organometallic compounds from their presence in the original crude oilthe most important of which are nickel and vanadium The metals especially vanadium are of particularly major significance for fuels burned in both diesel engines and boilers because when combined with sodium perhaps from brine contamination from the reservoir or remaining after the refinery dewateringdesalting process and other metallic compounds in critical propor tions can lead to the formation of high melting point ash which is corrosive to engine parts Other elements that occur in heavy fuel oils include iron potassium aluminum and siliconthe latter two metals are mainly derived from refinery catalyst fines The manufacture of fuel oils at one time largely involved using what was left after removing desired products from crude petroleum Now fuel oil manufacture is a complex matter of selecting and blending various petroleum fractions to meet definite specifications and the production of a homogeneous stable fuel oil requires experience backed by laboratory control Heavy fuel oil comprises all residual fuel oils and the constituents range from distillable con stituents to residual nondistillable constituents that must be heated to 260C 500F or more before they can be used The kinematic viscosity is above 10 centistokes at 80C 176F The flash point is always above 50C 122F and the density is always higher than 0900 In general heavy fuel oil usually contains cracked residua reduced crude or cracking coil heavy product which is mixed cut back to a specified viscosity with cracked gas oils and fractionator bottoms For some industrial purposes in which flames or flue gases contact the product ceramics glass heat treating and open hearth furnaces fuel oils must be blended to contain minimum sulfur contents and hence lowsulfur residues are preferable for these fuels 23232 Properties and Uses No 1 fuel oil is a petroleum distillate that is one of the most widely used of the fuel oil types It is used in atomizing burners that spray fuel into a combustion chamber where the tiny droplets bum while in suspension It is also used as a carrier for pesticides as a weed killer as a mold release agent in the ceramic and pottery industry and in the cleaning industry It is found in asphalt coat ings enamels paints thinners and varnishes No 1 fuel oil is a light petroleum distillate straight run kerosene consisting primarily of hydrocarbon derivatives in the range C9C16 Fuel oil l is very similar in composition to diesel fuel the primary difference is in the additives No 2 fuel oil is a petroleum distillate that may be referred to as domestic or industrial fuel oil The domestic fuel oil is usually lower boiling and a straightrun product It is used primarily for home heating Industrial distillate is a cracked product or a blend of both It is used in smelt ing furnaces ceramic kilns and packaged boilers No 2 fuel oil is characterized by hydrocarbon chain lengths in the C11C20 range The composition consists of aliphatic hydrocarbon derivatives straightchain alkane derivatives and cycloalkane derivatives 64 vv unsaturated hydrocarbon derivatives olefin derivatives 12 vv and aromatic hydrocarbon derivatives including alkyl benzenes and 2ring 3ring aromatic derivatives 35 vv but contains only low amounts of the polycyclic aromatic hydrocarbon derivatives 5 vv No 6 fuel oil also called Bunker C oil or residual fuel oil is the residuum from crude oil after naphthagasoline no 1 fuel oil and no 2 fuel oil have been removed No 6 fuel oil can be blended directly to heavy fuel oil or made into asphalt Residual fuel oil is more complex in composition and impurities than distillate fuels Limited data are available on the composition of no 6 fuel 67 Feedstock Composition and Properties oil Polycyclic aromatic hydrocarbon derivatives including the alkylated derivatives and metal containing constituents are components of no 6 fuel oil 2324 Gas Oil Atmospheric gas oil is a fraction of crude oil recovered through distillation and is the highest boiling fraction that can be distilled without coking short of a vacuum being pulled to lower the boiling temperature It is often used as a feedstock for a catalytic cracking process to produce more of the valuable lighter fractions including gases and naphtha The atmospheric gas oil fraction boiling range 215C345C 420F650F is usually taken to be a cut of straightrun distillate that boils at temperatures above those of the middle distillate range but below those of atmospheric residuals a boiling range that is in the order of 345C to approximately 535C 650C to approximately 1000F Thus there may be an overlap with the kerosene fraction The vacuum gas oil fraction has a boiling range in the order of 345C535C 650F1000F 23241 Composition Vacuum gas oil is one of those mystery products talked about by refiners but barely understood by those of us who are not engineers However it is an important intermediate feedstock that can increase the output of valuable diesel and gasoline from refineries Lighter shale crudes such as Eagle Ford can produce Vacuum gas oil material direct from primary distillation Today we shed some light on this semifinished refinery product Vacuum distillation recovers gas oil from the residual oil In layman terms vacuum distillation involves heating the residual oil in a vacuum so that the boiling point temperature is reduced This allows distillation at temperatures that are not possible in atmospheric distillation since otherwise coke from the heavy residual oil tends to solidify Vacuum distillation breaks out light and heavy gas oil fractions leaving vacuum residuum that can be further processed by a coker unit or sold as fuel oil The light and heavy gas oils output from the vacuum distillation column are known generically as vacuum gas oil or VGO There are many different names used in the United States and worldwide for vacuum gas oil but the basic division is between light vacuum gas oil and heavy vacuum gas oil 23242 Properties and Uses In a typical complex refinery such as are common in the United States vacuum gas oil is further processed in one of two types of catalytic cracking units These units use a combination of catalysts a substance that accelerates chemical reactions heat and pressure to crack vacuum gas oil into lowerboiling products 2325 Residua A resid residuum pl residua is the black viscous residue obtained from petroleum after nondestructive distillation has removed all the volatile materials The temperature of the distil lation is usually maintained below 350C 660F since the rate of thermal decomposition of petroleum constituents is minimal below this temperature but the rate of thermal decomposition of petroleum constituents is substantial above 350C 660F A residuum may be liquid at room temperature generally atmospheric residua or almost solid generally vacuum residua depend ing upon the nature of the crude oil Chapter 17 When a residuum is obtained from a crude oil and thermal decomposition has commenced it is more usual to refer to this product as pitch The differences between a parent petroleum and the residua are due to the relative amounts of various constituents present which are removed or remain by virtue of their relative volatility 23251 Composition The chemical composition of a residuum from an asphaltic crude oil is complex Physical methods of fractionation usually indicate high proportions of asphaltenes and resins even in amounts up to 68 Handbook of Petrochemical Processes 50 ww or higher of the residuum In addition the presence of ashforming metallic constituents including such organometallic compounds as those of vanadium and nickel is also a distinguishing feature of residua and the heavier oils Furthermore the deeper the cut into the crude oil the greater is the concentration of sulfur and metals in the residuum and the greater the deterioration in physical properties Chapter 17 2326 Used Lubricating Oil Used lubricating oil can be a raw material for converting to liquid fuels such as naphtha kerosene and light gas oil by using sulfated zirconia as a catalyst Speight and Exall 2014 Used lubricating oiloften referred to as waste oil without further qualificationis any lubricating oil whether refined from crude or synthetic components which has been contaminated by physical or chemi cal impurities as a result of use Lubricating oil loses its effectiveness during operation due to the presence of certain types of contaminants These contaminants can be divided into i extraneous contaminants and ii products of oil deterioration 23261 Composition Used mineralbased crankcase oil is the browntoblack oily liquid removed from the engine of a motor vehicle when the oil is changed It is similar to a heavy fraction of virgin mineral oil except it contains additional chemicals from its use as an engine lubricant The chemicals in the oil include hydrocarbon derivatives which are distilled from crude oil to form a base oil stock and various additives that improve the oils performance Used oil also contains chemicals formed when the oil is exposed to high temperatures and pressures inside an engine It also contains some metals from engine parts and small amounts of gasoline antifreeze and chemicals that come from gasoline when it burns inside the engine The chemicals found in used mineralbased crankcase oil vary depending on the brand and type of oil whether gasoline or diesel fuel was used the mechanical condition of the engine that the oil came from and the amount of use between oil changes Used oil is not naturally found in the environment 23262 Uses The inherent high energy content of many used lubricating oil streams may encourage the direct use of these streams as fuels without any pretreatment and processing and without any quality control or product specification Such direct uses do not always constitute good practice unless it can be demonstrated that combustion of the used oil can be undertaken in an environmentally sound manner The use of used oil as fuel is possible because any contaminants do not present problems on combustion or it can be burned in an environmentally sound manner without modification of the equipment in which it is being burned However using used oils as fuel needs to be subjected to treatments involving some form of settlement to remove sludge and suspended matter Simple treatment of this type can substantially improve the quality of the material by removing sludge and suspended matter carbon and to varying degrees heavy metals Speight and Exall 2014 However the constituents of used lubricating oil are the same type of constituents with the exception of the aromatic constituents produced during service of the gas oil fraction Speight 2014a Speight and Exall 2014 Thus reusing used lubricating oil is preferred to disposal and might give great environmental advantages Utilization and reusing in this case repurposing the used lubricating oil as feedstock to a catalytic cracking unit to produce the starting material hydrocarbon gases and naphthais preferred to disposal and also offers environmental benefits 24 HEAVY OIL EXTRA HEAVY OIL AND TAR SAND BITUMEN In the context of this book heavy oil extra heavy oil and tar sand bitumen typically has relatively low proportions of volatile compounds with low molecular weights and quite high proportions of high molecular weight compounds of lower volatility The high molecular weight fraction of a heavy 69 Feedstock Composition and Properties oil is comprised of complex assortment of different molecular and chemical typesa complex mix ture of compounds and not necessarily just paraffin derivatives or asphaltene constituentswith high melting points and high pour points that greatly contribute to the poor fluid properties of the heavy oil thereby contributing to low mobility compared to conventional crude oil The same is true for extra heavy oil and tar sand bitumen Speight 2013b 2013c 2014a 241 heavy oil The name heavy oil can often be misleading as it has also been used in reference to i fuel oil that contains residuum left over from distillation ie heavy fuel oil or residual fuel oil ii coal tar creo sote or iii viscous crude oil Thus for the purposes of this text the term is used to mean viscous crude oil Extra heavy oil has been included in many of these categories On the other hand tar sand bitumen often called simply bitumen is often confused with manufactured asphalt confusingly referred to as bitumen in many countries To add further to this confusion in some countries tar sand bitumen is referred to as natural as asphalt Heavy oil is a viscous type of crude oil that contains higher level of sulfur than conventional crude oil and occurs in similar locations to crude oil IEA 2005 Ancheyta and Speight 2007 Speight 2016b The nature of heavy oil is a problem for recovery operations and for refiningthe viscosity of the oil may be too high thereby leading to difficulties in recovery andor difficulties in refining the oil Speight 2016a 2017 However tar sand bitumen in terms of properties and behavior is far apart from conventional crude oil Tables 29 and 210 Figure 22 Success with this material and with extra heavy oil depends as much on understanding the fluid or nonfluid properties of the material and the behavior of the fluids in the deposit in which they occur as it does on knowing the geology of the deposit Speight 2013a 2013b 2013c 2014a The reason is that the chemical and physical differences between heavy oil extra heavy oil and tar sand bitumen oil ultimately affect the viscosity and other relevant properties which in turn influence the individual aspects of recovery and refining operations Heavy oil has a much higher viscosity and lower API gravity than conventional crude oil and recovery of heavy oil usually requires thermal stimulation of the reservoir The generic term heavy oil is often applied to a crude oil that has less than 20API and usually but not always has sulfur content higher than 2 ww Ancheyta and Speight 2007 Furthermore in contrast to conventional crude oils heavy oils are darker in color and may even be black 242 extra heavy oil The term heavy oil has also been arbitrarily incorrectly used to describe both the heavy oils that require thermal stimulation of recovery from the reservoir and the bitumen in bituminous sand tar sand formations from which the heavy bituminous material is recovered by a mining operation Extra heavy oil is a nondescriptive term related to viscosity of little scientific meaning that is usually applied to tar sand bitumenlike material The general difference is that extra heavy oil which may have properties similar to tar sand bitumen in the laboratory but unlike immobile tar sand bitumen in the deposit has some degree of mobility in the reservoir or deposit Tables 211 and 212 Delbianco and Montanari 2009 Speight 2014a An example is the extra heavy oil of the ZacaSisquoc extra heavy oil sometimes referred to as the ZacaSisquoc bitumen that has an API gravity in the order of 4060 The reservoir has average depth of 3500 ft average thickness of 1700 ft average temperature of 51C71C 125F160F and sulfur in the range of 688 ww Isaacs 1992 Villarroel and Hernández 2013 The deposit temperature is certainly equal to or above the pour point of the oil Isaacs 1992 This renders the oil capable of being pumped as a liquid from the deposit because of the high deposit temperature which is higher than the pour point of the oil The same rationale applied to the extra heavy oil found in the Orinoco deposits 70 Handbook of Petrochemical Processes TABLE 29 Simplified Differentiation between Conventional Crude Oil Tight Oil Heavy Oil Extra Heavy Oil and Tar Sand Bitumen Conventional crude oil Mobile in the reservoir API gravity 25 Highpermeability reservoir Primary recovery Secondary recovery Tight oil Similar properties to the properties of conventional crude oil API gravity 25 Immobile in the reservoir Lowpermeability reservoir Horizontal drilling into reservoir Fracturing typically multifracturing to release fluidsgases Medium crude oil Similar properties to the properties of conventional crude oil API gravity 2025 Highpermeability reservoir Primary recovery Secondary recovery Heavy crude oil More viscous than conventional crude oil API gravity 1020 Mobile in the reservoir Highpermeability reservoir Secondary recovery Tertiary recovery enhanced oil recoveryEOR eg steam stimulation Extra heavy oil Fluid andor mobile in the reservoir Similar properties to the properties of tar sand bitumen API gravity 10 Highpermeability reservoir Secondary recovery Tertiary recovery enhanced oil recoveryEOR such as steam stimulation Tar sand bitumen Immobile solid to nearsolid in the deposit API gravity 10 Highpermeability reservoir Mining often preceded by explosive fracturing Steamassisted gravity draining SAGD Solvent methods VAPEX Extreme heating methods Innovative methodsa a Innovative methods exclude tertiary recovery methods and methods such as SAGD VAPEX but does include variants or hybrids thereof 71 Feedstock Composition and Properties Thus extra heavy oil is a material that occurs in the solid or nearsolid state and generally has mobility under reservoir conditions While this type of oil resembles tar sand bitumen and does not flow easily extra heavy oil is generally recognized as having mobility in the reservoir compared to tar sand bitumen which is typically incapable of mobility free flow under reservoir conditions It is likely that the mobility of extra heavy oil is due to a high reservoir temperature that is higher than the pour point of the extra heavy oil or due to other factors is variable and subject to localized conditions in the reservoir 243 tar sand Bitumen The expression tar sand is commonly used in the crude oil industry to describe sandstone reservoirs that are impregnated with a heavy viscous black crude oil that cannot be retrieved through a well by conventional production techniques FE764 above However the term tar sand is actually a misnomer more correctly the name tar is usually applied to the heavy product remaining after the destructive distillation of coal or other organic matter Speight 2013d Current recovery operations of bitumen in tar sand formations are predominantly focused on a mining technique The term bitumen also on occasion referred to as native asphalt and extra heavy oil includes a wide variety of reddish brown to black materials of semisolid viscous to brittle character that can exist in nature with no mineral impurity or with mineral matter contents that exceed 50 ww and are often structurally dissimilar KamYanov et al 1995 Kettler 1995 Ratov 1996 Parnell et al 1996 Niu and Hu 1999 Meyer et al 2007 Speight 2014a Bitumen is found in deposits where the TABLE 210 Comparison of the Properties of Conventional Crude Oil with Athabasca Bitumena Property Athabasca Bitumen Conventional Crude Oil Specific gravity 103 085090 Viscosity cp 38C100F 750000 200 100C212F 11300 Pour point F 50 ca 20 Elemental analysis ww Carbon 83 86 Hydrogen 106 135 Nitrogen 05 02 Oxygen 09 05 Sulfur 49 20 Ash 08 0 Nickel ppm 250 100 Vanadium ppm 100 100 Fractional composition ww Asphaltenes pentane 17 100 Resins 34 200 Aromatics 34 300 Saturates 15 300 Carbon residue ww Conradson 14 100 a Extra heavy oil eg Zuata extra heavy oil has a similar analysis to tar sand bitumen Table 211 but some mobility in the deposit because of the relatively high temperature of the deposit 72 Handbook of Petrochemical Processes permeability is low and passage of fluids through the deposit can only be achieved by prior applica tion of fracturing techniques Tar sand bitumen is a highboiling material with little if any material boiling below 350C 660F and the boiling range approximately the same as the boiling range of an atmospheric resid uum Tar sands have been defined in the United States FE764 as the several rock types that contain an extremely viscous hydrocarbon which is not recoverable in its natural state by conventional oil well production methods including currently used enhanced recovery techniques The hydrocarbonbearing rocks are variously known as bitumenrocks oil impregnated rocks oil sands and rock asphalt API Gravity Type Property 50 Condensate Volatile low molecular weight hydrocarbon liquids 40 Conventional light crude oil Mobile liquid low yield 10 ww or even 5 vv of residuum 30 Medium gravity oil Mobile liquid low yield 10 vv of residuum 20 Heavy oil Mobile liquid high yield 10 vv of residuum 10 Extra heavy oil Mobile liquid in deposit high yield 20 vv of residuum Bitumen Immobile nearsolidsolid in deposit high yield 20 vv of residuum 0 FIGURE 22 General description of various feedstocks by API gravity TABLE 211 Comparison of Selected Properties of Athabasca Tar Sand Bitumen Alberta Canada and Zuata Extra Heavy Oil Orinoco Venezuela Athabasca Bitumen Zuata Extra Heavy Oil Whole oil API gravity 8 8 Sulfur ww 48 42 650F vv 85 86 Sulfur ww 54 46 Ni V ppm 420 600 CCR wwa 14 15 a Conradson carbon residue 73 Feedstock Composition and Properties The term natural state cannot be defined out of context and in the context of FEA Ruling 19764 and the term is defined in terms of the composition of the heavy oil or bitumen extra heavy oil adds a further dimension to this definition as it can be ascribed to the properties of the oil in the reser voir visàvis the properties of the oil under ambient conditions The final determinant of whether a reservoir is a tar sand deposit is the character of the viscous phase bitumen and the method that is required for recovery From this definition and by inference crude oil and heavy oil are recoverable by well production methods and currently used enhanced recovery techniques Fore convenience it is assumed that before depletion of the reservoir energy conventional crude oil is produced by primary and secondary techniques while heavy oil requires tertiary enhanced oil recovery EOR techniques and recovery of tar sand bitumen requires more advanced methods Speight 2014a While this is an oversimplification it may be used as a general guide for the recovery of the differ ent materials There has been the suggestion that tar sand bitumen differs from heavy oil by using an arbitrary illconceived limit of 10000 centipoises as the upper limit for heavy oil and the lower limit of tar sand bitumen Such a system based on one physical property viscosity is fraught with errors For example this requires that a tar sand bitumen could have a viscosity in the order of 10050 centipoises and an oil with a viscosity of 9950 centipoise is heavy oil Both numbers fall within the limits of experimental difference of the method used to determine viscosity The limits are the usual laboratory experimental difference be 3 or more likely the limits of accuracy of the method 5 to 10 there is the question of accuracy when tax credits for recovery of heavy oil extra heavy oil and tar sand bitumen are awarded In fact the inaccuracies ie the limits of experimen tal difference of the method of measuring viscosity also increase the potential for misclassification using this or any single property for classification purposes It is incorrect to refer to native bituminous materials as tar or pitch Although the word tar is descriptive of the black heavy bituminous material it is best to avoid its use with respect to natu ral materials and to restrict the meaning to the volatile or nearvolatile products produced in the destructive distillation of such organic substances as coal Speight 2013d In the simplest sense pitch is the distillation residue of the various types of tar Thus alternative names such as bitumi nous sand or oil sand are gradually finding usage with the former name bituminous sands more TABLE 212 Simplified Use of Pour Point and ReservoirDeposit Temperature to Differentiate between Heavy Oil Extra Heavy Oil and Tar Sand Bitumen Oil Location Temperature Effect on Oil Heavy oil Reservoir or deposit Higher than oil pour point Fluid andor mobile Mobile Surfaceambient Higher than oil pour point Fluid andor mobile Mobile Extra heavy oil Reservoir or deposit Higher than oil pour point Fluid andor mobile Mobile Surfaceambient Lower than oil pour point Solid to nearsolid Fluidity much reduced Immobile Tar sand bitumen Reservoir or deposit Lower than oil pour point Solid to nearsolid Not fluid Immobile Surfaceambient Lower than oil pour point Solid to nearsolid Not fluid Immobile 74 Handbook of Petrochemical Processes technically correct The term oil sand is also used in the same way as the term tar sand and these terms are used interchangeably throughout this text Bituminous rock and bituminous sand are those formations in which the bituminous material is found as a filling in veins and fissures in fractured rocks or impregnating relatively shallow sand sandstone and limestone strata These terms are in fact correct geological description of tar sand The deposits contain as much as 20 ww bituminous material and if the organic material in the rock matrix is bitumen it is usual although chemically incorrect to refer to the deposit as rock asphalt to distinguish it from bitumen that is relatively mineral free A standard test ASTM D4 2018 is available for determining the bitumen content of various mixtures with inorganic materials although the use of word bitumen as applied in this test might be questioned and it might be more appropriate to use the term organic residues to include tar and pitch If the material is of the asphaltitetype or asphaltoidtype the corresponding terms should be used rock asphaltite or rock asphaltoid Since the most significant property of tar sand bitumen is its immobility under the conditions of temperatures and pressure in the deposit the interrelated properties of API gravity ASTM D287 2018 and viscosity ASTM D445 2018 may present an indication but only an indication of the mobility of oil or immobility of bitumen but these properties only offer subjective descriptions of the oil in the reservoir The most pertinent and objective representation of this oil or bitumen mobil ity is the pour point ASTM D97 2018 which can be compared directly to the reservoirdeposit temperature Speight 2014a 2017 The pour point is the lowest temperature at which oil will move pour or flow when it is chilled without disturbance under definite conditions ASTM D97 2018 In fact the pour point of an oil when used in conjunction with the reservoir temperature give a better indication of the condition of the oil in the reservoir that the viscosity Thus the pour point and reservoir tempera ture present a more accurate assessment of the condition of the oil in the reservoir being an indi cator of the mobility of the oil in the reservoir Indeed when used in conjunction with reservoir temperature the pour point gives an indication of the liquidity of the heavy oil extra heavy oil or bitumen and therefore the ability of the heavy oil extra heavy oil to flow under reservoir condi tions In summary the pour point is an important consideration because for efficient production additional energy must be supplied to the reservoir by a thermal process to increase the reservoir temperature beyond the pour point For example Athabasca bitumen with a pour point in the range 50C100C 122F212F and a deposit temperature of 4C10C 39F50F is a solid or near solid in the deposit and will exhibit little or no mobility under deposit conditions Pour points of 35C60C 95F140F have been recorded for the bitumen in Utah with formation temperatures in the order of 10C 50F This indicates that the bitumen is solid within the deposit and therefore immobile The injection of steam to raise and maintain the reservoir temperature above the pour point of the bitumen and to enhance bitumen mobility is difficult in some cases almost impossible Conversely when the reservoir temperature exceeds the pour point the oil is fluid in the reservoir and therefore mobile The injection of steam to raise and maintain the reservoir temperature above the pour point of the bitumen and to enhance bitumen mobility is possible and oil recovery can be achieved REFERENCES Ancheyta J and Speight JG 2007 Hydroprocessing of Heavy Oils and Residua CRC Press Boca Raton FL API 2009 Refinery Gases Category Analysis and Hazard Characterization Submitted to the EPA by the American Petroleum Institute Petroleum HPV Testing Group HPV Consortium Registration 1100997 United States Environmental Protection Agency Washington DC June 10 ASTM 2018 Annual Book of Standards ASTM International West Conshohocken PA ASTM D4 2018 Standard Test 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SA and Makogon TY 2007 Natural Gas HydratesA Potential Energy Source for the 21st Century Journal of Petroleum Science and Engineering 5613 1431 Makogon YF 2010 Natural Gas HydratesA Promising Source of Energy Journal of Natural Gas Science and Engineering 21 4959 Meyer RF Attanasi ED and Freeman PA 2007 Heavy Oil and Natural Bitumen Resources in Geological Basins of the World USGS Open File Report No 20071084 United States Geological Survey Reston VA Mokhatab S Poe WA and Speight JG 2006 Handbook of Natural Gas Transmission and Processing Elsevier Amsterdam Netherlands Niu J and Hu J 1999 Formation and Distribution of Heavy Oil and Tar Sands in China Marine and Petroleum Geology 16 8595 Ohmes R 2014 Characterizing and Tracking Contaminants in Opportunity Crudes Digital Refining httpwwwdigitalrefiningcomarticle1000893Characterisingandtrackingcontaminantsin opportunitycrudeshtmlVJhFjV4AA accessed November 1 2014 Parkash S 2003 Refining Processes Handbook Gulf Professional Publishing Elsevier Amsterdam Netherlands Parnell J Monson B and Geng A 1996 Maturity and Petrography of Bitumens in the Carboniferous of Ireland International Journal of Coal Geology 29 2338 Rasi S Veijanen A and Rintala J 2007 Trace Compounds of Biogas from Different Biogas Production Plants Energy 32 13751380 Ratov AN 1996 Physicochemical Nature of Structure Formation in HighViscosity Crude Oils and Natural Bitumens and Their Rheological Differences Petroleum Chemistry 36 191206 Also Neftekhimiya 1996 363 195208 Seo Y Kang SP and Jang W 2009 Structure and Composition Analysis of Natural Gas Hydrates 13C NMR Spectroscopic and Gas Uptake Measurements of Mixed Gas Hydrates Journal of Physical Chemistry 11335 96419649 Shalaby HM 2005 Refining of Kuwaits Heavy Crude Oil Materials Challenges Proceedings Workshop on Corrosion and Protection of Metals Arab School for Science and Technology December 37 Kuwait Sloan ED Jr 1998a Gas Hydrates Review of PhysicalChemical Properties Energy Fuels 122 191196 77 Feedstock Composition and Properties Sloan ED Jr 1998b Clathrate Hydrates of Natural Gases 2nd Edition Marcel Dekker Inc New York Sloan ED Jr 2006 Clathrate Hydrates of Natural Gases 3rd Edition Marcel Dekker Inc New York Speight JG 1994 Chemical and Physical Studies of Petroleum Asphaltene constituents In Asphaltene constituents and Asphalts I Developments in Petroleum Science 40 TF Yen and GV Chilingarian Editors Elsevier Amsterdam Netherlands Chapter 2 Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG 2008 Synthetic Fuels Handbook Properties Processes and Performance McGrawHill New York Speight JG 2011a The Refinery of the Future Gulf Professional Publishing Elsevier Oxford UK Speight JG 2011b An Introduction to Petroleum Technology Economics and Politics Scrivener Publishing Salem MA Speight JG Editor 2011c The Biofuels Handbook Royal Society of Chemistry London UK Speight JG 2012 Crude Oil Assay Database Knovel Elsevier New York 2012 Online version available at http wwwknovelcomwebportalbrowsedisplayEXTKNOVELDISPLAYbookid5485VerticalID0 accessed June 4 2018 Speight JG 2013a Heavy Oil Production Processes Gulf Professional Publishing Elsevier Oxford UK Speight JG 2013b Heavy and Extra Heavy Oil Upgrading Technologies Gulf Professional Publishing Elsevier Oxford UK Speight JG 2013c Oil Sand Production Processes Gulf Professional Publishing Elsevier Oxford UK Speight J G 2013d The Chemistry and Technology of Coal 3rd Edition CRC Press Boca Raton FL Speight JG 2014a The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Speight JG 2014b High Acid Crudes Gulf Professional Publishing Elsevier Oxford UK Speight JG 2014c Oil and Gas Corrosion Prevention Gulf Professional Publishing Elsevier Oxford UK Speight JG and Exall DI 2014 Refining Used Lubricating Oils CRC Press Boca Raton FL Speight JG 2015 Handbook of Petroleum Product Analysis 2nd Edition John Wiley Sons Inc Hoboken NJ Speight JG 2016a Introduction to Enhanced Recovery Methods for Heavy Oil and Tar Sands 2nd Edition Gulf Professional Publishing Elsevier Oxford UK Speight JG 2016b Chapter 1 Hydrogen in Refineries In Hydrogen Science and Engineering Materials Processes Systems and Technology D Stolten and B Emonts Editors WileyVCH Verlag GmbH Co Weinheim Germany pp 318 Speight JG and Islam MR 2016 Peak EnergyMyth or Reality Scrivener Publishing Beverly MA Speight JG 2017 Handbook of Petroleum Refining CRC Press Boca Raton FL Speight JG 2018 Handbook of Natural Gas Analysis John Wiley Sons Inc Hoboken NJ Staley B and Barlaz MA 2009 Composition of Municipal Solid Waste in the United States and Implications for Carbon Sequestration and Methane Yield Journal of Environmental Engineering 13510 901909 Stern L Kirby S Durham W Circone S and Waite WF 2000 Laboratory Synthesis of Pure Methane Hydrate Suitable for Measurement of Physical Properties and Decomposition Behavior Proceedings of Natural Gas Hydrate in Oceanic and Permafrost Environments MD Max Editor Kluwer Academic Publishers Dordrecht Netherlands pp 323348 Stoll RG and Bryan GM 1979 Physical Properties of Sediments Containing Gas Hydrates Journal of Geophysical Research 84B4 16291634 Sun X Zhang Y Li X Cui G and Gu J 2013 A Case Study on Foamy Oil Characteristics of the Orinoco Belt Venezuela Advances in Petroleum Exploration and Development 51 3741 Taylor C 2002 Formation Studies of Methane Hydrates with Surfactants Proceedings of 2nd International Workshop On Methane Hydrates Washington DC Van Geem KM Reyniers MF and Marin GB 2008 Challenges of Modeling Steam Cracking of Heavy Feedstocks Oil Gas Science and Technology Rev IFP 631 7994 Villarroel T and Hernández R 2013 Technological Developments for Enhancing Extra Heavy Oil Productivity in Fields of the Faja Petrolifera del Orinoco FPO Venezuela Proceedings AAPG Annual Convention and Exhibition Pittsburgh PA May 1922 American Association of Petroleum Geologists Tulsa OK Wachtmeister H Linnea Lund L Aleklett K and Höök MM 2017 Production Decline Curves of Tight Oil Wells in Eagle Ford Shale Natural Resources Research 263 365377 Wang X and Economides MJ 2012 Natural Gas Hydrates as an Energy SourceRevisited 2012 Proceedings of SPE International Petroleum Technology Conference 2012 1 176186 Society of Petroleum Engineers Richardson TX Yang X and Qin M 2012 Natural Gas Hydrate as Potential Energy Resources in the Future Advanced Materials Research 462 221224 Yeung TW 2014 Evaluating Opportunity Crude Processing Digital Refining wwwdigitalrefiningcom article1000644 accessed October 25 2014 Taylor Francis 79 3 Other FeedstocksCoal Oil Shale and Biomass 31 INTRODUCTION Since the oil crises of the 1970s the idea of deriving essential chemical feedstocks from renewable resources renewable feedstocks in a sustainable manner has been frequently suggested as an alternative to producing chemicals from petroleumbased feedstocks imported under agreement from unstable political regions with the accompanying geopolitics that go with such agreements In addition to the geopolitics the common petrochemical feedstocks that are derived from natural gas and crude oil are in spite of discoveries of natural gas and crude oil in tight formations Chapter 2 and are depleting such as petroleum and natural gas The petrochemical industry uses petroleum and natural gas as feedstocks to make intermediates which are later converted to final products that people use such as plastics paints pharmaceuticals and many others In spite of the apparent plentiful supply of oil in tight formation such as the Bakken formation and the Eagle Ford formation in the United States which may be limited in terms of total produc ible reserves Wachtmeister et al 2017 the oil industry is planning for the future since some of the most prolific basins have begun to experience reduced production rates and are reaching or already into maturity At the same time the demand for oil continues to grow every year because of increased demands by the rapidly growing economies of China and India This decline in the availability of conventional crude oil combined with this rise in demand for oil and oilbased products has put more pressure on the search for alternate energy sources Speight 2008 2011a 2011b 2011c Several authors have correctly stated that petroleum is and will continue to be a major motivating force to the industrial society Natural gas and natural gas liquids are important and their role will continue in the near future in the industrial economy Some estimates suggest that relatively cheap hydrocarbonbased feedstocks will be available well into the next century although predicting the availability of such feedstock beyond the next 50 years is risky Speight 2011a 2011b Speight and Islam 2016 In fact the reality is that the supply of crude oil the basic feedstock for refineries and for the petrochemicals industry is finite and its dominant position will become unsustainable as supplydemand issues erode its economic advantage over other alternative feedstocks This situation will be mitigated to some extent by the exploitation of more technically challenging fossil resources and the introduction of new technologies for fuels and chemicals production from natural gas and coal Speight 2008 2014 More specifically as crude oil prices continue to fluctuate typically in an upward direction C1 chemistry based on coal gasification and converting coalderived synthesis gas to chemicals and other alternatives such as biomassderived chemical and biomassderived synthesis gas will become important In fact over the past two decades a series of technological advances has occurred that promise in concert to significantly improve the economic competitiveness of biobased pro cesses Speight 2008 Evaluation of this window of opportunity focuses on the inherent attributes of biological processes application of new technology to overcome past limitations and integration with nonbiological process steps In order to satisfy the demand for feedstocks for petrochemicals it will be necessary to develop the reservoirs of heavy oil and deposits of extra heavy oil and tar sand bitumen that are pre dominantly located in the Western hemisphere Chapter 2 These resources are more difficult and costly to extract so they have barely been touched in the past However through these resources 80 Handbook of Petrochemical Processes the world could soon have access to oil sources almost equivalent to those of the Middle East In fact with the variability and uncertainty of crude oil supply due to a variety of geopolitical issues Speight 2011b investments in the more challenging reservoirs tend to be on a variable acceleration deceleration slope Nevertheless the importance of heavy oil extra heavy oil and tar sand bitumen will continue to emerge as the demand for crude oil products remains high As this occurs it is worth moving ahead with heavy oil extra heavy oil and tar sand bitumen resources on the basis of obtaining a mea sure as yet undefined and countrydependent of oil independence These will lead eventually hopefully sooner rather than laterto the adoption of coal oil shale produced from kerogen in shale formations and renewable feedstocks as the source materials for the production of petro chemicals The term renewable feedstocks includes a huge number of materials such as agricultural crops rich in starch lignocellulosic materials biomass or biomass material recovered from a vari ety of processing wastes The general term biomass refers to any material derived from living organisms usually plants In contrast to depleting feedstocks such as natural gas and crude oil the production of biobased chemicals which can replace the petroleumderived chemicals will prove to be a reliable supply of resources for the future Existing chemical technology is continually being developed to pro vide chemicals and end products from biomass Bozell 1999 Besson et al 2014 Straathof 2014 Khoo et al 2015 For bioprocessesthe conversion of biomass into useful products such as fuels and petrochemicalsone opportunity that exists is the production of butanol from bioprocessing which could be a major commodity chemical that has application as a feedstock for such products as butyl butyrate Also chemicals such as xylose xylitol furfural tetrahydrofuran glucose gluconic acid sorbitol mannitol levulinic acid and succinic acid are materials that could be prepared from inexpensive cellulose and hemicellulosederived sugars available from clean biomass fractionation As further examples i anthraquinone a wellknown pulping catalyst and chemical intermedi ate can be prepared from lignin while butadiene and a variety of pentane derivatives can be pre pared using fast pyrolysis followed by catalytic upgrading on zeolitetype catalysts ii acetic acid can be produced From synthesis gas a route that appears to be an interesting match given the unique composition of synthesis gas available from biomass and makes possible a balanced process through intermediate methanol or ethanol without the costs of reforming the synthesis gas and iii peracetic acid is an oxidant that is a good nonchlorinecontaining pulp bleaching agent which would permit market penetration of this chemical into the pulp and paper industry However a basic understanding of reactions for selectively converting biomass and biomass derived materials into chemicals is needed A fundamental understanding of new catalytic processes for selectively manipulating and modifying carbohydrates lignin and other biomass fractions will greatly improve the ability to bring biomassderived products to market The behavior of oxygen ated molecules on zeolite and other shapeselective catalysts could lead to a better design of pro cesses for chemicals from biomass Developing special catalysts for biomass processing is not a high priority for the chemicals industry but is essential for this new field if it is to compete with petroleum resources and costeffectively produce fuels and chemicals Consequently there is a renewed interest in the utilization of plantbased matter as a raw material feedstock for the chemicals industry Plants accumulate carbon from the atmosphere via photosyn thesis and the widespread utilization of these materials as basic inputs into the generation of power fuels and chemicals is a viable route to reduce greenhouse gas emissions As a result the petroleum and petrochemical industries are coming under increasing pressure not only to compete effectively with global competitors utilizing more advantaged hydrocarbon feedstocks but also to ensure that its processes and products comply with increasingly stringent environmental legislation Reducing dependence of any country on imported crude oil is of critical importance for long term security and continued economic growth Supplementing petroleum consumption with renew able biomass resources is a first step toward this goal The realignment of the chemical industry 81 Coal Oil Shale and Biomass from one of the petrochemical refining to a biorefinery concept given time feasibly has become a national goal of many oilimporting countries However clearly defined goals are necessary for construction of a biorefinery and increasing the use of biomassderived feedstocks in industrial chemical production is important to keep the goal in perspective Clark and Deswarte 2008 In this context the increased use of biofuels should be viewed as one of a range of possible measures for achieving selfsufficiency in energy rather than a panacea Crocker and Crofcheck 2006 Thus in any text about the production of chemicals petrochemicals it would be a remiss to omit other sources of chemicals such as coal and biomass 32 COAL Coal which is currently considered the bad boy of fossil fuels due to environmental issues some of which are real and some of which are emotional may become more important both as an energy source and as the source of organic chemical feedstock in the 21st century The chemicalsfromcoal industry was born in the late 18th century at the time of the Industrial Revolution when power and chemicals from coal were everyday occurrences Thus the coal chemi cals industry refers to the conversion of coal into gas liquid solid fuels and chemicals after chemi cal processing with coal as raw material In the early days of the chemicalsfromcoal industry the term chemicals covered primarily ammonia hydrocarbon gases lowboiling aromatic derivatives benzene toluene and xylene BTX difficulttodefine tar acids difficulttodefine tar bases tar pitch and coke In the United States these chemicals were derived from coal almost exclusively through hightemperature byproduct carbonization In England and Europe these and other chemi cals have been obtained to some extent through various lowtemperature carbonization processes and by coal hydrogenation in England and Germany Speight 2013a Thus the processes for the production of chemicals from coal were predominantly coking gas ification liquefaction of coal as well as coal tar processing and carbide acetylene chemical engi neering The significant time frame for the production of chemicals from coal was the period from 1920 to 1940 after which World War II brought imperative demands for toluene ammonia and other chemicals that could not be met by the coke plants Petroleum and natural gas were used as raw materials and since that time they have dominated the chemical industry However as natural gas and crude oil resources of the world decrease they are of course nonrenewable resources the chemicalsfromcoal industry may once again realize broad prospects for development This must go along with the realization that emissions from coal plants can be reduced significantly by the installation of emissions reduction processes that have now been placed into operation in the coal generated power plants In the production technology of coal processing and utilization coking process technology is one of the earliest applications and it is still an important part of the chemical industry Coal gasification occupies an important position in the coal chemical industry and is used in the production of vari ous types of gas fuel It is a clean energy and is conducive to the improvement of living standards and environmental protections Synthetic gas produced by coal gasification is the raw material of many products such as synthetic liquid fuel and raw materials for the production of chemicals The direct coal liquefaction highpressure coal hydrogenation liquefaction for production of naphtha and kerosene and indirect coal liquefaction through gasification of coal for synthesis of gasoline and diesel can produce synthetic petroleum and chemical products Owen 1981 Speight 2013a In fact coal has several positive attributes when considered as a feedstock for aromatic chemi cals specialty chemicals and carbonbased materials Substantial progress in advanced polymer materials incorporating aromatic and polyaromatic units in their main chains has created new opportunities for developing valueadded or specialty organic chemicals from coal and tars from coal carbonization for coke making The decline of the coal tar industry has diminished the tra ditional sources of these chemicals A new coal chemistry for chemicals and materials from coal may involve direct and indirect coal conversion strategies as well as the coproduction approach 82 Handbook of Petrochemical Processes In addition the needs for environmentalprotection applications have also expanded market demand for carbon materials and carbonbased adsorbents 321 coal feedstocks By way of introduction coal is a natural combustible rock composed of an organic heterogeneous substance contaminated with variable amounts of inorganic compounds Coal is classified into dif ferent ranks according to the degree of chemical change that occurred during the decomposition of plant remains in the prehistoric period In general coals with a high heating value and high fixed carbon content are considered to have been subjected to more severe changes than those with lower heating values and fixed carbon contents For example peat which is considered a young coal has a low fixed carbon content and a low heating value Important coal ranks are anthracite which has been subjected to the most chemical change and is mostly carbon bituminous coal subbituminous coal and lignite The birth of coal chemical industry first appeared in the late 18th century and in the 19th century the complete system of coal chemical industry was set up After entering 20th century raw materi als of organic chemicals were changed into coal from the former agricultural and forestry prod ucts and then coal chemical industry became an important part of chemical industry After World War II the petrochemical industry saw rapid development which weakened the position taken up by coal chemical industry by changing raw materials from coal to petroleum and natural gas The organic matters and chemical structures of coal with condensed rings as their core units connected by bridged bonds can transform coal into various fuels and chemical products through hot working and catalytic processing Coal carbonization is the earliest and most important method Coal carbonization is mainly used to produce cokes for metallurgy and some secondary products like coal gas benzene meth ylbenzene etc Coal gasification takes up an important position in chemical industry City gas and varieties of fuel gases can be produced by coal gasification The common role of lowtemperature carbonization direct coal liquefaction and indirect coal liquefaction is to produce liquid fuels Thus for many years chemicals that have been used for the manufacture of such diverse mate rials as nylon styrene fertilizers activated carbon drugs and medicine as well as many others have been made from coal Gibbs 1961 Mills 1977 Pitt and Millward 1979 These products will expand in the future as petroleum and natural gas resources become strained to supply petrochemi cal feedstocks and coal becomes a predominant chemical feedstock once more Although many traditional markets for coal tar chemicals have been taken over by the petrochemical industry the position can change suddenly as oil prices fluctuate upwards Therefore the concept of using coal as a major source of chemicals can be very real indeed A complete description of the processes to produce all the possible chemical products is beyond the scope of this text In fact the production of chemicals from coal has been reported in numerous texts therefore it is not the purpose of this text to repeat these earlier works It is however the goal of this chapter to present indications of the extent to which chemicals can be produced from coal as well as indications of the variety of chemical types that arise from coal eg see Lowry 1945 Speight 2013a On the basis of the thermal chemistry of coal Speight 2013a many primary products of coal reactions are high molecular weight species often aromatic in nature that bear some relation to the carbon skeletal of coal The secondary products ie products formed by decomposition of the primary products of the thermal decomposition of coal are lower molecular weight species but are less related to the carbon species in the original coal as the secondary reaction conditions become more severe higher temperatures andor longer reaction times In very general terms it is these primary and secondary decomposition reactions of coal which are the means to produce chemical from coal There is some leeway in terms of choice of the reac tion conditions and there is also the option of the complete decomposition of coal ie gasification 83 Coal Oil Shale and Biomass and the production of chemicals from the synthesis gas a mixture of carbon monoxide CO and hydrogen H2 produced by the gasification process Chapter 5 Speight 2013a 322 ProPerties and comPosition Coal is a combustible dark brown to black organic sedimentary rock that occurs in coalbeds or coal seams Coal is composed primarily of carbon with variable amounts of hydrogen nitrogen oxygen and sulfur and may also contain mineral matter and gases as part of the coal matrix Coal begins as layers of plant matter that has accumulated at the bottom of a body of water after which through anaerobic metamorphic processes changes the chemical and physical properties of the plant remains occurred to create a solid material Coal is the most abundant fossil fuel in the United States having been used for several centuries and occurs in several regions Knowledge of the size distribution and quality of the coal resources is important for governmental planning industrial planning and growth the solution of current and future problems related to air water and land degradation and for meeting the short and longterm energy needs of the country Knowledge of resources is also important in planning for the exporta tion and importation of fuel The types of coal in increasing order of alteration are lignite brown coal subbituminous bituminous and anthracite It is believed that coal starts off as a material that is closely akin to peat which is metamorphosed due to thermal and pressure effects to lignite With the further passing of time lignite increases in maturity to subbituminous coal As this process of burial and alteration continues more chemical and physical changes occur and the coal is classified as bitu minous At this point the coal is dark and hard Anthracite is the last of the classifications and this terminology is used when the coal has reached ultimate maturation The degree of alteration or metamorphism that occurs as a coal matures from peat to anthracite is referred to as the rank of the coal which is the classification of a particular coal relative to other coals according to the degree of metamorphism or progressive alteration in the natural series from lignite to anthracite ASTM D388 This method of ranking coals used in the United States and Canada was developed by the American Society for Testing and Materials ASTM now ASTM International and are i heating value ii volatile matter iii moisture iv ash production by com bustion which is reflective of the mineral matter content and v fixed carbon Speight 2005 2013a Lowrank coal such as lignite has lower energy content because they have low carbon content They are lighter earthier and have higher moisture levels As time heat and burial pressure all increase the rank does as well Highrank coals including bituminous and anthracite coals contain more carbon than lowerrank coals which results in a much higher energy content They have a more vitreous shiny appearance and lower moisture content then lowerrank coals There are many compositional differences between the coals mined from the different coal deposits worldwide The different types of coal are most usually classified by rank which depends upon the degree of transformation from the original source ie decayed plants and is therefore a measure of a coals age As the process of progressive transformation took place the heating value and the fixed carbon content of the coal increased and the amount of volatile matter in the coal decreased 323 conversion The thermal properties of coal are important in determining the applicability of coal to a variety of conversion processes For example the heat content also called the heating value or calorific value Chapter 8 is often considered to be the most important thermal property However there are other thermal properties that are of importance insofar as they are required for the design of equipment that is to be employed for the utilization conversion thermal treatment of coal in processes such as combustion carbonization gasification and liquefaction Speight 2013 84 Handbook of Petrochemical Processes The thermal decomposition which includes pyrolysis processes and carbonization processes often may be used interchangeably However it is more usual to apply the term pyrolysis a ther mochemical decomposition of coal or organic material at elevated temperatures in the absence of oxygen which typically occurs under pressure and at operating temperatures above 430C 800F to a process which involves widespread thermal decomposition of coal with the ensuing production of a charcarbonized residue The term carbonization is more correctly applied to the process for the production of char or coke when the coal is heated at temperatures in excess of 500C 930F The ancillary terms vola tilization and distillation are also used from time to time but more correctly refer to the formation and removal of volatile products gases and liquids during the thermal decomposition process Thus carbonization is the destructive distillation of coal in the absence of air accompanied by the production of carbon coke as well as the production of liquid and gaseous products Next to combustion carbonization represents one of the most popular and oldest uses of coal The thermal decomposition of coal on a commercial scale is often more commonly referred to as carbonization and is more usually achieved by the use of temperatures up to 1500C 2730F The degradation of the coal is quite severe at these temperatures and produces in addition to the desired coke sub stantial amounts of gaseous products Coal liquefaction is a process used to convert coal a solid fuel into a substitute for liquid fuels such as diesel and gasoline Coal liquefaction has historically been used in countries without a secure supply of petroleum such as Germany during World War II and South Africa since the early 1970s The technology used in coal liquefaction is quite old and was first implemented during the 19th century to provide gas for indoor lighting Coal liquefaction may be used in the future to produce oil for transportation and heating in case crude oil supplies are ever disrupted The production of liquid fuels from coal is not new and has received considerable attention In fact the concept is often cited as a viable option for alleviating projected shortages of liquid fuels as well as offering some measure of energy independence for those countries with vast resources of coal who are also net importers of crude oil The gasification of coal or a derivative ie char produced from coal is essentially the conver sion of coal by any one of a variety of processes to produce combustible gases Speight 2013 With the rapid increase in the use of coal from the 15th century onwards it is not surprising that the concept of using coal to produce a flammable gas especially the use of the water and hot coal became commonplace In fact the production of gas from coal has been a vastly expanding area of coal technology leading to numerous research and development programs As a result the charac teristics of rank mineral matter particle size and reaction conditions are all recognized as having a bearing on the outcome of the process not only in terms of gas yields but also on gas composition and properties In fact the products of coal gasification are varied insofar as the gas composition varies with the system employed Furthermore it is emphasized that the gas product must be first freed from any pollutants such as particulate matter and sulfur compounds before further use par ticularly when the intended use is a watergas shift or methanation as might be necessary in the coaltogastochemicals industry In terms of coal use through conversion processes serious efforts have been made to reduce the environmental footprint left by such processes by the initiation of the Clean Coal Technology Demonstration Program that has laid the foundation for effective technologies now in use that have helped significantly lower emissions of sulfur dioxide SO2 nitrogen oxides NOx and airborne particulates The term clean coal technology refers to a new generation of advanced coal utilization technologies that are environmentally cleaner and in many cases more efficient and less costly than the older and more conventional coalusing processes Speight 2013 Clean coal technologies offer the potential for a more clean use of coal which will have a direct effect on the goal of the reduction of emissions and process waste into the environment thereby making a positive contribution to the resolution of issues relating to acid rain and global climate change 85 Coal Oil Shale and Biomass 324 coal tar chemicals The coal carbonization industry was established initially as a means of producing coke Chapter 16 but a secondary industry emerged in fact became necessary to deal with the secondary or byproducts namely gas ammonia liquor crude benzole and tar produced during carbonization Table 31 Speight 2013a Coal tar is a byproduct of the carbonization of coal to produce coke andor natural gas Physically coal tar is black or dark browncolored liquid or a highviscosity semisolid which is one of the byproducts formed when coal is carbonized Speight 2013a Coal tar usually takes the form of a viscous liquid or semisolid with a naphthalenelike odor Chemically coal tar is a complex com bination of polycyclic aromatic hydrocarbon PAH often represented as PNA as well derivatives phenol derivatives heterocyclic oxygen sulfur and nitrogen compound derivatives Because of its flammable composition coal tar is often used for fire boilers in order to create heat Before any heavy oil flows easily they must be heated Coal tar coal tar pitch and coal tar creosote are very similar mixtures obtained from the distil lation of coal tars The physical and chemical properties of each are similar although limited data are available for coal tar and coal tar pitch By comparison coal tar creosote is a distillation product of coal tar They have an oily liquid consistency and range in color from yellowishdark green to brown The coal tar creosotes consist of aromatic hydrocarbon derivatives anthracene naphtha lene and phenanthrene derivatives Typically polycyclic aromatic hydrocarbon derivativestwo ring naphthalene derivatives and higher condensed ring derivativesconstitute the majority of the creosote mixture Unlike the coal tar and coal tar creosote coal tar pitch is the nonvolatile residue produced during the distillation of coal tar The pitch is a shiny dark brown to black residue that contains polycyclic aromatic hydrocarbon derivatives and their methyl and polymethyl derivatives as well as heteronuclear compounds As an aside the nomenclature of the coal tar industry like that of the petroleum industry Speight 2014 2017 needs refinement and clarification Almost any black undefined semisolidtoliquid material is popularly and often incorrectly described as tar or pitch whether it be a manufactured product or a naturally occurring substance Chapter 16 However to be correct and to avoid any ambiguity use of these terms should be applied with caution The term tar is usually applied to the volatile and nonvolatile soluble products that are produced during the carbonization or destructive distillation thermal decomposition with the simultaneous removal of distillate of various organic materials By way of further definition distillation of the tar yields an oil volatile organic products often referred to as benzole and a nonvolatile pitch In addition the origin of the tar or pitch should be made clear by the use of an appropriate descriptor ie coal tar wood tar coal tar pitch and the like Thus the eventual primary products of the carbonization process Chapter 16 are coke coal tar and crude benzole which should not be mistaken for benzene although benzene can be isolated from benzole ammonia liquor and gas The benzole fraction contains a variety of compounds both aromatic and aliphatic in nature and can be conveniently regarded as an analog of petroleum naphtha Speight 2014 TABLE 31 Bulk Products ww from Coal Carbonization Product ww Lowtemperature Carbonization Hightemperature Carbonization Gas 5 20 Liquids 15 2 Tar 10 3 Coke 70 75 86 Handbook of Petrochemical Processes The yield of byproduct tar from a coke oven is on average 8595 US gallons 3236 L per ton of coal carbonized but the yield from a continuous vertical retort is approximately 155190 US gallons 6075 L per ton of coal carbonized In lowtemperature retorts the yield of tar varies over the range 190360 US gallons 75135 L per ton of coal Crude coal tar sometimes referred to as crude coke oven tar or simply coal tar is a byproduct collected during the carbonization of coal to make coke Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace to manufacture steel and in foundry operations Crude coal tar is a raw material that is further distilled to produce various carbon products refined tars and oils used as essential components in the production of aluminum rubber concrete plasticizers coatings and specialty chemicals Crude coal tars have been processed in the United States since Koppers Company completed the first byproduct coke ovens around 1912 During the distillation of crude coal tar lowdensity oil and mediumdensity oil are removed from the crude coal tar to produce various refined coal tar products These lowdensity and medium density oils represent 2050 ww of the crude coal tar depending upon the refined product that is desired Coal tar contains hundreds of chemical compounds that will have varying amounts of polycyclic aromatic hydrocarbon derivatives depending upon the source Refined tarbased coatings have a great advantage over asphalt in that it has better chemical resis tance than asphalt coatings Refined tarbased coatings hold up better under exposures of petroleum oils and inorganic acids Another outstanding quality of refined tarbased coatings is their extremely low permeability to moisture and there high dielectric resistance both of which contribute to the corrosion resistance Munger 1984 Coal tar is a complex mixture and the components range from lowboiling low molecular weight species such as benzene to high molecular weight polynuclear aromatic compounds Similar classes of chemical compounds occur in the tars usually with little regard to the method of manu facture but there are marked variations in the proportions present in the tars due to the type of coal the type of carbonizing equipment and the method of recovery Chapter 16 Coke oven tar contains relatively low proportions ca 3 of tar acids phenols vertical retort tars may contain up to 30 phenolic compounds Moreover the phenols in coke oven tars mainly comprise phenol methyl and polymethyl phenols eg cresols and xylenols and naphthols those in vertical retort tar are mainly xylenols and higherboiling phenols Coke oven tars contain only minor quantities of nonaromatic hydrocarbon derivatives whilst the vertical retort tars may have up to 6 of paraffinic compounds Lowtemperature tars are more paraffinic and phenolic as might be expected from relative lack of secondary reactions than are the continuous vertical retort tars Coke oven tars are comparatively rich in naphthalene and anthracene and distillation is often the means by which various chemicals can be recovered from these par ticular products On the other hand another objective of primary distillation is to obtain a pitch or refinedtar residue of the desired softening point If the main outlet for the pitch is as a briquetting Chapter 17 or electrode binder primary distillation is aimed at achieving a mediumsoft pitch as product or for the production of road asphalt In terms of composition the compounds positively identified as pitch components consist pre dominantly of condensed polynuclear aromatic hydrocarbon derivatives or heterocyclic compounds containing three to six rings Some methyl and hydroxyl substituent groups have also been observed and it is reasonable to assume that vertical retort pitches contain paraffinic constituents in addition McNeil 1966 Pitches are often characterized by solvent analysis and many specifications quote limits for the amounts insoluble in certain solvents Hoiberg 1966 Primary distillation of crude tar produces pitch nonvolatile residue and several distillate frac tions the amounts and boiling ranges of which are influenced by the nature of the crude tar which depends upon the coal feedstock and the processing conditions For example in the case of the tar from continuous vertical retorts the objective is to concentrate the tar acids phenol cresols and xylenols into carbolic oil fractions On the other hand the objective with coke oven tar is to 87 Coal Oil Shale and Biomass concentrate the naphthalene and anthracene components into naphthalene oil and anthracene oil respectively The products of tar distillation can be divided into refined products made by the further pro cessing of the fractions and bulk products which are pitch creosote and their blends Coal tar lowboiling oil or crude benzole is similar in chemical composition to the crude benzole recovered from the carbonization gases at gas works and in coke oven plants The main components are ben zene toluene and xylenes with minor quantities of aromatic hydrocarbon derivatives paraffins naphthenes cyclic aliphatic compounds phenols as well as sulfur and nitrogen compounds The first step in refining benzole is steam distillation is employed to remove compounds boiling below benzene Lowboiling naphtha and highboiling naphtha are the mixtures obtained when the 150C200C 300F390F fraction after removal of tar acids and tar bases is fractionated These naphtha fractions are used as solvents To obtain pure products the benzole can be distilled to yield a fraction containing benzene toluene and xylenes Benzene is used in the manufacture of numerous products including nylon gammexane polystyrene phenol nitrobenzene and aniline On the other hand toluene is a starting material in the preparation of saccharin trinitrotoluene and polyurethane foams The xylenes present in the lowboiling oil are not always separated into the individual pure isomers since xylene mixtures can be marketed as specialty solvents Higher boiling fractions of the distillate from the tar contain pyridine bases naphtha and coumarone resins Other tar bases occur in the higherboiling range and these are mainly quinoline isoquino line and quinaldine Pyridine has long been used as a solvent in the production of rubber chemicals textile water repellant agents and in the synthesis of drugs The derivatives 2benzylpyridine and 2 aminopyridine are used in the preparation of antihistamines Another market for pyridine is in the manufacture of the nonpersistent herbicides diquat and paraquat Alphapicoline C6H7N 2picoline 2methylpryridine is used for the production of 2 vinylpyridine which when copolymerized with 14butadiene CH2CHCHCH2 and styrene C6H5CHCH2 produces a used as a latex adhesive which is used in the manufacture of automobile tires Other uses are in the preparation of 2βmethoxyethyl pyridine known as Promintic an anthel mintic for cattle and in the synthesis of a 2picoline quaternary compound Amprolium which is used against coccidiosis in young poultry Betapicoline 3picoline 3methylpryridine can be oxidized to nicotinic acid which with the amide form nicotinamide belongs to the vitamin B complex both products are widely used to fortify human and animal diets γPicoline 4picoline 4methylpyridine is an intermediate in the manufacture of isonicotinic acid hydrazide Isoniazide which is a tuberculostatic drug The 26Lutidine 26dimethylpyridine can be converted to dipico linic acid which is used as a stabilizer for hydrogen peroxide and peracetic acid The taracid free and tarbase free coke oven naphtha can be fractionated to give a narrow boil ing fraction 170C185C 340F365F containing coumarone and indene This is treated with 2methylpyridine 26Lutidine 88 Handbook of Petrochemical Processes strong sulfuric acid to remove unsaturated components and is then washed and redistilled The concentrate is heated with a catalyst such as a boron fluoridephenol complex to polymerize the indene and part of the coumarone Unreacted oil is distilled off and the resins obtained vary from pale amber to dark brown in color They are used in the production of flooring tiles and in paints and polishes Naphthalene and several tar acids are the important products extracted from volatile oils from coal tar It is necessary to first extract the phenolic compounds from the oils and then to process the phenoldepleted oils for naphthalene recovery Tar acids are produced by extraction of the oils with aqueous caustic soda at a temperature sufficient to prevent naphthalene from crystallizing The phenols react with the sodium hydroxide to give the corresponding sodium salts as an aqueous extract known variously as crude sodium phenate sodium phenolate sodium carbolate or sodium cresylate The extract is separated from the phenolfree oils which are then taken for naphthalene recovery Phenol C6H5OH is a key industrial chemical however the output of phenol from coal tar is exceeded by that of synthetic phenol Phenol is used for the production of phenolformaldehyde resins while other important uses in the plastic field include the production of polyamides such as nylon of epoxy resins and polycarbonates based on bisphenol A and of oilsoluble resins from ptbutyl and poctyl phenols Phenol is used in the manufacture of pentachlorophenol which is used as a fungicide and in timber preservation Aspirin and many other pharmaceuticals certain detergents and tanning agents are all derived from phenol and another important use is in the manufacture of 24dichlorophenoxyacetic acid 24D which is a selective weed killer Orthocresol has been used predominantly for the manufacture of the selective weed killers 4chloro2methylphenoxyacetic acid MCPA and the corresponding propionic acid MCPP and the butyric acid MCPB as well as 24dinitroocresol DNOC a general herbicide insecticide Paracresol pHOC6H4CH3 has been used widely for the manufacture of BHT 26ditertiarybutyl 4hydroxytoluene an antioxidant 24Dichlorophenoxyacetic acid 4chloro2methylphenoxyacetic acid MCPA 24dinitroocresol DNOC 89 Coal Oil Shale and Biomass Metacresol and paracresol mixtures are used in the production of phenoplasts tritolyl phosphate plasticizers and petroleum additives Other outlets for cresylic acids are as agents for froth flotation metal degreasing as solvents for wirecoating resins antioxidants cutting oils nonionic detergents and disinfectants Naphthalene is probably the most abundant component in hightemperature coal tars The pri mary fractionation of the crude tar concentrates the naphthalene into oils which in the case of coke oven tar contain the majority 7590 ww of the total naphthalene After separation naphtha lene can be oxidized to produce phthalic anhydride which is used in the manufacture of alkyd and glyptal resins and plasticizers for polyvinyl chloride and other plastics The main chemical extracted on the commercial scale from the higherboiling oils bp 250C 480F is crude anthracene The majority of the crude anthracene is used in the manufacture of dyes after purification and oxidation to anthraquinone Coal tar creosote is the residual distillate oils obtained when the valuable components such as naphthalene anthracene tar acids and tar bases have been removed from the corresponding frac tions Figure 31 It is a brownishblackyellowishdark green oily liquid with a characteristic sharp odor obtained by the fractional distillation of crude coal tars The approximate distillation range is 200C400C 390F750F The chemical composition of creosotes is influenced by the origin of the coal and also by the nature of the distilling process as a result the creosote components are rarely consistent in their type and concentration Major uses for creosotes have been as a timber preservative as fluxing oils for pitch and bitumen and in the manufacture of lampblack and carbon black However the use of creosote as a timber preservative has recently come under close scrutiny as have many other illdefined products of coal processing Issues related to the seepage of such complex chemical mixtures into the surrounding environment have brought an awareness of the potential environmental and 26ditertiarybutyl4hydroxytoluene mcresol pcresol Phthalic anhydride 90 Handbook of Petrochemical Processes health hazards related to the use of such chemicals Stringent testing is now required before such chemicals can be used As a corollary to this section where the emphasis has been on the production of bulk chemicals from coal a tendencytobeforgotten item must also be included That is the mineral ash from coal processes Coal minerals are a very important part of the coal matrix and offer the potential for the recovery of valuable inorganic materials Speight 2013a However there is another aspect of the mineral content of coal that must be addressed and that relates to the use of the ash as materials for roadbed stabilization landfill cover cementing due to the content of pozzolanic materials and wall construction to mention only a few 33 OIL SHALE Oil shale represents a large and mostly untapped hydrocarbon resource Like tar sand oil sand in Canada and coal oil shale is considered unconventional because oil cannot be produced directly from the resource by sinking a well and pumping Oil has to be produced by thermal decomposition of the organic matter kerogen in the shale The organic material contained in the shale is called kerogen a solid material intimately bound within the mineral matrix However oil shale does not contain any oilthis must be produced by a process in which the kerogen is thermally decomposed cracked to produce the liquid product shale oil Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 Compared to crude oil shale oil obtained by retorting of oil shale is characterized by wide boiling range and by large concentrations of heteroelements and also by high content of oxygen nitrogen or sulfurcontaining compounds 331 shale oil Production Shale oil is produced from oil shale by the thermal decomposition of the kerogen component of oil shale Oil shale must be heated to temperatures between 400C and 500C 750F930F This heating process is necessary to convert the embedded sediments to kerogen oil and combustible gases Generally with solid fossil fuels the yield of the volatile products depends mainly on the hydrogen content in the convertible solid fuel Thus compared with coal oil shale kerogen contains more hydrogen and can produce relatively more oil and gas when thermally decomposed Speight 2008 2012 2013 From the standpoint of shale oil as a substitute for petroleum products the com position is of great importance FIGURE 31 Representation of the production and composition of coal tar creosote 91 Coal Oil Shale and Biomass The thermal processing of oil shale to oil has quite a long history and various facilities and technologies have been used including mining of the shale followed by thermal processing as well as in situ decomposition of the shale Speight 2008 2012 In principle there are two ways of accomplishing the thermal decomposition of the kerogen in the shale i lowtemperature processing semicoking or retortingby heating the oil shale up to about 500C 930F and ii hightemperature processingcokingheating up to 1000C1200C 1830F2190F A high yield deposit of oil shale will yield 25 gallons of oil per ton of oil shale In the miningthermal processing option ex situ production oil shale is mined crushed and then subjected to thermal processing at the surface in an oil shale retort Both pyrolysis and combustion have been used to treat oil shale in a surface retort In the second option in situ production the shale is left in place and the retorting eg heating of the shale occurs in the ground Generally sur face processing consists of three major steps i oil shale mining and ore preparation ii pyrolysis of oil shale to produce kerogen oil and iii processing kerogen oil to produce refinery feedstock and highvalue chemicals For deeper thicker deposits not as amenable to surface or deepmining methods shale oil can be produced by in situ technology In situ processes minimize or in the case of true in situ eliminate the need for mining and surface pyrolysis by heating the resource in its natural depositional setting Depending on the depth and other characteristics of the target oil shale deposits either surface mining or underground mining methods may be used Each method in turn can be further cat egorized according to the method of heating Another way in which the various retorting processes differ is the manner by which heat is provided to the shale by hot gasi by a solid heat carrier or ii by conduction through a heated wall After mining the oil shale is transported to a facility for retorting after which the oil must be upgraded by further processing before it can be sent to a refinery and the spent shale must be disposed often by putting it back into the mine Eventually the mined land is reclaimed Both mining and processing of oil shale involve a variety of environ mental impacts such as global warming and greenhouse gas emissions disturbance of mined land disposal of spent shale use of water resources and impacts on air and water quality 332 shale oil ProPerties Shale oil is a synthetic crude oil produced by retorting oil shale and is the pyrolysis product of the organic matter kerogen contained in oil shale The raw shale oil produced from retorting oil shale can vary in properties and composition Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 Compared with petroleum shale oil is high in nitrogen and oxygen compounds and a higher spe cific gravityon the order of 0910 owing to the presence of highboiling nitrogen sulfur and oxygencontaining compounds Shale oil also has a relatively high pour point and small quantities of arsenic and iron are present The chemical potential of oil shale as retort fuel to produce shale oil and from that liquid fuel and specialty chemicals has been used so far to a relatively small extent Using stepwise cracking various liquid fuels have been produced and even exported before World War II At the same time shale oils possess molecular structures of interest to the specialty chemicals industry and also a number of nonfuel specialty products have been marketed based on functional group broad range concentrate or even pure compound values Shale oil produced from kerogencontaining shale rock is a complex mixture of hydrocarbon derivatives and it is characterized using bulk properties of the oil Shale oil usually contains large quantities of olefin derivatives and aromatic hydrocarbon derivatives as well as significant quantities of heteroatom compounds nitrogencontaining compounds oxygencontaining compounds and sulfurcontaining compounds A typical shale oil composition includes nitrogen 152 ww oxygen 051 ww and sulfur 0151 ww as well as mineral particles and metalcontaining compounds Scouten 1990 Lee 1991 Lee 1991 Lee et al 2007 Speight 2008 Generally the oil is less fluid than crude oil which is reflected in the pour point that is in the order of 24C27C 92 Handbook of Petrochemical Processes 75F81F while conventional crude oil has a pour point in the order of 60C to 30C 76F to 86F which affects the ability of shale oil to be transported using unheated pipelines Shale oil also contains polycyclic aromatic hydrocarbon derivatives Based on large quantities of oxygencontaining compounds in the highboiling fraction asphalt blending material road asphalt construction mastics anticorrosion oils rubber softeners benzene and toluene for production of benzoic acid as well as solvent mixtures on pyrolysis of lower boiling fractions of shale oil are produced Higherboiling middistillate shale oil fractions having anti septic properties are used to produce effective oil for the impregnation of wood as a major shale oilderived specialty product Watersoluble phenols are selectively extracted from shale oil frac tionated and crystallized for production of pure 5methylresorcinol and other alkyl resorcinol derivatives and highvalue intermediates to produce tanning agents epoxy resins and adhesives diphenyl ketone and phenolformaldehyde adhesive resins rubber modifiers chemicals and pesti cides Some conventional products such as coke and various distillate fuels are produced from shale oil as byproducts However the presence of the polar constituents containing nitrogen and oxygen functions sul fur compounds are also issues worthy of consideration can cause shale oil to be incompatible with conventional petroleum feedstocks and petroleum products Speight 2014 As a result particular care must be taken to ensure that all the functions that cause such incompatibility are removed from the shale oil before it is blended with a conventional petroleum liquid 3321 Hydrocarbon Products The fundamental structure of the organic matter in oil shale gives rise to significant quantities of waxes consisting of long normal alkanes and the alkanes are distributed throughout the raw shale oil However the composition of shale oil depends on the shale from which it was obtained as well as on the retorting method by which it was produced Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 As compared with petroleum crude shale oil is highboiling viscous and is high in nitrogen and oxygen compounds Retorting processes which use flash pyrolysis produce more fragments containing high molecu lar weight and multiring aromatic structures Processes that use slower heating conditions with greater reaction times at low temperature 300C400C 570F750F tend to produce higher concentrations of nalkanes Naphthenearomatic compounds of intermediate boiling range such as 200C400C 390F750F also tend to be formed with the slower heating processes Saturated hydrocarbon derivatives in the shale oil include nalkane derivatives isoalkane deriv atives and cycloalkane derivatives and the alkene derivatives consist of nalkene derivatives iso alkene derivatives and cycloalkene derivatives while the main components of aromatic derivatives are monocyclic bicyclic and tricyclic aromatic derivatives and their alkylsubstituted homologues There is a variation of the distribution of saturated hydrocarbon derivatives alkene derivatives and aromatic derivatives in the different boiling ranges of the shale oil product Saturated hydrocarbon derivatives in the shale oil increase and the aromatic derivatives increase slightly with a rise in boil ing range while alkene derivatives decrease with a rise in boiling range A typical Green River shale oil contains 40 ww hydrocarbon derivatives and 60 ww hetero atomic organic compounds which contain nitrogen sulfur and oxygen The nitrogen occurs in ring compounds with nitrogen in the ring eg pyridines pyridines pyrroles as well as in nitriles and typically comprises 60 ww of the heteroatomic organic components Another 10 ww of these components contains organically bound sulfur compounds which exists in thiophenes as well as sulfides and disulfides The remaining 30 ww consists of oxygencontaining compounds which occur as phenols and carboxylic acids Shale oil not only contains a large variety of hydrocarbon compounds Table 32 but also has high nitrogen content compared to a nitrogen content of 0203 ww for a typical petroleum Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 In addition shale oil also has a high olefin and diolefin contentconstituents which are not present in petroleum and which require 93 Coal Oil Shale and Biomass attention during processing due to their tendency to polymerize and form gums and sediments fuel line deposits It is the presence of these olefin derivatives and diolefin derivatives in conjunction with high nitrogen content which gives shale oil the characteristic difficulty in refining Crude shale oil also contains appreciable amounts of arsenic iron and nickel that interfere with refining Other characteristic properties of shale oils are i high levels of aromatic compounds deleterious to kerosene and diesel fractions ii low hydrogentocarbon ratio iii low sulfur levels compared with most crudes available in the world though for some shale oils from the retorting of marine oil shale high sulfur compounds are present iv suspended solids finely divided rock typically due to entrainment of the rock in the oil vapor during retorting and v lowtomoderate levels of met als Thus because of the characteristics of shale oil further processes are needed to improve the properties of shale oil products The basic unit operations in the oil refining are distillation coking hydrotreating hydrocracking catalytic cracking and reforming The process selected will largely depend on the availability of equipment and the individual economics of the particular refinery Although the content of asphaltene constituents andor resin constituents in shale oil is low shale oil being a distillate productasphaltene constituents in shale oil may be unique since in shale oil it is high heteroatomic content that causes precipitation as an asphaltene fraction rather than high molecular weightfor example the hydroxypyridine derivatives are insoluble in low molecular weight alkane solvents The polarity of the nitrogen polycyclic aromatic constituents may also explain the specific properties of emulsification of water and metal complexes 3322 NitrogenContaining Compounds Nitrogen compounds in shale oil render technological difficulties in the downstream processing of shale oil in particular poisoning of the refining catalysts Such nitrogen compounds are all originated from the oil shale and the amount and types depend heavily on the geochemistry of oil shale deposits Since direct analysis and determination of molecular forms of nitrogencontaining compounds in oil shale rock is very difficult the analysis of shale oil that is extracted by retorting processes provides valuable information regarding the organonitrogen species in the oil shale The nitrogen content in the shale oil is relatively higher than in natural crude oil Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 The nitrogencontaining compounds identified in shale oils can be classified as basic weakly basic and nonbasic The basic nitrogen compounds in shale oils are pyridine quinoline acridine amine and their alkylsubstituted derivatives the weakly basic ones are pyrrole indole carbazole and their derivatives and the nitrile and amide homologues are the nonbasic constituents Most of these compounds are useful chemicals Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 although some of them are believed to affect the stability of shale oil Generally TABLE 32 Major Compound Types in Shale Oil Saturate Heteroatom systems paraffin benzothiophene cycloparaffin dibenzothiophene Olefin phenol Aromatic carbazole Benzene pyridine indan quinoline tetralin nitrile naphthalene ketone biphenyl pyrrole phenanthrene chrysene 94 Handbook of Petrochemical Processes basic nitrogen accounts for about onehalf of the total nitrogen and is evenly distributed in the different boiling point fractions Nitrogen compounds occur throughout the boiling ranges of the shale oil but have a decided tendency to exist in highboiling point fractions Pyrroletype nitrogen increases with a rise in the boiling point of the shale oil fractions Porphyrins may occur in the high boiling point fraction of the shale oil Of the nitrogencontaining compounds in the lowboiling 350C 660F shale oil fraction the majority contain one nitrogen atom Benzoquinoline derivatives principally acridine and alkyl substituted homologues could not be present significantly in the lowerboiling shale oil fractions because the boiling point of benzoquinoline and its alkylsubstituted homologues is higher than 350C 660F Organic nitrogencontaining compounds in the shale oil poison the catalysts in different cata lytic processes They also contribute to stability problems during storage of shale oil products since they induce polymerization processes which cause an increase in the viscosity and give rise to the odor and color of the shale oil product The high nitrogen content of shale oil could contribute to the surface and colloidal nature of shale oil which forms emulsions with water 3323 OxygenContaining Compounds The oxygen content of shale oil is much higher than in natural petroleum Low molecular weight oxygen compounds in shale oil are mainly phenolic constituentscarboxylic acids and nonacidic oxygen compounds such as ketones are also present Low molecular phenolic compounds are the main acidic oxygencontaining compounds in the lowboiling fraction of the shale oil and are usu ally derivatives of phenol such as cresol and polymethylated phenol derivatives The oxygen content of petroleum is typically in the order of 0110 ww whereas the oxygen contents in shale oils are much higher and vary with different shale oil Scouten 1990 Lee 1991 Lee et al 2007 In addition the oxygen content varies in different boiling point fractions of the shale oil In general it increases as the boiling point increases and most of the oxygen atoms are concentrated in the highboiling point fraction Other oxygencontaining constituents of shale oil include small amounts of carboxylic acids and nonacidic oxygencontaining compounds with a carbonyl functional group such as ketones alde hydes esters and amides are also present in the 350C 660F fraction of shale oil Ketones in the shale oil mainly exist as 2 and 3alkanones Other oxygencontaining compounds in the low boiling 350C 660F fraction include alcohols naphthol and ether constituents 3324 SulfurContaining Compounds Sulfur compounds in the shale oils include thiols sulfides thiophenes and other miscellaneous sulfur compounds Elemental sulfur is found in some crude shale oil but is absent in others Generally the sulfur content of oilshale distillates is comparable in weight percentage to crude oil Scouten 1990 Lee 1991 Lee et al 2007 Speight 2008 Refiners will be able to meet the current 500 ppm requirement by increasing the existing capacity of their hydrotreatment units and adding new units However refineries may face difficulty in treating diesel to below 500 ppm The remaining sulfur is bound in multiring thiophenetype compounds that prove difficult to hydrotreat because the molecular ring structure attaches the sulfur on two sides and if alkyl groups are pres ent provides steric protection for the sulfur atom Although these compounds occur throughout the range of petroleum distillates they are more concentrated in the residuum 34 BIOMASS Increasing attention has been and is being given to the possibility of utilizing photosyntheti cally active plants as natural solar energycapturing devices with the subsequent conversion of available plant energy into useful fuels or chemical feedstocks Table 33 Metzger 2006 Biddy et al 2016 Wu et al 2016 Acquisition of biological raw materials for energy capture follows 95 Coal Oil Shale and Biomass TABLE 33 Examples of Chemicals Produced from BioSources Chemical Comment 13Butadiene The building block for the production of polybutadiene and styrenerubber and butadiene rubber currently produced from petroleum as a byproduct of ethylene manufacturing can be produced through multiple biomass conversion strategies for the production of a direct renewable butadiene replacement 14Butanediol A building block for the production of polymers solvents and specialty chemicals bioderived butanediol is being produced on a commercial scale utilizing commodity sugars can be produced by the conversion of succinic acid to 14butanediol Ethyl lactate A biodegradable solvent produced by the esterification of ethanol and lactic acid primary use for ethyl lactate is as an industrial productthe properties and performance meet or exceed those of traditional solvents such as toluene methyl ethyl ketone and Nmethyl pyrrolidone in many applications the starting materials used to make ethyl lactate lactic acid and ethanol have a high potential to be made from lignocellulosic sugars Fatty alcohols Also called detergent alcohols are linear alcohols of 12 or more carbons used primarily to produce anionic and nonionic surfactants for household cleaners personal care derivatized by ethoxylation sulfation or sulfonation before use can be produced from tallow vegetable oils or petroleum also have the potential to be produced from renewable sources by autotrophic and heterotrophic algae or by the microbial fermentation of carbohydrates Furfural A heterocyclic aldehyde produced by the dehydration of xylose a monosaccharide often found in large quantities in the hemicellulose fraction of lignocellulosic biomass any material containing a large amount of pentose fivecarbon sugars such as arabinose and xylose can serve as a raw material for furfural production converted to furfuryl alcohol which is used for the production of foundry resins the anticorrosion properties of furfuryl alcohol is useful in the manufacture of furan fiberreinforced plastics for piping a broad spectrum of industrial applications such as the production of plastics pharmaceuticals agrochemical products and nonpetroleumderived chemicals not produced from fossil feedstocks may be for conversion to jet and diesel fuel blend stocks Glycerin A polyhydric alcohol and is a main component of triglycerides found in animal fats and vegetable oil The word glycerin generally applies to commercial products containing mostly glycerol the word glycerol most often refers specifically to the chemical compound 123propanetriol and to the anhydrous content in a glycerin product or in a formulation glycerin is the main byproduct of biodiesel production It is also generated in the oleochemical industry during soap production and is produced synthetically from propyl biodiesel and soap production accounts for most current glycerin production therefore the overall supply of glycerin is driven primarily by the demand for these products a feedstock for conversion to more valuable products such as epichlorohydrin and succinic acid emerging uses include animal feed and marine fuel Isoprene The building block for polyisoprene rubber styrene copolymers and butyl rubber produced by aerobic bioconversion of carbohydrates Lactic acid An alphahydroxy acid with dual functional groups most frequently occurring carboxylic acid in nature produced by microbial fermentation of carbohydrates used for applications in food pharmaceuticals personal care products industrial uses and polymers polylactic acid has gained popularity for use in food packaging disposable tableware shrink wrap and 3D printers 13Propanediol A linear aliphatic diol which makes it a useful chemical building block can be used for a variety of applications including polymers personal care products solvents and lubricants also used as a component in poly trimethylene terephthalate polymers which are used in textiles and fibers Continued 96 Handbook of Petrochemical Processes three main approaches i purposeful cultivation of socalled clergy crops ii harvesting natu ral vegetation and iii collection of agricultural wastes Thus in the context of this book bio mass refers to i energy crops grown specifically to be used as fuel such as fastgrowing trees or switch grass ii agricultural residues and byproducts such as straw sugarcane fiber and rice hulls and iii residues from forestry construction and other woodprocessing industries Detroy 1981 Vasudevan et al 2005 Wright et al 2006 Speight 2008 It is the term used to describe any material of recent biological origin including plant materials such as trees grasses agricultural crops and even animal manure that can be converted to a variety of feedstocks for the production of petrochemical products through primary andor secondary conversion methods Table 34 Biomass is a renewable energy source unlike the fossil fuel resources natural gas crude oil and coal but like the fossil fuels biomass is a form of stored solar energy Speight 2008 The energy of the sun is captured through the process of photosynthesis in growing plants One advantage of biofuel in comparison to most other fuel types is that it is biodegradable and thus relatively harm less to the environment if spilled TABLE 33 Continued Examples of Chemicals Produced from BioSources Chemical Comment Propylene glycol Also known as 12propanediol propaneI2diol and monopropylene glycol a viscous colorless odorless liquid that is nonvolatile at room temperature and is completely soluble in water used in the production of consumer products such as antiperspirants suntan lotions eye drops food flavorings and bulking agent in oral and topical drugs industrial grade propylene glycol is used in the production of unsaturated polyester resins for end use markets such as residential and commercial construction marine vessels passenger vehicles and consumer appliances also used as an engine coolant and antifreeze in place of ethylene glycol and in the airline industry as an airplane and runway deicing agent serves as a solvent enzyme stabilizer clarifying agent and diluent can be produced by hydrogenolysis of glycerin over mixedmetal catalysts or hydrocracking of sorbitol Succinic acid A dicarboxylic acid that can be produced from biomass and used as a precursor for the synthesis of highvalue products derived from renewable resources including commodity chemicals polymers surfactants and solvents pXylene Used to produce both terephthalic acid and dimethyl terephthalate which are raw materials for the production of polyethylene terephthalate bottles can be produced via the traditional biochemical fermentation process followed by upgrading thermochemical pyrolysis routes and hybrid thermochemicalbiochemical strategies of catalytic upgrading of sugars TABLE 34 Methods for the Conversion of Biomass to Petrochemical Feedstocks Feedstock Conversion Type Primary Method Product Secondary Method Biomass Biological conversion Fermentation Methane Sugar Protein Thermochemical conversion Pyrolysis Gas Oil Gasification Char Gasification Hydrocarbonization Gas Gasification Oil coke Gasification 97 Coal Oil Shale and Biomass In order to produce fuels and chemicals several currently available processes rely on entirely breaking down complex molecules before building up the desired compounds such as the case with syngas production to form alkanes and alcohols While biomass can also be converted into syngas an alternative and complimentary approach strategically converts biomass into chemical building blocks that retain features eg electrophilic or nucleophilic character that can be exploited in further manipulations Such platform chemicals can be generated through either chemical routes or biological processes A major issue in the use of biomass is one of feedstock diversity Biomassbased feedstock mate rials used in producing chemicals can be obtained from a large variety of sources If considered individually the number of potential renewable feedstocks can be overwhelming but they tend to fall into three simple categories i waste materials such as food processing wastes ii dedicated feedstock crops which includes and short rotation woody crops or herbaceous energy crops such as perennials or forage crops and iii conventional food crops such as corn and wheat In addi tion these raw materials are composed of several similar chemical constituents ie carbohydrates proteins lipids lignin and minerals Thermal or chemical processing of these materials is typically accomplished by novel separation and conversion methodology leading to chemicals similar to those from conventional petrochemical starting materials Bioprocesses focus on microbiological conversion of fermentable sugars that are derived from these materials by thermal chemical or enzymatic means to commodity and specialty chemicals Detroy 1981 Thus in choosing a feedstock for a given product it is important not to be diverted by semantic differences that arise due to its current usage Biomass components which are generally present in minor amounts include triglycerides sterols alkaloids resins terpenes terpenoids and waxes This includes everything from primary sources of crops and residues harvestedcollected directly from the land to secondary sources such as sawmill residuals to tertiary sources of postconsumer residuals that often end up in landfills A fourth source although not usually categorized as such includes the gases that result from anaerobic digestion of animal manure or organic waste in landfills Wright et al 2006 Speight 2008 Most present day production and use of biomass for energy is carried out in a very unsustainable manner with a great many negative environmental consequences If biomass is to supply a greater proportion of the worlds energy needs in the future the challenge will be to produce biomass and to convert and use it without harming the natural environment Technologies and processes exist today which if used properly make biomassbased fuels less harmful to the environment than fossil fuels Applying these technologies and processes on a sitespecific basis in order to minimize negative environmental impacts is a prerequisite for sustainable use of biomass energy in the future These technologies have the ability to be coordinated in a biorefinery A biorefinery Speight 2011c is the means by which biomass can be converted to other productsin the current context the other products are biofuels which have the potential to replace certain petroleumderived fuels In theory a biorefinery can use all kinds of biomass including wood and dedicated agricultural crops plant and animalderived waste municipal waste and aquatic biomass algae seaweeds A biorefinery produces a spectrum of marketable products and energy including intermediate and final products food feed materials chemicals fuels power andor heat However the differences in the various biomass feedstocks may dictate that a biorefin ery be constructed and operated on the basis of the chemical composition of the feedstock and the mean by which the feedstock is to be processed 341 Biomass feedstocks More generally biomass feedstocks are recognized or classified by the specific plant content of the feedstock or the manner in which the feedstocks is produced For example primary biomass feedstocks are thus primary biomass that is harvested or collected from the field or forest where it is grown Examples of primary biomass feedstocks currently being 98 Handbook of Petrochemical Processes used for bioenergy include grains and oilseed crops used for transportation fuel production plus some crop residues such as orchard trimmings and nut hulls and some residues from logging and forest operations that are currently used for heat and power production Secondary biomass feedstocks differ from primary biomass feedstocks in that the secondary feedstocks are a byproduct of processing of the primary feedstocks By processing it is meant that there is substantial physical or chemical breakdown of the primary biomass and production of byproducts processors may be factories or animals Field processes such as harvesting bundling chipping or pressing do not cause a biomass resource that was produced by photosynthesis eg tree tops and limbs to be classified as secondary biomass Specific examples of secondary biomass includes sawdust from sawmills black liquor which is a byproduct of paper making and cheese whey which is a byproduct of cheesemaking processes Manures from concentrated animal feed ing operations are collectable secondary biomass resources Vegetable oils used for biodiesel that are derived directly from the processing of oilseeds for various uses are also a secondary biomass resource Tertiary biomass feedstock includes postconsumer residues and wastes such as fats greases oils construction and demolition wood debris other waste wood from the urban environments as well as packaging wastes municipal solid wastes and landfill gases A category other wood waste from the urban environment includes trimmings from urban trees which technically fits the defi nition of primary biomass However because this material is normally handled as a waste stream along with other postconsumer wastes from urban environments and included in those statistics it makes the most sense to consider it to be part of the tertiary biomass stream Tertiary biomass often includes fats and greases which are byproducts of the reduction of ani mal biomass into component parts since most fats and greases and some oils are not available for bioenergy use until after they become a postconsumer waste stream Vegetable oils derived from processing of plant components and used directly for bioenergy eg soybean oil used in biodiesel would be a secondary biomass resource though amounts being used for bioenergy are most likely to be tracked together with fats greases and waste oils One aspect of designing a refinery for any feedstocks is the composition of the feedstocks For example a heavy oil refinery would differ somewhat from a conventional refinery and a refin ery for tar sand bitumen would be significantly different to both Speight 2008 2014 2017 Furthermore the composition of biomass is variable Speight 2008 which is reflected in the range of heat value heat content calorific value of biomass which is somewhat lesser than for coal and much lower than the heat value for petroleum generally falling in the range 60008500 Btulb Speight 2008 Moisture content is probably the most important determinant of heating value Airdried biomass typically has about 1520 moisture whereas the moisture content for oven dried biomass is around 0 Moisture content is also an important characteristic of coals varying in the range of 230 However the bulk density and hence energy density of most biomass feedstocks is generally low even after densification about 10 and 40 of the bulk density of most fossil fuels The production of fuels and chemicals from renewable plantbased feedstocks utilizing state oftheart conversion technologies presents an opportunity to maintain competitive advantage and contribute to the attainment of national environmental targets Bioprocessing routes have a number of compelling advantages over conventional petrochemicals production however it is only in the last decade that rapid progress in biotechnology has facilitated the commercialization of a number of plantbased chemical processes Plants offer a unique and diverse feedstock for chemicals and the production of biofuels from biomass requires some knowledge of the chemistry of biomass the chemistry of the individual constituents of biomass and the chemical means by which the biomass can be converted to fuel It is widely recognized that further significant production of plantbased chemicals will only be economically viable in highly integrated and efficient production complexes producing a diverse range of chemical products This biorefinery concept is analogous to conventional oil refineries and 99 Coal Oil Shale and Biomass petrochemical complexes that have evolved over many years to maximize process synergies energy integration and feedstock utilization to drive down production costs In addition the specific components of plants such as carbohydrates vegetable oils plant fiber and complex organic molecules known as primary and secondary metabolites can be utilized to produce a range of valuable monomers chemical intermediates pharmaceuticals and materials 3411 Carbohydrates Plants capture solar energy as fixed carbon during which carbon dioxide is converted to water and sugars CH2Ox CO H O CH O O 2 2 2 x 2 The sugars produced are stored in three types of polymeric macromolecules i starch ii cellulose and iii hemicellulose In general sugar polymers such as cellulose and starch can be readily broken down to their constituent monomers by hydrolysis preparatory to conversion to ethanol or other chemicals Vasudevan et al 2005 Speight 2008 In contrast lignin is an unknown complex structure con taining aromatic groups that is totally hypothetical and is less readily degraded than starch or cel lulose Although lignocellulose is one of the cheapest and most abundant forms of biomass it is difficult to convert this relatively unreactive material into sugars Among other factors the walls of lignocellulose are composed of lignin which must be broken down in order to render the cellulose and hemicellulose accessible to acid hydrolysis For this reason many efforts focused on ethanol production from biomass are based almost entirely on the fermentation of sugars derived from the starch in corn grain Carbohydrates starch cellulose sugars starch readily obtained from wheat and potato while cellulose is obtained from wood pulp The structures of these polysaccharides can be readily manip ulated to produce a range of biodegradable polymers with properties similar to those of conventional plastics such as polystyrene foams and polyethylene film In addition these polysaccharides can be hydrolyzed catalytically or enzymatically to produce sugars a valuable fermentation feedstock for the production of ethanol citric acid lactic acid and dibasic acids such as succinic acid 3412 Vegetable Oils Vegetable oil is obtained from seed oil plants such as palm sunflower and soya The predominant source of vegetable oils in many countries is rapeseed oil Vegetable oils are a major feedstock for the oleochemicals industry surfactants dispersants and personal care products and are now suc cessfully entering new markets such as diesel fuel lubricants polyurethane monomers functional polymer additives and solvents In many cases it has been advocated that vegetable oil and similar feedstocks be used as feed stocks for a catalytic cracking unit The properties of the products can be controlled by controlling the process variables including the cracking temperature as well as the type of catalyst used The production of biodiesel by direct esterification of fatty acids with short chain alcohols occurs in one step only whereby acidic catalysts can be used to speed up the reaction Demirbaş 2006 3413 Plant Fibers Lignocellulosic fibers extracted from plants such as hemp and flax can replace cotton and polyester fibers in textile materials and glass fibers in insulation products Lignin is a complex chemical that is most commonly derived from wood and is an integral part of the cell wall of plants The chemi cal structure of lignin is unknown and at best can only be represented by hypothetical formulas Lignin Latin lignumwood is one of most abundant organic chemicals on earth after cellulose and chitin By way of clarification chitin C8H13O5Nn is a longchain polymeric polysaccharide of βglucose that forms a hard semitransparent material found throughout the natural world Chitin is 100 Handbook of Petrochemical Processes the main component of the cell walls of fungi and is also a major component of the exoskeletons of arthropods such as the crustaceans eg crab lobster and shrimp and insects eg ants beetles and butterflies and the beaks of cephalopods eg squids and octopuses Lignin makes up about onequarter to onethird of the dry mass of wood and is generally con sidered to be a large crosslinked hydrophobic aromatic macromolecules with a molecular mass that is estimated to be in excess of 10000 Lignin fills the spaces in the cell wall between cellulose hemicellulose and pectin components and is covalently linked bonded to hemicellulose Lignin also forms covalent bonds with polysaccharides which enables crosslinking to different plant poly saccharides Lignin confers mechanical strength to the cell wall stabilizing the mature cell wall and therefore the entire plant 342 BiorefininG A petroleum refinery is a series of integrated unit processes by which petroleum can be converted to a slate of useful salable products A petroleum refinery as currently configured is unsuitable for processing raw or even partially processed biomass A typical refinery might be suitable for processing products such as gases liquid or solids products from biomass processing These prod ucts from biomass might be acceptable as a single feedstock to a specific unit or more likely as a feedstock to be blended with refinery streams to be coprocessed in various refinery units Thus a biorefinery might in the early stages of development be a series of unit processes which convert biomass to a primary product that requires further processing to become the final salable product The analogy is in the processing of bitumen from tar sand which is first processed to a synthetic crude oil primary processing and then sent to a refinery for conversion to salable fuel products Speight 2008 2014 2017 Analogous in many cases to the thermal decomposition of crude oil constituents in the flash pyrolysis hightemperature cracking and short residence time the products are ethylene ben zene toluene and the xylene isomers as well as carbon monoxide and carbon dioxide The type of biomass for example wood used influences the product distribution Steinberg et al 1992 Theoretically the flash pyrolysis process can use a wide range of biomass sources The process has much in common with the naphtha cracking process At this point in the context of flash pyrolysis it is worthy of note that plastic waste while not a biomass material can also be treated by flash pyrolysis to produce starting materials for petrochem ical manufacture In the process the mixed plastic waste is heated in an oxygenfree atmosphere At a temperature of several hundred degrees the constituents of the waste decompose to yield a mixture of gaseous liquid and solids The composition of the product depends on temperature and pressurethe higher the temperature the more gaseous products are formed An important frac tion of this gaseous product is ethylene if plastics are used as feedstock Biorefining in which biomass is converted into a variety of chemical products is not new if activities such as production of vegetable oils beer and wine requiring pretreatment are considered Many of these activities are known to have been in practice for millennia Biomass can be converted into commercial fuels suitable to substitute for fossil fuels These can be used for transportation heating electricity generation or anything else fossil fuels are used for The conversion is accom plished through the use of several distinct processes which include both biochemical conversion and thermal conversion to produce gaseous liquid and solid fuels which have high energy contents are easily transportable and are therefore suitable for use as commercial fuels Biorefining offers a method to accessing the integrated production of chemicals materials and fuels Although the concept of a biorefinery concept is analogous to that of an oil refinery the dif ferences in the various biomass feedstocks require a divergence in the methods used to convert the feedstocks to fuels and chemicals Speight 2014 2017 Thus a biorefinery like a petroleum refinery may need to be a facility that integrates biomass conversion processes and equipment to produce fuels power and chemicals from biomass In a manner similar to the petroleum refinery 101 Coal Oil Shale and Biomass a biorefinery would integrate a variety of conversion processes to produce multiple product streams such as motor fuels and other chemicals from biomass such as the inclusion of gasification processes and fermentation processes to name only two possible processes options In short a biorefinery should combine the essential technologies to transform biological raw materials into a range of industrially useful intermediates However the type of biorefinery would have to be differentiated by the character of the feedstock For example the crop biorefinery would use raw materials such as cereals or maize and the lignocellulose biorefinery would use raw mate rial with high cellulose content such as straw wood and paper waste As a petroleum refinery uses petroleum as the major input and processes it into many different products a biorefinery with feedstocks such as lignocellulosic biomass as the major input and would processes it into many different products Currently wetmill corn processing and pulp and paper mills can be categorized into biorefineries since they produce multiple products from biomass Research is currently being conducted to foster new industries to convert biomass into a wide range of products including ones that would otherwise be made from petrochemicals The idea is for bio refineries to produce both highvolume liquid fuels and highvalue chemicals or products in order to address national energy needs while enhancing operation economics However the different compositional nature of the biomass feedstock compared to crude oil will require the application of a wider variety of processing tools in the biorefinery Processing the individual components will utilize conventional thermochemical operations and stateoftheart bioprocessing techniques Although a number of new bioprocesses have been commercialized it is clear that economic and technical barriers still exist before the full potential of this area can be real ized The biorefinery concept could significantly reduce production costs of plantbased chemicals and facilitate their substitution into existing markets This concept is analogous to that of a modern oil refinery in that the biorefinery is a highly integrated complex that will efficiently separate bio mass raw materials into individual components and convert these into marketable products such as energy fuels and chemicals By analogy with crude oil every element of the plant feedstock will be utilized including the lowvalue lignin components A key requirement for the biorefinery is the ability of the refinery to develop process technol ogy that can economically access and convert the five and sixmembered ring sugars present in the cellulose and hemicellulose fractions of the lignocellulosic feedstock Although engineering technology exists to effectively separate the sugarcontaining fractions from the lignocellulose the enzyme technology to economically convert the five ring sugars to useful products requires further development Plants are very effective chemical minifactories or refineries insofar as they produce chemi cals by specific pathways The chemicals they produce are usually essential manufactures called metabolites including sugars and amino acids that are essential for the growth of the plant as well as more complex compounds Unlike petroleumderived in petrochemicals where most chemicals are built from the bottomup biofeedstocks already have some valuable products to skim off the top before being broken down and used to build new molecules As a feedstock biomass can be converted by thermal or biological routes to a wide range of useful forms of energy including process heat steam electricity as well as liquid fuels chemicals and synthesis gas As a raw material biomass is a nearly universal feedstock due to its versatility domestic availability and renewable character At the same time it also has its limitations For example the energy density of biomass is low compared to that of coal liquid petroleum or petro leumderived fuels The heat content of biomass on a dry basis 70009000 Btulb is at best comparable with that of a lowrank coal or lignite and substantially 50100 lower than that of anthracite most bituminous coals and petroleum Most biomass as received has a high burden of physically adsorbed moisture up to 50 by weight Thus without substantial drying the energy content of a biomass feed per unit mass is even less These inherent characteristics and limitations of biomass feedstocks have focused the development of efficient methods of chemically transforming and upgrading biomass feedstocks in a refinery 102 Handbook of Petrochemical Processes The sugarbase involves breakdown of biomass into raw component sugars using chemical and biological means The raw fuels may then be upgraded to produce fuels and chemicals that are inter changeable with existing commodities such as transportation fuels oils and hydrogen Although a number of new bioprocesses have been commercialized it is clear that economic and technical barriers still exist before the full potential of this area can be realized One concept gaining considerable momentum is the biorefinery which could significantly reduce production costs of plantbased chemicals and facilitate their substitution into existing markets This concept is analogous to that of a modern oil refinery in that the biorefinery is a highly integrated complex that will efficiently separate biomass raw materials into individual components and convert these into marketable products such as energy fuels and chemicals By analogy with crude oil every element of the plant feedstock will be utilized including the lowvalue lignin components However the different compositional nature of the biomass feedstock compared to crude oil will require the application of a wider variety of processing tools in the biorefinery Processing of the individual components will utilize conventional ther mochemical operations and stateoftheart bioprocessing techniques The production of biofuels in the biorefinery complex will service existing highvolume markets providing economyof scale benefits and large volumes of byproduct streams at minimal cost for upgrading to valuable chemicals A pertinent example of this is the production of glycerol glycerin as a byproduct in biodiesel plants Glycerol has high functionality and is a potential platform chemical for conversion into a range of highervalue chemicals The highvolume product streams in a biorefinery need not necessarily be a fuel but could also be a largevolume chemical intermediate such as ethylene or lactic acid In addition to a variety of methods techniques can be employed to obtain different product portfolios of bulk chemicals fuels and materials Biotechnologybased conversion processes can be used to ferment the biomass carbohydrate content into sugars that can then be further processed As one example the fermentation path to lactic acid shows promise as a route to biodegradable plastics An alternative is to employ thermochemical conversion processes which use pyrolysis or gasification of biomass to produce a hydrogenrich synthesis gas which can be used in a wide range of chemical processes A key requirement for delivery of the biorefinery is the ability of the refinery to develop and use process technology that can economically access and convert the five and sixmembered ring sug ars present in the cellulose and hemicellulose fractions of the lignocellulosic feedstock Although engineering technology exists to effectively separate the sugarcontaining fractions from the ligno cellulose the enzyme technology to economically convert the five ring sugars to useful products requires further development The construction of both large biofuel and renewable chemical production facilities coupled with the pace at which bioscience is being both developed and applied demonstrates that the utilization of nonfood crops will become more significant in the near term The biorefinery concept provides a means to significantly reduce production costs such that a substantial substitution of petrochemicals by renewable chemicals becomes possible However significant technical challenges remain before the biorefinery concept can be realized If the biorefinery is truly analogous to an oil refinery in which crude oil is separated into a series of products such as gasoline heating oil jet fuel and petrochemicals the biorefinery can take advantage of the differences in biomass components and intermediates and maximize the value derived from the biomass feedstock A biorefinery might for example produce one or several low volume but highvalue chemical products and a lowvalue but highvolume liquid transportation fuel while generating electricity and process heat for its own use and perhaps enough for sale of electricity The highvalue products enhance profitability the highvolume fuel helps meet national energy needs and the power production reduces costs and avoids greenhouse gas emissions The basic types of processes used to generate chemicals from biomass as might be incorporated into a biorefinery are i pyrolysis ii gasification iii anaerobic digestion and iv fermentation 103 Coal Oil Shale and Biomass 3421 Pyrolysis Pyrolysis is a medium temperature method which produces gas oil and char from crops which can then be further processed into useful fuels or feedstock Boateng et al 2007 Pyrolysis is the direct thermochemical conversion processes which include pyrolysis liquefaction and solvolysis Kavalov and Peteves 2005 Wood and many other similar types of biomass which contain lignin and cellulose such as agricultural wastes cotton gin waste wood wastes and peanut hulls can be converted through a thermochemical process such as pyrolysis into solid liquid or gaseous fuels Pyrolysis used to produce charcoal since the dawn of civilization is still the most common thermochemical conver sion of biomass to commercial fuel During pyrolysis biomass is heated in the absence of air and breaks down into a complex mix ture of liquids gases and a residual char If wood is used as the feedstock the residual char is what is commonly known as charcoal With more modern technologies pyrolysis can be carried out under a variety of conditions to capture all the components and to maximize the output of the desired product be it char liquid or gas Pyrolysis is often considered to be the gasification of bio mass in the absence of oxygen However the chemistry of each process may differ significantly In general biomass does not gasify as easily as coal and it produces other hydrocarbon compounds in the gas mixture exiting the gasifier this is especially true when no oxygen is used As a result typically an extra step must be taken to reform these hydrocarbon derivatives with a catalyst to yield a clean syngas mixture of hydrogen carbon monoxide and carbon dioxide Fast pyrolysis is a thermal decomposition process that occurs at moderate temperatures with a high heat transfer rate to the biomass particles and a short hot vapor residence time in the reaction zone Several reactor configurations have been shown to assure this condition and to achieve yields of liquid product as high as 75 based on the starting dry biomass weight They include bubbling fluid beds circulating and transported beds cyclonic reactors and ablative reactors Fast pyrolysis of biomass produces a liquid product pyrolysis oil or biooil that can be readily stored and transported Pyrolysis oil is a renewable liquid fuel and can also be used for production of chemicals Fast pyrolysis has now achieved a commercial success for production of chemicals and is being actively developed for producing liquid fuels Pyrolysis oil has been successfully tested in engines turbines and boilers and been upgraded to highquality hydrocarbon fuels In the 1990s several fast pyrolysis technologies reached nearcommercial status and the yields and properties of the generated liquid product biooil depend on the feedstock the process type and conditions and the product collection efficiency Direct hydrothermal liquefaction involves converting biomass to an oily liquid by contacting the biomass with water at elevated temperatures 300C350C 570F660F with sufficient pressure to maintain the water primarily in the liquid phase for residence times up to 30 min Alkali may be added to promote organic conversion The primary product is an organic liquid with reduced oxygen content about 10 and the primary byproduct is water containing soluble organic compounds The importance of the provisions for the supply of feedstocks as crops and other biomass are often underestimated since it is assumed that the supplies are inexhaustible While this may be true over the long term shortterm supply of feedstocks can be as much as risk as any venture 3422 Gasification Alternatively biomass can be converted into fuels and chemicals indirectly by gasification to syn gas followed by catalytic conversion to liquid fuels Molino et al 2016 Biomass gasification is a mature technology pathway that uses a controlled process involving heat steam and oxygen to convert biomass to hydrogen and other products without combustion and represents an efficient process for the production of chemicals and hydrogen Gasification is a process that converts organic carbonaceous feedstocks into carbon monoxide carbon dioxide and hydrogen by reacting the feedstock at high temperatures 700C 1290F 104 Handbook of Petrochemical Processes without combustion with a controlled amount of oxygen andor steam The resulting gas mixture synthesis gas syngas or producer gas is itself a fuel The power derived from carbonaceous feedstocks and gasification followed by the combustion of the product gases is considered to be a source of renewable energy if the gaseous products are from a source eg biomass other than a fossil fuel The carbon monoxide can then be reacted with water steam to form carbon dioxide and more hydrogen via a watergas shift reaction Adsorber or special membranes can separate the hydrogen from this gas stream The simplified reaction is C H O O H O CO CO H otherspecies 6 12 6 2 2 2 2 CO H O CO H watergasshiftreaction 2 2 2 This reaction scheme uses glucose as a surrogate for cellulose but it must be recognized that bio mass has highly variable composition and complexity with cellulose as one major component Coal has for many decades been the primary feedstock for gasification unitscoal can also be gasified in situ in the underground seam Speight 2013a but that is not the subject of this text and is not discussed further However with the concern on the issue of environmental pollutants and the potential shortage of coal in some areas there is a move to feedstocks other than coal for gasifica tion processes Gasification permits the utilization of various feedstocks coal biomass petroleum resids and other carbonaceous wastes to their fullest potential The advantage of the gasification process when a carbonaceous feedstock a feedstock containing carbon or hydrocarbonaceous feedstock a feedstock containing carbon and hydrogen is employed is that the product of focussynthesis gasis potentially more useful as an energy source and results in an overall cleaner process The production of synthesis gas is a more efficient production of an energy source than say the direct combustion of the original feedstock because synthesis gas can be converted via the FischerTropsch process into a range of synthesis liquid fuels suitable for using gasoline engines or diesel engines Chapter 10 Chadeesingh 2011 Biomass includes a wide range of materials that produce a variety of products which are depen dent upon the feedstock Balat 2011 Demirbaş 2011 Ramroop Singh 2011 Speight 2011a For example typical biomass wastes include wood material bark chips scraps and saw dust pulp and paper industry residues agricultural residues organic municipal material sewage manure and food processing byproducts Agricultural residues such as straws nut shells fruit shells fruit seeds plant stalks and stover green leaves and molasses are potential renewable energy resources Many developing countries have a wide variety of agricultural residues in ample quantities Large quantities of agricultural plant residues are produced annually worldwide and are vastly underuti lized Agricultural residues when used as fuel through direct combustion only a small percentage of their potential energy is available due to inefficient burners used Current disposal methods for these agricultural residues have caused widespread environmental concerns For example disposal of rice and wheat straw by openfield burning causes air pollution In addition the widely varying heat content of the different types of biomass varies widely and must be taken into consideration when designing any conversion process Jenkins and Ebeling 1985 Raw materials that can be used to produce biomass fuels are widely available and arise from a large number of different sources and in numerous forms Biomass can also be used to produce electricityeither blended with traditional feedstocks such as coal or by itself However each of the biomass materials can be used to produce fuel but not all forms are suitable for all the different types of energy conversion technologies such as biomass gasification Rajvanshi 1986 Brigwater 2003 Dasappa et al 2004 Speight 2011a Basu 2013 The main basic sources of biomass material are i wood including bark logs sawdust wood chips wood pellets and briquettes ii high yield energy crops such as wheat that are grown specifically for energy applications iii agricultural crop and animal residues like straw or slurry iv food waste both domestic and commercial and v industrial waste such as wood pulp or paper pulp For processing a simple form of biomass such 105 Coal Oil Shale and Biomass as untreated and unfinished wood may be cut into a number of physical forms including pellets and wood chips for use in biomass boilers and stoves Thermal conversion processes use heat as the dominant mechanism to convert biomass into another chemical form The basic alternatives of combustion torrefaction pyrolysis and gas ification are separated principally by the extent to which the chemical reactions involved are allowed to proceed mainly controlled by the availability of oxygen and conversion temperature Speight 2011a Many forms of biomass contain a high percentage of moisture along with carbohydrates and sugars and mineral constituentsboth of which can influence the viability of a gasification process Chapter 3the presence of high levels of moisture in the biomass reduces the temperature inside the gasifier which then reduces the efficiency of the gasifier Therefore many biomass gasifica tion technologies require that the biomass be dried to reduce the moisture content prior to feeding into the gasifier In addition biomass can come in a range of sizes In many biomass gasification systems the biomass must be processed to a uniform size or shape to feed into the gasifier at a con sistent rate and to ensure that as much of the biomass is gasified as possible Biomass such as wood pellets yard and crop wastes and the socalled energy crops such as switch grass and waste from pulp and paper mills can be used to produce ethanol and synthetic diesel fuel The biomass is first gasified to produce the synthetic gas synthesis gas and then converted via catalytic processes to these downstream products Furthermore most biomass gas ification systems use air instead of oxygen for the gasification reactions which is typically used in largescale industrial and power gasification plants Gasifiers that use oxygen require an air sepa ration unit to provide the gaseousliquid oxygen this is usually not costeffective at the smaller scales used in biomass gasification plants Airblown gasifiers use the oxygen in the air for the gasification reactions In general biomass gasification plants are much smaller than the typical coal or petroleum coke gasification plants used in the power chemical fertilizer and refining industriesthe sustainability of the fuel supply is often brought into question As such a biomass gasification plant is less expen sive to construct and has a smaller environmental footprint For example while a large industrial gasification plant may take up to 150 acres of land and process 250015000 tons per day of feed stock such as coal or petroleum coke the smaller biomass plants typically process 25200 tons of feedstock per day and take up less than 10 acres Biomass gasification has been the focus of research in recent years to estimate efficiency and performance of the gasification process using various types of biomass such as sugarcane residue Gabra et al 2001 rice hulls Boateng et al 1992 pine sawdust Lv et al 2004 almond shells Rapagnà and Latif 1997 Rapagnà et al 2000 wheat straw Ergudenler and Ghaly 1993 food waste Ko et al 2001 and wood biomass Pakdel and Roy 1991 Bhattacharya et al 1999 Chen et al 1992 Hanaoka et al 2005 Recently cogasification of various biomass and coal mixtures has attracted a great deal of interest from the scientific community Feedstock combinations includ ing Japanese cedar wood and coal Kumabe et al 2007 coal and saw dust coal and pine chips Pan et al 2000 coal and silver birch wood Collot et al 1999 and coal and birch wood Brage et al 2000 have been reported in gasification practice Cogasification of coal and biomass has some synergythe process not only produces a low carbon footprint on the environment but also improves the H2CO ratio in the produced gas which is required for liquid fuel synthesis Sjöström et al 1999 Kumabe et al 2007 In addition the inorganic matter present in biomass catalyzes the gasification of coal However cogasification processes require custom fittings and optimized processes for the coal and regionspecific wood residues While cogasification of coal and biomass is advantageous from a chemical viewpoint some practical problems are present on upstream gasification and downstream processes On the upstream side the particle size of the coal and biomass is required to be uniform for optimum gasification In addition moisture content and pretreatment torrefaction are very important during upstream processing 106 Handbook of Petrochemical Processes While upstream processing is influential from a material handling point of view the choice of gasifier operation parameters temperature gasifying agent and catalysts dictate the product gas composition and quality Biomass decomposition occurs at a lower temperature than coal and therefore different reactors compatible to the feedstock mixture are required Speight 2011c Brar et al 2012 Speight 2013a 2013b Furthermore feedstock and gasifier type along with operating parameters not only decide product gas composition but also dictate the amount of impurities to be handled downstream Downstream processes need to be modified if coal is cogasified with biomass Heavy metal and impurities such as sulfur and mercury present in coal can make synthesis gas difficult to use and unhealthy for the environment Alkali present in biomass can also cause corrosion problems high temperatures in downstream pipes An alternative option to downstream gas cleaning would be to process coal to remove mercury and sulfur prior to feeding into the gasifier However first and foremost coal and biomass require drying and size reduction before they can be fed into a gasifier Size reduction is needed to obtain appropriate particle sizes however drying is required to achieve moisture content suitable for gasification operations In addition biomass densification may be conducted to prepare pellets and improve density and material flow in the feeder areas It is recommended that biomass moisture content should be less than 15 ww prior to gasifica tion High moisture content reduces the temperature achieved in the gasification zone thus resulting in incomplete gasification Forest residues or wood has a fiber saturation point at 3031 moisture content dry basis Brar et al 2012 Compressive and shear strength of the wood increases with decreased moisture content below the fiber saturation point In such a situation water is removed from the cell wall leading to shrinkage The longchain molecule constituents of the cell wall move closer to each other and bind more tightly A high level of moisture usually injected in form of steam in the gasification zone favors formation of a watergas shift reaction that increases hydrogen concentration in the resulting gas The torrefaction process is a thermal treatment of biomass in the absence of oxygen usually at 250C300C 480F570F to drive off moisture decompose hemicellulose completely and par tially decompose cellulose Speight 2011a Torrefied biomass has reactive and unstable cellulose molecules with broken hydrogen bonds and not only retains 7995 of feedstock energy but also produces a more reactive feedstock with lower atomic hydrogencarbon and oxygencarbon ratios to those of the original biomass Torrefaction results in higher yields of hydrogen and carbon mon oxide in the gasification process Most small to mediumsized biomasswaste gasifiers are air blown operated at atmospheric pres sure and at temperatures in the range 800C100C 1470F2190F They face very different challenges compared to large gasification plantsthe use of a smallscale air separation plant should oxygen gasification be preferred Pressurized operation which eases gas cleaning may not be practical Biomass fuel producers coal producers and to a lesser extent waste companies are enthusi astic about supplying cogasification power plants and realize the benefits of cogasification with alternate fuels Speight 2008 2011a Lee and Shah 2013 Speight 2013a 2013b The benefits of a cogasification technology involving coal and biomass include the use of a reliable coal supply with gate fee waste and biomass that allows the economies of scale from a larger plant to be supplied just with waste and biomass In addition the technology offers a future option of hydrogen production and fuel development in refineries In fact oil refineries and petrochemical plants are opportunities for gasifiers when the hydrogen is particularly valuable Speight 2011b 2014 In addition while biomass may seem to some observers to be the answer to the global climate change issue the advantages and disadvantages must be considered carefully For example the advantages are i biomass is a theoretically inexhaustible fuel source ii when direct conversion of combustion of plant masssuch as fermentation and pyrolysisis not used to generate energy there is minimal environmental impact iii alcohols and other fuels produced by biomass are effi cient viable and relatively cleanburning and iv biomass is available on a worldwide basis 107 Coal Oil Shale and Biomass On the other hand the disadvantages include i the highly variable heat content of different bio mass feedstocks ii the high water content that can affect the process energy balance and iii there is a potential net loss of energy when a biomass plant is operated on a small scalean account of the energy put used to grow and harvest the biomass must be included in the energy balance 3423 Anaerobic Digestion Anaerobic digestion is a natural process and is the microbiological conversion of organic matter to methane in the absence of oxygen The biochemical conversion of biomass is completed through alcoholic fermentation to produce liquid fuels and anaerobic digestion or fermentation resulting in biogas hydrogen carbon dioxide ammonia and methane usually through four steps hydrolysis acidogenesis acetogenesis and methanogenesis Hydrolysis Carbohydrates sugars Fats fattyacids Proteins aminoacids Acidogenesis Sugars carbonacids alcohols hydrogen carbondioxide ammonia Fattyacids carbonacids alcohols hydrogencarbondioxide ammonia Aminoacids carbonacids alcohols hydrogencarbondioxide ammonia Acetogenesis Carbonacids alcohols aceticacid carbondioxide hydrogen Methanogenesis Aceticacid methane carbondioxide The decomposition is caused by natural bacterial action in various stages and occurs in a variety of natural anaerobic environments including water sediment waterlogged soils natural hot springs ocean thermal vents and the stomach of various animals eg cows The digested organic matter resulting from the anaerobic digestion process is usually called digestate Symbiotic groups of bacteria perform different functions at different stages of the digestion process There are four basic types of microorganisms involved i hydrolytic bacteria breakdown complex organic wastes into sugars and amino acids ii fermentative bacteria then convert those products into organic acids iii acidogenic microorganisms convert the acids into hydrogen carbon dioxide and acetate and iv methanogenic bacteria produce biogas from acetic acid hydrogen and carbon dioxide The process of anaerobic digestion occurs in a sequence of stages involving distinct types of bacteria Hydrolytic and fermentative bacteria first breakdown the carbohydrates proteins and fats present in biomass feedstock into fatty acids alcohol carbon dioxide hydrogen ammonia and sul fides This stage is called hydrolysis or liquefaction Next acetogenic acidforming bacteria fur ther digest the products of hydrolysis into acetic acid hydrogen and carbon dioxide Methanogenic methaneforming bacteria then convert these products into biogas 108 Handbook of Petrochemical Processes The combustion of digester gas can supply useful energy in the form of hot air hot water or steam After filtering and drying digester gas is suitable as fuel for an internal combustion engine which combined with a generator can produce electricity Future applications of digester gas may include electric power production from gas turbines or fuel cells Digester gas can substitute for natural gas or propane in space heaters refrigeration equipment cooking stoves or other equip ment Compressed digester gas can be used as an alternative transportation fuel There are three principal byproducts of anaerobic digestion i biogas ii acidogenic digestate and iii methanogenic digestate Biogas is a gaseous mixture comprising mostly methane and carbon dioxide and also containing a small amount of hydrogen and occasionally trace levels of hydrogen sulfide Since the gas is not released directly into the atmosphere and the carbon dioxide comes from an organic source with a short carbon cycle biogas does not contribute to increasing atmospheric carbon dioxide concentra tions because of this it is considered to be an environmentally friendly energy source The pro duction of biogas is not a steady stream it is highest during the middle of the reaction In the early stages of the reaction little gas is produced because the number of bacteria is still small Toward the end of the reaction only the hardest to digest materials remain leading to a decrease in the amount of biogas produced The second byproduct acidogenic digestate is a stable organic material comprised largely of lignin and chitin and a variety of mineral components in a matrix of dead bacterial cells some plas tic may also be present This resembles domestic compost and can be used as compost or to make lowgrade building products such as fiberboard The third byproduct is a liquid methanogenic digestate that is rich in nutrients and can be an excellent fertilizer dependent on the quality of the material being digested If the digested materials include low levels of toxic heavy metals or synthetic organic materials such as pesticides or poly chlorobiphenyls the effect of digestion is to significantly concentrate such materials in the digester liquor In such cases further treatment will be required in order to dispose of this liquid properly In extreme cases the disposal costs and the environmental risks posed by such materials can offset any environmental gains provided by the use of biogas This is a significant risk when treating sewage from industrialized catchments Nearly all digestion plants have ancillary processes to treat and manage all the byproducts The gas stream is dried and sometimes sweetened before storage and use The sludge liquor mixture has to be separated by one of a variety of ways the most common of which is filtration Excess water is also sometimes treated in sequencing batch reactors for discharge into sewers or for irrigation Digestion can be either wet or dry Dry digestion refers to mixtures which have a solid content of 30 or greater whereas wet digestion refers to mixtures of 15 or less In recent years increasing awareness that anaerobic digesters can help control the disposal and odor of animal waste has stimulated renewed interest in the technology New digesters now are being built because they effectively eliminate the environmental hazards of dairy farms and other animal feedlots Anaerobic digester systems can reduce fecal coliform bacteria in manure by more than 99 virtually eliminating a major source of water pollution Separation of the solids during the digester process removes about 25 of the nutrients from manure and the solids can be sold out of the drainage basin where nutrient loading may be a problem In addition the digesters ability to produce and capture methane from the manure reduces the amount of methane that otherwise would enter the atmosphere Scientists have targeted methane gas in the atmosphere as a contributor to global climate change Controlled anaerobic digestion requires an airtight chamber called a digester To promote bacterial activity the digester must maintain a temperature of at least 68F Using higher tem peratures up to 150F shortens processing time and reduces the required volume of the tank by 2540 However there are more species of anaerobic bacteria that thrive in the tempera ture range of a standard design mesophilic bacteria than there are species that thrive at higher temperatures thermophilic bacteria Hightemperature digesters also are more prone to upset 109 Coal Oil Shale and Biomass because of temperature fluctuations and their successful operation requires close monitoring and diligent maintenance The biogas produced in a digester digester gas is actually a mixture of gases with methane and carbon dioxide making up more than 90 of the total Biogas typically contains smaller amounts of hydrogen sulfide nitrogen hydrogen methyl mercaptans and oxygen Methane is a combustible gas The energy content of digester gas depends on the amount of methane it contains Methane content varies from about 55 to 80 Typical digester gas with a methane concentration of 65 contains about 600 Btu of energy per cubic foot There are three basic digester designs and all of them can trap methane and reduce fecal coliform bacteria but they differ in cost climate suitability and the concentration of manure solids they can digest i a covered lagoon digester ii a complete mix digester iii a plugflow digester A covered lagoon digester as the name suggests consists of a manure storage lagoon with a cover The cover traps gas produced during decomposition of the manure This type of digester is the least expensive of the three Covering a manure storage lagoon is a simple form of digester technology suitable for liquid manure with less than 3 solids For this type of digester an impermeable floating cover of industrial fabric covers all or part of the lagoon A concrete foot ing along the edge of the lagoon holds the cover in place with an airtight seal Methane produced in the lagoon collects under the cover A suction pipe extracts the gas for use Covered lagoon digesters require large lagoon volumes and a warm climate Covered lagoons have low capital cost but these systems are not suitable for locations in cooler climates or locations where a high water table exists A complete mix digester converts organic waste to biogas in a heated tank above or below ground A mechanical or gas mixer keeps the solids in suspension Complete mix digesters are expensive to construct and cost more than plugflow digesters to operate and maintain Complete mix digesters are suitable for larger manure volumes having solids concentration of 310 The reactor is a circular steel or poured concrete container During the digestion process the manure slurry is con tinuously mixed to keep the solids in suspension Biogas accumulates at the top of the digester The biogas can be used as fuel for an enginegenerator to produce electricity or as boiler fuel to produce steam Using waste heat from the engine or boiler to warm the slurry in the digester reduces reten tion time to less than 20 days A plugflow digester is suitable for ruminant animal manure that has a solids concentration of 1113 A typical design for a plugflow system includes a manure collection system a mixing pit and the digester itself In the mixing pit the addition of water adjusts the proportion of solids in the manure slurry to the optimal consistency The digester is a long rectangular container usually built belowgrade with an airtight expandable cover New material added to the tank at one end pushes older material to the opposite end Coarse solids in ruminant manure form a viscous material as they are digested limiting solids separation in the digester tank As a result the material flows through the tank in a plug Average retention time the time a manure plug remains in the digester is 2030 days Anaerobic digestion of the manure slurry releases biogas as the material flows through the digester A flexible impermeable cover on the digester traps the gas Pipes beneath the cover carry the biogas from the digester to an engine generator set A plugflow digester requires minimal maintenance Waste heat from the enginegenerator can be used to heat the digester Inside the digester suspended heating pipes allow hot water to circu late The hot water heats the digester to keep the slurry at 25C40C 77F104F a temperature range suitable for methaneproducing bacteria The hot water can come from recovered waste heat from an enginegenerator fueled with digester gas or from burning digester gas directly in a boiler Anaerobic digestion of biomass has been practiced for almost a century and is very popular in many developing countries such as China and India The organic fraction of almost any form of biomass including sewage sludge animal wastes and industrial effluents can be broken down through anaerobic digestion into methane and carbon dioxide This biogas is a reasonably clean 110 Handbook of Petrochemical Processes burning fuel that can be captured and put to many different end uses such as cooking heating or electrical generation 3424 Fermentation A number of processes allow biomass to be transformed into gaseous fuels such as methane or hydrogen Sørensen et al 2006 One pathway uses algae and bacteria that have been genetically modified to produce hydrogen directly instead of the conventional biological energy carriers A second pathway uses plant material such as agricultural residues in a fermentation process leading to biogas from which the desired fuels can be isolated This technology is established and in wide spread use for waste treatment but often with the energy produced only for onsite use which often implies less than maximum energy yields Finally hightemperature gasification supplies a crude gas which may be transformed into hydrogen by a second reaction step In addition to biogas there is also the possibility of using the solid byproduct as a biofuel Traditional fermentation plants producing biogas are in routine use ranging from farms to large municipal plants As feedstock they use manure agricultural residues urban sewage and waste from households and the output gas is typically 64 methane The biomass conversion process is accomplished by a large number of different agents from the microbes decomposing and hydrolyz ing plant material over the acidophilic bacteria dissolving the biomass in aquatic solution and to the strictly anaerobic methane bacteria responsible for the gas formation Operating a biogas plant for a period of some months usually makes the bacterial composition stabilize in a way suitable for obtaining high conversion efficiency typically above 60 the theoretical limit being near to 100 and it is found important not to vary the feedstock compositions abruptly if optimal opera tion is to be maintained Operating temperatures for the bacterial processes are only slightly above ambient temperatures eg in the mesophilic region around 30C The production of ethanol from corn is a mature technology that holds much potential Nichols et al 2006 Substantial cost reductions may be possible however if cellulosebased feedstocks are used instead of corn The feed for all ethanol fermentations is sugartraditionally a hexose a six carbon or C6 sugar such as those present naturally in sugar cane sugar beet and molasses Sugar for fermentation can also be recovered from starch which is actually a polymer of hexose sugars polysaccharide Biomass in the form of wood and agricultural residues such as wheat straw is viewed as a low cost alternative feed to sugar and starch It is also potentially available in far greater quantities than sugar and starch feeds As such it receives significant attention as a feed material for ethanol produc tion Like starch wood and agricultural residues contain polysaccharides However unlike starch while the cellulose fraction of biomass is principally a polymer of easily fermented C6 sugars the hemicellulose fraction is principally a polymer of C5 sugars with quite different characteristics for recovery and fermentation of the cellulose and hemicellulose in biomass are bound together in a complex framework of crystalline organic material known as lignin There are several different methods of hydrolysis i concentrated sulfuric acid ii dilute sulfu ric acid iii nitric acid and iv acid pretreatment followed by enzymatic hydrolysis The greatest potential for ethanol production from biomass however lies in enzymatic hydro lysis of cellulose The enzyme cellulase now used in the textile industry to stone wash denim and in detergents simply replaces the sulfuric acid in the hydrolysis step The cellulase can be used at lower temperatures 30C50C which reduces the degradation of the sugar In addition process improvements now allow simultaneous saccharification and fermentation SSF In the saccharifica tion and fermentation process cellulase and fermenting yeast are combined so that as sugars are produced the fermentative organisms convert them to ethanol in the same step Once the hydrolysis of the cellulose is achieved the resulting sugars must be fermented to pro duce ethanol In addition to glucose hydrolysis produces other sixcarbon sugars from cellulose and fivecarbon sugars from hemicellulose that are not readily fermented to ethanol by naturally occur ring organisms They can be converted to ethanol by genetically engineered yeasts that are currently 111 Coal Oil Shale and Biomass available but the ethanol yields are not sufficient to make the process economically attractive It also remains to be seen whether the yeasts can be made hardly enough for production of ethanol on a commercial scale The fermentation processes to produce propanol and butanol from cellulose are fairly tricky to execute and the Clostridium acetobutylicum currently used to perform these conversions pro duces an extremely unpleasant smell and this must be taken into consideration when designing and locating a fermentation plant This organism also dies when the butanol content of whatever it is fermenting rises to 7 For comparison yeast dies when the ethanol content of its feedstock hits 14 Specialized strains can tolerate even greater ethanol concentrationssocalled turbo yeast can withstand up to 16 ethanol However if ordinary Saccharomyces yeast can be modified to improve its ethanol resistance scientists may yet one day produce a strain of the Weizmann organ ism with a butanol resistance higher than the natural boundary of 7 This would be useful because butanol has a higher energy density than ethanol and because waste fiber left over from sugar crops used to make ethanol could be made into butanol raising the alcohol yield of fuel crops without there being a need for more crops to be planted Wet milling and dry milling are the means by which grain and straw fractions are processed into a variety of end products The processes encompass fermentation and distilling of grains wheat rye or maize Wet milling starts with watersoaking the grain adding sulfur dioxide to soften the kernels and loosen the hulls after which it is ground It uses wellknown technologies and allows separation of starch cellulose oil and proteins Dry milling grinds whole grains including germ and bran After grinding the flour is mixed with water to be treated with liquefying enzymes and further cooking the mash to breakdown the starch This hydrolysis step can be eliminated by simultaneously adding saccharifying enzymes and fermenting yeast to the fermenter simultaneous saccharification and fermentation After fermentation the mash called beer is sent through a multicolumn distillation system followed by concentration purification and dehydration of the alcohol The residue mash stillage is separated into a solid wet grains and liquid syrup phase that can be combined and dried to produce distillers dried grains with soluble constituents to be used as cattle feed Its nutritional characteristics and high vegetable fiber content make distillers dried grains with soluble constitu ents unsuitable for other animal species 343 chemicals from Biomass The production of biofuels to replace oil and natural gas is in active development focusing on the use of cheap organic matter usually cellulose agricultural and sewage waste in the efficient production of liquid and gas biofuels which yield high net energy gain The carbon in biofuels was recently extracted from atmospheric carbon dioxide by growing plants so burning it does not result in a net increase of carbon dioxide in the earths atmosphere As a result biofuels are seen by many as a way to reduce the amount of carbon dioxide released into the atmosphere by using them to replace nonrenewable sources of energy 3431 Gaseous Products Most biomass materials are easier to gasify than coal because they are more reactive with higher ignition stability This characteristic also makes them easier to process thermochemically into highervalue fuels such as methanol or hydrogen Ash content is typically lower than for most coals and sulfur content is much lower than for many fossil fuels Unlike coal ash which may contain toxic metals and other trace contaminants biomass ash may be used as a soil amend ment to help replenish nutrients removed by harvest A few biomass feedstocks stand out for their peculiar properties such as high silicon or alkali metal contentsthese may require special precautions for harvesting processing and combustion equipment Note also that mineral content can vary as a function of soil type and the timing of feedstock harvest In contrast to their fairly 112 Handbook of Petrochemical Processes uniform physical properties biomass fuels are rather heterogeneous with respect to their chemi cal elemental composition Biogas contains methane and can be recovered in industrial anaerobic digesters and mechani cal biological treatment systems Landfill gas is a less clean form of biogas which is produced in landfills through naturally occurring anaerobic digestion Unfortunately methane is a potent green house gas and should not be allowed to escape into the atmosphere When biomass is heated with no oxygen or only about onethird the oxygen needed for efficient combustion amount of oxygen and other conditions determine if biomass gasifies or pyrolyzes it gasifies to a mixture of carbon monoxide and hydrogen synthesis gas syngas Combustion is a function of the mixture of oxygen with the hydrocarbon fuel Gaseous fuels mix with oxygen more easily than liquid fuels which in turn mix more easily than solid fuels Syngas therefore inherently burns more efficiently and cleanly than the solid biomass from which it was made Producing gas from biomass consists of the following main reactions which occur inside a biomass gasifier i dryingbiomass fuels usually contain 1035 ww moisture and when bio mass is heated to 100C 212F the moisture is converted into steam ii pyrolysisafter drying as heating continues the biomass undergoes pyrolysis which involves thermal decomposition of the biomass without supplying any oxygen and a result the biomass is decomposed or separated into gases liquids and solids iii oxidation in which air is introduced into the gasifier after the decomposition process and during oxidation which takes place at temperatures in the order of 700C1400C 1290F2550F charcoal or the solid carbonized fuel reacts with the oxygen in the air to produce carbon dioxide and heat and iv reduction that occurs at higher temperatures and under reducing conditions that is when not enough oxygen is available the following reactions take place forming carbon dioxide hydrogen and methane C CO 2CO 2 C H O CO H 2 2 CO H O CO H 2 2 2 C 2H CH 2 4 Biomass gasification can thus improve the efficiency of largescale biomass power facilities such as those for forest industry residues and specialized facilities such as black liquor recovery boilers of the pulp and paper industry both major sources of biomass power Like natural gas syngas can also be burned in gas turbines a more efficient electrical generation technology than steam boilers to which solid biomass and fossil fuels are limited 3432 Liquid Products Ethanol is the predominant chemical produced from crops and has been used as fuel in the many countries such as United States since at least 1908 There are three wellknown methods to convert biomass into ethanol i direct fermentation of sugarstarchrich biomass such as sugar cane sugar beet or maize starch to ethanol in which microorganisms convert carbohydrates to ethanol under anaerobic conditions ii hydrolysis of lignocellulosic biomass eg agricultural waste wheat and wood followed by fermentation to ethanol Here again microorganisms convert carbohydrates to ethanol under anaerobic conditions and iii gasification of lignocellulosic biomass followed by either fermentation or chemical catalysis to ethanol Currently the production of ethanol by fermentation of cornderived carbohydrates is the main technology used to produce liquid fuels from biomass resources Furthermore amongst different biofuels suitable for application in transport bioethanol and biodiesel seem to be the most feasible ones at present The key advantage of bioethanol and biodiesel is that they can be mixed with 113 Coal Oil Shale and Biomass conventional petrol and diesel respectively which allows using the same handling and distribution infrastructure Another important strong point of bioethanol and biodiesel is that when they are mixed at low concentrations 10 bioethanol in petrol and 20 biodiesel in diesel no engine modifications are necessary Biologically produced alcohols most commonly ethanol and methanol and less commonly propanol and butanol are produced by the action of microbes and enzymes through fermentation Methanol is a colorless odorless and nearly tasteless alcohol and is also produced from crops and is also used as a fuel Methanol like ethanol burns more completely but releases as much or more carbon dioxide than its gasoline counterpart Propanol and butanol are considerably less toxic and less volatile than methanol In particular butanol has a high flashpoint of 35C which is a benefit for fire safety but may be difficult for start ing engines in cold weather Biodiesel is a dieselequivalent fuel derived from biological sources such as vegetable oils which can be used in unmodified diesel engine vehicles It is thus distinguished from the straight vegetable oils or waste vegetable oils used as fuels in some diesel vehicles In the current context biodiesel refers to alkyl esters made from the transesterification of vegetable oils or animal fats Biodiesel fuel is a fuel made from the oil of certain oilseed crops such as soybean canola palm kernel coconut sunflower safflower corn and a hundreds of other oilproducing crops The oil is extracted by the use of a press and then mixed in specific proportions with other agents which causes a chemical reaction The results of this reaction are two products biodiesel and soap After a final filtration the biodiesel is ready for use After curing the glycerin soap that is produced as a byproduct can be used as is or can have scented oils added before use In general biodiesel com pares well to petroleumbased diesel Lotero et al 2006 Pure biodiesel fuel 100 esters of fatty acids is called B100 When blended with diesel fuel the designation indicates the amount of B100 in the blend eg B20 is 20 vv B100 is 80 vv diesel and B5 used in Europe contains 5 vv of B100 in diesel fuel Pinto et al 2005 Hydrocarbon derivatives are products from various plant species belonging to different fami lies which convert a substantial amount of photosynthetic products into latex The latex of such plants contains liquid hydrocarbon derivatives of high molecular weight 10000 These hydrocarbon derivatives can be converted into highgrade transportation fuel ie petroleum Therefore hydrocarbonproducing plants are called petroleum plants or petroplants and their crop as petrocrop Natural gas is also one of the products obtained from hydrocarbon derivatives Thus petroleum plants can be an alternative source for obtaining petroleum to be used in diesel engines Normally some of the latexproducing plants of families Euphorbiaceae Apocynaceae Asclepiadaceae Sapotaceae Moraceae Dipterocarpaceae etc are petroplants Similarly sun flower family Composiae Hardwickia pinnata family Leguminosae are also petroplants Some algae also produce hydrocarbon derivatives However hydrocarbon derivatives as such are not usually produced from crops there being insufficient amount of the hydrocarbon derivatives present in the plant tissue to make the process economical However biodiesel is produced from crops thereby offering an excellent renewable fuel for diesel engines Biooil is a product that is produced by a totally different process than that used for biodiesel production The process fast pyrolysis flash pyrolysis occurs when solid fuels are heated at temperatures between 350C and 500C 570F930F for a very short period of time 2 s The biooils currently produced are suitable for use in boilers for electricity generation In another pro cess the feedstock is fed into a fluidized bed at 450C500C and the feedstock flashes and vapor izes The resulting vapors pass into a cyclone where solid particles char are extracted The gas from the cyclone enters a quench tower where they are quickly cooled by heat transfer using biooil already made in the process The biooil condenses into a product receiver and any noncondensable gases are returned to the reactor to maintain process heating The entire reaction from injection to quenching takes only two seconds 114 Handbook of Petrochemical Processes 3433 Solid Products Examples of solid chemicals from biomass feedstocks include wood and woodderived charcoal and dried dung particularly cow dung One widespread use of such fuels is in home cooking and heating The biofuel may be burned on an open fireplace or in a special stove The efficiency of this process may vary widely from 10 for a wellmade fire even less if the fire is not made carefully up to 40 for a customdesigned charcoal stove Inefficient use of fuel is a cause of deforestation though this is negligible compared to deliberate destruction to clear land for agricultural use but more importantly it means that more work has to be put into gathering fuel thus the quality of cook ing stoves has a direct influence on the viability of biofuels Investigation of the products produced during thermal decomposition pyrolysis is worthy of investigation since the potential to produce lower molecular weight feedstocks for a petrochemical plant is high 35 WASTE It would be remiss not to mention another potential feedstock for the production of chemicals waste material that is not included under the general category of biomass John and Singh 2011 Nonbiomass waste is a byproduct of life and civilization it is the material that remains after a useful component has been consumed From an economic perspective waste is a material involved in life or technology whose value today is less than the cost of its utilization From a regulatory viewpoint waste is anything discarded or that can no longer be used for its original purpose Waste is the general term though the other terms are used loosely as synonyms they have more specific meanings The term solid waste includes not only solid materials but also liquid and gases Domestic waste also known as rubbish garbage trash or junk is unwanted or undesired material Rubbish or trash are mixed household waste including paper and packaging food waste or garbage North America is kitchen and table waste and junk or scrap is metallic or industrial material The thermal pyrolysis of plastic wastes produces a broad distribution of hydrocarbons from methane to waxy products This process takes place at high temperatures The gaseous compounds generated can be burned out to provide the process heat requirements but the overall yield of valu able gasolinerange hydrocarbons is poor so that the pyrolysis process as a means for feedstock recycling of the plastic waste stream is rarely practiced on an industrial scale at present Predel and Kaminsky 2000 Kaminsky and Zorriqueta 2007 In contrast thermal cracking at low tem peratures is usually aimed at the production of waxy oil fractions which may be used in industrial units for steam cracking and in fluid catalytic cracking units Aguado et al 2002 An alternative to improve the yield of naphtha from the pyrolysis of plastic waste is to introduce suitable catalysts High conversion and interesting product distribution is obtained when plastics are cracked over zeolites Hernandez et al 2007 Moreover the catalytic cracking of polymers has proven itself to be a very versatile process since a variety of products can be obtained depending on parameters such as i the catalyst ii the polymer feedstocks iii the reactor type and iv the process param eters such as temperature pressure and residence time of the feedstock in the hot zone as well v as product removal from the hot zone Aguado and Serrano 1999 Demirbaş 2004 Scheirs and Kaminsky 2006 Marcilla et al 2008 AlSalem et al 2009 Sarker et al 2012 In addition urban waste domestic and industrial has considerable promise as a feedstock for gasification because it contains relatively more lignin which biological processes cannot convert Such waste is abundant in most countries and can be harnessed for production of fuels and petro chemical intermediates Knowing the potential of the waste for gasification and subsequent fuel production is essential for reducing pressure on traditional energy sources Also discarded tires can be reduced in size by grinding chipping pelletizing and passed through a classifier to remove the steel belting after which the chips are pyrolyzed for 1 h at a temperature of 300C500C 570F930F and then heated for 2 h in a closed retort to yield gas distillable 115 Coal Oil Shale and Biomass and char Discarded tires can also be shredded to 25 mm and ground to 24 mesh as a feedprepara tion step for occidental flash pyrolysis that involves flash pyrolysis and product collection The pyro lytic reaction occurs without the introduction of hydrogen or using a catalyst This yields a gaseous stream that is passed to a quench tower from which fuel oil and gas recycled to char fluidized and pyrolysis reactor as a supplemental fuel and carbon black 35 ww is produced In the Nippon Zeon process crushed tire chips undergo fluidized thermal cracking fluidized bed 400C600C 750F1110F which yields a gaseous stream that is passed to a quench tower from which gas and distillable oil is produced All of the end products produced could be used directly as a supplemen tal fuel source at the plant or sent offsite for petrochemical manufacture REFERENCES Aguado J and Serrano D 1999 Feedstock Recycling of Plastic Wastes of Chemistry Cambridge UK Aguado R Olazar M San Jose MJ Gaisan B and Bilbao J 2002 Wax Formation in the Pyrolysis of Poly ole fins in a Conical Spouted Bed Reactor Energy Fuels 166 14291437 AlSalem SM Lettieri P and Baeyens J 2009 Recycling and Recovery Routes of Plastic Solid Waste PSW A Review Waste Management 2910 26252643 ASTM D388 2018 Standard Classification of Coal by Rank Annual Book of Standards ASTM International West Conshohocken PA Balat M 2011 Chapter 3 Fuels from BiomassAn Overview In The Biofuels Handbook JG Speight Editor Royal Society of Chemistry London UK Part 1 Basu P 2013 Biomass Gasification Pyrolysis and 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and Zoriquetta IJN 2007 Catalytical and Thermal Pyrolysis of Polyolefins Journal of Analytical and Applied Pyrolysis 7912 368374 Kavalov B and Peteves SD 2005 Status and Perspectives of BiomasstoLiquid Fuels in the European Union European Commission Directorate General Joint Research Centre DG JRC Institute for Energy Petten The Netherlands Khoo HH Wong LL Tan J Isoni V and Sharratt P 2015 Synthesis of 2Methyl Tetrahydrofuran from Various Lignocellulosic Feedstocks Sustainability Assessment via LCA Resour Conserv Recy 95 174 Ko MK Lee WY Kim SB Lee KW and Chun HS 2001 Gasification of Food Waste with Steam in Fluidized Bed Korean Journal of Chemical Engineering 186 961964 Kumabe K Hanaoka T Fujimoto S Minowa T and Sakanishi K 2007 Cogasification of Woody Biomass and Coal with Air and Steam Fuel 86 684689 Lee S 1991 Oil Shale Technology CRC Press Boca Raton FL Lee S Speight JG and Loyalka SK 2007 Handbook of Alternative Fuel Technologies CRC Press Boca Raton FL Lee S and Shah YT 2013 Biofuels and Bioenergy CRC Press Boca Raton FL Lotero E Goodwin JG Jr Bruce DA Suwannakarn K Liu Y and Lopez DE 2006 The Catalysis of Biodiesel Synthesis Catalysis 19 4183 Lowry HH Editor 1945 Chemistry of Coal Utilization Vol 3 John Wiley Sons Inc New York Lv PM Xiong ZH Chang J Wu CZ Chen Y and Zhu JX 2004 An Experimental Study on Biomass AirSteam Gasification in a Fluidized Bed Bioresource Technology 951 95101 Marcilla A Beltran MI and Navarro R 2008 Evolution with the Temperature of the Compounds Obtained in the Catalytic Pyrolysis of Polyethylene over HUSY Industrial Engineering Chemistry Research 4718 68966903 McNeil D 1966 Coal Carbonization Products Pergamon Press London UK Mills GA 1977 Chem Tech 77 418 Metzger JO 2006 Production of Liquid Hydrocarbons from Biomass Angew Chem Int Ed 45 696698 Molino A Chianese S and Musmarra D 2016 Biomass Gasification Technology The State of the Art Overview Journal of Energy Chemistry 251 1025 Munger CG 1984 Corrosion Prevention by Protective Coating NACE International Houston TX p 32 Nichols NN Dien BS Bothast RJ and Cotta MA 2006 Chapter 4 The Corn Ethanol Industry In Alcoholic Fuels S Minteer Editor CRC Press Boca Raton FL 117 Coal Oil Shale and Biomass Owen J 1981 Conversion and Uses of Liquid Fuels from Coal Fuel 609 755761 Pakdel H and Roy C 1991 Hydrocarbon Content of Liquid Products and Tar from Pyrolysis and Gasification of Wood Energy Fuels 5 427436 Pan YG Velo E Roca X Manyà JJ and Puigjaner L 2000 FluidizedBed Cogasification of Residual BiomassPoor Coal Blends for Fuel Gas Production Fuel 79 13171326 Pinto AC Guarieiro LNN Rezende MJC Ribeiro NM Torres EA Lopes WA Pereira PAP and De Andrade JB 2005 Biodiesel An Overview J Braz Chem Soc 16 13131330 Pitt GJ and Millward GR Editors 1979 Coal and Modern Coal Processing An Introduction Academic Press Inc New York Predel M and Kaminsky W 2000 Pyrolysis of Mixed Polyolefins in a FluidizedBed Reactor and on a PyroGCMS to Yield Aliphatic Waxes Polymer Degradation and Stability 703 373385 Rajvanshi AK 1986 Biomass Gasification In Alternative Energy in Agriculture Vol 2 DY Goswami Editor CRC Press Boca Raton FL pp 83102 Ramroop Singh N 2011 Biofuel In The Biofuels Handbook JG Speight Editor Royal Society of Chemistry London UK Part 1 Chapter 5 Rapagnà NJ and Latif A 1997 Steam Gasification of Almond Shells in a Fluidized Bed Reactor The Influence of Temperature and Particle Size on Product Yield and Distribution Biomass and Bioenergy 124 281288 Rapagnà NJ and Kiennemann A and Foscolo PU 2000 SteamGasification of Biomass in a Fluidized Bed of Olivine Particles Biomass and Bioenergy 193 187197 Sarker M Rashid MM Rahman MS and Molla M 2012 A New Kind of Renewable Energy Production of Aromatic Hydrocarbons Naphtha Chemical by Thermal Degradation of Polystyrene PS Waste Plastic American Journal of Climate Change 20121 145153 Scheirs J and Kaminsky W 2006 Feedstock Recycling and Pyrolysis of Waste Plastics John Wiley Sons Inc Chichester UK Scouten C 1990 Oil Shale In Fuel Science and Technology Handbook JG Speight Editor Marcel Dekker Inc New York Shah S and Gupta MN 2007 Lipase catalyzed preparation of biodiesel from Jatropha oil in a solvent free system Process Biochemistry 42 409414 Sjöström K Chen G Yu Q Brage C and Rosén C 1999 Promoted Reactivity of Char in Cogasification of Biomass and Coal Synergies in the Thermochemical Process Fuel 78 11891194 Sørensen BE Njakou S and Blumberga D 2006 Gaseous Fuels Biomass Proceedings World Renewable Energy Congress IX WREN London Speight JG 1990 In Fuel Science and Technology Handbook JG Speight Editor Marcel Dekker Inc New York Chapter 37 Speight JG 2005 Handbook of Coal Analysis John Wiley Sons Inc Hoboken NJ Speight JG 2008 Synthetic Fuels Handbook Properties Processes and Performance McGrawHill New York Speight JG 2011a The Refinery of the Future Gulf Professional Publishing Elsevier Oxford UK Speight JG 2011b An Introduction to Petroleum Technology Economics and Politics Scrivener Publishing Salem MA Speight JG Editor 2011c The Biofuels Handbook The Royal Society of Chemistry London UK Speight JG 2012 Shale Oil Production Processes Gulf Professional Publishing Elsevier Oxford UK Speight JG 2013a The Chemistry and Technology of Coal 3rd Edition CRC Press Boca Raton FL Speight JG 2013b CoalFired Power Generation Handbook Scrivener Publishing Salem MA Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Speight JG and Islam MR 2016 Peak EnergyMyth or Reality Scrivener Publishing Beverly MA Speight JG 2017 Handbook of Petroleum Refining CRC Press Boca Raton FL Steinberg M Fallon PT and Ssundaram MS 1992 The Flash Pyrolysis and Methanolysis of Biomass Wood for the Production of Ethylene Benzene and Methanol In Novel Production Methods for Ethylene Light Hydrocarbons and Aromatics RC von Herausgeg LF Albright BL Crynes and S Nowak Editors Marcel Dekker Inc New York Straathof AJJ 2014 Transformation of Biomass into Commodity Chemicals Using Enzymes or Cells Chem Rev 1143 18711908 US DOE 2018 Fossil Energy Research Benefits Clean Coal Technology Demonstration Program United States Department of Energy Washington DC httpswwwenergygovsitesprodfilescctfactcard pdf accessed November 5 2018 118 Handbook of Petrochemical Processes Vasudevan P Sharma S and Kumar A 2005 Liquid Fuels from Biomass An Overview Journal of Scientific Industrial Research 64 822831 Wachtmeister H Lund L Aleklett K and Mikael Höök M 2017 Production Decline Curves of Tight Oil Wells in Eagle Ford Shale Natural Resources Research 263 365377 Wright L Boundy R Perlack R Davis S and Saulsbury B 2006 Biomass Energy Data Book 1st Edition Office of Planning Budget and Analysis Energy Efficiency and Renewable Energy United States Department of Energy Contract No DEAC0500OR22725 Oak Ridge National Laboratory Oak Ridge TN Wu L Moteki T Gokhale AA Flaherty DW and Toste1 FD 2016 Production of Fuels and Chemicals from Biomass Condensation Reactions and Beyond Chem 1 3258 July 7 2016 ª 2016 Elsevier Inc New York wwwsciencedirectcomsciencearticlepiiS2451929416300043 wwwcellcomchem fulltext S2451929416300043 119 4 Feedstock Preparation 41 INTRODUCTION A feedstock is raw material unprocessed material for a processing or manufacturing and which is an asset that is critical to the production of other products For example natural gas and crude oil are feedstock raw materials that provide finished products in the fuel industry The term raw material is used to denote material in an unprocessed or minimally processed state such as raw natural gas crude oil coal shale oil or biomass However coal oil shale and biomass tar sand are complex carbonaceous raw materials and are possible future energy and chemical sources but like all feedstocks for petrochemical production they must undergo sometimes lengthy and extensive processing before they become suitable gases and liquids that can be used for the production of the petrochemicals They will however be synthesis gas Chapter 5 which can be used as a precursor to a range of petrochemical products Chapter 10 In all cases contaminants such as nitrogen oxygen sulfur and metals must be removed before the feedstock is sent to one or more conversion units Typically in the natural gas and refining industries as well as in the coal oil shale and biomass industries the feedstock is not used directly as fuels or in the current context for the production of chemicals This is due to the complex nature of the feedstock and the presence of one or more of the aforementioned impurities that are corrosive or poisonous to processing catalysts It is therefore essential that any feedstock for use in the pro duction of petrochemical product should be contaminant free when it enters any one of the various reactors Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The petrochemical industry is concerned with the production and trade of petrochemical prod ucts whether it involves the manufacture of an intermediate product or the manufacture of a final sales product The industry directly interfaces with the petroleum industry especially the down stream sector A petroleum refinery produces olefin derivatives and aromatic derivatives by crack ing processes such as coking processes and fluid catalytic cracking processes In addition the stream cracking of natural gas methane also produces olefin derivatives Aromatic derivatives are produced by the catalytic reforming of naphtha The importance of olefin derivatives and aromatic derivatives is reflected in their use as the building blocks for a wide range of materials such as sol vent detergents adhesives plastics fibers and elastomers Moreover the importance of the purity of the feedstocks can be tested and assured by the application of standard test methods Speight 2015 2018 Typically the primary raw feedstocks natural gas and crude oil have been subjected to chemi cal andor physical changes refining after being recovered On the other hand the secondary raw materials or intermediates are obtained from natural gas and crude oil through different process ing schemes The intermediates may be lowboiling hydrocarbon derivatives such as methane CH4 and ethane C2H6 or higherboiling hydrocarbon derivatives such as propane C3H8 butane C4H10 and pentane C5H12 even mixtures such as naphtha or gas oil that are produced from crude oil as distillation fractions Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 However the feedstocks used for petrochemical production are varied and in the natural state as received are not suitable for use in petrochemical production For example natural gas as it is used by consumers is much different from the natural gas that is brought from underground forma tions to the wellhead Table 41 Although the processing of natural gas is in many respects less complicated than the processing and refining of crude oil it is equally necessary before its use by end users to assure the quality of the feedstocks or product to the end users are domestic users or commercial users as is the case with the petrochemical industry 120 Handbook of Petrochemical Processes Gas is often referred to as natural gas because it is a naturally occurring hydrocarbon mix ture that does contain some nonhydrocarbon constituents which might be labeled as impurities but often find use in other areas of technology For the most part natural gas consists mainly of methane which is the simplest hydrocarbon but nevertheless processing purification refining is required before transportation to the consumer In the crude oil industry naphtha is used as a feedstock for steam cracking to produce petro chemicals ethylene propylene and the production of aromatic petrochemical products benzene toluene and xylenes Also gas oil is used as a chemical feedstock for steam cracking although generally less preferred than naphtha and natural gas liquids NGLs including liquefied petroleum gases LPGs While the naphtha and gas oil produced in a refinery depend on the composition of feed crude petroleum utilized and in turn the crude oil regional source crude oil extracted from oil fields in Middle Eastern countries has different properties and amounts of contaminants compared with crude oil extracted from oil fields in Alaska These differences are also reflected in the quality of the naphtha and the gas oil and the impurities in these two liquids Furthermore the production of feedstocks by the thermal decomposition of coal oil shale and biomass will in each case produce a variety of products gases liquids and solids and the everypresent contaminants that must be removed before further processing In addition since the majority of the petrochemical feedstocks to produce the products rely upon the use of a gaseous or lowboiling feedstock the focus of the chapter is on gas cleaning and petroleum refining Thus it is the purpose of this chapter to present the methods by which various gaseous and liquid feedstocks can be processed and prepared for petrochemical production This requires removal of impurities that would otherwise be deleterious to petrochemical production and analytical assur ance that feedstocks are indeed free of deleterious contaminants Speight 2015 2018 42 GAS STREAMS Raw natural gas comes from three types of wells oil wells associated gas gas wells nonassoci ated gas and condensate wells condensate gas but also called nonassociated gas Associated gas can exist separate from oil in the formation free gas or dissolved in the crude oil dissolved gas Whatever the source of the natural gas once separated from the crude oil if present it commonly exists in mixtures with other hydrocarbon derivativesprincipally ethane propane butane and pentane isomers natural gas liquids as well as a mixture of higher molecular weight higher boiling hydrocarbon derivatives that are often referred to as natural gasoline NG In addition raw natural gas contains water vapor hydrogen sulfide H2S carbon dioxide helium nitrogen and TABLE 41 Constituents of Natural Gas Name Formula vv Methane CH4 85 Ethane C2H6 38 Propane C3H8 15 Butane C4H10 12 Pentane C5H12 15 Carbon dioxide CO2 12 Hydrogen sulfide H2S 12 Nitrogen N2 15 Helium He 05 Pentane pentane and higher molecular weight hydrocarbon derivatives including benzene and toluene 121 Feedstock Preparation other compounds Natural gas liquids are sold separately and have a variety of different uses such as providing feedstocks for oil refineries or petrochemical plants Trace quantities of sulfur compounds in hydrocarbon products can be harmful to many cata lytic chemical processes in which these products are used Maximum permissible levels of total sulfur are normally included in specifications for such hydrocarbon derivatives It is recommended that this test method be used to provide a basis for agreement between two laboratories when the determination of sulfur in hydrocarbon gases is important In the case of liquefied petroleum gas total volatile sulfur is measured on an injected gas sample One test method ASTM D3246 2018 describes a procedure for the determination of sulfur in the range from 15 to 100 mgkg ppm ww in hydrocarbon products that are gaseous at normal room temperature and pressure Acidic constituents such as carbon dioxide and hydrogen sulfide as well as mercaptan derivatives also called thiols RSH can contribute to corrosion of refining equipment harm catalysts pollute the atmosphere and prevent the use of hydrocarbon components in petrochemical manufacture Mokhatab et al 2006 Speight 2007 2014 When the amount of hydrogen sulfide is high it may be removed from a gas stream and converted to sulfur or sulfuric acid a recent option for hydrogen sulfide removal is the use of chemical scavengers Some natural gases contain sufficient carbon dioxide to warrant recovery as dry ice Gas streams produced during petroleum and natural gas refining are not always hydrocarbon in nature and may contain contaminants such as carbon oxides COx where x 1 andor 2 sulfur oxides SOx where x 2 andor 3 as well as ammonia NH3 carbonyl sulfide COS and mer captan derivatives RSH The presence of these impurities may eliminate some of the sweetening processes from use since some of these processes remove considerable amounts of acid gas but not to a sufficiently low concentration On the other hand there are those processes not designed to remove or incapable of removing large amounts of acid gases whereas they are capable of remov ing the acid gas impurities to very low levels when the acid gases are present only in lowtomedium concentration in the gas Katz 1959 Mokhatab et al 2006 Speight 2007 2014 421 sources The sources of the various gas streams that are used as petrochemical feedstocks are varied However in terms of gas cleaning ie removal of the contaminants before petrochemical produc tion the processes are largely the same but it is a question of degree For example gas streams for some sources may produce gases that may contain higher amounts of carbon dioxide andor hydrogen sulfide and therefore the processes will have to be selected accordingly Table 42 The same selection criteria apply to liquid streams whether the streams originate from natural gas or from crude oil 4211 Gas Streams from Natural Gas In addition to its primary importance as a fuel natural gas is also a source of hydrocarbon deriva tives for petrochemical feedstocks Although natural gas is mostly considered as a clean fuel as compared to other fossil fuels the natural gas found in reservoirs deposit is not necessarily clean and free of impurities Furthermore the natural gas processed at the wells will have different range of composition depending on type depth and location of the underground reservoirs of porous sedimentary deposit and the geology of the area Most often oil and natural gas are found together in a reservoir When the natural gas is produced from oil wells it is categorized as associated with dissolved in crude oil or nonassociated It is apparent that two gas wells producing from the same reservoir may have different compositions Further the composition of the gas produced from a given reservoir may differ with time as the small hydrocarbon molecules two to eight carbons in addition to methane that exist in a gaseous state at underground pressures will become liquid condense at normal atmospheric pressure in the reservoir Generally they are called condensates or natural gas liquids 122 Handbook of Petrochemical Processes While the major constituent of natural gas is methane there are components such as carbon diox ide CO2 hydrogen sulfide H2S and mercaptan derivatives thiols RSH as well as trace amounts of sundry other emissions such as carbonyl sulfide COS The fact that methane has a foreseen and valuable end use makes it a desirable product but in several other situations it is considered a pol lutant having been identified as a greenhouse gas In practice heaters and scrubbers are usually installed at or near to the wellhead The scrubbers serve primarily to remove sand and other largeparticle impurities and the heaters ensure that the temperature of the gas does not drop too low With natural gas that contains even low quantities of water natural gas hydrates CnH2n2xH2O tend to form when temperatures drop These hydrates are solid or semisolid compounds resembling icelike crystals If the hydrates accumulate they can impede the passage of natural gas through valves and gathering systems To reduce the occurrence of hydrates small natural gasfired heating units are typically installed along the gathering pipe wherever it is likely that hydrates may form TABLE 42 Brief Descriptions of the Major Unit Operations Unit Function Gasoil separator Separation of the gas stream and the crude oil at the top and bottom part of the cylindrical shell respectively by the action of pressure at the wellhead where gravity separates the gas hydrocarbon derivatives from the heavier oil Condensate separator Removal of condensate from the gas stream by mechanical separators at the wellhead In condensate treatment section two main operations namely water washing and condensate stabilization are performed Based on the quality of the associated water the condensate may require water wash to remove salts and additives Dehydrator Removal of water vapor using dehydration process so that the natural gas will be free from the formation of hydrates corrosion problem and dew point In this treatment process of absorption using ethylene glycol is used to remove water and other particles from the feed stream As another option adsorption process can also be used for water removal using drybed dehydration towers Acid gas removal unit Removal contaminates in the dry gas such as CO2 H2S some remaining water vapor inert gases such as helium and oxygen The use of alkanolamines or Benfield solution processes is mostly common to absorb CO2 and H2S from the feed gas Nitrogen extractor Removal of nitrogen from the stream using two common ways In the first type nitrogen is cryogenically separated from the gas stream by the difference in their boiling point In the second type separation of methane from nitrogen takes place using physical absorption process Usually regeneration is done by reducing the pressure If there were trace amounts of inert gases like helium then pressure swing adsorption unit can be used to extract them from the gas stream Also called the nitrogen rejection unit Demethanizer Separation of e methane from natural gas liquids using cryogenic processing or absorption techniques The demethanization process can take place in the plant or as nitrogen extraction process As compared to absorption method the cryogenic method is more efficient for the lighter liquids separation such as ethane Fractionator Separation of natural gas liquids present in the gas stream by varying the volatility of the hydrocarbon derivatives present in the stream In fractionation the natural gas liquids after the demethanizer is subjected to rise through towers and heated to increase the temperature of the gas stream in stages assisting the vapor and liquid phases thoroughly contacted allowing the components to vaporize and condense easily and separate and flow into specific holding tanks 123 Feedstock Preparation Natural gas hydrates are usually considered as possible nuisances in the development of oil and gas fields caution in handling the hydrates cannot be overemphasized because of their tendency to explosively decompose On the other hand if handled correctly and with caution hydrates can be used for the safe and economic storage of natural gas In remote offshore areas the use of hydrates for natural gas transportation is also presently considered as an economic alternative to the pro cesses based either on liquefaction or on compression 4212 Natural Gas Liquids and Liquefied Petroleum Gas Natural gas coming directly from a well contains higher molecular weight hydrocarbon derivatives often referred to as natural gas liquids that in most instances depending upon the market demand have a higher value as separate products and making it worthwhile to remove these constituents from the gas stream Mokhatab et al 2006 Speight 2007 AbdelAal et al 2016 The removal of natural gas liquids usually takes place in a relatively centralized processing plant and uses tech niques similar to those used to dehydrate natural gas There are two basic steps to the treatment of natural gas liquids in the natural gas stream In the first step the liquids must be extracted from the natural gas and in the second step the natural gas liquids must be separated into the base con stituents These two processes account for approximately 90 vv of the total production of natural gas liquids Natural gas liquids are the nonmethane constituents such as ethane propane butane and pen tanes and higher molecular weight hydrocarbon constituents which can be separated as liquids during gas processing Figures 41 and 42 The higher molecular weight constituents ie the C5 product are commonly referred to as gas condensate or natural gasoline Rich gas will have a high heating value and a high hydrocarbon dew point When referring to natural gas liquids in the gas stream the term gallon per thousand cubic feet is used as a measure of high molecular weight hydrocarbon content On the other hand the composition of nonassociated gas sometimes called well gas is deficient in natural gas liquids The gas is produced from geological formations that typically do not contain much if any hydrocarbon liquids FIGURE 41 Schematic diagram for the flow of natural gas cleaning options 124 Handbook of Petrochemical Processes Generally the hydrocarbon derivatives having a higher molecular weight than methane as well as any acid gases carbon dioxide and hydrogen sulfide are removed from natural gas prior to use of the gas as a fuel However since the composition of natural gas is never constant there are standard test methods by which the composition and properties of natural gas can be determined and thus prepared for use It is not the intent to cover the standard test methods in any detail in this text since descriptions of the test methods are available elsewhere Speight 2015 Speight 2018 4213 Gas Streams from Crude Oil There are two broad categories of gas that is produced from crude oil The first category is the asso ciated gas that originated from crude oil formations and also from condensate wells condensate gas but also called nonassociated gas Associated gas can exist separate from oil in the formation free gas or dissolved in the crude oil dissolved gas The second category of the gas produced during crude oil refining and the terms refinery gas and process gas are also often used to include all the gaseous products and byproducts that emanate from a variety of refinery processes Organic sulfur compounds and hydrogen sulfide are common contaminants that must be removed prior to most uses Gas with a significant amount of sulfur impurities such as hydrogen sulfide is termed sour gas and often referred to as acid gas Processed natural gas that is available to end users is tasteless and odorless However before gas is distributed to end users it is odorized by adding small amounts of thiols RSH also called mercaptans to assist in leak detection Processed natural gas is harmless to the human body but natural gas is a simple asphyxiant and can kill if it displaces air to the point where the oxygen content will not support life Once the composition of a mixture has been determined it is possible to calculate various proper ties such as specific gravity vapor pressure calorific value and dew point In liquefied petroleum gas where the composition is such that the hydrocarbon dew point is known to be low a dew point method will detect the presence of traces of water Typically natural gas samples are analyzed for molecular composition by gas chromatography and for stable isotopic composition by isotope ratio mass spectrometry Carbon isotopic composi tion was determined for methane CH4 ethane C2H6 propane C3H8 and butane particularly FIGURE 42 Representation of the integrated processing units in a gas processing plant 125 Feedstock Preparation isobutane C4H10 ASTM D3246 2018 Another important property of the gas streams discussed in this text is the hydrocarbon dew point The hydrocarbon dew point is reduced to such a level that retrograde condensation ie condensation resulting from pressure drop cannot occur under the worst conditions likely to be experienced in the gas transmission system Similarly the water dew point is reduced to a level sufficient to preclude formation of C1C4 hydrates in the system Generally pipeline owners prefer that the specifications for the transmission of natural gas limit the maximum concentration of water vapor allowed Excess water vapor can cause corrosive condi tions degrading pipelines and equipment The water can also condense and freeze or form methane hydrates Chapter 7 causing blockages Water vapor content also affects the heating value of natu ral gas thus influencing the quality of the gas In order to processassociated dissolved natural gas for further use petrochemical or other the gas must be separated from the oil in which it is dissolved and is most often performed using equip ment installed at or near the wellhead The actual process used to separate oil from natural gas as well as the equipment that is used can vary widely Although dry pipeline quality natural gas is virtually identical across different geographic areas raw natural gas from different regions will vary in composition Table 41 Chapter 2 and therefore separation requirements may emphasize or deemphasize the optional separation processes In many instances natural gas is dissolved in oil underground primarily due to the formation pressure When this natural gas and oil is produced it is possible that it will separate on its own and but in general a separator is required The conven tional type of separator is consisting of a simple closed tank where the force of gravity serves to separate the liquids like oil from the natural gas In certain instances however specialized equipment is necessary to separate oil and natural gas An example of this type of equipment is the lowtemperature separator This is most often used for wells producing highpressure gas along with light crude oil or condensate These separa tors use pressure differentials to cool the wet natural gas and separate the oil and condensate Wet gas enters the separator being cooled slightly by a heat exchanger The gas then travels through a high pressure liquid knockout pot that serves to remove any liquids into a lowtemperature sepa rator The gas then flows into this lowtemperature separator through a choke mechanism which expands the gas as it enters the separator This rapid expansion of the gas allows for the lowering of the temperature in the separator After removal of the liquids the dry gas is sent back through the heat exchanger where it is warmed by the incoming wet gas By varying the pressure of the gas in various sections of the separator it is possible to vary the temperature which causes the crude oil and some water to be condensed out of the wet gas stream On the other hand petroleum refining produces gas streams that contain substantial amounts of acid gases such as hydrogen sulfide and carbon dioxide These gas streams are produced during ini tial distillation of the crude oil and during the various conversion processes Of particular interest is the hydrogen sulfide H2S that arises from the hydrodesulfurization Chapter 10 and hydrocrack ing Chapter 11 of feedstocks that contain organically bound sulfur S H H S hydrocarbonderivatives feedstock 2 2 Petroleum refining involves with the exception of heavy crude oil primary distillation Chapter 7 that results in separation into fractions differing in carbon number volatility specific gravity and other characteristics The most volatile fraction that contains most of the gases which are generally dissolved in the crude is referred to as pipestill gas or pipestill light ends and consists essentially of hydrocarbon gases ranging from methane to butanes or sometimes pentanes The gas varies in composition and volume depending on crude origin and on any additions to the crude made at the loading point It is not uncommon to reinject light hydrocarbon derivatives such as propane and butane into the crude oil before dispatch by tanker or pipeline This results in a higher vapor pressure of the crude but it allows one to increase the quantity of light products obtained at the refinery Since light ends in most petroleum markets command a premium while 126 Handbook of Petrochemical Processes in the oil field itself propane and butane may have to be reinjected or flared the practice of spiking crude oil with liquefied petroleum gas is becoming fairly common In addition to the gases obtained by distillation of petroleum more highly volatile products result from the subsequent processing of naphtha and middle distillate to produce gasoline Hydrogen sul fide is produced in the desulfurization processes involving hydrogen treatment of naphtha distillate and residual fuel and from the coking or similar thermal treatments of vacuum gas oils VGOs and heavy feedstocks Chapter 8 The most common processing step in the production of gasoline is the catalytic reforming of hydrocarbon fractions in the heptane C7 to decane C10 range Additional gases are produced in thermal cracking processes such as the coking or visbreaking processes Chapter 8 for the processing of heavy feedstocks In the visbreaking process fuel oil is passed through externally fired tubes and undergoes liquidphase cracking reactions which result in the formation of lighter fuel oil components Oil viscosity is thereby reduced and some gases mainly hydrogen methane and ethane are formed Substantial quantities of both gas and carbon are also formed in coking both fluid coking and delayed coking in addition to the middle distil late and naphtha When coking a residual fuel oil or heavy gas oil the feedstock is preheated and contacted with hot carbon coke which causes extensive cracking of the feedstock constituents of higher molecular weight to produce lower molecular weight products ranging from methane via liquefied petroleum gases and naphtha to gas oil and heating oil Products from coking processes tend to be unsaturated and olefin components predominate in the tail gases from coking processes Another group of refining operations that contributes to gas production is that of the catalytic cracking processes Chapter 9 These consists of fluidbed catalytic cracking and there are many process variants in which heavy feedstocks are converted into cracked gas liquefied petroleum gas catalytic naphtha fuel oil and coke by contacting the heavy hydrocarbon with the hot catalyst Both catalytic and thermal cracking processes the latter being now largely used for the production of chemical raw materials result in the formation of unsaturated hydrocarbon derivatives par ticularly ethylene CH2CH2 but also propylene propene CH3CHCH2 isobutylene isobutene CH32CCH2 and the nbutenes CH3CH2CHCH2 and CH3CHCHCH3 in addition to hydro gen H2 methane CH4 and smaller quantities of ethane CH3CH3 propane CH3CH2CH3 and butanes CH3CH2CH2CH3 CH33CH Diolefin derivatives such as butadiene CH2CHCHCH2 are also present A further source of refinery gas is hydrocracking a catalytic highpressure pyrolysis process in the presence of fresh and recycled hydrogen Chapter 11 The feedstock is again heavy gas oil or residual fuel oil and the process is mainly directed at the production of additional middle distillates and gasoline Since hydrogen is to be recycled the gases produced in this process again have to be separated into lighter and heavier streams any surplus recycle gas and the liquefied petroleum gas from the hydrocracking process are both saturated In a series of reforming processes commercialized under names such as platforming paraffin and naphthene cyclic nonaromatic hydrocarbon derivatives are converted in the presence of hydro gen and a catalyst is converted into aromatic derivatives or isomerized to more highly branched hydrocarbon derivatives Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Catalytic reforming processes thus not only result in the formation of a liquid prod uct of higher octane number but also produce substantial quantities of gases The latter are rich in hydrogen but also contain hydrocarbon derivatives from methane to butanes with a preponderance of propane CH3CH2CH3 nbutane CH3CH2CH2CH3 and isobutane CH33CH The composition of the process gas varies in accordance with reforming severity and reformer feedstock All catalytic reforming processes require substantial recycling of a hydrogen stream Therefore it is normal to separate reformer gas into a propane CH3CH2CH3 andor a butane stream CH3CH2CH2CH3 plus CH33CH which becomes part of the refinery liquefied petroleum gas production and a lighter gas fraction part of which is recycled In view of the excess of hydro gen in the gas all products of catalytic reforming are saturated and there are usually no olefin gases present in either gas stream 127 Feedstock Preparation Gases from hydrocracking units and from catalytic reformer gas units are commonly used in catalytic desulfurization processes Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 In the latter feedstocks ranging from light to vacuum gas oils are passed at pressures of 5001000 psi with hydrogen over a hydrofining catalyst This results mainly in the conversion of organic sulfur compounds to hydrogen sulfide S H H S hydrocarbons feedstock 2 2 This process also produces some light hydrocarbon derivatives by hydrocracking Thus refinery gas streams while ostensibly being hydrocarbon in nature may contain large amounts of acid gases such as hydrogen sulfide and carbon dioxide Most commercial plants employ hydrogenation to convert organic sulfur compounds into hydrogen sulfide Hydrogenation is effected by means of recycled hydrogencontaining gases or external hydrogen over a nickel molybdate or cobalt molyb date catalyst The presence of impurities in gas streams may eliminate some of the sweetening processes since some processes remove large amounts of acid gas but not to a sufficiently low concentration On the other hand there are those processes not designed to remove or incapable of removing large amounts of acid gases whereas they are capable of removing the acid gas impurities to very low levels when the acid gases are present only in lowtomedium concentration in the gas Finally another acid gas hydrogen chloride HCl although not usually considered to be a major emission is produced from mineral matter and the brine that often accompany petroleum during production and is gaining increasing recognition as a contributor to acid rain However hydrogen chloride may exert severe local effects because it does not need to participate in any further chemi cal reaction to become an acid Under atmospheric conditions that favor a buildup of stack emissions in the areas where hydrogen chloride is produced the amount of hydrochloric acid in rain water could be quite high In summary refinery process gas in addition to hydrocarbon derivatives may contain other con taminants such as carbon oxides COx where x 1 andor 2 sulfur oxides SOx where x 2 and or 3 as well as ammonia NH3 mercaptan derivatives RSH and carbonyl sulfide COS From an environmental viewpoint petroleum processing can result in a variety of gaseous emissions It is a question of degree insofar as the composition of the gaseous emissions may vary from process to process but the constituents are in the majority of cases the same 422 Gas ProcessinG Treated natural gas consists mainly of methane the properties of both gases natural gas and meth ane are nearly similar However natural gas is not pure methane and its properties are modified by the presence of impurities such as nitrogen carbon dioxide and small amounts of unrecovered higherboiling nongaseous at STP hydrocarbon derivatives An important property of natural gas is its heating valuerelatively high amounts of nitrogen andor carbon dioxide reduce the heating value of the gas Pure methane has a heating value of 1009 Btuft3 This value is reduced to approxi mately 900 Btuft3 if the gas contains approximately 10 vv nitrogen and carbon dioxidethe heating value of either nitrogen or carbon dioxide is zero On the other hand the heating value of natural gas could exceed methanes due to the presence of higher molecular weight hydrocarbon derivatives which have higher heating values For example the heating value of ethane is 1800 Btuft3 and the heating value of a product gas is a function of the constituents present in the mixture In the natural gas trade a heating value of 1 million Btu is approximately equivalent to 1000 ft3 of natural gas For petrochemical use methane must be purified and sent to the petrochemical production site in a condition of acceptability so as not to interfere with deactivate or destroy the activity of any processes catalysts To reach the condition of acceptability the methane must be the end product 128 Handbook of Petrochemical Processes of treated by a series of processes that have successfully removed the contaminants Chapter 2 that are present in the raw untreated gas Thus gas processing also called gas cleaning or gas refining consists of separating all the various hydrocarbon derivatives and fluids from the pure natural gas Kidnay and Parrish 2006 Mokhatab et al 2006 Speight 2007 2014 While often assumed to be hydrocarbon derivatives in nature there are also components of the gaseous products that must be removed prior to release of the gases to the atmosphere or prior to use of the gas in another part of the refinery ie as a fuel gas or as a process feedstock The processes that have been developed to accomplish gas purification vary from a simple oncethrough wash operation to complex multistep recycling systems In many cases the process complexities arise because of the need for recovery of the materials used to remove the contami nants or even recovery of the contaminants in the original or altered form Katz 1959 Kohl and Riesenfeld 1985 Newman 1985 Speight 2007 Mokhatab et al 2006 Speight 2014 In addi tion to the corrosion of equipment by acid gases Speight 2014 the escape into the atmosphere of sulfurcontaining gases can eventually lead to the formation of the constituents of acid rain ie the oxides of sulfur sulfur dioxide SO2 and sulfur trioxide SO3 Similarly the nitrogen containing gases can also lead to nitrous and nitric acids through the formation of the oxides NOx where x 1 or 2 which are the other major contributors to acid rain The release of carbon dioxide and hydrocarbon derivatives as constituents of refinery effluents can also influence the behavior and integrity of the ozone layer Gas processing involves the use of several different types of processes to remove contaminants from gas streams but there is always overlap between the various processing concepts In addition the terminology used for gas processing can often be confusing andor misleading because of the overlap Curry 1981 Maddox 1982 Gas processing is necessary to ensure that the natural gas prepared for transportation usually by pipeline and for sales must be as clean and pure as the speci fications dictate Thus natural gas as it is used by consumers is much different from the natural gas that is brought from underground formations up to the wellhead Moreover although natural gas produced at the wellhead is composed primarily of methane it is by no means is pure The processes that have been developed to accomplish gas purification vary from a simple singlestage oncethrough washingtype operation to complex multistep recycling systems Speight 2007 Mokhatab et al 2006 Speight 2014 In many cases the process complexities arise because of the need for recovery of the materials used to remove the contaminants or even recovery of the contaminants in the original or altered form Katz 1959 Kohl and Riesenfeld 1985 Newman 1985 Kohl and Nielsen 1997 Mokhatab et al 2006 In addition the precise area of applica tion of a given process is difficult to define and several factors must be considered before pro cess selection i the types of contaminants in the gas ii the concentrations of contaminants in the gas iii the degree of contaminant removal desired iv the selectivity of acid gas removal required v the temperature of the gas to be processed vi the pressure of the gas to be processed vii the volume of the gas to be processed viii the composition of the gas to be processed ix the ratio of carbon dioxide to hydrogen sulfide ratio in the gas feedstock and x the desirability of sulfur recovery due to environmental issues or economic issues 4221 Acid Gas Removal In addition to water and natural gas liquids removal one of the most important parts of gas process ing involves the removal of hydrogen sulfide and carbon dioxide which are generally referred to as contaminants Natural gas from some wells contains significant amounts of hydrogen sulfide and carbon dioxide and is usually referred to as sour gas Sour gas is undesirable because the sulfur compounds it contains can be extremely harmful even lethal to breathe and the gas can also be extremely corrosive The process for removing hydrogen sulfide from sour gas is commonly referred to as sweetening the gas There are four general processes used for emission control often referred to in another more specific context as flue gas desulfurization i physical adsorption in which a solid adsorbent is 129 Feedstock Preparation used ii physical absorption in which a selective absorption solvent is used iii chemical absorp tion is which a selective absorption solvent is used iv and catalytic oxidation thermal oxidation Soud and Takeshita 1994 Speight 2007 Mokhatab et al 2006 Speight 2014 42211 Adsorption Adsorption is a physicalchemical phenomenon in which the gas is concentrated on the surface of a solid or liquid to remove impurities It must be emphasized that absorption differs from adsorp tion in that absorption is not a physicalchemical surface phenomenon but a process in which the absorbed gas is ultimately distributed throughout the absorbent liquid The process depends only on physical solubility and may include chemical reactions in the liquid phase chemisorption Common absorbing media used are water aqueous amine solutions caustic sodium carbonate and nonvolatile hydrocarbon oils depending on the type of gas to be absorbed On the other hand adsorption is usually a gassolid interaction in which an adsorbent such as activated carbon the adsorbent or adsorbing medium which can be regenerated upon desorption Mokhatab et al 2006 Speight 2007 2014 The quantity of material adsorbed is proportional to the surface area of the solid and consequently adsorbents are usually granular solids with a large surface area per unit mass Subsequently the captured adsorbed gas can be desorbed with hot air or steam either for recovery or for thermal destruction Adsorber units are widely used to increase a lowgas concentration prior to incineration unless the gas concentration is very high in the inlet air stream and the process is also used to reduce problem odors or obnoxious odors from gases There are several limitations to the use of adsorption systems but it is generally the case that the major limitation is the requirement for minimization of particulate matter andor condensation of liquids eg water vapor that could mask the adsorption surface and drastically reduce its efficiency In these processes a solid with a highsurface area is used Molecular sieves zeolites are widely used and are capable of adsorbing large amounts of gases In practice more than one adsorp tion bed is used for continuous operation One bed is in use while the other is being regenerated Regeneration is accomplished by passing hot dry fuel gas through the bed Molecular sieves are competitive only when the quantities of hydrogen sulfide and carbon disulfide are low Molecular sieves are also capable of adsorbing water in addition to the acid gases Noteworthy commercial processes used are the Selexol the Sulfinol and the Rectisol processes In these processes no chemical reaction occurs between the acid gas and the solvent The solvent or absorbent is a liquid that selectively absorbs the acid gases and leaves out the hydrocarbons In the Selexol process for example the solvent is dimethyl ether of polyethylene glycol Raw natural gas passes countercurrently to the descending solvent When the solvent becomes saturated with the acid gases the pressure is reduced and hydrogen sulfide and carbon dioxide are desorbed The solvent is then recycled to the absorption tower 42212 Absorption Absorption is achieved by dissolution a physical phenomenon or by reaction a chemical phenom enon Barbouteau and Dalaud 1972 Mokhatab et al 2006 Speight 2007 2014 In addition to economic issues or constraints the solvents used for gas processing should have i a high capacity for acid gas ii a low tendency to dissolve hydrogen iii a low tendency to dissolve low molecu lar weight hydrocarbon derivatives iv low vapor pressure at operating temperatures to minimize solvent losses v low viscosity vi low thermal stability vii absence of reactivity toward gas components viii low tendency for fouling ix a low tendency for corrosion and x economically acceptable Mokhatab et al 2006 Speight 2007 2014 The processes using ethanolamine and potassium phosphate are now widely used The etha nolamine process known as the Girbotol process removes acid gases hydrogen sulfide and car bon dioxide from liquid hydrocarbon derivatives as well as from natural and from refinery gases The Girbotol process uses an aqueous solution of ethanolamine H2NCH2CH2OH that reacts with 130 Handbook of Petrochemical Processes hydrogen sulfide at low temperatures and releases hydrogen sulfide at high temperatures The etha nolamine solution fills a tower called an absorber through which the sour gas is bubbled Purified gas leaves the top of the tower and the ethanolamine solution leaves the bottom of the tower with the absorbed acid gases The ethanolamine solution enters a reactivator tower where heat drives the acid gases from the solution Ethanolamine solution restored to its original condition leaves the bottom of the reactivator tower to go to the top of the absorber tower and acid gases are released from the top of the reactivator The process using potassium phosphate is known as phosphate desulfurization and it is used in the same way as the Girbotol process to remove acid gases from liquid hydrocarbon derivatives as well as from gas streams The treatment solution is a water solution of potassium phosphate K3PO4 which is circulated through an absorber tower and a reactivator tower in much the same way as the ethanolamine is circulated in the Girbotol process the solution is regenerated thermally 42213 Chemisorption Chemisorption chemical absorption processes are characterized by a high capability of absorbing large amounts of acid gases They use a solution of a relatively weak base such as monoethanol amine MEA The acid gas forms a weak bond with the base which can be regenerated easily Mono and diethanolamine DEA derivatives are frequently used for this purpose The amine con centration normally ranges between 15 and 30 Natural gas is passed through the amine solution where sulfides carbonates and bicarbonates are formed Diethanolamine is a favored absorbent due to its lower corrosion rate smaller amine loss potential fewer utility requirements and minimal reclaiming needs Diethanolamine also reacts reversibly with 75 of carbonyl sulfides COS while the mono reacts irreversibly with 95 of the carbonyl sulfide and forms a degradation product that must be disposed in an environmentally acceptable manner Treatment of gas to remove the acid gas constituents hydrogen sulfide and carbon dioxide is most often accomplished by contact of the natural gas with an alkaline solution The most commonly used treating solutions are aqueous solutions of the ethanolamine or alkali carbonates although a considerable number of other treating agents have been developed in recent years Mokhatab et al 2006 Speight 2007 2014 Most of these newer treating agents rely upon physical absorption and chemical reaction When only carbon dioxide is to be removed in large quantities or when only FIGURE 43 The amine olamine process Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Figure 46 p 708 131 Feedstock Preparation partial removal is necessary a hot carbonate solution or one of the physical solvents is the most economical selection The primary process Figure 43 for sweetening sour natural gas uses an amine olamine solu tion to remove the hydrogen sulfide the amine process The sour gas is run through a tower which contains the olamine solution There are two principle amine solutions used monoethanolamine and diethanolamine Either of these compounds in liquid form will absorb sulfur compounds from natural gas as it passes through The effluent gas is virtually free of sulfur compounds and thus loses its sour gas status Like the process for the extraction of natural gas liquids and glycol dehy dration the amine solution used can be regenerated for reuse Although most sour gas sweetening involves the amine absorption process it is also possible to use solid desiccants like iron sponge to remove hydrogen sulfide and carbon dioxide Mokhatab et al 2006 Speight 2007 AbdelAal et al 2016 Diglycolamine DGA is another amine solvent used in the Econamine process Figures 41 and 42 Absorption of acid gases occurs in an absorber containing an aqueous solution of digly colamine and the heated rich solution saturated with acid gases is pumped to the regenerator Diglycolamine solutions are characterized by low freezing points which make them suitable for use in cold climates The most wellknown hydrogen sulfide removal process is based on the reaction of hydrogen sulfide with iron oxide often also called the iron sponge process or the dry box method in which the gas is passed through a bed of wood chips impregnated with iron oxide The iron oxide process which was implemented during the 19th century and also referred to as the iron sponge process is the oldest and still the most widely used batch process for sweetening natural gas and natural gas liquids Mokhatab et al 2006 Speight 2006 2014 In the process Figure 44 the sour gas is passed down through the bed In the case where continuous regeneration is to be utilized a small concentration of air is added to the sour gas before it is processed This air serves to continuously regenerate the iron oxide which has reacted with hydrogen sulfide which serves to extend the onstream life of a given tower but probably serves to decrease the total amount of sulfur that a given weight of bed will remove The process is usually best applied to gases containing low to medium concentrations 300 ppm of hydrogen sulfide or mercaptan derivatives This process tends to be highly selective and does not normally remove significant quantities of carbon dioxide As a result the hydrogen sulfide stream from the process is usually high purity The use of iron oxide process for sweetening sour gas is FIGURE 44 Iron oxide process 132 Handbook of Petrochemical Processes based on adsorption of the acid gases on the surface of the solid sweetening agent followed by chemical reaction of ferric oxide Fe2O3 with hydrogen sulfide 2Fe O 6H S 2Fe S 6H O 2 3 2 2 3 2 The reaction requires the presence of slightly alkaline water and a temperature below 43C 110F and bed alkalinity pH 8 to 10 should be checked regularly usually on a daily basis The pH level is to be maintained through the injection of caustic soda with the water If the gas does not contain sufficient water vapor water may need to be injected into the inlet gas stream The ferric sulfide produced by the reaction of hydrogen sulfide with ferric oxide can be oxidized with air to produce sulfur and regenerate the ferric oxide 2Fe S 3O 2Fe O 6S 2 3 2 2 3 2S 2O 2SO 2 2 The regeneration step is exothermic and air must be introduced slowly so the heat of reaction can be dissipated If air is introduced quickly the heat of reaction may ignite the bed Some of the elemen tal sulfur produced in the regeneration step remains in the bed After several cycles this sulfur will form a cake over the ferric oxide decreasing the reactivity of the bed Typically after ten cycles the bed must be removed and a new bed should be introduced into the vessel The iron oxide process is one of several metal oxidebased processes that scavenge hydrogen sulfide and organic sulfur compounds mercaptan derivatives from gas streams through reactions with the solidbased chemical adsorbent Kohl and Riesenfeld 1985 They are typically non regenerable although some are partially regenerable losing activity upon each regeneration cycle Most of the processes are governed by the reaction of a metal oxide with hydrogen sulfide to form the metal sulfide For regeneration the metal oxide is reacted with oxygen to produce elemental sulfur and the regenerated metal oxide In addition to iron oxide the primary metal oxide used for dry sorption processes is zinc oxide In the zinc oxide process the zinc oxide media particles are extruded cylinders 34 mm in diam eter and 48 mm in length Kohl and Nielsen 1997 Mokhatab et al 2006 Speight 2007 Abdel Aal et al 2016 and react readily with the hydrogen sulfide ZnO H S ZnS H O 2 2 At increased temperatures 205C370C 400F700F zinc oxide has a rapid reaction rate there fore providing a short mass transfer zone resulting in a short length of unused bed and improved efficiency Removal of larger amounts of hydrogen sulfide from gas streams requires a continuous process such as the Ferrox process or the Stretford process The Ferrox process is based on the same chem istry as the iron oxide process except that it is fluid and continuous The Stretford process employs a solution containing vanadium salts and anthraquinone disulfonic acid Mokhatab et al 2006 AbdelAal et al 2016 Most hydrogen sulfide removal processes return the hydrogen sulfide unchanged but if the quan tity involved does not justify installation of a sulfur recovery plant usually a Claus plant it is nec essary to select a process that directly produces elemental sulfur In the BeavonStretford process a hydrotreating reactor converts sulfur dioxide in the offgas to hydrogen sulfide which is contacted with Stretford solution a mixture of vanadium salt anthraquinone disulfonic acid sodium carbon ate and sodium hydroxide in a liquidgas absorber The hydrogen sulfide reacts stepwise with sodium carbonate and anthraquinone disulfonic acid to produce elemental sulfur with vanadium 133 Feedstock Preparation serving as a catalyst The solution proceeds to a tank where oxygen is added to regenerate the reac tants One or more froth or slurry tanks are used to skim the product sulfur from the solution which is recirculated to the absorber 42214 Other Processes There is a series of alternate processes that involve i the use of chemical reactions to remove contaminants from gas streams or ii the use of specialized equipment to physically remove con taminants from gas streams As example of the first category ie the use of chemical reactions to remove contaminants from gas streams strong basic solutions are effective solvents for acid gases However these solutions are not normally used for treating large volumes of natural gas because the acid gases form stable salts which are not easily regenerated For example carbon dioxide and hydrogen sulfide react with aqueous sodium hydroxide to yield sodium carbonate and sodium sulfide respectively CO 2NaOH Na CO H O 2 2 3 2 H S 2NaOH Na S 2H O 2 2 2 However a strong caustic solution is used to remove mercaptans from gas and liquid streams In the Merox Process for example a caustic solvent containing a catalyst such as cobalt which is capable of converting mercaptans RSH to caustic insoluble disulfides RSSR is used for streams rich in mercaptans after removal of H2S Air is used to oxidize the mercaptans to disulfides The caustic solution is then recycled for regeneration The Merox process is mainly used for treatment of refin ery gas streams As one of the major contaminates in natural gas feeds carbon dioxide must optimally be removed as it reduces the energy content of the gas and affect the selling price of the natural gas Moreover it becomes acidic and corrosive in the presence of water that has a potential to damage the pipeline and the equipment system In addition when the issue of transportation of the natural gas to a very far distance is a concern the use of pipelines will be too expensive so that liquefied natural gas LNG gas to liquid and chemicals are considered to be an alternative option In a liquefied natural gas processing plant while cooling the natural gas to a very low temperature the CO2 can be frozen and block pipeline systems and cause transportation drawback Hence the presence of CO2 in natural gas remains one of the challenging gas separation problems in process engineering for CO2CH4 systems Therefore the removal of CO2 from the natural gas through the purification processes is vital for an improvement in the quality of the product Mokhatab et al 2006 Speight 2007 2014 Amine washing of gas emissions involves chemical reaction of the amine with any acid gases with the liberation of an appreciable amount of heat and it is necessary to compensate for the absorption of heat Amine derivatives such as ethanolamine monoethanolamine diethanolamine triethanolamine methyl diethanolamine MDEA diisopropanolamine DIPA and diglycolamine have been used in commercial applications Katz 1959 Kohl and Riesenfeld 1985 Maddox et al 1985 Polasek and Bullin 1985 Jou et al 1985 Pitsinigos and Lygeros 1989 Kohl and Nielsen 1997 Mokhatab et al 2006 Speight 2007 2014 AbdelAal et al 2016 The chemistry of the amine process also called the olamine process can be represented by simple equations for low partial pressures of the acid gases 2RNH H S RNH S 2 2 3 2 2RHN CO H O RNH CO 2 2 2 3 2 3 134 Handbook of Petrochemical Processes At high acid gas partial pressure the reactions will lead to the formation of other products RNH S H S 2RNH HS 3 2 2 3 RNH CO H O 2RNH HCO 3 2 3 2 3 3 The reaction is extremely rapid and the absorption of hydrogen sulfide is limited only by mass transferthis is not the case for carbon dioxideand the reaction is also more complex than these equations would indicate and can lead to a series on unwanted side reactions and byproducts Mokhatab et al 2006 Speight 2007 Regeneration of the amine olamine solution leads to near complete desorption of carbon dioxide and hydrogen sulfide A comparison between monoethanol amine diethanolamine and diisopropanolamine shows that monoethanolamine is the cheapest of the three olamines but exhibits the highest heat of reaction and corrosion On the other hand diiso propanolamine is the most expensive of the three olamines but exhibits the lowest heat of reaction with a lower propensity for corrosion Carbonate washing is a mild alkali process typically the alkali is potassium carbonate K2CO3 for gas processing for the removal of acid gases such as carbon dioxide and hydrogen sulfide from gas streams and uses the principle that the rate of absorption of carbon dioxide by potassium car bonate increases with temperature Mokhatab et al 2006 Speight 2007 2014 It has been demon strated that the process works best near the temperature of reversibility of the reactions K CO CO H O 2KHCO 2 3 2 2 3 K CO H S KHS KHCO 2 3 2 3 The Fluor process uses propylene carbonate to remove carbon dioxide hydrogen sulfide carbonyl sulfide water and higherboiling hydrocarbon derivatives C2 from natural gas AbdelAal et al 2016 Water washing in terms of the outcome is almost analogous to but often less effective than washing with potassium carbonate Kohl and Riesenfeld 1985 Kohl and Nielsen 1997 and it is also possible to carry out the desorption step by pressure reduction The absorption is purely physi cal and there is also a relatively high absorption of hydrocarbon derivatives which are liberated at the same time as the acid gases In chemical conversion processes contaminants in gas emissions are converted to compounds that are not objectionable or that can be removed from the stream with greater ease than the original constituents For example a number of processes have been developed that remove hydrogen sulfide and sulfur dioxide from gas streams by absorption in an alkaline solution Catalytic oxidation is a chemical conversion process that is used predominantly for destruc tion of volatile organic compounds and carbon monoxide These systems operate in a temperature regime in the order of 205C595C 400F1100F in the presence of a catalystin the absence of the catalyst the system would require a higher operating temperature The catalysts used are typically a combination of noble metals deposited on a ceramic base in a variety of configurations eg honeycombshaped to enhance good surface contact Catalytic systems are usually classified on the basis of bed types such as fixed bed or packed bed and fluid bed fluidized bed These systems generally have very high destruction efficiencies for most volatile organic compounds resulting in the formation of carbon dioxide water and varying amounts of hydrogen chloride from halogenated hydrocarbon derivatives The presence in emissions of chemicals such as heavy met als phosphorus sulfur chlorine and most halogens in the incoming air stream act as poison to the system and can foul up the catalyst Thermal oxidation systems without the use of catalysts also involve chemical conversion more correctly chemical destruction and operate at temperatures in excess of 815C 1500F or 220C610C 395F1100F higher than catalytic systems 135 Feedstock Preparation Other processes include the Alkazid process for removal of hydrogen sulfide and carbon diox ide using concentrated aqueous solutions of amino acids The hot potassium carbonate process decreases the acid content of natural and refinery gas from as much as 50 to as low as 05 and operates in a unit similar to that used for amine treating The GiammarcoVetrocoke process is used for hydrogen sulfide andor carbon dioxide removal In the hydrogen sulfide removal section the reagent consists of sodium carbonate Na2CO3 or potassium carbonate K2CO3 or a mixture of the carbonates which contains a mixture of arsenite derivatives and arsenate derivatives the carbon dioxide removal section utilizes hot aqueous alkali carbonate solution activated by arsenic trioxide As2O3 or selenous acid H2SeO3 or tellurous acid H2TeO3 A word of caution might be added about the last three chemicals which are toxic and can involve stringent environmentalrelated dis posal protocols Molecular sieves are highly selective for the removal of hydrogen sulfide as well as other sulfur compounds from gas streams and over continuously high absorption efficiency They are also an effective means of water removal and thus offer a process for the simultaneous dehydration and desulfurization of gas Gas that has excessively high water content may require upstream dehy dration Mokhatab et al 2006 Speight 2007 2014 AbdelAal et al 2016 The molecular sieve process is similar to the iron oxide process Regeneration of the bed is achieved by passing heated clean gas over the bed As the temperature of the bed increases it releases the adsorbed hydrogen sulfide into the regeneration gas stream The sour effluent regeneration gas is sent to a flare stack and up to 2 vv of the gas seated can be lost in the regeneration process A portion of the natural gas may also be lost by the adsorption of hydrocarbon components by the sieve Mokhatab et al 2006 Speight 2007 2014 In this process unsaturated hydrocarbon components such as olefin derivatives and aromatic derivatives tend to be strongly adsorbed by the molecular sieve Molecular sieves are susceptible to poisoning by such chemicals as glycols and require thorough gas cleaning methods before the adsorption step Alternatively the sieve can be offered some degree of protection by the use of guard beds in which a less expensive catalyst is placed in the gas stream before contact of the gas with the sieve thereby protecting the catalyst from poisoning This concept is analogous to the use of guard beds or attrition catalysts in the petroleum industry Other processes worthy of note include i the Selexol process ii the Sulfinol process iii the LOCAT process and iv the Sulferox process Mokhatab et al 2006 AbdelAal et al 2016 The Selexol process uses a mixture of the dimethyl ether of propylene glycol as a solvent It is nontoxic and its boiling point is not high enough for amine formulation The selectivity of the sol vent for hydrogen sulfide H2S is much higher than that for carbon dioxide CO2 so it can be used to selectively remove these different acid gases minimizing carbon dioxide content in the hydrogen sulfide stream sent to the sulfur recovery unit SRU and enabling regeneration of solvent for carbon dioxide recovery by economical flashing In the process a stream of natural gas is injected in the bottom of the absorption tower operated at 1000 psi The rich solvent is flashed in a flash drum flash reactor at 200 psi where methane is flashed and recycled back to the absorber and joins the sweet lowsulfur or nosulfur gas stream The solvent is then flashed at atmospheric pressure and acid gases are flashed off The solvent is then stripped by steam to completely regenerate the solvent which is recycled back to the absorber Any hydrocarbon derivatives are condensed and any remain ing acid gases are flashed from the condenser drum This process is used when there is a high acid gas partial pressure and no heavy hydrocarbon derivatives Diisopropanolamine can be added to this solvent to remove carbon dioxide to a level suitable for pipeline transportation The Sulfinol process uses a solvent that is a composite solvent consisting of a mixture of diiso propanolamine 3045 vv or MDEA sulfolane tetrahydrothiophene dioxide 4060 vv and water 515 vv The acid gas loading of the Sulfinol solvent is higher and the energy required for its regeneration is lower than those of purely chemical solvents At the same time it has the advantage over purely physical solvents that severe product specifications can be met more easily and coabsorption of hydrocarbon derivatives is relatively low Aromatic compounds 136 Handbook of Petrochemical Processes higher molecular weight hydrocarbon derivatives and carbon dioxide are soluble to a lesser extent The process is typically used when the hydrogen sulfidecarbon dioxide ratio is greater than 11 or where carbon dioxide removal is not required to the same extent as hydrogen sulfide removal The process uses a conventional solvent absorption and regeneration cycle in which the sour gas components are removed from the feed gas by countercurrent contact with a lean solvent stream under pressure The absorbed impurities are then removed from the rich solvent by stripping with steam in a heated regenerator column The hot lean solvent is then cooled for reuse in the absorber Part of the cooling may be by heat exchange with the rich solvent for partial recovery of heat energy The solvent reclaimer is used in a small ancillary facility for recovering solvent compo nents from higherboiling products of alkanolamine degradation or from other highboiling or solid impurities The LOCAT process uses an extremely dilute solution of iron chelates A small portion of the chelating agent is depleted in some side reactions and is lost with precipitated sulfur In this process sour gas is contacted with the chelating reagent in the absorber and H2S reacts with the dissolved iron to form elemental sulfur H S 2Fe S 2Fe 2H 2 3 2 The sulfur is removed from the regenerator to centrifugation and melting Application of heat is not required because of the exothermic reaction The reduced iron ion is regenerated in the regenerator by air blowing 4Fe O 2H O 4Fe 4OH 2 2 2 3 In the Sulferox process chelating iron compounds are the heart of the process Sulferox is a redox technology as is the LOCAT however in this case a concentrated iron solution is used to oxidize hydrogen sulfide to elemental sulfur Chelating agents are used to increase the solubility of iron in the operating solution As a result of high iron concentrations in the solution the rate of liquid circulation can be kept low and consequently the equipment is small As in the LOCAT process there are two basic reactions the first takes place in the absorber and the second takes place in the regenerator as in reaction The key to the Sulferox technology is the ligand used in the process which allows the process to use high total iron concentrations 1 ww in the process the acid gas enters the contactor where hydrogen sulfide is oxidized to produce elemental sulfur The treated gas and the Sulferox solution flow to the separator where sweet gas exits at the top and the solution is sent to the regenerator where ferrous iron Fe2 is oxidized by air to ferric iron Fe3 and the solution is regenerated and sent back to the contactor Sulfur settles in the regenerator and is taken from the bottom to filtration where sulfur cake is produced At the top of the regenerator spent air is released A makeup Sulferox solution is added to replace the degradation of the ligands Control of this degradation rate and purging of the degradation products ensures smooth operation of the process As an example of the second category ie the use of specialized equipment to physically remove contaminants from gas streams the removal of particulate matter dust control from gas streams is an absolute necessity if the stream is to be purified for use as a feedstock for petrochemical pro duction Historically particulate matter control has been one of the primary concerns of industries since the emission of particulate matter is readily observed through the deposition of fly ash and soot as well as in impairment of visibility Mody and Jakhete 1988 Different degrees of con trol can be achieved by use of various types of equipment but selection of the process equipment which depends upon proper characterization of the particulate matter emitted by a specific process the appropriate piece of equipment can be selected sized installed and performance tested The general classes of control devices for particulate matter are categorized as i cyclone collectors ii fabric filters and iii wet scrubbers 137 Feedstock Preparation Cyclone collectors are the most common of the inertial collector class and are effective in remov ing coarser fractions of particulate matter and operate by contacting the particles in the gas stream with a liquid In principle the particles are incorporated in a liquid bath or in liquid particles which are much larger and therefore more easily collected In the process the particleladen gas stream enters an upper cylindrical section tangentially and proceeds downward through a conical section Particles migrate by centrifugal force generated by providing a path for the carrier gas to be sub jected to a vortexlike spin The particles are forced to the wall and are removed through a seal at the apex of the inverted cone A reversedirection vortex moves upward through the cyclone and discharges through a topcenter opening Cyclones are often used as primary collectors because of their relatively low efficiency 5090 is usual Fabric filters are typically designed with nondisposable filter bags As the gaseous dust containing emissions flow through the filter media typically cotton polypropylene fiberglass or Teflon particulate matter is collected on the bag surface as a dust cake Fabric filters operate with collection efficiencies up to 999 although other advantages are evident but there are several issues that arise during use of such equipment Wet scrubbers are devices in which a countercurrent spray liquid is used to remove particles from an air stream Device configurations include plate scrubbers packed bed scrubbers orifice scrubbers venturi scrubbers and spray towers individually or in various combinations Wet scrub bers can achieve high collection efficiencies at the expense of prohibitive pressure drops The foam scrubber is a modification of a wet scrubber in which the particleladen gas is passed through a foam generator where the gas and particles are enclosed by small bubbles of foam Other methods include use of highenergy input venturi scrubbers or electrostatic scrubbers where particles or water droplets are charged and flux forcecondensation scrubbers where a hot humid gas is contacted with cooled liquid or where steam is injected into saturated gas In the latter scrubber the movement of water vapor toward the cold water surface carries the particles with it diffusiophoresis while the condensation of water vapor on the particles causes the particle size to increase thus facilitating collection of fine particles Electrostatic precipitators operate on the principle of imparting an electric charge to particles in the incoming air stream which are then collected on an oppositely charged plate across a high voltage field Particles of high resistivity create the most difficulty in collection Conditioning agents such as sulfur trioxide SO3 have been used to lower resistivity Important parameters include design of electrodes spacing of collection plates minimization of air channeling and collection electrode rapping techniques used to dislodge particles Techniques under study include the use of highvoltage pulse energy to enhance particle charging electronbeam ionization and wide plate spacing Electrical precipitators are capable of efficiencies 99 under optimum conditions but performance is still difficult to predict in new situations 4222 Recovery of Condensable Hydrocarbon Derivatives Hydrocarbon derivatives that are of higher molecular weight than methane that are present in natu ral gases are valuable raw materials and important fuels They can be recovered by lean oil extrac tion The first step in this scheme is to cool the treated gas by exchange with liquid propane The cooled gas is then washed with a cold hydrocarbon liquid which dissolves most of the condensable hydrocarbons The uncondensed gas is dry natural gas and is composed mainly of methane with small amounts of ethane and heavier hydrocarbon derivatives The condensed hydrocarbon deriva tives or natural gas liquids are stripped from the rich solvent which is recycled Dry natural gas may then be used either as a fuel or as a chemical feedstock Another way to recover natural gas liquids is by using cryogenic cooling cooling to very low temperatures in the order of 100C to 115C 150F to 175F which are achieved primarily through lowering the temperatures to below the dew point To prevent hydrate formation natural gas may be treated with glycols which dissolve water efficiently Ethylene glycol EG diethylene glycol DEG and triethylene glycol TEG are typical 138 Handbook of Petrochemical Processes solvents for water removal Triethylene glycol is preferable in vapor phase processes because of its low vapor pressure which results in less glycol loss The triethylene glycol absorber unit typically contains 612 bubblecap trays to accomplish the water absorption However more contact stages may be required to reach dew points below 40F Calculations to determine the number of trays or feet of packing the required glycol concentration or the glycol circulation rate require vaporliquid equilibrium data Predicting the interaction between triethylene glycol and water vapor in natural gas over a broad range allows the designs for ultralow dew point applications to be made One alternative to using bubblecap trays is adiabatic expansion of the inlet gas The inlet gas is first treated to remove water and acid gases and then cooled via heat exchange and refrigera tion Further cooling of the gas is accomplished through turbo expanders and the gas is sent to a demethanizer to separate methane from the higherboiling hydrocarbon derivatives often referred to as natural gas liquids NGLs Improved recovery of the higherboiling hydrocarbon derivatives could be achieved through better control strategies and use of online gas chromatographic analysis Membrane separation process are very versatile and are designed to process a wide range of feedstocks and offer a simple solution for removal and recovery of higherboiling hydrocarbon derivatives natural gas liquids from natural gas AbdelAal et al 2016 The separation process is based on highflux membranes that selectively permeates higherboiling hydrocarbon derivatives compared to methane and are recovered as a liquid after recompression and condensation The residue stream from the membrane is partially depleted of higherboiling hydrocarbon derivatives and is then sent to sales gas stream Gas permeation membranes are usually made with vitreous polymers that exhibit good selectivity but to be effective the membrane must be very permeable with respect to the separation process 42221 Extraction There are two principle techniques for removing natural gas liquids from the natural gas stream the absorption method and the cryogenic expander process In the process a turboexpander is used to produce the necessary refrigeration and very low temperatures and high recovery of light com ponents such as ethane and propane can be attained The natural gas is first dehydrated using a molecular sieve followed by cooling of the dry stream Figure 45 The separated liquid containing most of the heavy fractions is then demethanized and the cold gases are expanded through a turbine that produces the desired cooling for the process The expander outlet is a twophase stream that FIGURE 45 Drying using a molecular sieve Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Figure 44 p 706 139 Feedstock Preparation is fed to the top of the demethanizer column This serves as a separator in which i the liquid is used as the column reflux and the separator vapors combined with vapors stripped in the demetha nizer are exchanged with the feed gas and ii the heated gas which is partially recompressed by the expander compressor is further recompressed to the desired distribution pressure in a separate compressor The extraction of natural gas liquids from the natural gas stream produces both cleaner purer natural gas as well as the valuable hydrocarbon derivatives that are the natural gas liquids them selves This process allows for the recovery of approximately 9095 vv of the ethane originally in the gas stream In addition the expansion turbine is able to convert some of the energy released when the natural gas stream is expanded into recompressing the gaseous methane effluent thus sav ing energy costs associated with extracting ethane 42222 Absorption The absorption method of high molecular weight recovery of hydrocarbon derivatives is very simi lar to using absorption for dehydration Speight 2007 Mokhatab et al 2006 Speight 2014 The main difference is that in the absorption of natural gas liquids absorbing oil is used as opposed to glycol This absorbing oil has an affinity for natural gas liquids in much the same manner as gly col has an affinity for water Before the oil has picked up any natural gas liquids it is termed lean absorption oil The oil absorption process involves the countercurrent contact of the lean or stripped oil with the incoming wet gas with the temperature and pressure conditions programmed to maximize the dissolution of the liquefiable components in the oil The rich absorption oil sometimes referred to as fat oil containing natural gas liquids exits the absorption tower through the bottom It is now a mixture of absorption oil propane butanes pentanes and other higherboiling hydrocarbon deriva tives The rich oil is fed into lean oil stills where the mixture is heated to a temperature above the boiling point of the natural gas liquids but below that of the oil This process allows for the recovery of around 75 vv of the butane isomers and 8590 vv of the pentane isomers and higherboiling constituents from the natural gas stream The basic absorption process is subject to modifications that improve process effectiveness and even to target the extraction of specific natural gas liquids In the refrigerated oil absorption method where the lean oil is cooled through refrigeration propane recovery can be in the order of 90 vv and approximately 40 vv of the ethane can be extracted from the natural gas stream Extraction of the other higherboiling natural gas hydrocarbon derivatives is typically nearquantitative using this process The AET process for recovery of liquefied petroleum gas utilizes noncryogenic absorption to recover ethane propane and higherboiling constituents from natural gas streams The absorbed gases in the rich solvent from the bottom of the absorber column are fractionated in the solvent regenerator column which separates gases as an overhead fraction and lean solvent as a bottoms fraction After heat recuperation the lean solvent is presaturated with absorber overhead gases The chilled solvent flows in the top of the absorber column The separated gases are sent to storage 42223 Fractionation Fractionation processes are very similar to those processes classed as liquid removal processes but often appear to be more specific in terms of the objectives hence the need to place the fractionation processes into a separate category The fractionation processes are those processes that are used i to remove the more significant product stream first or ii to remove any unwanted light ends from the higherboiling liquid products In the general practice of natural gas processing the first unit is a deethanizer followed by a depropanizer then by a debutanizer and finally a butane fractionator Thus each column can oper ate at a successively lower pressure thereby allowing the different gas streams to flow from column to column by virtue of the pressure gradient without necessarily the use of pumps 140 Handbook of Petrochemical Processes The purification of hydrocarbon gases by any of these processes is an important part of refin ery operations especially in regard to the production of liquefied petroleum gas This is actually a mixture of propane and butane which is an important domestic fuel as well as an intermediate material in the manufacture of petrochemicals Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The presence of ethane in liquefied petroleum gas must be avoided because of the inability of this lighter hydrocarbon to liquefy under pressure at ambi ent temperatures and its tendency to register abnormally high pressures in the liquefied petroleum gas containers On the other hand the presence of pentane in liquefied petroleum gas must also be avoided since this particular hydrocarbon a liquid at ambient temperatures and pressures may separate into a liquid state in the gas lines Typically natural gas liquids are fractionated to produce three separate streams i an ethanerich stream which is used for producing ethylene ii liquefied petroleum gas which is a propanebutane mixture that is mainly used as a fuel or a chemical feedstock and is evolving into an important feedstock for olefin production and iii natural gasoline is mainly constituted of C5 hydrocarbon derivatives that is added to gasoline to raise its vapor pressure which is also evolving into an impor tant feedstock for olefin production Natural gas liquids may contain significant amounts of cyclo hexane a precursor for nylon Recovery of cyclohexane from natural gas liquids by conventional distillation is difficult and not economical because heptane C7H16 isomers are also present which boil at temperatures nearly identical to that of cyclohexanean extractive distillation process is preferred for cyclohexane recovery Thus after separation of the natural gas liquids from the natural gas stream they must be sepa rated fractionated into the individual constituents prior to sales The process of fractionation which is based on the different boiling points of the hydrocarbon derivatives that constitute the natural gas liquids occurs in stages with each stage involving separation of the hydrocarbon derivatives as individual products The process commences with the removal of the lowerboiling hydrocarbon derivatives from the feedstock The particular fractionators are used in the following order i the deethanizer which is used to separate the ethane from the stream of natural gas liquids ii the depropanizer which is used to separate the propane from the deethanized stream iii the debuta nizer which is used to separate the butane isomers leaving the pentane isomers and higherboiling hydrocarbon derivatives in the stream and iv the butane splitter or deisobutanizer which is used to separate nbutane and isobutane After the recovery of natural gas liquids sulfurfree dry natural gas methane may be liquefied for transportation through cryogenic tankers Further treatment may be required to reduce the water vapor below 10 ppm and carbon dioxide and hydrogen sulfide to less than 100 and 50 ppm respec tively Two methods are generally used to liquefy natural gas the expander cycle and mechanical refrigeration In the expander cycle part of the gas is expanded from a high transmission pressure to a lower pressure This lowers the temperature of the gas Through heat exchange the cold gas cools the incoming gas which in a similar way cools more incoming gas until the liquefaction tem perature of methane is reached In mechanical refrigeration a multicomponent refrigerant consisting of nitrogen methane eth ane and propane is used through a cascade cycle When these liquids evaporate the heat required is obtained from natural gas which loses energytemperature till it is liquefied The refrigerant gases are recompressed and recycled 42224 Enrichment The natural gas product fed into a petrochemical production system must meet specific quality mea sures in order for the pipeline grid to operate properly Consequently natural gas produced at the wellhead which in most cases contains contaminants and natural gas liquids must be processed ie cleaned before it can be safely delivered to the highpressure longdistance pipelines that transport the product to the consuming public Natural gas that is not within certain specific gravi ties pressures Btu content range or water content levels will cause operational problems pipeline 141 Feedstock Preparation deterioration or can even cause pipeline rupture Thus the purpose of enrichment is to produce natural gas for sale and enriched tank oil The tank oil contains more light hydrocarbon liquids than natural petroleum and the residue gas is drier leaner ie has lesser amounts of the higher molecu lar weight hydrocarbon derivatives Therefore the process concept is essentially the separation of hydrocarbon liquids from the methane to produce a lean dry gas The natural gas received and transported must especially in the United States and many other countries meet the quality standards specified by pipeline These quality standards vary from pipe line to pipeline and are usually a function of i the design of the pipeline system ii the design of any downstream interconnecting pipelines and iii the requirements of the customer In general these standards specify that the natural gas should i be within a specific Btu content range typically 1035 Btu ft3 50 Btu ft3 ii be delivered at a specified hydrocarbon dew point temperature level to prevent any vaporized gas liquid in the mix from condensing at pipeline pressure iii contain no more than trace amounts of elements such as hydrogen sulfide carbon dioxide nitrogen water vapor and oxygen iv be free of particulate solids and liquid water that could be detrimental to the pipeline or its ancillary operating equipment Gas processing equipment whether in the field or at processing treatment plants assures that these specifications can be met In most cases processing facilities extract contaminants and higherboiling hydrocarbon deriva tives from the gas stream but in some cases the gas processors blend some higherboiling hydro carbon derivatives into the gas stream in order to bring it within acceptable Btu levels For instance in some areas if the produced gas including coalbed methane CBM does not meet is below the Btu requirements of the pipeline operator in which case a blend of higher Btucontent natural gas or a propaneair mixture is injected to enrich the heat content Btu value prior for delivery to the pipeline In other instances such as at liquefied natural gas import facilities where the heat content of the regasified gas may be too high for pipeline receipt vaporized nitrogen may be injected into the natural gas stream to lower its Btu content Briefly and because it is sometimes combined with petroleumbased natural gas for process ing purposes coalbed methane is the generic term given to methane gas held in coal and released or produced when the water pressure within the buried coal is reduced by pumping from either vertical or inclined to horizontal surface holes Thermogenic coalbed methane is predominantly formed during the coalification process whereby organic matter is slowly transformed into coal by increasing temperature and pressure as the organic matter is buried deeper and deeper by additional deposits of organic and inorganic matter over long periods of geological time On the other hand latestage biogenic coalbed methane is formed by relatively recent bacterial processes involving naturally occurring bacteria associated with meteoric water recharge at outcrop or subcrop can dominate the generation of coalbed methane The amount of methane stored in coal is closely related to the rank and depth of the coal the higher the coal rank and the deeper the coal seam is presently buried causing pressure on coal the greater its capacity to produce and retain methane gas Gas derived from coal is generally pure and requires little or no processing because it is solely methane and not mixed with heavier hydrocarbon derivatives such as ethane which is often present in conventional natural gas The number of steps and the type of techniques used in the process of creating pipelinequality natural gas most often depends upon the source and makeup of the wellhead production stream Among the several stages of gas processing are i gasoil separation ii water removal iii liquids removal iv nitrogen removal v acid gas removal and vi fractionation In many instances pressure relief at the wellhead will cause a natural separation of gas from oil using a conventional closed tank where gravity separates the gas hydrocarbon derivatives from the heavier oil In some cases however a multistage gasoil separation process is needed to separate the gas stream from the crude oil These gasoil separators are commonly closed cylindrical shells horizontally mounted with inlets at one end an outlet at the top for removal of gas and an outlet at the bottom for removal of oil Separation is accomplished by alternately heating and cooling by compression the flow stream through multiple steps However the number of steps and the type 142 Handbook of Petrochemical Processes of techniques used in the process of creating pipelinequality natural gas most often depends upon the source and makeup of the gas stream In some cases several of the steps may be integrated into one unit or operation performed in a different order or at alternative locations leaseplant or not required at all 4223 Water Removal Water is a common impurity in gas streams and removal of water is necessary to prevent condensa tion of the water and the formation of ice or the formation of gas hydrates Gas hydrates are solid white compounds formed from a physicalchemical reaction between hydrocarbon derivatives and water under the high pressures and low temperatures used to transport natural gas via pipeline Hydrates reduce pipeline efficiency Water in the liquid phase causes corrosion or erosion problems in pipelines and equipment par ticularly when carbon dioxide and hydrogen sulfide are present in the gas The simplest method of water removal refrigeration or cryogenic separation is to cool the gas to a temperature at least equal to or preferentially below the dew point Figure 46 Mokhatab et al 2006 Speight 2007 2014 In addition to separating petroleum and some condensate from the wet gas stream it is neces sary to remove most of the associated water Most of the liquid free water associated with extracted natural gas is removed by simple separation methods at or near the wellhead However the removal of the water vapor that exists in solution in natural gas requires a more complex treatment This treatment consists of dehydrating the natural gas which usually involves one of two processes either absorption or adsorption Moisture may be removed from hydrocarbon gases at the same time as hydrogen sulfide is removed Moisture removal is necessary to prevent harm to anhydrous catalysts and to prevent the formation of hydrocarbon hydrates eg C3H818H2O at low temperatures A widely used dehy dration and desulfurization process is the glycolamine process in which the treatment solution is a mixture of ethanolamine and a large amount of glycol The mixture is circulated through an absorber and a reactivator in the same way as ethanolamine is circulated in the Girbotol process The glycol absorbs moisture from the hydrocarbon gas passing up the absorber the ethanolamine absorbs hydrogen sulfide and carbon dioxide The treated gas leaves the top of the absorber the spent ethanolamineglycol mixture enters the reactivator tower where heat drives off the absorbed acid gases and water FIGURE 46 The glycol refrigeration process Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Figure 42 p 702 143 Feedstock Preparation Absorption occurs when the water vapor is taken out by a dehydrating agent Adsorption occurs when the water vapor is condensed and collected on the surface In a majority of cases cooling alone is insufficient and for the most part impractical for use in field operations Other more conve nient water removal options use i hygroscopic liquids eg diethylene glycol or triethylene glycol and ii solid adsorbents or desiccants eg alumina silica gel and molecular sieves Ethylene glycol can be directly injected into the gas stream in refrigeration plants 42231 Absorption An example of absorption dehydration is known as glycol dehydrationthe principal agent in this process is diethylene glycol which has a chemical affinity for water Mokhatab et al 2006 Speight 2007 AbdelAal et al 2016 Glycol dehydration involves using a solution of a glycol such as diethylene glycol or triethylene glycol which is brought into contact with the wet gas stream in a contactor In practice absorption systems recover 9099 by volume of methane that would otherwise be flared into the atmosphere In the process a liquid desiccant dehydrator serves to absorb water vapor from the gas stream The glycol solution absorbs water from the wet gas and once absorbed the glycol particles become heavier and sink to the bottom of the contactor where they are removed The dry natural gas is then transported out of the dehydrator The glycol solution bearing all of the water stripped from the natural gas is recycled through a specialized boiler designed to vaporize only the water out of the solution The boiling point differential between water 100C 212F and glycol 204C 400F makes it relatively easy to remove water from the glycol solution As well as absorbing water from the wet gas stream the glycol solution occasionally carries with it small amounts of methane and other compounds found in the wet gas In order to decrease the amount of methane and other compounds that would otherwise be lost flash tank separator condensers are employed to remove these compounds before the glycol solution reaches the boiler The flash tank separator Chapter 6 consists of a device that reduces the pressure of the glycol solu tion stream allowing the methane and other hydrocarbon derivatives to vaporize flash The glycol solution then travels to the boiler which may also be fitted with air or watercooled condensers which serve to capture any remaining organic compounds that may remain in the glycol solution The regeneration stripping of the glycol is limited by temperature diethylene glycol and triethyl ene glycol decompose at or even before their respective boiling points Such techniques as stripping of hot triethylene glycol with dry gas eg heavy hydrocarbon vapors the Drizo process or vacuum distillation are recommended Another absorption process the Rectisol process is a physical acid gas removal process using an organic solvent typically methanol at subzero temperatures and characteristic of physical acid gas removal processes it can purify synthesis gas down to 01 ppm total sulfur including hydrogen sulfide H2S and carbonyl sulfide COS and carbon dioxide CO2 in the ppm range Mokhatab et al 2006 AbdelAal et al 2016 The process uses methanol as a wash solvent and the wash unit operates under favorable at temperatures below 0C 32F To lower the temperature of the feed gas temperatures it is cooled against the cold product streams before entering the absorber tower At the absorber tower carbon dioxide and hydrogen sulfide with carbonyl sulfide are removed By use of an intermediate flash coabsorbed products such as hydrogen and carbon monoxide are recovered thus increasing the product recovery rate To reduce the required energy demand for the carbon dioxide compressor the carbon dioxide product is recovered in two different pressure steps medium pressure and lower pressure The carbon dioxide product is essentially sulfurfree H2S free COSfree and water free The carbon dioxide products can be used for enhanced oil recovery EOR andor sequestration or as pure carbon dioxide for other processes 42232 Solid Adsorbents Adsorption is a physicalchemical phenomenon in which the gas is concentrated on the surface of a solid or liquid to remove impurities It must be emphasized that adsorption differs from absorption 144 Handbook of Petrochemical Processes in that absorption is not a physicalchemical surface phenomenon but a process in which the absorbed gas is ultimately distributed throughout the absorbent liquid Dehydration using a solid adsorbent or solid desiccant is the primary form of dehydrating natural gas using adsorption and usually consists of two or more adsorption towers which are filled with a solid desiccant Mokhatab et al 2006 Speight 2007 AbdelAal et al 2016 Typical desiccants include activated alumina or a granular silica gel material Wet natural gas is passed through these towers from top to bottom As the wet gas passes around the particles of desiccant material water is retained on the surface of these desiccant particles Passing through the entire desiccant bed almost all the water is adsorbed onto the desiccant material leaving the dry gas to exit the bottom of the tower There are several solid desiccants which possess the physical characteristic to adsorb water from natural gas These desiccants are generally used in dehydration systems consisting of two or more towers and associ ated regeneration equipment Molecular sievesa class of aluminosilicates which produce the lowest water dew points and which can be used to simultaneously sweeten dry gases and liquids Mokhatab et al 2006 Speight 2007 AbdelAal et al 2016are commonly used in dehydrators ahead of plants designed to recover ethane and other natural gas liquids These plants operate at very cold temperatures and require very dry feed gas to prevent formation of hydrates Dehydration to 100C 148F dew point is possible with molecular sieves Water dew points less than 100C 148F can be accom plished with special design and definitive operating parameters Mokhatab et al 2006 Molecular sieves are commonly used to selectively adsorb water and sulfur compounds from light hydrocarbon streams such as liquefied petroleum gas propane butane pentane light olefin deriva tives and alkylation feed Sulfur compounds that can be removed are hydrogen sulfide mercaptan derivatives sulfide derivatives and disulfide derivatives In the process the sulfur containing feed stock is passed through a bed of sieves at ambient temperature The operating pressure must be high enough to keep the feed in the liquid phase The operation is cyclic in that the adsorption step is stopped at a predetermined time before sulfur breakthrough occurs Sulfur and water are removed from the sieves by purging with fuel gas at 205C315C 400F600F Solidadsorbent dehydrators are typically more effective than liquid absorption dehydrators eg glycol dehydrators and are usually installed as a type of straddle system along natural gas pipelines These types of dehydration systems are best suited for large volumes of gas under very high pres sure and are thus usually located on a pipeline downstream of a compressor station Two or more towers are required due to the fact that after a certain period of use the desiccant in a particular tower becomes saturated with water To regenerate and recycle the desiccant a hightemperature heater is used to heat gas to a very high temperature and passage of the heated gas stream through a saturated desiccant bed vaporizes the water in the desiccant tower leaving it dry and allowing for further natural gas dehydration Although twobed adsorbent treaters have become more common while one bed is removing water from the gas the other undergoes alternate heating and cooling on occasion a threebed system is used one bed adsorbs one is being heated and one is being cooled An additional advan tage of the threebed system is the facile conversion of a twobed system so that the third bed can be maintained or replaced thereby ensuring continuity of the operations and reducing the risk of a costly plant shutdown Silica gel SiO2 and alumina Al2O3 have good capacities for water adsorption up to 8 by weight Bauxite crude alumina Al2O3 adsorbs up to 6 by weight water and molecular sieves adsorb up to 15 by weight water Silica is usually selected for dehydration of sour gas because of its high tolerance to hydrogen sulfide and to protect molecular sieve beds from plugging by sulfur Alumina guard beds serve as protectors by the act of attrition and may be referred to as an attri tion reactor containing an attrition catalyst Chapter 6 Speight 2014 may be placed ahead of the molecular sieves to remove the sulfur compounds Downflow reactors are commonly used for adsorption processes with an upward flow regeneration of the adsorbent and cooling using gas flow in the same direction as adsorption flow 145 Feedstock Preparation Solid desiccant units generally cost more to buy and operate than glycol units Therefore their use is typically limited to applications such as gases having a high hydrogen sulfide content very low water dew point requirements simultaneous control of water and hydrocarbon dew points In pro cesses where cryogenic temperatures are encountered solid desiccant dehydration is usually preferred over conventional methanol injection to prevent hydrate and ice formation Kidnay and Parrish 2006 4224 Nitrogen Removal Nitrogen may often occur in sufficient quantities in natural gas and consequently lower the heating value of the gas Thus several plants for nitrogen removal from natural gas have been built but it must be recognized that nitrogen removal requires liquefaction and fractionation of the entire gas stream which may affect process economics In some cases the nitrogencontaining natural gas is blended with a gas having a higher heating value and sold at a reduced price depending upon the thermal value Btuft3 For high flowrate gas streams a cryogenic process is typical and involves the use of the different volatility of methane bp 1616C2589F and nitrogen bp 1957C3203F to achieve sepa ration In the process a system of compression and distillation columns drastically reduces the tem perature of the gas mixture to a point where methane is liquefied and the nitrogen is not On the other hand for smaller volumes of gas a system utilizing pressure swing adsorption PSA is a more typical method of separation In pressure swing adsorption method methane and nitrogen can be separated by using an adsorbent with an aperture size very close to the molecular diameter of the larger species the methane which allows nitrogen to diffuse through the adsorbent This results in a purified natural gas stream that is suitable for pipeline specifications The adsorbent can then be regenerated leaving a highly pure nitrogen stream The pressure swing adsorption method is a flexible method for nitrogen rejection being applied to both small and large flow rates 4225 The Claus Process The Claus process is not so much a gas cleaning process but a process for the disposal of hydrogen sulfide a toxic gas that originates in natural gas as well as during crude oil processing such as in the coking catalytic cracking hydrotreating and hydrocracking processes Burning hydrogen sul fide as a fuel gas component or as a flare gas component is precluded by safety and environmental considerations since one of the combustion products is the highly toxic sulfur dioxide SO2 which is also toxic As described above hydrogen sulfide is typically removed from the refinery light ends gas streams through an olamine process after which application of heat regenerates the olamine and forms an acid gas stream Following from this the acid gas stream is treated to convert the hydrogen sulfide elemental sulfur and water The conversion process utilized in most modern refineries is the Claus process or a variant thereof The Claus process Figure 47 involves combustion of approximately onethird of the hydrogen sulfide to sulfur dioxide and then reaction of the sulfur dioxide with the remaining hydrogen sulfide in the presence of a fixed bed of activated alumina cobalt molybdenum catalyst resulting in the formation of elemental sulfur 2H S 3O 2SO 2H O 2 2 2 2 2H S SO 3S 2H O 2 2 2 Different process flow configurations are in use to achieve the correct hydrogen sulfidesulfur diox ide ratio in the conversion reactors In a splitflow configuration onethird split of the acid gas stream is completely combusted and the combustion products are then combined with the noncombusted acid gas upstream of the conversion reactors In a oncethrough configuration the acid gas stream is partially combusted by only providing sufficient oxygen in the combustion chamber to combust onethird of the acid gas 146 Handbook of Petrochemical Processes Two or three conversion reactors may be required depending on the level of hydrogen sulfide conversion required Each additional stage provides incrementally less conversion than the previous stage Overall conversion of 9697 vv of the hydrogen sulfide to elemental sulfur is achievable in a Claus process If this is insufficient to meet air quality regulations a Claus process tail gas treater is utilized to remove essentially the entire remaining hydrogen sulfide in the tail gas from the Claus unit The tail gas treater may employ employs a proprietary solution to absorb the hydrogen sulfide followed by conversion to elemental sulfur Table 43 The SCOT Shell Claus Offgas Treating unit is a most common type of tail gas unit and uses a hydrotreating reactor followed by amine scrubbing to recover and recycle sulfur in the form of hydrogen to the Claus unit In the process tail gas containing hydrogen sulfide and sulfur diox ide is contacted with hydrogen and reduced in a hydrotreating reactor to form hydrogen sulfide FIGURE 47 Claus process Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Figure 48 p 712 TABLE 43 Examples of Tail Gas Treating Processes Unit Function Caustic scrubbing An incinerator converts trace sulfur compounds in the offgas to sulfur dioxide that is contacted with caustic which is sent to the wastewater treatment system Polyethylene glycol Offgas from the Claus unit is contacted with this solution to generate an elemental sulfur product unlike the Beavon Stretford process no hydrogenation reactor is used to convert sulfur dioxide to hydrogen sulfide Selectox A hydrogenation reactor converts sulfur dioxide in the offgas to hydrogen sulfide a solid catalyst in a fixed bed reactor converts the hydrogen sulfide to elemental sulfur which is recovered for sales SulfiteBisulfite Following Claus reactors an incinerator converts trace sulfur compounds to sulfur dioxide which is then contacted with sulfite solution in an absorber where the sulfur dioxide reacts with the sulfite to produce a bisulfite solution the gas is then emitted to the stack the bisulfite is regenerated and liberated sulfur dioxide is sent to the Claus units for recovery 147 Feedstock Preparation and water The catalyst is typically cobaltmolybdenum on alumina The gas is then cooled in a water contractor The hydrogen sulfidecontaining gas enters an amine absorber which is typically in a system segregated from the other refinery amine systems The purpose of segregation is two fold i the tail gas treater frequently uses a different amine than the rest of the plant and ii the tail gas is frequently cleaner than the refinery fuel gas in regard to contaminants and segregation of the systems reduces maintenance requirements for the SCOT unit Amines chosen for use in the tail gas system tend to be more selective for hydrogen sulfide and are not affected by the high levels of carbon dioxide in the offgas The hydrotreating reactor converts sulfur dioxide in the offgas to hydrogen sulfide that is then contacted with a Stretford solution a mixture of a vanadium salt anthraquinone disulfonic acid sodium carbonate and sodium hydroxide in a liquidgas absorber AbdelAal et al 2016 The hydrogen sulfide reacts stepwise with sodium carbonate and the anthraquinone sulfonic acid to pro duce elemental sulfur with vanadium serving as a catalyst The solution proceeds to a tank where oxygen is added to regenerate the reactants One or more froth or slurry tanks are used to skim the product sulfur from the solution which is recirculated to the absorber Other tail gas treating pro cesses include i caustic scrubbing ii polyethylene glycol treatment iii Selectox process and iv a sulfitebisulfite tail gas treating Mokhatab et al 2006 Speight 2007 2014 A sulfur removal process Table 44 must be very precise since natural gas contains only a small quantity of sulfurcontaining compounds that must be reduced several orders of magnitude Most consumers of natural gas require less than 4 ppm in the gasa characteristic feature of natural gas that contains hydrogen sulfide is the presence of carbon dioxide generally in the range of 14 vv In cases where the natural gas does not contain hydrogen sulfide there may also be a relative lack of carbon dioxide 43 PETROLEUM STREAMS In a very general sense crude oil refining can be traced back over 5000 years to the times when asphalt materials and oils were isolated from areas where natural seepage occurred and the result ing bitumen was send for construction purposes Abraham 1945 Forbes 1958a 1958b 1959 Hoiberg 1960 Forbes 1964 Speight 1978 Any treatment of the asphalt such as hardening in the air prior to use or of the oil such as allowing for more volatile components to escape prior to use TABLE 44 Sulfur RemovalRecovery Processes Sodium hydrosulfide Fuel gas containing hydrogen sulfide is contacted with sodium hydroxide in an absorption column The resulting liquid is the product of sodium hydrosulfide NaHS Iron chelate Fuel gas containing hydrogen sulfide is contacted with iron chelate catalyst dissolved in solution hydrogen sulfide is converted to elemental sulfur which is recovered Stretford Similar to iron chelate except Stretford solution is used instead of iron chelate solution Ammonium thiosulfate In this process hydrogen sulfide is contacted with air to form sulfur dioxide which is contacted with ammonia in a series of absorption column to produce ammonium thiosulfate for offsite sale Hyperion Fuel gas is contacted over a solid catalyst to form elemental sulfur the sulfur is collected and sold The catalyst is comprised of iron and naphthoquinone sulfonic acid Sulfatreat The Sulfatreat material is a black granular solid powder the hydrogen sulfide forms a chemical bond with the solid when the bed reaches capacity the Sulfatreat solids are removed and replaced with fresh material The sulfur is not recovered Hysulf Hydrogen sulfide is contacted with a liquid quinone in an organic solvent such as nmethyl2pyrolidone NMP forming sulfur the sulfur is removed and the quinone reacted to its original state producing hydrogen gas 148 Handbook of Petrochemical Processes in lamps may be considered to be refining under the general definition of refining However crude oil refining as it is now practiced is a very recent science and many innovations evolved during the 20th century Briefly crude oil refining is the separation of crude oil into fractions and the subsequent treat ing of these fractions to yield marketable products Figure 48 Parkash 2003 Gary et al 2007 Speight 2008 2011 2014 2015 Hsu and Robinson 2017 Speight 2017 In fact a refinery is essentially a group of manufacturing plants which vary in number with the variety of products produced However in addition to the simplified schematic of a refinery the refinery for the present purposes can actually be considered as two refineriesi a section for lowviscosity feedstocks and ii a section for highviscosity feedstocks Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 In this way the processes can be selected and products manufactured to give a balanced opera tion in which the refinery feedstock oil is converted into a variety of products in amounts that are in accord with the demand for each For example the manufacture of products from the lowerboiling portion of crude oil automatically produces a certain amount of higherboiling components using distillation and various thermal processes Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 If the latter cannot be sold as say heavy fuel oil these products will accumulate until refinery storage facilities are full To prevent the occurrence of such a situation the refinery must be flexible and be able to change operations as needed This usually means more processes are required for refining the heavier feedstocks i thermal processes to change an excess of heavy fuel oil into more gasoline with coke as the residual product or ii a vacuum distillation process to separate the viscous feedstock into lubricating oil stocks and asphalt FIGURE 48 Schematic diagram of a conversion refinery showing the relative placement of the various pro cessing units 149 Feedstock Preparation To convert crude oil into desired products in an economically feasible and environmentally accept able manner Refinery process for crude oil are generally divided into three categories i separation processes of which distillation is the prime example ii conversion processes of which coking and catalytic cracking are prime example and iii finishing processes of which hydrotreating to remove sulfur is a prime example 431 refinery confiGuration The simplest refinery configuration is the topping refinery which is designed to prepare feedstocks for petrochemical manufacture or for production of industrial fuels Table 45 The topping refinery consists of tankage a distillation unit recovery facilities for gases and light hydrocarbon derivatives and the necessary utility systems steam power and water treatment plants Topping refineries pro duce large quantities of unfinished oils and are highly dependent on local markets but the addition of hydrotreating and reforming units to this basic configuration results in a more flexible hydroskim ming refinery which can also produce desulfurized distillate fuels and highoctane gasoline These refineries may produce up to half of their output as residual fuel oil and they face increasing market loss as the demand for lowsulfur even nosulfur and highsulfur fuel oil increases The most versatile refinery configuration is the conversion refinery which incorporates all the basic units found in both the topping and hydroskimming refineries but it also features gas oil con version plants such as catalytic cracking and hydrocracking units olefin conversion plants such as alkylation or polymerization units and frequently coking units for sharply reducing or elimi nating the production of residual fuels Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The predominant steps in a deep conversion are i catalytic cracking and ii hydrocrackingmodern conversion refineries may produce twothirds of their output as unleaded gasoline with the balance distributed between liquefied petroleum gas jet fuel diesel fuel and a small quantity of coke Many such refineries also incorporate solvent extraction processes for TABLE 45 Examples of Refinery Types Refinery Type Processes Type Complexity Comparativea Topping Distillation Skimming Low 1 Hydroskimming Distillation Hydroskimming Moderate 3 Reforming Hydrotreating Conversion Distillation Cracking High 6 Fluid catalytic cracking Hydrocracking Reforming Alkylation Hydrotreating Deep conversion Distillation Coking Very high 10 Coking Fluid catalytic cracking Hydrocracking Reforming Alkylation Hydrotreating a Indicates complexity on an arbitrary numerical scale of 110 with 1 being the least complex and 10 being the most complex 150 Handbook of Petrochemical Processes manufacturing lubricants and petrochemical units with which to recover propylene benzene toluene and xylenes for further processing into polymers Since a refinery is a group of integrated manufacturing plants Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 that are selected to give a balanced produc tion of salable products in amounts that are in accord with the demand for each it is necessary to prevent the accumulation of nonsalable products the refinery must be flexible and be able to change operations as needed The complexity of petroleum is emphasized insofar as the actual amount of the products vary significantly from one crude oil to another Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 In addition the configuration of refineries may vary from refinery to refinery Some refineries may be more oriented toward the production of gasoline large reforming andor catalytic cracking whereas the configuration of other refineries may be more oriented toward the production of middle distillates such as jet fuel and gas oil that can also lead to the production of petrochemical intermediates In addition the predominant processes that are used to produce starting materials for the pro duction of petrochemicals are the cracking process by which the molecular size of the crude oil constituents is reduced cracked to the required molecular dimensions of the petrochemical start ing materials The term cracking applies to the decomposition of petroleum constituents which is induced by elevated temperatures 350C 660F whereby the higher molecular weight constituents of petroleum are converted to lower molecular weight products Cracking reactions involve carbon carbon bond rupture and are thermodynamically favored at high temperature 432 crackinG Processes 4321 Thermal Cracking Processes With the dramatic increases in the number of gasolinepowered vehicles distillation processes Chapters 4 and 7 were not able to completely fill the increased demand for gasoline In 1913 the thermal cracking process was developed and is the phenomenon by which higherboiling higher molecular weight constituents in petroleum are converted into lowerboiling lower molecular weight products application of elevated temperatures usually in the order of 350C 660F Thermal cracking is the oldest and in principle the simplest refinery conversion process The temperature and pressure depends on the type of feedstock and the product requirements as well as the residence time Thermal cracking processes allow the production of lower molecular weight products such as the constituents of liquefied petroleum gas and naphthagasoline constituents from higher molecular weight fraction such as gas oils and residua The simplest thermal cracking processthe visbreaking process Chapters 4 and 8is used to upgrade fractions such as distilla tion residua and other heavy feedstocks Chapters 4 and 7 to produce fuel oil that meets specifica tions or feedstocks for other refinery processes Thus cracking is a phenomenon by which higherboiling constituents higher molecular weight constituents in petroleum are converted into lowerboiling lower molecular weight products However certain products may interact with one another to yield products having higher molecular weights than the constituents of the original feedstock Some of the products are expelled from the system as say gases gasolinerange materials kerosenerange materials and the various inter mediates that produce other products such as coke Materials that have boiling ranges higher than gasoline and kerosene may depending upon the refining options be referred to as recycle stock which is recycled in the cracking equipment until conversion is complete In thermal cracking processes some of the lower molecular weight products are expelled from the system as gases gasolinerange materials kerosenerange materials and the various intermedi ates that produce other products such as coke Materials that have boiling ranges higher than gaso line and kerosene may depending upon the refining options be referred to as recycle stock which is recycled in the cracking equipment until conversion is complete 151 Feedstock Preparation Thermal cracking is a free radical chain reaction A free radical in which an atom or group of atoms possessing an unpaired electron is very reactive often difficult to control and it is the mode of reaction of free radicals that determines the product distribution during thermal cracking ie noncatalytic thermal decomposition In addition a significant feature of hydrocarbon free radicals is the resistance to isomerization during the existence of the radical For example thermal cracking does not produce any degree of branching in the products by migration of an alkyl group other than that already present in the feedstock Nevertheless the classical chemistry of free radical for mation and behavior involves the following chemical reactionsit can only be presumed that the formation of free radicals during thermal noncatalytic cracking follows similar paths 1 Initiation reaction where a single molecule breaks apart into two free radicals Only a small fraction of the feedstock constituents may actually undergo initiation which involves breaking the bond between two carbon atoms rather than the thermodynamically stronger bond between a carbon atom and a hydrogen atom CH CH 2CH 3 3 3 2 Hydrogen abstraction reaction in which the free radical abstracts a hydrogen atom from another molecule CH CH CH CH CH CH 3 3 3 4 3 2 3 Radical decomposition reaction in which a free radical decomposes into an alkene CH CH CH CH H 3 2 2 2 4 Radical addition reaction in which a radical reacts with an alkene to form a single larger free radical CH CH CH CH CH CH CH CH 3 2 2 2 3 2 2 2 5 Termination reaction in which two free radicals react with each other to produce the products two common forms of termination reactions are recombination reactions in which two rad icals combine to form one molecule and disproportionation reactions in which one free radical transfers a hydrogen atom to the other to produce an alkene and an alkane CH CH CH CH CH CH 3 3 2 3 2 3 CH CH CH CH CH CH CH CH 3 2 3 2 2 2 3 3 The smaller free radicals hydrogen methyl and ethyl are more stable than the larger radicals They will tend to capture a hydrogen atom from another hydrocarbon thereby forming a saturated hydro carbon and a new radical In addition many thermal cracking processes and many different chemi cal reactions occur simultaneously Thus an accurate explanation of the mechanism of the thermal cracking reactions is difficult The primary reactions are the decomposition of higher molecular weight species into lower molecular weight products As the molecular weight of the hydrocarbon feedstock increases the reactions become much more complex lading to a wider variety of products For example using a more complex hydrocar bon dodecane C12H26 as the example two general types of reaction occur during cracking 1 The decomposition of high molecular weight constituents into lower molecular weight con stituents primary reactions CH CH CH CH CH CH CH CH 3 2 10 3 3 2 8 3 2 2 152 Handbook of Petrochemical Processes CH CH CH CH CH CH CH CHCH 3 2 10 3 3 2 7 3 2 3 CH CH CH CH CH CH CH CHCH CH 3 2 10 3 3 2 6 3 2 2 3 CH CH CH CH CH CH CH CHCH CH 3 2 10 3 3 2 5 3 2 2 2 3 CH CH CH CH CH CH CH CHCH CH 3 2 10 3 3 2 4 3 2 2 3 3 CH CH CH CH CH CH CH CHCH CH 3 2 10 3 3 2 3 3 2 2 4 3 CH CH CH CH CH CH CH CHCH CH 3 2 10 3 3 2 2 3 2 2 5 3 CH CH CH CH CH CH CH CHCH CH 3 2 10 3 3 2 3 2 2 6 3 CH CH CH CH CH CH CHCH CH 3 2 10 3 3 3 2 2 7 3 CH CH CH CH CH CHCH CH 3 2 10 3 4 2 2 8 3 2 Reactions by which some of the primary products interact to form higher molecular weight materials secondary reactions CH CH CH CH CH CH CH CH 2 2 2 2 3 2 2 RCH CH R CH CH crackedresiduum coke otherproducts 2 1 2 Thus from the chemistry of the thermal decomposing of pure compounds and assuming little interference from other molecular species in the reaction mixture it is difficult but not impossible to predict the product types that arise from the thermal cracking of various feedstocks However during thermal cracking all the reactions illustrated above can and do occur simultaneously and to some extent are uncontrollable However one of the significant features of hydrocarbonfree radi cals is their resistance to isomerization for example migration of an alkyl group and as a result thermal cracking does not produce any degree of branching in the products other than that already present in the feedstock Data obtained from the thermal decomposition of pure compounds indicate certain decompo sition characteristics that permit predictions to be made of the product types that arise from the thermal cracking of various feedstocks For example normal paraffin derivatives are believed to form initially higher molecular weight material which subsequently decomposes as the reaction progresses Other paraffinic materials and terminal olefin derivatives are produced An increase in pressure inhibits the formation of low molecular weight gaseous products and therefore promotes the formation of higher molecular weight materials Furthermore for saturated hydrocarbon derivatives the connecting link between gasphase pyrolysis and liquidphase thermal degradation is the concentration of alkyl radicals In the gas phase alkyl radicals are present in low concentration and undergo unimolecular radical decom position reactions to form αolefin derivatives and smaller alkyl radicals In the liquid phase alkyl radicals are in much higher concentration and prefer hydrogen abstraction reactions to radical decomposition reactions It is this preference for hydrogen abstraction reactions that gives liquid phase thermal degradation a broad product distribution Branched paraffin derivatives react somewhat differently to the normal paraffin derivatives dur ing cracking processes and produce substantially higher yields of olefin derivatives having one fewer 153 Feedstock Preparation carbon atoms than the parent hydrocarbon Cycloparaffin derivatives naphthenes react differently to their noncyclic counterparts and are somewhat more stable For example cyclohexane produces hydrogen ethylene butadiene and benzene alkylsubstituted cycloparaffin derivatives decompose by means of scission of the alkyl chain to produce an olefin and a methyl or ethyl cyclohexane The aromatic ring is considered fairly stable at moderate cracking temperatures 350C500C 660F930F Alkylated aromatic derivatives like the alkylated naphthenes are more prone to dealkylation than to ring destruction However ring destruction of the benzene derivatives occurs above 500C 930F but condensed aromatic derivatives may undergo ring destruction at some what lower temperatures 450C 840F Generally the relative ease of cracking of the various types of hydrocarbon derivatives of the same molecular weight is given in the following descending order i paraffin derivatives ii olefin derivatives iii naphthene derivatives and iv aromatic derivatives To remove any potential con fusion paraffin derivatives are the least stable and aromatic derivatives are the most stable Also within any type of hydrocarbon the higher molecular weight hydrocarbon derivatives tend to crack easier than the lighter ones Paraffin derivatives are by far the easiest hydrocarbon derivatives to crack with the rupture most likely to occur between the first and second carbon bonds in the lighter paraffin derivatives However as the molecular weight of the paraffin molecule increases rupture tend to occur nearer the middle of the molecule The main secondary reactions that occur in thermal cracking are polymerization and condensation Two extremes of the thermal cracking in terms of product range are represented by high temperature processes i steam cracking or ii pyrolysis Steam cracking is a process in which feedstock is decomposed into lower molecular weight often unsaturated products saturated hydro carbon derivatives Steam cracking is the key process in the petrochemical industry producing eth ylene CH2CH2 propylene CH3CHCH2 butylene CH3CH2CHCH2 andor CH3CHCHCH3 andor CH32CCH2 benzene C6H6 toluene C6H5CH3 ethylbenzene C6H5CH2CH3 and the xylene isomers 12CH3C6H4CH3 13CH3C6H4CH3 and 14CH3C6H4CH3 These intermediates are converted into a variety of polymers plastics solvents resins fibers detergents ammonia and other synthetic organic compounds In the process a gaseous or liquid hydrocarbon feed such as ethane or naphtha is diluted with steam and briefly heated in a furnace at approximately 850C 1560F in the absence of oxygen at a short residence time often in the order of milliseconds After the cracking temperature has been reached the products are rapidly quenched in a heat exchanger The products produced in the reac tion depend on the composition of the feedstock the feedstocksteam ratio the cracking tempera ture and the residence time Pyrolysis processes require temperatures in the order of 750C900C 1380F1650F to produce high yields of low molecular weight products such as ethylene for petrochemical use Delayed coking which uses temperature in the order of 500C 930F is used to produced distillates from nonvolatile residua as well as coke for fuel and other usessuch as the production of electrodes for the steel and aluminum industries 4322 Catalytic Cracking Processes Catalytic cracking is the thermal decomposition of petroleum constituents in the presence of a catalyst Thermal cracking has been superseded by catalytic cracking as the process for gasoline manufacture Indeed gasoline produced by catalytic cracking is richer in branched paraffin deriva tives cycloparaffin derivatives and aromatic derivatives which all serve to increase the quality of the gasoline Catalytic cracking also results in production of the maximum amount of butene derivatives and butane derivatives C4H8 and C4H10 rather than production of ethylene and ethane C2H4 and C2H6 Catalytic cracking processes evolved in the 1930s from research on petroleum and coal liquids The petroleum work came to fruition with the invention of acid cracking The work to produce liq uid fuels from coal most notably in Germany resulted in metal sulfide hydrogenation catalysts In the 1930 a catalytic cracking catalyst for petroleum that used solid acids as catalysts was developed 154 Handbook of Petrochemical Processes using acidtreated clay minerals Clay minerals are a family of crystalline aluminosilicate solids and the acid treatment develops acidic sites by removing aluminum from the structure The acid sites also catalyze the formation of coke and Houdry developed a moving bed process that continu ously removed the cooked beads from the reactor for regeneration by oxidation with air Although thermal cracking is a free radical neutral process catalytic cracking is an ionic pro cess involving carbonium ions which are hydrocarbon ions having a positive charge on a carbon atom The formation of carbonium ions during catalytic cracking can occur by i addition of a proton from an acid catalyst to an olefin andor ii abstraction of a hydride ion H from a hydro carbon by the acid catalyst or by another carbonium ion However carbonium ions are not formed by cleavage of a carboncarbon bond In essence the use of a catalyst permits alternate routes for cracking reactions usually by lower ing the free energy of activation for the reaction The acid catalysts first used in catalytic cracking were amorphous solids composed of approximately 87 silica SiO2 and 13 alumina Al2O3 and were designated as lowalumina catalysts However this type of catalyst is now being replaced by crystalline aluminosilicates zeolites or molecular sieves The first catalysts used for catalytic cracking were acidtreated clay minerals formed into beads In fact clay minerals are still employed as catalyst in some cracking processes Speight 2014 Clay minerals are a family of crystalline aluminosilicate solids and the acid treatment develops acidic sites by removing aluminum from the structure The acid sites also catalyze the formation of coke and the development of a moving bed process that continuously removed the cooked beads from the reactor reduced the yield of coke clay regeneration was achieved by oxidation with air Clays are natural compounds of silica and alumina containing major amounts of the oxides of sodium potassium magnesium calcium and other alkali and alkaline earth metals Iron and other transition metals are often found in natural clays substituted for the aluminum cations Oxides of virtually every metal are found as impurity deposits in clay minerals Clay minerals are layered crystalline materials They contain large amounts of water within and between the layers Heating the clays above 100C can drive out some or all of this water at higher temperatures the clay structures themselves can undergo complex solid state reactions Such behavior makes the chemistry of clays a fascinating field of study in its own right Typical clays include kaolinite montmorillonite and illite They are found in most natural soils and in large relatively pure deposits from which they are mined for applications ranging from adsor bents to paper making Once the carbonium ions are formed the modes of interaction constitute an important means by which product formation occurs during catalytic cracking For example isomerization either by hydride ion shift or by methyl group shift both of which occur readily The trend is for stabilization of the carbonium ion by movement of the charged carbon atom toward the center of the molecule which accounts for the isomerization of αolefin derivatives to internal olefin derivatives when car bonium ions are produced Cyclization can occur by internal addition of a carbonium ion to a double bond which by continuation of the sequence can result in aromatization of the cyclic carbonium ion Like the paraffin derivatives naphthenes do not appear to isomerize before cracking However the naphthenic hydrocarbon derivatives from C9 upward produce considerable amounts of aro matic hydrocarbon derivatives during catalytic cracking Reaction schemes similar to that outlined here provide possible routes for the conversion of naphthenes to aromatic derivatives Alkylated benzenes undergo nearly quantitative dealkylation to benzene without apparent ring degradation below 500C 930F However polymethly benzene derivatives undergo disproportionation and isomerization with very little benzene formation Coke formation is considered with just cause to a malignant side reaction of normal carbenium ions However while chain reactions dominate events occurring on the surface and produce the majority of products certain less desirable bimolecular events have a finite chance of involving the same carbenium ions in a bimolecular interaction with one another Of these reactions most will produce a paraffin and leave carbenecarboidtype species on the surface This carbenecarboidtype 155 Feedstock Preparation species can produce other products but the most damaging product will be one which remains on the catalyst surface and cannot be desorbed and results in the formation of coke or remains in a noncoke form but effectively blocks the active sites of the catalyst A general reaction sequence for coke formation from paraffin derivatives involves oligomeriza tion cyclization and dehydrogenation of small molecules at active sites within zeolite pores Alkanes alkenes Alkenes oligomers Oligomers naphthenes Naphthenes aromatics Aromatics coke Whether or not these are the true steps to coke formation can only be surmised The problem with this reaction sequence is that it ignores sequential reactions in favor of consecutive reactions And it must be accepted that the chemistry leading up to coke formation is a complex process consisting of many sequential and parallel reactions There is a complex and little understood relationship between coke content catalyst activity and the chemical nature of the coke For instance the atomic hydrogencarbon ratio of coke depends on how the coke was formed its exact value will vary from system to system And it seems that cata lyst decay is not related in any simple way to the hydrogentocarbon atomic ratio of the coke or to the total coke content of the catalyst or any simple measure of coke properties Moreover despite many and varied attempts there is currently no consensus as to the detailed chemistry of coke for mation There is however much evidence and good reason to believe that catalytic coke is formed from carbenium ions which undergo addition dehydrogenation and cyclization and elimination side reactions in addition to the mainline chain propagation processes 433 dehydroGenation Processes Dehydrogenation processes involve the use of chemical reactions by means of which less saturated and more reactive compounds can be produced Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 There are many important conversion processes in which hydrogen is directly or indirectly removed In the current context the largestscale dehydrogena tions are those of hydrocarbon derivatives such as the conversion of paraffin derivatives to olefin derivatives olefin derivatives to diolefin derivatives CH CH CH CH CH CH CH CH 2 2 2 3 2 2 2 CH CH CH CH CH CHCH CH 2 2 2 2 Another example is the conversion of cycloparaffin derivatives to aromatic derivativesthe sim plest example of which is the conversion of cyclohexane to benzene C6H12 C6H6 3H2 156 Handbook of Petrochemical Processes Dehydrogenation reactions of less specific character occur frequently in the refining and petro chemical industries where many of the processes have names of their own Some in which dehydro genation plays a large part are pyrolysis cracking gasification by partial combustion carbonization and reforming The common primary reactions of pyrolysis are dehydrogenation and carbon bond scission The extent of one or the other varies with the starting material and operating conditions but because of its practical importance methods have been found to increase the extent of dehydrogenation and in some cases to render it almost the only reaction Dehydrogenation is essentially the removal of hydrogen from the parent molecule For example at 550C 1025F nbutane loses hydrogen to produce butene1 and butene2 The development of selective catalysts such as chromic oxide chromia Cr2O3 on alumina Al2O3 has rendered the dehydrogenation of paraffin derivatives to olefin derivatives particularly effective and the forma tion of higher molecular weight material is minimized The extent of dehydrogenation visàvis carboncarbon bond scission during the thermal cracking of petroleum varies with the starting material and operating conditions but because of its practical importance methods have been found to increase the extent of dehydrogenation and in some cases to render it almost is the only reaction Naphthenes are somewhat more difficult to dehydrogenate and cyclopentane derivatives form only aromatic derivatives if a preliminary step to form the cyclohexane structure can occur Alkyl derivatives of cyclohexane usually dehydrogenate at 480C500C 895F930F and polycyclic naphthenes are also quite easy to dehydrogenate thermally In the presence of catalysts cyclohex ane and its derivatives are readily converted into aromatic derivatives reactions of this type are prevalent in catalytic cracking and reforming Benzene and toluene are prepared by the catalytic dehydrogenation of cyclohexane and methyl cyclohexane respectively Polycyclic naphthenes can also be converted to the corresponding aromatic derivatives by heat ing at 450C 840F in the presence of a chromiaalumina Cr2O3Al2O3 catalyst Alkyl aromatic derivatives also dehydrogenate to various products For example styrene is prepared by the cata lytic dehydrogenation of ethylbenzene Other alkylbenzenes can be dehydrogenated similarly iso propylbenzene yields αmethyl styrene In general dehydrogenation reactions are difficult reactions which require high temperatures for favorable equilibria as well as for adequate reaction velocities Dehydrogenation reactionsusing reforming reactions as the exampleare endothermic and hence have high heat requirements and active catalysts are usually necessary Furthermore since permissible hydrogen partial pressures are inadequate to prevent coke deposition periodic regenerations are often necessary Because of these problems with pure dehydrogenations many efforts have been made to use oxidative dehydro genations in which oxygen or another oxidizing agent combines with the hydrogen removed This expedient has been successful with some reactions where it has served to overcome thermodynamic limitations and cokeformation problems The endothermic heat of pure dehydrogenation may be supplied through the walls of tubes 26 in id by preheating the feeds adding hot diluents reheaters between stages or heat stored in periodically regenerated fixed or fluidized solid catalyst beds Usually fairly large temperature gradients will have to be tolerated either from wall to center of tube from inlet to outlet of bed or from start to finish of a processing cycle between regenerations The ideal profile of a constant tem perature or even a rising temperature is seldom achieved in practice In oxidative dehydrogenation reactions the complementary problem of temperature rise because of exothermic nature of the reac tion is encountered Other characteristic problems met in dehydrogenations are the needs for rapid heating and quenching to prevent side reactions the need for low pressure drops through catalyst beds and the selection of reactor materials that can withstand the operating conditions Selection of operating conditions for a straight dehydrogenation reaction often requires a com promise The temperature must be high enough for a favorable equilibrium and for a good reaction rate but not as high as to cause excessive cracking or catalyst deactivation The rate of the dehydro genation reaction diminishes as conversion increases not only because equilibrium is approached 157 Feedstock Preparation more closely but also because in many cases reaction products act as inhibitors The ideal tempera ture profile in a reactor would probably show an increase with distance but practically attainable profiles normally are either flat or show a decline Large adiabatic beds in which the decline is steep are often used The reactor pressure should be as low as possible without excessive recycle costs or equipment size Usually the pressure is close to near atmospheric pressure but reduced pressures have been used in the Houdry butane dehydrogenation process In any case the catalyst bed must be designed for a low pressure drop Rapid preheating of the feed is desirable to minimize cracking Usually this is done by mixing preheated feedstock with superheated diluent just as the two streams enter the reactor Rapid cool ing or quenching at the exit of the reactor is usually necessary to prevent condensation reactions of the olefinic products Materials of construction must be resistant to attack by hydrogen capable of prolonged operation at high temperature and not be unduly active for conversion of hydrocarbon derivatives to carbon Alloy steels containing chromium are usually favored although steel alloys containing nickel are also used but these latter alloys can cause problems arising from carbon for mation If steam is not present traces of sulfur compounds may be needed to avoid carbonization Both steam and sulfur compounds act to keep metal walls in a passive condition In fact fluid catalytic cracking has been the second major supplier of propylene after steam cracking and has proven high flexibility in feedstock and product slate Crude oil cracking in a fluid catalytic cracking process may appear as an ideal candidate to fulfill petrochemical producers needs Fluid catalytic cracking units usually run on vacuum distillation products namely vacuum gas oil and vacuum residue VR Also atmospheric residue AR can be used as a feedstock for the fluid catalytic cracking unit In some small refineries it was shown that the fluid catalytic cracking unit could substitute the main distillation unit separating and converting the heavy part of the crude oil all in once Problems associated with heavy material or metals in crude oil are readily addressed by residuum fluid catalytic cracking technology which treats precisely the heaviest part of the crude Lighter fractions of the crude especially the paraffinic naphtha will crack to a lower extent under traditional fluid catalytic cracking conditions This problem has also been studied by most of the refiners with the aim of increasing propylene and ethylene yield in the fluid catalytic cracking unit All the technologies developed to enhance olefin yield from fluid catalytic cracking are of high interest for converting crude to petrochemicals Parkash 2003 Gary et al 2007 Speight 2008 2011 2014 2015 Hsu and Robinson 2017 Speight 2017 Such a technology may probably be based on a conversion unit that can handle the highboiling constituents of the crude oil converting it partially to light olefin derivatives and reducing the amount of highboiling products to minimum A modified fluid catalytic cracking process would be an ideal candidate and other unitssuch as a steam cracking unitmay also be added to complement the fluid catalytic cracking unit to produce low molecular weight olefin derivatives from the lowerboiling fractions from the fluid catalytic unit 434 dehydrocyclization Processes Catalytic aromatization involving the loss of 1 mol of hydrogen followed by ring formation and fur ther loss of hydrogen has been demonstrated for a variety of paraffin derivatives typically nhexane and nheptane Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Thus nhexane can be converted to benzene heptane is converted to toluene and octane is converted to ethyl benzene and oxylene Conversion takes place at low pressures even atmo spheric and at temperatures above 300C 570F although 450C550C 840F1020F is the preferred temperature range The catalysts are metals or their oxides of the titanium vanadium and tungsten groups and are generally supported on alumina the mechanism is believed to be dehydrogenation of the paraffin to an olefin which in turn is cyclized and dehydrogenated to the aromatic hydrocarbon In support of this olefin derivatives can be converted to aromatic derivatives much more easily than the cor responding paraffin derivatives 158 Handbook of Petrochemical Processes 44 STREAMS FROM COAL OIL SHALE AND BIOMASS 441 coal 4411 Coal Gas Gases produced from coal invariably contain constituents that are damaging to the climate or environmentthese will be constituents such as carbon dioxide CO2 nitrogen oxides NOx sulfur oxides SOx dust and particles and toxins such as dioxin and mercury The processes that have been developed for gas cleaning vary from a simple oncethrough wash operation to complex multistep systems with options for recycle of the gases Speight 2007 Mokhatab et al 2006 Speight 2014 In some cases process complexities arise because of the need for recovery of the materials used to remove the contaminants or even recovery of the contaminants in the original form or in the altered form The purpose of preliminary cleaning of gases which arise from coal utilization is the removal of materials such as mechanically carried solid particles either process products andor dust as well as liquid vapors ie water tars and aromatics such as benzenes andor naphthalene derivatives in some instances preliminary cleaning might also include the removal of ammonia gas For example cleaning of town gas is the means by which the crude tarcarrying gases from retorts or coke ovens are first in a preliminary step freed from tarry matter condensable aromatics such as naphtha lene and second purified by removal of materials such as hydrogen sulfide other sulfur com pounds and any other unwanted components that will adversely affect the use of the gas In more general terms gas cleaning is divided into i removal of particulate impurities and ii removal of gaseous impurities For the purposes of this section the latter operation includes the removal of hydrogen sulfide carbon dioxide sulfur dioxide and the like There is also need for subdivision of these two categories as dictated by needs and process capa bilities i coarse cleaning whereby substantial amounts of unwanted impurities are removed in the simplest most convenient manner ii fine cleaning for the removal of residual impurities to a degree sufficient for the majority of normal chemical plant operations such as catalysis or prepara tion of normal commercial products or cleaning to a degree sufficient to discharge an effluent gas to atmosphere through a chimney iii ultrafine cleaning where the extra step is justified by the nature of the subsequent operations or the need to produce a particularly pure product Since coal is a complex heterogeneous material there is a wide variety of constituents that are not required in a final product and must be removed during processing Coal composition and char acteristics vary significantly there are varying amounts of sulfur nitrogen and trace metal species which must be disposed in the correct manner Speight 2008 Thus whether the process be gasifi cation to produce a pipeline quality gas or a series of similar steps for gas cleaning before use as a petrochemical feedstocks the stages required during this processing are numerous and can account for a major portion of a gas cleaning facility Generally the majority of the sulfur that occurs naturally in the coal is driven into the product gas Thermodynamically the majority of the sulfur should exist as hydrogen sulfide with smaller amounts of carbonyl sulfide COS and carbon disulfide CS2 However data from some operations show higher than expected from thermodynamic considerations concentrations of carbonyl sulfide and carbon disulfide The existence of mercaptan derivatives thiophene derivatives and other organic sulfur compounds in gasifier product gas will probably be a function of the degree of severity of the process contact ing schemes and heatup rate Those processes that tend to produce tarry products and oil products may also tend to drive off high molecular weight organic sulfur compounds into the raw product gas 4412 Coal Liquids The conversion of coal to liquids and the upgrading of the coal liquids have been considered as future alternatives of petroleum to produce synthetic liquid fuels Since the late 1970s coal liq uefaction processes have been developed into integrated twostage processes in which coal is 159 Feedstock Preparation hydroliquefied in the first stage and the coal liquids are upgraded in the second stage Upgrading of the coal liquids is an important aspect of this approach and may determine whether such liquefac tion can be economically feasible Liquid products from coal are generally different from those produced by petroleum refining particularly as they can contain substantial amounts of phenols Therefore there will always be some question about the place of coal liquids in refining operations In more generic terms the liquid products from coal may be classified as neutral oils essentially pure hydrocarbons tar acids phenols and tar bases basic nitrogen compounds that a refinery must accommodate to produce the necessary hydrocarbon derivatives for the production of petrochemicals The neutral oils making up 8085 vv of hydrogenated coal distillate are approximately half aromatic compounds including polycyclic aromatic hydrocarbons Typical components of the neu tral oils are benzene naphthalene and phenanthrene Hydroaromatic compounds cycloparaffins also called naphthenes are another important component of neutral oils Hydroaromatic com pounds are formed at high hydrogen pressures in the presence of a catalyst but in the presence of another species capable of accepting hydrogen such as unreacted coal hydroaromatic species lose hydrogen to form the thermodynamically more stable aromatic compounds and are important intermediates in the transfer of hydrogen to unreacted coal during liquidphase coal hydrogenation and solvent refining of coal The next most abundant component of neutral oil consists of liquid olefins The olefins are reac tive and tend to undergo polymerization oxidation and other reactions causing changes in the properties of the product with time On the other hand olefins are excellent raw materials for the manufacture of synthetic polymers Chapter 11 and other chemicals and thus can be valuable chemical byproducts in coal liquids In addition to neutral oil coal liquids contain tar acids consisting of phenolic compounds which may constitute from 5 to 15 ww of many coal liquids They constitute one of the major differences between coal liquids and natural petroleum which has a much lower content of oxygencontaining compounds and although tar acids are valuable chemical raw materials they are troublesome to catalysts in refining processes Tar bases containing basic nitrogen make up 24 ww of coal hydrogenation liquids Tar bases are made of a variety of compounds such as pyridine quinoline aniline and higher molecular weight analogs Because of these products coal liquids have remained largely unacceptable as refinery feed stocks because of their high concentrations of aromatic compounds and high heteroatom and metals content Speight 2008 2014 Successful upgrading process will have to achieve significant reduc tions in the content of the aromatic components 442 oil shale 4421 Oil Shale Gas Oil shale gas is produced by retorting pyrolysis of oil shale 2012 In the pyrolysis process oil shale is heated until the kerogen in the shale decomposes There is no exact formula for oil shale gasthe composition of the gas depends of retorted oil shale and exploited technology Typical components of oil shale gas are usually methane hydrogen carbon monoxide carbon dioxide and nitrogen as well as hydrocarbon derivatives such as ethylene The gas may also contain hydrogen sulfide and other impurities The initial composition of the crude shale oil produced in the retorting step is the primary influ ence in the design of the subsequent upgrading operation In particular nitrogen compounds sulfur compounds and other nonhydrocarbon constituents dictate the cleaning processes that are selected Mokhatab et al 2006 Speight 2018 This being the case the gas can be subjected to cleaning in a natural gas processing plant but only after detailed analysis of the gas The analysis would assist in the determination of not only 160 Handbook of Petrochemical Processes the constituents of the gas but also the relative amounts of each constituents and the necessary adjustment that would have to be made to accept the gas for cleaning in a conventional natural gas processing plant 4422 Shale Oil Shale oil is a synthetic crude oil produced by retorting oil shale and is the pyrolysis product of the organic matter kerogen contained in oil shale The raw shale oil produced from retorting oil shale can vary in properties and composition and as the oil exits the retort it is by no means a pure distil late and usually contains emulsified water and suspended solids Speight 2008 2012 Therefore the first step in upgrading is usually dewatering and desalting Furthermore if not removed the arsenic and iron in shale oil would poison and foul the supported catalysts used in hydrotreating Because these materials are soluble they cannot be removed by filtration Several methods have been used specifically to remove arsenic and iron Other methods involve hydrotreating these also lower sulfur olefin and diolefin contents and thereby make the upgraded product less prone to gum formation After these steps the shale oil may be suitable for admittance to typical refinery processing Compared with petroleum shale oil is high in nitrogen and oxygen compounds and a higher spe cific gravityin the order of 0910 owing to the presence of highboiling nitrogen sulfur and oxygencontaining compounds Shale oil also has a relatively high pour point and small quantities of arsenic and iron are also present The chemical potential of oil shales is as a retort fuel to produce shale oil and from that liquid fuel and specialty chemicals have been used so far to a relatively small extent Using stepwise crack ing various liquid fuels have been produced and even exported before World War II At the same time shale oils possess molecular structures of interest to the specialty chemicals industry and also a number of nonfuel specialty products have been marketed based on functional group broad range concentrate or even pure compound values Shale oil is a complex mixture of hydrocarbon derivatives and it is characterized using bulk prop erties of the oil Shale oil usually contains large quantities of olefin derivatives and aromatic hydro carbon derivatives as well as significant quantities of heteroatom compounds nitrogen containing compounds oxygencontaining compounds and sulfurcontaining compounds A typical shale oil composition includes nitrogen 152 ww oxygen 051 ww and sulfur 0151 ww as well as mineral particles and metalcontaining compounds Speight 2008 Generally the oil is less fluid than crude oil and becoming which is reflected in the pour point that is in the order of 24C27C 75F81F while conventional crude oil has a pour point in the order of 60C to 30C 76F to 86F that affects the ability of shale oil to be transported using unheated pipelines Shale oil also contains polycyclic aromatic hydrocarbon derivatives The initial composition of the crude shale oil produced in the retorting step is the primary influ ence in the design of the subsequent upgrading operation In particular nitrogen compounds sulfur compounds and organometallic compounds dictate the upgrading process that is selected Crude shale oil typically contains nitrogen compounds throughout the total boiling range of shale oil in concentrations that are 1020 times the amounts found in typical crude oils Speight 2012 Removal of the nitrogenbearing compounds is an essential requirement of the upgrading effort since nitrogen is poisonous to most catalysts used in subsequent refining steps and creates unaccept able amounts of NOx pollutants when nitrogencontaining fuels are burned As with shale oil gas the shale oil can be subjected to refining in a petroleum refinery but only after detailed analysis of the oil The analysis would assist in the determination of not only the con stituents of the oil but also the relative amounts of each constituents and the necessary adjustment that would have to be made to accept the oil by the refinery Thus upgrading activities are dictated by factors such as the initial composition of the oil shale the compositions of retorting products the composition and quality of desired petroleum feedstocks or petroleum end products of market quality and the decision to develop other byproducts such as sulfur and ammonia into salable products 161 Feedstock Preparation 443 Biomass The utilization of biomass to produce valuable products by thermal processes is an important aspect of biomass technology Speight 2008 Biomass pyrolysis gives usually rise to three phases i gases ii condensable liquids and iii charcoke However there are various types of related kinetic pathways ranging from very simple paths to more complex paths and all usually include several elementary processes occurring in series or in competition As anticipated the kinetic paths are different for cellulose lignin and hemicelluloses biomass main basic components and also for usual biomasses according to their origin composition and inorganic contents The main biomass constituentshemicellulose cellulose and lignincan be selectively devol atilized into valueadded chemicals This thermal breakdown is guided by the order of thermo chemical stability of the biomass constituents that ranges from hemicellulose as the least stable constituent to the more stablelignin exhibits an intermediate thermal degradation behavior Thus wood constituents are decomposed in the order of hemicellulosecelluloselignin with a restricted decomposition of the lignin at relatively low temperatures With prolonged heating condensation of the lignin takes place whereby thermally large stable macromolecules develop Whereas both hemicellulose and cellulose exhibit a relatively high devolatilization rate over a relatively narrow temperature range thermal degradation of lignin is a slowrate process that commences at a lower temperature when compared to cellulose Since the thermal stabilities of the main biomass constituents partially overlap and the thermal treatment is not specific a careful selection of temperatures heating rates and gas and solid resi dence times is required to make a discrete degasification possible when applying a stepwise increase in temperature Depending on these process conditions and parameters such as composition of the biomass and the presence of catalytically active materials the product mixture is expected to con tain degradation products from hemicellulose cellulose or lignin As stated elsewhere a major issue in the use of biomass is one of feedstock diversity Biomass based feedstock materials used in producing chemicals can be obtained from a large variety of sources If considered individually the number of potential renewable feedstocks can be over whelming but they tend to fall into three simple categories i waste materials such as food pro cessing wastes ii dedicated feedstock crops which includes and short rotation woody crops or herbaceous energy crops such as perennials or forage crops and iii conventional food crops such as corn and wheat In addition these raw materials are composed of several similar chemical con stituents ie carbohydrates proteins lipids lignin and minerals 4431 Biogas Most biomass materials are easier to convert to gas than coal because they are more reactive with higher ignition stability This characteristic also makes them easier to process thermochemically into highervalue fuels such as methanol or hydrogen Ash content is typically lower than in most coals and the sulfur content of the biomass is much lower than in many fossil fuels The mineral content of biomass can vary as a function of soil type and the timing of feedstock harvest Biogas contains methane and can be recovered in industrial anaerobic digesters and mechanical biological treatment systems Landfill gas is a less clean form of biogas which is produced in landfills through naturally occurring anaerobic digestion This being the case the gas can only be subjected to cleaning in a natural gas processing plant after detailed analysis of the gas The analysis would assist in the determination of not only the constituents of the gas but also the relative amounts of each constituents and the necessary adjustment that would have to be made to accept the gas for cleaning in a conventional natural gas processing plant 4432 Bioliquids Hydrocarbon derivatives are products of various plant species belonging to different families which convert a substantial amount of photosynthetic products into latex The latex of such plants contains 162 Handbook of Petrochemical Processes liquid hydrocarbon derivatives of high molecular weight These hydrocarbon derivatives can be converted into highgrade transportation fuel Biooil is a product that is produced by pyrolysis flash pyrolysis that occurs when solid fuels are heated at temperatures between 350C and 500C 570F930F for a very short period of time 2 s The biooils currently produced are suitable for use in boilers for electricity genera tion In another process the feedstock is fed into a fluidized bed at 450C500C 840F930F and the feedstock flashes and vaporizes The resulting vapors pass into a cyclone where solid particles char are extracted The gas from the cyclone enters a quench tower where they are quickly cooled by heat transfer using biooil already made in the process The biooil condenses into a product receiver and any noncondensable gases are returned to the reactor to maintain process heating Thus petroleum refineries can be an alternative source for obtaining petroleum to be used in diesel engines However hydrocarbon derivatives as such are not usually produced from crops there being insufficient amount of the hydrocarbon derivatives present in the plant tissue to make the process economical REFERENCES AbdelAal HK Aggour MA and Fahim MA 2016 Petroleum and Gas Field Processing CRC Press Boca Raton FL Abraham H 1945 Asphalts and Allied Substances Van Nostrand Scientific Publishers New York ASTM D3246 2018 Standard Test Method for Sulfur in Petroleum Gas by Oxidative Microcoulometry ASTM International West Conshohocken PA Barbouteau L and Dalaud R 1972 Chapter 7 In Gas Purification Processes for Air Pollution Control G Nonhebel Editor Butterworth and Co London UK Curry RN 1981 Fundamentals of Natural Gas Conditioning PennWell Publishing Co Tulsa OK Forbes R J 1958a A History of Technology Oxford University Press Oxford UK Forbes R J 1958b Studies in Early Petroleum Chemistry E J Brill Leiden The Netherlands Forbes RJ 1959 More Studies in Early Petroleum Chemistry EJ Brill Leiden The Netherlands Forbes R J 1964 Studies in Ancient Technology E J Brill Leiden The Netherlands Gary JG Handwerk GE and Kaiser MJ 2007 Petroleum Refining Technology and Economics 5th Edition CRC Press Boca Raton FL Hoiberg AJ 1960 Bituminous Materials Asphalts Tars and Pitches I II Interscience New York Hsu CS and Robinson PR Editors 2017 Handbook of Petroleum Technology Springer Cham Switzerland Jou FY Otto FD and Mather AE 1985 Chapter 10 In Acid and Sour Gas Treating Processes SA Newman Editor Gulf Publishing Company Houston TX Katz DK 1959 Handbook of Natural Gas Engineering McGrawHill Book Company New York Kidnay AJ and Parrish WR 2006 Fundamentals of Natural Gas Processing CRC Press Boca Raton FL Kohl AL and Riesenfeld FC 1985 Gas Purification 4th Edition Gulf Publishing Company Houston TX Kohl AL and Nielsen RB 1997 Gas Purification Gulf Publishing Company Houston TX Maddox RN 1982 Gas Conditioning and Processing Volume 4 Gas and Liquid Sweetening Campbell Publishing Co Norman OK Maddox RN Bhairi A Mains GJ and Shariat A 1985 Chapter 8 In Acid and Sour Gas Treating Processes SA Newman Editor Gulf Publishing Company Houston TX Mody V and Jakhete R 1988 Dust Control Handbook Noyes Data Corp Park Ridge NJ Mokhatab S Poe WA and Speight JG 2006 Handbook of Natural Gas Transmission and Processing Elsevier Amsterdam Netherlands Newman SA 1985 Acid and Sour Gas Treating Processes Gulf Publishing Houston TX Parkash S 2003 Refining Processes Handbook Gulf Professional Publishing Elsevier Amsterdam Netherlands Pitsinigos VD and Lygeros AI 1989 Predicting H2SMEA Equilibria Hydrocarbon Processing 584 4344 Polasek J and Bullin J 1985 Chapter 7 In Acid and Sour Gas Treating Processes SA Newman Editor Gulf Publishing Company Houston TX 163 Feedstock Preparation Soud H and Takeshita M 1994 FGD Handbook No IEACR65 International Energy Agency Coal Research London UK Speight JG 1978 Personal Observations at Archeological Digs at The Cities of Babylon Calah Nineveh and Ur College of Science University of Mosul Iraq Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG 2008 Synthetic Fuels Handbook Properties Processes and Performance McGrawHill New York Speight JG Editor 2011 The Biofuels Handbook Royal Society of Chemistry London UK Speight JG 2012 Shale Oil Production Processes Gulf Professional Publishing Elsevier Oxford UK Speight JG 2014 The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Speight JG 2015 Handbook of Petroleum Product Analysis 2nd Edition John Wiley Sons Inc Hoboken NJ Speight JG 2017 Handbook of Petroleum Refining CRC Press Boca Raton FL Speight JG 2018 Handbook of Natural Gas Analysis John Wiley Sons Inc Hoboken NJ Taylor Francis 165 5 Feedstock Preparation by Gasification 51 INTRODUCTION The influx of viscous feedstocks such as heavy oil extra heavy oil and tar sand bitumen into refin eries creates and will continue to create challenges but at the same time it also creates opportuni ties by improving the ability of refineries to handle viscous feedstocks thereby enhancing refinery flexibility to meet the increasingly stringent product specifications for refined fuels Speight 2013a 2014a 2014b Upgrading viscous feedstocks is an increasingly prevalent means of extracting the maximum amount of liquid fuels from each barrel of crude oil that enters the refinery Although solvent deasphalting processes Chapter 14 and coking processes Chapter 10 are used in refiner ies to upgrade viscous feedstocks to intermediate products which are then processed further to produce transportation fuels the integration of viscous feedstock processing units and gasifica tion presents some unique synergies that will enhance the performance of the future refinery by preparing otherwise difficult to refine feedstocks to feedstocks that are suitable for the production of petrochemicals Figures 51 and 52 Wallace et al 1998 Furimsky 1999 Penrose et al 1999 Gray and Tomlinson 2000 Abadie and Chamorro 2009 Wolff and Vliegenthart 2011 Speight 2011b 2014a Gasification offers more scope for recovering products from waste than incineration When waste is burnt in a modern incinerator the only practical product is energy whereas the gases oils and solid char from pyrolysis and gasification cannot only be used as a fuel but also purified and used as a feedstock for petrochemicals and other applications Many processes also produce a stable granulate instead of an ash that can be more easily and safely utilized In addition some processes are targeted at producing specific recyclables such as metal alloys and carbon black From waste gasification in particular it is feasible to produce hydrogen that many see as an increasingly valu able resource Gasification can be used in conjunction with gas engines and potentially gas turbines to obtain higher conversion efficiency than conventional fossil fuel energy generation By displacing fossil fuels waste pyrolysis and gasification can help meet renewable energy targets address concerns FIGURE 51 The gasification process can accommodate a variety of carbonaceous feedstocks 166 Handbook of Petrochemical Processes about global warming and contribute to achieving Kyoto Protocol commitments Conventional incineration used in conjunction with steamcycle boilers and turbine generators achieves lower efficiency Many of the processes fit well into a modern integrated approach to waste management They can be designed to handle the waste residues and are fully compatible with an active program of composting for the waste fraction that is subject to decay and putrefaction A wide range of materials can be handled by gasification technologies and specific processes have been optimized to handle particular feedstock eg tire pyrolysis and sewage sludge gasifica tion while others have been designed to process mixed wastes For example recovering energy from agricultural and forestry residues household and commercial waste materials recycling auto shredder residue electrical and electronic scrap tires mixed plastic waste and packaging residues are feasible processes Briefly gasification is a process in which combustible materials are partially oxidized or partially combusted The product of gasification is a combustible synthesis gas also referred to as syngas Because gasification involves the partial rather than complete oxidization of the feed gasification processes operate in an oxygenlean environment The process has grown from a predominately coal conversion process used for making town gas for industrial lighting to an advanced process for the production of multiproduct carbonbased fuels from a variety of feedstocks such as crude oil viscous feedstocks biomass or other carbonaceous feedstocks Figure 51 Kumar et al 2009 Speight 2013a 2014a 2014b Luque and Speight 2015 Gasification is an appealing process for the utilization of relatively inexpensive feedstocks that might otherwise be declared as waste and sent to a landfill where the production of methanea socalled greenhouse gaswill be produced or combusted which may not depending upon the feedstock be energy efficient Overall use of a gasification technology Speight 2013a 2014b with the necessary gas cleanup options can have a smaller environmental footprint and lesser effect on the environment than landfill operations or combustion of the waste In fact there are strong indi cations that gasification is a technically viable option for the waste conversion including residual waste from separate collection of municipal solid waste MSW The process can meet existing emission limits and can have a significant effect on the reduction of landfill disposal using known gasification technologies Arena 2012 Speight 2014b Luque and Speight 2015 or thermal plasma Fabry et al 2013 In the gasification process organic carbonaceous feedstocks into carbon monoxide carbon dioxide and hydrogen by reacting the feedstock at high temperatures 700C 1290F without FIGURE 52 Gasification as might be employed onsite in a refinery Source National Energy Technology Laboratory United States Department of Energy Washington DC wwwnetldoegovtechnologies coalpower gasificationgasifipedia7advantages734refineryhtml 167 Feedstock Preparation by Gasification combustion with a controlled amount of oxygen andor steam Marano 2003 Lee et al 2007 Higman and Van der Burgt 2008 Speight 2008 Sutikno and Turini 2012 Speight 2013a 2014b Unconventional carbonaceous feedstocks include solids liquids and gases such as heavy oil extra heavy oil tar sand bitumen residua and biomass Speight 2014b The gasification is not a single step process but involves multiple subprocesses and reactions The generated synthesis gas has wide range of applications ranging from power generation to chemicals production The power derived from the gasification of carbonaceous feedstocks followed by the combustion of the product gases is considered to be a source of renewable energy of derived gaseous products Table 51 that are generated from a carbonaceous source eg biomass other than a fossil fuel Speight 2008 Indeed the increasing interest in gasification technology reflects a convergence of changes in providing energy to the marketplace i the maturity of gasification technology and ii the extremely low emissions from integrated gasification combined cycle IGCC plants especially air emissions and iii the potential for control of greenhouse gases Speight 2014b Another advan tage of gasification is the use of synthesis gas is potentially more efficient as compared to direct combustion of the original fuel because it can be i combusted at higher temperatures ii used in fuel cells iii used to produce methanol and hydrogen iv converted via the FischerTropsch FT process into a range of synthesis liquid fuels suitable for use of gasoline engines or diesel engines Chadeesingh 2011 Luque and Speight 2015 Coal has been the primary feedstock for gasification units for many decades However there is a move to feedstocks other than coal for gasification processes with the concern on the issue of envi ronmental pollutants and the potential shortage for coal in some area except at the United States Speight 2014b Nevertheless coal still prevails as a gasification feedstock and will remain so for at least several decades into the future if not well into the next century Speight 2011b 2013a Luque and Speight 2015 The gasification process can also utilize carbonaceous feedstocks which would otherwise have been disposed eg biodegradable waste Coal gasification plants are cleaner with respect to standard pulverized coal combustion facil ities producing fewer sulfur and nitrogen byproducts which contribute to smog and acid rain For this reason gasification appeals as a way to utilize relatively inexpensive and expansive coal reserves while reducing the environmental impact Indeed the increasing mounting interest in coal gasification technology reflects a convergence of two changes in the electricity generation market place i the maturity of gasification technology and ii the extremely low emissions from IGCC plants especially air emissions and the potential for lower cost control of greenhouse gases than other coalbased systems Fluctuations in the costs associated with natural gasbased power which is viewed as a major competitor to coalbased power can also play a role Furthermore gasification TABLE 51 Gasification Products Product Properties Low Btu gas 150300 Btuscf Approximately 50 vv nitrogen Smaller amounts of carbon monoxide and hydrogen Some carbon dioxide Trace amounts of methane Medium Btu gas 300550 Btuscf Predominantly carbon monoxide and hydrogen Small amounts of methane Some carbon dioxide High Btu gas 9801080 Btuscf Predominantly methanetypically 85 vv 168 Handbook of Petrochemical Processes permits the utilization of various feedstocks coal biomass crude oil resids and other carbona ceous wastes to their fullest potential Speight 2013a 2014b Orhan et al 2014 Thus power developers would be well advised to consider gasification as a means of converting coal to gas Liquid fuels including gasoline diesel naphtha and jet fuel are usually processed from crude oil in the refinery Speight 2014a However with fluctuating availability and varying prices of crude oil liquid fuels from coal coaltoliquids CTL and liquid fuels from biomass biomasstoliquids BTL are always under consideration as alternative routes used for liquid fuel production Both coal and biomass are converted to synthesis gas which is subsequently converted into a mixture of liquid products by FT processes Chadeesingh 2011 Speight 2013a Adhikari et al 2015 The liquid fuel obtained after FT synthesis is eventually upgraded using known crude oil refinery tech nologies to produce gasoline naphtha diesel fuel and jet fuel Chadeesingh 2011 Speight 2014a 52 GASIFICATION CHEMISTRY It is important to distinguish gasification from pyrolysis The main difference between pyrolysis and gasification is the absence of a gasifying agent in the case of pyrolysis Pyrolysis is a ther mal degradation of organic compounds at a range of temperatures in the order of 300C900C 570F1650F under oxygendeficient circumstances to produce various forms of products such as gases often referred to as biogas a liquid product referred to as called biooil and a solid product referred to as biochar whereas gasification is a thermal cracking of solid carbonaceous material into a combustible gas mixture mainly composed of hydrogen carbon monoxide CO carbon dioxide CO2 and methane CH4 and other gases with some byproducts solid char or slag oils and water The produced gaseous product has chemical composition and properties that are largely affected by the operational conditions throughout pyrolysis and gasification such as reactor temperature residence time pressure that are affected by the feedstock type and composition as well as the reactor geometry Thus pyrolysis and gasification are complex chemical mechanisms which incorporate several operational and environmental challenges of carbonbased feedstock In the current context gasification involves the thermal decomposition of the feedstock and the reaction of the feedstock carbon and other pyrolysis products with oxygen water and fuel gases such as methane and is represented by a sequence of simple chemical reactions Table 52 However the gasification process is often considered to involve two distinct chemical stages i devolatilization TABLE 52 Reactions that Occur During Gasification of a Carbonaceous Feedstock 2C O 2CO 2 C O2 CO2 C CO 2CO 2 CO H O CO H shift reaction 2 2 2 C H O CO H water gasreaction 2 2 C 2H CH 2 4 2H O 2H O 2 2 2 CO 2H CH OH 2 3 CO 3H CH H O methanation reaction 2 4 2 CO 4H CH 2H O 2 2 4 2 C 2H O 2H CO 2 2 2 2C H C H 2 2 2 CH 2H O CO 4H 4 2 2 2 169 Feedstock Preparation by Gasification of the feedstock to produce volatile matter and char ii followed by char gasification which is complex and specific to the conditions of the reactionboth processes contribute to the complex kinetics of the gasification process Sundaresan and Amundson 1978 Gasification of a carbonaceous material in an atmosphere of carbon dioxide can be divided into two stages i pyrolysis and ii gasification of the pyrolytic char In the first stage pyrolysis removal of moisture content and devolatilization occurs at comparatively lower temperature In the second stage gasification of the pyrolytic char is achieved by reaction with oxygencarbon dioxide mixtures at high temperature In nitrogen and carbon dioxide environments from room tempera ture to 1000C 1830F the mass loss rate of pyrolysis in nitrogen may be significant differently sometime lower depending on the feedstock to mass loss rate in carbon dioxide which may be due in part to the difference in properties of the bulk gases 521 General asPects Generally the gasification of carbonaceous feedstocks such as heavy oil extra heavy oil tar sand bitumen crude oil residua biomass and waste includes a series of reaction steps that convert the feedstock into synthesis gas carbon monoxide CO plus hydrogen H2 and other gaseous products This conversion is generally accomplished by introducing a gasifying agent air oxygen andor steam into a reactor vessel containing the feedstock where the temperature pressure and flow pattern moving bed fluidized or entrained bed are controlled The gaseous productsother than carbon monoxide and hydrogenand the proportions of these product gases such as carbon dioxide CO2 methane CH4 water vapor H2O hydrogen sulfide H2S and sulfur dioxide SO2 depends on i the type of feedstock ii the chemical composition of the feedstock iii the gasifying agent or gasifying medium as well as iv the thermodynamics and chemistry of the gasification reactions as controlled by the processoperating parameters Singh et al 1980 Pepiot et al 2010 Shabbar and Janajreh 2013 Speight 2013a 2013b 2014b In addi tion the kinetic rates and extents of conversion for the several chemical reactions that are a part of the gasification process are variable and are typically functions of i temperature ii pressure iii reactor configuration iv gas composition of the product gases and v whether or not these gases influence the outcome of the reaction Johnson 1979 Speight 2013a 2013b 2014b In a gasifier the feedstock is exposed to high temperatures generated from the partial oxida tion of the carbon As the particle is heated any residual moisture assuming that the feedstock has been prefired is driven off and further heating of the particle begins to drive off the volatile gases Discharge of the volatile products will generate a wide spectrum of hydrocarbon derivatives ranging from carbon monoxide and methane to longchain hydrocarbon derivatives comprising distillable tar and nondistillable pitch The complexity of the products will also affect the prog ress and rate of the reaction when each product is produced by a different chemical process at a different rate At a temperature above 500C 930F the conversion of the feedstock to char and ash is completed In most of the early gasification processes this was the desired byproduct but for gas generation the char provides the necessary energy to effect further heating andtypically the char is contacted with air or oxygen and steam to generate the product gases Furthermore with an increase in heating rate feedstock particles are heated more rapidly and are burned in a higher temperature region but the increase in heating rate has almost no substantial effect on the mechanism Irfan 2009 Most notable effects in the physical chemistry of the gasification process are those effects due to the chemical character of the feedstock as well as the physical composition of the feedstock Speight 2011a 2013a 2014a 2014b In more general terms of the character of the feedstock gas ification technologies generally require some initial processing of the feedstock with the type and degree of pretreatment a function of the process andor the type of feedstock Another factor often presented as very general rule of thumb is that optimum gas yields and gas quality are obtained at operating temperatures of approximately 595C650C 1100F1200F A gaseous product with 170 Handbook of Petrochemical Processes a higher heat content BTUft3 can be obtained at lower system temperatures but the overall yield of gas determined as the fueltogas ratio is reduced by the unburned char fraction With some feedstocks the higher the amounts of volatile material produced in the early stages of the process the higher the heat content of the product gas In some cases the highest gas quality may be produced at the lowest temperatures but when the temperature is too low char oxidation reaction is suppressed and the overall heat content of the product gas is diminished All such events serve to complicate the reaction rate and make derivative of a global kinetic relationship applicable to all types of feedstock subject to serious question and doubt Depending on the type of feedstock being processed and the analysis of the gas product desired pressure also plays a role in product definition In fact some or all of the following processing steps will be required i pretreatment of the feedstock ii primary gasification of the feedstock iii secondary gasification of the carbonaceous residue from the primary gasifier iv removal of carbon dioxide hydrogen sulfide and other acid gases v shift conversion for adjustment of the carbon mon oxidehydrogen mole ratio to the desired ratio and vi catalytic methanation of the carbon monoxide hydrogen mixture to form methane If high heat content highBtu gas is desired all of these process ing steps are required since gasifiers do not typically yield methane in the significant concentration 522 Pretreatment While feedstock pretreatment for introduction into the gasifier is often considered to be a physi cal process in which the feedstock is prepared for gasifiertypically as pellets or finely ground feedstockthere are chemical aspects that must also be considered Some feedstocks especially certain types of coal display caking or agglomerating charac teristics when heated Speight 2013a and these coal types are usually not amenable to treatment by gasification processes employing fluidized bed or movingbed reactors in fact caked coal is difficult to handle in fixed bed reactors The pretreatment involves a mild oxidation treatment that destroys the caking characteristics of coals and usually consists of lowtemperature heating of the coal in the presence of air or oxygen While this may seemingly be applicable to coal gasification only this form of coal pretreatment is particularly important when a noncoal feedstock is cogasified with coal Cogasification of other feedstocks such as coal and especially biomass with crude oil coke offers a bridge between the depletion of crude oil stocks when coal is used as well as a supplementary feedstock based on renewable energy sources biomass These options can contribute to reduce the crude oil depen dency and carbon dioxide emissions since biomass is known to be neutral in terms of carbon dioxide emissions The high reactivity of biomass and the accompanying high production of volatile prod ucts suggest that some synergetic effects might occur in simultaneous thermochemical treatment of petcoke and biomass depending on the gasification conditions such as i feedstock type and origin ii reactor type and iii process parameters Penrose et al 1999 Gray and Tomlinson 2000 McLendon et al 2004 Lapuerta et al 2008 Fermoso et al 2009 Shen et al 2012 Khosravi and Khadse 2013 Speight 2013a 2014a 2014b Luque and Speight 2015 For example carbonaceous fuels are gasified in reactors a variety of gasifiers such as the fixed or moving bed fluidized bed entrained flow and molten bath gasifiers have been developed that have differing feedstock requirements Table 53 Shen et al 2012 Speight 2014b If the flow patterns are considered the fixed bed and fluidized bed gasifiers intrinsically pertain to a countercurrent reactor in which the fuels are usually sent into the reactor from the top of the gasifier whereas the oxidant is blown into the reactor from the bottom With regard to the entrained flow reactor it is necessary to pulverize the feedstock such as coal and petcoke On the other hand when the feed stock is sent into an entrained flow gasifier the fuels can be in either form of dry feed or slurry feed In general dryfeed gasifiers have the advantage over slurryfeed gasifiers in that the former can be operated with lower oxygen consumption Moreover dryfeed gasifiers have an additional degree of freedom that makes it possible to optimize synthesis gas production Shen et al 2012 171 Feedstock Preparation by Gasification 523 reactions Gasification involves the thermal decomposition of feedstock and the reaction of the feedstock carbon and other pyrolysis products with oxygen water and fuel gases such as methane The presence of oxygen hydrogen water vapor carbon oxides and other compounds in the reac tion atmosphere during pyrolysis may either support or inhibit numerous reactions with car bonaceous feedstocks and with the products evolved The distribution of weight and chemical composition of the products are also influenced by the prevailing conditions ie temperature heating rate pressure and residence time and last but by no means least the nature of the feedstock Speight 2014a 2014b If air is used for combustion the product gas will have a heat content of ca 150300 Btu ft3 depending on process design characteristics and will contain undesirable constituents such as carbon dioxide hydrogen sulfide and nitrogen The use of pure oxygen although expensive results in a product gas having a heat content in the order of 300400 Btuft3 with carbon diox ide and hydrogen sulfide as byproducts both of which can be removed from low or medium heat content lowBtu or mediumBtu gas by any of several available processes Speight 2013a 2014a If a high heat content highBtu gas 9001000 Btuft3 is required efforts must be made to increase the methane content of the gas The reactions which generate methane are all exothermic and have negative values but the reaction rates are relatively slow and catalysts may therefore be necessary to accelerate the reactions to acceptable commercial rates Indeed the overall reactivity of the feedstock and char may be subject to catalytic effects It is also possible that the mineral con stituents of the feedstock such as the mineral matter in coal and biomass may modify the reactivity by a direct catalytic effect Davidson 1983 Baker and Rodriguez 1990 Mims 1991 Martinez Alonso and Tascon 1991 In the process the feedstock undergoes three processes in its conversation to synthesis gas the first two processes pyrolysis and combustion occur very rapidlyall of which are highly dependent upon the properties of the biomass Figure 53 In pyrolysis char is produced as the feedstock heats up and volatiles are released In the combustion process the volatile products and some of the char reacts with oxygen to produce various products primarily carbon dioxide and carbon monoxide and the heat required for subsequent gasification reactions Finally in the gasification process the feedstock char reacts with steam to produce hydrogen H2 and carbon monoxide CO TABLE 53 Characteristics of the Different Types of Gasifiers Gasifier Type Fuel Properties Fixedmoving bed Particle size 110 cm Mechanically stable fuel particles unblocked passage of gas through the bed Pellets or briquettes preferred Updraft configuration more tolerant to biomass moisture content up to 4050 ww Drying occurs as biomass moves down the gasifier Fluidized bed Ash melting temperature of fuel higher limit for operating temperature Fuel particle size relatively small to ensure good contact with bed material typically 40 mm Good fuel flexibility due to high thermal inertia of the bed Entrained bed Fuel particle size 50 µm Pulverized for high fuel conversion in short residence times Low moisture content Ash melting behavior can influence for reactorprocess design 172 Handbook of Petrochemical Processes Combustion 2C O 2CO H O feedstock 2 2 Gasification C H O H CO feedstock 2 2 CO H O H CO 2 2 2 The resulting synthesis gas is approximately 63 vv carbon monoxide 34 vv hydrogen and 3 vv carbon dioxide At the gasifier temperature the ash and other feedstock mineral matter liquefies and exits at the bottom of the gasifier as slag a sandlike inert material that can be sold as a coproduct to other industries eg road building The synthesis gas exits the gasifier at pressure and high temperature and must be cooled prior to the synthesis gas cleaning stage Although processes that use the high temperature to raise highpressure steam are more efficient for electricity production fullquench cooling by which the synthesis gas is cooled by the direct injection of water is more appropriate for hydrogen production Fullquench cooling provides the necessary steam to facilitate the watergas shift reaction in which carbon monoxide is converted to hydrogen and carbon dioxide in the presence of a catalyst WaterGas Shift Reaction CO H O CO H 2 2 2 This reaction maximizes the hydrogen content of the synthesis gas which consists primarily of hydrogen and carbon dioxide at this stage The synthesis gas is then scrubbed of particulate matter and sulfur is removed via physical absorption Speight 2013a 2014a The carbon dioxide is cap tured by physical absorption or a membrane and either vented or sequestered Thus in the initial stages of gasification the rising temperature of the feedstock initiates devol atilization and the breaking of weaker chemical bonds to yield volatile tar volatile oil phenol derivatives and hydrocarbon gases These products generally react further in the gaseous phase to form hydrogen carbon monoxide and carbon dioxide The char fixed carbon that remains after FIGURE 53 Biomass properties that influence the gasification process 173 Feedstock Preparation by Gasification devolatilization reacts with oxygen steam carbon dioxide and hydrogen Overall the chemistry of gasification is complex but can be conveniently and simply represented by the following reactions C O CO H 3934MJkmol 2 2 r 51 C O CO H 1114MJkmol 12 2 r 52 C H O H CO H 1305MJkmol 2 2 r 53 C CO 2CO H 1707MJkmol 2 r 54 CO H O H CO H 402MJkmol 2 2 2 r 55 C 2H CH H 747MJkmol 2 4 r 56 The designation C represents carbon in the original feedstock as well as carbon in the char formed by devolatilization of the feedstock Reactions 51 and 52 are exothermic oxidation reactions and provide most of the energy required by the endothermic gasification reactions 53 and 54 The oxidation reactions occur very rapidly completely consuming all the oxygen present in the gasifier so that most of the gasifier operates under reducing conditions Reaction 55 is the watergas shift reaction where water steam is converted to hydrogenthis reaction is used to alter the hydrogen carbon monoxide ratio when synthesis gas is the desired product such as for use in FT processes Reaction 56 is favored by high pressure and low temperature and is thus mainly important in lower temperature gasification systems Methane formation is an exothermic reaction that does not consume oxygen and therefore increases the efficiency of the gasification process and the final heat content of the product gas Overall approximately 70 of the heating value of the product gas is associated with the carbon monoxide and hydrogen but this varies depending on the gasifier type and the process parameters Speight 2011a Chadeesingh 2011 Speight 2013a In essence the direction of the gasification process is subject to the constraints of thermody namic equilibrium and variable reaction kinetics The combustion reactions reaction of the feed stock or char with oxygen essentially go to completion The thermodynamic equilibrium of the rest of the gasification reactions are relatively well defined and collectively have a major influence on thermal efficiency of the process as well as on the gas composition Thus thermodynamic data are useful for estimating key design parameters for a gasification process such as i calculating of the relative amounts of oxygen andor steam required per unit of feedstock ii estimating the composition of the produced synthesis gas and iii optimizing process efficiency at various oper ating conditions Other deductions concerning gasification process design and operations can also be derived from the thermodynamic understanding of its reactions Examples include i production of synthesis gas with low methane content at high temperature which requires an amount of steam in excess of the stoichiometric requirement ii gasification at high temperature which increases oxygen con sumption and decreases the overall process efficiency iii production of synthesis gas with a high methane content which requires operation at low temperature approximately 700C 1290F but the methanation reaction kinetics will be poor without the presence of a catalyst Relative to the thermodynamic understanding of the gasification process the kinetic behavior is much more complex In fact very little reliable global kinetic information on gasification reactions exists partly because it is highly dependent on i the chemical nature of the feed which varies significantly with respect to composition mineral impurities ii feedstock reactivity and iii pro cess parameters such as temperature pressure and residence time In addition physical character istics of the feedstock or char also play a role in phenomena such boundarylayer diffusion pore diffusion and ash layer diffusion which also influence the kinetic outcome Furthermore certain 174 Handbook of Petrochemical Processes impurities in fact are known to have catalytic activity on some of the gasification reactions which can have further influence on the kinetic imprint of the gasification reactions 5231 Primary Gasification Primary gasification involves thermal decomposition of the raw feedstock via various chemical pro cesses and many schemes involve pressures ranging from atmospheric to 1000 psi Air or oxygen may be admitted to support combustion to provide the necessary heat The product is usually a low heat content lowBtu gas ranging from a carbon monoxidehydrogen mixture to mixtures contain ing varying amounts of carbon monoxide carbon dioxide hydrogen water methane hydrogen sul fide nitrogen and typical tarlike products of thermal decomposition of carbonaceous feedstocks are complex mixtures and include hydrocarbon oils and phenolic products Dutcher et al 1983 Speight 2011a 2013a 2014b Devolatilization of the feedstock occurs rapidly as the temperature rises above 300C 570F During this period the chemical structure is altered producing solid char tar products condens able liquids and low molecular weight gases Furthermore the products of the devolatilization stage in an inert gas atmosphere are very different from those in an atmosphere containing hydrogen at elevated pressure In an atmosphere of hydrogen at elevated pressure additional yields of methane or other low molecular weight gaseous hydrocarbon derivatives can result during the initial gasifica tion stage from reactions such as i direct hydrogenation of feedstock or semichar because of any reactive intermediates formed and ii the hydrogenation of other gaseous hydrocarbon derivatives oils tars and carbon oxides Again the kinetic picture for such reactions is complex due to the varying composition of the volatile products which in turn are related to the chemical character of the feedstock and the process parameters including the reactor type A solid char product may also be produced and may represent the bulk of the weight of the original feedstock which determines to a large extent the yield of char and the composition of the gaseous product 5232 Secondary Gasification Secondary gasification usually involves the gasification of char from the primary gasifier which is typically achieved by reaction of the hot char with water vapor to produce carbon monoxide and hydrogen C H O CO H char 2 2 The reaction requires heat input endothermic for the reaction to proceed in its forward direction Usually an excess amount of steam is also needed to promote the reaction However excess steam used in this reaction has an adverse effect on the thermal efficiency of the process Therefore this reaction is typically combined with other gasification reactions in practical applications The hydrogencarbon monoxide ratio of the product synthesis gas depends on the synthesis chemistry as well as process engineering The mechanism of this reaction section is based on the reaction between carbon and gaseous reactants not for reactions between feedstock and gaseous reactants Hence the equations may oversimply the actual chemistry of the steam gasification reaction Even though carbon is the domi nant atomic species present in feedstock feedstock is more reactive than pure carbon The presence of various reactive organic functional groups and the availability of catalytic activity via naturally occurring mineral ingredients can enhance the relative reactivity of the feedstockfor example anthracite which has the highest carbon content among all ranks of coal Speight 2013a is most difficult to gasify or liquefy After the rate of devolatilization has passed a maximum of another reaction becomes important in this reaction which the semichar is converted to char sometimes erroneously referred to as stable char primarily through the evolution of hydrogen Thus the gasification process occurs 175 Feedstock Preparation by Gasification as the char reacts with gases such as carbon dioxide and steam to produce carbon monoxide and hydrogen The resulting gas producer gas or synthesis gas may be more efficiently converted to electricity than is typically possible by direct combustion of the char Also corrosive elements in the ash may be refined out by the gasification process allowing hightemperature combustion of the gas from otherwise problematic feedstocks Speight 2011a 2013a 2014b Oxidation and gasification reactions consume the char and the oxidation and the gasification kinetic rates follow Arrheniustype dependence on temperature On the other hand the kinetic parameters are feedstockspecific and there is no true global relationship to describe the kinetics of char gasificationthe characteristics of the char are also feedstockspecific The complexity of the reactions makes the reaction initiation and the subsequent rates subject to many factors any one of which can influence the kinetic aspects of the reaction Although the initial gasification stage devolatilization is completed in seconds or even less at elevated temperature the subsequent gasification of the char produced at the initial gasification stage is much slower requiring minutes or hours to obtain significant conversion under practical conditions and reactor designs for commercial gasifiers are largely dependent on the reactivity of the char and also on the gasification medium Johnson 1979 Sha 2005 Thus the distribution and chemical composition of the products are also influenced by the prevailing conditions ie tempera ture heating rate pressure residence time etc and last but not least the nature of the feedstock Also the presence of oxygen hydrogen water vapor carbon oxides and other compounds in the reaction atmosphere during pyrolysis may either support or inhibit numerous reactions with feed stock and with the products evolved The reactivity of char produced in the pyrolysis step depends on nature of the feedstock and increases with oxygen content of the feedstock but decreases with carbon content In general char produced from a lowcarbon feedstock is more reactive than char produced from a highcarbon feedstock The reactivity of char from a lowcarbon feedstock may be influenced by catalytic effect of mineral matter in char In addition as the carbon content of the feedstock increases the reactive functional groups present in the feedstock decrease and the char becomes more aromatic and cross linked in nature Speight 2013a Therefore char obtained from highcarbon feedstock contains a lesser number of functional groups and higher proportion of aromatic and crosslinked structures which reduce reactivity The reactivity of char also depends upon thermal treatment it receives during formation from the parent feedstockthe gasification rate of char decreases as the char preparation temperature increases due to the decrease in active surface areas of char Therefore a change of char preparation temperature may change the chemical nature of char which in turn may change the gasification rate Typically char has a higher surface area compared to the surface area of the parent feedstock even when the feedstock has been pelletized and the surface area changes as the char under goes gasificationthe surface area increases with carbon conversion reaches maximum and then decreases These changes in turn affect gasification ratesin general reactivity increases with the increase in surface area The initial increase in surface area appears to be caused by cleanup and widening of pores in the char The decrease in surface area at highcarbon conversion may be due to coalescence of pores which ultimately leads to collapse of the pore structure within the char Heat transfer and mass transfer processes in fixed or moving bed gasifiers are affected by com plex solids flow and chemical reactions Coarsely crushed feedstock settles while undergoing heat ing drying devolatilization gasification and combustion Also the feedstock particles change in diameter shape and porositynonideal behavior may result from certain types of chemical struc tures in the feedstock gas bubbles and channel and a variable void fraction may also change heat and mass transfer characteristics An important factor is the importance of the pyrolysis temperature as a major factor in the ther mal history and consequently in the thermodynamics of the feedstock char However the thermal history of a char should also depend on the rate of temperature rise to the pyrolysis temperature 176 Handbook of Petrochemical Processes and on the length of time the char is kept at the pyrolysis temperature soak time which might be expected to reduce the residual entropy of the char by employing a longer soak time Alkali metal salts are known to catalyze the steam gasification reaction of carbonaceous materi als including coal The process is based on the concept that alkali metal salts such as potassium carbonate sodium carbonate potassium sulfide sodium sulfide and the like will catalyze the steam gasification of feedstocks The order of catalytic activity of alkali metals on the gasification reaction is CesiumCs rubidiumRb potassiumK sodiumNa lithiumLi Catalyst amounts in the order of 1020 ww potassium carbonate will lower bituminous coal gasifier temperatures from 925C 1695F to 700C 1090F and that the catalyst can be intro duced to the gasifier impregnated on coal or char In addition tests with potassium carbonate showed that this material also acts as a catalyst for the methanation reaction In addition the use of catalysts can reduce the amount of tar formed in the process In the case of catalytic steam gasification of coal carbon deposition reaction may affect catalyst life by fouling the catalyst active sites This carbon deposition reaction is more likely to take place whenever the steam concentration is low Rutheniumcontaining catalysts are used primarily in the production of ammonia It has been shown that ruthenium catalysts provide 510 times higher reactivity rates than other catalysts However ruthenium quickly becomes inactive due to its necessary supporting material such as activated carbon which is used to achieve effective reactivity However during the process the carbon is consumed thereby reducing the effect of the ruthenium catalyst Catalysts can also be used to favor or suppress the formation of certain components in the gas eous product by changing the chemistry of the reaction the rate of reaction and the thermodynamic balance of the reaction For example in the production of synthesis gas mixtures of hydrogen and carbon monoxide methane is also produced in small amounts Catalytic gasification can be used to either promote methane formation or suppress it 5233 WaterGas Shift Reaction The watergas shift reaction shift conversion is necessary because the gaseous product from a gasifier generally contains large amounts of carbon monoxide and hydrogen plus lesser amounts of other gases Carbon monoxide and hydrogen if they are present in the mole ratio of 13 can be reacted in the presence of a catalyst to produce methane However some adjustment to the ideal ratio 13 is usually required and to accomplish this all or part of the steam is treated according to the wastegas shift shift conversion reaction This involves reacting carbon monoxide with steam to produce a carbon dioxide and hydrogen whereby the desired 13 mole ratio of carbon monoxide to hydrogen may be obtained COg H Og CO g H g 2 2 2 Even though the watergas shift reaction is not classified as one of the principal gasification reac tions it cannot be omitted in the analysis of chemical reaction systems that involve synthesis gas Among all reactions involving synthesis gas this reaction equilibrium is least sensitive to the temperature variationthe equilibrium constant is least strongly dependent on the temperature Therefore the reaction equilibrium can be reversed in a variety of practical process conditions over a wide range of temperature The watergas shift reaction in its forward direction is mildly exothermic and although all the participating chemical species are in gaseous form the reaction is believed to be heterogeneous insofar as the chemistry occurs at the surface of the feedstock and the reaction is actually cat alyzed by carbon surfaces In addition the reaction can also take place homogeneously as well 177 Feedstock Preparation by Gasification as heterogeneously and a generalized understanding of the watergas shift reaction is difficult to achieve Even the published kinetic rate information is not immediately useful or applicable to a practical reactor situation Synthesis gas from a gasifier contains a variety of gaseous species other than carbon monoxide and hydrogen Typically they include carbon dioxide methane and water steam Depending on the objective of the ensuing process the composition of synthesis gas may need to be preferentially readjusted If the objective of the gasification process is to obtain a high yield of methane it would be preferred to have the molar ratio of hydrogen to carbon monoxide at 31 COg 3H g CH g H Og 2 4 2 On the other hand if the objective of generating synthesis gas is the synthesis of methanol via a vapor phase lowpressure process the stoichiometrically consistent ratio between hydrogen and car bon monoxide would be 21 In such cases the stoichiometrically consistent synthesis gas mixture is often referred to as balanced gas whereas a synthesis gas composition that is substantially deviated from the principal reactions stoichiometry is called unbalanced gas If the objective of synthesis gas production is to obtain a high yield of hydrogen it would be advantageous to increase the ratio of hydrogen to carbon monoxide by further converting carbon monoxide and water into hydrogen and carbon dioxide via the watergas shift reaction The watergas shift reaction is one of the major reactions in the steam gasification process where both water and carbon monoxide are present in ample amounts Although the four chemical species involved in the watergas shift reaction are gaseous compounds at the reaction stage of most gas pro cessing the watergas shift reaction in the case of steam gasification of feedstock predominantly takes place on the solid surface of feedstock heterogeneous reaction If the product synthesis gas from a gasifier needs to be reconditioned by the watergas shift reaction this reaction can be cata lyzed by a variety of metallic catalysts Choice of specific kinds of catalysts has always depended on the desired outcome the prevail ing temperature conditions composition of gas mixture and process economics Typical cata lysts used for the reaction include catalysts containing iron copper zinc nickel chromium and molybdenum 5234 Carbon Dioxide Gasification The reaction of carbonaceous feedstocks with carbon dioxide produces carbon monoxide Boudouard reaction and like the steam gasification reaction is also an endothermic reaction Cs CO g 2COg 2 The reverse reaction results in carbon deposition carbon fouling on many surfaces including the catalysts and results in catalyst deactivation This gasification reaction is thermodynamically favored at high temperatures 680C 1255F which is also quite similar to the steam gasification If carried out alone the reaction requires high temperature for fast reaction and high pressure for higher reactant concentrations for significant conversion but as a separate reaction a variety of factors come into play i low conversion ii slow kinetic rate and iii low thermal efficiency Also the rate of the carbon dioxide gasification of a feedstock is different to the rate of the carbon dioxide gasification of carbon Generally the carboncarbon dioxide reaction follows a reaction order based on the partial pressure of the carbon dioxide that is approximately 10 or lower whereas the feedstockcarbon dioxide reaction follows a reaction order based on the par tial pressure of the carbon dioxide that is 10 or higher The observed higher reaction order for the feedstock reaction is also based on the relative reactivity of the feedstock in the gasification system 178 Handbook of Petrochemical Processes 5235 Hydrogasification Not all high heat content highBtu gasification technologies depend entirely on catalytic methana tion and in fact a number of gasification processes use hydrogasification that is the direct addition of hydrogen to feedstock under pressure to form methane C 2H CH char 2 4 The hydrogenrich gas for hydrogasification can be manufactured from steam and char from the hydrogasifier Appreciable quantities of methane are formed directly in the primary gasifier and the heat released by methane formation is at a sufficiently high temperature to be used in the steam carbon reaction to produce hydrogen so that less oxygen is used to produce heat for the steam carbon reaction Hence less heat is lost in the lowtemperature methanation step thereby leading to higher overall process efficiency Hydrogasification is the gasification of feedstock in the presence of an atmosphere of hydrogen under pressure Thus not all high heat content highBtu gasification technologies depend entirely on catalytic methanation and in fact a number of gasification processes use hydrogasification that is the direct addition of hydrogen to feedstock under pressure to form methane C H CH feedstock 2 4 The hydrogenrich gas for hydrogasification can be manufactured from steam by using the char that leaves the hydrogasifier Appreciable quantities of methane are formed directly in the primary gasifier and the heat released by methane formation is at a sufficiently high temperature to be used in the steamcarbon reaction to produce hydrogen so that less oxygen is used to produce heat for the steamcarbon reaction Hence less heat is lost in the lowtemperature methanation step thereby leading to higher overall process efficiency The hydrogasification reaction is exothermic and is thermodynamically favored at low tempera tures 670C 1240F unlike the endothermic both steam gasification and carbon dioxide gas ification reactions However at low temperatures the reaction rate is inevitably too slow Therefore a high temperature is always required for kinetic reasons which in turn requires high pressure of hydrogen which is also preferred for equilibrium considerations This reaction can be catalyzed by salts such as potassium carbonate K2CO3 nickel chloride NiCl2 iron chloride FeCl2 and iron sulfate FeSO4 However use of a catalyst in feedstock gasification suffers from difficulty in recov ering and reusing the catalyst and the potential for the spent catalyst becoming an environmental issue In a hydrogen atmosphere at elevated pressure additional yields of methane or other low molecu lar weight hydrocarbon derivatives can result during the initial feedstock gasification stage from direct hydrogenation of feedstock or semichar because of active intermediate formed in the feed stock structure after pyrolysis The direct hydrogenation can also increase the amount of feedstock carbon that is gasified as well as the hydrogenation of gaseous hydrocarbon derivatives oil and tar The kinetics of the rapidrate reaction between gaseous hydrogen and the active intermediate depends on hydrogen partial pressure PH2 Greatly increased gaseous hydrocarbon derivatives pro duced during the initial feedstock gasification stage are extremely important in processes to convert feedstock into methane synthetic natural gas substitute natural gas SNG 5236 Methanation Several exothermic reactions may occur simultaneously within a methanation unit A variety of metals have been used as catalysts for the methanation reaction the most common and to some extent the most effective methanation catalysts appear to be nickel and ruthenium with nickel being the most widely used Cusumano et al 1978 Ruthenium Ru nickel Ni cobalt Co iron Fe molybdenum Mo 179 Feedstock Preparation by Gasification Nearly all the commercially available catalysts used for this process are however very susceptible to sulfur poisoning and efforts must be taken to remove all hydrogen sulfide H2S before the cata lytic reaction starts It is necessary to reduce the sulfur concentration in the feed gas to less than 05 ppm vv in order to maintain adequate catalyst activity for a long period of time The synthesis gas must be desulfurized before the methanation step since sulfur compounds will rapidly deactivate poison the catalysts A processing issue may arise when the concentration of carbon monoxide is excessive in the stream to be methanated since large amounts of heat must be removed from the system to prevent high temperatures and deactivation of the catalyst by sintering as well as the deposition of carbon To eliminate this problem temperatures should be maintained below 400C 750F The methanation reaction is used to increase the methane content of the product gas as needed for the production of high Btu gas 4H CO CH 2H O 2 2 4 2 4H CO CH 2H O 2 2 4 2 2CO C CO2 CO H O CO H 2 2 2 Among these the most dominant chemical reaction leading to methane is the first one Therefore if methanation is carried out over a catalyst with a synthesis gas mixture of hydrogen and carbon monoxide the desired hydrogencarbon monoxide ratio of the feed synthesis gas is around 31 The large amount of water vapor produced is removed by condensation and recirculated as process water or steam During this process most of the exothermic heat due to the methanation reaction is also recovered through a variety of energy integration processes Whereas all the reactions listed above are quite strongly exothermic except the forward watergas shift reaction which is mildly exothermic the heat release depends largely on the amount of carbon monoxide present in the feed synthesis gas For each 1 vv carbon monoxide in the feed synthesis gas an adiabatic reaction will experience a 60C 108F temperature rise which may be termed as adiabatic temperature rise 53 GASIFICATION PROCESSES Gasification is an established triedandtrue method that can be used to convert crude oil coke petcoke heavy oil extra heavy oil tar sand bitumen and other refinery viscous feedstocks streams such as vacuum residua visbreaker tar and deasphalter pitch into power steam and hydrogen for use in the production of cleaner transportation fuels The main requirement for a gasification feedstock is that it contains both hydrogen and carbon A number of factors have increased the interest in gasification applications in crude oil refinery operations i coking capacity has increased with the shift to heavier more sour crude oils being supplied to the refiners ii hazardous waste disposal has become a major issue for refiners in many countries iii there is strong emphasis on the reduction of emissions of criteria pollutants and greenhouse gases iv requirements to produce ultralowsulfur fuels are increasing the hydrogen needs of the refineries and v the requirements to produce lowsulfur fuels and other regulations could lead to refiners falling short of demand for lowerboiling products such as gasoline and jet and diesel fuel The typical gasification system incorporated into the refinery consists of several process plants including i a feedstock preparation area ii the type of gasifier iii a gas cleaning section iv a sulfur recovery unit SRU and v downstream process options that are dependent on the nature of the products 180 Handbook of Petrochemical Processes The gasification process can provide highpurity hydrogen for a variety of uses within the refinery Hydrogen is used in the refinery to remove sulfur nitrogen and other impurities from intermediate to fin ished product streams and in hydrocracking operations for the conversion of highboiling distillates and oils into lowboiling products such as naphtha kerosene and diesel Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Furthermore electric power and highpressure steam can be generated by the gasification of crude oil coke and viscous feedstocks to drive mostly small and intermittent loads such as compressors blowers and pumps Steam can also be used for process heating steam tracing partial pressure reduction in fractionation systems and stripping lowboiling components to stabilize process streams Also the gasification system and refinery operations can share common process equipment This usually includes an amine stripper or sulfur plant waste water treat ment and cooling water systems Mokhatab et al 2006 Speight 2007 2014a 531 Gasifiers A gasifier differs from a combustor in that the amount of air or oxygen available inside the gasifier is carefully controlled so that only a relatively small portion of the fuel burns completely The par tial oxidation process provides the heat and rather than combustion most of the carboncontaining feedstock is chemically broken apart by the heat and pressure applied in the gasifier resulting in the chemical reactions that produce synthesis gas However the composition of the synthesis gas will vary because of dependence upon the conditions in the gasifier and the type of feedstock Minerals in the fuel ie the rocks dirt and other impurities which do not gasify separate and leave the bot tom of the gasifier either as an inert glasslike slag or other marketable solid products Four types of gasifier are currently available for commercial use i the countercurrent fixed bed ii cocurrent fixed bed iii the fluidized bed and iv the entrained flow Speight 2008 2013a In a fixed bed process the coal is supported by a grate and combustion gases steam air oxygen etc pass through the supported coal whereupon the hot produced gases exit from the top of the reactor Heat is supplied internally or from an outside source but caking coals cannot be used in an unmodified fixed bed reactor Due to the liquidlike behavior the fluidized beds are very well mixed which effectively eliminates the concentration and temperature gradients inside the reactor The process is also fairly simple and reliable to operate as the bed acts as a large thermal reservoir that resists rapid changes in temperature and operation conditions The disadvantages of the process include the need for recircula tion of the entrained solids carried out from the reactor with the fluid and the nonuniform residence time of the solids that can cause poor conversion levels The abrasion of the particles can also contribute to serious erosion of pipes and vessels inside the reactor Kunii and Levenspiel 2013 The countercurrent fixed bed up draft gasifier consists of a fixed bed of carbonaceous fuel eg coal or biomass through which the gasification agent steam oxygen andor air flows in counter current configuration The ash is either removed dry or as a slag The nature of the gasifier means that the fuel must have high mechanical strength and must be noncaking so that it will form a permeable bed although recent developments have reduced these restrictions to some extent The throughput for this type of gasifier is relatively low Thermal efficiency is high as the gas exit temperatures are rela tively low and as a result tar and methane production is significant at typical operation temperatures so product gas must be extensively cleaned before use or recycled to the reactor The cocurrent fixed bed down draft gasifier is similar to the countercurrent type but the gasifi cation agent gas flows in cocurrent configuration with the fuel downwards hence the name down draft gasifier Heat needs to be added to the upper part of the bed either by combusting small amounts of the fuel or from external heat sources The produced gas leaves the gasifier at a high temperature and most of this heat is often transferred to the gasification agent added in the top of the bed Since all tars must pass through a hot bed of char in this configuration tar levels are much lower than the countercurrent type In the fluidized bed gasifier the fuel is fluidized in oxygen or air and steam The temperatures are relatively low in dry ash gasifiers so the fuel must be highly reactive lowgrade coals are 181 Feedstock Preparation by Gasification particularly suitable The fluidized bed system uses finely sized coal particles and the bed exhibits liquidlike characteristics when a gas flows upward through the bed Gas flowing through the coal produces turbulent lifting and separation of particles and the result is an expanded bed having greater coal surface area to promote the chemical reaction but such systems have a limited ability to handle caking coals The agglomerating gasifiers have slightly higher temperatures and are suit able for higherrank coals Fuel throughput is higher than the fixed bed but not as high as for the entrained flow gasifier The conversion efficiency is typically low so recycle or subsequent combus tion of solids is necessary to increase conversion Fluidized bed gasifiers are most useful for fuels that form highly corrosive ash that would damage the walls of slagging gasifiers The ash is removed dry or as high molecular weight agglomerated materialsa disadvantage of biomass feedstocks is that they generally contain high levels of corrosive ash In the entrained flow gasifier a dry pulverized solid an atomized liquid fuel or a fuel slurry is gasified with oxygen much less frequent air in cocurrent flow The high temperatures and pressures also mean that a higher throughput can be achieved but thermal efficiency is somewhat lower as the gas must be cooled before it can be sent to a gas processing facility All entrained flow gasifiers remove the major part of the ash as a slag as the operating temperature is well above the ash fusion temperature the entrained system is suitable for both caking and noncak ing coals Entrained flow reactors use atomized liquid slurry or dry pulverized solid as a feedstock Once pumped inside the gasifier the feedstock is gasified with oxygen in a cocurrent flow The tem peratures are usually very high in comparison to fluidized beds ranging from 1300C to 1500C 2370F2730F Hightemperature cracks the feedstock into lowerboiling products In IGCC systems the synthesis gas is cleaned of its hydrogen sulfide ammonia and particulate matter and is burned as fuel in a combustion turbine much like natural gas is burned in a turbine The combustion turbine drives an electric generator Hot air from the combustion turbine can be channeled back to the gasifier or the air separation unit ASU while exhaust heat from the com bustion turbine is recovered and used to boil water creating steam for a steam turbine generator The use of these two types of turbinesa combustion turbine and a steam turbinein combina tion known as a combined cycle is one reason why gasificationbased power systems can achieve unprecedented power generation efficiencies Gasification also offers more scope for recovering products from waste than incineration Speight 2014b When waste is burnt in an incinerator the only practical product is energy whereas the gases oils and solid char from pyrolysis and gasification can not only be used as a fuel but also purified and used as a feedstock for petrochemicals and other applications Many processes also produce a stable granulate instead of an ash which can be more easily and safely utilized In addi tion some processes are targeted at producing specific recyclables such as metal alloys and carbon black From waste gasification in particular it is feasible to produce hydrogen which many see as an increasingly valuable resource IGCC is used to raise power from viscous feedstocks The value of these refinery residuals includ ing crude oil coke will need to be considered as part of an overall upgrading project Historically many delayed coking projects have been evaluated and sanctioned on the basis of assigning zero value to crude oil coke having highsulfur and high metal content While there are many alternate uses for the synthesis gas produced by gasification and a com bination of productsutilities can be produced in addition to power A major benefit of the IGCC concept is that power can be produced with the lowest sulfur oxide Sox and nitrogen oxide NOx emissions of any liquidsolid feed power generation technology 532 ft synthesis The synthesis reaction is dependent on a catalyst mostly an iron or cobalt catalyst where the reac tion takes place There is either a lowtemperature FischerTropsch process LTFT process or 182 Handbook of Petrochemical Processes hightemperature FischerTropsch process HTFT process with temperatures ranging between 200C and 240C 390F and 465F for LTFT and between 300C and 350C 570F and 660oF for HTFT The HTFT uses an iron catalyst and the LTFT either an iron or a cobalt catalyst The different catalysts include also nickelbased and rutheniumbased catalysts which also have enough activity for commercial use in the process The reactors are the multitubular fixed bed the slurry or the fluidized bed with either fixed or circulating bed reactor The fixed bed reactor consists of thousands of small tubes with the catalyst as surfaceactive agent in the tubes Water surrounds the tubes and regulates the temperature by settling the pressure of evaporation The slurry reactor is widely used and consists of fluid and solid elements where the catalyst has no particularly position but flows around as small pieces of cata lyst together with the reaction components The slurry and fixed bed reactor are used in LTFT The fluidized bed reactors are diverse but characterized by the fluid behavior of the catalyst The HTFT technology uses a fluidized catalyst at 300C330C Originally circulating fluid ized bed units were used Synthol reactors Since 1989 a commercialscale classical fluidized bed unit has been implemented and improved upon The LTFT technology has originally been used in tubular fixed bed reactors at 200C230C This produces a more paraffinic and waxy product spectrum than the hightemperature technology A new type of reactor the Sasol slurry phase dis tillate reactor has been developed and is in commercial operation This reactor uses a slurry phase system rather than a tubular fixed bed configuration and is currently the favored technology for the commercial production of synfuels Under most circumstances the production of synthesis gas by reforming natural gas will be more economical than from coal gasification but sitespecific factors need to be considered In fact any technological advance in this field such as better energy integration or the oxygen transfer ceramic membrane reformer concept will speed up the rate at which the synfuels technology will become common practice There are large coal reserves which may increasingly be used as a fuel source during oil deple tion Since there are large coal reserves in the world this technology could be used as an interim transportation fuel if conventional oil were to become more expensive Furthermore combination of biomass gasification and FT synthesis is a very promising route to produce transportation fuels from renewable or green resources Although the focus of this section has been on the production of hydrocarbon derivatives from synthesis gas it is worthy of note that clean synthesis gas can also be used i as chemical building blocks to produce a broad range of chemicals using processes well established in the chemical and petrochemical industry ii as a fuel producer for highly efficient fuel cells which run off the hydrogen made in a gasifier or perhaps in the future hydrogen turbines and fuel cell turbine hybrid systems and iii as a source of hydrogen that can be separated from the gas stream and used as a fuel or as a feedstock for refineries which use the hydrogen to upgrade crude oil products The aim of underground or in situ gasification of coal is the conversion into combustible gases by combustion of a coal seam in the presence of air oxygen or oxygen and steam Thus seams that were considered to be inaccessible unworkable or uneconomical to mine could be put to use In addition strip mining and the accompanying environmental impacts the problems of spoil banks acid mine drainage and the problems associated with use of highash coal are minimized or even eliminated The principles of underground gasification are very similar to those involved in the aboveground gasification of coal The concept involves the drilling and subsequent linking of two boreholes so that gas will pass between the two Combustion is then initiated at the bottom of one borehole injec tion well and is maintained by the continuous injection of air In the initial reaction zone combus tion zone carbon dioxide is generated by the reaction of oxygen air with the coal C O CO coal 2 2 183 Feedstock Preparation by Gasification The carbon dioxide reacts with coal partially devolatilized further along the seam reduction zone to produce carbon monoxide C CO 2CO coal 2 In addition at the high temperatures that can frequently occur moisture injected with oxygen or even moisture inherent in the seam may also react with the coal to produce carbon monoxide and hydrogen C H O CO H coal 2 2 The gas product varies in character and composition but usually falls into the low heat low Btu category ranging from 125 to 175 Btuft3 533 feedstocks For many decades coal has been the primary feedstock for gasification units but recent concerns about the use of fossil fuels and the resulting environmental pollutants irrespective of the various gas cleaning processes and gasification plant environmental cleanup efforts there is a move to feed stocks other than coal for gasification processes Speight 2013a 2014b But more pertinent to the present text the gasification process can also use carbonaceous feedstocks which would otherwise have been discarded and unused such as waste biomass and other similar biodegradable wastes Various feedstocks such as biomass crude oil resids and other carbonaceous wastes can be used to their fullest potential In fact the refining industry has seen fit to use viscous feedstock gasification as a source of hydrogen for the past several decades Speight 2014a Gasification processes can accept a variety of feedstocks but the reactor must be selected on the basis of feedstock properties and behavior in the process The advantage of the gasification process when a carbonaceous feedstock a feedstock containing carbon or hydrocarbonaceous feedstock a feedstock containing carbon and hydrogen is employed is that the product of focussynthesis gas is potentially more useful as an energy source and results in an overall cleaner process The produc tion of synthesis gas is a more efficient production of an energy source than say the direct combustion of the original feedstock because synthesis gas can be i combusted at higher temperatures ii used in fuel cells iii used to produce methanol iv used as a source of hydrogen and v particularly because the synthesis gas can be converted via the FT process into a range of synthesis liquid fuels suitable for use gasoline engines for diesel engines or for wax production 5331 Heavy Feedstocks Gasification is the only technology that makes possible a zero residue target for refineries contrary to all conversion technologies including thermal cracking catalytic cracking cooking deasphalt ing hydroprocessing etc which can only reduce the bottom volume with the complication that the residue qualities generally get worse with the degree of conversion Speight 2014a The flexibility of gasification permits to handle any type of refinery residue including crude oil coke tank bottoms and refinery sludge and make available a range of valueadded products including electricity steam hydrogen and various chemicals based on synthesis gas chemistry methanol ammonia methyl tertbutyl ether MTBE tertamyl methyl ether TAME acetic acid and formaldehyde Speight 2008 2013a The environmental performance of gasification is unmatched No other technology processing lowvalue refinery residues can come close to the emission levels achievable with gasification Speight 2013a 2013b 2014a 2014b Gasification is also a method for converting crude oil coke and other refinery nonvolatile waste streams often referred to as refinery residuals and include but not limited to atmospheric residuum vacuum residuum visbreaker tar and deasphalter pitch into power steam and hydrogen for use in 184 Handbook of Petrochemical Processes the production of cleaner transportation fuels The main requirement for a gasification feedstock is that the feedstock it contains both hydrogen and carbon and several suitable feedstocks are produced onsite as part of typical refinery processing Speight 2011b The typical gasification system incor porated into a refinery consists of several process units including feed preparation the gasifier an ASU synthesis gas cleanup SRU and downstream process options depending on target products The benefits of the addition of a gasification system in a refinery to process crude oil coke or other residuals include i production of power steam oxygen and nitrogen for refinery use or sale ii source of synthesis gas for hydrogen to be used in refinery operations as well as for the produc tion of lowerboiling refinery products through the FT synthesis iii increased efficiency of power generation improved air emissions and reduced waste stream versus combustion of crude oil coke or residues or incineration iv no offsite transportation or storage for crude oil coke or residuals and v the potential to dispose of waste streams including hazardous materials Marano 2003 Gasification can provide highpurity hydrogen for a variety of uses within the refinery Speight 2014a Hydrogen is used in refineries to remove sulfur nitrogen and other impurities from interme diate to finished product streams and in hydrocracking operations for the conversion of highboiling distillates into lowerboiling products naphtha kerosene and lowboiling gas oil Hydrocracking and severe hydrotreating require hydrogen which is at least 99 vv while less severe hydrotreating can work with gas streams containing 90 vv pure hydrogen Electric power and highpressure steam can be generated via gasification of crude oil coke and residuals to drive mostly small and intermittent loads such as compressors blowers and pumps Steam can also be used for process heating steam tracing partial pressure reduction in fraction ation systems and stripping lowboiling components to stabilize process streams Carbon soot is produced during gasification which ends up in the quench water The soot is transferred to the feedstock by contacting in sequence the quench water blowdown with naphtha and then the naphthasoot slurry with a fraction of the feed The soot mixed with the feed is finally recycled into the gasifier thus achieving 100 conversion of carbon to gas 5332 Solvent Deasphalter Bottoms The deasphalting unit deasphalter is a unit in a petroleum refinery for bitumen upgrader that sepa rates an asphaltlike product from petroleum heavy oil or bitumen The deasphalter unit is usually placed after the vacuum distillation tower where by the use of a lowboiling liquid hydrocarbon sol vent such as propane or butane under pressure the insoluble asphaltlike product deasphalter bot toms is separated from the feedstockthe other output from the deasphalter is deasphalted oil DAO The solvent deasphalting process has been employed for more than six decades to separate high molecular weight fractions of crude oil boiling beyond the range of economical commercial distilla tion The earliest commercial applications of solvent deasphalting used liquid propane as the solvent to extract highquality lubricating oil bright stock from vacuum residue The process has been extended to the preparation of catalytic cracking feeds hydrocracking feeds hydrodesulfurization feedstocks and asphalts The latter product asphalt also called deasphalter bottoms is used for i road asphalt manufacture ii refinery fuel or iii gasification feedstock for hydrogen production In fact the combination of ROSE solvent deasphalting and gasification has been commercially proven at the ERG Petroli refinery Bernetti et al 2000 The combination is very synergistic and offers a number of advantages including a lowcost feedstock to the gasifier thus enhancing the refinery economics and converts lowvalue feedstock to highvalue products such as power steam hydrogen and chemical feedstock The process also improves the economics of the refinery by eliminatingreducing the production of lowvalue fuel oil and maximizing the production of trans portation fuel 5333 Asphalt Tar and Pitch The terms asphalt tar and pitch are nondescript terms that are often applied in a refinery to any viscous black difficulttoidentify product The terms are often applied the insoluble product from 185 Feedstock Preparation by Gasification a deasphalting unit also called deasphalter bottoms The terms will be covered in this subsection because of the application of the nomenclature to the products of other processes Asphalt does not occur naturally but is manufactured from crude oil and is a black or brown material that has a consistency varying from a viscous liquid to a glassy solid Speight 2014a To a point asphalt can resemble bitumen isolated form tar sand formation hence the tendency to refer to bitumen incorrectly as native asphalt It is recommended that there be differentiation between asphalt manufactured and bitumen naturally occurring other than by use of the qualify ing terms crude oil and native since the origins of the materials may be reflected in the resulting physicochemical properties of the two types of materials It is also necessary to distinguish between the asphalts which originate from crude oil by refining and the product in which the source of the asphalt is a material other than crude oil eg Wurtzilite asphalt Speight 2014a In the absence of a qualifying word it should be assumed that the word asphalt with or without qualifiers such as cutback solvent and blown which indicate the process used to produce the asphalt refers to the product manufactured from crude oil When the asphalt is produced simply by distillation of an asphaltic crude oil the product can be referred to as residual asphalt or straightrun asphalt For example if the asphalt is prepared by solvent extraction of viscous feedstock or by lowerboiling hydrocarbon propane precipitation or if blown or otherwise treated the term should be modified accordingly to qualify the product eg solvent asphalt propane asphalt blown asphalt Asphalt softens when heated and is elastic under certain conditions and has many uses For exam ple the mechanical properties of asphalt are of particular significance when it is used as a binder or adhesive The principal application of asphalt is in road surfacing that may be done in a variety of ways Other important applications of asphalt include canal and reservoir linings dam facings and sea works The asphalt so used may be a thin sprayed membrane covered with earth for protection against weathering and mechanical damage or thicker surfaces often including riprap crushed rock Asphalt is also used for roofs coatings floor tiles soundproofing waterproofing and other building construction elements and in a number of industrial products such as batteries For certain applica tions an asphaltic emulsion is prepared in which fine globules of asphalt are suspended in water Tar is a product of the destructive distillation of many bituminous or other organic materi als and is a brown to black oily viscous liquid to semisolid material However tar is most com monly produced from bituminous coal and is generally understood to refer to the product from coal although it is advisable to specify coal tar if there is the possibility of ambiguity The most important factor in determining the yield and character of the coal tar is the carbonizing tempera ture Three general temperature ranges are recognized and the products have acquired the des ignations low temperature tar approximately 450C700C 540F1290F midtemperature tar approximately 700C900C 1290F1650F and hightemperature tar approximately 900C1200C 1650F2190F Tar released during the early stages of the decomposition of the organic material is called primary tar since it represents a product that has been recovered without the secondary alteration that results from prolonged residence of the vapor in the heated zone Treatment of the distillate boiling up to 250C 480F of the tar with caustic soda causes sepa ration of a fraction known as tar acids acid treatment of the distillate produces a variety of organic nitrogen compounds known as tar bases The residue left following removal of the highboiling distillate is pitch a black hard and highly ductile material that is the dark browntoblack non distillable residue Coal tar pitch is a soft to hard and brittle substance containing chiefly aromatic resinous com pounds along with aromatic and other hydrocarbon derivatives Pitch is used chiefly as road tar in waterproofing roofs and other structures and to make electrodes Wood tar pitch is a bright lus trous substance containing resin acids it is used chiefly in the manufacture of plastics and insulating materials and in caulking seams Pitch derived from fats fatty acids or fatty oils by distillation are usually soft substances containing polymers and decomposition products they are used chiefly in varnishes and paints and in floor coverings 186 Handbook of Petrochemical Processes Any of the above derivatives can be used as a gasification feedstock The properties of asphalt change markedly during the aging process oxidation in service to the point where the asphalt fails to perform the task for which it was designed In some case the asphalt is recovered and reprocessed for additional use or it may be sent to a gasifier 5334 Petroleum Coke Coke is the solid carbonaceous material produced from crude oil during thermal processing More particularly coke is the residue left by the destructive distillation ie thermal cracking such as the delayed coking process of crude oil residua The coke formed in catalytic cracking operations is usually nonrecoverable because of the materials deposited on the catalyst during the process and such coke is often employed as fuel for the process Gray and Tomlinson 2000 Speight 2014a It is often characterized as a solid material with a honeycombtype of appearance having highcarbon content 95 ww with some hydrogen and depending on the process as well as sulfur and nitrogen The color varies from gray to black and the material is insoluble in organic solvents Typically the composition of crude oil coke varies with the source of the crude oil but in gen eral large amounts of high molecular weight complex hydrocarbon derivatives rich in carbon but correspondingly poor in hydrogen make up a high proportion The solubility of crude oil coke in carbon disulfide has been reported to be as high as 5080 but this is in fact a misnomer and is due to soluble product adsorbed on the cokeby definition coke is the insoluble honeycomb mate rial that is the end product of thermal processes However coke is not always a product with little usethree physical structures of coke can be produced by delayed coking i shot coke ii sponge coke or iii needle coke which finds different uses within the industry Shot coke is an abnormal type of coke resembling small balls Due to mechanisms not well understood the coke from some coker feedstocks forms into small tight nonattached clusters that look like pellets marbles or ball bearings It usually is a very hard coke ie low Hardgrove grind ability index Speight 2013a Such coke is less desirable to the end users because of difficulties in handling and grinding It is believed that feedstocks high in asphaltene constituents and low API gravity favor shot coke formation Blending aromatic materials with the feedstock andor increasing the recycle ratio reduces the yield of shot coke Fluidization in the coke drums may cause formation of shot coke Occasionally the smaller shot coke may agglomerate into ostrich eggsized pieces Such coke may be more suitable as a gasification feedstock Sponge coke is the common type of coke produced by delayed coking units It is in a form that resembles a sponge and has been called honeycombed Sponge coke mostly used for anodegrade carbon is dull and black having porous amorphous structure Needle coke acicular coke is a special quality coke produced from aromatic feed stocks is silvergray having crystalline broken needle structure and is believed to be chemically produced through crosslinking of condensed aromatic hydrocarbon derivatives during coking reactions It has a crystalline structure with more unidirectional pores and is used in the production of electrodes for the steel and aluminum indus tries and is particularly valuable because the electrodes must be replaced regularly Crude oil coke is employed for a number of purposes but its chief use is depending upon the degree of purityie contains a low amount of contaminants for the manufacture of carbon elec trodes for aluminum refining which requires a highpurity carbon low in ash and sulfur free the volatile matter must be removed by calcining In addition to its use as a metallurgical reducing agent crude oil coke is employed in the manufacture of carbon brushes silicon carbide abrasives and structural carbon eg pipes and Raschig rings as well as calcium carbide manufacture from which acetylene is produced Coke CaC2 CaC H O HC CH 2 2 187 Feedstock Preparation by Gasification The flexibility of the gasification technology permits the refinery to handle any kind of refinery residue including crude oil coke tank bottoms and refinery sludge and makes available a range of valueadded products electricity steam hydrogen and various chemicals based on synthesis gas chemistry methanol ammonia MTBE TAME acetic acid and formaldehyde Speight 2008 2013a With respect to gasification no other technology processing lowvalue refinery residues can come close to the emission levels achievable with gasification Speight 2014a and is projected to be a major part of the refinery of the future Speight 2011b Gasification is also a method for converting crude oil coke and other refinery nonvolatile waste streams often referred to as refinery residuals and include but not limited to atmospheric residuum vacuum residuum visbreaker tar and deasphalter pitch into power steam and hydrogen for use in the production of cleaner transportation fuels And as for the gasification of coal and biomass Speight 2013a Luque and Speight 2015 the main requirement for a feedstock to a gasification unit is that the feedstock contains both hydrogen and carbon of which a variety of feedstocks are available from the throughput of a typical refinery Table 54 The typical gasification system incorporated into the refinery consists of several process plants including i feed preparation ii the gasifier iii an ASU iv synthesis gas cleanup v SRU and vi downstream process options such as FischerTropsch synthesis FTS and methanol synthesis depending on the desired product slate The benefits to a refinery for adding a gasification system for crude oil coke or other residuals are i production of power steam oxygen and nitrogen for refinery use or sale ii source of synthesis gas for hydrogen to be used in refinery operations and for the production of lowerboiling refinery products through FTS iii increased efficiency of power generation improved air emissions and reduced waste stream versus combustion of crude oil coke or viscous feedstock or incineration iv no offsite transportation or storage for crude oil coke or viscous feedstock and v the potential to dispose waste streams including hazardous materials Gasification of coke can provide highpurity hydrogen for a variety of uses within the refin ery such as i sulfur removal ii nitrogen removal as well as removal of other impurities from intermediate to finished product streams and in hydrocracking operations for the conversion of highboiling distillates into lowerboiling products such as naphtha kerosene and lowboiling gas oil Speight 2014a Hydrocracking and severe hydrotreating require hydrogen which is at least 99 vv pure while less severe hydrotreating can require gas stream containing hydrogen in the order of 90 vv purity Electric power and highpressure steam can be generated by the gasification of crude oil coke and viscous feedstocks to drive mostly small and intermittent loads such as compressors blowers and pumps Steam can also be used for process heating steam tracing partial pressure reduction in fractionation systems and stripping lowboiling components to stabilize process streams During gasification some soot typically 99 carbon is produced which ends up in the quench water The soot is transferred to the feedstock by contacting in sequence the quench water blow down with naphtha and then the naphthasoot slurry with a fraction of the feed The soot mixed with the feed is recycled to the gasifier thus achieving 100 conversion of carbon to gas TABLE 54 Types of Feedstocks Produced OnSite that Are Available for Gasification Ultimate Analysis Vacuum Resid Visbreaker Bottoms Asphalt Petroleum Coke Carbon ww 849 861 851 886 Hydrogen ww 104 104 91 28 Nitrogen ww 05 06 07 11 Sulfur ww 42 24 51 73 Oxygen ww 05 00 Ash ww 00 01 02 188 Handbook of Petrochemical Processes 5335 Coal Coal is a fossil fuel formed in swamp ecosystems where plant remains were saved from oxidation and biodegradation by water and mud Chapter 3 Speight 2013a Coal is a combustible organic sedimentary rock composed primarily of carbon hydrogen and oxygen as well as other minor ele ments including sulfur formed from ancient vegetation and consolidated between other rock strata to form coal seams The harder forms can be regarded as organic metamorphic rock eg anthracite coal because of a higher degree of maturation Coal is the largest single source of fuel for the generation of electricity worldwide Speight 2013b as well as the largest source of carbon dioxide emissions which have been implicated as the primary cause of global climate change although the debate still rages as to the actual cause or causes of climate change Coal is found as successive layers or seams sandwiched between strata of sandstone and shale and extracted from the ground by coal miningeither underground coal seams underground mining or by openpit mining surface mining Coal remains in adequate supply and at current rates of recovery and consumption the world global coal reserves have been variously estimated to have a reservesproduction ratio of at least 155 years However as with all estimates of resource longevity coal longevity is subject to the assumed rate of consumption remaining at the current rate of consumption and moreover to tech nological developments that dictate the rate at which the coal can be mined But most importantly coal is a fossil fuel and an unclean energy source that will only add to global warming In fact the next time electricity is advertised as a clean energy source just consider the means by which the majority of electricity is producedalmost 50 of the electricity generated in the United States derives from coal EIA 2007 Speight 2013a Coal occurs in different forms or types Speight 2013a Variations in the nature of the source material and local or regional the variations in the coalification processes cause the vegetal matter to evolve differently Various classification systems thus exist to define the different types of coal Using the American Society for Testing and Materials ASTM now ASTM International system of classification ASTM D388 2015 the coal precursors are transformed over time as geological processes increase their effect over time into i Lignite also referred to as brown coal is the lowest rank of coal and used almost exclu sively as fuel for steamelectric power generation Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age ii Subbituminous coal the properties range from those of lignite to those of bituminous coal and is used primarily as fuel for steamelectric power generation iii Bituminous coala dense coal usually black sometimes dark brown often with well defined bands of brittle and dull material used primarily as fuel in steamelectric power generation with substantial quantities also used for heat and power applications in manu facturing and to make coke iv Anthracitethe highest rank a harder glossy black coal used primarily for residential and commercial space heating Chemically coal is a hydrogendeficient hydrocarbon with an atomic hydrogentocarbon ratio near 08 as compared to crude oil hydrocarbon derivatives which have an atomic hydrogentocarbon ratio approximately equal to 2 and methane CH4 that has an atomic carbontohydrogen ratio equal to 4 For this reason any process used to convert coal to alternative fuels must add hydro gen or redistribute the hydrogen in the original coal to generate hydrogenrich products and coke Speight 2013a The chemical composition of the coal is defined in terms of its proximate and ultimate elemental analyses Speight 2013a The parameters of proximate analysis are moisture volatile matter ash and fixed carbon Elemental analysis ultimate analysis encompasses the quantitative determination 189 Feedstock Preparation by Gasification of carbon hydrogen nitrogen sulfur and oxygen within the coal Additionally specific physical and mechanical properties of coal and particular carbonization properties are also determined Carbon monoxide and hydrogen are produced by the gasification of coal in which a mixture of gases is produced In addition to carbon monoxide and hydrogen methane and other hydrocarbon derivatives are also produced depending on conditions Gasification may be accomplished either in situ or in processing plants In situ gasification is accomplished by controlled incomplete burning of a coalbed underground while adding air and steam The gases are withdrawn and may be burned to produce heat generate electricity or are utilized as synthesis gas in indirect liquefaction as well as for the production of chemicals Producing diesel and other fuels from coal can be performed through the conversion of coal to synthesis gas a combination of carbon monoxide hydrogen carbon dioxide and methane Synthesis gas is subsequently reacted through FTS processes to produce hydrocarbon derivatives that can be refined into liquid fuels By increasing the quantity of highquality fuels from coal while reducing costs research into this process could help mitigating the dependence on everincreasingly expen sive and depleting stocks of crude oil While coal is an abundant natural resource its combustion or gasification produces both toxic pollutants and greenhouse gases By developing adsorbents to capture the pollutants mercury sul fur arsenic and other harmful gases scientists are striving not only to reduce the quantity of emit ted gases but also to maximize the thermal efficiency of the cleanup Gasification thus offers one of the cleanest and versatile ways to convert the energy contained in coal into electricity hydrogen and other sources of power Turning coal into synthesis gas is not a new concept in fact the basic technology dates back to preWorld War II In fact a gasification unit can process virtually all the viscous feedstock and wastes that are produced in refineries leading to enhanced yields of highvalue products and hence their competitiveness in the market by deeper upgrading of their crude oil 5336 Biomass Biomass can be considered as any renewable feedstock that is in principle be carbon neutral while the plant is growing it uses the suns energy to absorb the same amount of carbon from the atmo sphere as it releases into the atmosphere Speight 2008 2011a Raw materials that can be used to produce biomass derived fuels are widely available they come from a large number of different sources and in numerous forms Rajvanshi 1986 The main basic sources of biomass include i wood including bark logs sawdust wood chips wood pellets and briquettes ii high yield energy crops such as wheat grown specifically for energy applications iii agricultural crops and residues eg straw and iv industrial waste such as wood pulp or paper pulp For processing a simple form of biomass such as untreated and unfinished wood may be converted into a number of physical forms including pellets and wood chips for use in biomass boilers and stoves Biomass includes a wide range of materials that produce a variety of products which are depen dent upon the feedstock Balat 2011 Demirbaş 2011 Ramroop Singh 2011 Speight 2011a In addition the heat content of the different types of biomass widely varies and has to be taken into consideration when designing any conversion process Jenkins and Ebeling 1985 Thermal conversion processes use heat as the dominant mechanism to convert biomass into another chemical form The basic alternatives of combustion torrefaction pyrolysis and gasifica tion are separated principally by the extent to which the chemical reactions involved are allowed to proceed mainly controlled by the availability of oxygen and conversion temperature Speight 2011a Energy created by burning biomass fuel wood also known as dendrothermal energy is par ticularly suited for countries where fuel wood grows more rapidly eg tropical countries There is a number of other less common more experimental or proprietary thermal processes that may 190 Handbook of Petrochemical Processes offer benefits including hydrothermal upgrading and hydroprocessing Some have been developed to be compatible with high moisture content biomass eg aqueous slurries and allow them to be converted into more convenient forms Some of the applications of thermal conversion are combined heat and power CHP and cofiring In a typical dedicated biomass power plant efficiencies range from 7 to 27 In contrast biomass cofiring with coal typically occurs at efficiencies close to those of coal combustors 3040 Baxter 2005 Liu et al 2011 Many forms of biomass contain a high percentage of moisture along with carbohydrates and sugars and mineral constituentsboth of which can influence the economics and viability of a gasification process The presence of high levels of moisture in biomass reduces the temperature inside the gasifier which then reduces the efficiency of the gasifier Many biomass gasification tech nologies therefore require dried biomass to reduce the moisture content prior to feeding into the gasifier In addition biomass can come in a range of sizes In many biomass gasification systems biomass must be processed to a uniform size or shape to be fed into the gasifier at a consistent rate as well as to maximize gasification efficiency Biomass such as wood pellets yard and crop waste and energy crops including switch grass and waste from pulp and paper mills can also be employed to produce bioethanol and synthetic diesel Biomass is first gasified to produce synthesis gas and then subsequently converted via cata lytic processes to the aforementioned downstream products Biomass can also be used to produce electricityeither blended with traditional feedstocks such as coal or by itself Shen et al 2012 Khosravi and Khadse 2013 Speight 2014b Most biomass gasification systems use air instead of oxygen for gasification reactions which is typically used in largescale industrial and power gasification plants Gasifiers that use oxygen require an ASU to provide the gaseousliquid oxygen this is usually not costeffective at the smaller scales used in biomass gasification plants Airblown gasifiers utilize oxygen from air for gasifica tion processes In general biomass gasification plants are comparatively smaller to those of typical coal or crude oil coke plants used in the power chemical fertilizer and refining industries As such they are less expensive to build and have a smaller environmental footprint While a large industrial gasification plant may take up 150 acres of land and process 250015000 tonsday of feedstock eg coal or crude oil coke smaller biomass plants typically process 25200 tons of feedstock per day and take up less than 10 acres Finally while biomass may seem to some observers to be the answer to the global climate change issue advantages and disadvantages of biomass as feedstock must be considered carefully Table 55 Also while taking the issues of global climate change into account it must not be TABLE 55 The Advantages and Disadvantages of Using Biomass as a Feedstock for Energy Production and Chemicals Production Advantages Theoretically inexhaustible fuel source Minimal environmental impact when processes such as fermentation and pyrolysis are used Alcohols and other fuels produced by biomass are efficient viable and relatively cleanburning Biomass is available on a worldwide basis Disadvantages Could contribute to global climate change and particulate pollution when direct combustion is employed Production of biomass and the technological conversion to alcohols or other fuels can be expensive Life cycle assessments should be considered to address energy input and output Possibly a net loss of energy when operated on a small scaleenergy is required to grow the biomass 191 Feedstock Preparation by Gasification ignored that the earth is in an interglacial period where warming will take place The extent of this warming is not knownno one was around to measure the temperature change in the last intergla cial periodand by the same token the contribution of anthropological sources to global climate change cannot be measured accurately 5337 Solid Waste Waste may be MSW which had minimal presorting or refusederived fuel RDF with signifi cant pretreatment usually mechanical screening and shredding Other more specific waste sources excluding hazardous waste and possibly including crude oil coke may provide niche opportunities for coutilization Bridgwater 2003 Arena 2012 Speight 2013a 2014b The traditional wastetoenergy plant based on massburn combustion on an inclined grate has a low public acceptability despite the very low emissions achieved over the last decade with modern flue gas cleanup equipment This has led to difficulty in obtaining planning permissions to construct needed new wastetoenergy plants After much debate various governments have allowed options for advanced waste conversion technologies gasification pyrolysis and anaerobic digestion but will only give credit to the proportion of electricity generated from nonfossil waste Use of waste materials as cogasification feedstocks may attract significant disposal credits Ricketts et al 2002 Cleaner biomass materials are renewable fuels and may attract premium prices for the electricity generated Availability of sufficient fuel locally for an economic plant size is often a major issue as is the reliability of the fuel supply Use of more predictably available coal alongside these fuels overcomes some of these difficulties and risks Coal could be regarded as the base feedstock that keeps the plant running when the fuels producing the better revenue streams are not available in sufficient quantities Coal characteristics are very different to younger hydrocarbon fuels such as biomass and waste Hydrogentocarbon ratios are higher for younger fuels as is the oxygen content This means that reactivity is very different under gasification conditions Gas cleaning issues can also be very different being sulfur a major concern for coal gasification and chlorine compounds and tars more important for waste and biomass gasification There are no current proposals for adjacent gasifiers and gas cleaning systems one handling biomass or waste and one coal alongside each other and feeding the same power production equipment However there are some advantages to such a design as compared with mixing fuels in the same gasifier and gas cleaning systems Electricity production or combined electricity and heat production remain the most likely area for the application of gasification or cogasification The lowest investment cost per unit of electric ity generated is the use of the gas in an existing large power station This has been done in several large utility boilers often with the gas fired alongside the main fuel This option allows a compara tively small thermal output of gas to be used with the same efficiency as the main fuel in the boiler as a large efficient steam turbine can be used It is anticipated that addition of gas from a biomass or wood gasifier into the natural gas feed to a gas turbine to be technically possible but there will be concerns as to the balance of commercial risks to a large power plants and the benefits of using the gas from the gasifier Furthermore the disposal of municipal and industrial waste has become an important problem because the traditional means of disposal landfill are much less environmentally acceptable than previously Much stricter regulation of these disposal methods will make the economics of waste processing for resource recovery much more favorable One method of processing waste streams is to convert the energy value of the combustible waste into a fuel One type of fuel attainable from waste is a low heating value gas usually 100150 Btuscf which can be used to generate process steam or to generate electricity Coprocessing such waste with coal is also an option Speight 2008 2013a 2014b Cogasification technology varies being usually sitespecific and high feedstock dependent At the largest scale the plant may include the well proven fixed bed and entrained flow gasification 192 Handbook of Petrochemical Processes processes At smaller scales emphasis is placed on technologies which appear closest to commercial operation Pyrolysis and other advanced thermal conversion processes are included where power generation is practical using the onsite feedstock produced However the needs to be addressed are i core fuel handling and gasificationpyrolysis technologies ii fuel gas cleanup and iii conver sion of fuel gas to electric power Ricketts et al 2002 Waste may be MSW that had minimal presorting or RDF with significant pretreatment usu ally mechanical screening and shredding Other more specific waste sources excluding hazardous waste and possibly including crude oil coke may provide niche opportunities for coutilization Coutilization of waste and biomass with coal may provide economies of scale that help achieve the above identified policy objectives at an affordable cost In some countries governments propose cogasification processes as being well suited for communitysized developments suggesting that waste should be dealt with in smaller plants serving towns and cities rather than moved to large central plants satisfying the socalled proximity principal In fact neither biomass nor wastes are currently produced or naturally gathered at sites in suf ficient quantities to fuel a modern large and efficient power plant Disruption transport issues fuel use and public opinion all act against gathering hundreds of megawatts MWe at a single location Biomass or wastefired power plants are therefore inherently limited in size and hence in efficiency labor costs per unit electricity produced and in other economies of scale The production rates of municipal refuse follow reasonably predictable patterns over time periods of a few years Recent experience with the very limited current biomass for energy harvesting has shown unpredictable variations in harvesting capability with long periods of zero production over large areas during wet weather The situation is very different for coal This is generally mined or imported and thus large quan tities are available from a single source or a number of closely located sources and supply has been reliable and predictable However the economics of new coalfired power plants of any technology or size have not encouraged any new coalfired power plant in the gas generation market The potential unreliability of biomass longerterm changes in refuse and the size limitation of a power plant using only waste andor biomass can be overcome combining biomass refuse and coal It also allows benefit from a premium electricity price for electricity from biomass and the gate fee associated with waste If the power plant is gasificationbased rather than direct combustion further benefits may be available These include a premium price for the electricity from waste the range of technologies available from the gas to electricity part of the process gas cleaning prior to the main combustion stage instead of after combustion and public image which is generally better for gasification as compared to combustion These considerations lead to current studies of co gasification of wastesbiomass with coal Speight 2008 For largescale power generation 50 MWe the gasification field is dominated by plant based on the pressurized oxygenblown entrained flow or fixed bed gasification of fossil fuels Entrained gasifier operational experience to date has largely been with wellcontrolled fuel feedstocks with shortterm trial work at low cogasification ratios and with easily handled fuels Analyses of the composition of MSW indicate that plastics do make up measureable amounts 510 or more of solid waste streams Many of these plastics are worth recovering as energy In fact many plastics particularly the polyolefin derivatives have high calorific values and simple chemical constitutions of primarily carbon and hydrogen As a result waste plastics are ideal can didates for the gasification process Because of the myriad of sizes and shapes of plastic products size reduction is necessary to create a feed material of a size less than 2 in in diameter Some forms of waste plastics such as thin films may require a simple agglomeration step to produce a particle of higher bulk density to facilitate ease of feeding A plastic such as highdensity polyethylene processed through a gasifier is converted to carbon monoxide and hydrogen and these materials in turn may be used to form other chemicals including ethylene from which the polyethylene is producedclosed the loop recycling 193 Feedstock Preparation by Gasification 5338 Black Liquor Black liquor is the spent liquor from the Kraft process in which pulpwood is converted into paper pulp by removing lignin and hemicellulose constituents as well as other extractable materials from wood to free the cellulose fibers The equivalent spent cooking liquor in the sulfite process is usu ally called brown liquor but the terms red liquor thick liquor and sulfite liquor are also used Approximately seven units of black liquor are produced in the manufacture of one unit of pulp Biermann 1993 Black liquor comprises an aqueous solution of lignin residues hemicellulose and the inorganic chemical used in the process and 15 ww solids of which 10 ww are inorganic and 5 ww are organic Typically the organic constituents in black liquor are 4045 ww soaps 3545 ww lignin and 1015 ww other miscellaneous organic materials The organic constituents in the black liquor are made up of wateralkalisoluble degradation components from the wood Lignin is partially degraded to shorter fragments with sulfur contents in the order of 12 ww and sodium content at approximately 6 ww of the dry solids Cellulose and hemicellulose is degraded to aliphatic carboxylic acid soaps and hemicellulose fragments The extractable constituents yield tall oil soap and crude turpentine The tall oil soap may contain up to 20 ww sodium Lignin components currently serve for hydrolytic or pyrolytic conversion or combustion Alternatively hemicellulose constituents may be used in fermentation processes Gasification of black liquor has the potential to achieve higher overall energy efficiency as com pared to those of conventional recovery boilers while generating an energyrich synthesis gas The synthesis gas can then be burned in a gas turbine combined cycle system BLGCCblack liquor gasification combined cycleand similar to IGCC to produce electricity or converted through catalytic processes into chemicals or fuels eg methanol dimethyl ether FT hydrocarbon deriva tives and diesel fuel 54 GASIFICATION IN A REFINERY Gasification in the refinery is a known method for converting petroleum coke petcoke and other refinery waste streams and residuals vacuum residual visbreaker tar and deasphalter pitch into power steam and hydrogen for use in the production of cleaner transportation fuels Table 54 The main requirement for a gasification feedstock is that it contains both hydrogen and carbon The gasification of refinery feedstocks and other carbonaceous feedstocks has been used for many years to convert organic solids and liquids into useful gaseous liquid and cleaner solid fuels Speight 2011a Brar et al 2012 In the current context Figures 51 and 52 there are a large num ber of different feedstock types for use in a refinerybased gasifier each with different characteris tics including size shape bulk density moisture content energy content chemical composition ash fusion characteristics and homogeneity of all these properties Speight 2013a 2014a 2014b Coal and crude oil coke are used as primary feedstocks for many large gasification plants worldwide Additionally a variety of biomass and wastederived feedstocks can be gasified with wood pel lets and chips waste wood plastics MSW RDF agricultural and industrial wastes sewage sludge switch grass discarded seed corn corn stover and other crop residues all being used Moreover gas ification is i a wellestablished technology ii has broad flexibility of feedstocks and operation and iii is the most environmentally friendly route for handling these feedstocks for power production Typically like all gasification processes the process is carried out at high temperature 1000C 1830F producing synthesis gas syngas some carbon black and ash as major products the amount of ash depends upon the amount of mineral matter in the feedstock IGCC is an alternative process for residua conversion and is a known and used technology within the refining industry for 1 hydrogen production 2 fuel gas production and 3 power generation which when coupled with efficient gas cleaning methods has minimum effect on the environment low SOx and NOx Wolff and Vliegenthart 2011 Speight 2013a 2013b 2014b 194 Handbook of Petrochemical Processes The gasification of coal biomass crude oil or any carbonaceous residues is generally aimed to feedstock conversion to gaseous products In fact depending on the previously described type of gasifier eg airblown enriched oxygenblown and the operating conditions gasification can be used to produce a fuel gas that is suitable for several applications Thus gasification offers one of the most versatile methods with a reduced environmental impact with respect to combustion to convert carbonaceous feedstocks into electricity hydrogen and other valuable energy products The ability of the gasification process to handle noncoal unconventional feedstocks such as heavy crude oil extra heavy crude oil tar sand bitumen or any refinery residual stream enhances the economic potential of most refineries and oil fields Upgrading heavy crude oileither in the oil field at the source or residua in the refineryis and will continue to be an increasingly preva lent means of extracting maximum value from each barrel of oil produced Speight 2011a 2014 Upgrading can convert marginal heavy crude oil into light highervalue crude and can convert heavy sour refinery bottoms into valuable transportation fuels On the other hand most upgrading techniques leave behind an even heavier residue and the costs deposition of such a byproduct may approach the value of the production of liquid fuels and other salable products In short the gasifica tion of residua petroleum coke or other heavy feedstocks to generate synthesis gas produces a clean fuel for firing in a gas turbine Gasification for electric power generation enables the use of a common technology in modern gasfired power plants combined cycle to recover more of the energy released by burning the fuel The use of these two types of turbines in the combined cycle system involves i a combustion tur bine and ii a steam turbine The increased efficiency of the combined cycle for electrical power generation results in a 50 vv decrease in carbon dioxide emissions compared to conventional coal plants Gasification units could be modified to further reduce their climate change impact because a large part of the carbon dioxide generated can be separated from the other product gas before com bustion eg carbon dioxide can be separatedsequestered from gaseous byproducts by using adsor bents eg metalorganic frameworks MOFs to prevent its release to the atmosphere Gasification has also been considered for many years as an alternative to combustion of solid or liquid fuels Gaseous mixtures are simpler to clean as compared to solid or highviscosity liquid fuels Cleaned gases can be used in internal combustionbased power plants that would suffer from severe fouling or corrosion if solid or lowquality liquid fuels were burned inside them In fact the hot synthesis gas produced by gasification of carbonaceous feedstocks can then be processed to remove sulfur compounds mercury and particulate matter prior to its use as fuel in a combustion turbine generator to produce electricity The heat in the exhaust gases from the combus tion turbine is recovered to generate additional steam This steam along with the steam produced by the gasification process drives a steam turbine generator to produce additional electricity In the past decade the primary application of gasification to power production has become more common due to the demand for high efficiency and low environmental impact As anticipated the quality of the gas generated in a system is influenced by feedstock charac teristics gasifier configuration as well as the amount of air oxygen or steam introduced into the system The output and quality of the gas produced is determined by the equilibrium established when the heat of oxidation combustion balances the heat of vaporization and volatilization plus the sensible heat temperature rise of the exhaust gases The quality of the outlet gas BTUft3 is determined by the amount of volatile gases such as hydrogen carbon monoxide water carbon dioxide and methane in the gas stream With some feedstocks the higher the amounts of volatile produced in the early stages of the process the higher the heat content of the product gas In some cases the highest gas quality may be produced at lower temperatures However char oxidation reaction is suppressed when the temperature is too low and the overall heat content of the product gas is diminished Gasification agents are normally air oxygenenriched air or oxygen Steam is sometimes added for temperature control heating value enhancement or allowing the use of external heat allother mal gasification The major chemical reactions break and oxidize hydrocarbon derivatives to give 195 Feedstock Preparation by Gasification a product gas containing carbon monoxide carbon dioxide hydrogen and water Other important components include hydrogen sulfide various compounds of sulfur and carbon ammonia low boiling hydrocarbon derivatives and highboiling tars Depending on the employed gasifier technology and operating conditions significant quantities of water carbon dioxide and methane can be present in the product gas as well as a number of minor and trace components Under reducing conditions in the gasifier most of the feedstock sulfur converts to hydrogen sulfide H2S but 310 converts to carbonyl sulfide COS Organically bound nitrogen in the coal feedstock is generally converted to gaseous nitrogen N2 but some ammonia NH3 and a small amount of hydrogen cyanide HCN are also formed Any chlorine in the coal is converted to hydrogen chloride HCl with some chlorine present in the particulate matter fly ash Trace elements such as mercury and arsenic are released during gasification and partition among the different phases eg fly ash bottom ash slag and product gas 541 Gasification of heavy feedstocks The gasification process can be used to convert viscous feedstocks such as heavy oil extra heavy oil tar sand bitumen vacuum residua and deasphalter bottoms into synthesis gas which is primar ily hydrogen and carbon monoxide Wallace et al 1998 Speight 2014a 2017 The heat generated by the gasification reaction is recovered as the product gas is cooled For example when the quench version of Texaco gasification is employed the steam generated is of medium and low pressure Note that the lowlevel heat used for deasphalting integration is the last stage of cooling the synthesis gas In addition integration of solvent deasphaltinggasification facility is an alternative for upgrading viscous oils economically Wallace et al 1998 An integrated solvent deasphaltinggasification unit can increase the throughput or the crude flexibility of the refinery without creating a new highly undesirable viscous oil stream Typically the addition of a solvent deasphalting unit to process vacuum tower bottoms increases a refinerys production of diesel oil The DAO is converted to die sel using hydrotreating and catalytic cracking Chapter 11 Unfortunately the deasphalter bottoms often need to be blended with product diesel oil to produce a viable outlet for these bottoms A gasifi cation process is capable of converting these deasphalter bottoms to synthesis gas which can then be converted to hydrogen for use in hydrotreating and hydrocracking processes The synthesis gas may also be used by in cogeneration facilities to provide lowcost power and steam to the refinery If the refinery is part of a petrochemical complex the synthesis gas can be used as a chemical feedstock The heat generated by the gasification reaction is recovered as the product gas is cooled 542 Gasification of heavy feedstocks with coal For many decades coal has been the primary feedstock for gasification unitscoal can also be gasified in situ in the underground seam Speight 2013a Luque and Speight 2015 but that is not the subject of this text and is not discussed further However with the concern on the issue of environmental pollutants and the potential shortage of coal in some areas there is a move to feedstocks other than coal for gasification processes Gasification permits the utilization of various feedstocks coal biomass crude oil resids and other carbonaceous wastes to their fullest poten tial Thus power developers would be well advised to consider gasification as a means of convert ing coal to gas Coal is a combustible organic sedimentary rock composed primarily of carbon hydrogen and oxygen formed from ancient vegetation and consolidated between other rock strata to form coal seams The harder forms such as anthracite coal can be regarded as organic metamorphic rocks because of a higher degree of maturation Speight 2013a Coal is the largest single source of fuel for the generation of electricity worldwide EIA 2007 Speight 2013b as well as the largest source of carbon dioxide emissions which have been implicated rightly or wrongly as the primary cause of global climate change Speight 2013b Speight and Islam 2016 Many of the proponents of 196 Handbook of Petrochemical Processes global climate change forget or refuse to acknowledge that the earth is in an interglacial period when warming and climate change can be expectedthis was reflected in the commencement of the melting of the glaciers approximately 11000 years ago Thus considering the geological sequence of events the contribution of carbon dioxide from anthropogenic sources is not known with any degree of accuracy Coal occurs in different forms or types Speight 2013a Variations in the nature of the source material and local or regional the variations in the coalification processes cause the vegetal matter to evolve differently Thus various classification systems exist to define the different types of coal Thus as geological processes increase their effect over time the coal precursors are transformed over time into i lignitealso referred to as brown coal and is the lowest rank of coal that is used almost exclusively as fuel for steamelectric power generation jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age ii subbitu minous coal which exhibits properties ranging from those of lignite to those of bituminous coal are used primarily as fuel for steamelectric power generation iii bituminous coal which is a dense coal usually black sometimes dark brown often with welldefined bands of bright and dull material is used primarily as fuel in steamelectric power generation with substantial quantities also used for heat and power applications in manufacturing and to make coke and iv anthracite which is the highest rank coal and is a hard glossy black coal used primarily for residential and commercial space heating Chemically coal is a hydrogendeficient hydrocarbon with an atomic hydrogentocarbon ratio near 08 as compared to crude oil hydrocarbon derivatives which have an atomic hydrogentocarbon ratio approximately equal to 2 and methane CH4 that has an atomic carbontohydrogen ratio equal to 4 For this reason any process used to convert coal to alternative fuels must add hydrogen or redistribute the hydrogen in the original coal to produce hydrogenrich products and coke Speight 2013a Gas turbine improvements lead to a number of power plants where fuels usually coal are gasified with a viscous feedstock and the gas is cleaned and used in a combined cycle gas turbine power plant Such power plants generally have higher capital cost higher operating cost and lower availability than conventional combustion and steam cycle power plant on the same fuel Efficiencies of the most sophisticated plants have been broadly similar to the best conventional steam plants with losses in gasification and gas cleaning being balanced by the high efficiency of combined cycle power plants Environmental aspects resulting from the gas cleaning before the main combustion stage have often been excellent even in plants with exceptionally high levels of contaminants in the feedstock fuels 543 Gasification of heavy feedstocks with Biomass Gasification is an established technology Hotchkiss 2003 Speight 2013a Comparatively bio mass gasification has been the focus of research in recent years to estimate efficiency and perfor mance of the gasification process using various types of biomass such as sugarcane residue Gabra et al 2001 rice hulls Boateng et al 1992 pine sawdust Lv et al 2004 almond shells Rapagnà and Latif 1997 Rapagnà et al 2000 wheat straw Ergudenler and Ghaly 1993 food waste Ko et al 2001 and wood biomass Pakdel and Roy 1991 Bhattacharya et al 1999 Chen et al 1992 Hanaoka et al 2005 Recently cogasification of various biomass and coal mixtures has attracted a great deal of interest from the scientific community Feedstock combinations including Japanese cedar wood and coal Kumabe et al 2007 coal and saw dust coal and pine chips Pan et al 2000 coal and silver birch wood Collot et al 1999 and coal and birch wood Brage et al 2000 have been reported in gasification practices Cogasification of coal and biomass has some synergythe process not only produces a low carbon footprint on the environment but also improves the H2CO ratio in the produced gas which is required for liquid fuel synthesis Sjöström et al 1999 Kumabe et al 2007 In addition the inorganic matter present in biomass catalyzes the gasification of coal However cogasification processes require custom fittings and optimized processes for the coal and regionspecific wood residues 197 Feedstock Preparation by Gasification While cogasification of coal and biomass is advantageous from a chemical viewpoint some practical problems are present on upstream gasification and downstream processes On the upstream side the particle size of the coal and biomass is required to be uniform for optimum gasification In addition moisture content and pretreatment torrefaction are very important during upstream processing While upstream processing is influential from a material handling point of view the choice of gasifier operation parameters temperature gasifying agent and catalysts dictate the product gas composition and quality Biomass decomposition occurs at a lower temperature than coal and therefore different reactors compatible to the feedstock mixture are required Brar et al 2012 Furthermore feedstock and gasifier type along with operating parameters not only decide product gas composition but also dictate the amount of impurities to be handled downstream Downstream processes need to be modified if coal is cogasified with biomass Heavy metals and other impuri ties such as sulfurcontaining compounds and mercury present in coal can make synthesis gas difficult to use and unhealthy for the environment Alkali present in biomass can also cause cor rosion problems high temperatures in downstream pipes An alternative option to downstream gas cleaning would be to process coal to remove mercury and sulfur prior to feeding into the gasifier However first and foremost coal and biomass require drying and size reduction before they can be fed into a gasifier Size reduction is needed to obtain appropriate particle sizes however drying is required to achieve moisture content suitable for gasification operations In addition biomass densification may be conducted to prepare pellets and improve density and material flow in the feeder areas It is recommended that biomass moisture content should be less than 15 ww prior to gasification High moisture content reduces the temperature achieved in the gasification zone thus resulting in incomplete gasification Forest residues or wood has a fiber saturation point at 30 31 moisture content dry basis Brar et al 2012 Compressive and shear strength of the wood increases with decreased moisture content below the fiber saturation point In such a situation water is removed from the cell wall leading to shrinkage The longchain molecule constituents of the cell wall move closer to each other and bind more tightly A high level of moisture usually injected in form of steam in the gasification zone favors formation of a watergas shift reaction that increases hydrogen concentration in the resulting gas The torrefaction process is a thermal treatment of biomass in the absence of oxygen usually at 250C300C to drive off moisture decompose hemicellulose completely and partially decompose cellulose Speight 2011a Torrefied biomass has reactive and unstable cellulose molecules with broken hydrogen bonds and not only retains 7995 of feedstock energy but also produces a more reactive feedstock with lower atomic hydrogencarbon and oxygencarbon ratios to those of the original biomass Torrefaction results in higher yields of hydrogen and carbon monoxide in the gasification process Finally the presence of mineral matter in the coalbiomass feedstock is not appropriate for fluid ized bed gasification Low melting point of ash present in woody biomass leads to agglomeration that causes defluidization of the ash and sintering deposition as well as corrosion of the gasifier construction metal bed Biomass containing alkali oxides and salts are likely to produce clinkering slagging problems from ash formation McKendry 2002 Thus it is imperative to be aware of the melting of biomass ash its chemistry within the gasification bed no bed silicasand or calcium bed and the fate of alkali metals when using fluidized bed gasifiers Most small to mediumsized biomasswaste gasifiers are air blown operating at atmospheric pressure and at temperatures in the range of 800C100C 1470F2190F They face very dif ferent challenges compared to large gasification plantsthe use of smallscale air separation plant should oxygen gasification be preferred Pressurized operation which eases gas cleaning may not be practical Biomass fuel producers coal producers and to a lesser extent waste companies are enthusiastic about supplying cogasification power plants and realize the benefits of cogasification with alternate fuels Lee 2007 Speight 2008 2011a Lee and Shah 2013 Speight 2013a 2013b The benefits 198 Handbook of Petrochemical Processes of a cogasification technology involving coal and biomass include the use of a reliable coal supply with gatefee waste and biomass that allows the economies of scale from a larger plant to be sup plied just with waste and biomass In addition the technology offers a future option of hydrogen production and fuel development in refineries In fact oil refineries and petrochemical plants are opportunities for gasifiers when the hydrogen is particularly valuable Speight 2011b 2014a 544 Gasification of heavy feedstocks with waste Waste may be MSW that had minimal presorting or RDF with significant pretreatment usually mechanical screening and shredding Other more specific waste sources excluding hazardous waste and possibly including crude oil coke may provide niche opportunities for coutilization John and Singh 2011 For largescale power generation 50 MWe the gasification field is dominated by plant based on the pressurized oxygenblown entrained flow or fixed bed gasification of fossil fuels The use of fuel cells with gasifiers is frequently discussed but the current cost of fuel cells is such that their use for mainstream electricity generation is uneconomic In summary coal may be cogasified with waste or biomass for environmental technical or commercial reasons It allows larger more efficient plants than those sized for grown biomass or arising waste within a reasonable transport distance specific operating costs are likely to be lower and fuel supply security is assured 55 GAS PRODUCTION AND OTHER PRODUCTS The gasification of a carbonaceous feedstock ie char produced from the feedstock is the conver sion of the feedstock by any one of a variety of processes to produce gaseous products that are combustible as well as a wide range of chemical products from synthesis gas Figure 54 With the rapid increase in the use of coal from the 15th century onwards it is not surprising that the concept of using coal to produce a flammable gas especially the use of the water and hot coal became common place van Heek and Muhlen 1991 As a result the characteristics of rank mineral matter particle size and reaction conditions are all recognized as having a bearing on the outcome of the process not only in terms of gas yields but also on gas properties van Heek and Muhlen 1991 The products from the gasification of the process may be of low medium or high heat content highBtu as dictated by the process as well as by the ultimate use for the gas FIGURE 54 Potential products from heavy feedstock gasification 199 Feedstock Preparation by Gasification Baker and Rodriguez 1990 Probstein and Hicks 1990 Lahaye and Ehrburger 1991 Matsukata et al 1992 Speight 2013a The ability of a refinery to efficiently accommodate heavy crude oils or heavy bottom streams such as deasphalter bottoms and visbreaker bottoms enhances the economic potential of the refin ery and the development of heavy oil and tar sand resources A refinery with the flexibility to meet the increasing product specifications for fuels through the ability to upgrade heavy feedstocks is an increasingly attractive means of extracting maximum value from each barrel of oil produced Upgrading can convert marginal heavy crude oil into light higher value crude and can convert heavy sour refinery bottoms into valuable transportation fuels On the downside most upgrading processes also produce an even heavier residue whose disposition costs may approach the value of the upgrade itself For example solvent deasphalting and residue coking are used in heavy crudebased refiner ies to upgrade heavy bottom streams to intermediate products that may be processed to produce transportation fuels The technology may also be used in the oil field to enhance the value of heavy crude oil before the feedstock reaches the refinery and a beneficial use is often difficult to find for the byproducts from these processes 551 Gaseous Products The products of gasification are varied insofar as the gas composition varies with the system employed Speight 2013a It is emphasized that the gas product must be first freed from any pollutants such as particulate matter and sulfur compounds before further use particularly when the intended use is a watergas shift or methanation Cusumano et al 1978 Probstein and Hicks 1990 5511 Synthesis Gas Synthesis gas is comparable in its combustion efficiency to natural gas Speight 2008 Chadeesingh 2011 which reduces the emissions of sulfur nitrogen oxides and mercury resulting in a much cleaner fuel Nordstrand et al 2008 Sondreal et al 2004 Yang et al 2007 Wang et al 2008 The resulting hydrogen gas can be used for electricity generation or as a transport fuel The gasifica tion process also facilitates capture of carbon dioxide emissions from the combustion effluent see discussion of carbon capture and storage below Although synthesis gas can be used as a standalone fuel the energy density of synthesis gas is approximately half that of natural gas and is therefore mostly suited for the production of transpor tation fuels and other chemical products Synthesis gas is mainly used as an intermediary building block for the final production synthesis of various fuels such as SNG methanol and synthetic crude oil fuel dimethyl ethersynthesized gasoline and diesel fuel Chadeesingh 2011 Speight 2013a At this point and in order to dismiss any confusion that may arise synthesis gas as gen erated from biomass is not the same as biogas Biogas is a clean and renewable form of energy generated from biomass that could very well substitute for conventional sources of energy The gas is generally composed of methane 5565 carbon dioxide 3545 nitrogen 03 hydrogen 01 and hydrogen sulfide 01 The use of synthesis gas offers the opportunity to furnish a broad range of environmentally clean fuels and chemicals and there has been steady growth in the traditional uses of synthesis gas Almost all hydrogen gas is manufactured from synthesis gas and there has been an increase in the demand for this basic chemical In fact the major use of synthesis gas is in the manufacture of hydrogen for a growing number of purposes especially in crude oil refineries Speight 2014a Methanol not only remains the second largest consumer of synthesis gas but has shown remarkable growth as part of the methyl ethers used as octane enhancers in automotive fuels The FTS remains the third largest consumer of synthesis gas mostly for transportation fuels but also as a growing feedstock source for the manufacture of chemicals including polymers 200 Handbook of Petrochemical Processes The hydroformylation of olefin derivatives the Oxo reaction a completely chemical use of synthe sis gas is the fourth largest use of carbon monoxide and hydrogen mixtures A direct application of synthesis gas as fuel and eventually also for chemicals that promises to increase is its use for IGCC units for the generation of electricity and also chemicals crude oil coke or viscous feedstocks Holt 2001 Finally synthesis gas is the principal source of carbon monoxide which is used in an expanding list of carbonylation reactions which are of major industrial interest 5512 Low Btu Gas During the production of gas by oxidation with air the oxygen is not separated from the air and as a result the gas product invariably has a low Btu content low heat content 150300 Btuft3 Several important chemical reactions and a host of side reactions are involved in the manufacture of low heat content gas under the hightemperature conditions employed Chadeesingh 2011 Speight 2013a Low heat content gas contains several components four of which are always major compo nents present at levels of at least several percent a fifth component methane is marginally a major component The nitrogen content of low heat content gas ranges from somewhat less than 33 vv to slightly more than 50 vv and cannot be removed by any reasonable means the presence of nitrogen at these levels makes the product gas low heat content by definition The nitrogen also strongly limits the applicability of the gas to chemical synthesis Two other noncombustible components water H2O and carbon dioxide CO further lower the heating value of the gas water can be removed by condensation and carbon dioxide by relatively straightforward chemical means The two major combustible components are hydrogen and carbon monoxide the H2CO ratio varies from approximately 23 to 32 Methane may also make an appreciable contribution to the heat content of the gas Of the minor components hydrogen sulfide is the most significant and the amount produced is in fact proportional to the sulfur content of the feedstock Any hydrogen sulfide present must be removed by one or more of several procedures Mokhatab et al 2006 Speight 2007 2014a Low heat content gas is of interest to industry as a fuel gas or even on occasion as a raw amate rial from which ammonia methanol and other compounds may be synthesized 5513 Medium Btu Gas Medium Btu gas medium heat content gas has a heating value in the range 300550 Btuft3 and the composition is much like that of low heat content gas except that there is virtually no nitrogen The primary combustible gases in medium heat content gas are hydrogen and carbon monoxide Medium heat content gas is considerably more versatile than low heat content gas like low heat content gas medium heat content gas may be used directly as a fuel to raise steam or used through a combined power cycle to drive a gas turbine with the hot exhaust gases employed to raise steam but medium heat content gas is especially amenable to synthesize methane by methanation higher hydrocarbon derivatives by FTS methanol and a variety of synthetic chemicals The reactions used to produce medium heat content gas are the same as those employed for low heat content gas synthesis the major difference being the application of a nitrogen barrier such as the use of pure oxygen to keep diluent nitrogen out of the system In medium heat content gas the H2CO ratio varies from 23 to 31 and the increased heating value correlates with higher methane and hydrogen contents as well as with lower carbon dioxide contents Furthermore the very nature of the gasification process used to produce the medium heat content gas has a marked effect upon the ease of subsequent processing For example the CO2acceptor product is quite amenable to use for methane production because it has i the desired H2CO ratio just exceeding 31 ii an initially high methane content and iii relatively low water and carbon dioxide contents Other gases may require appreciable shift reaction and removal of large quantities of water and carbon dioxide prior to methanation 201 Feedstock Preparation by Gasification 5514 High Btu Gas High Btu gas high heat content gas is essentially pure methane and often referred to as SNG Speight 1990 2013a However to qualify as substitute natural gas a product must contain at least 95 methane giving an energy content heat content of synthetic natural gas in the order of 9801080 Btuft3 The commonly accepted approach to the synthesis of high heat content gas is the catalytic reac tion of hydrogen and carbon monoxide 3H CO CH H O 2 4 2 To avoid catalyst poisoning the feed gases for this reaction must be quite pure and therefore impu rities in the product are rare The large quantities of water produced are removed by condensation and recirculated as very pure water through the gasification system The hydrogen is usually present in slight excess to ensure that the toxic carbon monoxide is reacted this small quantity of hydrogen will lower the heat content to a small degree The carbon monoxidehydrogen reaction is somewhat inefficient as a means of producing meth ane because the reaction liberates large quantities of heat In addition the methanation catalyst is troublesome and prone to poisoning by sulfur compounds and the decomposition of metals can destroy the catalyst Hydrogasification may be thus employed to minimize the need for methanation C 2H2 CH feedstock 4 The product of hydrogasification is far from pure methane and additional methanation is required after hydrogen sulfide and other impurities are removed 552 liquid Products The production of liquid fuels from a carbonaceous feedstock via gasification is often referred to as the indirect liquefaction of the feedstock Speight 2013a 2014a In these processes the feedstock is not converted directly into liquid products but involves a twostage conversion operation in which the feedstock is first converted by reaction with steam and oxygen to produce a gaseous mixture that is composed primarily of carbon monoxide and hydrogen synthesis gas The gas stream is subsequently purified to remove sulfur nitrogen and any particulate matter after which it is cata lytically converted to a mixture of liquid hydrocarbon products The synthesis of hydrocarbon derivatives from carbon monoxide and hydrogen synthesis gas the FTS is a procedure for the indirect liquefaction of various carbonaceous feedstocks Speight 2011a 2011b This process is the only liquefaction scheme currently in use on a relatively large commercial scale for the production of liquid fuels from coal using the FT process Thus the feedstock is converted to gaseous products at temperatures in excess of 800C 1470F and at moderate pressures to produce synthesis gas C H O CO H feedstock 2 2 In practice the FT reaction is carried out at temperatures of 200C350C 390F660F and at pressures of 754000 psi The hydrogencarbon monoxide ratio is typically in the order of 221 or 251 since up to three volumes of hydrogen may be required to achieve the next stage of the liquid production the synthesis gas must then be converted by means of the watergas shift reaction to the desired level of hydrogen CO H O CO H 2 2 2 202 Handbook of Petrochemical Processes After this the gaseous mix is purified and converted to a wide variety of hydrocarbon derivatives nCO 2n 1 H C H nH O 2 n 2n 2 2 These reactions result primarily in low and mediumboiling aliphatic compounds suitable for gaso line and diesel fuel 553 solid Products The solid product solid waste of a gasification process is typically ash which is the oxides of met als containing constituents of the feedstock The amount and type of solid waste produced is very much feedstock dependent The waste is a significant environmental issue due to the large quantities produced chiefly fly ash if coal is the feedstock or a cofeedstock and the potential for leaching of toxic substances such as heavy metals such as lead and arsenic into the soil and groundwater at disposal sites At the high temperature of the gasifier most of the mineral matter of the feedstock is transformed and melted into slag an inert glasslike material and under such conditions nonvolatile metals and mineral compounds are bound together in molten form until the slag is cooled in a water bath at the bottom of the gasifier or by natural heat loss at the bottom of an entrained bed gasifier Slag production is a function of mineral matter content of the feedstockcoal produces much more slag per unit weight than crude oil coke Furthermore as long as the operating temperature is above the fusion temperature of the ash slag will be produced The physical structure of the slag is sensitive to changes in operating temperature and pressure of the gasifier and a quick physical examination of the appearance of the slag can often be an indication of the efficiency of the conversion of feedstock carbon to gaseous product in the process Slag is comprised of black glassy silicabased materials and is also known as frit which is a high density vitreous and abrasive material low in carbon and formed in various shapes from jag ged and irregular pieces to rod and needlelike forms Depending upon the gasifier process param eters and the feedstock properties there may also be residual carbon char Vitreous slag is much preferable to ash because of its habit of encapsulating toxic constituents such as heavy metals into a stable nonleachable material Leachability data obtained from different gasifiers unequivocally shows that gasifier slag is highly nonleachable and can be classified as nonhazardous Because of its particular properties and nonhazardous nontoxic nature slag is relatively easily marketed as a byproduct for multiple advantageous uses which may negate the need for its longterm disposal The physical and chemical properties of gasification slag are related to i the composition of the feedstock ii the method of recovering the molten ash from the gasifier and iii the proportion of devolatilized carbon particles char discharged with the slag The rapid waterquench method of cooling the molten slag inhibits recrystallization and results in the formation of a granular amor phous material Some of the differences in the properties of the slag may be attributed to the specific design and operating conditions prevailing in the gasifiers Char is the finer component of the gasifier solid residuals composed of unreacted carbon with vari ous amounts of siliceous ash Char can be recycled back into the gasifier to increase carbon usage and has been used as a supplemental fuel source for use in a combustor The irregularly shaped particles have a welldefined pore structure and have excellent potential as an adsorbent and precursor to acti vated carbon In terms of recycling char to the gasifier a property that is important to fluidization is the effective particle density If the char has a large internal void space the density will be much less than that of the feedstock especially coal or char from slow carbonization of a carbonaceous feedstock 56 THE FUTURE The future depends very much on the effect of gasification processes on the surrounding envi ronment It is these environmental effects and issues that will direct the success of gasification 203 Feedstock Preparation by Gasification In fact there is the distinct possibility that within the foreseeable future the gasification process will increase in popularity in crude oil refineriessome refineries may even be known as gasifica tion refineries Speight 2011b A gasification refinery would have as the center piece gasification technology as is the case of the Sasol refinery in South Africa Couvaras 1997 The refinery would produce synthesis gas from the carbonaceous feedstock from which liquid fuels would be manu factured using the FTS technology In fact gasification to produce synthesis gas can proceed from any carbonaceous material including biomass Inorganic components of the feedstock such as metals and minerals are trapped in an inert and environmentally safe form as char which may be used as a fertilizer Biomass gas ification is therefore one of the most technically and economically convincing energy possibilities for a potentially carbon neutral economy The manufacture of gas mixtures of carbon monoxide and hydrogen has been an important part of chemical technology for about a century Originally such mixtures were obtained by the reac tion of steam with incandescent coke and were known as water gas Eventually steam reforming processes in which steam is reacted with natural gas methane or crude oil naphtha over a nickel catalyst found wide application for the production of synthesis gas A modified version of steam reforming known as autothermal reforming which is a combina tion of partial oxidation near the reactor inlet with conventional steam reforming further along the reactor improves the overall reactor efficiency and increases the flexibility of the process Partial oxidation processes using oxygen instead of steam also found wide application for synthesis gas manufacture with the special feature that they could utilize lowvalue feedstocks such as viscous crude oil residues In recent years catalytic partial oxidation employing very short reaction times milliseconds at high temperatures 850C1000C is providing still another approach to synthe sis gas manufacture Hickman and Schmidt 1993 In a gasifier the carbonaceous material undergoes several different processes i pyrolysis of carbonaceous fuels ii combustion and iii gasification of the remaining char The process is very dependent on the properties of the carbonaceous material and determines the structure and compo sition of the char which will then undergo gasification reactions As crude oil supplies decrease the desirability of producing gas from other carbonaceous feed stocks will increase especially in those areas where natural gas is in short supply It is also antici pated that costs of natural gas will increase thereby allowing the gasification process to compete as an economically viable process The conversion of the gaseous products of gasification processes to synthesis gas a mixture of hydrogen H2 and carbon monoxide CO in a ratio appropriate to the application needs additional steps after purification The product gasescarbon monoxide carbon dioxide hydrogen methane and nitrogencan be used as fuels or as raw materials for chemical or fertilizer manufacture Gasification by means other than the conventional methods has also received some attention and has provided rationale for future processes Rabovitser et al 2010 In the process a carbo naceous material and at least one oxygen carrier are introduced into a nonthermal plasma reactor at a temperature in the range of approximately 300C to 700C 570F1290F and a pressure in a range from atmospheric pressure to approximate 1030 psi and a nonthermal plasma discharge is generated within the nonthermal plasma reactor The carbonaceous feedstock and the oxygen carrier are exposed to the nonthermal plasma discharge resulting in the formation of a product gas which comprises substantial amounts of hydrocarbon derivatives such as methane hydrogen andor carbon monoxide Furthermore gasification and conversion of carbonaceous solid fuels to synthesis gas for appli cation of power liquid fuels and chemicals is practiced worldwide Crude oil coke coal biomass and refinery waste are major feedstocks for an onsite refinery gasification unit The concept of blending of a variety of carbonaceous feedstocks such as coal biomass or refinery waste with a viscous feedstock of the coke from the thermal processing of the viscous feedstock is advantageous in order to obtain the highest value of products as compared to gasification of crude oil coke alone 204 Handbook of Petrochemical Processes Furthermore based on gasifier type cogasification of carbonaceous feedstocks can be an advan tageous and efficient process In addition the variety of upgrading and delivery options that are available for application to synthesis gas enable the establishment of an integrated energy supply system whereby synthesis gases can be upgraded integrated and delivered to a distributed network of energy conversion facilities including power CHP and combined cooling heating and power sometime referred to as trigeneration as well as used as fuels for transportation applications As a final note the production of chemicals from biomass is based on thermochemical conver sion routes which are in turn based on biomass gasification Roddy and MansonWhitton 2012 The products are i a gas which is the desired product and ii a solid ash residue whose composi tion depends on the type of biomass Continuous gasification processes for various feedstocks have been under development since the early 1930s Ideally the gas produced would be a mixture of hydrogen and carbon monoxide but in practice it also contains methane carbon dioxide and a range of contaminants A variety of gasification technologies is available across a range of sizes from small updraft and downdraft gasifiers through a range of fluidized bed gasifiers at an intermediate scale and on to larger entrained flow and plasma gasifiers Bridgwater 2003 Roddy and MansonWhitton 2012 In an updraft gasifier the oxidant is blown up through the fixed gasifier bed with the syngas exiting at the top whereas in a downdraft gasifier the oxidant is blown down through the reactor with the synthesis gas exiting at the bottom Gasification processes tend to operate either above the ash melting temperature typically 1200C 2190F or below the ash melting temperature typically 1000C 1830F 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Processes Energy 589 905914 Sjöström K Chen G Yu Q Brage C and Rosén C 1999 Promoted Reactivity of Char in Cogasification of Biomass and Coal Synergies in the Thermochemical Process Fuel 78 11891194 Sondreal E A Benson S A Pavlish J H and Ralston NVC 2004 An Overview of Air Quality III Mercury Trace Elements and Particulate Matter Fuel Processing Technology 85 425440 Speight JG 1990 Chapter 33 In Fuel Science and Technology Handbook JG Speight Editor Marcel Dekker Inc New York Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG 2008 Synthetic Fuels Handbook Properties Processes and Performance McGrawHill New York Speight JG Editor 2011a Biofuels Handbook Royal Society of Chemistry London UK Speight JG 2011b The Refinery of the Future Gulf Professional Publishing Elsevier Oxford UK Speight JG 2013a The Chemistry and Technology of Coal 3rd Edition CRC Press Boca Raton FL Speight JG 2013b CoalFired Power Generation Handbook Scrivener Publishing Salem MA Speight JG 2014a The Chemistry and Technology of Petroleum 5th Edition CRC Press Boca Raton FL Speight JG 2014b Gasification of Unconventional Feedstocks Gulf Professional Publishing Elsevier Oxford UK Speight JG and Islam MR 2016 Peak EnergyMyth or Reality Scrivener Publishing Beverly MA Speight JG 2017 Handbook of Petroleum Refining CRC Press Boca Raton FL Sundaresan S and Amundson NR 1978 Studies in Char GasificationI A lumped Model Chemical Engineering Science 34 345354 Sutikno T and Turini K 2012 Gasifying Coke to Produce Hydrogen in Refineries Petroleum Technology Quarterly Q3 105 208 Handbook of Petrochemical Processes Van Heek KH Muhlen HJ 1991 In Fundamental Issues in Control of Carbon Gasification Reactivity J Lahaye and P Ehrburger Editors Kluwer Academic Publishers Inc Dordrecht The Netherlands p 1 Wallace PS Anderson MK Rodarte AI and Preston WE 1998 Heavy Oil Upgrading by the Separation and Gasification of Asphaltenes Proceedings of Presented at the Gasification Technologies Conference San Francisco CA October wwwglobalsyngasorguploadseventLibrarygtc9817ppdf Wang Y Duan Y Yang L Jiang Y Wu C Wang Q and Yang X 2008 Comparison of Mercury Removal Characteristic between Fabric Filter and Electrostatic Precipitators of CoalFired Power Plants Journal of Fuel Chemistry and Technology 361 2329 Wolff J and Vliegenthart E 2011 Gasification of Heavy Ends Petroleum Technology Quarterly Q2 15 Yang H Xua Z Fan M Bland AE and Judkins RR 2007 Adsorbents for Capturing Mercury in CoalFired Boiler Flue Gas Journal of Hazardous Materials 146 111 209 6 Chemicals from Paraffin Hydrocarbons 61 INTRODUCTION Natural gas and crude oil are primary feedstocks and continue to be the main sources of sec ondary feedstocks for the production of petrochemicals For example methane from natural gas as well as other lowboiling low molecular weight hydrocarbon derivatives is recovered for use as feedstocks for the production of olefin derivatives and diolefin derivatives In addition the gas eous constituents from crude oil associated natural gas as well as refinery gases from different crude oil processing schemessuch as cracking and reforming processes Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017are important sources for olefin derivatives Paraffin hydrocarbon derivatives ie hydrocarbon derivatives with the general formula CnH2n2 that are used for producing petrochemical products range from methane CH4 to the higher molecular weight hydrocarbon derivatives that exist in various distillate fractions such as naphtha kerosene and gas oil as well as the nonvolatile residua resids residues Table 61 The proportion of pure hydrocarbon derivatives in residua is typically at a low level and most of the constituents of residua also contain heteroatoms nitrogen oxygen sulfur and metals in various molecular locations Speight 2014a Chemically paraffin derivatives are relatively inactive compared to olefin derivatives diolefin derivatives and aromatic derivatives However these compounds paraffin derivatives are the pre cursors for olefin derivatives through a variety of cracking processes the C6C9 paraffin deriva tives and cycloparaffin derivatives are especially important for the production of aromatic products TABLE 61 Names of the Simple Saturated Paraffin and Cycloparaffin and Unsaturated Olefin and Acetylene Hydrocarbon Derivatives Number of Carbon Atoms Alkane Single Bond CnH2n2 Alkene Double Bond CnH2n Alkyne Triple Bond CnH2n2 Cycloalkane CnH2n Diene CnH2n2 1 Methane NA NA NA NA 2 Ethane Ethylene ethene Acetylene ethyne NA NA 3 Propane Propylene propene Propyne methylacetylene Cyclopropane Propadiene 4 Butane Butylene butene Butyne Cyclobutane Butadiene 5 Pentane Pentene Pentyne Cyclopentane Pentadiene 6 Hexane Hexene Hexyne Cyclohexane Hexadiene 7 Heptane Heptene Heptyne Cycloheptane Heptadiene 8 Octane Octene Octyne Cyclooctane Octadiene 9 Nonane Nonene Nonyne Cyclononane Nonadiene 10 Decane Decene Decyne Cyclodecane Decadiene 11 Undecane Undecene Undecyne Cycloundecane Undecadiene 12 Dodecane Dodecene Dodecyne Cyclododecane Dodecadiene NA not applicable to this formula 210 Handbook of Petrochemical Processes through reforming Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Briefly and by way of introduction the term steam cracking unit refers to all processes inside the battery limits of a steam cracker and typically consist of three sections i the pyrolysis section ii the primary fractionationcompression section and iii the product recoveryseparation The pyrolysis section is the heart of a steam cracking unit The feedstock first enters the convection section of a pyrolysis furnace in which the feedstock such as naphtha is vaporized with slightly superheated steam and is passed into long 1225 m narrow tubes 25125 mm in diam eter which are fabricated from iron chromium and nickel alloys The steam is added to reduce par tial pressure of products and to prevent unwanted side reactions Pyrolysis takes place mainly in the radiant section of the furnace in the absence of a catalyst where tubes are externally heated from 750C to 900C up to 1100C 1380F1650F and up to 2010F where the feedstock is cracked thermally decomposed to lower molecular weight products After leaving the furnace the hot gas mixture is quenched in a series of heat exchangers to approximately about 350C 650F This avoids degradation by secondary reactions but the heat exchangers are prone to fouling ie coke formation on the walls Further cooling of the gas mixture is achieved using a liquid quench oil Primary fractionation applies to liquid feedstocks such as naphtha and gas oil only and not for gaseous feedstocks such as ethane In the primary fractionator gas mixtures are first cooled to around 150C 300F and most benzene toluene and xylenes BTX and fuel oils are condensed In the quench water tower water from dilution steam is recovered for recycling The steam is passed through four or five stages of gas compression with temperatures at approximately 15C100C 59F212F then cooling and finally cleanup to remove acid gases carbon dioxide and water A common issue with compression is fouling buildup of solid byproducts in the cracked gas com pressors and aftercoolers Wash oil and water are used to reduce fouling The product recoveryseparation section is essentially a separation process through distilla tion refrigeration and extraction The equipment includes chilling trains and fractionation towers which include refrigeration demethanizer deethanizer depropanizer and finally a debutanizer Demethanization requires very low temperatures in the order of 114C 173F Ethylene and ethane separation often requires large distillation columns with 120180 trays and high reflux ratios Undesired acetylene is removed through catalytic hydrogenation or extractive distillation Similarly propane and propylene are reboiled with quench water at approximately 80C 176F and separated into the depropanizer Ethylene and propylene refrigeration systems can be operated at low temperatures within 10C to 150C 14 and 238F for cooling and high pressure 220450 psi for compression Ethane and propane are either recycled as feedstocks or burned or exported as fuels A considerable amount of ethylene is condensed and recovered through turboexpanders Methane and hydrogen are separated at cryogenic temperatures by turbocompressors Generally ethane steam cracking also requires three sections that are similar to those in the case of naphtha steam cracking process However ethane steam cracking requires slightly higher temperature in the furnace a higher capacity of the deethanizer but less infrastructure facilities An additional issue is the potential for coking to occur The reactions leading to the formation of coke results in the deposition of the coke carbon on the furnace coils and therefore reduces the effectiveness of the furnace Although the presence of steam reduces some coking regular decoking still is required in various parts of the pyrolysis section Before decoking feedstocks are removed from the furnace after which highpressure steam and air are fed to the furnace as it is heated up to 880C900C or even up to 1100C up to 1100C 1615F1650F and up to 2010F Coke on the inner surfaces of the wall and tubes is either washed away with highpressure water or removed mechanically A typical steam cracker has six to eight furnaces to accommodate onstream opera tion and offstream maintenance Similar decoking though far less frequent is also required for the heat exchangers that are associated with furnaces heat exchanger foiling is a common occurrence in hightemperature operations Parkash 2003 Gary et al 2007 Speight 2014a 2014b Hsu and Robinson 2017 Speight 2017 211 Chemicals from Paraffin Hydrocarbons This chapter presents to the reader a selection of the chemical and physical properties of the methane CH4 and butane C4H10 paraffin derivatives The chemical and physical properties of the higher molecular weight paraffin derivatives that are typically present as mixtures in the various distillates fractions of crude oil are also presented 62 METHANE Methane CH4 is the simplest alkane and the principal component of natural gas usually 7090 vv Katz 1959 Kohl and Riesenfeld 1985 Maddox et al 1985 Newman 1985 Kohl and Nielsen 1997 Mokhatab et al 2006 Speight 2014a Methane CH4 commonly often incor rectly known as natural gas is colorless and naturally odorless and burns efficiently without many byproducts It is also known as marsh gas or methyl hydride and is easily ignited The vapor is lighter than air Table 62 Under prolonged exposure to fire or intense heat the containers may rupture in a violent explosion Methane is used in making other chemicals and as a constituent of the fuel natural gas In addition there is a large but unknown amount of methane in gas hydrates methane clathrates in the ocean floors and significant amounts of methane are produced anaerobically by methanogen esis Other sources include mud volcanoes such as those that occur regularly in Trinidad which are connected with deep geological faults landfills and livestock primarily ruminants from enteric fermentation Natural gas can be used as a source of hydrocarbon derivatives eg ethane and propane that are higher molecular weight than methane and that are important chemical intermediates The preparation of chemicals and chemical intermediates from methane natural gas should not be restricted to those described here but should be regarded as some of the building blocks of the petrochemical industry In addition to methane being the major constituent of natural gas the products of the gasifica tion of carbonaceous feedstocks also contain methane The commonly accepted approach to the synthesis of methane from the carbonaceous feedstock is the catalytic reaction of hydrogen and carbon monoxide CO 3H CH H O 2 4 2 TABLE 62 Properties of Methane Chemical formula CH4 Molar mass 1604 gmol Appearance Colorless gas Odor Odorless Density 0656 gL gas 25C 1 atm 0716 gL gas 0C 1 atm 042262 gcm3 liquid 162C Liquid density 04226 Vapor density air 1 055 Melting point 1825C 2964F 907K Boiling point 16149C 25868F 11166K Solubility in water 227 mgL Solubility Soluble in ethanol diethyl ether benzene toluene methanol acetone Flash point 188C 3064F 851K Autoignition temperature 537C 999F 810 K Explosive limits 4417 vv in air 212 Handbook of Petrochemical Processes A variety of metals have been used as catalysts for the methanation reaction the most common and to some extent the most effective methanation catalysts appear to be nickel and ruthenium with nickel being the most widely used The synthesis gas must be desulfurized before the methanation step since sulfur compounds will rapidly deactivate poison the catalysts Also the composition of the products of gasification processes are varied insofar as the gas composition varies with the feedstock and the system employed Speight 2014c It is emphasized that the gas product must be first freed from any pollutants such as particulate matter and sulfur compounds before further use particularly when the intended use is a watergas shift or methanation Mokhatab et al 2006 Speight 2007 2013 2014a 2014a The production of methane from the carbonaceous feedstock does not depend entirely on cata lytic methanation and in fact a number of gasification processes use hydrogasification that is the direct addition of hydrogen to the carbonaceous feedstock under pressure to form methane C 2H CH coal 2 4 The hydrogenrich gas for the hydrogasification process can be manufactured from steam by using the char that leaves the hydrogasifier Appreciable quantities of methane are formed directly in the primary gasifier and the heat released by methane formation is at a sufficiently high temperature to be used in the steamcarbon reaction to produce hydrogen so that less oxygen is used to produce heat for the steamcarbon reaction Hence less heat is lost in the lowtemperature methanation step thereby leading to higher overall process efficiency Methane is a major raw material for many chemical processes and the potential number of chem icals that can be produced from methane is almost limitless Indeed methane can be converted to a wide variety of chemicals in addition to serving as a source of synthesis gas This leads to a wide variety of chemicals which involve chemistry ie the chemistry of methane and other onecarbon compounds In this aspect the use of coal and other carbonaceous feedstocks for the production of chemicals is similar to the chemistry employed in the synthesis of chemicals from the gasification products of the carbonaceous feedstock In the chemical industry methane is the feedstock of choice for the production of hydrogen methanol acetic acid and acetic anhydride To produce any of these chemicals methane is first made to react with steam in the presence of a nickel catalyst at high temperatures 700C1100C 1290F2010F CH H O CO 3H 4 2 2 The synthesis gas is then reacted in various ways to produce a wide variety of products In addition acetylene is prepared by passing methane through an electric arc When methane is made to react with chlorine gas various chloromethane derivatives are produced chloromethane CH3Cl dichloromethane CH2Cl2 chloroform CHCl3 and carbon tetrachloride CCl4 However the use of these chemicals is decliningacetylene may be replaced by less costly substitutes and the chloromethane derivatives are used less often because of health and environmental concerns It must be recognized that there are many other options for the formation of chemical intermedi ates and chemicals from methane by indirect routes ie other compounds are prepared from the methane that are then used as further sources of petrochemical products In summary methane can be an important source of petrochemical intermediates and solvents 621 Physical ProPerties At room temperature and standard pressure STP methane is a colorless and odorless gas Methane has a boiling point of 161C 2578F at a pressure of one atmosphere 147 psi Methane is lighter than air having a specific gravity of 0554 Table 62 and burns readily in air forming car bon dioxide and water vapor the flame is pale slightly luminous and very hot The boiling point 213 Chemicals from Paraffin Hydrocarbons of methane is 162C 2596F and the melting point is 1825C 2965F Methane in general is very stable but mixtures of methane and air with the methane content between 5 and 14 vv are explosive Explosions of such mixtures have been a frequent occurrence in coal mines and have been the cause of many mine disasters Methane is lighter than air having a specific gravity of 0554 Table 62 and burns readily in air forming carbon dioxide and water vapor the flame is pale slightly luminous and very hot The boiling point of methane is 162C 2596F and the melting point is 1825C 2965F Methane is a relatively potent greenhouse gas and compared with carbon dioxide it has a high global warming potential of 72 calculated over a period of 20 years or 25 for a time period of 100 years Methane in the atmosphere is eventually oxidized producing carbon dioxide and water As a result methane in the atmosphere has a halflife of 7 years 622 chemical ProPerties Structurally methane is a tetrahedral molecule with four equivalent carbonhydrogen CH bonds The primary chemical reactions of methane are combustion steam reforming to synthesis gas syngas mixtures of carbon monoxide and hydrogen and halogenation Typically the chemical reactions of methane are difficult to control Although there is great interest in converting methane into useful or more easily liquefied compounds the only practical processes are relatively unselective There are two types of routes through which methane gas can be converted into olefin derivatives i indirect routes via syngas or ethane and ii direct routes directly from methane to low boiling olefin derivatives Another indirect route is methane to olefin derivatives via FischerTropsch liquids and the subsequent conversion to highvalue chemicals by means of steam cracking The direct route from methane to olefin derivatives is a modified FischerTropsch reaction but this route is technically difficult because of low selectivity to lowboiling olefin derivatives and the high yield of high molecular weight hydrocarbon derivatives Wang et al 2003 Typically in the chemical industry methane is converted by the steam reforming process to synthesis gas also called syngas which is a mixture of carbon monoxide and hydrogen which is an important building block for many chemicals using the FischerTropsch process Chapter 10 Speight 2013 2014a The process that employs a nickelbased catalyst and requires high tempera ture that is in the order of 700C1100C 1290F2010F CH H O CO 3H steamreformingprocess 4 2 2 Similarly in the HaberBosch synthesis of ammonia from air natural gas methane is reduced to a mixture of carbon dioxide water and ammonia CH H O CO 3H steammethanereforming 4 2 2 CO H O CO H hydrogenproduction 2 2 2 3H N 2NH HaberBoschprocess 2 2 3 Other commercially viable processes that use methane as a chemical feedstock include the cata lytic oxidation to methanol which is based on the oxidative coupling of methane and the direct reaction of methane with sulfur trioxide to produce methane sulfonic acid 2CH O 2CH OH 4 2 3 CH SO CH SO H 4 3 3 3 214 Handbook of Petrochemical Processes The combustion of methane is an exothermic reaction that can be represented by a simple equation that reflects the thermal oxidation of methane to carbon dioxide and water CH 2O CO 2H O 4 2 2 2 The reaction however is a multiple step reaction and can be generally represented by the following equations in which the species M signifies an energetic third body from which energy is trans ferred during a molecular collision Thus CH M CH H M 4 3 CH O CH HO 4 2 3 2 CH HO CH 2OH 4 2 3 CH OH CH H O 4 3 2 O H O OH 2 CH O CH OH 4 3 CH O CH O OH 3 2 2 CH O O CHO OH 2 CH O OH CHO H O 2 2 CH O H CHO H 2 2 CHO O CO OH CHO OH CO H O 2 CHO H CO H2 H O H OH 2 H OH H H O 2 2 CO OH CO H 2 H OH M H O M 2 H H M H M 2 H O M HO M 2 2 As illustrated formaldehyde HCHO is an early intermediate product and oxidation of formalde hyde gives the formyl radical HCO which then produce carbon monoxide CO Any resulting hydrogen oxidizes to water or other intermediates Finally the carbon monoxide is oxidized to carbon dioxide The overall reaction rate is a function of the concentration of the various entities 215 Chemicals from Paraffin Hydrocarbons during the combustion process The higher the temperature the greater the concentration of radical species and more rapid the combustion process In the partial oxidation reaction Arutyunov 2007 methane and other hydrocarbon deriva tives in natural gas react with a limited amount of oxygen typically from air that is not enough to completely oxidize the hydrocarbon derivatives to carbon dioxide and water With less than the stoichiometric amount of oxygen available the reaction products contain primarily hydrogen and carbon monoxide and nitrogen if the reaction is carried out with air rather than pure oxygen and a relatively small amount of carbon dioxide and other compounds Subsequently in a watergas shift reaction the carbon monoxide reacts with water to form carbon dioxide and more hydrogen 2CH O 2CO 2H partialoxidationof methane 4 2 2 CO H O CO H watergasshift 2 2 2 The partial oxidation reaction is an exothermic process and the process is typically much faster than steam reforming and requires a smaller reactor vessel This process initially produces less hydrogen per unit of the input fuel than is obtained by steam reforming of the same fuel 623 chemicals from methane Methane CH4 is a onecarbon paraffinic hydrocarbon that is not very reactive under normal condi tions It is a colorless gas that is insoluble in wateris the first member of the alkane series CnH2n2 and is the main component of natural gas It is also a byproduct in all gas streams from processing crude oils It is a colorless odorless gas that is lighter than air Table 62 Only a few chemicals can be produced directly from methane under relatively severe conditions Chlorination of methane is only possible by thermal or photochemical initiation Methane can be partially oxidized with a limited amount of oxygen or in presence of steam to a synthesis gas mixture Many chemicals can be produced from methane via the more reactive synthesis gas mixture Synthesis gas Chapter 10 is the precursor for two major chemicals ammonia and methanol Both compounds are the hosts for many important petrochemical products A few chemicals are based on the direct reaction of methane with other reagents These are carbon disulfide hydrogen cyanide chlorometh anes and synthesis gas mixture Currently a redox fuel cell based on methane is being developed The availability of hydrogen from catalytic reforming operations has made its application eco nomically feasible in a number of petroleumrefining operations Previously the chief sources of largescale hydrogen used mainly for ammonia manufacture were the cracking of methane or natural gas and the reaction between methane and steam In the latter at 900C1000C 1650F1830F conversion into carbon monoxide and hydrogen results CH H O CO 3H 4 2 2 If this mixture is treated further with steam at 500C over a catalyst the carbon monoxide present is converted into carbon dioxide and more hydrogen is produced CO H O H CO 2 2 2 The reduction of carbon monoxide by hydrogen is the basis of several syntheses including the manufacture of methanol and higher alcohols Chapter 8 Indeed the synthesis of hydrocarbon derivatives by the FischerTropsch reaction has received considerable attention nCO 2nH CH nH O 2 2 n 2 216 Handbook of Petrochemical Processes This occurs in the temperature range 200C350C 390F660F which is sufficiently high for the watergas shift to take place in presence of the catalyst CO H O CO H 2 2 2 The major products are olefin derivatives and paraffin derivatives together with some oxygen containing organic compounds in the product mix may be varied by changing the catalyst or the temperature pressure and carbon monoxidehydrogen ratio The hydrocarbon derivatives formed are mainly aliphatic and on a molar basis methane is the most abundant the amount of higher hydrocarbon derivatives usually decreases gradually with increase in molecular weight Isoparaffin formation is more extensive over zinc oxide ZnO or thoria ThO2 at 400C500C 750F930F and at higher pressure Paraffin waxes are formed over ruthenium catalysts at relatively low temperatures 170C200C 340F390F high pres sures 1500 psi and with a carbon monoxidehydrogen ratio The more highly branched product made over the iron catalyst is an important factor in a choice for the manufacture of automotive fuels On the other hand a highquality diesel fuel paraffin character can be prepared over cobalt Secondary reactions play an important part in determining the final structure of the product The olefin derivatives produced are subjected to both hydrogenation and doublebond shifting toward the center of the molecule cis and trans isomers are formed in about equal amounts The propor tions of straightchain molecules decrease with rise in molecular weight but even so they are still more abundant than branchedchain compounds up to approximately C10 The small amount of aromatic hydrocarbon derivatives found in the product covers a wide range of isomer possibilities In the C6C9 range benzene toluene ethylbenzene xylene npropyl and isopropylbenzene methyl ethyl benzene derivatives and trimethyl benzene derivatives have been identified naphthalene derivatives and anthracene derivatives are also present Paraffin hydrocarbon derivatives are less reactive than olefin derivatives only a few chemicals are directly based on them Nevertheless paraffinic hydrocarbon derivatives are the starting materials for the production of olefin derivatives Methanes relation with petrochemi cals is primarily through synthesis gas Chapter 5 Ethane on the other hand is a major feed stock for steam crackers for the production of ethylene Few chemicals could be obtained from the direct reaction of ethane with other reagents The higher paraffin derivativespropane butanes pentanes and higher molecular weight paraffin derivativesalso have limited direct use in the chemical industry except for the production of light olefin derivatives through steam cracking 6231 Carbon Disulfide Methane reacts with sulfur an active nonmetal element of group 6A at high temperatures to pro duce carbon disulfide CS2 Activated alumina or clay is used as the catalyst at approximately 675C 1245F and 30 psi The process starts by vaporizing pure sulfur mixing it with methane and passing the mixture over the alumina catalyst CH 4S CS 2H S 4 2 2 Hydrogen sulfide a coproduct is used to recover sulfur by the Claus reaction A carbon disul fide yield of 8590 based on methane is anticipated An alternative route for carbon disul fide is by the reaction of liquid sulfur with charcoal However this method is not used very much Carbon disulfide is primarily used to produce rayon and cellophane regenerated cellulose and is also used to produce carbon tetrachloride using iron powder as a catalyst at 30C 86F 217 Chemicals from Paraffin Hydrocarbons CS 3Cl CCl S Cl 2 2 4 2 2 The sulfur chloride is an intermediate that is then reacted with carbon disulfide to produce more carbon tetrachloride and sulfur 2S Cl CS CCl 6S 2 2 2 4 Thus the overall reaction is CS 2Cl CCl 2S 2 2 4 Carbon disulfide is also used to produce xanthate derivatives ROCSSNa as an ore flotation agent and ammonium thiocyanate NH4SCH as a corrosion inhibitor in ammonia handling systems 6232 Ethylene Ethylene is considered to be one of the most important raw materials in the chemical industry Its significance is driven by its molecular structure ie carboncarbon double bonds H2CCH2 This πbond is responsible for its chemical reactivity The double bond is also a place of high electron density therefore it is susceptible to attack by electrophiles It is a volatile substance colorless at room temperature noncorrosive nontoxic flammable gas slightly soluble in water and soluble in most organic solvents It has boiling and melting points of 104C and 1692C respectively at a pressure of 1 atm Ethylene is a very active chemical as exemplified by the reaction between eth ylene and water to produce ethyl alcohol Most of the ethylene reactions are catalyzed by transition metals which bind transiently to the ethylene using both the π and π orbitals Ethylene is also an active alkylating agent which can be used for the production of important monomers such as ethyl benzene EB which is dehydrogenated to styrene Ethylene is an important petrochemical starting material and is used extensively for produc tion of polyethene highdensity polyethylene HDPE lowdensity polyethylene LDPE and linear lowdensity polyethylene LLDPE as well as a major feedstock for the manufacture of ethylene dichloride CH2ClCH2Cl vinyl chloride CH2CHCl and the cyclic ethylene oxide In the modern petroleum refinery ethylene is generated from various process units along with liquid products such as naphtha kerosene and gas oil Naphtha from the refineries widely transported to petrochemical plants to produce ethylene and convert into above valuable chemical products One of the technologies used in present industries for ethylene production is by naphtha cracking technology Traditionally ethylene is produced by way of naphtha cracking and steam cracking of ethane Salkuyeh and Adams 2015 Ethylene can also be produced using natural gas as a feedstock either via the direct route that involves oxidative coupling of methane or via the indirect route that involves methanol to olefin MTO process OrtizEspinoza et al 2015 Salkuyeh and Adams 2015 Dutta et al 2017 In the process the feedstock preheated by a heat exchanger mixed with steam and then further heated to its incipient cracking temperature 500C680C 930F1255F depending upon the feedstock At this point the heated feedstock enters a reactor typically a fired tubular reactor where it is heated to cracking temperatures 750C785C 1380F1605F During this reaction hydrocarbons in the feedstock are cracked to produce lower molecular weight products including ethylene The cracking reaction is highly endothermic and therefore high energy rates are needed The cracking coils are designed to optimize the temperature and pressure profiles in order to maxi mize the yield of desired or value products Short residence times in the furnace are also important as they increase the yields of primary products such as ethylene and propylene Long residence times will favor the secondary reactions Thus 218 Handbook of Petrochemical Processes Methane conversion and selectivity toward ethylene for the oxidative coupling reaction depends on the methaneoxygen ratio A lower methaneoxygen ratio decreases the selectivity toward ethylene production but does increase methane conversion Because of the low conversion and poor selectivity of the process unreacted methane and byproducts produced such as ethane and higher molecular weight hydrocarbon derivatives as well as carbon monoxide hydrogen carbon dioxide and water need to be separated to obtain a highpurity ethylene as the final product Water is removed partially during the multistage compression and a molecular sieve unit to remove the remaining water 6233 Hydrogen Cyanide Hydrogen cyanide hydrocyanic acid HCN is a colorless liquid boiling point 256C 781F that is miscible with water producing a weakly acidic solution It is a highly toxic compound but a very useful chemical intermediate with high reactivity It is used in the synthesis of acrylonitrile and adiponitrile which are important monomers for plastic and synthetic fiber production Hydrogen cyanide is produced by the Andrussaw process which involves the hightemperature reaction of ammonia methane and air over a platinum catalyst The reaction is exothermic and the released heat is used to supplement the required catalystbed energy 2CH 2NH 2HCN 6H O 4 3 2 A platinumrhodium alloy is used as a catalyst at 1100C 2010F Approximately equal amounts of ammonia and methane with 75 vol air are introduced to the preheated reactor The catalyst has several layers of wire gauze with a special mesh size approximately 100 mesh On the other hand the Degussa process involves the reaction of ammonia with methane in absence of air using a platinum aluminumruthenium alloy as a catalyst at approximately 1200C 2190F The reaction produces hydrogen cyanide and hydrogen and the yield is over 90 CH NH HCN 3H 4 3 2 Hydrogen cyanide may also be produced by the reaction of ammonia and methanol in presence of oxygen NH CH OH O HCN 3H O 3 3 2 2 Hydrogen cyanide is a reactant in the production of acrylonitrile methyl methacrylates from acetone adiponitrile and sodium cyanide It is also used to make oxamide a longlived fertilizer that releases nitrogen steadily over the vegetation period Oxamide is produced by the reaction of hydrogen cyanide with water and oxygen using a copper nitrate catalyst at about 70C 158F and atmospheric pressure 6234 Chloromethane Derivatives The ease with which chlorine can be introduced into the molecules of all the hydrocarbon types pres ent in petroleum has resulted in the commercial production of a number of widely used compounds Feedstocksteam Primary Reactions Secondary Reactions Ethylene C4 products Propylene C5 products Acetylene C6 products Hydrogen Aromatic derivatives Methane C7 products Hydrocarbons Higher molecular weight products 219 Chemicals from Paraffin Hydrocarbons With saturated hydrocarbon derivatives the reactions are predominantly substitution of hydrogen by chloride and are strongly exothermic difficult to control and inclined to become explosively violent RH Cl RCl HCl 2 Moderately high temperatures are used about 250C300C 480F570F for the thermal chlori nation of methane but as the molecular weight of the paraffin increases the temperature may gener ally be lowered A mixture of chlorinated derivatives is always obtained and many variables such as choice of catalyst dilution of inert gases and presence of other chlorinating agents antimony pentachloride sulfuryl chloride and phosgene have been tried in an effort to direct the path of the reaction Methane yields four compounds upon chlorination in the presence of heat or light CH Cl CH ClCH Cl CHCl CCl 4 2 3 2 2 3 4 These compounds known as chloromethane or methyl chloride dichloromethane or methylene chloride trichloromethane or chloroform and tetrachloromethane or carbon tetrachloride are used as solvents or in the production of chlorinated materials The successive substitution of methane hydrogens with chlorine produces a mixture of four chloromethanes i Methyl chloride CH3Cl also known as monochloromethane ii methylene dichloride CH2Cl2 also known as dichloromethane iii chloroform CHC13 also known as tri chloromethane and iv carbon tetrachloride CC14 also known as tetrachloromethane Each of these four compounds has many industrial applications Methane is the most difficult alkane to chlorinate The reaction is initiated by chlorine free radi cals obtained via the application of heat thermal or light hv Thermal chlorination more widely used industrially occurs at approximately 350C370C 660F700F and atmospheric pressure A typical product distribution for a feedstock methanechlorine ratio of 17 vv is methyl chloride 587 vv methylene dichloride 293 vv chloroform 97 vv and carbon tetrachloride 23 vv The first step in the process involves the breaking of the chlorinechlorine bond which forms two chlorine Cl free radicals after which the chlorine free radical reacts with methane to form a methyl free radical CH3 and hydrogen chloride The methyl radical then reacts in a subsequent step with a chlorine molecule forming methyl chloride and a chlorine radical Cl CH CH HCl 4 3 CH Cl CH Cl Cl 3 2 3 The freshly generated chlorine radical Cl atom either attacks another methane molecule and repeats the above reaction or it reacts with a methyl chloride molecule to form a chloromethyl free radical CH2Cl in which the free electron resides on the carbon atom and hydrogen chloride Cl CH Cl CCH Cl 3 2 The chloromethyl free radical then attacks another chlorine molecule and produces dichlorometh ane along with a Cl atom CH Cl Cl CH Cl Cl 2 2 2 2 This formation of chlorine free radicals continues until all chlorine is consumed Chloroform and carbon tetrachloride are formed in a similar way by reaction of dichloromethyl CHC12 and trichloromethyl CC13 free radicals with chlorine 220 Handbook of Petrochemical Processes Product distribution among the products depends primarily on the mole ratio of the reactants in the feedstock For example the yield of methyl chloride CH3Cl chloromethane could be increased to 80 vv by increasing the methanechlorine mole ratio to 101 at 450C 840F If dichlorometh ane is the desired product the methanechlorine mole ratio is lowered and the monochlorometh ane recycled Decreasing the methanechlorine mole ratio generally increases polysubstitution and hence the yield of chloroform and carbon tetrachloride An alternative way to produce methyl chloride monochloromethane is the reaction of methanol with hydrogen chloride HCl Methyl chloride could be further chlorinated to give a mixture of chloromethanes methylene dichloride chloroform and carbon tetrachloride The major use of methyl chloride is to produce silicon polymers Other uses include the synthesis of tetramethyl lead as a gasoline octane booster a methylating agent in methyl cellulose produc tion a solvent and a refrigerant Methylene dichloride has a wide variety of markets for example a paint remover as well as a degreasing solvent a blowing agent for polyurethane foams and a solvent for cellulose acetate Chloroform is mainly used to produce chlorodifluoromethane also known as Fluorocarbon 22 by the reaction with hydrogen fluoride CHC1 2HF CHCl F 2HC1 3 2 2 This compound is used as a refrigerant and as an aerosol propellant It is also used to synthesize tetrafluoroethylene which is polymerized to a heatresistant polymer Teflon CHCl F CF CF 2HCl 2 2 2 2 Carbon tetrachloride is used to produce chlorofluorocarbons CFCs such as trichlorofluorometh ane CCl3F and dichlorodifluoromethane CC12F2 by the reaction with hydrogen fluoride using an antimony pentachloride SbC15 catalyst CCl HF CCl F 2HCl 4 3 CC1 2HF CC1 F 2HC1 4 2 2 The product mixture is composed of trichlorofluoromethane Freon11 and dichlorodifluorometh ane Freon12 These compounds are used as aerosols and as refrigerants However because of the depleting effect of chlorofluorocarbons on the ozone layer the production of these compounds has been reduced considerably 6235 Synthesis Gas Synthesis gas may be produced from a variety of feedstocks such as from natural gas CH4 by the steam reforming process The first step in the process is to ensure that the methane feedstock is free from hydrogen sulfide The purified gas is then mixed with steam and introduced to the first reactor primary reformer The reactor is constructed from vertical stainless steel tubes lined in a refrac tory furnace The steam to natural gas ratio varies from 4 to 5 depending on natural gas composition natural gas may contain ethane and heavier hydrocarbon derivatives and the pressure used A promoted nickeltype catalyst contained in the reactor tubes is used at temperature and pressure ranges of 700C800C 1290F1470F and 450750 psi respectively The reforming reaction is equilibrium limited It is favored at high temperatures low pressures and a high steam to carbon ratio These conditions minimize methane slip at the reformer outlet and yield an equilib rium mixture that is rich in hydrogen The product gas from the primary reformer is a mixture of hydrogen H2 carbon monoxide CO carbon dioxide CO2 unreacted methane CH4 and steam H2O The predominant process reactions are 221 Chemicals from Paraffin Hydrocarbons CH H O CO 3H 4 2 2 CH 2H O CO 4H 4 2 2 2 For the production of methanol this mixture could be used directly with no further treatment except adjusting the hydrogenCO CO2 ratio to approximately 21 For the production of hydrogen for ammonia synthesis however further treatment steps are needed First the required amount of nitrogen for ammonia must be obtained from atmospheric air This is achieved by partially oxidiz ing unreacted methane in the exit gas mixture from the first reactor in another reactor secondary reforming The main reaction occurring in the secondary reformer is the partial oxidation of methane with a limited amount of air The product is a mixture of hydrogen carbon dioxide carbon monoxide plus nitrogen which does not react under these conditions 2CH O 2CO 2H 4 2 2 The reactor temperature can reach over 900C 1650F in the secondary reformer due to the exo thermic reaction heat The second step after secondary reforming is removing carbon monoxide which poisons the catalyst used for ammonia synthesis This is done in three further steps i shift conversion ii carbon dioxide removal and iii methanation of the remaining carbon monoxide and carbon dioxide In the shift converter carbon monoxide is reacted with steam to give carbon dioxide and hydro gen The feed to the shift converter contains large amounts of carbon monoxide which should be oxidized An iron catalyst promoted with chromium oxide is used at a temperature range of 425C500C 795F930F to enhance the oxidation CO H O CO H 2 2 2 Exit gases from the shift conversion are treated to remove carbon dioxide This may be done by absorbing carbon dioxide in a physical or chemical absorption solvent or by adsorbing it using a special type of molecular sieves Carbon dioxide recovered from the treatment agent as a byprod uct is mainly used with ammonia to produce urea The product is a pure hydrogen gas containing small amounts of carbon monoxide and carbon dioxide which are further removed by methanation Catalytic methanation is the reverse of the steam reforming reaction Hydrogen reacts with car bon monoxide and carbon dioxide converting them to methane Methanation reactions are exother mic and methane yield is favored at lower temperatures 3H CO CH H O 2 4 2 4H CO CH 2H O 2 2 4 2 The forward reactions are also favored at higher pressures However the space velocity becomes high with increased pressures and contact time becomes shorter decreasing the yield The actual process conditions of pressure temperature and space velocity are practically a compromise of several factors Raney nickel is the preferred catalyst Typical methanation reactor operating condi tions are 200C300C 390F570F and approximately 150 psi The product is a gas mixture of hydrogen and nitrogen having an approximate ratio of 31 for ammonia production Many chemicals are produced from synthesis gas as a consequence of the high reactivity associ ated with hydrogen and carbon monoxide gases the two constituents of synthesis gas The reactiv ity of this mixture was demonstrated during World War II when it was used to produce alternative hydrocarbon fuels using FischerTropsch technology Chapter 10 222 Handbook of Petrochemical Processes Synthesis gas is also an important building block for aldehydes from olefin derivatives The catalytic hydroformylation reaction Oxo reaction is used with many olefin derivatives to produce aldehydes and alcohols of commercial importance The two major chemicals based on synthesis gas are ammonia and methanol Each compound is a precursor for many other chemicals From ammo nia urea nitric acid hydrazine acrylonitrile methylamines and many other minor chemicals are produced Each of these chemicals is also a precursor to many other chemicals Methanol the second major product from synthesis gas is a unique compound of high chemical reactivity as well as good fuel properties It is a building block for many reactive compounds such as formaldehyde acetic acid and methylamine It also offers an alternative way to produce hydro carbon derivatives in the gasoline range Mobil to gasoline process also called the MTG process In the Mobil to gasoline process methanol is the feedstock for the production of gasoline which represents a competing technology to the traditional FischerTropsch process Instead of the tra ditional FischerTropsch technology to convert syngas to liquids to be further refined into end products such as gasoline the Mobil to gasoline process follows a methanol synthesis unit with a methanol to gasoline synthesis process that yields gasoline very close to the final fuel specifica tions requiring minimal end processing This process may also prove to be a competitive source for producing light olefin derivatives in the future Synthesis gas conversion processes are significantly more advanced in development than direct or other twostep methane conversion schemes Indirect gas conversion processes are currently practiced for methanol synthesis and for hydrocarbon formation via the FischerTropsch synthesis Dieselrange hydrocarbon derivatives via FischerTropsch synthesis and gasoline via Mobil to gasoline processes can be produced These indirect processes have continued to evolve as continu ous improvements have come about from advances in synthesis gas generation from the design and deployment of threephase bubble columns for synthesis gas conversion and from the develop ment of improved catalytic materials for the selective synthesis of paraffin derivatives intermediate size αolefin derivatives and higher alcohols Small modular gas conversion plants using catalytic partial oxidation in monolith reactors and carbon monoxide hydrogenation in bubble columns may also create future opportunities for combining hydrogen and power generation with the synthesis of commodity petrochemicals and even of liquid fuels Selective pathways for ethylene and propylene from synthesis gas remain unavailable because Florytype chain growth kinetics leads to broad carbon number distributions The most promising approach uses acidcatalyzed chain growth reactions of methanol within shapeselective channels in pentasil zeolites and silicoaluminophosphate microporous materials in a threestep process requir ing synthesis gas generation methanol synthesis and methanoltoolefin derivatives or methanol togasoline MTG conversion The latter must be carried out in fluid bed or moving bed reactors because of the need for frequent regeneration Currently available technologies use silicoalumino phosphate materials or modified pentasil zeolites in order to provide optimum shape selective envi ronments for the synthesis of light olefin derivatives Intermediate range αolefin derivatives C5C15 can be produced with modest selectivity from CO and H2 on promoted ironbased catalysts The valuable midrange paraffin derivatives and the smaller olefin derivatives formed as byproducts are much more valuable than the paraffin derivatives formed and useful only as fuels Higher alcohol synthesis is also restricted to broad product distributions governed by stochastic chain growth kinetics Recently bifunctional catalysts consisting of metal sites for hydrogenation reactions and basic sites for alcohol coupling steps have led to high selectivity to branched alcohols Chain growth appears to be restricted to C4 and C5 alcohols by the chemical constraints of base catalyzed aldol condensation reactions High 2methyl1butanol yields 200300 gkgcath have been recently reported on Pdbased bifunctional catalysts but at very high pressures 200 bar and temperatures 400C450C 750F840F Dimethyl ether DME isomerization and aldol condensation of olefin derivatives with methanol using acidbased bifunctional catalysts provide alternate but unexplored pathways to overcome the C1C2 conversion bottleneck during CO hydro genation to form higher alcohols 223 Chemicals from Paraffin Hydrocarbons 6236 Urea The major end use of ammonia is the fertilizer field for the production of urea ammonium nitrate and ammonium phosphate and sulfate Anhydrous ammonia could be directly applied to the soil as a fertilizer Urea is gaining wide acceptance as a slowacting fertilizer Ammonia is the precursor for many other chemicals such as nitric acid hydrazine acrylonitrile and hexamethylenediamine Ammonia having three hydrogen atoms per molecule may be viewed as an energy source It has been proposed that anhydrous liquid ammonia may be used as a clean fuel for the automotive industry The oxidation reaction the combustion reaction is 4NH 3O 2N 6H O 3 2 2 2 Compared with hydrogen anhydrous ammonia is more manageable and can be stored in iron or steel containers and could be transported commercially via pipeline railroad tanker cars and high way tanker trucks Only nitrogen and water are produced However many factors must be considered such as the coproduction of nitrogen oxides the economics related to retrofitting of auto engines etc The fol lowing describes the important chemicals based on ammonia The highest fixed nitrogencontaining fertilizer 467 ww urea is a white solid that is soluble in water and alcohol It is usually sold in the form of crystals prills flakes or granules Urea is an active compound that reacts with many reagents It forms adducts and clathrates with many sub stances such as phenol and salicylic acid By reacting with formaldehyde it produces an important commercial polymer urea formaldehyde resins that is used as glue for particle board and plywood The technical production of urea is based on the reaction of ammonia with carbon dioxide The reaction occurs in two steps ammonium carbamate is formed first followed by a decomposition step of the carbamate to urea and water The first reaction is exothermic and the equilibrium is favored at lower temperatures and higher pressures Higher operating pressures are also desirable for the separation absorption step that results in a higher carbamate solution concentration A higher ammonia ratio than stoichiometric is used to compensate for the ammonia that dissolves in the melt The reactor temperature ranges between 170C and 220C 340F395F at a pressure of about 3000 psi The second reaction represents the decomposition of the carbamate The reaction condi tions are 200C 390F and 450 psi 2NH CO H NCOONH 3 2 2 4 H NCOONH H NCONH H O 2 4 2 2 2 Decomposition in presence of excess ammonia limits corrosion problems and inhibits the decom position of the carbamate to ammonia and carbon dioxide The urea solution leaving the carbamate decomposer is expanded by heating at low pressures and ammonia recycled The resultant solution is further concentrated to a melt which is then prilled by passing it through special sprays in an air stream The major use of urea is the fertilizer field About 10 of urea is used for the production of adhe sives and plastics urea formaldehyde and melamine formaldehyde resins Animal feed accounts for about 5 of the urea produced Urea possesses a unique property of forming adducts with nparaffin derivatives This is used in separating C12C14 nparaffin derivatives from kerosene for detergent production 6237 Methyl Alcohol Methyl alcohol methanol CH3OH is the first member of the aliphatic alcohol family Methanol was originally produced by the destructive distillation of wood wood alcohol for charcoal produc tion Currently it is mainly produced from synthesis gas 224 Handbook of Petrochemical Processes As a chemical compound methanol is highly polar and hydrogen bonding is evidenced by its relatively highboiling temperature 65C 149F high heat of vaporization and low volatility Due to the high oxygen content of methanol 50 ww it is being considered as a gasoline blending compound to reduce carbon monoxide and hydrocarbon emissions in automobile exhaust gases It was also tested for blending with gasolines due to the highoctane number RON 112 During the late 1970s and early 1980s many experiments tested the possible use of pure straight methanol as an alternative fuel for gasoline cars Several problems were encountered however in its use as a fuel such as starting a cold engine due to its high vaporization heat heat of vaporization is 37 times that of gasoline its lower heating value which is approximately half that of gasoline and its cor rosive properties However methanol is a potential fuel for gas turbines because it burns smoothly and has exceptionally low nitrogen oxide emission levels Due to the high reactivity of methanol many chemicals could be derived from it For example it could be oxidized to formaldehyde an important chemical building block carbonylated to acetic acid and dehydrated and polymerized to hydrocarbon derivatives in the gasoline range methanoltogasoline process Much of the current work is centered on the use of shape selective catalysts to convert methanol to light olefin derivatives as a possible future source of ethylene and propylene Methanol is produced by the catalytic reaction of carbon monoxide and hydrogen synthesis gas Because the ratio of COH2 in synthesis gas from natural gas is approximately 13 and the stoichio metric ratio required for methanol synthesis is 12 carbon dioxide is added to reduce the surplus hydrogen An energyefficient alternative to adjusting the carbon monoxidehydrogen ratio is to combine the steam reforming process with autothermal reforming combined reforming so that the amount of natural gas fed is that required to produce a synthesis gas with a stoichiometric ratio of approximately 1205 If an autothermal reforming step is added pure oxygen should be used This is a major difference between secondary reforming in case of ammonia production where air is used to supply the needed nitrogen An added advantage of combined reforming is the decrease in the emissions of nitrogen oxides NOx The following reactions are representative for methanol synthesis CO 2H CH OH 2 3 CO 3H CH OH H O 2 2 3 2 Old processes use a zincchromium oxide catalyst at a highpressure range of approximately 4000 6200 psi for methanol production A lowpressure process has been developed by ICI operating at about 700 psi using an active copperbased catalyst at 240C 430F The synthesis reaction occurs over a bed of heterogeneous catalyst arranged in either sequential adiabatic beds or placed within heat transfer tubes The reaction is limited by equilibrium and methanol concentration at the converters exit rarely exceeds 7 The converter effluent is cooled to 40C 104F to condense product methanol and the unreacted gases are recycled Crude methanol from the separator con tains water and low levels of byproducts which are removed using a twocolumn distillation system As a methylating agent it is used with many organic acids to produce the methyl esters such as methyl acrylate methyl methacrylate methyl acetate and methyl terephthalate Methanol is also used to produce dimethyl carbonate DMC and methyltbutyl ether an important gasoline additive It is also used to produce synthetic gasoline using a shapeselective catalyst methanolto gasoline process Olefin derivatives from methanol may be a future route for ethylene and propylene in com petition with steam cracking of hydrocarbon derivatives The use of methanol in fuel cells is being investigated Fuel cells are theoretically capable of converting the free energy of oxidation of a fuel into electrical work In one type of fuel cells the cathode is made of vanadium which catalyzes the reduction of oxygen while the anode is iron III which oxidizes methane to CO2 and iron II is formed in aqueous sulfuric acid H2SO4 225 Chemicals from Paraffin Hydrocarbons Commercial methanol synthesis processes use indirect routes based on synthesis gas inter mediates These processes lead to much higher methanol yields 2530 yield per pass and 99 CH3OH selectivity Synthesis gas generation requires high temperatures and large capital investments but recent process improvements that combine partial oxidation and steam reform ing in a nearly thermoneutral process have led to practical thermal efficiencies 7172 for the overall methanol synthesis process very close to theoretical thermal efficiency values 842 Recent development in the use of adiabatic monolith reactors for partial methane oxi dation to synthesis gas have provided a novel and useful approach especially for smallscale methanol synthesis applications that cannot exploit the beneficial economies of scale of steam reforming and autothermal reforming processes The chemical and structural integrity of noble metal catalytic coatings in these monolith reactors and the mixing and handling of explosive CH4O2 mixtures remain challenging issues in the design of the short contact time reactors for the production of synthesis gas Recent advances in the design of ceramic membranes for oxygen and hydrogen transport may become useful in decreasing or eliminating air purification costs and in driving endothermic steam reforming reactions to higher conversions or lower operating temperatures Such ceramic membranes have advanced beyond their status as a laboratory curi osity and into developmental consortia but their reliable practical implementation will require additional advances in the synthesis and stabilization of thin metal oxide films within novel reactor geometries as well as the development of faster proton conductors for the case of hydro gen separation schemes Methanol can also be formed via other indirect routes such as via processes involving the for mation of methyl bisulfate on Hg complexes followed by its conversion to methanol via hydrolysis and by the regeneration of the sulfuric acid oxidant by SO2 oxidation Methyl bisulfate yields can reach 7080 because of the low reactivity of methyl bisulfate relative to methanol and even methane Turnover rates are very low in the temperature tolerated by these homogeneous catalysts and Hg organometallic complexes and sulfuric acid are very toxic and difficult to handle and regen erate More recent studies have increased the stability of these catalysts by introducing more stable ligands and eliminated Hgbased materials with Ptbased homogeneous catalysts This approach involves a new type of protected intermediate methyl bisulfate and leads to higher methanol yields than in commercial routes based on synthesis gas It is however neither a direct route to methanol and involves three steps including a very costly oxidant regeneration step and a deprotection step limited by thermodynamics Oxychlorination provides another indirect route to methanol and to hydrocarbon derivatives via acidcatalyzed hydration or oligomerization of methyl chloride It involves the use and the costly regeneration of Cl2 and it requires corrosionresistant vessels and significant temperature cycling of process streams CH3Cl yields of 2530 have been achieved with yield losses predominately to CO2 and CH2Cl2 An additional chemical hurdle in these processes is the low selectivity to monochlorinated products Higher yields will require more selective monochlorination and lower combustion rates of these desired intermediates These improvements appear unlikely because of the kinetic instability of CH3Cl relative to CH4 and of the thermodynamic stability of the sequential CO2 and CH2Cl2 products Once methanol is produced it can be converted to dimethyl ether CH3OCH3 2CH OH CH OCH H O 3 3 3 2 The dimethyl ether can then be converted into olefin derivatives through olefin synthesis reac tions In the process a fluidized or fixed bed reactor is used and the temperature is maintained below 600C 1110Fcompared to a temperature regime of 750C900C 1380F1650F in steam crackingand a pressure in the order of 1545 psi As in the steam cracking process high severity high temperature low pressure and short resident time favors ethylene production over propylene production In this process step dehydration catalysts are used There are basically two 226 Handbook of Petrochemical Processes major catalyst families ZSM zeolite silicon microspores doped with metal ions such as Mn Sb Mg or Ba and silicoaluminophosphate molecular sieve doped with metal ions such as Mn Ni or Co The main differences between ZSM and silicoaluminophosphate catalysts are pore sizes and acidity which are the main causes for shape selectivity ZSM catalysts have shape selectivity favoring propylene and heavy hydrocarbon derivatives over ethylene Also they reportedly lead to less formation of aromatic coke and carbon oxides than silicoaluminophosphate catalysts and moreover silicoaluminophosphate catalysts have a shape selectivity favoring light olefin deriva tives over highboiling hydrocarbon derivatives The subsequent cooling recovery and separation processes are quite similar to those of steam cracking One difference is that after the recovery and separation of C4C5 the olefin upgrading sometimes referred to as olefin conversion process converts C4C5 to ethylene and propylene The composition and yield of final products depend on catalysts reactor configurations and severity such as temperature residence time Polymergrade light olefin derivatives of high purity 97 99 are the major products 6238 Formaldehyde The main industrial route for producing formaldehyde HCHO is the catalyzed air oxidation of methanol CH OH O HCHO H O 3 2 2 A silvergauze catalyst is still used in some older processes that operate at a relatively higher tem perature about 500C Some processes use an ironmolybdenum oxide catalyst and chromium oxide or cobalt oxide can be used to dope the catalyst The oxidation reaction is exothermic and occurs at approximately 400C425C 750F800F and atmospheric pressure Excess air is used to keep the methanol air ratio below the explosion limits Onestep homogeneous oxidation of methane at high pressures and temperatures has led to the synthesis of methanol with yields in the order of 4 The rapid subsequent combustion reactions of methanol to form CO2 limit conversions in practice while the explosive nature of the required reactant mixtures creates engineering challenges in the design of mixing schemes and pressure ves sels Solid catalysts have not led to yield improvements because surface sites activate CH bonds in both methane and methanol Staged O2 introduction using multiple injectors or dense oxygen conducting membranes are also unlikely to increase yields because the rates of activation of CH bonds in CH3OH and CH4 appear to depend similarly on O2 concentrations Continuous extraction of methanol can prevent combustion but requires its selective absorption adsorption or permeation above ambient temperatures none of which are currently possible as well as a low conversion per pass The introduction of sites for methanol conversion to hydrocarbon derivatives into homoge neous methane to methanol oxidation reactors may provide a less costly product separation scheme as well as the protection of activated CH4 as methanol as aromatic molecules that are considerably less reactive than methanol Formaldehyde is the simplest and most reactive aldehyde Condensation polymerization of form aldehyde with phenol urea or melamine produces phenolformaldehyde urea formaldehyde and melamine formaldehyde resins respectively These are important glues used in producing particle board and plywood A catalyst system based on SiO2 prepared by wet impregnation method with vanadium and molybdenum were prepared and tested for biogas methane partial oxidation to formaldehyde In general a vanadium pentoxidesilica V2O5SiO2 is a catalyst for the partial oxidation of bio gas methane to formaldehyde Singh et al 2010 As methane conversion increases formaldehyde selectivity also increases up to a reaction temperature in the order of 600C 1110F and then decreases because of the decline in the selectivity for formaldehyde formation at high temperatures because of the decomposition of formaldehyde 227 Chemicals from Paraffin Hydrocarbons HCHO CO H2 The vanadium pentoxide catalyst exhibits a heterolytic oxygen exchange mechanism similar to molybdenum trioxide MoO3 Singh et al 2010 Condensation of formaldehyde with acetaldehyde in presence of a strong alkali produces pentae rythritol a polyhydric alcohol that is used for alkyd resin production 4HCHO CH CHO NaOH C CH OH HCOONa 3 2 4 Pentaerythritol sodium formate Formaldehyde reacts with ammonia and produces hexamethylene tetramine hexamine which is a crosslinking agent for phenolic resins 6HCHO 4NH CH N 6H O 3 2 6 4 2 Methyl chloride is produced by the vaporphase reaction of methanol and hydrogen chloride CH OH HCl CH Cl H O 3 3 2 Many catalysts are used to effect the reaction such as zinc chloride on pumice cuprous chloride and ignited alumina gel The reaction conditions are 350C 660F at nearly atmospheric pressure Methyl chloride may also be produced directly from methane with other chloromethanes Zinc chloride is also a catalyst for a liquidphase process using concentrated hydrochloric acid at 100C150C 212F300F Hydrochloric acid may be generated in situ by reacting sodium chloride with sulfuric acid However methyl chloride from methanol may be further chlorinated to produce dichloromethane chloroform and carbon tetrachloride Methyl chloride is primarily an intermediate for the production of other chemicals Other uses of methyl chloride have been mentioned with chloromethane derivatives The carbonylation of methanol is currently one of the major routes for acetic acid production The basic liquidphase process developed by BASF uses a cobalt catalyst at 250C and a high pressure of about 70 atm The newer process uses a rhodium complex catalyst in presence of methyl iodide CH3I which acts as a promoter The reaction occurs at 150C 300F and atmospheric pressure CH OH CO CH COOH 3 3 Acetic acid is also produced by the oxidation of acetaldehyde and the oxidation of nbutane However acetic acid from the carbonylation route has an advantage over the other commercial processes because both methanol and carbon monoxide come from synthesis gas and the process conditions are quite mild The main use of acetic acid is to produce vinyl acetate 44 followed by acetic acid esters 13 and acetic anhydride 12 Vinyl acetate is used for the production of adhesives film paper and textiles Acetic acid is also used to produce pharmaceuticals dyes and insecticides Chloroacetic acid from acetic acid is a reactive intermediate used to manufacture many chemicals such as gly cine and carboxymethyl cellulose Dimethyl carbonate COOCH32 is a colorless liquid with a pleasant odor It is soluble in most organic solvents but insoluble in water The classical synthesis of dimethyl carbonate is the reaction of methanol with phosgene Because phosgene is toxic a nonphosgene route may be preferred The new route reacts methanol with urea over a tin catalyst However the yield is low Using electron donor solvents such as trimethylene glycol dimethyl ether and continually distilling off the product increases the yield H NCONH 2CH OH CH OC OOCH 2NH 2 2 3 3 3 3 228 Handbook of Petrochemical Processes Dimethyl carbonate is used as a specialty solvent It could be used as an oxygenate to replace methyl tertiary butyl ether MTBE It has almost three times the oxygen content as methyl tertiary butyl ether It has also a highoctane rating However it must be evaluated in regard to economics and toxicity Methylamine derivatives can be synthesized by alkylating ammonia with methyl halides or with methyl alcohol The reaction with methanol usually occurs at approximately 500C 930F and 300 psi in the presence of an aluminum silicate or phosphate catalyst The alkylation does not stop at the monomethylamine stage because the produced amine is a better nucleophile than ammonia The product distribution at equilibrium is monomethylamine 43 dimethylamine 24 and trimethylamine 33 CH OH NH CH NH H O 3 3 3 2 2 CH OH CH NH CH NH H O 3 3 2 3 2 2 CH OH CH NH CH NH H O 3 3 2 3 2 2 To improve the yield of monomethylamine and dimethylamine a shapeselective catalyst has been tried Carbogenic sieves are microporous materials similar to zeolites which have catalytic as well as shapeselective properties Combining the amorphous aluminum silicate catalyst used for producing the amines with carbogenic sieves gave higher yields of the more valuable monomethyl amine and dimethylamine Dimethylamine is the most widely used of the three amines Excess methanol and recycling monomethylamine increases the yield of dimethylamine The main use of dimethylamine is the synthesis of dimethylformamide and dimethylacetamide which are solvents for acrylic and polyurethane fibers Monoethylamine is used in the synthesis of Sevin an important insecticide Trimethylamine has only one major use the synthesis of choline a highenergy additive for poultry feed Methanol may have a more important role as a basic building block in the future because of the multiple sources of synthesis gas The reaction of methanol over a ZSM5 catalyst could be consid ered as dehydration oligomerization reaction It may be simply represented as nCH OH H CH H nH O 3 2 n 2 In this equation CH2n represents the hydrocarbon derivatives paraffin derivatives olefin derivatives aromatic derivatives The hydrocarbon derivatives obtained are in the gasoline range Converting methanol to hydrocarbon derivatives is not as simple as it looks from the previ ous equation Many reaction mechanisms have been proposed and most of them are centered on the intermediate formation of dimethyl ether followed by olefin formation Olefin derivatives are thought to be the precursors for paraffin derivatives and aromatic derivatives The product distribu tion is influenced by the catalyst properties as well as the various reaction parameters The catalyst activity and selectivity are functions of acidity crystalline size silicaalumina ratio and even the synthetic procedure The important property of ZSM5 and similar zeolites is the intercrystalline catalyst sites which allow one type of reactant molecule to diffuse while denying diffusion to others This property which is based on the shape and size of the reactant molecules as well as the pore sizes of the cata lyst is called shape selectivity Chen and Garwood document investigations regarding the various aspects of ZSM5 shape selectivity in relation to its intercrystalline structure and pore structure In general two approaches have been found that enhance selectivity toward light olefin for mation One approach is to use catalysts with smaller pore sizes such as crionite chabazite and 229 Chemicals from Paraffin Hydrocarbons zeolite T The other approach is to modify ZSM5 and similar catalysts by reducing the pore size of the catalyst through incorporation of various substances in the zeolite channels andor by lower ing the acidity by decreasing the alumina Al2O3silica SiO3 ratio This latter approach is used to stop the reaction at the olefin stage thus limiting the steps up to the formation of olefin derivatives and suppressing the formation of higher hydrocarbon derivatives 6239 Aldehyde Derivatives Hydroformylation of olefin derivatives Oxo reaction produces aldehydes with one more carbon than the reacting olefin For example when ethylene is used propionaldehyde is produced This reaction is especially important for the production of higher aldehydes that are further hydroge nated to the corresponding alcohols The reaction is catalyzed with cobalt or rhodium complexes Olefin derivatives with terminal double bonds are more reactive and produce aldehydes which are hydrogenated to the corresponding primary alcohols With olefin derivatives other than ethylene the hydroformylation reaction mainly produces a straight chain aldehyde with variable amounts of branched chain aldehydes The reaction could be generally represented as 2RCHCH 2H 2CO RCH CH CHO RCH CH CHO 2 2 2 2 3 The largest commercial process is the hydroformylation of propene which yields nbutyraldehyde and isobutyraldehyde The nButyraldehyde nbutanal is either hydrogenated to nbutanol or transformed to 2ethyl hexanol via aldol condensation and subsequent hydrogenation The 2ethyl hexanol is an important plasticizer for polyvinyl chloride PVC Other olefin derivatives applied in the hydroformylation process with subsequent hydrogenation are propylene trimer and tetramer for the production of decyl and tridecyl alcohols respectively and C7 olefin derivatives from copoly mers of C3 and C4 olefin derivatives for isodecyl alcohol production Several commercial processes are currently operative Some use rhodium catalyst complex incor porating phosphine ligands at relatively lower temperatures and pressures and produce less branched aldehydes Older processes use a cobalt carbonyl complex at higher pressures and temperatures and produce a higher ratio of the branched aldehydes The hydroformylation reaction using phosphine ligands occurs in an aqueous medium A higher catalyst activity is anticipated in aqueous media than in hydrocarbon derivatives Selectivity is also higher Having more than one phase allows for complete separation of the catalyst and the products 62310 Ethylene Glycol Ethylene glycol could be produced directly from synthesis gas using a rhodium catalyst at 230C 445F at very high pressure 50000 psi 3H 2CO HOCH CH OH 2 2 2 Other routes have been tried starting from formaldehyde or paraformaldehyde One process reacts formaldehyde with carbon monoxide and hydrogen hydroformylation at approximately 110C 230F and 4000 psi using a rhodium triphenyl phosphine catalyst with the intermediate forma tion of glycolaldehyde Glycolaldehyde is then reduced to ethylene glycol 2CO 2H HOCH CHO 2 2 HOCH CHO H HOCH CH OH 2 2 2 2 In the DuPont process the oldest syngas process to produce ethylene glycol formaldehyde is reacted with carbon monoxide in the presence of a strong mineral acid The intermediate is glycolic 230 Handbook of Petrochemical Processes acid which is esterified with methanol The ester is then hydrogenated to ethylene glycol and meth anol which is recovered HCHO CO H O HOCH CO H 2 2 2 HOCH CO H CH OH HOCH CO CH H O 2 2 3 2 2 3 2 HOCH CO CH 2H HOCH CH OH CH OH 2 2 3 2 2 2 3 62311 Nitration Hydrocarbon derivatives that are usually gaseous including normal and isopentane react smoothly in the vapor phase with nitric acid to give a mixture of nitrocompounds but there are side reac tions mainly of oxidation Only mononitroderivatives are obtained with the lower paraffin deriva tives as high temperatures and they correspond to those expected if scission of a CC and CH bond occurs Ethane for example yields nitromethane and nitroethane CH HNO CH NO H O 4 3 3 2 2 On the other hand more complex chemicals yield a more complex product mixpropane yields nitromethane nitroethane 1nitropropane and 2nitropropane The nitroderivatives of the lower paraffin derivatives are colorless and noncorrosive and are used as solvents or as starting materials in a variety of syntheses For example treatment with inorganic acids and water yields fatty acids RCO2H and hydroxylamine NH2OH salts and con densation with an aldehyde RCHO yields nitroalcohols RCHNO2OH 62312 Oxidation The oxidation of hydrocarbon derivatives and hydrocarbon mixtures has received considerable attention but the uncontrollable nature of the reaction and the mixed character of the products have made resolution of the reaction sequences extremely difficult Therefore it is not surprising that except for the preparation of mixed products having specific properties such as fatty acids hydro carbon derivatives higher than pentanes are not employed for oxidation because of the difficulty of isolating individual compounds Methane undergoes two useful reactions at 90C 195F in the presence of iron oxide Fe3O4 as a catalyst CH H O CO 3H 4 2 2 CO H O CO H 2 2 2 Alternatively partial combustion of methane can be used to provide the required heat and steam The carbon dioxide produced then reacts with methane at 900C 1650F in the presence of a nickel catalyst CH 2O O 2H O 4 2 2 2 CO CH 2CO 2H 2 4 2 CH H O CO 3H 4 2 2 Methanol methyl alcohol CH3OH is the second major product produced from methane Synthetic methanol has virtually completely replaced methanol obtained from the distillation of wood its 231 Chemicals from Paraffin Hydrocarbons original source material One of the older trivial names used for methanol was wood alcohol The synthesis reaction takes place at 350C and 300 atm in the presence of ZnO as a catalyst 2CH O 2CH OH 4 2 3 An example of a methanetomethanol is the Lurgi MegaMethanol process in which methane is first fed into a prereforming reactor where it is partially reformed with steam to syngas with a hydrogencarbon dioxide ratio in the order of 35 Prereforming reduces coking in the subsequent steps Unreformed methane is further converted to synthesis gas in the autothermal reforming reac tor with oxygen as a reforming agent at approximately 1000C 1830F Autothermal reforming has two stages i a partial oxidative noncatalytic process in which methane is partially oxidized to produce syngas and ii a catalytic steam reforming process in which unconverted methane is further reformed into synthesis gas After these two stages the synthesis syngas is converted into raw methanol not yet dewatered through an exothermic synthesis process with a temperature range of 200C280C 390F535F Methanol is then oxidized by oxygen from air to formaldehyde sometimes referred to as methanal 2CH OH O 2CH O 2H O 3 2 2 2 Formaldehyde is used to produce synthetic resins either alone or with phenol urea or melamine other uses are minor By analogy to the reaction with oxygen methane reacts with sulfur in the presence of a catalyst to give the carbon disulfide used in the rayon industry CH 4Sg CS 2H S 4 2 2 The major nonpetrochemical use of methane is in the production of hydrogen for use in the Haber synthesis of ammonia Ammonia synthesis requires nitrogen obtained from air and hydrogen The most common modern source of the hydrogen consumed in ammonia production about 95 of it is methane When propane and butane are oxidized in the vapor phase without a catalyst at 270C350C 520F660F and at 503000 psi a wide variety of products is obtained including C1C4 acids C2C7 ketones ethylene oxide esters formals acetals and others Cyclohexane is oxidized commercially and is somewhat selective in its reaction with air at 150C250C 300F480F in the liquid phase in the presence of a catalyst such as cobalt ace tate Cyclohexanol derivatives are the initial products but prolonged oxidation produces adipic acid On the other hand oxidation of cyclohexane and methylcyclohexane over vanadium pentoxide at 450C500C 840F930F affords maleic and glutaric acids 62313 Carboxylic Acids The preparation of carboxylic acids from petroleum particularly from paraffin wax for esterifica tion to fats or neutralization to form soaps has been the subject of a large number of investigations Wax oxidation with air is comparatively slow at low temperature and normal pressure very little reaction taking place at 110C 230F with a wax melting at 55C 130F after 280 h At higher temperatures the oxidation proceeds more readily maximum yields of mixed alcohol and high molecular weight acids are formed at 110C140C 230F285F at 60150 psi higher tempera tures 140C160C 285F320F result in more acid formation 62314 Alkylation Alkylation chemistry contributes to the efficient utilization of C4 olefin derivatives generated in the cracking operations Isobutane has been added to butenes and other lowboiling olefin derivatives 232 Handbook of Petrochemical Processes to give a mixture of highly branched octane derivatives eg heptane derivatives by alkylation The reaction is thermodynamically favored at low temperatures 20C and thus very powerful acid catalysts are employed Typically sulfuric acid 85100 anhydrous hydrogen fluoride or a solid sulfonic acid is employed as the catalyst in these processes The first step in the process is the formation of a carbocation by combination of an olefin with an acid proton CH CCH H CH C 3 2 2 3 3 Step 2 is the addition of the carbocation to a second molecule of olefin to form a dimer carbocation The extensive branching of the saturated hydrocarbon results in highoctane In practice mixed butenes are employed isobutylene 1butene and 2butene and the product is a mixture of isomeric octanes that has an octane number of 9294 With the phaseout of leaded additives in our motor gasoline pools octane improvement is a major challenge for the refining industry Alkylation is one answer 62315 Thermolysis Although there are relatively unreactive organic molecules paraffin hydrocarbon derivatives are known to undergo thermolysis when treated under hightemperature lowpressure vaporphase con ditions The cracking chemistry of petroleum constituents has been extensively studied Albright et al 1992 Cracking is the major process for generating ethylene and the other olefin derivatives that are the reactive building blocks of the petrochemical industry Chenier 2002 AlMegren and Xiao 2016 In addition to thermal cracking other very important processes that generate sources of hydrocarbon raw materials for the petrochemical industry include catalytic reforming alkylation dealkylation isomerization and polymerization Cracking reactions involve the cleavage of carboncarbon bonds with the resulting redistribution of hydrogen to produce smaller molecules Thus cracking of petroleum or petroleum fractions is a process by which larger molecules are converted into smaller lowerboiling molecules In addition cracking generates two molecules from one with one of the product molecules saturated paraffin and the other unsaturated olefin At the high temperatures of refinery crackers usually 500C 950F there is a thermody namic driving force for the generation of more molecules from fewer molecules that is cracking is favored Unfortunately in the cracking process certain products interact with one another to produce products of increased molecular weight over that in the original feedstock Thus some products are taken off from the cracker as useful light products olefin derivatives gasoline and others but other products include heavier oil and coke Paraffinwax ROH RCO H alcohol 2 acid Acids from formic HCO2H to that with a 10carbon atom chain CH3CH29CO2H have been identified as products of the oxidation of paraffin wax Substantial quantities of waterinsoluble acids are also produced by the oxidation of paraffin wax but apart from determination of the aver age molecular weight ca 250 very little has been done to identify individual numbers of the product mixture The pyrolysis of methane to form acetylene alkyne derivatives olefin derivatives and arenes is highly endothermic and requires very high temperatures and concurrent combustion of methane as a fuel in order to provide the enthalpy of reaction in a heat exchange furnace At these high tem peratures homogeneous pathways lead to acetylene polynuclear aromatic derivatives and soot as the preferred products for both kinetics and thermodynamic reasons Thermal efficiencies are low because of the extreme temperature cycling required for process streams and because of the rapid quenching protocols used to restrict chain growth and soot formation The low pressures required 233 Chemicals from Paraffin Hydrocarbons by thermodynamics and the slow homogeneous reactions lead to large reactor vessels which must be protected against carbon deposition and metal dusting corrosion by using coatings or specialized materials of construction Recently several approaches have addressed these limitations and they have led to significant control of methane pyrolysis selectivity One approach involves the synthe sis of benzene and ethylene with 3040 yields per pass using homogeneous pyrolysis reactors and the rapid thermal quenching of reaction products Another improvement uses shapeselective catalysts based on molybdenum and tungsten species held within shapeselective channels in pen tasil zeolites HZSM5 where chain growth to form polynuclear aromatic derivatives is spatially restricted and the presence of CH4 activation sites on the surface of carbide clusters leads to CH4 pyrolysis reactions at much lower temperatures 700C than for homogeneous pathways The addi tion of small amounts of CO2 during CH4 pyrolysis on these catalysts and the selective deactivation of acid sites on external zeolite surfaces have led to marked improvements in catalyst stability and to lower selectivity to hydrocarbon derivatives larger than naphthalene The combination of such cata lysts with hydrogen removal by ceramic membranes remains a promising but challenging approach to the direct conversion of methane to larger hydrocarbon derivatives A twostep cyclic process involving the deposition of CHx fragments from methane on metal surfaces at 200C300C 390F570F and the coupling of such fragments during a subsequent hydrogenation cycle has led to very low yields of C2 hydrocarbon derivatives Product yields are constrained by the unfavorable thermodynamics of this overall process at low temperatures and by the selectivity losses to surface carbon which also cause rapid deactivation and loss of methane reactants A more promising and thermodynamically feasible cyclic strategy involves the formation of relatively pure H2 streams using CH4H2O cyclic processes on solids that can generate reactive carbon and H2 during the CH4 cycle and remove the carbon as CO while producing additional H2 during subsequent contact with steam 624 oxidative couPlinG In the oxidative coupling process methane CH4 and oxygen react over a catalyst to form water and a methyl radical CH3 often referred to as partial oxidation The methyl radicals combine to form a higher molecular weight alkane mostly ethane C2H6 which dehydrogenates into ethylene CH2CH2 Complete oxidation rapid formation of carbon dioxide before the radicals link up to form ethane and ethylene is an undesired reaction The function of the catalyst is to control the oxidation so that reactions can be kept on the desired path and catalysts used are mostly oxides of alkali alkaline earth and other rare earth metals Hydrogen and steam are sometimes added in order to reduce coking on catalysts The compression separation and recovery sections of these processes are similar to those of ethane steam cracking except for the sections for watercarbon dioxide removal and methanization Ethylenecontaining gas streams are compressed and water is condensed after which the gases pass through an acid gas removal system where carbon dioxide is removed Additional water is removed in a refrigeration unit and then completely removed along with carbon dioxide In the methaniza tion section carbon monoxide carbon dioxide and hydrogen are converted to methane which is recycled as a feedstock to increase the total yield From the remaining stream ethylene ethane propylene and propane are separated through C2 and C3 separation respectively Oxidative coupling combines at the molecular level methane dimerization via radicallike path ways with the removal of the hydrogen formed often before recombinative desorption to form H2 via oxidation steps Ethane and ethylene are the predominant hydrocarbon derivatives formed Heterogeneous catalysts improve the yields and selectivity attainable in homogeneous coupling reactions but the active surface sites in these materials also activate CH bonds in ethane and ethylene leading to secondary combustion reactions which limit attainable yields to 2025 and lead to significant formation of CO2 These secondary pathways are very exothermic and they place significant heat transfer loads on the catalytic reactors The use of cyclic strategies using 234 Handbook of Petrochemical Processes lattice oxygen and moving or fluid bed reactors provides an attractive alternate option which avoids unselective homogeneous combustion pathways and uses the heat capacity of the solids to increase the efficiency to heat removal during reaction Protecting strategies in oxidative coupling can lead to twostep processes similar to those for methanol synthesis In principle synthesis gas methyl bisulfate or methyl chloride intermediates can be used to form ethylene but ethylene formation from these protected intermediates is not very selective and the overall processes is not environ mentally benign Other protecting strategies have been attempted or at least proposed in order to increase C2 yields in oxidative methane coupling The separation of ethylene from the reactor effluent using cationexchange zeolites has been carried out and it has led to slight C2 yield improvements The low adsorption temperatures required and the lack of adsorption selectivity for ethane however limit the practical applications of these approaches The in situ conversion of ethane and ethylene to aromatic derivatives using cationexchange zeolites after oxidative coupling can lead to the simpler separation of aromatic derivatives from the product stream but in a process for the synthesis of aromatic derivatives instead of ethylene Finally yields improvements can result from the separa tion of methane and oxygen reactants in space via membranes or in time via cyclic reactors The first approach exploits any differences in kinetic oxygen response between the coupling and the product combustion reactions O2 is introduced along the reactor via multiple injectors or oxygen conducting membrane walls Low O2 concentrations can also be achieved using backmixed fluid ized beds operated at high oxygen conversion levels The staging of the oxidant along a tubular reactor has not led to significant improvements apparently as a result of the similar kinetic dependences of CH4 and C2 activation steps on O2 concentration Detailed kinetic simulations have shown that distributed oxygen introduction is unlikely to give C2 yields above 3540 Laboratory tests have shown that poor radial disper sion of the oxygen feed can lead to high local O2 concentrations which can cause stable flames and structural damage at membrane walls Detailed kinetic and process simulations have sug gested that continuous ethylene removal from a recycle stream can lead to 7585 C2 yields during oxidative coupling of methane When the removal of ethylene requires temperatures significantly lower than for oxidative coupling the required recycle ratios become impractical because extensive thermal cycling leads to secondlaw inefficiencies and to large capital and operating costs associated with heat exchange and recompression These constraints can be overcome by designing absorbers or membranes that remove ethylene selectively from dilute streams containing ethane CH4 CO2 H2O and O2 at typical oxidative coupling temperatures A reactionseparation protocol using simulated chromatographic reactors has led to 6570 ethylene yields The practical use of these reactors as moving beds however requires porous solids that separate C2 from methane and oxygen at elevated temperatures using adsorption capillary condensation or diffusion differences among these components Cationexchanged zeolites and microporous carbons are promising as materials for the separation of ethylene from such mixtures but optimum operating temperatures remain well below those required for oxida tive coupling Oxidative coupling of methane can be carried out without contact between hydrocarbon deriva tives and O2 using cyclic reactors or hydrogenconducting membranes High C2 yields 2528 can be achieved by cycling reducible oxides between a methane activation reactor and a solids reoxi dation vessel This cyclic process can maintain constant temperatures during solids recycle and uses air instead of pure O2 as the oxidant but the process requires complex handling of solids in fluidized beds Such redox cycles can be carried out within a single vessel by internally segregating a fluid bed into a reaction zone and an oxidative regeneration zone The appropriate design oxygen donor solids can be used to the amount of and rate of reaction of the available lattice oxygen These cyclic oxidative coupling schemes remain of fundamental and practical interest in the activation and conversion of methane via oxidative routes 235 Chemicals from Paraffin Hydrocarbons Another type of cyclic reactor uses hydrogen absorption into a solid during methane pyrolysis and the removal of the absorbed hydrogen as water in subsequent oxidation cycles This approach has been recently reported for dehydrogenation reactions of higher alkanes In such cyclic schemes pyrolysis and oxidation are separated temporally In the mathematically analogous cata lytic membrane process reactants are separated spatially using a diffusion barrier that permits only hydrogen transport Experimental tests using thick membrane disks of hydrogenconducting perovskites led to very low methane conversion rates and C2 yields Significant improvements are possible by combining cationexchanged zeolites for selective methane pyrolysis at low tem peratures with much thinner oxide films the successful synthesis of which has been recently reported Hydrogen transport rates at the H2 pressures prevalent during methane pyrolysis how ever must be improved significantly before practical applications of such schemes can be seri ously considered 63 ETHANE Ethane C2H6 is a twocarbon alkane that at standard temperature and pressure is a colorless odorless gas Ethane is isolated on an industrial scale from natural gas and as a byproduct of petroleum refining Its chief use is as petrochemical feedstock for ethylene production usually by pyrolysis Vincent et al 2008 CH CH CH CH H 3 3 2 2 2 After methane ethane is the secondlargest component of natural gas Natural gas from different gas fields varies in ethane content from less than 1 to more than 6 vv Prior to the 1960s ethane and larger molecules were typically not separated from the methane component of natural gas but simply burnt along with the methane as a fuel Currently ethane is an important petrochemical feedstock and it is separated from the other components of natural gas in most gas processing plants Ethane can also be separated from petroleum gas a mixture of gaseous hydrocarbon deriva tives that arises as a byproduct of petroleum refining The main source for ethane is natural gas liquids NGLs Approximately 40 of the available ethane is recovered for chemical use The only large consumer of ethane is the steam cracking pro cess for ethylene production Thus ethane is most efficiently separated from methane by liquefying it at cryogenic temperatures Various refrigeration strategies exist the most economical process presently in wide use employs turboexpansion and can recover over 90 of the ethane in natural gas In this process chilled gas expands through a turbine as it expands its temperature drops to about 100C At this low temperature gaseous methane can be separated from the liquefied ethane and heavier hydrocarbon derivatives by distillation Further distillation then separates ethane from the propane and heavier hydrocarbon derivatives 631 Physical ProPerties Ethane C2H6 CH3CH3 is a colorless odorless gaseous hydrocarbon belonging to the paraffin series that is structurally the simplest hydrocarbon that contains a single carboncarbon bond Table 63 Ethane is an important constituent of natural gas that also occurs dissolved in crude petroleum and as a byproduct of petroleum refining it is also produced by the carbonization of coal Ethane has a boiling point of 885C 1273F and melting point of 1828C 2970F Solid ethane exists in several modifications On cooling under normal pressure the first modifica tion to appear is a plastic crystal crystallizing in the cubic system In this form the positions of 236 Handbook of Petrochemical Processes the hydrogen atoms are not fixed the molecules may rotate freely around the long axis Cooling this ethane below approximately 899K 1832C 2978F changes it to monoclinic metastable ethane Ethane is only very sparingly soluble in water When ethane is combusted in excess air it produces carbon dioxide and water with a heating value of 1800 Btuft3 approximately double that produced from methane As a constituent of natu ral gas ethane is normally burned with methane as a fuel gas Ethanes relation with petrochemicals is mainly through its cracking to ethylene 632 chemical ProPerties Chemically ethane can be considered as two methyl groups joined that is a dimer of methyl groups The chemistry of ethane involves chiefly free radical reactions Ethane can react with the halogens especially chlorine and bromine by free radical halogenation which proceeds through the propagation of the ethyl radical C H Cl C H Cl Cl 2 5 2 2 5 Cl C H C H HCl 2 6 2 5 Because halogenated ethane derivatives can undergo further free radical halogenation this process results in a mixture of several halogenated products In the chemical industry more selective chemi cal reactions are used for the production of any particular twocarbon haloalkane The complete combustion of ethane produces carbon dioxide and water according to the chemi cal equation 2C H 7O 4CO 6H O 2 6 2 2 2 Combustion may also occur without an excess of oxygen forming a mix of amorphous carbon and carbon monoxide 2C H O 4C 6H O 2 6 2 2 2C H 5O 4CO 6H O 2 6 2 2 2C H 4O 2C 2CO 6H O 2 6 2 2 TABLE 63 Properties of Ethane Chemical formula C2H6 Molar mass 3007 gmol Appearance Colorless gas Odor Odorless Density 13562 mgcm3 at 0C 05446 gcm3 at 184 K Liquid density 0446 at 0C Vapor density air 1 105 Melting point 1828C 2969F 904K Boiling point 885C 1274F 1846K Flash point 944C 1379F Solubility in water 568 mgL Explosive limits 312 vv in air 237 Chemicals from Paraffin Hydrocarbons Combustion occurs by a complex series of free radical reactions An important series of reaction in ethane combustion is the combination of an ethyl radical with oxygen and the subsequent breakup of the resulting peroxide into ethoxy and hydroxyl radicals Thus C H O C H OO 2 5 2 2 5 C H OO HR C H OOH R 2 5 2 5 C H OOH C H O OH 2 5 2 5 The principal carboncontaining products of incomplete ethane combustion are singlecarbon com pounds such as carbon monoxide and formaldehyde HCHO One important route by which the carboncarbon bond in ethane is broken to yield these singlecarbon products is the decomposition of the ethoxy radical into a methyl radical and formaldehyde which can in turn undergo further oxidation C H O CH HCHO 2 5 3 Minor products in the incomplete combustion of ethane include acetaldehyde CH3CHO methane CH4 methanol CH3OH and ethanol CH3CH2OH At higher temperatures especially in the range 600C900C 11101650F ethylene CH2CH2 is a significant product C H O CH CH OOH 2 5 2 2 2 Similar reactions with agents other than oxygen as the hydrogen abstractor are involved in the production of ethylene from ethane in steam cracking Speight 2014a The chief use of ethane is as a feedstock for ethylene production by steam cracking in which the ethane is diluted with steam and briefly heated to very high temperatures typically 900C 1650F or even higher CH CH CH CH H 3 3 2 2 2 Ethane is favored for ethylene productiona basic petrochemical feedstockthe steam cracking of ethane is selective for ethylene while the steam cracking of higher molecular weight hydrocarbon derivatives yields a product mixture that contains less ethylene but more of the higher molecu lar weight olefin derivatives such as propylene CH3CHCH2 butadiene CHCHCHCH2 and aromatic hydrocarbon derivatives 633 chemicals from ethane In addition to the chlorination of methane other examples of the chlorination reaction include the formation of ethyl chloride by the chlorination of ethane CH CH Cl CH CH Cl HCl 3 3 2 3 2 The byproduct hydrogen chloride may be used for the hydrochlorination of ethylene to produce more ethyl chloride Hydrochlorination of ethylene however is the main route for the production of ethyl chloride CH CH HCl CH CH Cl 2 2 3 2 238 Handbook of Petrochemical Processes Ethyl chloride CH3CH2Cl is also prepared by the direct addition of hydrogen chloride HCl to eth ylene CH2CH2 or by reacting ethyl ether CH3CH2OCH2CH3 or ethyl alcohol CH3CH2OH with hydrogen chloride The chlorination of npentane and isopentane does not take place in the liquid or vapor phase below 100C 212F in the absence of light or a catalyst but above 200C 390F and it proceeds smoothly by thermal action alone The hydrolysis of the mixed chlorides obtained yields all the isomeric amyl C5 alcohols except isoamyl alcohol Reaction with acetic acid produces the corresponding amyl acetates which find wide use as solvents Major uses of ethyl chloride are the manufacture of tetraethyl lead and the synthesis of insecticides It is also used as an alkylating agent and as a solvent for fats and wax A small portion of vinyl chloride is produced from ethane by means of the Transcat process in which a combination of chlorination oxychlorination and dehydrochlorination reactions occur in a molten salt reactor The reaction occurs over a copper oxychloride catalyst at a wide temperature range of 310C640C 590F1185F During the reaction the copper oxychloride is converted to copperI chloride CuCl and copperII chloride CuCl2 which are air oxidized to regenerate the catalyst Vinyl chloride is an important monomer for polyvinyl chloride The main route for obtaining this monomer however is via ethylene An approach to utilize ethane as an inexpensive chemical intermediate is to ammoxidize it to acetonitrile CH3CN The reaction takes place in presence of a cobaltBzeolite 2CH CH 2NH 3O 4CH CN 3H O 3 3 3 2 3 2 64 PROPANE Propane is produced as a byproduct of two other processes i natural gas processing and ii petro leum refining The processing of natural gas involves removal of butane propane and large amounts of ethane from the raw gas to prevent condensation of these volatiles in natural gas pipelines Additionally crude oil refineries produce some propane as a byproduct of cracking processes Parkash 2003 Gary et al 2007 Speight 2007 2014a Hsu and Robinson 2017 Speight 2017 Propane can also be produced as a biofuel by the thermal conversion of various types of biomass Speight 2011 Propane is produced from both crude oil refining and natural gas processing Propane is not pro duced for its own sake but is a byproduct of these two other processes Natural gas plant production of propane primarily involves extracting materials such as propane and butane from natural gas to prevent these liquids from condensing and causing operational problems in natural gas pipelines Similarly when oil refineries make major products such as motor gasoline diesel and heating oil some propane is produced as a byproduct of those processes Propane has a wide variety of uses worldwide including small domestic heating applications to large industrial and manufacturing processes Some of the more common uses of propane are for residential and commercial heating and cooking motor fuel use in vehicles irrigation pumps and power generation agricultural crop drying and weed control and as a raw material in the petro chemical industry to make things such as plastics alcohol fibers and cosmetics 641 Physical ProPerties Propane C3H8 CH3CH2CH3 is a threecarbon alkane that is a gas at standard temperature and pressure but compressible to a transportable liquid It is a gaseous paraffin hydrocarbon C3H8 having a boiling point of 423 440F and a melting point of 1877C 3058F Table 64 Propane may be handled as a liquid at ambient temperatures and moderate pressures Commercial propane as sold on the various markets may include varying amounts of ethane butanes and lique fied refinery gases 239 Chemicals from Paraffin Hydrocarbons Liquid propane is a selective hydrocarbon solvent used to separate paraffinic constituents in lube oil base stocks from harmful asphaltic materials It is also a refrigerant for liquefying natural gas and used for the recovery of condensable hydrocarbon derivatives from natural gas 642 chemical ProPerties Propane is a more reactive paraffin than ethane and methane This is due to the presence of two secondary hydrogens that could be easily substituted Chapter 6 Propane is obtained from natural gas liquids or from refinery gas streams Liquefied petroleum gas LPG is a mixture of propane and butane and is mainly used as a fuel The heating value of propane is 2300 Btuft3 Liquefied petroleum gas is currently an important feedstock for the production of olefin derivatives for petrochemical use Propane is an odorless nontoxic hydrocarbon C3H8 gas at normal pressures and temperatures ASTM D2163 2016 When pressurized it is a liquid with an energy density 270 times greater than its gaseous form A gallon of liquid propane has about 25 less energy than a gallon of gasoline Propane is a simple asphyxiant and since unlike methane propane is denser than air it may accumulate in low spaces such as depressions in the surface of the earth and near the floor in domestic and industrial building If a leak in a propane fuel system occurs the gas will tend to sink into any enclosed area and thus poses a risk of explosion and fire The typical scenario is a leak ing cylinder stored in a basement the propane leak drifts across the floor to the pilot light on the furnace or water heater and results in an explosion or fire This property makes propane generally unsuitable as a fuel for boats One hazard associated with propane storage and transport is known as a BLEVE boiling liquid expanding vapor explosion Propane is stored under pressure at room temperature and propane and its mixtures will flash evaporate at atmospheric pressure and cool well below the freezing point of water The cold gas which appears white due to moisture condensing from the air may cause frostbite Propane undergoes dehydrogenation to propylene by a catalytic cracking process CH CH CH CH CH CH H 3 2 3 3 2 2 Propane undergoes combustion reactions in a similar fashion to other alkanes but exhibits several different degrees of complexity Qin et al 2000 Put simply in the presence of excess oxygen propane burns to form water and carbon dioxide C H 5O 3CO 4H O 3 8 2 2 2 TABLE 64 Properties of Propane Chemical formula C3H8 Molar mass 4410 gmol Appearance Colorless gas Odor Odorless Density 20098 kgm3 at 0C 1013 kPa Liquid density 0493 at 25C Vapor density air 1 205 Melting point 1877C 3058F 855K Boiling point 4225 to 4204C 4405 to 4367F Flash point 104C 155F Solubility in water 47 mgL at 0C Explosive limits 2395 vv in air 240 Handbook of Petrochemical Processes When insufficient oxygen is present for complete combustion incomplete combustion occurs allowing carbon monoxide andor soot carbon to be formed as well 2C H 9O 4CO 2CO 8H O 3 8 2 2 2 C H 2O 3C 4H O 3 8 2 2 Propane combustion is much cleaner than gasoline combustion though not as clean as natural gas methane combustion The presence of carboncarbon bonds plus the multiple bonds of propylene CH3CHCH2 and butylene CH3CHCHCH3 CH3CH2CHCH2 create organic exhausts besides carbon dioxide and water vapor during typical combustion These bonds also cause propane to burn with a visible flame Chemicals directly based on propane are few although as mentioned propane and liquefied petroleum gas are important feedstocks for the production of olefin derivatives Propylene has always been obtained as a coproduct with ethylene from steam cracking processes 643 chemicals from ProPane A major use of propane recovered from natural gas is the production of light olefin derivatives by steam cracking processes However more chemicals can be obtained directly from propane by reaction with other reagents than from ethane This may be attributed to the relatively higher reactivity of propane than ethane due to presence of two secondary hydrogens which are easily substituted 6431 Oxidation The noncatalytic oxidation of propane in the vapor phase is nonselective and produces a mixture of oxygenated products Oxidation at temperatures below 400C 750F produces a mixture of alde hydes acetaldehyde and formaldehyde and alcohols methyl alcohol and ethyl alcohol CH CH CH O CH CHO HCHO CH OH CH CH OH 3 2 3 3 3 3 2 At higher temperatures propylene and ethylene are obtained in addition to hydrogen peroxide CH CH CH O CH CH CH CH CH H O 3 2 3 3 2 2 2 2 2 Due to the nonselectivity of this reaction separation of the products is complex and the process is not industrially attractive 6432 Chlorination Chemically methane typical of alkanes undergoes very few reactions One of these reactions is halogenation or the substitution of hydrogen with halogen to form a halomethane This is a very important reaction providing alternative pathway for methane activation for the production of synthetic crude oil fuels and chemicals Industrial use of this process will not only eliminate the expensive air separation plants but as well produce far less greenhouse gases Gasphase thermal oxidation and catalytic oxidative methanation process are suitable for industrial application The proposed process is based on elimination of need for air separation for oxygen production hence the gasphase thermal chlorination is selected Rozanov and Treger 2010 AlvarezGalvan et al 2011 Treger et al 2012 Rabiu and Yusuf 2013 Methane chlorination is a radical reaction characterized by poor selectivity Rozanov and Treger 2010 forming a products stream consisting of equilibrium concentration of all the chloro methane derivatives 241 Chemicals from Paraffin Hydrocarbons CH Cl CH Cl HCl 4 2 3 CH Cl Cl CH Cl HCl 3 2 2 2 CH Cl Cl CHCl HCl 2 2 2 3 CHCl Cl CCl HCl 3 2 4 The process conditions can be selected to maximize the proportions of di and trichlorometh anes To produce the higher chloroderivatives methyl chloride is separated from the products and recycled with unreacted methane When ironbased catalysts are employed the polymerization of methylene chloride CH2Cl2 and chloroform CHCl3 to higher molecular weight hydrocarbon derivatives mainly olefin derivatives can be achieved Hence the emphasis is to maximize the yield and recovery of these compounds for the feasibility of this process Chlorination of propane with chlorine at 480C640C 895F1185F yields a mixture of perchloroethylene Perchlor and carbon tetrachloride CH CH CH 8Cl CCl CCl CCl 8HCl 3 2 3 2 2 2 4 Carbon tetrachloride is usually recycled to produce more perchloroethylene 2CC1 CCl CCl 2Cl 4 2 2 2 Perchlor may also be produced from ethylene dichloride 12dichloroethane through an oxychlorinationoxyhydrochlorination process trichloroethylene Trichlor is coproduced Perchlor and Trichlor are used as metal degreasing agents and as solvents in dry cleaning Perchlor is also used as a cleaning and drying agent for electronic equipment and as a fumigant Further to the chlorination of methane a modified process for the conversion of natural gas to transportation fuels and chemicals consists of three principal steps i production of chlorometh ane compounds ii conversion of the chloromethane derivatives to hydrocarbon derivatives and iii chlorine recovery The first step involves gasphase thermal or catalytic selective chlorination of methane to predominantly dichloromethane and trichloromethane after which the monochloro methane is separated and recycled In the second step the chloromethane is fed into a moving bed reactor packed with an ironbased FischerTropsch catalyst and wherein it is converted to predomi nantly olefin hydrocarbon derivatives FischerTropsch products and hydrogen chloride gas The hydrogen chloride byproduct is separated from the FischerTropsch products to obtain premium fuels The process features a close chlorine loop and the Deacon reaction a reaction for obtaining chlorine gas by passing air and hydrogen chloride over a heated catalyst as copper chloride is used to recover chlorine from the hydrogen chloride byproduct so that effectively there is no net con sumption of chlorine in the overall process Finally the plant employs a hydrolyser to regenerate the chloride catalyst Rabiu and Yusuf 2013 The overall reaction can be represented as nCH O C H nH O 4 2 n 2n 2 6433 Dehydrogenation Dehydrogenation of paraffin derivatives yields olefins However in the petrochemical industry ole fins are not a final product but rather building blocks for manufacturing the most used chemical commodities A reliable dehydrogenation technology allows for the design of integrated schemes for fuels and petrochemicals from natural gas and is becoming a promising alternative feedstock for the new century due to its abundant reserves and low cost In a refinery the availability of a dehy drogenation technology permits innovation in the design of new process schemes by formulating 242 Handbook of Petrochemical Processes new components for gasoline and diesel fuel Petrochemical intermediates propylene highpurity isobutylene butadiene butylene isomers and components for the blending in the final product that will become gasoline isooctane alkylates or for the diesel pool high cetane diesel longchain linear oxygenates are made conveniently available through paraffin dehydrogenation Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 In order to dehydrogenate a saturated noncyclic hydrocarbon process temperatures are typi cally in the order of 500C600C 930F1110F In general terms various metals are used as catalystsexamples are nickel Ni platinum Pt palladium Pd and iron Fe are suitable and also the oxides zinc ZnO chromium Cr2O3 and iron Fe2O3 Under certain conditions a diene rather than an alkene may form from nbutane during dehydrogenation Again in general terms carbonhydrogen bonds are broken to form a double bond For example in the dehydrogenation of nbutane a mixture of isomers may form From isobutane isobutylene may be obtained 2CH CH CH CH CH CH CHCH CH CHCH CH 2H 3 2 2 3 3 3 2 2 3 2 CH CHCH CH C CH H 3 2 3 3 2 2 3 The reactor for obtaining the two butylene isomers from nbutane is typically a tubular device In the dehydrogenation of butane the feedstocks is introduced into the reactor in compressed form in normal conditions butane is in the gaseous form which is easily converted to the liquid form at 05C 311F The butane is moved to the heat exchangerby means of a piston device where it is heated evaporated and thus changes back to the gaseous form Then in the reactor the butane is heated to the temperature required for the reaction approximately 500C 932F On contacting the catalyst the butane vapor dehydrogenates forming a mixture of unreacted nbutane butylenes butene1 and butene2 hydrogen and secondary products Typically the contact time of the butane with the catalyst is in the order of less than 3 s otherwise a large quantity of secondary products byproducts including soot may form which affects the yield of the desired products After the separation of any secondary products butane and butylene in the mixture butylene may be subjected to further dehydrogenation to produce 13butadiene CH2CHCHCH2 With the chromiaalumina catalyst at a temperature of 450C650C 840F1200F butadiene13 forms from butane Thus CH CH CH CH CH CHCH CH 2H 3 2 2 3 2 2 2 In dehydrogenation butane does not form in a cycle and does not form cyclobutene because cyclob utene has an unstable structure at the reaction temperature it is also capable of thermally breaking down to ethylene СН2СН2 Dehydrogenation reactions find wide application in production of a variety of products such as hydrogen olefin derivatives polymers and oxygenates ie production of light C3C4 olefin derivatives higherboiling olefin derivatives C4C8 for detergents polypropylene styrene alde hydes and ketones The demand for basic chemicals such as acrylonitrile oxo alcohols ethylene and propylene oxides are rapidly growing and as a result the dehydrogenation of lower alkanes is a rapidly expanding business The dehydrogenation process and thus the extent of the equilibrium and the rate of the reac tion are favored at high temperatures and at a low pressure because the volume of reaction prod ucts exceeds that of reactants Removal of hydrogen from the products improves the equilibrium extent and reaction rate of dehydrogenation Gasphase dehydrogenation is favored by low partial pressures of the reactants and dehydrogenation catalysts are less sensitive than hydrogenation cata lysts to poisons such as deactivation by coke formation and deposition of the coke on the catalyst 243 Chemicals from Paraffin Hydrocarbons This leads to irreversible deactivation due to phase transformation sintering and volatilization of the components of the catalyst at the high temperatures involved In addition to the examples presented above more specifically the dehydrogenation process involves the following parameters the reactants are in the gas phase Supported noble metals Pt Pd Rh Ru Re PtRe Supported transition metals Ni Co Fe Cu Mo Catalyst supports yAl2O3 SiO2 TiO2 zeolites kieselguhr Raney type metal catalyst Ni CuNi Oxide catalysts Cr2O3 Fe2O3 Al2O3Cr2O3 Fe2O3K2CO3Cr2O3 Ca3NiPO43Cr2O3 Reactors Tubular reactor Multitray fixed bed reactor Moving bed reactor Fluidized bed reactor Important industrial dehydrogenation process includes the following 1 The catalytic dehydrogenation of propane is a selective reaction that produces mainly propene CH CH CH CH CH CH 3 2 3 3 2 The process could also be used to dehydrogenate butane isobutane or mixed liquefied petroleum gas feedstocks It is a singlestage system operating at a temperature range of 540C680C Conversions in the range of 5565 are attainable and selectivity may reach up to 95 As an example the UOP Oleflex process that can be used for the catalytic dehydro genation of isobutane normal butane or mixed butanes to make iso normal or mixed butylenes Traditionally this process has been used throughout the world to enable the production of gasoline blending components The process employs a proprietary platinum on alumina catalyst doped with tin and alkali metals between 500C and 700C 930F and 1290F Dehydrogenation is highly selective resulting in yields in excess of 90 vv This process was based on the Pacol process in which normal paraffins C10C14 alkane derivatives are dehydrogenated in a vaporphase reaction to corresponding monoolefins over a highly selective and active catalyst for detergent manufacture The Phillips steam active reforming STAR process is used to dehydrogenate lower paraffins propane or butanes into their corresponding olefins propylene or butylenes which can be further processed to valuable downstream products In the process as an example a 0206 ww platinum on alumina Al2O3 catalyst doped with zinc and tin is used to dehydrogenate propane diluted with steam The catalyst is importantly waterstable allowing the steamdilution to drive the equilibrium toward dehydrogenation On the other hand the Catofin and LindeBASF processes employ chromiumbased catalysts The Catofin dehydrogenation process uses fixed bed reactors with a catalyst and operating conditions that are selected to optimize the complex relationship among conver sion selectivity and energy consumption The overall selectivity of isobutane to isobutyl ene via the CATOFIN process is greater than 90 ww and the selectivity of propane to propylene is greater than 86 ww The Linde catalyst is composed of 18 parts chromia Cr2O3 and 025 parts zirconia ZrO2 on alumina Al2O3 with a trace of potassium ions K The active site structure is controversial but the catalytic cycle involves chromium Cr3 and Cr4 244 Handbook of Petrochemical Processes 2 Preparation of butadiene by dehydrogenation of nbutane and nbutenes using several dif ferent catalyst types CH CH CH CH CH CH CH CH H 3 2 2 3 3 2 2 2 A12O3Cr2O3 catalyst Fluidized bed reactor 560C600C 1040F1110F CH CH CH CH CH CHCH CH H 3 2 2 2 2 2 Fe2O3K2CO3Cr2O3 or Ca3NiPO43Cr2O3 catalyst 600C660C 1110F1220F The Houdry dehydrogenation process was originally designed to produce butenes at less than atmospheric pressure for the production of butenes and was also used for butadi ene production in 1940s using chromiaalumina catalyst Catadiene process CH CH CH CH CH CHCHCH 2H 3 2 2 3 2 2 2 Cr2O3 supported on Al2O3 catalyst Adiabatic reactor 620C700C 1150F1290F Also Cr2O3 supported on Al2O3 catalyst fluidized bed 550C600C 1020F1110F The Catadiene dehydrogenation process is a reliable proven route for the production of 13 butadiene from nbutane or a mix of nbutane and nbutenes Lummus Technology has exclusive worldwide licensing rights to this technology The catalyst is produced by Clariant a leading company in the development of process catalysts Also the Catadiene is the only commercial technology available for onpurpose production of nbutylene isomers and butadiene from nbutane Due to the lower process temperature the process provides high conversion and selectivity for conversion of nbutane to nbutylenes and butadiene The process employs multiple reactors operating in a cyclic manner with an automated program so that the flow of process streams is continuous In addition the process unit can be operated to coproduce butylenes and butadiene or to produce only butadiene 3 Dehydrogenation of isopentane to isoprenea twostep process The dehydrogenation of isopentane to isoprene can be achieved by two stages in which isopentane in the first stage is dehydrogenated to amylene derivatives which is further dehydrogenated to isoprene in the second stage of the process as shown below CH CH CH CH CH C H mono olefinderivatives H 3 3 2 3 5 10 2 CH CH CH CH CH C H mono olefinderivatives H 3 3 2 3 5 10 2 Cr2O3 supported on Al2O3 catalyst Fluidized bed reactor 530C610C 985F1030F C H mono olefinderivatives CH C CH CHCH H 5 10 2 3 2 2 Ca3NiPO43Cr2O3 catalyst 550C650C 1020F1200F 245 Chemicals from Paraffin Hydrocarbons A onestep method is also available In this method the dehydrogenation of isopentane and isopentaneisoamylene mixtures is carried out on the same catalyst without intermedi ate separation of isopentane and isoamylene derivatives An important advantage of the twostep process is the possibility of the use of highly selective catalyst at each stage and high energy consumption significantly undermines the competitiveness of the twostep method in comparison with the onestep method 4 Dehydrogenation of ethylbenzene to styrene The development of commercial processes for the manufacture of styrene based on the dehydrogenation of ethylbenzene was achieved in the 1930s The need for synthetic styrenebutadiene rubber SBR during World War II provided the impetus for largescale production After 1946 this capacity became available for the manufacture of a high purity monomer that could be polymerized to a stable clear colorless and cheap plastic polystyrene and styrene copolymers Peacetime uses of styrenebased plastics expanded rapidly and polystyrene is now one of the least expensive thermoplastics on a costper volume basis Styrene itself is a liquid that can be handled easily and safely The activity of the vinyl group makes styrene easy to polymerize and copolymerize The direct dehydrogenation of ethylbenzene to styrene is carried out in the vapor phase with steam over a catalyst consisting primarily of iron oxide The reaction is endothermic and can be accomplished either adiabatically or isothermally Both methods are used in practice C H CH CH C H CHCH 6 5 2 3 6 5 2 Fe2O3Cr2O3 catalyst Adiabatic reactor 580C650C 1075F1200F or isothermal tubular reactor 580C610C 1075F1130F The major reaction is the reversible endothermic conversion of ethylbenzene to styrene and hydrogen that is C H CH CH C H CH CH H 6 5 2 3 6 5 2 2 This reaction proceeds thermally with low yield and catalytically with high yield As it is a reversible gasphase reaction producing 2 mol of product from 1 mol of starting material low pressure favors the forward reaction Competing thermal reactions degrade ethylben zene to benzene and also to carbon and styrene as well as to toluene C H CH CH C H CH CH 6 5 2 3 6 6 2 2 C H CH CH 8C 5H 6 5 2 3 2 C H CH CH H C H CH CH 6 5 2 3 2 6 5 3 4 The issue with the production of carbon is that the carbon is a catalyst poison When potassium is incorporated into the iron oxide catalyst the catalyst becomes selfcleaning through enhancement of the reaction of carbon with steam to give carbon dioxide which is removed in the reactor vent gas C 2H O CO 2H 2 2 2 Typical operating conditions in commercial reactors are approximately 620C 1150F and as low a pressure as practicable The overall yield depends on the relative amounts of 246 Handbook of Petrochemical Processes catalytic conversion to styrene and thermal cracking to byproducts At equilibrium under typical conditions the reversible reaction results in about 80 conversion of ethylbenzene The dehydrogenation of ethylbenzene is carried out in the presence of steam because i the steam lowers the partial pressure of ethylbenzene shifting the equilibrium toward styrene and minimizing the loss to thermal cracking ii the steam supplies the necessary heat of reaction and iii the steam cleans the catalyst by reacting with carbon to produce carbon dioxide and hydrogen 5 Oxidative dehydrogenation of nbutylene to butadiene Butadiene is produced as a byproduct of the steam cracking process used to produce ethylene and other olefin derivatives When mixed with steam and briefly heated to very high temperatures often over 900C 1650F aliphatic hydrocarbon derivatives give up hydrogen to produce a complex mixture of unsaturated hydrocarbon derivatives including butadiene The quantity of butadiene produced depends on the hydrocarbon derivatives used as the feedstock Lowboiling feedstocks feeds such as ethane yield primarily ethylene but higher molecular weight feedstocks favor the formation of higher molecular weight olefins butadiene and aromatic hydrocarbon derivatives The butadi ene is typically isolated from the other fourcarbon hydrocarbon derivatives produced in steam cracking by extractive distillation using a polar aprotic such as acetonitrile Nmethyl2pyrrolidone furfural or dimethylformamide from which it is then recov ered by distillation In the 1960s the process to produce butadiene from normal butene derivatives by oxidative dehydrogenation using a catalyst was developed Since that time various dehydrogenation pro cesses have been described and developed Passmann 1970 Dumez and Froment 1976 Park et al 2016 In fact the gradually increasing demand on 13butadiene CH2CHCHCH2 has led to further development of this alternative production routes Thus catalytic oxidative dehydrogenation of 1butene to 13butadiene using carbon dioxide as a mild oxidant has been systematically studied over Fe2O3Al2O3 catalysts Yan et al 2015 2CH CH CH CH O 2CH CHCH CH 2H O 3 2 2 2 2 2 Acetonitrile boiling point 81ºC 178ºF Nmethyl2pyrrolidone boiling point 202ºC 396ºF Furfural boiling point 162ºC 324ºF Dimethylformamide boiling point 152ºC 305ºF 247 Chemicals from Paraffin Hydrocarbons Fe2O3ZnOCr2O3 or Ca3NiPO43Cr2O3 catalyst 350C450C 660F840F The loaded ferric oxide Fe2O3 promotes oxygen mobility and modifies the surface acidity of the alumina Al2O3 which leads to a higher 1butene conversion and butadiene selectivity 6434 Nitration Nitrating propane produces a complex mixture of nitrocompounds ranging from nitromethane to nitropropanes The presence of lower nitroparaffin derivatives is attributed to carboncarbon bond fission occurring at the temperature used Temperatures and pressures are in the order of 390C440C 735F825F and 100125 psi respectively Increasing the mole ratio of propane to nitric acid increases the yield of nitropropane derivatives Nitropropane derivatives are good solvents for vinyl and epoxy resins and are also used to manu facture rocket propellants Nitropropane reacts with formaldehyde producing nitroalcohol derivatives CH CH CH NO HCHO CH CH CH NO CH OH 3 2 2 2 3 2 2 2 These difunctional compounds are versatile solvents 65 BUTANE ISOMERS Like propane butanes are obtained from natural gas liquids and from refinery gas streams The C4 acyclic paraffin consists of two isomers nbutane and isobutane 2methylpropane The physical as well as the chemical properties of the two isomers are quite different due to structural differences There are two isomers of butane In the IUPAC system of nomenclature however the name butane refers only to the nbutane iso mer CH3CH2CH2CH3 Butane derivatives are highly flammable colorless easily liquefied gases that quickly vaporize at room temperature nButane isobutane 248 Handbook of Petrochemical Processes The butane isomers present in natural gas can be separated from the large quantities of lower boiling gaseous constituents such as methane and ethane by absorption in a light oil The butane thus obtained can be stripped from the absorbent along with propane and marketed as liquefied petroleum gas that meets the required specifications or they can be separated from the propane and then from each other by fractional distillation nbutane boils at 05 C 311 F Table 65 isobutane boils at 117 C 109F Table 66 Butane derivatives that are formed by catalytic cracking and other refinery processes can be recovered by absorption into a light oil Commercially nbutane can be added to gasoline to increase its volatility as an aid to ignition in cold climates Transformed to isobutane in a refinery process known as isomerization it can be reacted with certain other hydrocarbon derivatives such as butylene to form valuable highoctane constituents of gasoline Like propane nbutane is mainly obtained from natural gas liquids It is also a byproduct from different refinery operations Currently the major use of nbutane is to control the vapor pressure of product gasoline Due to new regulations restricting the vapor pressure of gasoline this use is expected to be substantially reduced Surplus nbutane could be isomerized to isobutane which is currently in high demand for producing isobutene Isobutene is a precursor for methyl and ethyl tertiary butyl ethers ETBEs which are important octane number boosters Another alternative TABLE 65 Properties of nButane Chemical formula C4H10 Molar mass 5812 gmol Appearance Colorless gas Odor Gasolinelike or natural gaslike Density 248 kgm3 at 15C 59F Liquid density 0573 at 25C Vapor density air 1 21 Melting point 140 to 134C 220 to 209F Boiling point 1 to 1C 30F34F Solubility in water 61 mgL at 20C 68F Explosive limits 1985 vv in air TABLE 66 Properties of isobutane Chemical formula C4H10 Molar mass 5812 gmol Appearance Colorless gas Odor Odorless Density 251 kgm3 at 15C 100 kPa Liquid density 0551 at 25C Vapor density 201 Melting point 15942C 25496F Boiling point 117C 109F Solubility in water 489 mgL at 25C 77F Explosive limits 1884 in air 249 Chemicals from Paraffin Hydrocarbons outlet for surplus nbutane is its oxidation to maleic anhydride Almost all new maleic anhydride processes are based on butane oxidation nButane has been the main feedstock for the production of butadiene However this process has been replaced by steam cracking hydrocarbon derivatives which produce considerable amounts of byproduct butadiene 651 Physical ProPerties nButane CH3CH2CH2CH3 is a colorless gas with a boiling point of 1C 30F that unlike the first three alkanes is very soluble in water Table 66 The principal raw materials for its produc tion are petroleum and liquefied natural gas It forms an explosive and flammable mixture with air at low concentrations Its main uses in industry are as a raw material in the production of butadiene and acetic acid It is also used as a domestic fuel as a gasoline blending component as a solvent and as a refrigerant The isobutane CH32CHCH3 is also a colorless gas with a boiling point of 117C 109F that is also soluble in water Table 66 Although the physical properties of isobutane are similar to the properties of nbutane isobutane exhibits markedly different chemical behavior Isobutane is obtained by petroleum fractionation of natural gas or by isomerization of butane It forms an explosive and flammable mixture with air at low concentrations Its main uses are as a raw mate rial in organic synthesis for the production of synthetic rubber and in the production of branched hydrocarbon derivatives of highoctane grading 652 chemical ProPerties In the presence of excess oxygen butane burns to form carbon dioxide and water vapor 2C H 13O 8CO 10H O 4 10 2 2 2 On the other hand when the supply of oxygen is limited carbon soot or carbon monoxide may also be formed 2C H 9O 8CO 10H O 4 10 2 2 nButane is the feedstock for the DuPont catalytic process for the preparation of maleic anhydride Thus 2CH CH CH CH 7O 2C H CO O 8H O 3 2 2 3 2 2 2 2 2 Maleic anhydride is a solid compound that melts at 53C 127F is soluble in water alcohol and acetone but insoluble in hydrocarbon solvents The production of maleic anhydride from nbutenes is a catalyzed reaction occurring at approximately 400C440C and 3045 psi A catalyst consist ing of a mixture of oxide of molybdenum vanadium and phosphorous may be used Maleic anhydride 250 Handbook of Petrochemical Processes nButane like all hydrocarbon derivatives undergoes free radical chlorination providing both 1chlorobutane CH3CH2CH2CH2Cl and 2chlorobutane CH3CH2CH2CClCH3 as well as more highly chlorinated derivatives The relative rates of the chlorination are partially explained by the differing bond dissociation energy for the two types of CH bonds Isobutane on the other hand is a much more reactive compound due to the presence of a tertiary hydrogen Butane is primarily used as a fuel gas within liquefied petroleum gas Like ethane and propane the main chemical use of butane is as feedstock for steam cracking units for olefin production Dehydrogenation of nbutane to butenes and to butadiene is an important route for the produc tion of synthetic rubber nButane is also a starting material for acetic acid and maleic anhydride production Due to its higher reactivity isobutane is an alkylating agent of light olefin derivatives for the pro duction of alkylates Alkylates are a mixture of branched hydrocarbon derivatives in the gasoline range having highoctane ratings Chapter 3 Dehydrogenation of isobutane produces isobutene which is a reactant for the synthesis of methyl tertiary butyl ether This compound is currently in high demand for preparing unleaded gasoline due to its high octane rating and clean burning prop erties Octane ratings of hydrocarbon derivatives are noted later in this chapter The chemistry of nbutane is more varied than that of propane partly because nbutane has four secondary hydrogen atoms available for substitution and three carboncarbon bonds that can be cracked at high temperatures viz Like propane the noncatalytic oxidation of butane yields a variety of products including organic acids alcohols aldehydes ketones and olefin derivatives Although the noncatalytic oxidation of butane produces mainly aldehyde derivatives and alcohol derivatives the catalyzed oxidation yields predominantly acid derivatives 653 chemicals from Butane 6531 Oxidation The oxidation of nbutane represents a good example illustrating the effect of a catalyst on the selec tivity for a certain product The non catalytic oxidation of nbutane is nonselective and produces a mixture of oxygenated compounds including formaldehyde acetic acid acetone and alcohols nButane isobutane 251 Chemicals from Paraffin Hydrocarbons Typical weight yields when nbutane is oxidized in the vapor phase at a temperature range of 360C450C 680F840F and approximately 100 psi are formaldehyde 33 acetaldehyde 31 methanol 20 acetone 4 and mixed solvents 12 On the other hand the catalytic oxidation of nbutane either using cobalt or manganese acetate produces acetic acid at 7580 yield Byproducts of commercial value are obtained in variable amounts In the Celanese process the oxidation reaction is performed at a temperature range of 150C225C 300F435F and a pressure of approximately 800 psi CH CH CH CH 3O 2CH CO H H O 3 2 2 3 2 3 2 2 The main byproducts are formic acid ethanol methanol acetaldehyde acetone and methyl ethyl ketone MEK When manganese acetate is used as a catalyst more formic acid 25 is obtained at the expense of acetic acid Catalytic oxidation of nbutane at 490 915F over a cerium chloride CoMo oxide catalyst produces maleic anhydride Other catalyst systems such as ironvanadium pentoxidephosphorous pentoxide over silica alu mina are used for the oxidation In the Monsanto process nbutane and air are fed to a multitube fixed bed reactor which is cooled with molten salt The catalyst used is a proprietary modified vana dium oxide The exit gas stream is cooled and crude maleic anhydride is absorbed then recovered from the solvent in the stripper Another process for the partial oxidation of nbutane to maleic anhydride the DuPont process uses a circulating fluidized bed reactor Solids flux in the riser reactor is high and the superficial gas velocities are also high which encounters short residence times usually in seconds The developed catalyst for this process is based on vanadiumphosphorous oxides that provide the oxygen needed for oxidation The selective oxidation of nbutane to maleic anhydride involves a redox mechanism where the removal of eight hydrogen atoms as water and the insertion of three oxygen atoms into the butane molecule occur The reaction temperature is approximately 500C 930F Subsequent hydrogenation of maleic anhydride produces tetrahydrofuran Oxidation of nbutane to maleic anhydride is becoming a major source for this important chemi cal Maleic anhydride could also be produced by the catalytic oxidation of nbutene isomers and benzene The principal use of maleic anhydride is in the synthesis of unsaturated polyester resins These resins are used to fabricate glass fiberreinforced materials Other uses include fumaric acid alkyd resins and pesticides Maleic acid esters are important plasticizers and lubricants Maleic anhydride could also be a precursor for 14butanediol Thus 2C H CO O HOCH CH CH CH OH 2 2 2 2 2 2 2 Maleic anhydride 252 Handbook of Petrochemical Processes 6532 Production of Aromatics Liquefied petroleum gas a mixture of propane and butane isomers is catalytically reacted to pro duce an aromaticrich product The first step is assumed to be the dehydrogenation of propane and butane to the corresponding olefin derivatives followed by oligomerization to C6 C7 and C8 olefin derivatives These compounds are then dehydrocyclized to benzenetoluenexylene aromatic derivatives The following reaction sequence illustrates the formation of benzene from 2propane 2CH CH CH CH CH CH CH CH CH 2H 3 2 3 3 2 2 2 2 2 Although olefin derivatives are intermediates in this reaction the final product contains a very low olefin concentration The overall reaction is endothermic due to the predominance of dehydro genation and cracking Methane and ethane are byproducts from the cracking reaction The process consists of a reactor section continuous catalyst regeneration unit and product recov ery section Stacked radialflow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the continuous catalyst regeneration unit The reactor feed consists solely of liquefied petroleum gas plus the recycle of unconverted feed components no hydrogen is recycled The liquid product contains about 92 ww benzene toluene and xylenes with a balance of C9 aromatic derivatives and a low nonaromatic content Therefore the product could be used directly for the recov ery of benzene by fractional distillation without the extraction step needed in catalytic reforming 6533 Isomerization Because of the increasing demand for isobutylene for the production of oxygenates as gasoline addi tives a substantial amount of nbutane is isomerized to isobutane which is further dehydrogenated to isobutene The Butamer process has a fixed bed reactor containing a highly selective catalyst that promotes the conversion of nbutane to isobutane equilibrium mixture Isobutane is then separated in a deisobutanizer tower The nbutane is recycled with makeup hydrogen The isomerization reac tion occurs at a relatively low temperature CH CH CH CH CH CHCH 3 2 2 3 3 2 3 Isobutane 654 chemicals from isoButane Isobutane is mainly used as an alkylating agent to produce different compounds alkylates with a highoctane number for blending with other constituents to manufacture gasoline pool Isobutane is in high demand as an isobutene precursor for producing oxygenates such as methyl and ethyl ter tiary butyl ethers Accordingly greater amounts of isobutane are produced from nbutane through isomerization followed by dehydrogenation to isobutene The Catofin process is currently used to dehydrogenate isobutane to isobutene Alternatively isobutane could be thermally cracked to yield predominantly isobutene plus propane Other byproducts are fuel gas and C5 liquid The steam cracking process is made of three sections i a cracking furnace ii a vapor recovery section and iii a product fractionation section 66 LIQUID PETROLEUM FRACTIONS AND RESIDUES Liquid petroleum fractions and residua are not typically composed of hydrocarbon derivatives but are more likely composed of hydrocarbonaceous derivatives in which a high proportion of the 253 Chemicals from Paraffin Hydrocarbons molecular constituents may contain derivatives of sulfur nitrogen oxygen and metals Nevertheless it is opportune at this time in the text to present a description of these various fractions and the means by which they can be used as feedstocks to produce precursors that are suitable for the manu facture of petrochemical products In the modern refinery the typical product split between fuels and chemicals for traditional medium conversion fuel refineries has been about 95 fuels to 5 chemicals However the modern refinery is exhibiting a trend that is to change the refining complex product slate and crude oil refin ing is shifting from an emphasis on transportation fuels to higher margin chemical products With this focus each component of the petrochemical complex is evaluated for its potential to contribute to increased production of the desired chemical product slate Meanwhile environmental regu lations continue to become more onerous affecting suitability of technologies and configuration choices As a result the technologies and the process configurations chosen for a modern refinery chemical complex must evolve to meet these emerging challenges Since crude oil fraction particu larly the higherboiling fractions can be a significant portion of the refinery feedstock conversion of these fractions has become an important factor in maximizing chemical production and meet ing evolving environmental standards Conversion processes convert relatively lowvalue fractions such as gas oil fuel oil and resid to highervalue products Liquid petroleum fractions are light naphtha heavy naphtha kerosene and gas oil which are also sources of starting chemicals for petrochemical products Table 67 The bottom product from distillation units is the residue These mixtures are intermediates through which other reactive intermediates are obtained Heavy naphtha is a source of aromatic derivatives via catalytic reform ing and of olefin derivatives from steam cracking units Gas oils and residues are sources of olefin derivatives through cracking and pyrolysis processes Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 High molecular weight nparaffin derivatives are obtained from different petroleum fractions through physical separation processes Those in the range of C8C14 are usually recovered from the kerosene fraction Vaporphase adsorption using a molecular sieve is used to achieve the separation The nparaffin derivatives are then desorbed by the action of ammonia Continuous operation is possible by using two adsorption sieve columns one bed is onstream while the other bed is being desorbed nParaffin derivatives could also be separated by forming an adduct with urea For a paraffinic hydrocarbon to form an adduct under ambient temperature and atmospheric pressure the compound must contain a long unbranched chain of at least six carbon atoms Ease of adduct formation and adduct stability increases with increase of chain length As with shorterchain nparaffin derivatives the longerchain compounds are not highly reac tive However they may be oxidized chlorinated dehydrogenated sulfonated and fermented under special conditions The C5C17 paraffin derivatives are used to produce olefin derivatives or mono chlorinated paraffin derivatives for the production of detergents TABLE 67 Crude Oil Fractions as Sources of Petrochemicals Petroleum Fraction Source Intermediate Feedstock Naphtha Distillation thermal and catalytic cracking Ethylene propylene butane butadiene benzene toluene xylenes Kerosene Distillation thermal and catalytic cracking Linear nC10C14 alkanes Gas oil Distillation thermal and catalytic cracking Ethylene propylene Butylenes butadiene Wax Dewaxing C6C20 alkanes 254 Handbook of Petrochemical Processes 661 naPhtha Naphtha is a generic term normally used in the petroleum refining industry for the overhead liquid fraction obtained from atmospheric distillation units Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 The approximate boiling range of light straight run naphtha LSR is 35C90C while it is about 80C200C for heavy straightrun naphtha Naphtha is also obtained from other refinery processing units such as catalytic cracking hydro cracking and coking units The composition of naphtha which varies appreciably depends mainly on the crude type and whether it is obtained from atmospheric distillation or other processing units In terms of alternate feedstocks Chapter 3 coal can be converted into naphtha via either direct or indirect liquefaction Speight 2013 Subbituminous coal geologically young and brown coal lignite are more suitable for direct coal liquefaction than bituminous coal A wellknown pro cess is the Bergius process in which coal is first ground into fine particles and then mixed with a highboiling aromatic solvent recovered later at about 450C to form a slurry that is rich in aromatic constituents Through a lowseverity catalytic hydrogenation process the slurry is refined into liquid products including naphtha In contrast to FischerTropsch naphtha with no aromatic constituents the naphtha produced by this route is rich in aromatic constituents Coal can also be converted into naphtha via FischerTropsch processes indirect liquefaction In the process coal is first converted into syngas through gasification and the synthesis gas is then converted into FischerTropsch liquids that are similar to those from natural gastoliquid pro cesses As with FischerTropsch naphtha derived from methane steam cracking of FischerTropsch naphtha derived from coal can lead to a high yield of lowboiling olefin derivatives In contrast to natural gastoliquid processes FischerTropsch naphtha production from coal requires extensive gas cleanup after coal gasification eg removal of sulfur and other impurities such as metals with the use of solvents and absorbents Similar to methane and coal biomass can also be converted into FischerTropsch naphtha through FischerTropsch processes As with FischerTropsch naphtha derived from methane and coal the FischerTropsch naphtha derived from biomass has a high paraffin content and leads to high yields of lowerboiling olefin derivatives if it is used in steam cracking However FischerTropsch naphtha production from raw biomass must deal with the high water content of the biomass Plastic waste especially polyolefin derivatives eg the polypropylene used in plastic bags can be converted into naphtha and other hydrocarbon derivatives eg mostly highboiling oils through a series of liquefaction pyrolysis and separation processes which involve the use of hydrogen steam and catalysts The naphtha produced is similar to naphtha derived from crude oil and if used in steam cracking can lead to a similar yield of light olefin derivatives Currently the domi nant methods to dispose plastic waste are landfills incineration or making secondary plastics The utilization of plastic waste for the production of naphtha and petrochemicals is a potential method for plastic waste disposal Stoddard solvent is a chemical mixture containing hydrocarbon derivatives that range from C7C12 with the majority of hydrocarbon derivatives in the C9C11 range and therefore relates to a mediumtohighboiling naphtha The hydrocarbon derivatives composing Stoddard solvent are 3050 vv alkane derivatives 3040 vv cycloalkane derivatives and l020 vv aromatic derivatives Stoddard solvent is considered to be a form of naphtha but not all forms of naphtha are considered to be Stoddard solvent Stoddard solvent is produced from straightrun distillate of paraffinic or mixed base crude oil and must meet the specifications of the American Society for Testing and Materials designation for Type I mineral spirits Stoddard solvent ASTM D235 2018 6611 Physical Properties Naphtha is often divided into two main types aliphatic and aromatic The two types differ in two ways first in the kind of hydrocarbon derivatives making up the solvent and second in the methods used for their manufacture Aliphatic solvents are composed of paraffinic hydrocarbon derivatives 255 Chemicals from Paraffin Hydrocarbons and cycloparaffin derivatives naphthene derivatives and may be obtained directly from crude petroleum by distillation The second type of naphtha contains aromatic derivatives usually alkyl substituted benzene and is very rarely if at all obtained from petroleum as straightrun materials In terms of the physical propertiesin this case the boiling rangethere are three types of naphtha that are being used in basic petrochemicals production today they are differentiated here because different kinds of naphtha lead to different mixes of light olefin derivatives but which can vary in boiling range and composition depending upon the refinery processes used to produce the naphtha Light naphtha lowboiling naphtha is also called paraffinic naphtha contains hydrocarbon derivatives in the molecular range C5H12C6H14 and is a byproduct of a petroleum refinery A small amount of light naphtha also comes from natural gas condensates in oil and natural gas fields Steam cracking of light naphtha leads to a high yield of light olefin derivatives Naphtha made from FischerTropsch processes often referred to as FischerTropsch naphtha or FT naphtha is also a lowboiling naphtha that leads to a higher ethylene yield than regular lowboiling naphtha Heavy naphtha highboiling naphtha is also called nonnormal paraffinic naphtha contains hydrocarbon derivatives in the molecular in the range of C7H16C9H20 and is richer in aromatic derivatives than lowboiling naphtha Since the octane number of this naphtha is low it cannot directly be used as transportation fuel and therefore is often converted through a reforming step into highoctane naphtha that is a suitable blend stock for gasoline manufacture However it can also be used for petrochemicals production Full range naphtha is a mixture of light and heavy naphtha which contains hydrocarbon deriva tives in the molecular range of C5H12C9H20 in the range of C5H129H20 It is the most common type of naphtha used in steam cracking 6612 Chemical Properties Naphtha from atmospheric distillation is characterized by an absence of olefinic compounds Its main constituents are straight and branched chain paraffin derivatives cycloparaffin derivatives naphthene derivatives and aromatic derivatives and the ratios of these components are mainly a function of the crude origin Naphtha obtained from cracking units generally contain variable amounts of olefin derivatives higher ratios of aromatic derivatives and branched paraffin deriva tives Due to presence of unsaturated compounds they are less stable than straightrun naphthas On the other hand the absence of olefin derivatives increases the stability of naphthas produced by hydrocracking units In refining operations however it is customary to blend one type of naphtha with another to obtain a required product or feedstock Selecting the naphtha type can be an important processing procedure For example a paraffinic base naphtha is a better feedstock for steam cracking units because paraffin derivatives are cracked at relatively lower temperatures than cycloparaffin derivatives Alternately a naphtha rich in cyclo paraffin derivatives would be a better feedstock to catalytic reforming units because cycloparaffin derivatives are easily dehydrogenated to aromatic compounds The main use of naphtha in the petroleum industry is in gasoline production Light naphtha is normally blended with reformed gasoline from catalytic reforming units to increase its volatility and to reduce the aromatic content of the product gasoline Heavy naphtha from atmospheric distillation units or hydrocracking units has a lowoctane rat ing and it is used as a feedstock to catalytic reforming units Catalytic reforming is a process of upgrading low octane naphtha to a highoctane reformate by enriching it with aromatic derivatives and branched paraffin derivatives The octane rating of gasoline fuels is a property related to the spontaneous ignition of unburned gases before the flame front and causes a high pressure A fuel with a lowoctane rating produces a strong knock while a fuel with a highoctane rating burns smoothly without detonation Octane rating is measured by an arbitrary scale in which isooctane 224trimethylpentane is given a value of 100 and nheptane a value of zero A fuels octane num ber equals the percentage of isooctane in a blend with nheptane 256 Handbook of Petrochemical Processes The octane number is measured using a singlecylinder engine CFR engine with a variable compression ratio The octane number of a fuel is a function of the different hydrocarbon constitu ents present In general aromatic derivatives and branched paraffin derivatives have higher octane ratings than straightchain paraffin derivatives and cycloparaffin derivatives Naphtha is also a major feedstock to steam cracking units for the production of olefin derivatives This route to olefin derivatives is especially important in places such as Europe where ethane is not readily available as a feedstock because most gas reservoirs produce nonassociated gas with a low ethane content 6613 Chemicals from Naphtha Lowboiling naphtha containing hydrocarbon derivatives in the C5C7 range is a feedstock in Europe for producing acetic acid by oxidation Similar to the catalytic oxidation of nbutane the oxidation of lowboiling naphtha is performed at approximately the same temperature and pressure ranges 170C200C 340F390F 700 psi in the presence of manganese acetate catalyst The yield of acetic acid is approximately 40 ww Lowboilingnaphtha C C hydrocarbons O CH COOH byproducts H O 5 7 2 3 2 The product mixture contains essentially oxygenated compounds such as carboxylic acid deriva tives alcohol derivatives ester derivatives aldehyde derivatives and ketone derivatives As many as 13 distillation columns are used to separate the complex mixture The number of products could be reduced by recycling most of them to extinction Naphtha is also a commonly used feedstock for the production of synthesis gas which is used to synthesize methanol and ammonia Chapter 10 Another important role for naphtha is its use as a feedstock for steam cracking units for the production of lowboiling olefin derivatives On the other hand highboiling naphtha on the other hand is a major feedstock for catalytic reforming The product reformate containing a high percentage of C6C8 aromatic hydrocarbon derivatives is used to make gasoline Reformates are also extracted to separate the aromatic derivatives as intermedi ates for petrochemicals In the ethylene production process straightrun naphtha or hydrocracked naphtha used as feed stock in commercially established ethylene production industries A cracking furnace having a separate convection section for preheating and a radiant section is used The interior of the furnace contains burners placed along the sidewalls or at the bottom of the furnace Temperature in the furnace continuously maintained between 950C and 1000C 1740F1830F by the series of burners controlling a relatively low pressure 75 psi pressure is maintained in the tubes by the naphtha feed pumps The fresh naphtha feedstock is preheated by a heat exchanger that uses the cracked products stream that comes out from the furnace The preheated naphtha is mixed with steam and passes to the convective section Its temperature is raised to 300C 570F temperature and pass to the radiation section of the furnace for further increasing to 800C 1470F This is the condition where naphtha is cracked into simple compounds Steam is added to dilute the feedstock and to prevent the coke formation at the cracking zone Hightemperature product gas is cooled by remov ing the latent heat of water in steam generators and transfer line heat exchangers operate with high thermal efficiency during cooling the product gas Products from C2 to C4 are formed during crack ing along with some quantity of benzene toluene xylene isomers ethyl benzene hydrogen and fuel oil Optimum values of residence time steam ratio as well as temperature and pressure effect the byproducts formation An oil quenching mechanism is used to cool the furnace effluent gas and the recovered heat is used to produce lowpressure steam in the plant utility Gas oil and fuel oil are obtained when the gas is passed to the primary fractionators The volatile components from the primary fractionators are cooled where the high molecu lar weight hydrocarbon derivatives above C3 are liquefied and separated through separators 257 Chemicals from Paraffin Hydrocarbons The cracked products are passed through coolers and compressors at 30C 86F and 450 psi where separation of C3 C4 C5 and C6 components takes place by partial fractionation and liquefaction This can be done in four stages i cooling the whole mass of gas to 30C 86F under 525 psi to liquefy C4 and heavier constituents ii the uncondensed gas is subjected to severe conditions ie up to 30C 86F and 300 psi whereby propane condenses leaving ethane and ethylene in gaseous form iii dry gas constituting methane and hydrogen is separated from ethaneethylene mixture this mixture is used as a refrigerant Acidic constituents such as carbon monoxide carbon dioxide hydrogen sulfide and sulfur dioxide are removed in acid gas removing unit After the treatment the outlet gas is predominantly a mixture of methane hydrogen ethylene ethane and slight amount of acetylene 1 Hydrogen is separated initially then the gas is liquefied Hydrogen gas is puri fied and part of it is sent to hydrogenation units to convert acetylene and propadiene to ethylene and propane respectively Tail gas obtained from demethanizer is abundant in methane and used in fuel system The gases are sent to acid gas removal unit demethanizer for methane removal and hydrogen purification unit Tail gas is removed and then traces of acetylene are converted into ethylene by hydrogenation Then it is sent to ethylene splitter for separation of ethylene The ethane and ethylene are liquefied and fractionated The heavy bottoms of first stage unit are processed for C3 and heavy ends 662 kerosene Kerosene a distillate fraction higherboiling than naphtha is normally a product from distilling crude oils under atmospheric pressures Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 It may also be obtained as a product from thermal and catalytic cracking or hydrocracking units Kerosene from cracking units is usually less stable than kero sene produced from atmospheric distillation and hydrocracking units due to presence of variable amounts of olefinic constituents 6621 Physical Properties Kerosene kerosine also called paraffin or paraffin oil is usually a clear colorless liquid but often a pale yellow liquid which does not stop flowing except at very low temperature normally below 30C However kerosene containing high olefin and nitrogen contents may develop some color pale yellow after being produced It is obtained from petroleum and used for burning in lamps and domestic heaters or furnaces as a fuel or fuel component for jet engines and as a solvent for greases and insecticides Kerosene is intermediate in volatility between naphtha gas oil It is a medium oil distilling between 150C and 300C 300F570F Kerosene has a flash point about 25C 77F and is suitable for use as an illuminant when burned in a wide lamp The term kerosene is also too often incorrectly applied to various fuel oils but a fuel oil is actually any liquid or liquid petroleum prod uct that produces heat when burned in a suitable container or that produces power when burned in an engine 6622 Chemical Properties Chemically kerosene is a mixture of hydrocarbon derivatives the chemical composition depends on its source but it usually consists of about ten different hydrocarbon derivatives each contain ing10 to 16 carbon atoms per molecule the constituents include ndodecane nC12H26 alkyl ben zenes and naphthalene and its derivatives Kerosene is less volatile than gasoline it boils between 140C 285F and 320C 610F Kerosene because of its use as a burning oil must be free of aromatic and unsaturated hydro carbons as well as free of the more obnoxious sulfur compounds The desirable constituents of kerosene are saturated hydrocarbons and it is for this reason that kerosene is manufactured as a straightrun fraction not by a cracking process 258 Handbook of Petrochemical Processes Although the kerosene constituents are predominantly saturated materials there is evidence for the presence of substituted tetrahydronaphthalene Dicycloparaffin derivatives also occur in substantial amounts in kerosene Other hydrocarbons with both aromatic and cycloparaffin rings in the same molecule such as substituted indan also occur in kerosene The predominant struc ture of the dinuclear aromatics appears to be that in which the aromatic rings are condensed such as naphthalene whereas the isolated tworing compounds such as biphenyl are only present in traces if at all The main constituents of kerosene obtained from atmospheric and hydrocracking units are par affin derivatives cycloparaffin derivatives and aromatic derivatives Kerosines with highnormal paraffin content are suitable feedstocks for extracting C C14 nparaffin derivatives which are used for producing biodegradable detergents Chapter 6 Currently kerosene is mainly used to produce jet fuels after it is treated to adjust its burning quality and freezing point Before the widespread use of electricity kerosene was extensively used to fuel lamps and is still used for this purpose in remote areas It is also used as a fuel for heating purposes 6623 Chemicals from Kerosene Kerosene has been an important household fuel since the mid19th century In developed countries its use has greatly declined because of electrification However in developing countries kerosenes use for cooking and lighting remains widespread This review focuses on household kerosene uses mainly in developing countries their associated emissions and their hazards Kerosene is often advocated as a cleaner alternative to solid fuels biomass and coal for cooking and kerosene lamps are frequently used when electricity is unavailable Although present in varying quantities depending on fuel source and quality naphthalene ben zene nhexane toluene and the xylene isomers are among several chemicals present in kerosene However in the present context chemicals can be obtained from kerosene in a manner similar to the production of chemicals from naphthaby means of the steam cracking process 663 Gas oil Gas oil is a higherboiling petroleum fraction than kerosene Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 It can be obtained from the atmospheric distillation of crude oils atmospheric gas oil AGO from vacuum distillation of topped crudes vacuum gas oil VGO or from cracking and hydrocracking units The conventional process for olefin is steam cracking of C2C4 lowboiling paraffin derivatives from natural gas or from refinery gas streams However the increasing demand for gaseous fuel and the rising price of natural gas have limited the supply of light hydrocarbon derivatives As an answer to this increasing demand fluid catalytic cracking FCC is traditionally the dominant refinery conversion process for producing highoctane gasoline Driven by an increased demand for light olefin derivatives worldwide fluid catalytic cracking is also an option to yield petrochemical feedstocks from heavy oils through the innovation of hardware operating parameters and catalyst formulation In this respect a number of fluid catalytic cracking technologies have been developed including i deep catalytic cracking DCC ii the catalytic pyrolysis process CPP iii ultimate catalytic cracking UCC and iv highseverity fluid catalytic cracking HSFCC Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 6631 Physical Properties Atmospheric gas oil has a relatively lower density and sulfur content than vacuum gas oil pro duced from the same crude The aromatic content of gas oils varies appreciably depending mainly on the crude type and the process to which it has been subjected For example the aro matic content is approximately 10 for light gas oil and may reach up to 50 for vacuum and cracked gas oil 259 Chemicals from Paraffin Hydrocarbons 6632 Chemical Properties Atmospheric gasoil is a distillation fraction derived from an atmospheric distillation unit and it is primarily made up of molecules with 1420 carbon atoms The atmospheric gas oil distillation has a boiling range between 215C and 343C 420F650F The primary use of atmospheric gas oil is as a blendstock to produce diesel fuel or heating oil However it must typically go through a distillate hydrotreating unit first to remove sulfur The higherboiling fraction of the gas oil can also be fed into a catalytic cracking unit when a refinery is trying to maximize the yield of naphtha over kerosene as well as lowboiling products for petro chemical manufacture 6633 Chemicals from Gas Oil The primary uses for gas oil are the production of fuels A secondary use is as a feedstock for steam cracking to produce petrochemicals ethylene propylene and the production of aromatic petro chemical products benzene toluene and xylene isomers Gas oil is used as a chemical feedstock for steam cracking although generally less preferred than naphtha and natural gas liquids includ ing liquefied petroleum gases The gas oil output of a refinery depends on the composition of crude oil feedstock which in turn is dependent upon the crude oil regional source In addition naphthenic crude oils tend to produce relatively greater quantities of naphtha than the paraffinic crudes of the same specific gravity which produce higher relative amounts of gas oils Many compound classes have been identified by GC GCTOFMS such as tri tetra and pentacyclic terpane derivatives sterane derivatives and hopane derivatives Several polycyclic aromatic hydrocarbons PAHs such as fluorene phenanthrene pyrene and benzoghiperylene sulfur compounds such as alkyl benzothiophene derivatives alkyl dibenzothiophene derivatives and alkyl benzonaphthothiophene derivatives and alkylphenol derivatives Avila et al 2012 The separation of individual chemicals or even chemical streams from such a mixture is an indomi table task and as a result gas oil like other complex petroleum products best serves as a cracking stock to produce the starting materials for petrochemical production A major use of gas oil is as a fuel for diesel engines Another important use is as a feedstock to cracking and hydrocracking units Gases produced from these units are suitable sources for light olefin derivatives and liquefied petroleum gas which may be used as a fuel as a feedstock to steam cracking units for olefin production or as a feedstock for a Cyclar unit which can be used for the production of aromatic derivatives from liquefied petroleum gas In the UOPBP process benzene toluene and xylenes are produced by dearomatization of propane and butane The process consists of reaction system continuous regeneration of catalyst and product recovery The catalyst is a zeolitetype catalyst with a nonnoble metal promoter Gosling et al 1999 The Cyclar process is used to convert liquefied petroleum gas directly into a liquid aromatics product in a single operation The process is divided into three major sections i the reactor sec tion includes a radialflow reactor stack combined feed exchanger and heaters ii the catalyst regenerator section includes a regenerator stack and catalyst transfer system and iii the prod uct recovery section which includes product separators compressors stripper and gas recovery equipment Fresh feedstock and recycle are combined and heat exchanged against reactor effluent after which the combined feedstock is then raised to reaction temperature in the charge heater and sent to the reactor section where four adiabatic radialflow reactors are arranged in one or more vertical stacks The catalyst flows by gravity down the stack while the charge flows radi ally across the annular catalyst beds Between each reactor the charge is reheated to reaction temperature in an interreactor heater The effluent from the last reactor is split into vapor and liquid products in a separator The liquid is sent to a stripper where lowboiling saturates are removed from the C6 aromatic product The vapor from the separator is compressed and sent to a gas recovery section typically a cryogenic unit for separation into a 95 pure hydrogen product stream a fuel gas stream of light saturates and a recycle stream of unconverted liquefied petro leum gas 260 Handbook of Petrochemical Processes As expected under the process parameters coke is deposited on the catalyst and to combat this deactivation effect the partially deactivated catalyst is continually withdrawn from the bottom of the reactor stack and transferred to the catalyst regenerator The catalyst flows down through the regenerator where the accumulated carbon is burned off and the regenerated catalyst is lifted with hydrogen to the top of the reactor stack The principal operating variables for the Cyclar process are temperature space velocity pressure and feedstock composition The temperature must be high enough to ensure nearly complete conversion of reaction intermediates in order to produce a liquid product that is essentially free of nonaromatic impurities but low enough to minimize nonselective thermal reactions Space velocity is optimized against conversion within this temperature range to obtain high product yields with minimum operating costs Reaction pressure has a major impact on process performance The RZPlatforming process is a fixed bed system that is well suited for use in aromatics pro duction facilities particularly for those producers who require large amounts of benzene The pro cess uses the RZ100 catalyst to convert feedstock components C6 and C7 paraffins into aromatic derivatives The process is primarily used for situations where higher yields of benzene and toluene are desired The ability of the process to handle lowboiling paraffin feedstocks and its flexibility in processing straightrun naphtha fractions provide many options for improving aromatics production and supplying needed hydrogen either in new units or in existing aromatics facilities 664 fuel oil Fuel oil is classified in several ways but generally may be divided into two main types distillate fuel oil and residual fuel oil Distillate fuel oil is vaporized and condensed during a distillation process and thus have a definite boiling range and do not contain highboiling constituents A fuel oil that contains any amount of the residue from crude distillation of thermal cracking is a residual fuel oil The terms distillate fuel oil and residual fuel oil are losing their significance since fuel oil is now made for specific uses and may be either distillates or residuals or mixtures of the two The terms domestic fuel oil diesel fuel oil and heavy fuel oil are more indicative of the uses of fuel oils Heavy fuel oil comprises all residual fuel oils including those obtained by blending Heavy fuel oil constituents range from distillable constituents to residual nondistillable constituents that must be heated to 260C 500F or more before they can be used The kinematic viscosity is above 10 centistokes at 80C 176F The flash point is always above 50C 122F and the density is always higher than 0900 In general heavy fuel oil usually contains cracked residua reduced crude or cracking coil heavy product which is mixed cut back to a specified viscosity with cracked gas oils and fractionator bottoms For some industrial purposes in which flames or flue gases contact the product ceramics glass heat treating and open hearth furnaces fuel oils must be blended to con tain minimum sulfur contents and hence lowsulfur residues are preferable for these fuels Example of fuel oil types are No 1 fuel oil is a petroleum distillate that is one of the most widely used of the fuel oil types It is used in atomizing burners that spray fuel into a combustion chamber where the tiny droplets bum while in suspension It is also used as a carrier for pesticides a weed killer a mold release agent in the ceramic and pottery industry and in the cleaning industry It is found in asphalt coatings enamels paints thinners and varnishes No 1 fuel oil is a light petroleum distillate straightrun kerosene consisting primarily of hydrocarbons in the range C9C16 Fuel oil l is very similar in composition to diesel fuel the primary difference is in the additives No 2 fuel oil is a petroleum distillate that may be referred to as domestic or industrial The domestic fuel oil is usually lowerboiling and a straightrun product It is used primarily for home heating Industrial distillate is a cracked product or a blend of both It is used in smelting furnaces ceramic kilns and packaged boilers No 2 fuel oil is characterized by hydrocarbon chain lengths in the C11C20 range The composition consists of aliphatic hydrocarbon derivatives straight chain alkanes and cycloalkanes 64 12 unsaturated hydrocarbon derivatives olefin derivatives 261 Chemicals from Paraffin Hydrocarbons 12 and aromatic hydrocarbon derivatives including alkyl benzenes and 2ring 3ring aro matic derivatives 35 but contains only low amounts 5 of the polycyclic aromatic hydrocar bon derivatives No 6 fuel oil also called Bunker C oil or residual fuel oil is the residuum from crude oil after naphthagasoline no 1 fuel oil and no 2 fuel oil have been removed No 6 fuel oil can be blended directly to heavy fuel oil or made into asphalt Residual fuel oil is more complex in composition and impurities than distillate fuels Limited data are available on the composition of no 6 fuel oil Polycyclic aromatic hydrocarbon derivatives including the alkylated derivatives and metal containing constituents are components of no 6 fuel oil Since the boiling ranges sulfur contents and other properties of even the same fraction vary from crude oil to crude oil and with the way the crude oil is processed it is difficult to specify which fractions are blended to produce specific fuel oils In general however furnace fuel oil is a blend of straightrun gas oil and cracked gas oil to produce a product boiling in the 175C345C 350F50F range Residual fuel oil is generally known as the bottom product from atmospheric distillation units Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Fuel oils produced from cracking units are unstable When used as fuels they produce smoke and deposits that may block the burner orifices The constituents of residual fuels are more complex than those of gas oils A major part of the polynuclear aromatic compounds asphaltenes and heavy metals found in crude oils is concentrated in the residue The main use of residual fuel oil is for power generation It is burned in directfired furnaces and as a process fuel in many petroleum and chemical companies Due to the low market value of fuel oil it is used as a feedstock to catalytic and thermal cracking units 6641 Physical Properties The physical properties of fuel oil are dependent upon the grade and method of production In gen eral terms fuel oil is any liquid fuel that is burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power The term fuel oil is also used in a stricter sense to refer only to the highestboiling commercial fuel that can be obtained from crude oil 6642 Chemical Properties As with the physical properties the chemical properties of fuel oil are dependent upon the grade and method of production Typically fuels oil grades consist of higher molecular weight hydrocarbon derivatives particularly alkane derivative cycloalkane derivatives and aromatic derivatives The chain length varies with the type of fuel oil For example More specifically all fuel oils consist of complex mixtures of aliphatic and aromatic hydrocar bons The aliphatic alkanes paraffins and cycloalkanes naphthenes are hydrogen saturated and compose approximately 8090 of the fuel oils Aromatics eg benzene and olefins eg sty rene and indene compose 1020 and l respectively of the fuel oils Fuel oil no 1 straightrun kerosene is a light distillate which consists primarily of hydrocarbons in the C9C16 range fuel oil no 2 is a heavier usually blended distillate with hydrocarbons in the C11C20 range Straightrun distillates may also be used to produce fuel oil no 1 and diesel fuel oil no 1 Diesel fuel no 1 and no 2 are similar in chemical composition to fuel oil no 1 and fuel oil no 2 respectively with the exception of the additives Name Type Chain Lengtha No 1 fuel oil Distillate 916 No 2 fuel oil Distillate 1020 No 6 fuel oil Residual 2070 a For illustrative purposes only 262 Handbook of Petrochemical Processes Diesel fuels predominantly contain a mixture of C10C19 hydrocarbons which include approximately 64 aliphatic hydrocarbons 12 olefinic hydrocarbons and 35 aromatic hydrocarbons Jet fuels are based primarily on straightrun kerosene as well as additives All of the above fuel oils contain less than 5 polycyclic aromatic hydrocarbons Fuel no 4 marine die sel fuel is less volatile than diesel fuel no 2 and may contain up to 15 residual process streams in addition to more than 5 polycyclic aromatic hydrocarbons Residual fuel oils are generally more complex in composition and impurities than distillate fuel oils therefore a specific composition cannot be determined Sulfur content in residual fuel oils has been reported to be from 018 to 436 by weight 6643 Chemicals from Fuel Oil Many compound classes have been identified in fuel oils but the separation of individual chemi cals or even chemical streams from such a mixture is an indomitable task and as a result gas oil like other complex petroleum products best serves as a cracking stock to produce the starting materials for petrochemical production Residues containing high levels of heavy metals are not suitable for catalytic cracking units These feedstocks may be subjected to a demetallization process to reduce their metal contents For example the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane which separates the residue into oil with a low metal and asphaltene content and asphalt with high metal content Demetallized oils could be processed by direct hydrocatalysis Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Another approach used to reduce the harmful effects of heavy metals in petroleum residues is metal passivation In this process an oilsoluble treating agent containing antimony is used that deposits on the catalyst surface in competition with contaminant metals thus reducing the catalytic activity of these metals in promoting coke and gas formation Metal passivation is especially important in fluid catalytic cracking processes Additives that improve fluid catalytic cracking processes were found to increase catalyst life and improve the yield and quality of products Residual fuel oils Chapter 2 with high heavy metal content can serve as feedstocks for ther mal cracking units such as delayed coking Lowmetal fuel oils are suitable feedstocks to catalytic cracking units Product gases from cracking units may be used as a source for light olefin deriva tives and liquefied petroleum gas for petrochemical production Residual fuel oils are also feed stocks for steam cracking units for the production of olefin derivatives 665 resids A resid residuum pl residua is the residue obtained from petroleum after nondestructive distil lation has removed all the volatile materials Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 The temperature of the distillation is usually maintained below 350C 660F since the rate of thermal decomposition of petroleum constituents is minimal below this temperature but the rate of thermal decomposition of petroleum constituents is substantial above 350C 660F Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 Resids are black viscous materials and are obtained by distillation of a crude oil under atmospheric pressure atmospheric residuum or under reduced pressure vacuum residuum They may be liquid at room temperature generally atmospheric residua or almost solid generally vacuum residua depending upon the nature of the crude oil When a residuum is obtained from a crude oil and thermal decomposition has commenced it is more usual to refer to this product as pitch Speight 2014a The differences between a parent petroleum and the residua are due to the relative amounts of various constituents present which are removed or remain by virtue of their relative volatility 263 Chemicals from Paraffin Hydrocarbons 6651 Physical Properties The chemical composition of a residuum from an asphaltic crude oil is complex Physical methods of fractionation usually indicate high proportions of asphaltenes and resins even in amounts up to 50 or higher of the residuum In addition the presence of ashforming metallic constituents including such organometallic compounds as those of vanadium and nickel is also a distinguishing feature of residua and the heavier oils Furthermore the deeper the cut into the crude oil the greater is the concentration of sulfur and metals in the residuum and the greater the deterioration in physical properties Chapter 17 666 used luBricatinG oil Used lubricating oiloften referred to as waste oil without further qualificationis any lubricating oil whether refined from crude or synthetic components which has been contaminated by physical or chemical impurities as a result of use Speight and Exall 2014 Lubricating oil loses its effec tiveness during operation due to the presence of certain types of contaminants These contaminants can be divided into i extraneous contaminants and ii products of oil deterioration Extraneous contaminants are introduced from the surrounding air and by metallic particles from the engine Contaminants from the air are dust dirt and moisturein fact air itself may be considered as a contaminant since it can cause foaming of the oil The contaminants from the engine are i metal lic particles resulting from wear of the engine ii carbonaceous particles due to incomplete fuel combustion iii metallic oxides present as corrosion products of metals iv water from leakage of the cooling system v water as a product of fuel combustion and vi fuel or fuel additives or their byproducts which might enter the crankcase of engines In terms of the products of oil deterioration many products are formed during oil deterioration Some of these important products are i sludge which is a mixture of oil water dust dirt and carbon particles that results from the incomplete combustion of the fuels Sludge may deposit on various parts of the engine or remain in colloidal dispersion in the oil ii lacquer which is a hard or gummy substance that deposits on engine parts as a result of subjecting sludge in the oil to high temperature operation and iii oilsoluble products which result from oxidation and remain in the oil and cannot be filtered out and deposit on the engine parts The quantity and distribution of engine deposits vary widely depending on the conditions at which the engine is operated At low temperatures carbonaceous deposits originate mainly from incomplete combustion products of the fuel and not from the lubricating oil At high temperature the increase in lacquer and sludge depos its may be caused by the lubricating oil 667 naPhthenic acids Naphthenic acids are a mixture of cycloparaffins with alkyl side chains ending with a carboxylic group Speight 2014d The low molecular weight naphthenic acids 812 carbons are compounds having either a cyclopentane or a cyclohexane ring with a carboxyalkyl side chain These com pounds are normally found in middle distillates such as kerosene and gas oil Naphthenic acids constitute about 50 ww of the total acidic compounds in crude oils Naphthenicbased crude oils contain a higher percentage of naphthenic acids Consequently it is more economical to isolate these acids from naphthenicbased crude oils The production of naphthenic acids from middle distillates occurs by extraction with 710 caustic solution 264 Handbook of Petrochemical Processes The sodium salts which are soluble in the lower aqueous layer are separated from the hydrocar bon layer and treated with a mineral acid to spring out the acids The free acids are then dried and distilled Using strong caustic solutions for the extraction may create separation problems because naphthenic acid salts are emulsifying agents Free naphthenic acids are corrosive and are mainly used as their salts and esters The sodium salts are emulsifying agents for preparing agricultural insecticides additives for cutting oils and emulsion breakers in the oil industry Other metal salts of naphthenic acids have many varied uses For example calcium naphthenate is a lubricating oil additive and zinc naphthenate is an antioxi dant Lead zinc and barium naphthenate derivatives are wetting agents used as dispersion agents for paints Some oilsoluble metal naphthenate derivatives such as those of zinc cobalt and lead are used as driers in oilbased paints Among the diversified uses of naphthenate derivatives is the use of aluminum naphthenate derivatives as gelling agents for gasoline flame throwers napalm Manganese naphthenate derivatives are wellknown oxidation catalysts Cresylic acid is a commercial mixture of phenolic compounds including phenol cresol deriva tives and xylenol derivatives This mixture varies widely according to its source Cresylic acid derivatives constitute part of the oxygen compounds found in crudes that are concentrated in the naphtha fraction obtained principally from naphthenic and asphalticbased crudes Phenolic com pounds which are weak acids are extracted with relatively strong aqueous caustic solutions Originally cresylic acid was obtained from caustic waste streams that resulted from treating light distillates with caustic solutions to reduce H2S and mercaptans Currently most of these streams are hydrodesulfurized and the product streams practically do not contain phenolic compounds However cresylic acid is still obtained to a lesser extent from petroleum fractions especially cracked gasolines which contain higher percentages of phenols It is also extracted from coal liquids Strong alkaline solutions are used to extract cresylic acid The aqueous layer contains in addition to sodium phenate and cresylate a small amount of sodium naphthenate derivatives and sodium mercaptide derivatives The reaction between cresols and sodium hydroxide gives sodium cresylate Mercaptans in the aqueous extract are oxidized to the disulfides which are insoluble in water and can be separated from the cresylate solution by decantation 2RSH O RSSR H O 2 2 Free cresylic acid is obtained by treating the solution with a weak acid or dilute sulfuric acid Refinery flue gases containing carbon dioxide are sometimes used to release cresylic acid Aqueous streams with low cresylic acid concentrations are separated by adsorption by passing them through one or more beds containing a high adsorbent resin The resin is regenerated with 1 sodium hydroxide solution It should be noted that the extraction of cresylic acid does not create an isolation problem with naphthenic acids which are principally present in heavier fractions Naphthenic acids which are relatively stronger acids lower pKa value are extracted with less concentrated caustic solution Cresylic acid is mainly used as degreasing agent and as a disinfectant of a stabilized emulsion in a soap solution Cresols are used as flotation agents and as wire enamel solvents Tricresyl phosphate derivatives are produced from a mixture of cresols and phosphorous oxychloride The esters are plasticizers for vinyl chloride polymers and are also used as gasoline additives for reducing carbon deposits in the combustion chamber 668 chemicals from liquid Petroleum fractions and residues In texts on the production of petrochemical products much space is typically given to the use of the gaseous hydrocarbon derivatives as feedstocks for petrochemical processes The higherboiling fraction of petroleum naphtha kerosene fuel oil gas oil and residua is not always included It is therefore appropriate at this point of the text to include such fractions as feedstocks for petrochemi cal production 265 Chemicals from Paraffin Hydrocarbons 6681 Oxidation Oxidation is a process in which a chemical change because of the addition of oxygen or the interac tion of oxygen with the chemical to remove hydrogen ie oxidative dehydrogenation Oxidation can occur in the presence or absence of a catalyst The catalytic oxidation of longchain paraffin derivatives C18C30 derivatives over manganese salts produces a mixture of fatty acids with different chain lengths Temperature and pressure ranges of 105C120C 220F250F and 220900 psi respectively are used About 60 ww yield of fatty acid derivatives up to the C14 fatty acid derivatives is obtained 2RCH CH CH CH R 5O R CH CO H RCH CO H H O 2 2 n 2 2 2 2 n 2 2 2 2 These acids are used for making soaps The main source for fatty acids for soap manufacture however is the hydrolysis of fats and oils a nonpetroleum source nParaffin derivatives can also be oxidized to alcohols by a dilute oxygen stream 34 oxygen by volume in the presence of a mineral acid The acid converts the alcohols to esters which prohibit further oxidation of the alcohols to fatty acids The obtained alcohols are also secondary These alcohols are of commercial importance for the production of nonionic detergents ethoxylate derivatives 6682 Chlorination Chlorination is a reaction that falls under the groups of reactions known as halogenation The ease of halogenation is influenced by the halogenfluorine fluorination and chlorine are more electro philic and are more aggressive halogenating agents while bromine bromination is a weaker halo genating agent than both fluorine and chlorine and iodine iodination is the least reactive halogen The facility of dehydrohalogenation follows the reverse trend iodine is most easily removed from organic compounds and organofluorine compounds are highly stable In the current context both saturated and unsaturated compounds react directly with chlorine the former usually requiring UV light to initiate homolysis of chlorine Chlorination is conducted on a largescale industrially major processes include routes to 12dichloroethane a precursor to polyvinyl chloride as well as various chlorinated ethane derivatives as solvents Chlorination of nparaffin derivatives C10C14 in the liquid phase produces a mixture of chloro paraffin derivatives Selectivity to monochlorination could be increased by limiting the reaction to a low conversion and by decreasing the chlorine to hydrocarbon ratio Substitution of secondary hydrogen predominates Thus RCH CH R Cl RCHClCH R HCl 2 2 2 2 Monochloroparaffin derivatives in this range may be dehydrochlorinated to the corresponding monoolefin derivatives and used as alkylating agents for the production of biodegradable deter gents Alternatively the Monochloroparaffin derivatives are used directly to alkylate benzene in presence of a Lewis acid catalyst to produce alkylates for the detergent production On the other hand polychlorination can be carried out on the whole range of nparaffin derivatives from C10 to C30 at a temperature range of 80C120C 176F248F using a high chlorineparaffin ratio The product has a chlorine content of approximately 70 Polychloro paraffin derivatives are used as cutting oil additives plasticizers and retardant chemicals 6683 Sulfonation Sulfonation is a chemical reaction in which the sulfonic acid functional group SO3H is introduced into a molecule Michael and Weiner 1936 For example sulfonation with sulfur trioxide and sul furic acid converts benzene into benzene sulfonic acid 266 Handbook of Petrochemical Processes Linear secondary alkane sulfonates are produced by the reaction between sulfur dioxide and C15C17 nparaffin derivatives RH SO O H O RSO H H SO 2 2 2 3 2 4 The reaction is catalyzed by ultraviolet light with a wavelength between 3300 and 3600 A The sulfonate derivatives are nearly 100 biodegradable soft and stable in hard water and have good washing properties Sodium alkanesulfonates can also be produced from the free radical addition of sodium bisulfite and alpha olefin derivatives RCH CH NaHSO RCH CH SO Na 2 3 2 2 3 The sulfonation reaction is an important reaction in chemistry and is used in many aspects of the petrochemical industry such as color developers flame retardants and pharmaceutical products 6684 Other Products Cresylic acid is mainly used as degreasing agent and as a disinfectant of a stabilized emulsion in a soap solution Cresol derivatives are used as flotation agents and as wire enamel solvents Tricresyl phosphate derivatives are produced from a mixture of cresols and phosphorous oxychloride The esters are plasticizers for vinyl chloride polymers and are also used as gasoline additives for reduc ing carbon deposits in the combustion chamber Cresylic acid is also used in resins disinfectants solvents and electrical insulation Naphthenic acid is removed from petroleum fractions not only to minimize corrosion but also to recover commercially useful products The greatest current and historical usage of naphthenic acid is in metal naphthenate derivatives Naphthenic acids are recovered from petroleum distillates by alkaline extraction and then regenerated via an acidic neutralization process and then distilled to remove impuri ties Naphthenic acids sold commercially are categorized by acid number impurity level and color and used to produce metal naphthenate derivatives and other derivatives such as esters and amides Salts of naphthenic acids are widely used as hydrophobic sources of metal ions in diverse applica tions Aluminum salts of naphthenic acids and palmitic acid hexadecanoic acid CH3CH214CO2H were combined during World War II to produce napalm REFERENCES Albright LF Crynes BL and Nowak S 1992 Novel Production Methods for Ethylene Light Hydrocarbons and Aromatic derivatives Marcel Dekker Inc New York AlMegren H and Xiao T 2016 Petrochemical Catalyst Materials Processes and Emerging Technologies IGI Global Hershey PA AlvarezGalvan MC Mota N and Ojeda M 2011 Direct Methane Conversion Routes to Chemicals and Fuels Catalysis Today 1711 1523 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Mathur AK 2010 Direct Catalytic Conversion of Biogas Methane to Formaldehyde International Journal of ChemTech Research 21 476482 Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG Editor 2011 The Biofuels Handbook Royal Society of Chemistry London UK Speight JG 2013 The Chemistry and Technology of Coal 3rd Edition CRC Press Boca Raton FL Speight JG 2014a The Chemistry and Technology of Petroleum 4th Edition CRC Press Boca Raton FL Speight JG 2014b Oil and Gas Corrosion Prevention Gulf Professional Publishing Elsevier Oxford UK Speight JG 2014c Gasification of Unconventional Feedstocks Gulf Professional Publishing Elsevier Oxford UK 268 Handbook of Petrochemical Processes Speight JG 2014d High Acid Crudes Gulf Professional Publishing Elsevier Oxford UK Speight JG and Exall DI 2014 Refining Used Lubricating Oils CRC Press Boca Raton FL Speight JG 2017 Handbook of Petroleum Refining CRC Press Boca Raton FL Treger YA Rozanov VN and Sokolova SV 2012 Producing Ethylene and Propylene from Natural Gas via the Intermediate Synthesis of Methyl Chloride and Its Sub sequent Catalytic Pyrolysis Catalysis in Industry 44 231235 Vincent RS Lindstedt RP Malika NA Reid IAB and Messenger BE 2008 The Chemistry of Ethane Dehydrogenation over a Supported Platinum Catalyst Journal of Catalysis 260 3764 Wang C Xu L and Wang Q 2003 Review of Directly Producing Light Olefins via CoHydrogenation Journal of Natural Gas Chemistry 121 1016 Yan W Luo J Kouk QY Zheng JE Zhong Z Liu Y and Borgna A 2015 Improving Oxidative Dehydrogenation of 1Butene to 13Butadiene on Al2O3 by Fe2O3 Using CO2 as a Soft Oxidant Applied Catalysis A General 50811 6167 269 7 Chemicals from Olefin Hydrocarbons 71 INTRODUCTION Olefin derivatives CnH2n such as ethylene CH2CH2 are the basic building blocks for a host of chemical products These unsaturated materials enter into polymers and rubbers and with other reagents and react to form a wide variety of useful compounds including alcohols epoxides amines and halides Olefin derivatives are present in the gaseous products of catalytic cracking processes Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 that offer promising source materials Cracking paraffin hydrocarbon derivatives and heavy oils also produces olefin derivatives For example cracking ethane propane butane and other feedstock such as gas oil naphtha and residua produces ethylene Propylene also known as propene or methyl ethylene is produced from thermal and catalytic cracking of naphtha and gas oils as well as propane and butane The most important olefin derivatives used for the production of petrochemicals are ethylene CH2CH2 propylene CH2CHCH2 the butylene isomers CH3CH2CHCH2 and CH3CHCHCH3 and isoprene CH2CCH3CHCH2 Olefin derivatives are not typical constitu ents of natural gas but do occur in refinery gas which can be complex mixtures of hydrocarbon gases Table 71 and nonhydrocarbon gases Chapter 1 Many low molecular weight olefin deriva tives and diolefin derivatives which are produced in the refinery are isolated for petrochemical use Speight 2014 The individual products are i ethylene ii propylene and iii 13butadiene CH2CHCHCH2 Butadiene can be recovered from refinery streams as butadiene as butylene derivatives or as butane derivatives the latter two on appropriate heated catalysts dehydrogenate to give 13butadiene CH CHCH CH CH CHCH CH H 2 2 3 2 2 2 CH CH CH CH CH CHCH CH 3 2 2 3 2 2 An alternative source of butadiene is ethanol which on appropriate catalytic treatment also gives the compound diolefin 2C H OH CH CHCH CH 2H O 2 5 2 2 2 Olefin derivatives present in the gaseous product streams from catalytic cracking processes offer promising source of these materials Cracking paraffin hydrocarbon derivatives and heavy oils also produces olefin derivatives For example cracking ethane propane butane and other feedstock such as gas oil naphtha and residua produces ethylene Propylene is produced from thermal and catalytic cracking of naphtha and gas oils as well as propane and butane As far as can be determined the first largescale petrochemical process was the sulfuric acid absorption of propylene CH3CHCH2 from refinery cracked gases to produce isopropyl alcohol CH32CHOH CH CH CH H O CH CHOH 3 2 2 3 2 270 Handbook of Petrochemical Processes The interest in thermal reactions of hydrocarbon derivatives has been high since the 1920s when alcohols were produced from the ethylene and propylene formed during petroleum cracking The range of products formed from petroleum pyrolysis has widened over the past six decades to include the main chemical building blocks These include ethane ethylene propane propylene butane derivatives butadiene and aromatic derivatives Additionally other commercial products from thermal reactions of petroleum include coke carbon and asphalt Ethylene manufacture is achieved using a variety of processes Table 72 of which the steam cracking process is in widespread practice throughout the world The operating facilities are similar to gas oil cracking units operating at temperatures of 840C 1550F and at low pressures 24 psi Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 Steam is added to the vaporized feed to achieve a 5050 mixture and furnace residence times are only 0205 s Ethane extracted from natural gas is the predominant feedstock for ethylene cracking units Propylene and butylene are largely derived from catalytic cracking units and from cracking a naphtha or lowboiling gas oil fraction to produce a full range of olefin products TABLE 71 Possible Constituents of Natural Gas and Refinery Process Gas Streams Gas Molecular Weight Boiling Point 1 atm C F Density at 60F 156C 1 atm gL Relative to Air 1 Methane 16043 1615 2587 06786 05547 Ethylene 28054 1037 1547 11949 09768 Ethane 30068 886 1275 12795 10460 Propylene 42081 477 539 18052 14757 Propane 44097 421 438 18917 15464 12Butadiene 54088 109 516 23451 19172 13Butadiene 54088 44 241 23491 19203 1Butene 56108 63 207 24442 19981 cis2Butene 56108 37 387 24543 20063 trans2Butene 56108 09 336 24543 20063 isobutene 56104 69 196 24442 19981 nButane 58124 05 311 25320 20698 isobutane 58124 117 109 25268 20656 TABLE 72 Example of Processes By Which Ethylene Is Produced Thermal cracking Fluidized bed cracking Catalytic pyrolysis and catalytic partial oxidation Membrane dehydrogenation of ethane Oxidative dehydrogenation of ethane by using nickel oxidebased catalyst Methane oxidative coupling technology Dehydration of ethanol Methanol conversion to ethylene Disproportionation of propylene Ethylene from coal by the FischerTropsch process Ethylene reclamation from the refinery byproduct and offgases 271 Chemicals from Olefin Hydrocarbons The majority of the propylene used in the petrochemical industry is made from propane which is obtained from natural gas stripper plants or from refinery gases Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 CH CH CH CH CH CH H 3 2 3 3 2 2 The uses of propylene include gasoline polypropylene isopropanol trimers and tetramers for detergents propylene oxide PO cumene and glycerin Two butylene derivatives 1butylene or 1butene CH3CH2CHCH2 and 2butylene or 2butene CH3CHCHCH3 are industrially significant The latter has end uses in the production of butyl rubber and polybutylene plastics On the other hand 1butylene is used in the production of 13 butadiene CH2CHCHCH2 for the synthetic rubber industry Butylene derivatives arise pri marily from refinery gases or from the cracking of other fractions of crude oil Butadiene can be recovered from refinery streams as butadiene as butylene derivatives or as butanes the latter two on appropriate heated catalysts dehydrogenate to give 13butadiene CH CHCH CH CH CHCH CH H 2 2 3 2 2 2 CH CH CH CH CH CHCH CH 3 2 2 3 3 2 An alternative source of butadiene is ethanol which on appropriate catalytic treatment also gives the compound diolefin 2C H OH CH CHCH CH 2H O 2 5 2 2 2 Olefin derivatives containing more than four carbon atoms are in little demand as petrochemicals and thus are generally used as fuel The single exception to this is 2methyl13butadiene or iso prene which has a significant use in the synthetic rubber industry It is more difficult to make than is 13butadiene Some is available in refinery streams but more is manufactured from refinery stream 2butylene by reaction with formaldehyde CH CH CHCH HCHO CH CH CH CH CH H O 3 3 2 3 2 2 72 CHEMICALS FROM ETHYLENE Ethylene ethene C2H4 the first member of the olefin series RCHCH2 where R can be hydrogen atom or an alkyl group starting with the methyl group CH3 is a colorless gas with a sweet odor It is slightly soluble in water and alcohol Ethylene is a normally gaseous olefinic compound having a boiling point of approximately 104C 155F It may be handled as a liquid at very high pressures and low temperatures Table 73 Ethylene is a valuable starting chemical because it is the source of a vast array of commercial chemicals This unique position of ethylene among other hydrocarbon intermediates is due to some favorable properties inherent in the ethylene molecule such as i simple structure with high reactiv ity ii relatively inexpensive compound iii easily produced from any hydrocarbon source through steam cracking and in high yields and iv less byproducts generated from ethylene reactions with other compounds than from other olefin derivatives Ethylene is a constituent of refinery gases especially those produced from catalytic cracking units Ethylene is made normally by cracking an ethane or naphtha feedstock in a hightemperature furnace and subsequent isolation from other components by distillation The major uses of ethylene are in the production of ethylene oxide ethylene dichloride and the polyethylene polymers Other uses include the coloring of fruit rubber products ethyl alcohol and medicine anesthetic 272 Handbook of Petrochemical Processes Ethylene manufacture via the steam cracking process is in widespread practice throughout the world The operating facilities are similar to gas oil cracking units operating at temperatures in the order of 840C 1550F and at low pressure 24 psi Ethylene is a highly active compound that reacts easily by addition to many chemical reagents For example ethylene with water forms ethyl alcohol Addition of chlorine to ethylene produces ethyl ene dichloride 12dichloroethane CH2ClCH2Cl which is cracked to vinyl chloride CH2CHCl which is an important precursor for the manufacture of plastics CH ClCH Cl CH CHCl HCl 2 2 2 Ethylene is also an active alkylating agent For example the alkylation of benzene with ethylene pro duces ethyl benzene EB C6H5C2H5 which is dehydrogenated to styrene Styrene is a monomer used in the manufacture of many commercial polymers and copolymers Ethylene can be polymerized to different grades of polyethylene derivatives HCH2CH2nH or copolymerized with other olefin deriv atives Catalytic oxidation of ethylene produces ethylene oxide which is hydrolyzed to ethylene glycol Figure 71 Ethylene glycol CH2OHCH2OH is a monomer for the production of synthetic fibers Ethylene reacts by addition to many inexpensive reagents such as water chlorine hydrogen chlo ride and oxygen to produce valuable chemicals Figure 72 It can be initiated by free radicals or FIGURE 71 Manufacture of ethylene glycol TABLE 73 Properties of Ethylene Chemical formula C2H4 Molar mass 2805 gmol Appearance Colorless gas Density 1178 kgm3 at 15C gas Melting point 1692C 2726F 1040K Boiling point 1037C 1547F 1695K Solubility in water 35 mg100 mL 17C 29 mgL Solubility in ethanol 422 mgL Solubility in diethyl ether Good 273 Chemicals from Olefin Hydrocarbons by coordination catalysts to produce polyethylene the largestvolume thermoplastic polymer It can also be copolymerized with other olefin derivatives producing polymers with improved properties For example when ethylene is polymerized with propylene a thermoplastic elastomer is obtained 721 alcohols Most ethanol is produced from sugar eg starch from maize grains or sucrose from sugarcane fermentation using the yeast species Saccharomyces cerevisiae Recent efforts have suggested that edible sugars be replaced with lignocellulosic biomass eg corn stover as the process feed stock which may reduce the cost of bioethanol and decrease emissions of greenhouse gases simultaneously The earliest method for conversion of olefin derivatives into alcohols involved their absorption in sulfuric acid to form esters followed by dilution and hydrolysis generally with the aid of steam In the case of ethyl alcohol the direct catalytic hydration of ethylene can be employed Ethylene is readily absorbed in 98100 sulfuric acid at 75C80C 165F175F and both ethyl and diethyl sulfate are formed hydrolysis takes place readily on dilution with water and heating The direct hydration of ethylene to ethyl alcohol is practiced over phosphoric acid on diatoma ceous earth or promoted tungsten oxide under 100 psi pressure and at 300C 570F CH CH H O C H OH 2 2 2 2 5 Ethylene of high purity is required in direct hydration than in the acid absorption process and the conversion per pass is low but high yields are possible by recycling Propylene and the normal butylene derivatives can also be hydrated directly FIGURE 72 Chemicals from ethylene 274 Handbook of Petrochemical Processes Ethylene produced from ethane by cracking is oxidized in the presence of a silver catalyst to ethylene oxide 2H C CH O C H O 2 2 2 2 4 The vast majority of the ethylene oxide produced is hydrolyzed at 100C to ethylene glycol C H O H O HOCH CH OH 2 4 2 2 2 Approximately 70 of the ethylene glycol produced is used as automotive antifreeze and a majority of the remainder is used in the synthesis of polyesters Of the higher olefin derivatives one of the first alcohol syntheses practiced commercially was that of isopropyl alcohol from propylene Sulfuric acid absorbs propylene more readily than it does ethylene but care must be taken to avoid polymer formation by keeping the mixture relatively cool and using acid of about 85 strength at 300400 psi pressure dilution with inert oil may also be necessary Acetone is readily made from isopropyl alcohol either by catalytic oxidation or by dehy drogenation over metal usually copper catalysts 1Butanol may be produced from syngas via methanol and subsequent alcohol homologation however the currently favored route involves the stereoselective rhodiumcatalyzed hydrofor mylation of propylene to nbutyraldehyde followed by hydrogenation to 1butanol Scheme 1A Alternatively 1butanol may be produced by microbial fermentation using organisms such as Clostridium acetobutylicum which provides mixtures of acetone 1butanol and ethanol ABE fer mentation or other species that produce 1butanol exclusively The Guerbet reaction of bioethanol which is more easily produced by fermentation and separated at higher titers provides an alternative route for 1butanol production Secondary butyl alcohol is formed on absorption of 1butylene or 2butylene by 7880 sulfu ric acid followed by dilution and hydrolysis Secondary butyl alcohol is converted into methyl ethyl ketone MEK by catalytic oxidation or dehydrogenation There are several methods for preparing higher alcohols One method in particular the so called Oxo reaction and involves the direct addition of carbon monoxide CO and a hydro gen H atom across the double bond of an olefin to form an aldehyde RCHO which in turn is reduced to the alcohol RCH2OH Hydroformylation the Oxo reaction is brought about by contacting the olefin with synthesis gas 11 carbon monoxidehydrogen at 75C200C 165F390F and 15004500 psi over a metal catalyst usually cobalt The active catalyst is held to be cobalt hydrocarbonyl HCOCO4 formed by the action of the hydrogen on dicobalt octacarbonyl CO2CO8 A wide variety of olefin derivatives enter the reaction those containing terminal unsaturated being the most active The hydroformylation is not specific the hydrogen and carbon monoxide added across each side of the double bond Thus propylene gives a mixture of 60 nbutyraldehyde and 40 isobutyraldehyde Terminal RCHCH2 and nonterminal R1CHCHR2 where R1 and R2 may be the same or different groups olefin derivatives such as 1pentene CH3CH2CH2CHCH2 and 2pentene CH3CH2CHCHCH3 give essentially the same distribution of straightchain and branchedchain C6 aldehydes indicating that rapid isomerization takes place Simple branched structures add mainly at the terminal carbon isobutylene forms 95 isovaleraldehyde and 5 trimethyl acetaldehyde also called pivaldehyde IsoValeraldehyde 275 Chemicals from Olefin Hydrocarbons Commercial application of the synthesis has been most successful in the manufacture of iso octyl alcohol from a refinery C3C4 copolymer decyl alcohol from propylene trimer and tridecyl alcohol from propylene tetramer Important outlets for the higher alcohols lie in their sulfonation to make detergents and the formation of esters with dibasic acids for use as plasticizers and synthetic lubricants The hydrolysis of ethylene chlorohydrin HOCH2CH2Cl or the cyclic ethylene oxide produces ethylene glycol HOCH2CH2OH The main use for this chemical is for antifreeze mixtures in auto mobile radiators and for cooling aviation engines considerable amounts are used as ethylene glycol dinitrate in lowfreezing dynamite Propylene glycol is also made by the hydrolysis of the respective chlorohydrin or oxide Glycerin CH2OHCHOHCH2OH can be derived from propylene by hightemperature chlori nation to produce alkyl chloride followed by hydrolysis to allyl alcohol and then conversion with aqueous chloride to glycerol chlorohydrin a product that can be easily hydrolyzed to glycerol glyc erin Glycerin has found many uses over the years important among these are as solvent emollient sweetener in cosmetics and as a precursor to nitroglycerin and other explosives The hydrogenolysis of renewable triglycerides derived from vegetable oils offers a pathway to desirable C8 alcohols At high H2 pressures Zn and Cubased heterogeneous catalysts reduce both carboxylic groups as well as CC bonds in unsaturated fatty acids and esters to give a range of higher alcohols Alcohols can also be generated from fatty acids by oxidative cleavage using Ru Os or Pd catalysts and oxidants such as ozone O3 sodium periodate NaIO4 or hydrogen peroxide H2O2 The resulting shorterchain aldehydes and acids can be readily hydrogenated to form the desired alcohols 722 alkylation Alkylation is the transfer of an alkyl group from one molecule to another The alkyl group may be transferred as an alkyl carbocation a free radical a carbanion or a carbene and any equivalent of these groups An alkyl group is a piece of a molecule with the general formula CnH2n1 where n is the integer depicting the number of carbons linked together For example a methyl group n 1 CH3 is a fragment of a methane CH4 molecule Alkylating agents utilize selective alkyla tion by adding the desired aliphatic carbon chain to the previously chosen starting molecule Alkyl groups can also be removed dealkylation Alkylating agents are often classified according to their nucleophilic or electrophilic character In the context of refining operations alkylation refers to for example the alkylation of isobutane with an olefin such as the alkylation of isobutane with propylene to produce 24dimethyl pentane which is used as a blend stock to increase the octane number of gasoline Ethylene is an active alkylating agent It can be used to alkylate aromatic compounds using FriedelCrafts type catalysts Commercially ethylene is used to alkylate benzene using a zeolite catalyst for the production of ethyl benzene a precursor for styrene Trimethyl aldehyde Isobutane propylene 24dimethyl pentane 276 Handbook of Petrochemical Processes Alkylation chemistry contributes to the efficient utilization of C4 olefin derivatives generated in the cracking operations Speight 2007 Isobutane has been added to butylene derivatives and other lowboiling olefin derivatives to give a mixture of highly branched octanes eg heptanes by a pro cess called alkylation The reaction is thermodynamically favored at low temperatures 20C and thus very powerful acid catalysts are employed Typically sulfuric acid 85100 anhydrous hydrogen fluoride or a solid sulfonic acid is employed as the catalyst in these processes The first step in the process is the formation of a carbocation by combination of an olefin with an acid proton CH C CH H CH C 3 2 2 3 3 Step 2 is the addition of the carbocation to a second molecule of olefin to form a dimer carbocation The extensive branching of the saturated hydrocarbon results in high octane In practice mixed butylenes are employed isobutylene 1butylene and 2butylene and the product is a mixture of isomeric octanes that has an octane number of 9294 With the phaseout of leaded additives in our motor gasoline pools octane improvement is a major challenge for the refining industry Alkylation is one option Hydroalkylation reactions can increase the carbon number of furans and phenols and are an appealing alternative to simple hydrodeoxygenation of the reactants In addition a combination of hydrogen transfer and acidcatalyzed alkylation reaction produced bicyclohexane derivatives from the reaction of phenol and substituted phenol derivatives over a number of solid Brønsted acid catalysts including Amberlyst15 sulfated zirconia heteropolyacids and zeo lites Importantly Hbzeolites gave high yields of polycyclic alkylation products even within liquid water whereas meso and macroporous solid acids showed little reactivity The hydroalkylation of mcresol over Pt and Pdcontaining zeolites HY and HMOR gave a distribution of products con taining two or more sixcarbon rings eg dimethyl bicyclohexane derivatives Yields for the alkyla tion products and the related intermediates including methylcyclohexanone approached 80 after the ratio of the metal to acid sites was tuned to optimize the rates of hydrogen transfer dehydration and alkylation steps Overall such alkylation reactions of substituted furan derivatives and phenol deriva tives obtained from pyrolysis of lignin can produce polycyclic hydrocarbon derivatives eg C14 that may be ring opened and used as fuels Recent and promising work shows that transalkylation reactions of 25dimethylfuran from glucose isomerization and dehydration with ethylene obtained from etha nol dehydration followed by isomerization can produce pxylene 14CH3C6H4CH3 with selectivity of 75 and 90 at acid sites within HY and Hbzeolites respectively This chemistry provides a renewable pathway from sugars to the production of building block aromatics which are critical for the production of polyesters among other polymers and have higher value than precursors to fuels 723 haloGen derivatives Halogenation is a chemical reaction that involves the addition of one or more halogens fluorine chlorine bromine or iodine to a compound The reaction pathway and the stoichiometry of the C6H6 CH2CH2 C6H5CH2CH3 C6H5CH2CH3 C6H5CHCH2 277 Chemicals from Olefin Hydrocarbons reaction depend on the structural features and functional groups of the organic substrate as well as on the specific halogen Inorganic compounds such as metals also undergo halogenation The ease of halogenation ie the reaction rate is influenced by the halogen Fluorine and chlo rine are more electrophilic and are more aggressive halogenating agents Bromine is a weaker halo genating agent than both fluorine and chlorine while iodine is the least reactive of the halogens The ease reaction rate of dehydrohalogenation follows the reverse trend iodine is most easily removed from organic compounds while and organofluorine compounds are very stable Several pathways exist for the halogenation of organic compounds including free radical halo genation electrophilic halogenation and halogen addition The structure of the substrate is one factor that determines the pathway Saturated hydrocarbons typically do not add halogens but undergo free radical halogenation involving substitution of hydrogen atoms by halogen The chem istry of the halogenation of alkanes is usually determined by the relative weakness of the available carbonhydrogenation CH bonds The preference for reaction at tertiary and secondary positions results from greater stability of the corresponding free radicals and the transition state leading to the products Generally at ordinary temperatures chlorine reacts with olefin derivatives by addition Thus ethylene is chlorinated to 12dichloroethane dichloroethane or to ethylene dichloride H C CH Cl H ClCCH Cl 2 2 2 2 2 H C CH Cl H ClCCH Cl 2 2 2 2 2 There are some minor uses for ethylene dichloride but about 90 of it is cracked to vinyl chloride the monomer of polyvinyl chloride PVC H ClCCH Cl HCl H C CHCl 2 2 2 At slightly higher temperatures olefin derivatives and chlorine react by substitution of a hydrogen atom by a chlorine atom Thus in the chlorination of propylene a rise of 50C 90F changes the product from propylene dichloride CH3CHClCH2Cl to allyl chloride CH2CHCH2Cl 724 oxyGen derivatives Oxidation is a process in which a chemical substance changes because of the addition of oxygen or the removal of hydrogen The most striking industrial olefin oxidation process involves ethylene which is air oxidized over a silver catalyst at 225C325C 435F615F to give pure ethylene oxide in yields ranging from 55 to 70 Also esters R1CO2R2 where R1 and R2 can be the same alkyl groups or dif ferent alkyl groups are formed directly by the addition of acids to olefin derivatives mercaptans by the addition of hydrogen sulfide to olefin derivatives sulfides by the addition of mercaptans to olefin derivatives and amines by the addition of ammonia and other amines to olefin derivatives represented simply as RCH CH CH CO H RCH CH CO CH 2 3 2 2 2 2 3 Acetate ester RCH CH H S RCH CH SH 2 2 2 2 Mercaptan R CH CH R SH R CH CH SR 1 2 2 1 2 2 2 Sulfide RCH CH NH RCH CH NH 2 3 2 2 2 Amine 278 Handbook of Petrochemical Processes Analogous higher olefin oxides can be prepared from propylene butadiene octene dodecene and styrene via the chlorohydrin route or by reaction with peracetic acid Acrolein is formed by air oxidation or propylene over a supported cuprous oxide catalyst or by condensing acetaldehyde and formaldehyde CH CH CH O CH CHCHO 3 2 2 CH CHO HCHO CH CHCHO H O 3 2 2 When acrolein and air are passed over a catalyst such as cobalt molybdate acrylic acid is pro duced or if acrolein is reacted with ammonia and oxygen over molybdenum oxide the product is acrylonitrile 2CH CHCHO O 2CH CHCOOH 2 2 2 2CH CHCHO O 2NH 2CH CHC N 3H O 2 2 3 2 2 Similarly propylene may be converted to acrylonitrile 2CH CH CH 2NH 3O 2CH CHC N 6H O 3 2 3 2 2 2 Acrolein and acrylonitrile are important starting materials for the synthetic materials acrylates Acrylonitrile is also used in plastics which are made by copolymerization of acrylonitrile with styrene or with a styrenebutadiene mixture Oxidation of the higher olefin derivatives by air is difficult to control but at temperatures between 350C and 500C 660F and 930F maleic acid is obtained from amylene and a vana dium pentoxide catalyst higher yields of the acid are obtained from hexene heptene and octene Ethylene can be oxidized to a variety of useful chemicals The oxidation products depend primar ily on the catalyst used and the reaction conditions although ethylene oxide is considered to be the most important oxidation product of ethylene Acetaldehyde CH3CHO and vinyl acetate CH3CO2CHCH2 are also oxidation products obtained from ethylene under special catalytic conditions Ethylene oxide is a colorless gas that liquefies when cooled below 12C 54F which is highly soluble in water and in organic solvents Ethylene oxide also called oxirane by the International Union of Pure and Applied Chemistry IUPAC is a cyclic ether and the simplest epoxide a threemembered ring consisting of one oxygen atom and two carbon atoms Ethylene oxide is a colorless and flammable gas with a faintly sweet odor Because it is a strained ring conformation ethylene oxide easily participates in several of additional reactions that result in ringopening Ethylene oxide is a precursor for many chemicals of great commercial importance including ethylene glycols ethanolamine derivatives and alcohol ethoxylate derivatives Acrolein Ethylene oxide 279 Chemicals from Olefin Hydrocarbons Ethylene oxide was first reported in 1859 by the French chemist Charles Adolph Wurtz who prepared it by treating 2chloroethanol with potassium hydroxide ClCH CH OH KOH CH CH O KCl H O 2 2 2 2 2 In the current petrochemical industry the main route to ethylene oxide is oxygen or air oxidation of ethylene over a silver catalyst 2CH CH O 2 CH CH O 2 2 2 2 2 The formation of ethylene oxide by these routes is reaction that is highly exothermic the excessive temperature increase reduces ethylene oxide yield and causes catalyst deterioration Thus a con comitant reaction is the complete oxidation of ethylene to carbon dioxide and water CH CH 3O 2CO 2H O 2 2 2 2 2 Excessive oxidation can be minimized by using modifiers such as organic chlorides It seems that silver is a unique epoxidation catalyst for ethylene All other catalysts are relatively ineffective and the reaction to ethylene is limited among lower olefin derivatives Propylene and butylene isomers do not form epoxides through this route Using oxygen as the oxidant versus air is currently favored because it is more economical In the process compressed oxygen ethylene and recycled gas are fed to a multitubular reac tor The temperature of the oxidation reaction is controlled by boiling water in the shell side of the reactor Effluent gases are cooled and passed to the scrubber where ethylene oxide is absorbed as a dilute aqueous solution Unreacted gases are recycled Epoxidation reaction occurs at approximately 200C300C 390F570F with a short residence time of 1 s A selectivity of 7075 can be reached for the oxygenbased process Selectivity is the ratio of moles of eth ylene oxide produced per mole of ethylene reacted Ethylene oxide selectivity can be improved when the reaction temperature is lowered and the conversion of ethylene is decreased higher recycle of unreacted gases Ethylene oxide is a highly active intermediate It reacts with all compounds that have a labile hydrogen such as water alcohols organic acids and amines The epoxide ring opens and a new compound with a hydroxyethyl group is produced The addition of a hydroxyethyl group increases the water solubility of the resulting compound Further reaction of ethylene oxide produces polyeth ylene oxide derivatives with increased water solubility 7241 Ethylene Glycol Ethylene glycol HOCH2CH2OH is colorless syrupy liquid that is readily soluble in water The boil ing and the freezing points of ethylene glycol are 1972C 3869F and 132C 82F respectively Ethylene glycol is one of the monomers for polyesters and the most widely used synthetic fiber polymers The main route for producing ethylene glycol also known in the gas processing industry as MEG Chapter 4 is the hydration of ethylene oxide in presence of dilute sulfuric acid CH CH HOCH CH OH 2 2 2 2 The hydrolysis reaction occurs at a temperature range of 50C100C 112F212F and the reac tion time is approximately 30 min Diethylene glycol also known in the gas processing industry as DEG and triethylene glycol also known in the gas processing industry as TEG are coproducts with ethylene the monoglycol 280 Handbook of Petrochemical Processes 2CH CH HOCH CH OCH CH OH 2 2 2 2 2 2 2CH CH HOCH CH OCH CH OCH CH OH 2 2 2 2 2 2 2 2 In the process increasing the waterethylene oxide ratio and decreasing the contact time decreases the formation of higher glycols A waterethylene oxide ratio in the order of 10 is typically used to produce a yield in the order of 90 ww yield of the monoglycol In addition the diethylene gly col and the triethylene glycol derivatives have wide commercial use in the gas processing industry Chapter 4 The reaction occurs at approximately 80C130C 176F266F using a catalyst Many cata lysts have been tried for this reaction and there is an indication that the best catalyst types are those of the tertiary amine and quaternary ammonium functionalized resins This route produces ethylene glycol of a high purity and avoids selectivity problems associated with the hydrolysis of ethylene oxide The coproduct dimethyl carbonate is a liquid soluble in organic solvents It is used as a specialty solvent a methylating agent in organic synthesis and a monomer for polycarbonate resins It may also be considered as a gasoline additive due to its high oxygen content and its high octane rating Ethylene glycol could also be obtained directly from ethylene by two methods the Oxirane acetoxylation and the Teijin oxychlorination processes In the Oxirane process ethylene is reacted in the liquid phase with acetic acid in the presence of a tellurium oxide TeO2 catalyst at approxi mately 160C 320F and 400 psi The product is a mixture of monoacetate and the diacetate of ethylene glycol after which the acetates are hydrolyzed to ethylene glycol and acetic acid The hydrolysis reaction occurs at approximately 107C130C 214F266F and 80 psi Acetic acid is then recovered for further use 2CH CH 3CH CO H TeO CH CO CH CH OH CH CO CH CH O CCH 3H O 2 2 3 2 2 3 2 2 2 3 2 2 2 2 3 2 CH CO CH CH OH CH CO CH CH O CCH 2HOCH CH OH 3CH CO H 3 2 2 2 3 2 2 2 2 3 2 2 3 2 A higher glycol yield approximately 94 than from the ethylene oxide process is anticipated However there are certain problems inherent in the Oxirane process such as corrosion caused by acetic acid and the incomplete hydrolysis of the acetates Also the separation of the glycol from unhydrolyzed monoacetate is hard to accomplish The Teijin oxychlorination on the other hand is considered a modern version of the Wurtz chlorohydrin process now obsolete for the production of ethylene oxide In this process eth ylene chlorohydrin is obtained by the catalytic reaction of ethylene with hydrochloric acid in presence of thallium chloride TlCl3 catalyst Ethylene chlorohydrin is then hydrolyzed in situ to ethylene glycol CH CH H O TlCl HOCH CH Cl TlCl HCl 2 2 2 3 2 2 HOCH CH Cl H O HOCH CH OH HCl 2 2 2 2 2 Catalyst regeneration occurs by the reaction of thallium I chloride TlCl with copperII chloride in the presence of oxygen or air The formed cuprous chloride CuCl is reoxidized by the action of oxygen in the presence of hydrogen chloride HCl A new route to ethylene glycol from ethylene oxide via the intermediate formation of ethylene carbonate has recently been developed Ethylene carbonate CH2O2CO is classified as the car bonate ester of ethylene glycol and carbonic acid H2CO3 At room temperature 25C 77F eth ylene carbonate is a transparent crystalline solid practically odorless and colorless and somewhat soluble in water In the liquid state mp 34C37C 94F99F it is a colorless odorless liquid 281 Chemicals from Olefin Hydrocarbons Ethylene carbonate is produced by the catalyzed reaction between ethylene oxide and carbon dioxide CH O CO CH O CO 2 2 2 2 2 Similarly ethylene carbonate may also be formed by the reaction of carbon monoxide ethylene oxide and oxygen Alternatively it can be obtained by the reaction of phosgene and methanol 2 CH O 2CO O 2 CH O CO 2 2 2 2 2 Ethylene carbonate can also be produced from the reaction of urea and ethylene glycol using zinc oxide ZnO as a catalyst at a temperature of 150C 300F H NCOCNH HOCH CH OH CH O CO 2NH 2 2 2 2 2 2 3 Ethylene carbonate is a reactive chemical and may be converted to dimethyl carbonate a useful solvent that also finds use as a methylating agent by means of a transesterification reaction with methyl alcohol C H CO 2CH OH CH OCO CH HOC H OH 2 4 3 3 3 2 3 2 4 Dimethyl carbonate may itself be similarly converted by transesterification to diphenyl carbonate CH OCO CH 2C H OH C H OCO C H 2CH OH 3 2 3 6 5 6 5 2 6 5 3 7242 Ethoxylates Ethoxylates are the products of ethoxylation reactions in which ethylene oxide is added to a sub strate The most widely used reaction relative to the petrochemical industry is alkoxylation which involves the addition of epoxides to substrates Typically esters R1CO2R2 are formed directly by the addition of acids to olefin derivatives mercaptans by the addition of hydrogen sulfide to olefin derivatives sulfides by the addition of mercaptans to olefin derivatives and amines by the addition of ammonia and other amines to olefin derivatives In the usual application alcohol derivatives and phenol derivatives are converted into estertype products with the general formula ROC2H4nOH where n ranges from 1 to as high as 10 Such compounds are called alcohol ethoxylates Alcohol ethoxylate derivatives are often converted to related species called ethoxy sulfate derivatives Alcohol ethoxylates and ethoxy sulfate derivatives are surfactants that are used widely in many commercial products including cosmetic products The reaction between ethylene oxide and longchain fatty alcohols or fatty acids is called eth oxylation Ethoxylation of C10 to C14 linear alcohol derivatives and linear alkylphenol derivatives produces nonionic detergents The reaction with alcohols could be represented as ROH CH CH O RO CH CH O H 2 2 2 2 n The solubility of the ethoxylate derivatives can be varied by adjusting the number of ethylene oxide units in the molecule The solubility is also a function of the chain length of the alkyl group in the alcohol or in the phenol and longerchain alkyl groups reduce water solubility In practice the number of ethylene oxide units and the chain length of the alkyl group are varied to either produce watersoluble or oilsoluble surfaceactive agents Linear alcohols used for the production of ethoxylates are produced by the oligomerization of ethylene using Ziegler catalysts or by the Oxo reaction using alpha olefin derivatives Similarly esters of fatty acids and polyethylene glycols are produced by the reaction of longchain fatty acids and ethylene oxide 282 Handbook of Petrochemical Processes 7243 Ethanolamines The ethanolamine derivatives also called olamine derivatives comprise a group of amino alcohol derivatives and contain both a primary amine NH2 function and a primary alcohol CH2OH function Ethanolamine is a colorless viscous liquid with an odor that is reminiscent to the odor of ammonia The olamine family includes ethanolamine HOCH2CH2NH2 2aminoethanol also called monoethanolamine MEA diethanolamine DEA HOCH2CH2NHCH2CH2OH and triethanolamine TEA These ethanolamine derivatives have been and continue to be used widely in the gas processing industry for the removal of acid gases from gas streams Chapter 4 Kohl and Riesenfeld 1985 Maddox et al 1985 Newman 1985 Kohl and Nielsen 1997 Kidnay and Parrish 2006 Mokhatab et al 2006 Speight 2007 2014 They are also used to manufacture detergents metalworking fluids and as gas sweetening Triethanolamine is used in detergents and cosmetics applications and as a cement additive Ethanolamine derivatives are prepared by the reaction of aqueous ammonia and ethylene oxide and the product monoethanolamine reacts with a second and third equivalent of ethylene oxide to give diethanolamine and triethanolamine CH CH O NH HOCH CH NH 2 2 3 2 2 2 H NCH CH OH CH CH O HN CH CH OH 2 2 2 2 2 2 2 2 HN CH CH OH CH CH O N CH CH OH 2 2 2 2 2 2 2 3 The reaction conditions are approximately 30C40C 86F104F and atmospheric pressure 147 psi The relative ratios of the ethanolamine derivatives produced depend principally on the ethyl ene oxideammonia ratio A low ethylene oxideammonia ratio increases monoethanolamine yield Increasing this ratio increases the yield of diethanolamine and triethanolamine derivatives 7244 13Propanediol 13Propanediol although a product related to propylene is included here because of the production of this product from an ethylene derivative namely ethylene oxide 13Propanediol is a colorless liquid that boils at 210C 410F which is soluble in water alcohol and ether and is used as an intermediate for polyester production This diol can be produced via the hydroformylation of ethylene oxide which yields 3hydroxypropionaldehyde Hydrogenation of the product produces 13propanediol CH CH O HCHO HOCH CH CHO 2 2 2 2 HOCH CH CHO H HOCH CH CH OH 2 2 2 2 2 2 The catalyst is a cobalt carbonyl that is prepared in situ from cobaltous hydroxide and nonyl pyri dine as the promotor Oxidation of the aldehyde produces 3hydroxypropionic acid HOCH CH CHO O HOCH CH CO H H O 2 2 2 2 2 2 2 13Propanediol and 3hydroxypropionic acid could also be produced from acrolein by hydrolysis of the acrolein followed by hydrogenation of the 3hydroxypropionaldehyde CH CHCHO H O HOCH CH CHO 2 2 2 2 HOCH CH CHO H HOCH CH CH OH 2 2 2 2 2 2 283 Chemicals from Olefin Hydrocarbons 7245 Acetaldehyde Acetaldehyde CH3CHO is an intermediate for many chemicals such as acetic acid nbutanol pen taerythritol and polyacetaldehyde It is a colorless liquid with a pungent odor It is a reactive com pound with no direct use except for the synthesis of other compounds For example it is oxidized to acetic acid and acetic anhydride CH CHO O CH CO H CH CO O 3 3 2 3 2 It is a reactant in the production of 2ethylhexanol for the synthesis of plasticizers and also in the production of pentaerythritol a polyhydric compound used in alkyd resins There are many ways to produce acetaldehyde Historically it was produced either by the silver catalyzed oxidation or by the chromiumactivated coppercatalyzed dehydrogenation of ethanol 2CH CH OH O 2CH CHO 2H O 3 2 2 3 2 Currently acetaldehyde is obtained from ethylene by using a homogeneous catalyst Wacker cata lyst The catalyst allows the reaction to occur at much lower temperatures typically 130C 266F than those used for the oxidation or the dehydrogenation of ethanol approximately 500C for the oxidation and 250C for the dehydrogenation Ethylene oxidation is carried out through oxidationreduction redox The overall reaction is the oxidation of ethylene by oxygen as represented by 2CH CH O 2CH CHO 2 2 2 3 The Wacker process uses an aqueous solution of palladiumII chloride copperII chloride catalyst system In the course of the reaction the ethylene is oxidized to acetaldehyde and the palladium Pd2 ions are reduced to palladium metal CH CH H O PdCl CH CHO 2HCl Pd 2 2 2 2 3 o The formed palladium Pdo is then reoxidized by the action of CuII ions which are reduced to CuI ions Pd 2CuC1 PdCl 2CuCl o 2 2 The reduced CuI ions are reoxidized to CuII ions by reaction with oxygen and HCl 4CuCl O 4HCl 4CuCl H O 2 2 2 The oxidation reaction may be carried out in a singlestage or a two stage process In the single stage ethylene oxygen and recycled gas are fed into a vertical reactor containing the catalyst solution Heat is controlled by boiling off some of the water The reaction conditions are approxi mately 130C 266F and 45 psi In the twostage process the reaction occurs under relatively higher pressure approximately 120 psi to ensure higher ethylene conversion The reaction tem perature is approximately 130C 266F The catalyst solution is then withdrawn from the reac tor to a tubeoxidizer to enhance the oxidation of the catalyst at approximately 150 psi The yield of acetaldehyde from either process is about 95 Byproducts from this reaction include acetic acid ethyl chloride chloroacetaldehyde and carbon dioxide The Wacker reaction can also be carried out for other olefin derivatives with terminal double bonds With propylene for example approximately 90 yield of acetone is obtained 1Butylene gave approximately 80 yield of methyl ethyl ketone 284 Handbook of Petrochemical Processes Acetic acid is obtained from different sources Carbonylation of methanol is currently the major route Oxidation of butane derivatives and butylene derivatives is an important source of acetic acid It is also produced by the catalyzed oxidation of acetaldehyde 2CH CHO O 2CH CO H 3 2 3 2 The reaction occurs in the liquid phase at approximately 65C 149F using manganese acetate MnOCOCH32 as a catalyst Vinyl acetate CH3COOCHCH2 is a reactive colorless liquid that polymerizes easily if not sta bilized It is an important monomer for the production of polyvinyl acetate polyvinyl alcohol and vinyl acetate copolymers Vinyl acetate was originally produced by the reaction of acetylene and acetic acid in the presence of mercuryII acetate Currently it is produced by the catalytic oxidation of ethylene with oxygen with acetic acid as a reactant and palladium as the catalyst 2CH CH 2CH CO H O 2CH CHOCOCH H O 2 2 3 2 2 2 3 2 The process is similar to the catalytic liquidphase oxidation of ethylene to acetaldehyde The dif ference between the two processes is the presence of acetic acid In practice acetaldehyde is a major coproduct The mole ratio of acetaldehyde to vinyl acetate can be varied from 031 to 25113 The liquidphase process is not used extensively due to corrosion problems and the formation of a fairly wide variety of byproducts In the vaporphase process oxyacylation of ethylene is carried out in a tubular reactor at approxi mately 116C 240F and 75 psi The palladium acetate is supported on carriers resistant to attack by acetic acid Conversions of about 1015 based on ethylene are normally used to operate safely outside the explosion limits approximately 10 vv A selectivity in the order of 9194 based on ethylene is attainable nButanol is normally produced from propylene by the Oxo reaction sometimes known as hydroformylation It may also be obtained from the aldol condensation of acetaldehyde in presence of a base Hydroformylation also known as oxo synthesis or oxo process is an industrial process for the production of aldehyde derivatives from alkene derivatives This chemical reaction results in the addition of a formyl group HCO and a hydrogen atom to a carboncarbon double bond It is an important reaction because aldehydes are easily converted into many secondary products For example the resulting aldehyde derivatives are hydrogenated to alcohol derivatives that are converted to detergent products Hydroformylation is also used in the specialty chemicals industry and is especially relevant to the synthesis of fragrances and drugs In the process an alkene derivative is treated with carbon monoxide and hydrogen at high pressure in the order of 1501500 psi at a temperature in the range between 40C to 200C 104F390F The reaction is an example of homogeneous catalysis since the transition metal catalyst is invariably soluble in the reaction medium Manganese acetate 285 Chemicals from Olefin Hydrocarbons By way of clarification the IUPAC definition defines a transition metal as quote an element whose atom has a partially filled d subshell or which can give rise to cations with an incomplete d subshell end quote Most scientists describe a transition metal as any element in the dblock of the periodic table which includes groups 312 on the periodic table In actual practice the fblock lanthanide and actinide series are also considered transition metals and are called inner transition metals The word transition was first used to describe the elements now known as the dblock by the English chemist Charles Bury in 1921 who referred to a transition series of elements during the change of an inner layer of electrons from a stable group of 8 to1 of 18 or from 18 to 32 725 carBonylation Carbonylation refers to reactions in which the carbon monoxide moiety is introduced into organic and inorganic substrates Carbon monoxide is abundantly available and conveniently reactive so it is widely used as a reactant in industrial chemistry Several industrially useful organic chemicals are prepared by carbonylation reactions which can be highly selective reactions Carbonylation reactions produce organic carbonyl derivatives ie compounds that contain the carbonyl CO functional group such as aldehyde derivatives CHO ketone derivatives CO carboxylic acid derivatives CO2H and ester derivatives CO2R where R is an alkyl group Carbonylation reac tions are the basis of two main types of reactions i hydroformylation and ii the Reppe reaction The hydroformylation reaction entails the addition of both carbon monoxide and hydrogen to unsaturated organic compounds typically alkene derivatives The usual products are aldehyde derivatives RCH CH H CO RCH CH CHO 2 2 2 2 The reaction requires metal catalysts that bind the carbon monoxide and the hydrogen to the alkene The Reppe reaction involves the addition of carbon monoxide and an acidic hydrogen donor to the organic substrate Commercial processes using this type of chemistry include the Monsanto process and the Cativa process which converts methanol to acetic acidacetic anhydride is prepared by a related carbonylation of methyl acetate CH3COOCH3 In the related hydrocar boxylation and hydroesterification reaction alkene derivatives CC and alkyne derivatives CC are the substrates This method is used in industry to produce propionic acid from ethylene RCH CH H O CO RCH CH CO H 2 2 2 2 2 These reactions require metal catalysts which bind and activate the carbon monoxide For example in the industrial synthesis of ibuprofen Chapter 12 a benzylic alcohol derivative is converted to the corresponding carboxylic acid via a palladiumcatalyzed carbonylation reaction ArCH CH OH CO ArCH CH CO H 3 3 2 The liquidphase reaction of ethylene with carbon monoxide and oxygen oxidative carbonylation over a palladiumcopper Pd2Cu2 catalyst system produces acrylic acid CH2CHCO2H The yield based on ethylene is about 85 Reaction conditions are approximately 140C 285F and 1100 psi 2CH CH 2CO O 2CH CHCO H 2 2 2 2 2 The catalyst is similar to that of the Wacker reaction for ethylene oxidation to acetaldehyde how ever this reaction occurs in presence of carbon monoxide 286 Handbook of Petrochemical Processes 726 chlorination The direct addition of chlorine to ethylene produces ethylene dichloride 12dichloroethane Ethylene dichloride is the main precursor for vinyl chloride which is an important monomer for polyvinyl chloride plastics and resins Other uses of ethylene dichloride include its formulation with tetraethyl and tetramethyl lead solutions as a lead scavenger as a degreasing agent and as an inter mediate in the synthesis of many ethylene derivatives The reaction of ethylene with hydrogen chloride on the other hand produces ethyl chloride This compound is a smallvolume chemical with diversified uses alkylating agent refrigerant solvent Ethylene reacts also with hypochlorous acid yielding ethylene chlorohydrin CH CH HOCl ClCH CH OH 2 2 2 2 Ethylene chlorohydrin via this route was previously used for producing ethylene oxide through an epoxidation step Currently the catalytic oxychlorination route the Teijin process discussed earlier in this chapter is an alternative for producing ethylene glycol where ethylene chlorohydrin is an intermediate In organic synthesis ethylene chlorohydrin is a useful agent for introducing the ethyl hydroxy group It is also used as a solvent for cellulose acetate 7261 Vinyl Chloride Vinyl chloride CH2CHCl is a reactive gas soluble in alcohol but slightly soluble in water It is the most important vinyl monomer in the polymer industry Vinyl chloride monomer was originally produced by the reaction of hydrochloric acid and acetylene in the presence of mercuric chloride HgCl2 catalyst The reaction is straightforward and proceeds with high conversion 96 based on acetylene HC CH HCl CH 2 CHCl However ethylene as a cheap raw material has replaced acetylene for obtaining vinyl chloride The production of vinyl chloride via ethylene is a threestep process The first step is the direct chlori nation of ethylene to produce ethylene dichloride Either a liquidphase or a vaporphase process is used The exothermic reaction occurs at 40C50C 104F122F and approximately 60 psi in the presence of a catalyst such as ferric chloride FeCl3 cupric chloride CuCl2 or antimony trichloride SbCl3 ethylene dibromide may also be used as a catalyst The second step is the dehy drochlorination of ethylene dichloride to vinyl chloride and hydrogen chloride The pyrolysis reac tion occurs at approximately 500C 930F and 370 psi in the presence of an adsorbentsuch as pumice on charcoalto remove the hydrogen chloride from the product mix The third step the oxychlorination of ethylene uses byproduct hydrogen chloride from the previous step to produce more ethylene dichloride Thus CH CH Cl CH ClCH Cl 2 2 2 2 2 CH ClCH Cl CH CHCl HCl 2 2 2 CH CH Cl CH ClCH Cl 2 2 2 2 2 The ethylene dichloride from the third step is combined with that produced from the chlorination of ethylene and introduced to the pyrolysis furnace The reaction conditions are approximately 225C 435F and 3060 psi In practice the three steps chlorination oxychlorination and dehydrochlo rination are integrated in one process so that no chlorine is lost 287 Chemicals from Olefin Hydrocarbons 7262 Perchloroethylene and Trichloroethylene Perchloroethylene and trichloroethylene could be produced from ethylene dichloride by an oxychlori nationoxyhydrochlorination process without byproduct hydrogen chloride A special catalyst is used 2ClCH CH Cl Cl O ClCH CCl Cl C CCl H O 2 2 2 2 2 2 2 2 A fluid bed reactor is used at moderate pressures at approximately 450C 840F The reactor efflu ent containing chlorinated organics water a small amount of hydrogen chloride carbon dioxide and other impurities is condensed in a watercooled graphite exchanger cooled in a refrigerated condenser and then scrubbed Separation of perchloroethylene from trichloroethylene occurs by successive distillation Perchloroethylene and trichloroethylene may also be produced from chlorination of propane 727 hydration A hydration reaction is a chemical reaction in which a substance combines with water In the current context water is added to an unsaturated substrate which is usually an alkene or an alkyne Ethyl alcohol CH3CH2OH production is considered by many to be the oldest profession in the world without going into detail about any other possible competitor Carbohydrate fermentation is still the main route to ethyl alcohol in many countries with abundant sugar and grain sources The earliest method for conversion of olefin derivatives into alcohols involved their absorption in sulfuric acid to form esters followed by dilution and hydrolysis generally with the aid of steam In the case of ethyl alcohol the direct catalytic hydration of ethylene can be employed Ethylene is readily absorbed in 98100 sulfuric acid at 75C80C 165F175F and both ethyl and diethyl sulfate are formed hydrolysis takes place readily on dilution with water and heating CH CH H O CH CH OH 2 2 2 3 2 In the process the firstformed mono ethyl sulfate and diethyl sulfate derivatives are hydrolyzed with water to ethanol and sulfuric acid which is regenerated The direct hydration of ethylene with water is the process currently used The hydration is carried out in a reactor at approximately 300C 570F and 1000 psi The reaction is favored at relatively lower temperature and higher pressures Phosphoric acid on diatomaceous earth is the catalyst To avoid catalyst losses a waterethylene mole ratio less than one is used Conversion of ethylene is limited under these conditions and unre acted ethylene is recycled The many used of ethanols many uses can be conveniently divided into solvent use and chemical use As a solvent ethanol dissolves many organicbased materials such as fats oils and hydrocar bon derivatives As a chemical intermediate ethanol is a precursor for acetaldehyde acetic acid and diethyl ether and it is used in the manufacture of glycol ethyl ether derivatives ethylamine derivatives and many ethyl esters Ethylene produced from ethane by cracking is oxidized in the presence of a silver catalyst to ethylene oxide 2H C CH O C H O 2 2 2 2 4 The vast majority of the ethylene oxide produced is hydrolyzed at 100C to ethylene glycol C H O H O HOCH CH OH 2 4 2 2 2 The majority of the ethylene glycol produced commercially is used as automotive antifreeze and much of the rest is used in the synthesis of polyesters 288 Handbook of Petrochemical Processes Of the higher olefin derivatives one of the first alcohol syntheses practiced commercially was that of isopropyl alcohol from propylene Sulfuric acid absorbs propylene more readily than it does ethylene but care must be taken to avoid polymer formation by keeping the mixture relatively cool and using acid of about 85 strength at 300400 psi pressure dilution with inert oil may also be necessary Acetone is readily made from isopropyl alcohol either by catalytic oxidation or by dehy drogenation over metal usually copper catalysts Secondary butyl alcohol is formed on absorption of 1butylene or 2butylene by 7880 sulfu ric acid followed by dilution and hydrolysis Secondary butyl alcohol is converted into methyl ethyl ketone by catalytic oxidation or dehydrogenation There are several methods for preparing higher alcohols One method in particular is the so called Oxo reaction and involves the direct addition of carbon monoxide CO and a hydrogen H atom across the double bond of an olefin to form an aldehyde RCHO which in turn is reduced to the alcohol RCH2OH Hydroformylation the Oxo reaction is brought about by contacting the olefin with synthesis gas 11 carbon monoxidehydrogen at 75C200C 165F390F and 15004500 psi over a metal catalyst usually cobalt The active catalyst is held to be cobalt hydro carbonyl HCOCO4 formed by the action of the hydrogen on dicobalt octacarbonyl 728 oliGomerization Oligomerization is the addition of one olefin molecule to a second and to a third plus higher num bers to form a dimer or a trimer The reaction is normally acidcatalyzed When propylene or butyl ene derivatives are used the formed compounds are branched because an intermediate carbocation is formed These compounds were used as alkylating agents for producing benzene alkylates but the products were nonbiodegradable Oligomerization of ethylene using a Ziegler catalyst produces unbranched alpha olefin deriva tives in the C12 to C16 range by an insertion mechanism A similar reaction using triethylaluminum produces linear alcohols for the production of biodegradable detergents Dimerization of ethylene to 1butylene has been developed recently by using a selective titaniumbased catalyst The C12 to C16 alpha olefin derivatives are produced by dehydrogenation of nparaffins dehydro chlorination of monochloroparaffin derivatives or by oligomerization of ethylene using trialkyl aluminum Ziegler catalyst Iridium complexes also catalyze the dehydrogenation of nparaffins to aolefin derivatives The reaction uses a soluble iridium catalyst to transfer hydrogen to the olefinic acceptor The triethylaluminum and 1butylene are recovered by the reaction between tributylaluminum and ethylene CH CH CH CH Al 3CH CH CH CH H Al 3CH CH CH CH 3 2 2 2 3 2 2 3 2 3 2 2 Alpha olefin derivatives are important compounds for producing biodegradable detergents They are sulfonated and neutralized to alpha olefin sulfonate derivatives RCH CH SO RCH CHSO H 2 3 3 RCH CHSO H NaOH RCH CHSO Na H O 3 3 2 Alkylation of benzene using alpha olefin derivatives produces linear alkylbenzenes which are further sulfonated and neutralized to linear alkylbenzene sulfonates LABS These compounds constitute with alcohol ethoxy sulfate derivatives and ethoxylate derivatives the basic active ingre dients for household detergents Alpha olefin derivatives could also be carbonylated in presence of an alcohol using a cobalt catalyst to produce esters 289 Chemicals from Olefin Hydrocarbons RCH CH CO R OH RCH CH CO R 2 1 2 2 2 1 Transesterification with pentaerythritol produces pentaerythritol ester derivatives and releases the alcohol Linear C21 to C26 alcohol derivatives are important chemicals for producing various compounds such as plasticizers detergents and solvents The production of linear alcohols involves the hydro formylation the Oxo reaction of alpha olefin derivatives followed by hydrogenation They are also produced by the oligomerization of ethylene using aluminum alkyls Ziegler catalysts The Alfol process for producing linear primary alcohols is a fourstep process In the first step triethylaluminum is produced by the reaction of ethylene with hydrogen and aluminum metal 6CH CH 3H 3Al 3 CH CH Al 2 2 2 3 2 3 In the next step ethylene is polymerized by the action of triethylaluminum at approximately 120C 248F and 1900 psi to trialkylaluminum Typical reaction time is approximately 140 min for an average C12 alcohol production The oxidation of triethylaluminum is carried out between 20C and 50C 68F122F in air to aluminum trialkoxide derivatives 2 CH CH Al 3O 2 CH CH O Al 3 2 3 2 3 2 3 The final step is the hydrolysis of the trialkoxide derivative with water to the corresponding even numbered primary alcohols Alumina is coproduced and is characterized by its high activity and purity CH CH O Al H O CH CH OH Al O 3 2 3 2 3 2 2 3 Linear alcohols in the range of C10 to C12 are used to make plasticizers Those in the range of C12 to C16 range are used for making biodegradable detergents They are either sulfated to linear alkyl sulfate derivatives ionic detergents or reacted with ethylene oxide to the ethoxylated linear alcohols non ionic detergents The C16 to C18 alcohols are modifiers for wash and wear polymers The higher molec ular weight alcohols ie the C20 to C26 alcohols are synthetic lubricants and moldrelease agents 729 Polymerization The polymerization of ethylene under pressure 15003000 psi at 110C120C 230F250F in the presence of a catalyst or initiator such as a 1 solution of benzoyl peroxide in methanol produces a polymer in the 20003000 molecular weight range Chapter 11 Polymerization at 1500030000 psi and 180C200C 355F390F produces a wax melting at 100C 212F and 1500020000 molecular weight but the reaction is not as straightforward as the equation indicates since there are branches in the chain However considerably lower pressures can be used over cata lysts composed of aluminum alkyls R3Al in presence of titanium tetrachloride TiCl4 supported chromic oxide CrO3 nickel NiO or cobalt CoO on charcoal and promoted molybdenaalumina MoO2Al2O3 which at the same time give products more linear in structure Polypropylenes can be made in similar ways and mixed monomers such as ethylenepropylene and ethylenebutylene mixtures can be treated to give high molecular weight copolymers of good elasticity Polyethylene has excellent electrical insulating properties its chemical resistance toughness machinability low density light weight and high strength make it suitable for many other uses Lower molecular weight polymers such as the dimers trimers and tetramers are used as such in motor gasoline The materials are normally prepared over an acid catalyst Propylene tri mer dimethyl heptene derivatives and tetramer trimethyl nonene derivatives are applied in the 290 Handbook of Petrochemical Processes alkylation of aromatic hydrocarbon derivatives for the production of alkylaryl sulfonate detergents and also as olefincontaining feedstocks in the manufacture of C10 and C13 oxoalcohols Phenol is alkylation by the trimer to make nonylphenol a chemical intermediate for the manufacture of lubri cating oil detergents and other products Isobutylene also forms several series of valuable products the di and triisobutylenes make excellent motor and aviation gasoline components they can also be used as alkylating agents for aromatic hydrocarbon derivatives and phenols and as reactants in the oxoalcohol synthe sis Polyisobutylene derivatives in the viscosity range of 55000 SUS 38C 100F have been employed as viscosity index improvers in lubricating oils 1Butylene CH3CH2CHCH2 and 2butylene CH3CHCHCH3 participate in polymerization reactions by the way of butadiene CH2CHCHCH2 the dehydrogenation product which is copolymerized with styrene 235 to form GRS rubber and with acrylonitrile 25 to form GRN rubber Derivatives of acrylic acid butyl acrylate ethyl acrylate 2ethylhexyl acrylate and methyl acry late can be homopolymerized using peroxide initiators or copolymerized with other monomers to generate acrylic or aclryloid resins 7210 1 Butylene The Institut Français du Pétrole process is used to produce butylene1 1butene by dimerizing eth ylene A homogeneous catalyst system based on a titanium complex is used The reaction is a con certed coupling of two molecules on a titanium atom affording a titanium IV cyclic compound which then decomposes to 1butylene by an intramolecular hydrogen transfer reaction The Alphabutol process operates at low temperatures 50C55C 122F131F and relatively low pressures 330400 psi The process operates in the liquid phase using a soluble catalyst sys tem which avoids isomerization of 1butene to 2butene There is no need for superfractionation of the product stream The process scheme includes four sections the reactor the cocatalyst injection catalyst removal and distillation The continuous cocatalyst injection of an organobasic com pound deactivates the catalyst downstream of the reactor withdrawal valve to limit isomerization of 1butylene to 2butylene 7211 Polymerization The polymerization of ethylene under pressure 15003000 psi at 110C120C 230F250F in the presence of a catalyst or initiator such as a 1 solution of benzoyl peroxide in methanol produces a polymer in the 20003000 molecular weight range Polymerization at 1500030000 psi and 180C200C 355F390F produces a wax melting at 100C 212F and 1500020000 molecular weight but the reaction is not as straightforward as the equation indicates since there are branches in the chain However considerably lower pressures can be used over catalysts com posed of aluminum alkyls R3Al in presence of titanium tetrachloride TiCl4 supported chromic oxide CrO3 nickel NiO or cobalt CoO on charcoal and promoted molybdenaalumina MoO2 Al2O3 which at the same time give products more linear in structure Polypropylenes can be made in similar ways and mixed monomers such as ethylenepropylene and ethylenebutylene mixtures can be treated to give high molecular weight copolymers of good elasticity Polyethylene has excel lent electrical insulating properties its chemical resistance toughness machinability low density light weight and high strength make it suitable for many other uses 291 Chemicals from Olefin Hydrocarbons 73 CHEMICALS FROM PROPYLENE Propylene is an unsaturated organic hydrocarbon C3H6 CH3CHCH2 that has one double bond and is a colorless gas Table 74 It is a byproduct of crude oil refining and natural gas processing During oil refining propylene CH3CHCH2 like ethylene CH2CH2 is produced as a result of the thermal decomposition cracking of higher molecular weight hydrocarbon derivatives A major source of propylene is naphtha cracking intended to produce ethylene but it also results from refinery cracking producing other products Propylene can be separated by fractional distillation from hydrocarbon mixtures obtained from cracking and other refining processes refinery grade propylene is about 5070 Propane dehydrogenation converts propane CH3CH2CH3 into propylene CH3CHCH2 and byproduct hydrogen CH CH CH CH CH CH H 3 2 3 3 2 2 The propylene from propane yield is in the order of 85 mol Reaction byproducts mainly hydro gen are usually used as fuel for the propane dehydrogenation reaction As a result propylene tends to be the only product unless local demand exists for hydrogen In fact a large proportion of the propylene is made from propane which is obtained from natural gas stripper plants or from refinery gases Like ethylene propylene is a reactive alkene that can be obtained from refinery gas streams especially those from cracking processes The main source of propylene however is steam crack ing of hydrocarbon derivatives where it is coproduced with ethylene There is no special process for propylene production except the dehydrogenation of propane CH CH CH Catalyst CH CH CH H 3 2 3 3 2 2 Increasing the yield of the valuable low molecular weight olefin derivatives especially propylene and the butylene derivatives remains a major challenge for many integrated refineries As global petrochemical demand for propylene continues to grow opportunities for improved production routes will emerge Propylene has been considered as a byproduct of ethylene production via the steam cracking of naphtha or other feedstocks However this route has not always able to keep up with propylene demand To make up this shortfall refineries may isolate propylene from the gaseous effluents of fluid catalytic cracking FCC units and purify it to either chemical grade or polymer grade propyl ene While many refineries are of necessity accepting heavy crude oil as the refinery feedstock the fluid catalytic cracking product slate is increasingly shifting toward the production of lowboiling olefin derivatives mainly propylene More stringent specifications for gasoline are needed in the future for which the current fluid catalytic cracking product slate is not optimal because of high aromatics and olefin derivatives content TABLE 74 Properties of Propylene Chemical formula C3H6 Molar mass 4208 gmol Appearance Colorless gas Density 181 kgm3 gas 1013 bar 15C 6139 kgm3 liquid Melting point 1852C 3014F 880K Boiling point 476C 537F 2256K Solubility in water 061 gm3 292 Handbook of Petrochemical Processes The conventional fluid catalytic cracking unit is typically operated at low to moderate sever ity with flexibility to swing between maximum distillate and maximum gasoline mode Aitani 2006 23 This unit yields 34 ww propylene Improvements in fluid catalytic cracking cata lysts process design hardware and operation severity can boost propylene yield up to 25 ww or higher In fluid catalytic cracking practice there are several options to increase the selectivity to low molecular weight olefin derivatives Aitani 2006 which are i dedicated fluid catalytic cracking catalysts ii ZSM5 additives iii higher severity operation ie higher cracking temperature and iv naphtha recycle Maadhah et al 2008 Conventional fluid catalytic cracking catalyst compositions contain a catalytic cracking com ponent and amorphous alumina which is necessary to provide the bottoms conversion Catalytic cracking components are crystalline compounds such as faujasitetype Y zeolite as well as amor phous alumina may also be used as a binder to provide a matrix with enough binding function to properly bind the crystalline cracking component when present ZSM5 based additive containing a small pore zeolite 5575 Å is commonly added to the cracking catalyst in fluid catalytic cracking to enhance gasoline octane and olefin derivatives production especially propylene One costeffective way to increase the propylene yield from the fluid catalytic cracking unit is the use of specialized catalysts that contain ZSM5 zeolite An increasing number of refiners use as much as 10 ww of ZSM5 additives to obtain more than a 9 ww yield of propylene Because of its unique pore structure ZSM5 limits access to only linear or slightly branched hydrocarbon mol ecules within the gasoline boiling point range ZSM5based additive acts mainly by cracking C6 naphtha olefin derivatives to smaller olefin derivatives such as propylene and butylenes Maadhah et al 2008 These catalysts and additives increase the yield of propylene and other low molecular weight olefin derivatives at the expense of gasoline and distillate products The cracking of low molecular weight hydrocarbon derivatives is another excellent option for the fluid catalytic crackingbased refinery to produce and recover propylene Naphtha is the most common feedstock used in fluid catalytic cracking units for the incremental production of propyl ene Various process schemes for naphtha cracking in the fluid catalytic cracking unit have been suggested and the simplest option consists of feeding and cracking naphtha together with gas oil feed Naphtha may also be injected at the bottom of the fluidized riser reactor before regenerated TABLE 75 Processes by Which Propylene Can Be Produced Process Name DeveloperLicensor Propylene Yield ww Comments Deep Catalytic Cracking DCCI and II RIPPSinopecStone Webster 146288 Commercialized Catalytic Pyrolysis Process CPP RIPPSinopecStone Webster 246 Vacuum gas oil VGO and heavy feeds HighSeverity FCC HSFCC NipponKFUPMJCCP Saudi Aramco 1725 High severity temperature Indmax Indian Oil CoABB Lummus 1725 Upgrades heavy cuts at high catalystoil ratio Maxofin ExxonMobil and KBR 18 Variations to increase propylene NEXCC Fortum 16 High CO short contact time PetroFCC UOP 22 Additional reaction severity along with RxCat design Selective Component Cracking SCC ABB Lummus 24 High Severity operation temperature catalystoil ratio HighOlefins FCC Petrobras 2025 High temperature catalystoil ration 293 Chemicals from Olefin Hydrocarbons catalyst contacts gas oil feed where it may be cracked at higher temperature and catalystoil CO ratio The need for a higher cracking temperature a shorter contact time and a higher catalystoil ratio lead to the conclusion that the mechanical restrictions of existing fluid catalytic cracking units prevent the optimization of the conventional process for maximum olefin production Despite the various fluid catalytic cracking technologies available to increase the yield of propylene Table 75 there remains the need to improve production of propylene The main objective of the highseverity FCC HSFCC process is to produce significantly more propylene and highoctane number naph tha The conceptual process and preliminary feasibility study of the HSFCC process started in the mid1990s Fujiyama et al 2005 Maadhah et al 2008 The uses of propylene include gasoline 80 polypropylene isopropanol trimers and tetra mers for detergents propylene oxide cumene and glycerin Propylene can be polymerized alone or copolymerized with other monomers such as ethylene Many important chemicals are based on propylene such as isopropanol allyl alcohol glycerol and acrylonitrile Propylene is used as a feed stock for a wide range of polymers product intermediates and chemicals Major propylene deriva tives include polypropylene acrylonitrile propylene oxide oxoalcohol derivatives and cumene As an olefin propylene is a reactive compound that can react with many common reagents used with ethylene such as water chlorine and oxygen to produce a variety of chemicals Figure 73 FIGURE 73 Chemicals from propylene 294 Handbook of Petrochemical Processes However structural differences between these two olefin derivatives result in different reactivity toward these reagents For example direct oxidation of propylene using oxygen does not produce propylene oxide as in the case of ethylene Instead an unsaturated aldehyde acrolein is obtained This could be attributed to the ease of oxidation of allylic hydrogens in propylene Similar to the oxidation reaction the direct catalyzed chlorination of propylene produces allyl chloride through substitution of allylic hydrogens by chlorine Substitution of vinyl hydrogens in ethylene by chlo rine however does not occur under normal conditions The current chemical demand for propylene is a little over onehalf that for ethylene This is somewhat surprising because the added complexity of the propylene molecule due to presence of a methyl group should permit a wider spectrum of end products and markets However such a difference can lead to the production of undesirable byproducts and it frequently does This may explain the relatively limited use of propylene in com parison to ethylene Nevertheless many important chemicals are produced from propylene As is the case for ethylene moisture in propylene is critical Several field tests and a few labora tory tests are in use by individual firms but no standard method for moisture has been adopted to date The problems in sampling for moisture content especially in the less than 10 ppm range are hard to overcome The trace impurities in 90 or better propylene which is used in polymeriza tion processes become quite critical Hydrogen oxygen and carbon monoxide are determined by one technique and acetylene ethylene butylenes butadiene methyl acetylene and propadiene are determined by using a very sensitive analytical method Propylene concentrates are mixtures of propylene and other hydrocarbon derivatives princi pally propane and trace quantities of ethylene butylenes and butanes Propylene concentrates may vary in propylene content from 70 mol up to over 95 mol and may be handled as a liquid at normal temperatures and moderate pressures Propylene concentrates are isolated from the furnace products mentioned in the preceding paragraph on ethylene Higher purity propylene streams are further purified by distillation and extractive techniques Propylene concentrates are used in the production of propylene oxide isopropyl alcohol polypropylene and the synthesis of isoprene As with any gas stream propylene concentrate streams typically require a component analysis depending upon their final use The appropriate method for the determination is by gas chromatog raphy Another gas chromatographic method is used to identify major impurities 731 oxidation The direct oxidation of propylene using air or oxygen produces acrolein Acrolein may further be oxidized to acrylic acid which is a monomer for polyacrylic resins Ammoxidation of propylene is considered under oxidation reactions because it is thought that a common allylic intermediate is formed in both the oxidation and ammoxidation of propylene to acrolein and to acrylonitrile respectively The use of peroxides for the oxidation of propylene produces propylene oxide This compound is also obtained via a chlorohydrination of propylene followed by epoxidation Acrolein 2propenal is an unsaturated aldehyde with a disagreeable odor When pure it is a colorless liquid that is highly reactive and polymerizes easily if not inhibited The main route to produce acrolein is through the catalyzed air or oxygen oxidation of propylene CH CH CH O CH CHCHO H O H 3405 KJmol 3 2 2 2 2 Transition metal oxides or their combinations with metal oxides from the lower row 5A elements were found to be effective catalysts for the oxidation of propylene to acrolein Two examples of com mercially used catalysts are supported CuO used in the Shell process and Bi2Oi MoO3 used in the Sohio process In both processes the reaction is carried out at temperature and pressure ranges of 300C360C and 1530 psi respectively In the Sohio process a mixture of propylene air and steam is introduced to the reactor The hot effluent is quenched to cool the product mixture and to remove the gases Acrylic acid a byproduct from the oxidation reaction is separated in a stripping tower where 295 Chemicals from Olefin Hydrocarbons the acroleinacetaldehyde mixture enters as an overhead stream Acrolein is then separated from acet aldehyde in a solvent extraction tower Finally acrolein is distilled and the solvent is recycled A proposed mechanism for the oxidation of propylene to acrolein is by a first step abstraction of an allylic hydrogen from an adsorbed propylene by an oxygen anion from the catalytic lattice to form an allylic intermediate The next step is the insertion of a lattice oxygen into the allylic species This creates oxidedeficient sites on the catalyst surface accompanied by a reduction of the metal The reduced catalyst is then reoxidized by adsorbing molecular oxygen which migrates to fill the oxidedeficient sites Thus the catalyst serves as a redox system The main use of acrolein is to produce acrylic acid and its esters Acrolein is also an inter mediate in the synthesis of pharmaceuticals and herbicides It may also be used to produce glyc erol by reaction with isopropanol discussed later in this chapter 2Hexanedial which could be a precursor for adipic acid and hexamethylenediamine may be prepared from acrolein tailtotail dimerization of acrolein using ruthenium catalyst that produces trans2hexanedial The trimer trans6hydroxy5formyl27octadienal is coproduced Acrolein may also be a precursor for 13propanediol Hydrolysis of acrolein produces 3hydroxypropionaldehyde which could be hydro genated to 13propanediol The diol could also be produced from ethylene oxide Chapter 7 There are several ways to produce acrylic acid Currently the main process is the direct oxida tion of acrolein over a combination molybdenumvanadium oxide catalyst system In many acrolein processes acrylic acid is made the main product by adding a second reactor that oxidizes acrolein to the acid The reactor temperature is approximately 250C 2CH CHCHO O 2CH CHCO H 2 2 2 2 Acrylic acid is usually esterified to acrylic esters by adding an esterification reactor The reaction occurs in the liquid phase over an ionexchange resin catalyst An alternative route to acrylic esters is via a Bpropiolactone intermediate The lactone is obtained by the reaction of formaldehyde and ketene a dehydration product of acetic acid The acidcatalyzed ring opening of the fourmembered ring lactone in the presence of an alcohol produces acrylic esters Acrylic acid and its esters are used to produce acrylic resins Depending on the polymerization method the resins could be used in the adhesive paint or plastic industry Shell has coproduced propylene oxide and styrene using the styrene monomer propylene oxide process SMPO process Buijink et al 2008 The heart of the process is formed by the catalytic epoxidation of propylene with ethylbenzene hydroperoxide using a silicasupported titanium cata lyst The SMPO process comprises four main reaction steps 296 Handbook of Petrochemical Processes The first step is the airoxidation of ethyl benzene to ethylbenzene hydroperoxide EBHP which is performed in a series of large horizontal bubblecolumn reactors that are equipped with baffles and heatingcooling coils Air is introduced via separate middle and side spargers The gas outlet stream besides unconverted oxygen contains a very significant amount of ethyl benzene from evaporation stripping and which is recovered in a condensing column and recycled to the reactor train The subsequent step the epoxidation of propylene by ethyl benzene hydroperoxide is carried out in the liquid phase over a heterogeneous catalyst to produce crude propylene oxide and methyl phenyl carbinol MPC The feed to the reactors consists of makeup and recycle propylene and ethyl benzene hydroperoxide in ethyl benzene The reaction train consists of a number of adiabatic fixed bed reactors with interstage cooling Deactivated catalyst is replaced incinerated to remove residual hydrocarbon derivatives The product from the epoxidation reactor is sent to the crude propylene oxide recovery unit that contains a number of distillation columns in which this product is sepa rated into unreacted propylene for recycle to the epoxidation section crude propylene oxide ethyl benzene and styrene precursors mainly methyl phenyl carbinol and methyl phenyl ketone MPK Lowboiling hydrocarbon derivatives can be used as fuel The crude propylene oxide unit is purified in a finishing unit which consists of a number of distillation columns in which water is removed by azeotropic distillation with normal butane and aldehydes and light and heavy ends are also removed from the crude propylene oxide Prior to entering the methyl phenyl carbinol dehydration step the ethyl benzene methyl phenyl carbinol and methyl phenyl ketone stream from the propylene oxide recovery unit is washed and ethyl ben zene is removed by distillation The methyl phenyl carbinol and the methyl phenyl ketone are sent to the dehydration reactors where methyl phenyl carbinol is dehydrated to styrene using one of the commercially available catalysts The reactor product is separated into crude styrene which is sent to the styrene monomer SM finishing unit and methyl phenyl ketone with traces of methyl phe nyl carbinol which is sent to a catalytic hydrogenation unit The product containing methyl phenyl carbinol and some ethyl benzene and methyl phenyl ketone is recycled to the styrene monomer reaction unit 732 ammoxidation Ammoxidation refers to a reaction in which a methyl group with allyl hydrogens is converted to a nitrile group using ammonia and oxygen in the presence of a mixed oxidebased catalyst A success ful application of this reaction produces acrylonitrile from propylene CH CH CH NH 112O CH CHCN 3H O 3 2 3 2 2 2 As with other oxidation reactions ammoxidation of propylene is highly exothermic so an efficient heat removal system is essential Acetonitrile and hydrogen cyanide are byproducts that may be recovered for sale Acetonitrile CH3CN is a high polarity aprotic solvent used in DNA synthesizers high performance liquid chromatography HPLC and electrochemistry It is an important solvent for extracting butadiene from C4 streams Both fixed and fluid bed reactors are used to produce acrylonitrile but most modern processes use fluid bed systems The MontedisonUOP process uses a highly active catalyst that gives 956 propylene conversion and a selectivity above 80 for acrylonitrile The catalysts used in ammoxi dation are similar to those used in propylene oxidation to acrolein Oxidation of propylene occurs readily at 322C 612F over BiMo catalysts However in the presence of ammonia the conversion of propylene to acrylonitrile does not occur until approximately 400C 750F This may be due to the adsorption of ammonia on cata lytic sites that block propylene chemisorption As with propylene oxidation the first step in the ammoxidation reaction is the abstraction of an alpha hydrogen from propylene and formation of 297 Chemicals from Olefin Hydrocarbons an allylic intermediate Although the subsequent steps are not well established it is believed that adsorbed ammonia dissociates on the catalyst surface by reacting with the lattice oxygen produc ing water The adsorbed NH species then reacts with a neighboring allylic intermediate to yield acrylonitrile Acrylonitrile is mainly used to produce acrylic fibers resins and elastomers Copolymers of acrylonitrile with butadiene and styrene are the ABS resins and those with styrene are the styreneacrylonitrile resins that are important plastics Most of the production was used for ABS resins and acrylic and monoacrylic fibers Acrylonitrile is also a precursor for acrylic acid by hydrolysis and for adiponitrile by an electrodimerization Adiponitrile is an important intermediate for producing nylon 66 There are other routes for its production The way to produce adiponitrile via propylene is the electrodimerization of acrylonitrile Propylene oxide is similar in its structure to ethylene oxide but due to the presence of an addi tional methyl group it has different physical and chemical properties It is a liquid that boils at 34C 93F and it is only slightly soluble in water Ethylene oxide a gas is very soluble in water The main method to obtain propylene oxide is chlorohydrination followed by epoxidation This older method still holds a dominant role in propylene oxide production Chlorohydrination is the reaction between an olefin and hypochlorous acid Ethylene oxide also called epoxyethane oxirane is a cyclic ether and is the simplest epoxide with faintly sweet odor and colorless flammable gas at room temperature Ethylene oxide is impor tant to the production of detergents thickeners solvents plastics and various organic chemicals such as ethylene glycol ethanolamine derivatives simple and complex glycols polyglycol ethers and other compounds It is extremely flammable and explosive and is used as the main ingredient in the manufacturing of thermobaric weapons The synthesis of ethylene oxide was first reported in 1859 when it was prepared it by treating 2chloroethanol with potassium hydroxide This reaction is carried out at elevated temperature and beside sodium hydroxide or potassium hydroxide calcium hydroxide barium hydroxide magnesium hydroxide or carbonates of alkali or alkaline earth metals can be used In addition ethylene can be oxidized directly to ethylene oxide using peroxy acids such as peroxybenzoic or metachloroperoxybenzoic acid In 1914 BASF formerly known as Badische Anilin Soda Fabrik first started the synthesis of ethylene oxide by chlorohydrin process Later an efficient direct oxidation of ethylene by air was invented by Lefort in 1931 and in 1937 Union Carbide opened the first plant using this process The process was further improved in 1958 by Shell Oil Co by replacing air with oxygen and using elevated temperature of 200C300C 390F570F and pressure is composed of three major steps i synthesis of ethylene chlorohydrin ii dehydrochlorination of ethylene chlorohydrin to ethylene oxide and iii purification of ethylene oxide In the process for the production of ethylene oxide on a commercial scale the main reactor consists of thousands of catalyst tubes in bundles The catalyst packed in these tubes is in the form of spheres or rings of diameter 310 mm The operating conditions of 200C300C with a pressure of 13 MPa prevail in the reactor The cooling system of the reactor can be used to maintain this temperature With the aging of the catalyst its selectivity decreases and it produces more exothermic side products ClCH2CH2OH KOH KCl H2O sometime written as CH2CH2O 298 Handbook of Petrochemical Processes of CO2 After the gaseous stream from the main reactor containing ethylene oxide 12 and CO2 5 is cooled it is then passed to the ethylene oxide scrubber Here water is used as the scrubbing media which wash away majority of ethylene oxide along with some amounts of CO2 N2 CH2CH2 CH4 and aldehydes A small proportion of the gas leaving the ethylene oxide scrubber 0102 is removed continuously to prevent the buildup of inert compounds which are introduced as impuri ties with the reactants The aqueous stream resulting from the above scrubbing process is then sent to the ethylene oxide desorber Here ethylene oxide is obtained as the overhead product whereas the bottom product obtained is known as the glycol bleed The ethylene oxide stream is stripped of its lowboiling components and then distilled in order to separate it into water and ethylene oxide The recycle stream obtained from the ethylene oxide scrubber is compressed and a sidestream is fed to the CO2 scrubber Here CO2 gets dissolved into the hot aqueous solution of potassium carbon ate The dissolution of CO2 is not only a physical phenomenon but a chemical phenomenon as well for the CO2 reacts with potassium carbonate to produce potassium hydrogen carbonate K CO CO H O 2KHCO 2 3 2 2 3 The potassium carbonate solution is then sent to the CO2 descrubber where CO2 is descrubbed stepwise usually two steps flashing The first step is done to remove the hydrocarbon gases and the second step is employed to strip off CO2 Ethylene oxide is one of the most commonly used sterilization methods in the healthcare indus try because of its nondamaging effects for delicate instruments and devices that require steriliza tion and for its wide range of material compatibility Ethylene oxide is used as an accelerator of maturation of tobacco leaves and fungicide Ethylene is used in the synthesis of 2butoxyethanol which is a solvent used in many products Ethylene oxide can readily react with divergent com pounds with the opening of the ring its typical reactions are with nucleophiles which proceed via the SN2 mechanism both in acidic and alkaline media When propylene is the reactant propylene chlorohydrin is produced The reaction occurs at approximately 35C 95F and normal pressure without any catalyst CH CH CH HOCl CH CHOHCH Cl 3 2 3 2 Propylene chlorohydrin Approximately 8790 yield could be achieved The main byproduct is propylene dichloride 69 The next step is the dehydrochlorination of the chlorohydrin with a 5 CaOH2 solution Propylene oxide is purified by steam stripping and then distillation Byproduct propylene dichlo ride may be purified for use as a solvent or as a feed to the perchloroethylene process The main disadvantage of the chlorohydrination process is the waste disposal of calcium chloride CaCl2 The second important process for propylene oxide is epoxidation with peroxides Many hydro peroxides have been used as oxygen carriers for this reaction Examples are tbutyl hydroperoxide ethylbenzene hydroperoxide and peracetic acid An important advantage of the process is that the coproducts from epoxidation have appreciable economic values Epoxidation of propylene with ethylbenzene hydroperoxide is carried out at approximately 130C 266F and 500 psi in presence of molybdenum catalyst A conversion of 98 on the hydroperoxide has been reported The coproduct aphenyl ethyl alcohol could be dehydrated to styrene Ethylbenzene hydroperoxide is produced by the uncatalyzed reaction of ethylbenzene with oxygen C H CH CH O C H CH CH OOH 6 5 2 3 2 6 5 3 299 Chemicals from Olefin Hydrocarbons Similar to ethylene oxide the hydration of propylene oxide produces propylene glycol Propylene oxide also reacts with alcohols producing polypropylene glycol ethers which are used to produce polyurethane foams and detergents Isomerization of propylene oxide produces allyl alcohol a precursor for glycerol Propylene glycol 12propanediol CH3CHOHCH2OH is produced by the hydration of propyl ene oxide in a manner similar to that used for ethylene oxide Depending on the propylene oxidewater ratio di tripropylene glycol and polypropylene glycol derivatives can be made the main products The reaction between propylene oxide and carbon dioxide produces propylene carbonate The reaction conditions are approximately 200C and 80 atm A yield of 95 is anticipated Propylene carbonate is a liquid used as a specialty solvent and a plasticizer Allyl alcohol is produced by the catalytic isomerization of propylene oxide at approximately 280C The reaction is catalyzed with lithium phosphate A selectivity around 98 could be obtained at a propylene oxide conversion around 25 Allyl alcohol is used in the plasticizer industry as a chemical intermediate and in the production of glycerol Glycerol 123propanetriol CH2OHCHOHCH2OH is a trihydric alcohol of great utility due to the presence of three hydroxyl groups It is a colorless somewhat viscous liquid with a sweet odor Glycerin is the name usually used by pharmacists for glycerol There are different routes for obtain ing glycerol It is a byproduct from the manufacture of soap from fats and oils a nonpetroleum source Glycerol is also produced from allyl alcohol by epoxidation using hydrogen peroxide or a peracid similar to epoxidation of propylene The reaction of allyl alcohol with hydrogen peroxide produces glycidol as an intermediate which is further hydrolyzed to glycerol Other routes for obtaining glycerol are also based on propylene 733 oxyacylation Like vinyl acetate from ethylene allyl acetate is produced by the vaporphase oxyacylation of propyl ene The catalyzed reaction occurs at approximately 180C 355F and 60 psi over a PdKOAc catalyst Propylene glycol 300 Handbook of Petrochemical Processes 2CH CH CH 2CH CO H O 2CH CHCH OCOCH H O 3 2 3 2 2 2 2 3 2 Allyl acetate is a precursor for 14butanediol via a hydrocarbonylation route which produces 4acetoxybutanal The reaction proceeds with a CoCO8 catalyst in benzene solution at approxi mately 125C 257F and 3000 psi The typical mole hydrogencarbon monoxide ratio is 21 The reaction is exothermic and the reactor temperature may reach 180C 355F during the course of the reaction Selectivity to 4acetoxybutanal is approximately 65 at 100 allyl acetate conversion 734 chlorination Allyl chloride CH2CHCH2Cl is a colorless liquid insoluble in water but soluble in many organic solvents It has a strong pungent odor and an irritating effect on the skin As a chemical allyl chlo ride is used to make allyl alcohol glycerol and epichlorohydrin The production of allyl chloride could be achieved by direct chlorination of propylene at high temperatures approximately 500C and 1 atm The reaction substitutes of an allylic hydrogen with a chlorine atom Hydrogen chloride is a byproduct from this reaction CH CHCH Cl CH CHCH Cl HCl 2 3 2 2 2 The major byproducts are cis13dichloropropylene and trans13dichloropropylene which are used as soil fumigants The most important use of allyl chloride is to produce glycerol via an epichlorohydrin intermedi ate The epichlorohydrin is hydrolyzed to glycerol CH CHCH Cl Cl H O ClCH CHOHCH Cl HCl 2 2 2 2 2 2 2ClCH CHOHCH Cl Ca OH 2CH CHCH Cl CaC1 2H O 2 2 2 2 2 2 2 Glycerol a trihydric alcohol is used to produce polyurethane foams and alkyd resins It is also used in the manufacture of plasticizers 735 hydration Isopropanol 2propanol CH3CHOHCH3 is an important alcohol of great synthetic utility It is the secondlargest volume alcohol after methanol 1998 US production was approximately 15 billion pounds and it was the 49thranked chemical Isopropanol under the name isopropyl alcohol was the first industrial chemical synthesized from a petroleumderived olefin 1920 The production of isopropanol from propylene occurs by either a direct hydration reaction the newer method or by the older sulfation reaction followed by hydrolysis In the direct hydration method the reaction could be effected either in a liquid or in a vapor phase process The slightly exothermic reaction evolves 515 KJmol CH CH CH H O CH CHOHCH 3 2 2 3 3 In the liquidphase process high pressures in the range of 12001500 psi are used A sulfo nated polystyrene cationexchange resin is the catalyst commonly used at about 150C 300F An isopropanol yield of 935 can be realized at 75 propylene conversion The only important by product is diisopropyl ether about 5 Gasphase hydration on the other hand is carried out at temperatures above 200C 390F and approximately 370 psi The Imperial Chemical Industries ICI process employs tungsten oxide WO3 on a silica carrier as catalyst Older processes still use the sulfation route The process is similar to that used for ethylene in the presence of sulfuric acid 301 Chemicals from Olefin Hydrocarbons but the selectivity is a little lower than the modern vaporphase processes The reaction conditions are milder than those used for ethylene Isopropanol is a colorless liquid having a pleasant odor it is soluble in water It is more soluble in hydrocarbon liquids than methanol or ethanol For this reason small amounts of isopropanol may be mixed with methanolgasoline blends used as motor fuels to reduce phase separation prob lems About 50 of isopropanol use is to produce acetone Other important synthetic uses are to produce esters of many acids such as acetic isopropyl acetate solvent for cellulose nitrate myristic and oleic acids used in lipsticks and lubricants Isopropyl palmitate is used as an emulsifier for cosmetic materials Isopropyl alcohol is a solvent for alkaloids essential oils and cellulose derivatives Acetone 2propanone is produced from isopropanol by a dehydrogenation oxidation or a com bined oxidation dehydrogenation route The dehydrogenation reaction is carried out using ei ther copper or zinc oxide catalyst at approximately 450C550C 840F1020F A 95 yield is obtained The direct oxidation of propylene with oxygen is a noncatalytic reaction occurring at approxi mately 90C140C 194F284F and 200300 psi In this reaction hydrogen peroxide is copro duced with acetone At 15 isopropanol conversion the approximate yield of acetone is 93 and that for hydrogen peroxide is 87 2CH CHOHCH O 2CH COCH H O 3 3 2 3 3 2 2 The oxidation process uses air as the oxidant over a silver or copper catalyst The conditions are similar to those used for the dehydrogenation reaction Acetone can also be coproduced with allyl alcohol in the reaction of acrolein with isopropanol The reaction is catalyzed with an MgO and ZnO catalyst combination at approximately 400C 750F and 1 atm It appears that the hydrogen produced from the dehydrogenation of isopropanol and adsorbed on the catalyst surface selectively hydrogenates the carbonyl group of acrolein CH CHOHCH CH CHCHO CH COCH CH CHCH OH 3 3 2 3 3 2 2 A direct route for acetone from propylene was developed using a homogeneous catalyst similar to the Wacker system PdCl2CuCl2 The reaction conditions are similar to those used for ethylene oxidation to acetaldehyde Most acetone is currently obtained via a cumene hydroperoxide process where it is coproduced with phenol Acetone is a volatile liquid with a distinct sweet odor It is miscible with water alcohols and many hydrocarbon derivatives For this reason it is a highly desirable solvent for paints lacquers and cellulose acetate As a symmetrical ketone acetone is a reactive compound with many synthetic uses Among the important chemicals based on acetone are methylisobutyl ketone methyl methac rylate ketene and diacetone alcohol Mesityl oxide is an alphabeta unsaturated ketone of high reactivity It is used primarily as a solvent It is also used for producing methylisobutyl ketone Mesityl oxide is produced by the dehy dration of acetone Hydrogenation of mesityl oxide produces methylisobutyl ketone a solvent for paints and varnishes Methyl methacrylate CH2CHCOOCH3 is produced by the hydrocyanation of acetone using hydrogen cyanide HCN The resulting cyanohydrin is then reacted with sulfuric acid and metha nol producing methyl methacrylate One disadvantage of this process is the waste ammonium hydrosulfate NH4HSO4 stream 302 Handbook of Petrochemical Processes Methacrylic acid is also produced by the air oxidation of isobutylene or the ammoxidation of isobutylene to methacrylonitrile followed by hydrolysis Methacrylic acid and its esters are useful vinyl monomers for producing polymethacrylate resins which are thermosetting polymers The extruded polymers are characterized by the transparency required for producing glasslike plastics commercially known as Plexiglas Bisphenol A is a solid material in the form of white flakes insoluble in water but soluble in alco hols As a phenolic compound it reacts with strong alkaline solutions Bisphenol A is an important monomer for producing epoxy resins polycarbonates and polysulfone derivatives It is produced by the condensation reaction of acetone and phenol in the presence of hydrogen chloride In the process to produce Bisphenol A acetone and excess phenol are reacted by condensation in an ionexchange resincatalyzed reactor system to produce Bisphenol A water and various byproducts Distillation removes water and unreacted acetone from the reactor effluent Acetone and lights are adsorbed into phenol in the light ends adsorber to produce a recycle acetone stream The bot toms from the distillation column is sent to the crystallization feed preconcentrator which distills phenol and concentrates the Bisphenol A to a level suitable for crystallization which is then sepa rated from byproducts in a solvent crystallization and recovery system to produce the adduct of Bisphenol A and phenol The mother liquor from the purification system is distilled in the solvent recovery column to recover dissolved solvent after which the solventfree mother liquor stream is recycled to the reaction system A purge from the mother liquor is sent to the purge recovery system along with the recovered process water to recover phenol The recovered purified adduct is processed in a finishing system to remove phenol from product and the resulting molten Bisphenol A is solidified produce a product prill suitable for sales 736 addition of orGanic acids Isopropyl acetate is produced by the catalytic vaporphase addition of acetic acid to propylene A high yield of the ester can be produced in high yield approximately 99 ww CH CH CH CH COOH CH COOCH CH 2 2 3 3 3 2 Isopropyl acetate is used as a solvent for coatings and printing inks It is generally interchangeable with methyl ethyl ketone CH3CH2COCH3 and ethyl acetate CH3CO2C2H5 Isopropyl acrylate is produced by an acidcatalyzed addition reaction of acrylic acid to propyl ene The reaction occurs in the liquid phase at about 100C CH CH CH CH CHCOOH CH CHCOOCH CH 2 2 2 2 3 2 Due to unsaturation of the ester it can be polymerized and used as a plasticizer 737 hydroformylation The reaction of propylene with carbon monoxide and hydrogen produces nbutyraldehyde as the main product Isobutyraldehyde is a byproduct 2CH CH CH 2CO 2H CH CH CH CHO CH CHCHO 3 2 2 3 2 2 Butyraldehyde 3 2 Isobutyraldehyde n 303 Chemicals from Olefin Hydrocarbons Butyraldehyde derivatives are usually hydrogenated to the corresponding alcohols They are also intermediate species for other chemicals For example nButanol CH3CH2CH2CH2OH is produced by the catalytic hydrogenation of nbutyraldehyde The reaction is carried out at relatively high pressures The yield is high CH CH CH CHO H CH CH CH CH OH 3 2 2 2 3 2 2 2 nButanol is primarily used as a solvent or as an esterifying agent The ester with acrylic acid for example is used in the paint adhesive and plastic industries An alternative route for nbutanol is through the aldol condensation of acetaldehyde Chapter 7 2Ethylhexanol CH3CH2CH2CH2CHC2H5CH2OH is a colorless liquid soluble in many organic solvents It is one of the chemicals used for producing polyvinyl chloride plasticizers by reacting with phthalic acid the product is di2ethylhexyl phthalate 2Ethylhexanol is produced by the aldol condensation of butyraldehyde The reaction occurs in presence of aqueous caustic soda and produces 2ethyl3hydroxyhexanal The aldehyde is then dehydrated and hydrogenated to 2ethylhexanol 738 disProPortionation Olefin derivatives could be catalytically converted into shorter and longerchain olefin derivatives through a catalytic disproportionation reaction For example propylene will be disproportion ate over different catalysts yielding ethylene and butylenes Approximate reaction conditions are 400C 750F and 120 psi 2CH CH CH CH CH CH CH CHCH 3 2 2 2 3 3 The utility with respect to propylene is to convert excess propylene to olefin derivatives of greater economic value 739 alkylation Propylene could be used as an alkylating agent for aromatics An important reaction with great commercial use is the alkylation of benzene to cumene for phenol and acetone production 74 CHEMICALS FROM C4 OLEFINS The C4 olefin derivatives produce fewer chemicals than either ethylene or propylene However C4 olefin derivatives and diolefin derivatives are precursors for some significant bigvolume chemi cals and polymers such as methyltbutyl ether MTBE adiponitrile 14butanediol and poly butadiene Butadiene is not only the most important monomer for synthetic rubber production but also a chemical intermediate with a high potential for producing useful compounds such as 304 Handbook of Petrochemical Processes sulfolane by reaction with SO2 1 4butanediol by acetoxylationhydrogenation and chloroprene by chlorinationdehydrochlorination Two butylenes 1butylene CH3CH2CHCH2 and 2butylene CH3CHCHCH3 are industrially significant The latter has end uses in the production of butyl rubber and polybutylene plastics On the other hand 1butylene is used in the production of 13butadiene CH2CHCHCH2 for the synthetic rubber industry Butylenes arise primarily from refinery gases or from the cracking of other fractions of crude oil 741 Butylene Butylene also known as butene C4H8 is a series of alkene derivatives and the word butylene butene may refer to any of the individual compounds or to a mixture of them They are colorless gases that are present in crude oil as a minor constituent in quantities that are too small for viable extraction Butylene is therefore obtained by catalytic cracking of longchain higher molecular weight hydrocarbon derivatives that are produced during crude oil refining Cracking produces a mixture of products and the butylene is extracted from this by fractional distillation Butylenes butene derivatives are byproducts of refinery cracking processes and steam cracking units for ethylene production Dehydrogenation of butanes is a second source of butylenes However this source is becoming more important because isobutylene a butylene isomer is currently highly demanded for the production of oxygenates as gasoline additives The three isomers constituting nbutylenes are 1butylene cis2butylene and trans2butylene This gas mixture is usually obtained from the C4 olefin fraction of catalytic processes and steam cracking processes after separation of isobutylene Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The mixture of isomers may be used directly for reac tions that are common for the three isomers and produce the same intermediates and hence the same products Alternatively the mixture may be separated into two streams one constituted of nbutylene 1butylene Table 76 and the other of cis 2butylene and trans2butylene mixture Table 77 Each stream produces specific chemicals Approximately 70 of nbutylene is used as a comonomer with ethylene to produce linear lowdensity polyethylene LLDPE Another use of nbutylene is for the synthesis of butylene oxide The rest is used with the 2butylenes to produce other chemicals nButylene could also be isomerized to isobutylene CH CH CH CH CH C CH 3 2 2 3 2 2 1Butylene cis2Butylene trans2Butylene 305 Chemicals from Olefin Hydrocarbons The industrial reactions involving cis2butylene and trans2butylene are the same and produce the same products There are also addition reactions where both 1butylene and 2butylene give the same product For this reason it is economically feasible to isomerize Ibutylene to 2butylene cis and trans and then separate the mixture The isomerization reaction yields two streams one of 2butylene and the other of isobutylene which are separated by fractional distillation each with a purity of 8090 An alternative method for separating the butylenes is by extracting isobutylene due to its higher reactivity in cold sulfuric acid which polymerizes it to di and triisobutylene The dimer and tri mer of isobutylene have highoctane ratings and are added to the gasoline pool Butylene concentrates are mixtures of 1butylene cis2butylene and trans2butylene2 and sometimes isobutylene 2methyl propylene C4H8 TABLE 76 Properties of nButylene Chemical formula C4H8 Molar mass 5611 gmol Appearance Colorless gas Odor Slightly aromatic Density 062 gcm3 Melting point 1853C 3015F 878K Boiling point 647C 2035F 26668K Solubility in water 0221 g100 mL Solubility Soluble in alcohol ether benzene Refractive index nD 13962 TABLE 77 Properties of 2Butylene cis2Butylene Plus trans2Butylene Chemical formula C4H8 Molar mass 56106 gmol Density 0641 gmL cis at 37C 0626 gmL trans at 09C Melting point 1389C cis 1055C trans Boiling point 37C cis 09C trans 1Butylene cis2Butylene trans2Butylene 306 Handbook of Petrochemical Processes These products are stored as liquids at ambient temperatures and moderate pressures Various impurities such as butane butadiene and the C5 hydrocarbon derivatives are generally found in butylene concentrates Virtually all of the butylene concentrates are used as a feedstock for either i an alkylation plant where isobutane and butylenes are reacted in the presence of either sulfuric acid or hydrofluoric acid to form a mixture of C7 to C9 paraffins used in gasoline or ii butylene dehydrogenation reactors for butadiene production The major quality criterion for butylene concentrates is the distribution of butylenes which is measured along with other components by gas chromatography Trace impurities generally checked are sulfurcontaining derivatives chlorinecontaining derivatives and acetylene derivatives These impurities are known catalyst poisons that interfere with to the point of destroy catalyst activity or at best become unwanted impurities in the final product When butylene concentrates are used as the feedstock for an alkylation unit the diolefin content becomes important because of the potential for further reaction to produce unwanted higher molecular weight products Speight 2014 2017 The above sections have focused on natural gas and refinery gases which are primarily produced in petroleum refineries as the lowboiling fractions of distillation and cracking processes or in gas plants that separate natural gas and natural gas liquids Substances in both categories have high vapor pressure and moderate to high water solubility The gas mixtures are composed primarily of paraf finic and olefinic hydrocarbon derivatives mostly containing one to six carbon atoms C1 to C6 or in some cases to C8 Some of the mixtures may contain varying amounts of other components includ ing hydrogen nitrogen and carbon dioxide The refinery gas streams also contain olefin constituents that are produced by various cracking processes and some streams also contain varying amounts of other chemicals including ammonia hydrogen nitrogen hydrogen sulfide mercaptans carbon mon oxide carbon dioxide 13butadiene andor benzene There are however two other gas streams that must be given consideration here because of their increasing importance as fuel gases and these are i biomethane which falls into the category of biogas and ii landfill gas which may also be include in the biogas category but for the purpose of this text is included as a separate gas stream 7411 Oxidation The mixture of nbutylenes 1butylene and the 2butylene isomers can be oxidized to different products depending on the reaction conditions and the catalyst The three commercially important oxidation products are acetic acid maleic anhydride and methyl ethyl ketone Due to the presence of a terminal double bond in 1butylene oxidation of this isomer via a chlorohydrination route is similar to that used for propylene Currently the major route for obtaining acetic acid ethanoic acid CH3CO2H is the carbonyl ation of methanol Chapter 5 It may also be produced by the catalyzed oxidation of nbutane The production of acetic acid from nbutylene mixture is a vaporphase catalytic process The oxidation reaction occurs at approximately 270C 520F over a titanium vanadate catalyst A 70 acetic acid yield has been reported The major byproducts are carbon oxides 25 and maleic anhydride 3 CH CH CHCH 2O 2CH COOH 3 3 2 3 Acetic acid may also be produced by reacting a mixture of nbutylenes with acetic acid over an ion exchange resin The formed secbutyl acetate is then oxidized to yield three moles of acetic acid CH CH CHCH CH CH CH CH 2CH COOH 2CH COCH CH CH CH 3 3 3 2 2 3 3 3 2 3 secButyl acetate isobutylene 2methylpropylene 2methyl propylene 307 Chemicals from Olefin Hydrocarbons 2CH COCH CH CH CH 2O 3CH COOH 3 3 2 3 2 3 The reaction conditions are approximately 100C120C 212F248F and 220375 psi The oxi dation step is noncatalytic and occurs at approximately 200C 390F and 900 psi An acetic acid yield of 58 could be obtained Byproducts are formic acid 6 higherboiling compounds 3 and carbon oxides 28 Acetic acid is a versatile reagent It is an important esterifying agent for the manufacture of cel lulose acetate for acetate fibers and lacquers vinyl acetate monomer and ethyl and butyl acetates Acetic acid is used to produce pharmaceuticals insecticides and dyes It is also a precursor for chloroacetic acid and acetic anhydride The 1994 US production of acetic acid was approximately 4 billion pounds Acetic anhydride acetyl oxide CH3COOCOCH3 is a liquid with a strong offensive odor It is an irritating and corrosive chemical that must be handled with care The production of acetic anhydride from acetic acid occurs via the intermediate formation of ketene CH2CO where one mole of acetic acid loses one mole of water The ketene further reacts with one mole acetic acid yielding acetic anhydride CH C O CH CO H CH COOCOCH 2 3 2 3 3 Acetic anhydride is mainly used to make acetic esters and acetyl salicylic acid aspirin Methyl ethyl ketone 2butanone CH3CH2COCH3 is a colorless liquid similar to acetone but its boiling point is higher 795C 175F The production of methyl ethyl ketone from nbutylene isomers is a liquidphase oxidation process similar to that used to produce acetaldehyde from eth ylene using a Wackertype catalyst PdC12CuC12 The reaction conditions are similar to those for ethylene The yield of methyl ketone is in the order of 88 ww Methyl ethyl ketone may also be produced by the catalyzed dehydrogenation of secbutanol over zinc oxide or brass at about 500C The yield from this process is approximately 95 Methyl ethyl ketone is used mainly as a solvent in vinyl and acrylic coatings in nitrocellulose lacquers and in adhesives It is a selective solvent in dewaxing lubricating oils where it dissolves the oil and leaves out the wax Methyl ethyl ketone is also used to synthesize various compounds such as methyl ethyl ketone peroxide a polymerization catalyst used to form acrylic and polyester polymers and methyl pentynol by reacting with acetylene Methyl pentynol is a solvent for polyamides a corrosion inhibi tor and an ingredient in the synthesis of hypnotics Maleic anhydride a solid compound that melts at 53C 127F is soluble in water alcohol and acetone but insoluble in hydrocarbon solvents The production of maleic anhydride from nbutylenes is a catalyzed reaction occurring at approximately 400C440C 750F825F and 3060 psi A special catalyst constituted of an oxide mixture of molybdenum vanadium and phosphorous may be used Approximately 45 yield of maleic anhydride could be obtained from this route Other routes to maleic anhydride are the oxidation of nbutanea major source for this compoundand the oxidation of benzene Maleic anhydride 308 Handbook of Petrochemical Processes Maleic anhydride is important as a chemical because it polymerizes with other monomers while retaining the double bond as in unsaturated polyester resins These resins which represent the largest end use of maleic anhydride are employed primarily in fiberreinforced plastics for the construction marine and transportation industries Maleic anhydride can also modify drying oils such as linseed and sunflower As an intermediate maleic anhydride is used to produce malathion an insecticide In addition maleic anhydride is used in the manufacture of maleic hydrazide a plant growth regulator Maleic anhydride is also a precursor for 14butanediol through an esterification route followed by hydrogenation In this process excess ethyl alcohol esterifies maleic anhydride to monoethyl maleate In a second step the monoester catalytically esterifies to the diester Excess ethanol and water are then removed by distillation Selectivity to the coproducts is high but the ratios of the coproducts may be controlled with appropriate reactor operating conditions Biomass can also be employed as the starting material from which sugar derivatives are pro duced followed by subsequent acidcatalyzed reactions to produce levulinic acid can be hydroge nated to yield 2methyl tetrahydrofuran Khoo et al 2015 Butylene oxide like propylene oxide is produced by the chlorohydrination of 1butylene with HOCl followed by epoxidation Butylene oxide may be hydrolyzed to butylene glycol which is used to make plasticizers 12Butylene oxide is a stabilizer for chlorinated solvents and also an interme diate in organic synthesis such as in surfactants and pharmaceuticals 7412 Hydration secButanol 2butanol secbutyl alcohol CH3CHOHCH2CH3 is a liquid with a strong character istic odor Its normal boiling point is 995C 211F which is near to waters The alcohol is soluble Malathion Maleic hydrazide 309 Chemicals from Olefin Hydrocarbons in water but less so than isopropyl and ethyl alcohols secButanol is produced by a reaction of sul furic acid with a mixture of nbutylenes followed by hydrolysis Both 1butylene and cis2butylene and trans2butylene yield the same carbocation intermediate which further reacts with the sulfuric acid H2SO4 or solutions to produce a sulfate mixture The sulfation reaction occurs in the liquid phase at approximately 35C 95F An 85 ww alcohol yield could be realized The reaction is similar to the sulfation of ethylene or propylene and results in a mixture of secbutyl hydrogen sulfate and disecbutyl sulfate The mixture is further hydrolyzed to secbutanol and sulfuric acid The only important byproduct is disecbutyl ether which may be recovered The major use of secbutanol is to produce methyl ethyl ketone by dehy drogenation as mentioned earlier 2Butanol is also used as a solvent a paint remover and an inter mediate in organic synthesis 7413 Isomerization nButylene could be isomerized to isobutylene using Shell FER catalyst which is active and selec tive The nbutylene mixture from the steam cracking unit or from the fluid catalytic cracking unit after removal of C5 olefin derivatives via selective hydrogenation step passes to the isomerization unit It has been proposed that after the formation of a butyl carbocation a cyclopropyl carbocation is formed which gives a primary carbenium ion that produces isobutylene By way of explanation a carbenium ion is a positive ion with the structure RRRC that is it is a chemical species with a trivalent carbon that bears a formal positive charge Carbenium ions are generally highly reactive due to having an incomplete octet of electrons However certain carbenium ions such as the tropylium ion are relatively stable due to the positive charge being delocalized between the carbon atoms By way of further explanation the tropylium ion is an aromatic chemical species with a formula of C7H7 The name derives from the molecule tropine itself named for the molecule atropine The ion can be produced from cycloheptatriene and bromine Salts of the tropylium cation can be stable In the older literature the name carbonium ion was used for this class of chemical species but now the name carbonium ion refers exclusively to the family of carbocations in which the charged carbon is pentavalent 7414 Metathesis Metathesis is a catalyzed reaction that converts two olefin molecules into two different olefin deriva tives It is an important reaction for which many mechanistic approaches have been proposed by scientists working in the fields of homogenous catalysis and polymerization One approach is the formation of a fluxional fivemembered metallocycle Another approach is a stepwise mechanism that involves the initial formation of a metal carbene followed by the formation of a fourmembered metallocycle species Olefin metatheses are equilibrium reactions among the tworeactant and twoproduct olefin mol ecules If chemists design the reaction so that one product is ethylene for example they can shift The Tropylium ion 310 Handbook of Petrochemical Processes the equilibrium by removing it from the reaction medium Because of the statistical nature of the metathesis reaction the equilibrium is essentially a function of the ratio of the reactants and the temperature For an equimolar mixture of ethylene and 2butylene at 350C 660F the maximum conversion to propylene is 63 Higher conversions require recycling unreacted butylenes after fractionation This reaction was first used to produce 2butylene and ethylene from propylene The reverse reaction is used to prepare polymer grade propylene from 2butylene and ethylene CH CH CH CH CH 2CH CH CH 3 2 2 2 3 2 The metathetic reaction occurs in the gas phase at relatively high temperatures 150C350C 300F660F with molybdenum or tungstensupported catalysts or at low temperature 250C 480F with rheniumbased catalyst in either liquid or gas phase The liquidphase process gives a better conversion Equilibrium conversion in the range of 5565 could be realized depending on the reaction temperature In this process the C4 feedstock is mainly composed of 2butylene1butylene does not favor this reaction but reacts differently with olefin derivatives producing metathetic byproducts The reaction between 1butylene and 2butylene for example produces propylene and 2pentylene The amount of 2pentylene depends on the ratio of 1butylene in the feedstock 3Hexene is also a byproduct from the reaction of two butylene molecules ethylene is also formed during this reaction 7415 Oligomerization The 2butylene cis and trans isomers after separation of 1butylene can be oligomerized in the liquid phase on a heterogeneous catalyst system to yield mainly C8 olefin derivatives and C12 ole fin derivatives The reaction is exothermic and requires a multitubular carbon steel reactor The exothermic heat is absorbed by water circulating around the reactor shell Either a singlestage or a twostage system is used The process can be made to produce either more linear or more branched oligomers Linear oligomers are used to produce nonyl alcohols for plasticizers alkyl phenols for surfactants and tridecyl alcohols for detergent intermediates Branched oligomers are valuable gasoline components 742 isoButylene Isobutylene CH2CCH32 is a reactive C4 olefin Table 78 Until recently almost all isobutylene was obtained as a byproduct with other C4 hydrocarbons from different cracking processes It was mainly used to produce alkylates for the gasoline pool A small portion was used to produce chemicals such as isoprene and diisobutylene However increasing demand for oxygenates from isobutylene has called for other sources nButane is currently used as a precursor for isobutylene The first step is to isomerize nbutane to isobutane then dehydrogenate it to isobutylene This serves the dual purpose of using excess nbutane that must be removed from gasolines due to new rules governing gasoline vapor pressure TABLE 78 Properties of isobutylene Chemical formula C4H8 Molar mass 56106 gmol Appearance Colorless gas Density 05879 gcm3 liquid Melting point 1403C 2205F 1328K Boiling point 69C 196F 2662K Solubility in water Insoluble 311 Chemicals from Olefin Hydrocarbons and producing the desired isobutylene Currently the major use of isobutylene is to produce methyl tbutyl ether CH33COCH3 Methyl tertbutyl ether is a colorless liquid with a distinctive anestheticlike odor Vapors are heavier than air and narcotic This ether has a boiling point 55C 131F with a flash point of 8C 18F it is less dense than water and miscible in water 7421 Oxidation Much like the oxidation of propylene which produces acrolein and acrylic acid the direct oxi dation of isobutylene produces methacrolein and methacrylic acid The catalyzed oxidation reac tion occurs in two steps due to the different oxidation characteristics of isobutylene an olefin and methacrolein an unsaturated aldehyde In the first step isobutylene is oxidized to methac rolein CH2CCH3CHO over a molybdenum oxidebased catalyst in a temperature range of 350C400C 650F750F The process pressures are a little above atmospheric pressure on the order of 1525 psi In the second step methacrolein is oxidized to methacrylic acid at a relatively lower temperature range of 250C350C 480F650F A molybdenum supported compound with specific promoters catalyzes the oxidation Methacrylic acid CH2CCH3COOH is a carboxylic acid that exists as a colorless viscous liquid is with an acrid unpleasant odor It is soluble in warm water and miscible with most organic solvents Methacrylic acid is produced industrially on a large scale as a precursor to it is the ester derivatives such as the methyl methacrylate monomer leading to polymethyl methacrylate The methacrylates have numerous uses most notably in the manufacture of polymers with trade names such as Lucite and Plexiglas Methacrylic acid and methacrylates are also produced by the hydrocyanation of acetone followed by hydrolysis and esterification Chapter 8 Ammoxidation of isobutylene to produce methacryloni trile is a similar reaction to ammoxidation of propylene to acrylonitrile 7422 Epoxidation Isobutylene oxide is produced in a way similar to propylene oxide and butylene oxide by a chloro hydrination route followed by reaction with CaOH2 Direct catalytic liquidphase oxidation using stoichiometric amounts of thallium acetate catalyst in aqueous acetic acid solution has been reported An isobutylene oxide yield of on the order of 82 ww is possible Direct noncatalytic liquidphase oxidation of isobutylene to isobutylene oxide gave low yield 287 plus a variety of oxidation products such as acetone tbutyl alcohol TBA and isobutylene glycol Hydrolysis of isobutylene oxide in the presence of an acid produces isobutylene glycol Isobutylene glycol may also be produced by a direct catalyzed liquidphase oxidation of isobu tylene with oxygen in presence of water Methyltbutyl ether Isobutylene oxide 312 Handbook of Petrochemical Processes 2CH C CH CH O 2H O CH C CH OH CH OH 3 3 2 2 2 3 3 2 The catalyst is similar to the Wackercatalyst system used for the oxidation of ethylene to acetalde hyde Instead of PdCl2CuCl2 used with ethylene a TlCl3CuCl2 catalyst is employed 7423 Addition of Alcohols The reaction between isobutylene methyl alcohol and ethyl alcohol is an addition reaction cata lyzed by a heterogeneous sulfonated polystyrene resin When methanol is used a 98 yield of methyltbutyl ether is obtained Ethyltbutyl ether ETBE is also produced by the reaction of ethanol and isobutylene under similar conditions with a heterogeneous acidic ionexchange resin catalyst similar to that with methyltbutyl ether 7424 Hydration The acidcatalyzed hydration of isobutylene produces tbutyl alcohol The reaction occurs in the liquid phase in the presence of 5065 sulfuric acid at mild temperatures 10C30C 50F86F TBA is used as a chemical intermediate because a tertiary butyl carbocation forms easily It is also used as a solvent in pharmaceutical formulations a paint remover and a highoctane gasoline additive The alcohol is a major byproduct from the synthesis of propylene oxide using tertiary butyl hydroperoxide Surplus tbutyl alcohol could be used to synthesize highly pure isobutylene by a dehydration step CH COH CH C CH H O 3 3 3 2 2 2 7425 Carbonylation The addition of carbon monoxide to isobutylene under high pressures and in the presence of an acid produces a carbon monoxideolefin complex an acyl carbocation Hydrolysis of the complex at lower pressures yields trimethyl acetic acid also known as neopentane acid CH33CCOOH In the process isobutene is hydrocarboxylated by means of the Koch reaction CH C CH CO H O CH CCO H 3 2 2 2 3 3 2 The reaction requires an acid catalyst such as hydrogen fluoridetertbutyl alcohol or isobutyl alcohol can also be used in place of isobutene The reaction is a special case of hydrocarboxylation reaction that does not rely on metal catalysts but instead the process is catalyzed by strong acids such as sulfuric acid or the combination of phosphoric acid and boron trifluoride Trimethyl acetic acid is an intermediate and an esterifying agent used when a stable neo structure is needed This colorless odiferous acid is solid at room temperature A common abbreviation for the pivalyl or pivaloyl group tBuCO is piv and for pivalic acid tBuCOOH is PivOH 7426 Dimerization A dimerization reaction is an addition reaction in which two molecules of the same compound react with each other to give the adduct The reaction can be represented very simply as A A A2 In this reaction A A are separate molecules and A2 is the dimer Isobutylene could be dimerized in the presence of an acid catalyst to diisobutylene The product is a mixture of diisobutylene isomers which are used as alkylating agents in the plasticizer industry and as a lube oil additive dimerization of olefin derivatives is noted in Chapter 3 313 Chemicals from Olefin Hydrocarbons 75 CHEMICALS FROM DIOLEFINS Dienes are aliphatic compounds having two double bonds When the double bonds are separated by only one single bond the compound is a conjugated diene conjugated diolefin Nonconjugated diolefin derivatives have the double bonds separated isolated by more than one single bond This latter class is of little industrial importance Each double bond in the compound behaves indepen dently and reacts as if the other is not present Examples of nonconjugated dienes are 14pentadiene and 14cyclohexadiene Examples of conjugated dienes are 13butadiene and 13cyclohexadiene Butadiene CH2CHCHCH2 is a diolefin hydrocarbon derivative with high potential in the chemical industry Butadiene is a colorless gas that is insoluble in water but soluble in alcohol and which can be liquefied easily under pressure Table 79 This reactive compound polymerizes readily in the presence of free radical initiators Butadiene 13Butadiene CH2CHCHCH2 the simplest conjugated diene is a colorless gas that is easily condensed to a liquid and is important as a monomer in the production of synthetic rubber An important difference between conjugated and nonconjugated dienes is that the former com pounds can react with reagents such as chlorine yielding 12 and 14addition products For exam ple the reaction between chlorine and 13butadiene produces a mixture of 14dichloro2butylene and 34dichloro1butylene Butadiene is mainly obtained as a byproduct from the steam cracking of hydrocarbon derivatives and from catalytic cracking These two sources account for over 90 of butadiene demand The remainder comes from dehydrogenation of nbutane or nbutylene streams Chapter 3 Butadiene is easily polymerized and copolymerized with other monomers It reacts by addition to other reagents such as chlorine hydrocyanic acid and sulfur dioxide producing chemicals of great commercial value Butadiene is obtained mainly as a coproduct with other low molecular weight olefin derivatives from steam cracking units for ethylene production Other sources of butadiene are the catalytic dehydrogenation of butanes and butylenes and dehydration of 14butanediol Butadiene is a col orless gas with a mild aromatic odor Its specific gravity is 06211 at 20C 68F and its boiling temperature is 44C 241F 751 chemicals from Butadiene Butadiene is by far the most important monomer for synthetic rubber production It can be polymer ized to polybutadiene or copolymerized with styrene to styrenebutadiene rubber often referred to as SBR Butadiene is an important intermediate for the synthesis of many chemicals such as hexa methylenediamine and adipic acid Both are monomers for producing nylon Chloroprene is another butadiene derivative for the synthesis of neoprene rubber TABLE 79 Properties of Butadiene Chemical formula C4H6 Molar mass 540916 gmol Appearance Colorless gas or refrigerated liquid Odor Mildly aromatic or gasolinelike Density 06149 gcm3 at 25C solid 064 gcm3 at 6C liquid Melting point 1089C 1640F 1642K Boiling point 44C 241F 2688K Solubility in water 13 gL at 5C 735 mgL at 20 Solubility Very soluble in acetone soluble in ether ethanol Vapor pressure 24 atm 20C Refractive indexnD 14292 314 Handbook of Petrochemical Processes When polymerizing dienes for synthetic rubber production coordination catalysts are used to direct the reaction to yield predominantly 14addition polymers Chapter 11 discusses addition polymerization The following reviews some of the physical and chemical properties of butadiene and isoprene 7511 Adiponitrile Adiponitrile a colorless liquid is slightly soluble in water but soluble in alcohol The main use of adiponitrile is to make nylon 66 The production of adiponitrile from butadiene starts by a free rad ical chlorination which produces a mixture of 14dichloro2butylene and 34dichlorolbutylene 2CH CHCH CH 2Cl ClCH CH CHCH Cl CH CHCHC1CH Cl 2 2 2 2 2 2 2 The vaporphase chlorination reaction occurs at approximately 200C300C 390F570F The dichlorobutylene mixture is then treated with sodium cyanide NaCN or with hydrogen cyanide HCN in presence of copper cyanide The product 14dicyano2butylene is obtained in high yield because allylic rearrangement to the more thermodynamically stable isomer occurs during the cya nation reaction ClCH CH CHCH Cl CH CHCHClCH Cl 4NaCN 2NCCH CH CHCH CN 4NaCl 2 2 2 2 2 2 The dicyano compound is then hydrogenated over a platinum catalyst to adiponitrile NCCH CH CHCH CN H NC CH CN 2 2 2 2 4 Adiponitrile Adiponitrile may also be produced by the electrodimerization of acrylonitrile or by the reaction of ammonia with adipic acid followed by twostep dehydration reactions 7512 Hexamethylenediamine Hexamethylenediamine also called 16diaminohexane and 16hexanediamine also known as hexamethylenediamine H2NCH26NH2 is a colorless solid soluble in both water and alcohol It is the second monomer used to produce nylon 66 with adipic acid or its esters The main route for the production of hexamethylene diamine is the liquidphase catalyzed hydrogenation of adiponitrile NC CH CN 4H H N CH NH 2 4 2 2 2 6 2 The reaction conditions are approximately 200C 390F and 450 psi over a cobaltbased catalyst 7513 Adipic Acid Adipic acid HOOCCH24COOH hexanedioic acid is an important dicarboxylic acid It exists as a white crystalline powder and is used mainly as a precursor for the production of nylon Adipic acid may be produced by a liquidphase catalytic carbonylation of butadiene A catalyst of rhodium dichloride RhCl2 and methyl iodide CH3I is used at approximately 220C 430F and 1100 psi Adipic acid yield is about 49 Both αglutaric acid 25 and valeric acid 26 are coproduced CH CHCH CH 2CO 2H O HOOC CH COOH 2 2 2 2 4 Another route to adipic acid occurs via a sequential carbonylation isomerization hydroformylation reactions 315 Chemicals from Olefin Hydrocarbons CH CHCH CH CO CH OH CH CH CH CH COCH 2 2 3 3 2 2 CH CH CHCH COCH 2CO 3H CH C CH COCH H O 3 2 3 2 3 2 4 3 2 CH C CH COCH O HOC CH COCH HOOC CH COOH 3 2 4 3 2 2 4 3 2 4 The main process for obtaining adipic acid is the catalyzed oxidation of cyclohexane Chapter 10 Adipic acid is also produced from a mixture of cyclohexanol and cyclohexanone KA oil the abbreviation of ketonealcohol oil The KA oil is oxidized with nitric acid to yield adipic acid via a multistep pathway In the initial reaction the cyclohexanol is converted to the ketone releasing nitrous acid HOC H HNO OC CH HNO H O 6 11 3 2 5 2 2 Among its many reactions the cyclohexanone is nitrosated followed by scission of the carbon carbon CC bond HNO HNO NO NO H O 2 3 3 2 OC H NO OC H 2NO H 6 10 6 9 Related processes start from cyclohexanol which is obtained by the hydrogenation of phenol 7514 Butanediol The production of 14butanediol HOCH2CH2CH2CH2OH from propylene via the carbonylation of allyl acetate 14Butanediol from maleic anhydride is discussed later in this chapter An alterna tive route for the diol is through the acetoxylation of butadiene with acetic acid followed by hydro genation and hydrolysis The first step is the liquidphase addition of acetic acid to butadiene The acetoxylation reaction occurs at approximately 80C 176F and 400 psi over a PdTe catalyst system The reaction favors the 14addition product l4diacetoxy2butylene Hydrogenation of diacetoxy butylene at 80C 176F and 900 psi over a NiZn catalyst yields 14diacetoxybutane The latter compound is hydro lyzed to 14butanediol and acetic acid The acetic acid is then recovered and recycled Butanediol is mainly used for the production of thermoplastic polyesters 7515 Chloroprene Chloroprene 2chloro 13butadiene CH2CHCClCH2 a conjugated nonhydrocarbon diolefin is a liquid that boils at 592C 1386F and while only slightly soluble in water it is soluble in alco hol The main use of chloroprene is to polymerize it to neoprene rubber Butadiene produces chloroprene through a hightemperature chlorination to a mixture of dichlorobutylene isomers which is isomerized to 34dichloro lbutylene This compound is then dehydrochlorinated to chloroprene Sulfolane tetramethylene sulfone is produced by the reaction of butadiene and sulfur dioxide followed by hydrogenation The optimum temperature for highest sulfolene yield is approximately 75C 167F At approxi mately 125C 257F sulfolene decomposes to butadiene and sulfur dioxide This simple method Sulfolene Sulfolane 316 Handbook of Petrochemical Processes could be used to separate butadiene from a mixture of C4 olefin derivatives because the olefin derivatives do not react with sulfur dioxide Sulfolane is a watersoluble biodegradable and highly polar compound valued for its solvent properties It can be used for the delignification of wood polymerization and fiber spinning elec troplating bathes and as a solvent for selectively extracting aromatics from reformates and coke oven products 7516 Cyclic Oligomers Butadiene could be oligomerized to cyclic dienes and trienes using certain transition metal com plexes Commercially a mixture of titanium tetrachloride TiCl4 and Al2Cl3C2H5 is used that gives predominantly cis trans trans159cyclododecatriene along with approximately 5 of the dimer 15cyclooctadiene24 159Cyclododecatriene is a precursor for dodecanedioic acid through a hydrogenation step followed by oxidation The diacid is a monomer for the production of nylon 612 Cyclododecane from cyclododecatriene may also be converted to the C12 lactam which is polymerized to nylon12 752 isoPrene Isoprene 2methyl13butadiene CH2CCH3CHCH2 is a colorless liquid with a boiling point of 341C 934F The compound is soluble in alcohol but not in water Isoprene is the second important conjugated diene for synthetic rubber production The main source for isoprene is the dehydrogenation of C5 olefin derivatives tertiary amylene derivatives obtained by the extraction of a C5 fraction from catalytic cracking units It can also be produced through several synthetic routes using reactive chemicals such as isobutylene formaldehyde and propylene The main use of isoprene is the production of polyisoprene It is also a comonomer with isobutylene for butyl rubber production The simplest method of isoprene production involves the extraction of the isoprene from the C5 fraction of liquid petroleum pyrolysis This fraction is produced as a byproduct in the production of ethylene and propylene In another process the twostep production of isoprene from isobutylene and formaldehyde isobutylene is condensed with formaldehyde in the presence of an acidic catalyst such as diluted sulfuric acid to form 44dimethyldioxane13 after which the dioxane derivative is decomposed into isoprene on a solid phosphate catalyst such as calcium phosphate In each of these steps there are multiple side reactions The selectivity of phosphate catalyst is increased by its continuous activation in the process by the introduction of small amounts of phosphoric acid vapor directly into the catalysis zone which leads to the formation of acidic phosphates on the surface of the calcium phosphate catalyst Ca PO H PO 3CaHPO 3 4 2 3 4 4 Also coke is deposited on the surface of the catalyst and the catalyst should be regenerated at 23 h intervals by burning off the coke in a stream of air mixed with steam at temperatures above 500C 930F 76 CHEMICALS FROM ACETYLENE Although not strictly an olefin by virtue of the presence of a triple bond acetylene HCCH is included here as a valuable source of petrochemical products because of the reactivity and the vari ety of product that can be produced from this alkyne Acetylene is the simplest member of alkyne hydrocarbon derivatives Table 710 and is the only petrochemical produced in significant quantity which contains a triple bond and is a major interme diate species but such compounds are not easily shipped and as a consequence are typically used at 317 Chemicals from Olefin Hydrocarbons or close to the point of origin Acetylene can be made by hydrolysis of calcium carbide produced in the electric furnace from calcium oxide CaO and carbon CaC 2H O HC CH Ca OH 2 2 2 An alternative method of manufacturing acetylene is by cracking methane 2CH HC CH 6H 4 2 This process produces only onethird of the methane input as acetylene the remainder being burned in the reactor Similar reactions employing heavier fractions of crude oil are being used increasingly since the availability or necessity of heavy crude oil as a refinery feedstock is increasing In the first half of the 20th century acetylene was the most important of all starting materials for organic synthesis Acetylene is a colorless combustible gas with a distinctive odor When acetylene is liquefied compressed heated or mixed with air it becomes highly explosive As a result special precautions are required during its production and handling The most common use of acetylene is as a raw material for the production of various organic chemicals including 14butanediol which is widely used in the preparation of polyurethane and polyester plastics The second most common use is as the fuel component in oxyacetylene welding and metal cutting Some commercially use ful acetylene compounds include acetylene black which is used in certain drycell batteries and acetylenic alcohols which are used in the synthesis of vitamins Acetylene was discovered in 1836 when Edmund Davy was experimenting with potassium car bide One of his chemical reactions produced a flammable gas which is now known as acetylene In 1859 acetylene was produced by striking and electric arc using carbon electrodes in an atmosphere of hydrogen Thus 2C H HC CH 2 The electric arc tore carbon atoms away from the electrodes and bonded them with hydrogen atoms to form acetylene molecules He called this gas carbonized hydrogen By the late 1800s a method had been developed for making acetylene by reacting calcium car bide with water This generated a controlled flow of acetylene that could be combusted in air to produce a brilliant white light Carbide lanterns were used by miners and carbide lamps were used for street illumination before the general availability of electric lights In 1897 Georges Claude and A Hess noted that acetylene gas could be safely stored by dissolving it in acetone Nils Dalen used this new method in 1905 to develop longburning automated marine and railroad signal lights In 1906 Dalen went on to develop an acetylene torch for welding and metal cutting TABLE 710 Properties of Acetylene Chemical formula C2H2 Molar mass 2604 gmol Appearance Colorless gas Odor Odorless Density 1097 gL 1097 kgm3 Melting point 808C 1134F 1923K Triple point at 127 atm Sublimation conditions 84C 119F 189K 1 atm Solubility in water Slightly soluble Vapor pressure 442 atm 20C 318 Handbook of Petrochemical Processes Currently there are several routes to acetylene Hydrocarbon derivatives are the major feed stocks either in the form of natural gas in partial oxidation processes or as byproducts in ethylene production However coal is becoming an everincreasing source of acetylene in countries with plentiful and cheap coal supplies such as China for the production of vinyl chloride and this source of lower cost acetylene may prove to be the impetus for returning acetylene to its place as a major chemical feedstock especially when the current variability especially the upward mobility of crude oil prices and improvements in the safety cost and environmental protection of the calcium carbide process for the production of acetylene The classic commercial route to acetylene first developed in the late 1800s is the calcium car bide route in which lime is reduced by carbon in the form of coke in an electric furnace to yield calcium carbide During this process a considerable amount of heat is produced which is removed to prevent the acetylene from exploding This reaction can occur via wet or dry processes depend ing on how much water is added to the reaction process The calcium carbonate is first converted into calcium oxide and the coal into coke The two are then reacted with each other to form calcium carbide and carbon monoxide CaO 3C CaC CO 2 The calcium carbide is then hydrolyzed to produce acetylene CaC 2H O C H Ca OH 2 2 2 2 2 Acetylene can also be manufactured by the partial oxidation partial combustion combustion of methane with oxygen The process employs a homogeneous gas phase hydrogen halide catalyst other than hydrogen fluoride to promote the pyrolytic oxidation of methane The homogeneous gas phase catalyst employed can also consist of a mixture of gaseous hydrogen halide and gaseous halogen or a halogen gas The electric arc or plasma pyrolysis of coal can also be used to produce acetylene The electric arc process involves a onemegawatt arc plasma reactor which utilizes a DC electric arc to generate and maintain a hydrogen plasma The coal is then fed into the reactor and is heated to a high tem perature as it passes through the plasma It is then partially gasified to yield acetylene hydrogen carbon monoxide hydrogen cyanide and several hydrocarbon derivatives Acetylene can also be produced as a byproduct of ethylene steam cracking The use of acetylene as a commodity feedstock decreased due to the competition of cheaper more readily accessible and workable olefin derivatives when these olefin derivatives were produced from lowcost petroleum products With the rising cost of crude oil natural gas and the associated olefin derivatives feed stocks such as naphtha ethane propane etc the olefin derivatives prices are no longer low enough to preclude the possibility of using acetylene Additionally regional shortages of these olefin deriva tives and their feedstocks have forced the search for alternate routes to the commodity chemicals Between 1960s and 1970s when worldwide acetylene production peaked it served as the pri mary feedstock for a wide variety of commodity and specialty chemicals Advances in olefin deriv atives technology concerns about acetylene safety but mostly loss of cost competitiveness reduced and effectively limited the importance of acetylene Now with the current rise in petroleum prices acetylene is finding a new place in the chemical industry Acetylene is the only petrochemical produced in significant quantity which contains a triple bond and is a major intermediate species The usefulness of acetylene is partly due to the variety of additional reactions which its triple bond undergoes and partly due to the fact that its weakly acidic hydrogen atoms are replaceable by reaction with strong bases to form acetylide salts However acetylene is not easily shipped and as a consequence its consumption is close to the point of origin However acetylene was largely replaced by olefin feedstocks such as ethylene and propylene because of its high cost of production and the safety issues of handling acetylene at high pressures 319 Chemicals from Olefin Hydrocarbons Its use has largely been eliminated except for the continued and in some instances growing pro duction of vinyl chloride monomer CH2CHCl 14butanediol HOCH2C2CH2CH2OH and car bon black Up until the 1970s acetylene was a basic chemical raw material used for the production of a wide range of chemicals Figure 74 In the presence of metal catalysts acetylene can react to yield a wide range of industrially signifi cant chemicals For example acetylene reacts with alcohol derivatives hydrogen cyanide hydrogen chloride or carboxylic acid derivatives to yield vinyl derivatives In addition acetylene reacts with carbonyl groups to yield ethynyl alcohols As an example acetylene reacts with formaldehyde to yield 14butynediol HCHO HC CH HOCH CC CH OH 2 2 14Butynediol is a precursor to 14butanediol HOCH2CH2CH2CH2OH and 2butylene14diol HOCH2CHCHCH2OH by hydrogenation It is also used in the manufacture of herbicides textile FIGURE 74 Chemicals from acetylene and end uses 320 Handbook of Petrochemical Processes additives corrosion inhibitors plasticizers synthetic resins and polyurethane derivatives It is also the major raw material used in the synthesis of vitamin B6 as well as for brightening preserving and inhibiting nickel plating 2Butylene14diol also reacts with a mixture of chlorine and hydro chloric acid to give mucochloric acid HO2CCClCClCHO Acetylene reacts with carbon monoxide to yield acrylic acid or in the presence of an alcohol derivative the product is an acrylic ester Acetylene will cyclize to produce benzene or cyclooctatetraene Under basic conditions at 50C80C 122F176F at 300375 psi acetylene reacts with iron pentacarbonyl to yield dihydroxybenzene of which there are three isomers Table 711 Fe CO 4HC CH 2H O 2C H OH FeCO 5 2 6 4 2 3 Acetylene is used as a special fuel gas oxyacetylene torches and as a chemical raw material In fact historically acetylene has been used to produce many important chemicals 1 Vinyl chloride monomer was first produced by reacting acetylene with hydrogen chloride Acetylenebased technology predominated until the early 1950s Due to the high energy input needed in the acetylenebased process and the hazards of handling acetylene the ethylenebased route has become the predominant one However the acetylenebased route does have its advantages such as countries where there is a shortage of ethylene cracker feedstock TABLE 711 The Isomers of Dihydroxybenzene Ortho Isomer Meta Isomer Para Isomer Catechol also called pyrocatechol 12benzenediol obenzenediol 12dihydroxybenzene odihydroxybenzene Resorcinol also called 13benzenediol mbenzenediol 13dihydroxybenzene mdihydroxybenzene resorcin Hydroquinone also called 14benzenediol pbenzenediol 14dihydroxybenzene pdihydroxybenzene 321 Chemicals from Olefin Hydrocarbons 2 Acrylonitrile Hydrogen cyanide added to acetylene produces acrylonitrile used as an intermediate in the production of nitrile rubbers acrylic fibers and insecticides 3 Vinyl Acetate Acetic acid added to acetylene forms vinyl acetate used as an intermediate in polymerized form for films and lacquers 4 Vinyl Ether Alcohol added to acetylene yields vinyl ether used as an anesthetic 5 Acetaldehyde Water added to acetylene produces acetaldehyde used as a solvent and fla voring in food cosmetics and perfumes 6 12Dichloroethane Chlorine added to acetylene forms 12dichloroethylene used pri marily as a feedstock for vinyl chloride monomer which in turn is the monomer for the widely used plastic polyvinyl chloride 7 14Butynediol Formaldehyde added to acetylene produces 14butynediol which is then hydrogenated to 14butanediol and used as a chain extender for polyurethane These res ins include urethane foams for cushioning material carpet underlay and bedding insula tion in refrigerated appliances and vehicles sealants caulking and adhesives 8 Acrylate Esters Acetylene reacts with carbon monoxide and alcohol forming acrylate esters used in the manufacture of Plexiglass and safety glasses 9 Polyacetylene Acetylene can polymerize forming polyacetylene The delocalized elec trons of the alternating single and double bonds between carbon atoms give polyacetylene its conductive properties Doping of polyacetylene makes this polymer a better conductor Polyacetylene is used in rechargeable batteries that could be used in electric cars and could also replace copper wires in aircraft because of the low density light weight 10 Polydiacetylene Polydiacetylene is also a polymer of the future It behaves as a photocon ductor and could be used for timetemperature indicators or monitoring of irradiation 11 In another aspect of acetylene chemistry tetrahydrofuran can be synthesized by the reac tion of formaldehyde with acetylene to make 2butyne14diol which is then hydrogenated and cyclized in two more steps to yield tetrahydrofuran Based on its availability its many uses and prospective uses acetylene is a feedstock for petrochem ical production that is worthy of consideration Acetylene is used as a special fuel gas oxyacetylene torches and as a chemical raw material REFERENCES Aitani A 2006 Propylene production In Encyclopedia of Chemical Processing S Lee Editor Taylor Francis New York pp 24612466 Buijink JKF Lange JP Bos ANR Horton AD and Niele FGM 2008 Propylene epoxidation via shells SMPO process 30 years of research and operation In Mechanisms in Homogeneous and Heterogeneous Epoxidation Catalysis ST Oyama Editor Elsevier BV Amsterdam 322 Handbook of Petrochemical Processes Fujiyama Y Redhwi H Aitani A Saeed R and Dean C September 26 2005 Demonstration plant for new FCC technology yields increased propylene Oil Gas Journal 6267 Gary JG Handwerk GE and Kaiser MJ 2007 Petroleum Refining Technology and Economics 5th Edition CRC Press Taylor Francis Group Boca Raton FL Hsu CS and Robinson PR Editors 2017 Handbook of Petroleum Technology Springer International Publishing AG Cham Khoo HH Wong LL Tan J Isoni V and Sharratt P 2015 Synthesis of 2methyl tetrahydrofuran from various lignocellulosic feedstocks Sustainability assessment via LCA Resource Conservation Recycling 95 174182 Kidnay AJ and Parrish WR 2006 Fundamentals of Natural Gas Processing CRC Press Taylor Francis Group Boca Raton FL Kohl AL and Nielsen RB 1997 Gas Purification Gulf Publishing Company Houston TX Kohl AL and Riesenfeld FC 1985 Gas Purification 4th Edition Gulf Publishing Company Houston TX Maadhah A Fujiyama Y Redhwi H AbulHamayel M Aitani A Saeed M and Dean C 2008 A new catalytic cracking process to maximize refinery propylene The Arabian Journal for Science and Engineering 331B 1728 Maddox RN Bhairi A Mains GJ and Shariat A 1985 Chapter 8 Olamine processes In Acid and Sour Gas Treating Processes SA Newman Editor Gulf Publishing Company Houston TX Mokhatab S Poe WA and Speight JG 2006 Handbook of Natural Gas Transmission and Processing Elsevier Amsterdam Newman SA 1985 Acid and Sour Gas Treating Processes Gulf Publishing Houston TX Parkash S 2003 Refining Processes Handbook Gulf Professional Publishing Elsevier Amsterdam Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG 2014 The Chemistry and Technology of Petroleum 4th Edition CRCTaylor and Francis Group Boca Raton FL Speight JG 2017 Handbook of Petroleum Refining CRC Press Taylor Francis Group Boca Raton FL 323 8 Chemicals from Aromatic Hydrocarbons 81 INTRODUCTION Aromatic compounds sometimes referred to as arenes are those compounds that contain one or more benzene rings or similar ring structures Table 81 March 1985 many of which occur in crude oil and crude oil products Parkash 2003 Gary et al 2007 Speight 2014 Hsu and Robinson 2017 Speight 2017 The majority of the aromatic compounds for petrochemical use are produced in various refinery streams and which are then separated into fractions of which the most significant constituents are benzene C6H6 methylbenzene or toluene C6H5CH3 and the dimethylbenzene TABLE 81 Representative SingleRing Aromatic Compounds 324 Handbook of Petrochemical Processes derivatives or xylene derivatives CH3C6H4CH3 with the tworing condensed aromatic compound naphthalene C10H8 also being a source of petrochemicals Benzene toluene BT the benzene toluene and xylene isomers BTX and benzene toluene ethylbenzene and xylene isomers BTEX are the aromatic hydrocarbons with a widespread use as petrochemicals to produce a variety of products Figure 81 FIGURE 81 Chemicals from Benzene Toluene and the Xylene isomers 325 Chemicals from Aromatic Hydrocarbons Ethylbenzene C6H5CH2CH3 is often included in such mixtures as BTEX and is a valuable starting material for the production of styrene C6H5CHCH2 The C8 aromatic derivatives are important precursors for many commercial chemicals and poly mers such as phenol trinitrotoluene TNT nylons and plastics Another compound that has found wide use in the explosive field is 246trinitrophenol also called picric acid Aromatic compounds are characterized by having a stable ring structure due to the overlap of the πorbitals resonance Accordingly they do not easily add to reagents such as halogens and acids as do alkenes Aromatic hydrocarbon derivatives are susceptible however to electrophilic substitu tion reactions in presence of a catalyst Aromatic hydrocarbon derivatives are generally nonpolar They are not soluble in water but they dissolve in organic solvents such as hexane diethyl ether and carbon tetrachloride In the traditional chemical industry aromatic derivatives such as benzene toluene and the xylene were made from coal during the course of carbonization in the production of coke and town gas A much larger volume of these chemicals are now made as refinery byproducts A further source of supply is the aromaticrich liquid fraction produced in the cracking of naphtha or low boiling gas oils during the manufacture of ethylene and other olefin derivatives Aromatic compounds are valuable starting materials for a variety of chemical products Reforming processes have made benzene toluene xylene and ethylbenzene economically available from petroleum sources In the catalytic reforming process a mixture of hydrocarbon derivatives with boiling points between 60C and 200C 140F390F is blended with hydrogen and then exposed to a bifunctional platinum chloride or a rhenium chloride catalyst at 500C525C 930F975F and pressures ranging from 120 to 750 psi Under these conditions aliphatic hydrocarbon derivatives form rings and lose hydrogen to become aromatic hydrocarbons The aromatic products of the reaction are then separated from the reaction mixture the reformate by extraction using a solvent such as diethylene glycol HOCH2CH2OH or sulfolane The benzene is then separated from the other aromatic derivatives by distillation The extraction step of aromatics from the reformate is designed to produce a mixture of aromatic derivatives with lowest nonaromatic components Recovery of the aromatic derivatives commonly referred to as benzene toluene and xylene isomers involves such extraction and distillation steps In similar fashion to this catalytic reforming process UOP and BP have commercialized a method to produce aromatic derivatives from liquefied petroleum gas LPG which is predominantly Sulfolane 326 Handbook of Petrochemical Processes propane CH3CH2CH3 and butane CH3CH2CH2CH3 In this process benzene toluene and the xylene isomers are produced by dearomatization of propane and butane The process consists of reaction system continuous regeneration of catalyst and product recovery The catalyst is a zeolite type catalyst with a nonnoble metal promoter Gosling et al 1999 They are generally recovered by extractive or azeotropic distillation by solvent extraction with waterglycol mixtures or liquid sulfur dioxide or by adsorption Naphthalene and methylnaphtha lenes are present in catalytically cracked distillates A substantial part of the benzene consumed is now derived from petroleum and it has many chemical uses Benzene toluene the xylene isomers and ethylbenzene are obtained mainly from the catalytic reforming of highboiling naphtha The product reformate is rich in C6 C7 and C8 aromatic derivatives which could be extracted by a suitable solvent such as sulfolane or ethylene glycol These solvents are characterized by a high affinity for aromatic derivatives good thermal stability and rapid phase separation Aromatic compounds are valuable starting materials for a variety of chemical products Reforming processes have made benzene toluene xylene and ethylbenzene economically available from petroleum sources They are generally recovered by extractive or azeotropic distillation by solvent extraction with waterglycol mixtures or liquid sulfur dioxide or by adsorption Naphthalene and methylnaphthalenes are present in catalytically cracked distillates A substantial part of the benzene consumed is now derived from petroleum and it has many chemical uses Aromatic compounds such as benzene toluene and the xylenes are major sources of chemicals Figure 81 For example benzene is used to make styrene C6H5CHCH2 the basic ingredient of polystyrene plastics as well as paints epoxy resins glues and other adhesives The process for the manufacture of styrene proceeds through ethylbenzene which is produced by reaction of benzene and ethylene at 95C 203F in the presence of a catalyst C H CH CH C H CH CH 6 6 2 2 6 5 2 3 In the presence of a catalyst and superheated steam ethylbenzene dehydrogenates to styrene C H CH CH C H CH CH H 6 5 2 3 6 5 2 2 Toluene is usually added to the gasoline pool or used as a solvent but it can be dealkylated to benzene by catalytic treatment with hydrogen C H CH H C H CH 6 5 3 2 6 6 4 Similar processes are used for dealkylation of methylsubstituted naphthalene Toluene is also used to make solvents gasoline additives and explosives Toluene is usually in demand as a source of trinitrotoluene but has fewer chemical uses than benzene Alkylation with ethylene followed dehydrogenation yields αmethylstyrene C6H5CCH3CH2 which can be used for polymerization Alkylation of toluene with pro pylene tetramer yields a product suitable for sulfonation to a detergentgrade surfaceactive compound Aromatic derivatives are more resistant to oxidation than the paraffin hydrocarbon derivatives and higher temperatures are necessary the oxidation is carried out in the vapor phase over a catalyst generally supported vanadium oxide Orthoxylene is oxidized by nitric acid to phthalic anhydride mxylene to isophthalic acid and pxylene with nitric acid to terephthalic acid These acid products are used in the manufacture of fibers plastics plasticizers and the like Phthalic anhydride is also produced in good yield by the air oxidation of naphthalene at 400C450C 750F840F in the vapor phase at about 25 psi over a fixed bed vanadium pentox ide catalyst Terephthalic acid is produced in a similar manner from pxylene and an intermediate 327 Chemicals from Aromatic Hydrocarbons in the process ptoluic acid CH3C6H4CO2H can be isolated because it is slower to oxidize than the pxylene starting material The Tetra extraction process by Union Carbide uses tetraethylene glycol as a solvent The feed reformate which contains a mixture of aromatic derivatives paraffins and naphthene derivatives after heat exchange with hot raffinate is countercurrently contacted with an aqueous tetraethylene glycol solution in the extraction column The hot rich solvent containing benzenetoluenexylene aromatic derivatives is cooled and introduced into the top of a stripper column The aromatic deriv atives extract is then purified by extractive distillation and recovered from the solvent by steam stripping Extractive distillation is also feasible and the raffinate constituted mainly of paraffins isoparaffins and cycloparaffins is washed with water to recover traces of solvent and then sent to storage The solvent is recycled to the extraction tower The extract which is composed of benzene toluenexylene derivatives and ethylbenzene is then fractionated Benzene and toluene are recov ered separately and ethylbenzene and xylenes are obtained as a mixture C8 aromatic derivatives Due to the narrow range of the boiling points of C8 aromatic derivatives separation by fractional distillation is difficult especially when the xylene isomers are taken into consideration and require separation Table 82 A superfractionation technique is used to segregate ethylbenzene from the xylene mixture Because pxylene is the most valuable isomer for producing synthetic fibers it is usually recovered from the xylene mixture Fractional crystallization used to be the method for separating the isomers but the yield was only 60 Currently industry uses continuous liquid phase adsorption separation processes The overall yield of pxylene is increased by incorporating an isomerization unit to isomerize oxylene and mxylene to pxylene An overall yield of 90 pxylene could be achieved In this process partial conversion of ethylbenzene to benzene also occurs The catalyst used is shape selective and contains ZSM5 zeolite Briefly isomerization is the process by which one molecule is transformed into another molecule which has exactly the same number of atoms but the atoms have a different arrangement For exam ple in the alkane series straightchain alkanes are converted to branched isomers by heating in the presence of a platinum or acid catalyst 2CH CH CH CH CH CH CH CH CH CH CH C CH CH 3 2 2 2 3 Pentane 3 2 3 3 2methylbutane 3 3 2 3 22dimethlpropane n In the aromatic hydrocarbon series the isomerization of the xylene isomers is the most wellknown process The composition of the product mix is dependent upon i the composition of the feedstock which can be one isomer or all three isomers ii the process parameter and iii the catalyst Xylenes are produced mainly as part of the benzene toluene and the xylene isomers aromatics mix that is extracted from the product of catalytic reforming the reformate In some molecules and under some conditions isomerization occurs spontaneously Many isomers are roughly equal in bond energy and so exist in approximately amounts provided that they can interconvert somewhat freely that is the energy barrier between the two isomers is not too high However when the isomerization occurs intramolecular it is considered a rearrangement reaction 328 Handbook of Petrochemical Processes The ExxonMobil XyMax2 vaporphase isomerization for xylenes isomerization features a higher activity catalyst higher weight hourly space velocity WHSV and expanded temperature window The process requires lower catalyst volumes than any process currently in service achieves higher ethylbenzene conversion per pass and offers the flexibility of operating at temperatures similar to or lower than existing processes The advantages of the process are i higher weight hourly space velocity ii lower catalyst inventory iii high pxylene approach to equilibrium iv lower reactor temperature v lower hydrogen to hydrocarbon ratio vi higher conversion of ethyl benzene and vii higher benzene product purity The isomerization reactions of aromatic hydrocarbon derivatives proceed during implementation of such catalytic processes as reforming cracking and also in isomerization processes of alkyl aro matic hydrocarbon derivatives Xylene and ethylbenzene isomerization processes have a great practical importance Isomerization takes place in disproportionation and transalkylation processes of methyl benzenes also intended for manufacturing para and orthoxylenes used for production of terephthalic acid and phthalic anhydride oligopolyesters fibers varnishes plasticizers and other products However due to the peculiarities of xylene thermodynamic equilibrium minor change of xylene equilibrium concentration with the temperature corrosion aggressiveness and nonregenerability of catalytic systems with high acidity catalysts based on aluminum chloride or boron fluoride did not get extensive industrial application The most widespread xylene isomerization catalysts became the ones of two types based on amorphous or crystalline aluminosilicates and also similar to them heterogeneous catalysts containing platinum Depending on the composition of the xylene mixture aluminosilicate catalysts Al2O3SiO2 operating at atmospheric pressure and in the temperature range from 450C to 550C 840F1020F are used Over these catalysts ethylbenzene is exposed generally to dispropor tionation that determines short cycle length of catalyst operation The recommended content of ethylbenzene in isomerization feed should not exceed 613 While oxylene and pxylene yield makes about 93 wt The introduction of platinum introduction in aluminosilicate catalyst and application of hydrogen pressure the Octafining process provides ethylbenzene C6H5C2H5 conversion into xylenes CH3C6H4CH3 in the order of 6070 In the Isomar process the use of halogenpromoted aluminoplatinum catalyst is used and the process is used to maximize the recovery of a particular xylene isomer from a mixture of C8 aromatic isomers The process is most often applied to pxylene recovery but it can also be used to maximize the recovery of oxylene or mxylene In the case of pxylene recovery a feedstock consisting of mixed isomers of xylene is charged to a Parex process unit where the pxylene isomer is preferen tially extracted The raffinate from the Parex unit almost entirely depleted of pxylene is then sent to the Isomar unit The Isomar unit reestablishes an equilibrium distribution of xylene isomers TABLE 82 Properties of the Xylene Isomers Common name Xylene oXylene mXylene pXylene Systematic name Dimethylbenzene 12Dimethylbenzene 13Dimethylbenzene 14Dimethylbenzene Other names Xylol oXylol oXylene mXylol mXylene pXylol pXylene Molecular formula C8H10 Density and phase 0864 gmL liquid 088 gmL liquid 086 gmL liquid 086 gmL liquid Solubility in water Practically insoluble Soluble in Nonpolar Solvents such as Aromatic Hydrocarbons Melting point 474C 533F 25C 13F 48C 54F 13C 55F Boiling point 1385C 2813F 144C 291F 139C 282F 138C 280F Flash point 30C 86F 17C 63F 25C 77F 25C 77F 329 Chemicals from Aromatic Hydrocarbons essentially creating additional pxylene from the remaining oxylene and mxylene Effluent from the Isomar unit is then recycled back to the Parex unit for recovery of additional pxylene In this way the oxylene and mxylene and ethylbenzene are recycled to extinction Depending on the type of catalyst ethylbenzene is converted into xylene isomers or benzene In another aspect of aromatics production the MX Sorbex process recovers mxylene from mixed xylenes and uses adsorptive separation for highly efficient and selective recovery at high purity of molecular species that cannot be separated by conventional fractionation The process simulates a moving bed of adsorbent with continuous countercurrent flow of liquid feed over a solid bed of adsor bent Feed and products enter and leave the adsorbent bed continuously at nearly constant composi tions The fresh feedstock is pumped to the adsorbent chamber mXylene is separated from the feed in the adsorbent chamber and leaves to the extract column The dilute extract is then fractionated to pro duce 995 ww mxylene as the bottoms product The desorbent is taken from the overhead and recir culated back to the adsorbent chamber All the other components present in the feedstock are rejected in the adsorbent chamber and removed to the raffinate column The dilute raffinate is then fractionated to recover desorbent as the overhead product and recirculated back to the adsorbent chamber The Sulfolane process also spelled Sulpholane process combines liquidliquid extraction with extractive distillation to recover highpurity aromatics from hydrocarbon mixtures such as reformed petroleum naphtha reformate pyrolysis naphtha or coker light oil The solvent used in the Sulfolane process was developed by Shell Oil Co in the early 1960s and is still the most efficient solvent available for recovery of aromatic derivatives In the process the feedstock enters the extractor and flows upward countercurrent to a stream of lean solvent As the feed flows through the extractor aromatics are selectively dissolved in the solvent A raffinate stream very low in aromatics content is withdrawn from the top of the extrac tor The rich solvent loaded with aromatics exits the bottom of the extractor and enters the stripper The lighter nonaromatic constituents taken overhead are recycled to the extractor to displace higher molecular weight nonaromatic constituents from the solvent The bottoms stream from the strip per substantially free of nonaromatic impurities is sent to a column where the aromatic product is separated from the solvent Because of the large difference in boiling point between the solvent and the highest molecular weight higherboiling aromatic component this separation is accomplished with minimal energy input Lean solvent from the bottom of the recovery column is returned to the extractor where the extract is recovered overhead and sent on to distillation columns downstream for recovery of the individual benzene toluene and xylene derivatives The raffinate stream exits the top of the extrac tor and is directed to the raffinate wash column In the wash column the raffinate is contacted with water to remove dissolved solvent The solventrich water is vaporized in the water stripper and then used as stripping steam in the recovery column The raffinate product exits the top of the raffinate wash column The raffinate product is commonly used for gasoline blending or ethylene production Contaminants that are the most difficult to eliminate in the extraction section are easiest to eliminate in the extractive distillation section and vice versa This hybrid combination of techniques allows sulfolane units to process feedstocks of much broader boiling range than would be possible by either technique alone A single sulfolane unit can be used for simultaneous recovery of high purity C6 to C9 aromatic derivatives with individual aromatic components recovered downstream by simple fractionation The emphasis on the production of aromatic products is that aromatic compounds such as ben zene toluene and the xylenes are major sources of chemicals For example benzene is used for the production of styrene C6H5CHCH2 the basic ingredient of polystyrene plastics as well as paints epoxy resins glues and other adhesives The process for the manufacture of styrene pro ceeds through ethylbenzene which is produced by reaction of benzene and ethylene at 95C 203F in the presence of a catalyst C H CH CH C H CH CH 6 6 2 2 6 5 2 3 330 Handbook of Petrochemical Processes In the presence of a catalyst and superheated steam ethylbenzene dehydrogenates to styrene C H CH CH C H CH CH H 6 5 2 3 6 5 2 2 Toluene is usually added to the gasoline pool or used as a solvent but it can be dealkylated to ben zene by catalytic treatment with hydrogen C H CH H C H CH 6 5 3 2 6 6 4 In this toluene is mixed with hydrogen then passed over a chromium molybdenum or platinum oxide catalyst at 500C600C 930F1110F and 600900 psi Higher temperatures may be substituted for the catalyst If the raw material stream contains much nonaromatic components paraffin derivatives or naphthene derivatives those are likely decomposed to lower hydrocarbons such as methane which increases the consumption of hydrogen A typical reaction yield exceeds 95 Xylene isomers and higher molecular weight aromatic derivatives can be used in place of toluene with similar efficiency The irreversible reaction is accompanied by an equilibrium side reaction that produces biphenyl at higher temperature 2C H C H C H H 6 6 6 5 6 5 2 Biphenyl is notable as a starting material for the production of polychlorinated biphenyls PCBs derivative which were once widely used as dielectric fluids and heat transfer agents Of the xylenes oxylene is used to produce phthalic anhydride and other compounds Another xylene pxylene is used in the production of polyesters in the form of terephthalic acid or its methyl ester Figure 81 Terephthalic acid is produced from pxylene by two reactions in four steps The first of these is oxidation with oxygen at 190C 375F CH C H CH O HOOCC H CH 3 6 4 3 2 6 4 3 This is followed by formation of the methyl ester at 150C 302F HOOCC H CH CH OH HOOCC H CH 6 4 3 3 6 4 3 Repetition of these steps gives the methyl diester of terephthalic acid CH OOCC H CH O CH OOCC H CCOOH CH OOCC H CCOOH CH OH CH OOCC H CCOOCH 3 6 4 3 2 3 6 4 3 6 4 3 3 6 4 3 This diester CH3OOCC6H4CCOOCH3 when polymerized with ethylene glycol at 200C 390F yields the polymer after loss of methanol to give a monomer The polymerization step requires a catalyst In the process to produce terephthalic acid the crude acid is produced by the catalytic oxida tion of pxylene with air in the liquid phase using acetic acid as a solvent The feedstock mix pxylene solvent and catalyst is continuously fed with compressed air to the ecolumn oxidizer which operates at moderate temperature The oxidizer product is purified in a separation step in which the impurities are removed from the product by exchanging the reaction liquor with lean solvent from the solvent recovery system The reactor overheadmainly reaction water acetic acid and nitrogenare sent to the solvent recovery system where water is separated from the solvent by distillation The offgas is sent to a regenerative thermal oxidation unit for further cleaning 331 Chemicals from Aromatic Hydrocarbons To produce polymergrade terephthalic acid the crude acid is purified in a postoxidation step at elevated temperature The post oxidizers serve as reactors to increase the conversion of the partially oxidized compounds to terephthalic acid Aromatic derivatives are more resistant to oxidation than the paraffin hydrocarbon derivatives and higher temperatures are necessary the oxidations are carried out in the vapor phase over a catalyst generally supported by vanadium oxide Orthoxylene is oxidized by nitric acid to phthalic anhydride mxylene to isophthalic acid and pxylene with nitric acid to terephthalic acid These acid products are used in the manufacture of fibers plastics plasticizers and the like Phthalic anhydride is also produced in good yield by the air oxidation of naphthalene at 400C450C 750F840F in the vapor phase at about 25 psi over a fixed bed vanadium pentox ide catalyst Terephthalic acid is produced in a similar manner from pxylene and an intermediate in the process ptoluic acid can be isolated because it is slower to oxidize than the pxylene starting material The primary sources of benzene toluene and xylenes are refinery streams especially from catalytic reforming and cracking and pyrolysis gasoline from steam cracking and from coal liq uids Mixtures of benzene toluene and the xylene isomers and in some cases ethyl benzene are extracted from these streams using selective solvents such as sulfolene or ethylene glycol The extracted components are separated through lengthy fractional distillation crystallization and isomerization processes The reactivity of C6 C7 C8 aromatic derivatives is mainly associated with the benzene ring Aromatic compounds in general are liable for electrophilic substitution Most of the chemicals produced directly from benzene are obtained from its reactions with electrophilic reagents Benzene could be alkylated nitrated or chlorinated to important chemicals that are precursors for many commercial products Toluene and xylenes methylbenzenes are substituted benzenes Although the presence of methyl substituents activates the benzene ring for electrophilic attack the chemistry of methyl benzenes for producing commercial products is more related to reactions with the methyl than with the phenyl group As an electronwithdrawing substituent of methane the phenyl group influences the methyl hydrogens and makes them more available for chemical attack The methyl group could be easily oxidized or chlorinated as a result of the presence of the phenyl substituent 82 CHEMICALS FROM BENZENE Benzene C6H6 is the simplest aromatic hydrocarbon and by far the most widely used one Before 1940 the main source of benzene and substituted benzene was coal tar Currently it is mainly obtained from catalytic reforming Other sources are pyrolysis gasolines and coal liquids Benzene has a unique structure due to the presence of six delocalized pielectrons that encompass the six carbon atoms of the hexagonal ring Thus benzene a doublebond conjugated six member hydro carbon ring can be represented by two structures that are equivalent in energy Benzene could be represented by two resonating Kekulé structures It may also be represented as a hexagon with a circle in the middle The circle is a symbol of the πcloud encircling the benzene ring The delocalized electrons associated with the benzene ring impart very special properties to 332 Handbook of Petrochemical Processes aromatic hydrocarbon derivatives They have chemical properties of singlebond compounds such as paraffin hydrocarbon derivatives and double bond compounds such as olefin derivatives as well as many properties of their own Benzene is used mainly as an intermediate or starting material to make other chemicals Table 83 above all ethylbenzene cumene cyclohexane nitrobenzene and alkylbenzene The predominant process is the manufacture of ethylbenzene C6H5CH2CH3 which is a precursor to styrene C6H5CHCH2 from which polymers and plastics are manufactured The production of styrene increased dramatically during the 1940s when it was used as a feedstock for synthetic rubber In the process to manufacture styrene ethylbenzene is mixed in the gas phase with 1015 times its volume of hightemperature steam and then passed over a solid cata lyst bed Most ethylbenzene dehydrogenation catalysts are based on ferric oxide Fe2O3 promoted by potassium oxide K2O or potassium carbonate K2CO3 A typical styrene plant consists of two or three reactors in series which operate under vacuum to enhance the conversion and selectivity Typical perpass conversions are ca65 for two reactors TABLE 83 Routes from Benzene to Other Petrochemical Products Primary Product Secondary Product Tertiary Product Quaternary Product Benzene Ethylbenzene Styrene Polystyrene Cumene Acetone Phenol Bisphenol A Polycarbonates Epoxy resins Phenolic resins Cyclohexane Adipic acid Nylon 66 Caprolactam Nylon 66 Aniline Chlorobenzenes Benzene ethylene ethylbenzene Styrene 333 Chemicals from Aromatic Hydrocarbons and 7075 for three reactors Selectivity to styrene is 9397 The main byproducts are benzene and toluene Because styrene and ethylbenzene have similar boiling points 145C and 136C 293F and 276F respectively their separation requires tall distillation towers and high returnreflux ratios Styrene tends to polymerize at the distillation temperatures and to minimize this problem older styrene plants added elemental sulfur to inhibit the polymerization Styrene is also coproduced commercially in a process in which ethylbenzene is treated with oxygen to form the ethylbenzene hydroperoxide which is used to oxidize propylene to propylene oxide The resulting 1phenylethanol is dehydrated to produce styrene Styrene can also be produced from toluene and methanol However this process has suffered from the competing decomposition of methanol The methanol decomposition can be diminished process using a process in which the parameters are 400C425C 750F795F and atmospheric pressure by forcing the reactants through a zeolite catalyst yielding a mixture of styrene and ethylbenzene with a total styrene yield of over 60 Another route to styrene involves the reaction of benzene and ethane and the reactants along with ethylbenzene are fed to a dehydrogenation reactor with a catalyst capable of simultaneously producing styrene and ethylbenzene The dehydrogenation effluent is cooled and separated and the ethylene stream is recycled to the alkylation unit The process attempts to overcome previous shortcomings in earlier attempts to develop production of styrene from ethane and benzene such as inefficient recovery of aromatics production of high levels of highboiling constituents and tars and inefficient separation of hydrogen and ethane Lesser amounts of benzene are used to make some types of rubber lubricants dyes drugs explosives and pesticides Toluene is often used as a substitute for benzene for instance as a fuel additive The solvent properties of the two are similar but toluene is less toxic and has ahigh0boil ing constituents wider liquid range Aromatic hydrocarbon derivatives like paraffin hydrocarbon derivatives react by substitution but by a different mechanisms under milder reaction conditions Aromatic compounds react by additions only under several reaction conditions For example electrophilic substitution of benzene using nitric acid produces nitrobenzene under normal conditions while the addition of hydrogen to benzene occurs in presence of catalyst only under high pressure to give cyclohexane Monosubstitution can occur at any one of the six equivalent carbon atoms of the ring Most of the monosubstituted benzenes have common names such as toluene methylbenzene phenol hydroxy benzene and aniline aminobenzene When two hydrogens in the ring are substituted by the same reagent three isomers are possible The prefixes ortho meta and para are used to indicate the loca tion of the substituents in 12 13 or 14positions for example xylene isomers 334 Handbook of Petrochemical Processes Benzene is an important chemical intermediate and is the precursor for many commercial chem icals and polymers such as phenol styrene for polystyrene derivatives and caprolactam for nylon 6 Chapter 10 discusses chemicals based on benzene Benzene C6H6 is the most important aromatic hydrocarbon It is the precursor for many chemi cals that may be used as end products or intermediates Almost all compounds derived directly from benzene are converted to other chemicals and polymers For example hydrogenation of ben zene produces cyclohexane Oxidation of cyclohexane produces cyclohexanone which is used to make caprolactam for nylon manufacture Due to the resonance stabilization of the benzene ring it is not easily polymerized However products derived from benzene such as styrene phenol and maleic anhydride can polymerize to important commercial products due to the presence of reac tive functional groups Benzene could be alkylated by different alkylating agents hydrogenated to cyclohexane nitrated or chlorinated The chemistry for producing the various chemicals from benzene is discussed in this section 821 alkylation Benzene can be alkylated in the presence of a Lewis or a Bronsted acid catalyst Olefin derivatives such as ethylene propylene and C12C14 alpha olefin derivatives are used to produce benzene alkyl ates which have great commercial value Alkyl halides such as monochloroparaffin derivatives also serve this purpose The first step in alkylation is the generation of a carbocation carbonium ion When an olefin is the alkylating agent a carbocation intermediate forms RCH CH H RCHCH 2 3 Carbon cations also form from an alkyl halide when a Lewis acid catalyst is used Aluminum chloride is the commonly used FriedelCrafts alkylation catalyst RCl AlCl R AlCl 3 4 The next step is an attack by the carbocation on the benzene ring followed by the elimination of a proton and the formation of a benzene alkylate The acidcatalyzed alkylation of benzene with alkenes is an established commercial process to produce a wide range of alkylbenzenes The alkylation of benzene with ethylene CH2CH2 and propylene CH3CHCH2 is used to manufacture ethylbenzene C6H5CH2CH3 and isopropyl ben zene C6H5CHCH32 which are the intermediates in styrene and phenol production respectively Weissermel and Arpe 2003 In addition ethylene and propylene can be replaced by ethane and propane Kato et al 2001 Huang et al 2007 The alkylation of benzene with low molecular weight alkane derivatives occurs in the gas phase in the presence of solid bifunctional metalacid catalysts which includes the dehydrogenation of alkane on metal sites to form alkene and hydro gen step 1 followed by the alkylation of benzene with the alkene on acid sites step 2 Alotaibi et al 2017 Ethylbenzene is a colorless aromatic liquid with a boiling point of 1362C 2772F very close to that of pxylene 335 Chemicals from Aromatic Hydrocarbons This complicates separating it from the C8 aromatic equilibrium mixture obtained from catalytic reforming processes Ethylbenzene obtained from this source however is small compared to the synthetic route The main process for producing ethylbenzene is the catalyzed alkylation of benzene with ethylene Many different catalysts are available for this reaction Promoted aluminum chloride AlCl3HCl is commonly used Ethyl chloride may be substituted for hydrogen chloride on a mole formole basis Typical reaction conditions for the liquidphase aluminum chloridecatalyzed process are 40C100C 104F212F and 30120 psi Diethylbenzene and higher alkylated benzenes also form They are recycled and dealkylated to ethylbenzene The vaporphase Badger process which has been in commercial use since 1980 can accept dilute ethylene streams such as those that occur in the effluent gas FCC off gas from a fluid catalytic cracking unit A zeolitetype heterogeneous catalyst is used in a fixed bed process The reaction conditions are 420C 790F and 200300 psi Over 98 ww yield is obtained at 90 conversion Polyethyl benzene and unreacted benzene are recycled and join the fresh feed to the reactor The reactor effluent is fed to the benzene fractionation system to recover unreacted benzene The bottoms fraction containing ethylbenzene and heavier polyalkylated derivatives are fraction ated in two columns The first column separates the ethylbenzene product and the other separates polyethyl benzene for recycling Ethylbenzene is mainly used to produce styrene Styrene vinylbenzene C6H5CHCH2 is a liquid bp 1452C 2614F that polymerizes easily when initiated by a free radical or when exposed to light Dehydrogenation of ethylbenzene to styrene occurs over a wide variety of metal oxide catalysts Oxides of Fe Cr Si Co Zn or their mixtures can be used for the dehydrogenation reaction Typical reaction conditions for the vaporphase process are 600C700C 1130F1290F at or below atmospheric pressure Approximately 90 styrene yield is obtained at 3040 conversion Ethylbenzene Styrene 336 Handbook of Petrochemical Processes In the MonsantoLummus Crest process fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam The steam acts as a heating medium and as a dilu ent The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts Radial beds minimize pressure drops across the reactor An alternative route for producing styrene is to dimerize butadiene to 4vinyl1cyclohexene ollowed by catalytic dehydrogenation to styrene The process involves cyclodimerization of butadi ene over a proprietary copperloaded zeolite catalyst at moderate temperature and pressure 100C 212F and 250 psi To increase the yield the cyclodimerization step takes place in a liquidphase process over the catalyst Selectivity for vinyl cyclohexene VCH was over 99 In the second step vinyl cyclohexene is oxidized with oxygen over a proprietary oxide catalyst in presence of steam Conversion over 90 and selectivity to styrene of 92 could be achieved Another approach is the oxidative coupling of toluene to stilbene one of the two stereoisomers cistrans of 12diphenylethene followed by disproportionation to styrene and benzene High temperatures are needed for this reaction and the yields are low Cumene isopropyl benzene bp 1527C 3069F a liquid is soluble in many organic solvents but not in water It is present in low concentrations in light refinery streams such as reformates and coal liquids It may be obtained by distilling these fractions The main process for producing cumene is a synthetic route where benzene is alkylated with propylene to isopropyl benzene Either a liquid or a gasphase process is used for the alkylation reac tion In the liquidphase process low temperatures and pressures approximately 50C 122F and 75 psi are used with sulfuric acid as a catalyst Small amounts of ethylene can be tolerated since ethylene is quite unreactive under these conditions Butylene derivatives are relatively unimportant because butylbenzene can be removed as bottoms from the cumene column In the vaporphase process the reaction temperature and pressure are approximately 250C 480F and 600 psi Phosphoric acid on Kieselguhr is a commonly used catalyst To limit polyal kylation a mixture of propenepropane feed is used Propylene can be as low as 40 of the feed mixture A high benzenepropylene ratio is also used to decrease polyalkylation transStilbene cisStilbene Cumene 337 Chemicals from Aromatic Hydrocarbons In the UOP process fresh propylene feed is combined with fresh and recycled benzene then passed through heat exchangers and a steam preheater before being charged to the upflow reactor which operates at 200C260C 390F500F and 375 psi The solid phosphoric acid catalyst provides an essentially complete conversion of propylene on a onepass basis The typical reactor effluent yield contains 948 ww cumene and 31 ww diisopropylbenzene The remaining 21 is primarily higher molecular weight aromatic compounds This high yield of cumene is achieved without transalkylation of diisopropylbenzene and is unique to the solid phosphoric acid catalyst process The cumene product is 999 wt pure and the high molecular weight aromatic derivatives which have an octane number of 109 can either be used as highoctane gasolineblending components or combined with additional benzene and sent to a transalkylation section of the plant where diiso propylbenzene is converted to cumene The overall yields of cumene for this process are typically 9798 ww with transalkylation and 9496 ww without transalkylation In the MonsantoLummus Crest cumene process dry benzene fresh and recycled and pro pylene are mixed in the alkylation reaction zone with aluminum chloride AlCl3 and hydrogen chloride catalyst at a temperature of less than 135C 275F The effluent from the alkylation zone is combined with recycled polyisopropyl benzene and fed to the transalkylation zone where the polyisopropyl benzene derivatives are transalkylated to produce cumene The strongly acidic catalyst is separated from the organic phase by washing the reactor effluent with water and caustic The distillation system is designed to recover a highpurity cumene product The unconverted benzene and polyisopropyl benzene are separated and recycled to the reaction system Propane in the propylene feed is recovered as liquid petroleum gas The overall yields of cumene for this process can be high as 99 ww based on benzene and 98 ww based on propylene These pro cesses have also been used extensively for the production of ethylbenzene than for the production of cumene There are also two processes that use zeolitebased catalyst systems which were developed in the late 1980s The goal is to reduce pollution using catalyst system that was developed from the mordenitezeolite group to replace phosphoric acid or aluminum chloride catalysts The new cata lysts eliminate the disposal of acid wastes and handling of corrosive materials In one of these processes Unocal introduced a fixed bed liquidphase reactor system based on a Ytype zeolite catalyst The selectivity to cumene is generally between 70 and 90 ww The remaining components are primarily polypropyl benzene derivatives which are transalkylated to cumene in a separate reaction zone to give an overall yield to cumene in the order of about 99 ww The distillation requirements involve the separation of propane for LPG use the recycling of excess benzene to polypropyl benzene for transalkylation to cumene and the production of purified cumene product The second zeolite process is based on the concept of catalytic distillation which is a combina tion of catalytic reaction and distillation in a single column The basic principle is to use the heat of reaction directly to supply heat for fractionation This concept has been applied commercially for the production of methyl tertbutyl ether MTBE but has not yet been applied commercially to cumene Phenol hydroxybenzene C6H5OH is produced from cumene by a twostep process In the first step cumene is oxidized with air to cumene hydroperoxide The reaction conditions are approxi mately 100C130C 212F266F and 3045 psi in the presence of a metal salt catalyst 338 Handbook of Petrochemical Processes In the second step the hydroperoxide is decomposed in the presence of an acid to phenol and acetone The reaction conditions are a temperature of approximately 80C 176F and slightly below atmospheric pressure In this process cumene is oxidized in the liquid phase The oxidation product is concentrated to 80 cumene hydroperoxide by vacuum distillation To avoid decomposition of the hydroperoxide it is transferred immediately to the cleavage reactor in the presence of a small amount of sulfuric acid The cleavage product is neutralized with alkali before it is finally purified After an initial distillation to split the coproducts phenol and acetone each is purified in separate distillation and treating trains An acetone finishing column distills product acetone from an acetone wateroil mixture The oil which is mostly unreacted cumene is sent to cumene recovery Acidic impurities such as acetic acid and phenol are neutralized by caustic injection Previously phenol was produced from benzene by sulfonation followed by caustic fusion to sodium phenate Phenol is released from the sodium salt of phenol by the action of carbon dioxide or sulfur dioxide Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium platinum palladium or iridium The oxidizing agent is nitrous oxide which is unavoid able by a byproduct from the oxidation of a cyclohexanonecyclohexanol mixture to adipic acid using nitric acid as the oxidant Phenol is also produced from chlorobenzene and from toluene via a benzoic acid intermediate Phenol a white crystalline mass with a distinctive odor becomes reddish when subjected to light It is highly soluble in water and the solution is weakly acidic Phenol and acetone produce bis phenol A an important monomer for epoxy resins and polycarbonates It is produced by condensing acetone and phenol in the presence of hydrogen chloride HCl or by using a cationexchange resin Important chemicals derived from phenol are salicylic acid acetyl salicylic acid aspirin 24dichlorophenoxy acetic acid 240 and 245triphenoxy acetic acid 245T which are selec tive herbicides and pentachlorophenol a wood preservative Other halophenol derivatives are miticides bactericides and leather preservatives Phenol can be alkylated to alkylphenols These compounds are widely used as nonionic surfac tants antioxidants and monomers in resin polymer applications An alkyl phenol 339 Chemicals from Aromatic Hydrocarbons Phenol is also a precursor for aniline The major process for aniline C6H5NH2 is the hydrogena tion of nitrobenzene Linear alkylbenzene is an alkylation product of benzene used to produce biodegradable anionic detergents The alkylating agents are either linear C12 to C14 monoolefin derivatives or mono chloroalkane derivatives The linear olefin derivatives alpha olefin derivatives are produced by polymerizing ethylene using Ziegler catalysts Chapter 7 or by dehydrogenating nparaffins extracted from kerosene Monochloroalkane derivatives on the other hand are manufactured by chlorinating the corresponding nparaffins Dehydrogenation of n paraffins to monoolefin deriva tives using a newly developed dehydrogenation catalyst which is highly active and allows a higher perpass conversion to monoolefin derivatives Because the dehydrogenation product contains a higher concentration of olefin derivatives for a given alkylate production rate the total hydrocar bon feed to the hydrogen fluoride HF alkylation unit is substantially reduced Alkylation of benzene with linear monoolefin derivatives is industrially preferred The Detal process combines the dehydrogenation of nparaffins and the alkylation of benzene Monoolefin derivatives from the dehydrogenation section are introduced to a fixedbed alkylation reactor over a heterogeneous solid catalyst Older processes use hydrogen fluoride catalysts in a liquidphase process at a temperature range of 40C70C 104F158F Detergent manufacturers buy linear alkylbenzene sulfonate it with sulfur trioxide SO3 and then neutralize it with sodium hydroxide NaOH to produce linear alkylbenzene sulfonate LABS the active ingredient in detergents 822 chlorination Chlorination of benzene is an electrophilic substitution reaction in which Cl serves as the electro phile The reaction occurs in the presence of a Lewis acid catalyst such as iron III chloride ferric chloride FeCl3 The products are a mixture of mono and dichlorobenzene derivatives The ortho and the paradichlorobenzene derivatives are more common than metadichlorobenzene The ratio of the monochloro to dichloro products essentially depends on the benzenechlorine ratio and the residence time The ratio of orthodichlorobenzene plus the ortho and paradichlorobenzene to the metadichlorobenzene depends mainly on the reaction temperature and residence time Typical liquidphase reaction conditions for the chlorination of benzene using ferric chloride catalyst are 80C100C 176F212F and atmospheric pressure When a high benzeneCl2 ratio is used the product mixture is approximately 80 monochlorobenzene 15 pdichlorobenzene and 5 odichlorobenzene Continuous chlorination processes permit the removal of monochloro benzene as it is formed resulting in lower yields of higher chlorinated benzene Monochlorobenzene is also produced in a vaporphase process at approximately 300C The byproduct hydrogen chloride goes into a regenerative oxychlorination reactor The catalyst is a pro moted copper oxide on a silica carrier 4HCl O 2Cl 2H O 2 2 2 Higher conversions have been reported when temperatures of 235C315C 455F600F and pressures of 4080 psi are used Monochlorobenzene is the starting material for many compounds including phenol and aniline Others such as DDT chloronitrobenzene derivatives polychlorobenzene derivatives and biphenyl derivatives do not have as high a demand for monochlorobenzene as aniline and phenol 340 Handbook of Petrochemical Processes 823 hydroGenation Benzene and its derivatives convert to cyclohexane by hydrogenation Cyclohexane is a colorless liquid insoluble in water but soluble in hydrocarbon solvents alcohol and acetone As a cyclic paraffin it can be easily dehydrogenated to benzene The dehydrogenation of cyclohexane and its derivatives present in naphthas to aromatic hydrocarbon derivatives is an important reaction in the catalytic reforming process Essentially all of the cyclohexane is oxidized either to a cyclohexanone cyclohexanol mixture used for making caprolactam or to adipic acid These are monomers for mak ing nylon 6 and nylon 66 The process involves the use of high pressures of hydrogen in the presence of heterogenous cata lysts such as finely divided nickel Although alkene derivatives can be hydrogenated at temperatures neat to ambient benzene and related compounds are more reluctant substrates requiring tempera tures 100C 212F This reaction is practiced on a large scale industrially In the absence of the catalyst benzene is impervious to hydrogen Hydrogenation cannot be stopped to give cyclohexene or cyclohexadiene derivatives which are valuable petrochemical starting materials The hydrogenation of benzene produces cyclohexane Many catalyst systems such as Nialumina and NiPd are used for the reaction General reaction conditions are 160C 320F to 220C 425F and 375450 psi Higher temperatures and pressures may also be used with sulfided catalysts Older methods use a liquidphase process New gasphase processes operate at higher tempera tures with noble metal catalysts Using high temperatures accelerates the reaction at a faster rate The hydrogenation of benzene to cyclohexane is characterized by a highly exothermic reaction and a significant decrease in the product volume from 4 to 1 Equilibrium conditions are therefore strongly affected by temperature and pressure Intermediate products in which the double bonds have survived are not produced However the Birch reduction reaction offers access to substituted 14cyclohexadiene derivatives Birch 1944 1945 1946 1947ab Birch and Smith 1958 The reaction converts aromatic com pounds having a benzenoid ring system into 14cyclohexadiene derivatives in which two hydrogen atoms have been attached on opposite ends of the molecule The process uses sodium lithium or potassium in liquid ammonia and an alcohol such as ethanol or tertbutyl alcohol The reactions of benzene derivatives with various substituents leads to the products with the most highly substituted double bonds The effect of electronwithdrawing substituents on the Birch Reduction varies For example the reaction of benzoic acid leads to 25cyclohexadienecarboxylic acid which can be rationalized on the basis of the carboxylic acid stabilizing an adjacent anion Alkene double bonds are only reduced if they are conjugated with the benzene ring and occa sionally isolated terminal alkenes will be reduced 341 Chemicals from Aromatic Hydrocarbons Cyclohexane is oxidized in a liquidphase process to a mixture of cyclohexanone and cyclohexa nol The reaction conditions are 95C120C at approximately 10 atm in the presence of a cobalt acetate and orthoboric acid catalyst system About 95 yield can be obtained The mixture of cyclohexanone and cyclohexanol sometimes referred to as KA oil is used to produce caprolactam the monomer for nylon 6 Caprolactam is also produced from toluene through the intermediate formation of cyclohexane carboxylic acid Cyclohexane is also a precursor for adipic acid Oxidizing cyclohexane in the liquidphase at lower temperatures and for longer residence times than for KA oil with a cobalt acetate catalyst produces adipic acid Adipic acid may also be produced from butadiene via a carbonylation route CH CHCH CH HOOC CH COOH H O 2 2 2 4 2 Adipic acid and its esters are used to make nylon 66 It may also be hydrogenated to 16hexanediol which is further reacted with ammonia to hexamethylenediamine HOOC CH COOH 4H HO CH OH 2H O HO CH OH 2NH H N CH NH 2H O 2 4 2 2 4 2 2 4 3 2 2 6 2 2 Hexamethylenediamine is the second monomer for nylon 66 Briefly and by way of explanation nylon 66 nylon 66 nylon 66 or nylon 66 is a type of polyamide or nylon of which there are many types The two most common for textile and plastics industries are nylon 6 and nylon 66 The latter nylon 66 is made of two monomers and each mono mer hexamethylenediamine and adipic contains 6 carbon atoms which give nylon 66 its name Nylon 66 is synthesized by polycondensation of hexamethylenediamine and adipic acid Chapter 11 Equivalent amounts of hexamethylenediamine and adipic acid are combined with water in a reactor This is crystallized to make nylon salt an ammoniumcarboxylate mixture HOOC CH COOH H N CH NH OC CH CONH CH NH 2 1 H O 2 4 2 2 6 2 2 4 2 6 2 n n n n The nylon salt is passed into a reaction vessel where polymerization process takes place either in batches or continuously Removal of the water drives the reaction toward polymerization through the formation of amide bonds from the acid and amine functions The molten nylon 66 can either be 342 Handbook of Petrochemical Processes extruded and granulated at this point or directly spun into fibers by extrusion through a spinneret a small metal plate with fine holes and cooling to form filaments 824 nitration Similar to the alkylation and the chlorination of benzene the nitration reaction is an electrophilic substitution of a benzene hydrogen a proton with a nitronium NO2 moiety to produce nitroben zene C6H5NO2 The liquidphase reaction occurs in presence of both concentrated nitric and sulfu ric acids at approximately 50C 122F Concentrated sulfuric acid has two functions it reacts with nitric acid to form the nitronium ion and it absorbs the water formed during the reaction which shifts the equilibrium to the formation of nitrobenzene HNO 2H SO 2HSO H O NO 3 2 4 4 3 2 Most of the nitrobenzene produced is used to make aniline Other uses include synthesis of quino line benzidine and as a solvent for cellulose ethers Aniline aminobenzene C6H5NH2 is an oily liquid that turns brown when exposed to air and light The compound is an important dye precursor The main process for producing aniline is the hydrogenation of nitrobenzene The overall process starts with benzene Briefly benzene is nitrated with a concentrated mixture of nitric acid HNO3 and sulfuric acid H2SO4 at 50C60C 122F140F to yield nitrobenzene The nitrobenzene is then hydrogenated typically at 200C300C 390F570F in the presence of metal catalysts Typically the hydrogenation reaction occurs at approximately 270C 520F and slightly above atmospheric pressure approximately 2025 psi over a CuSilica catalyst About a 95 yield is obtained An alternative way to produce aniline is through ammonolysis of either chloro benzene or phenol The reaction of chlorobenzene with aqueous ammonia occurs over a copper salt catalyst at approximately 210C 410F and 950 psi The yield of aniline from this route is also about 96 More specifically in the DupontKBR process benzene is nitrated with mixed acid nitric and sulfuric at high efficiency to produce nitrobenzene in a dehydrating nitration system which uses an inert gas to remove the water of nitration from the reaction mixture thus eliminating the energy intensive and highcost sulfuric acid concentration system As the inert gas passes through the system it becomes humidified removing the water of reaction from the reaction mixture Most of the energy required for the gas humidification comes from the heat of nitration The wet gas is condensed and the inert gas is recycled to the nitrator The condensed organic phase is recycled to the nitrator while the aqueous phase is sent to effluent treatment The reaction mixture is phase separated and the sulfuric acid is returned to the nitrator The crude nitrobenzene is washed to remove residual acid and the impurities formed during the nitration reaction The product is then distilled and residual benzene is recovered and recycled Purified nitrobenzene is fed together with hydrogen into a liquidphase plugflow hydrogenation reactor The supported noble metal catalyst has a high selectivity and the nitrobenzene conversion per pass is 100 The reaction conditions are optimized to achieve essentially quantitative yields and the reactor effluent is free of nitrobenzene The reactor product is sent to a dehydration column to remove the water of reaction followed by a purification column to produce highquality aniline product 343 Chemicals from Aromatic Hydrocarbons Alternatively aniline can be prepared from ammonia and phenol from the cumene process cumenephenol process Hock process which is a process for synthesizing phenol and acetone from benzene and propylene The term process name arise from cumene isopropyl benzene the intermediate material during the process This process converts two relatively cheap starting materials benzene and propylene into two more valuable chemicals phenol C6H5OH and acetone CH3COCH3 Other reactants required are oxygen from air and small amounts of a radical initiator Most of the worldwide production of phenol and acetone is now based on this method In commerce three brands of aniline are distinguished aniline oil for blue which is pure aniline aniline oil for red a mixture of equimolecular quantities of aniline orthotoluidine oCH3C6H4NH2 12CH3C6H4NH2 and paratoluidine pCH3C6H4NH2 14CH3C6H4NH2 and aniline oil for safranin which contains aniline and orthotoluidine and is obtained from the distillate Many analogues of aniline are known where the phenyl group is further substituted These include chemical such as toluidine derivatives xylidine derivatives chloroaniline derivatives aminoaniline derivatives and aminobenzoic acid derivatives These chemicals are often are prepared by nitration of the substituted aromatic compounds followed by reduction For example this approach is used to convert toluene into toluidine derivatives and chlorobenzene into 4chloroanilinew Alternatively using BuchwaldHartwig coupling or Ullmann reaction approaches aryl halides can be aminated with aqueous or gaseous ammonia Ammonolysis of phenol occurs in the vapor phase In the process a mixed feed of ammonia and phenol is heated and passed over a heterogeneous catalyst in a fixedbed system Ono and Ishida 1981 The reactor effluent is cooled the condensed material distilled and the unreacted ammonia recycled The process can be represented simply as C H OH NH C H NH H O 6 5 3 6 5 2 2 825 oxidation Benzene oxidation is the oldest method to produce maleic anhydride The reaction occurs at approximately 380C 715F and atmospheric pressure A mixture of vanadium pentoxide V2O5 with another metal oxide is the usual catalyst Benzene conversion reaches 90 but selectivity to maleic anhydride is only 5060 the other 4050 is completely oxidized to carbon dioxide Currently the major route to maleic anhydride especially for the newly erected processes is the oxidation of butane Chapter 6 Maleic anhydride also comes from oxidation of nbutenes 83 CHEMICALS FROM TOLUENE Toluene also known as toluol the IUPAC systematic name is methylbenzene is an aromatic hydro carbon that is colorless and waterinsoluble It is a monosubstituted benzene derivative consisting of a methal CH3 group attached to the ring Toluene is predominantly used as an industrial feedstock and a solvent Cumene 344 Handbook of Petrochemical Processes The methylbenzene derivatives toluene and the xylene isomers occur in small quantities in naphtha and higherboiling fractions of petroleum Those presently of commercial importance are toluene oxylene pxylene and to a much lesser extent mxylene The primary sources of toluene and the xylene isomers are reformates from catalytic reforming units gasoline from catalytic cracking and pyrolysis naphtha from steam reforming of naphtha and gas oils As men tioned earlier solvent extraction is used to separate these aromatic derivatives from the reformate mixture Toluene and xylenes have chemical characteristics similar to benzene but these charac teristics are modified by the presence of the methyl substituents Although such modification activates the ring toluene and xylenes have less chemicals produced from them than from ben zene Currently the largest single use of toluene is to convert it to benzene The para isomer of xylene pxylene 14CH3C6H4CH3 is mainly used to produce terephthalic acid for polyesters whereas the ortho isomer oxylene 12CH3C6H4CH3 is mainly used to produce phthalic anhy dride for plasticizers Toluene methylbenzene C6H5CH3 is similar to benzene as a mononuclear aromatic but it is more active due to presence of the electrondonating methyl group However toluene is much less useful than benzene because it produces more polysubstituted products Most of the toluene extracted for chemical use is converted to benzene via dealkylation or disproportionation The rest is used to produce a limited number of petrochemicals The main reactions related to the chemical use of toluene other than conversion to benzene are the oxidation of the methyl substituent and the hydrogenation of the phenyl group Electrophilic substitution is limited to the nitration of toluene for producing the mononitro derivative mononitro toluene MNT and dinitrotoluene derivatives These compounds are important synthetic intermediates Generally toluene behaves as a typical aromatic hydrocarbon in electrophilic substitution reac tions The methyl group has greater electronreleasing properties than a hydrogen atom in the same ring position and thus toluene is more reactive than benzene toward electrophilic reagent As example toluene can be sulfonated to yield ptoluene sulfonic acid 14CH3C6H4SO3H and is chlorinated by chlorine in the presence of ferric chloride FeCl3 to yield the ortho and para isomers of chlorotoluene 12CH3C6H4Cl and 14CH3C6H4Cl In addition to reactions involving the ringcarbon atoms the methyl group of toluene is also susceptible to reaction For example toluene reacts with potassium permanganate to yield ben zoic acid C6H5CO2H and also with chromyl chloride to yield benzaldehyde C6H5CHO Other reactions of the methyl group include halogenation such as the reaction with Nbromosuccinimide in the presence of azobisisobutyronitrile abbreviated AIBN CH32CCN2N2 to yield benzyl bromide C6H5CH2Cl The same conversion can be achieved using with elemental bromine Br2 in the presence of ultraviolet UV light or even sunlight Toluene may also be brominated by treating it with hydrogen bromide HBr and hydrogen peroxide H2O2 in the presence of light C H CH Br C H CH Br HBr C H CH Br Br C H CHBr HBr 6 5 3 2 6 5 2 6 5 2 2 6 5 2 Hydrogenation of toluene yields methylcyclohexane in the presence of a catalyst and a high pressure of hydrogen The various reactions of toluene are presented in the section below Toluene 345 Chemicals from Aromatic Hydrocarbons 831 carBonylation The carbonylation reaction of toluene with carbon monoxide in the presence of HFBF3 catalyst produces ptolualdehyde A high yield results 96 based on toluene and 98 based on CO pTolualdehyde CH3C6H4CHO can be oxidized to terephthalic acid 14C6H4CO2H2 an important monomer for polyesters pTolualdehyde is also an intermediate in the synthesis of perfumes dyes and pharmaceuticals 832 chlorination The chlorination of toluene by substituting the methyl hydrogens is a free radical reaction A mix ture of three chlorides benzyl chloride C6H5CH2Cl benzal chloride C6H5CHCl2 and benzotri chloride C6H5CCl3 results The ratio of the chloride mixture mainly derives from the toluenechlorine ratio and the contact time Benzyl chloride is produced by passing dry chlorine into boiling toluene 110C 230F until reaching a density of 1283 At this density the concentration of benzyl chloride reaches the maxi mum Light can initiate the reaction Benzyl chloride can produce benzyl alcohol by hydrolysis represented simply as C H CH Cl H O C H CH OH HCl 6 5 2 2 6 5 2 Benzyl alcohol is a precursor for butyl benzyl phthalate a vinyl chloride plasticizer Benzyl chloride is also a precursor for phenylacetic acid via the intermediate benzyl cyanide Phenylacetic acid is used to make phenobarbital a sedative and penicillin G Benzal chloride is hydrolyzed to benzaldehyde and benzotrichloride is hydrolyzed to benzoic acid C H CHCl C H CHO C H CCl C H CO H 6 5 2 6 5 6 5 3 6 5 2 pTolualdehyde 4Methylbenzaldehyde Terephthalic acid Benzene14dicarboxylic acid Benzyl chloride 346 Handbook of Petrochemical Processes Chlorinated toluene derivatives are not largevolume chemicals but they are precursors for many syn thetic chemicals and pharmaceuticals For example benzyl chloride is the precursor to benzyl esters which are used as plasticizers flavorings and and perfumes Phenylacetic acid C6H5CH2CO2H a precursor to pharmaceuticals is produced from benzyl cyanide which is generated by treatment of benzyl chloride with sodium cyanide C H CH Cl C NaCl 6 5 2 Benzyl chloride will also react with an alcohol to yield the corresponding benzyl ether carboxylic acid and benzyl ester Benzoic acid C6H5COOH can be prepared by oxidation of benzyl chloride in the presence of alkaline potassium permanganate KMnO4 C H CH Cl 2KOH 2 O C H COOK KCl H O 6 5 2 6 5 2 Benzyl chloride also reacts readily with metallic magnesium to produce a Grignard reagent C H CH Cl Mg C H CH ClMgCl 6 5 2 6 5 2 The Grignard reaction is an organometallic chemical reaction in which alkyl vinyl or aromatic magnesium halide will add to a carbonyl group CO in an aldehyde or ketone Figure 82 Thus A Grignard reagent is a strong nucleophiles that can form new carboncarbon bonds In reac tions involving Grignard reagents it is important to exclude water and air which rapidly destroy the reagent by protonolysis or oxidation Since most Grignard reactions are conducted in anhydrous diethyl ether or tetrahydrofuran side reactions with air are limited by the protective blanket pro vided by solvent vapors Although the reagents still need to be dry ultrasound can allow Grignard reagents to form in wet solvents by activating the magnesium such that it consumes the water FIGURE 82 Common reactions of Grignard reagents 347 Chemicals from Aromatic Hydrocarbons 833 dealkylation Dealkylation in the current context is the removal of an alky group from an aromatic ring Rabinovich and Maslyanskii 1973 Noda et al 2009 In the same context hydrodealkylation is a chemical reaction that often involves reacting with an aromatic hydrocarbon derivative such as toluene in the presence of hydrogen to form a simpler aromatic hydrocarbon devoid of the alkyl groups An example is the conversion of 124trilethylbenzene 124CH33C6H3 to xylene CH3C6H4CH3 The process requires high temperature and high pressure or the presence of a cata lyst containing transition metals such as chromium and molybdenum Toluene is dealkylated to benzene over a hydrogenationdehydrogenation catalyst such as nickel Doumani 1958 The hydrodealkylation is essentially a hydrocracking reaction favored at higher temperatures and pressures The reaction occurs at approximately 700C 1290F and 600 psi A high benzene yield of about 96 or more can be achieved C H CH H C H CH 6 5 3 2 6 6 4 Hydrodealkylation of toluene and xylenes with hydrogen is noted in Chapter 3 Dealkylation also can be effected by steam The reaction occurs at 600C800C 1110F1470F over Y La Ce Pr Nd Sm or Th compounds NiCr2O3 catalysts and NiAlO3 catalysts at tempera tures between 320C630C 610F1165F Yields of about 90 are obtained This process has the advantage of producing rather than using hydrogen In the same vein as dealkylation transalkylation is a chemical reaction involving the transfer of an alkyl group from one organic compound to another For example the reaction is used for the transfer of methyl and ethyl groups between benzene rings which is of considerable value to the petrochemical industry for the manufacture of pxylene and styrene as well as other aromatic com pounds Motivation for using transalkylation reactions is based on a difference in production and demand for benzene toluene and the xylene isomers Transalkylation can convert toluene which is overproduced into benzene and xylene which are underproduced Zeolite catalysts are often used as transalkylation reactions The Tatoray process is used to selectively convert toluene and C9 aromatic derivative into ben zene and xylene isomers The process consists of a fixed bed reactor and product separation section The fresh feedstock is combined with hydrogenrich recycle gas preheated in a combined feed exchanger and heated in a fired heater The hot feed vapor goes to the reactor The reactor effluent is cooled in a combined feed exchanger and sent to a product separator Hydrogenrich gas is taken off the top of the separator mixed with makeup hydrogen gas and recycled back to the reactor Liquid from the bottom of the separator is sent to a stripper column where the overhead gas is exported to the fuel gas system The overhead liquid may be sent to a debutanizer column The products from the bottom of the stripper are recycled back to the benzenetoluene fractionation section of the aromatics complex In a modern aromatics complex this process is integrated between the aromatics extraction and xylene recovery sections of the plant Extracted toluene is fed to the Tatoray process unit rather than being blended into the gasoline pool or sold for solvent applications To maximize the production of paraxylene from the complex the byproduct can also be fed to the Tatoray process unit This shifts the chemical equilibrium from benzene production to xylene isomers production In recent years the demand for paraxylene has outstripped the supply of mixed xylene isomers The Tatoray process provides an ideal way to produce additional mixed xylenes from toluene and heavy aromat ics Incorporating a Tatoray process unit into an aromatics complex can more than double the yield of pxylene from a naphtha feedstock In another process the PXPlus process toluene is converted to benzene and xylene isomers The process is paraselective with the product having a concentration of pxylene in the xylene fraction in the order 90 vv which substantially is higher than the equilibrium value of 25 vv that is 348 Handbook of Petrochemical Processes achieved by toluene and C9 aromatic transalkylation in the Tatoray process Due to the similarity of operating temperature and pressure to that of many refining and petrochemical reactor systems existing equipment can often be repurposed for the PXPlus unit The PXPlus process can also be used for largescale grassroot facilities where sufficient toluene is available and where significant quantities of benzene are desired along with pxylene 834 disProPortionation Transalkylation as used by the petrochemical industry is often used to convert toluene into ben zene and xylenes This is achieved through a disproportion reaction of toluene in which one toluene molecule transfers its methyl group to another one The catalytic disproportionation of toluene in the presence of hydrogen produces benzene and a xylene mixture Disproportionation is an equilibrium reaction with a 58 conversion per pass theo retically possible The reverse reaction is the transalkylation of xylenes with benzene Typical conditions for the disproportionation reaction are 450C530C 840F985F and 300 psi A mixture of cobaltmolybdenum CoOMoO3 aluminosilicatealumina catalyst can be used Conversions of approximately 40 are normally used to avoid more side reactions and faster catalyst deactivation The equilibrium constants for this reaction are not significantly changed by shifting from liquid to vapor phase or by large temperature changes Currently zeolites especially those of ZSM5 type are preferred for their higher activities and selectivity They are also more stable thermally Modifying ZSM5 zeolites with phosphorous boron or magnesium compounds produces xylene mixtures rich in the pisomer 7090 ww Diethylbenzene derivatives are produced as sideproducts of the alkylation of benzene with eth ylene Since there is only a limited market for diethylbenzene much of it is recycled by transalkyl ation give ethylbenzene 835 nitration Nitration of toluene is the only important reaction that involves the aromatic ring rather than the aliphatic methyl group The methyl group of toluene makes it around 25 times more reactive than benzene in electrophilic aromatic substitution reactions Toluene undergoes nitration to give ortho and paranitrotoluene 22CH3C6H4NO2 and 24CH3C6H4NO2 isomers but if heated it can give dinitrotoluene and ultimately the explosive trinitrotoluene Humphrey 1916 Toluene 12dinitrotoluene 14dinitrotoluene 246trinitrotoluene The nitration reaction occurs with an electrophilic substitution by the nitronium ion The reaction conditions are milder than those for benzene due to the activation of the ring by the methyl substitu ent and a mixture of NT derivatives is the result The two important monosubstituted NT derivatives are o and pnitrotoluene derivatives oNitrotoluene pNitrotoluene 349 Chemicals from Aromatic Hydrocarbons Methyl nitrobenzene also called mononitro toluene is a group of three organic compounds that are nitroderivatives of toluene or alternatively methyl derivatives of nitrobenzenethe chemical formula is C6H4CH3NO2 Mononitro toluene exists in three isomers and each isomer differs by the relative position of the methyl group and the nitrogroup i orthonitrotoluene onitrotoluene or 2nitrotoluene is a pale yellow liquid with a subtle characteristic smell reminiscent of bitter almonds that is nonhygroscopicthe tendency to absorb moisture from the airand noncorrosive ii metanitrotoluene mnitrotoluene or 3nitrotoluene is a yellowishgreenish to yellow liquid with weak fragrance and iii paranitrotoluene pnitrotoluene or 4nitrotoluene is a pale yellow material that forms rhombic crystals and has a characteristic odor of bitter almonds and is almost insoluble in water The typical use of NT is in production of pigments antioxidants agricultural chemicals and photographic chemicals The MNT derivatives are usually reduced to corresponding toluidine derivatives Table 84 which are used in the manufacture of dyes and rubber chemicals CH C H NO H CH C H NH 3 6 4 2 3 6 4 2 Dinitrotoluene derivatives are produced by nitration of toluene with a mixture of concentrated nitric and sulfuric acid at approximately 80C The main products are 24dinitrotoluene CH3C6H324 NO22 and 26dinitrotoluene CH3C6H326NO22 The dinitrotoluene derivatives are important precursors for toluene diisocyanate derivatives monomers used to produce polyurethanes The mix ture of toluene diisocyanate derivatives is synthesized from dinitrotoluene derivatives by a firststep hydrogenation to the corresponding diamines The diamines are then treated with phosgene to form the toluene diisocyanate derivatives in an approximate 85 ww yield based on toluene An alterna tive route for the production of toluene diisocyanate derivatives is through a liquidphase carbonyl ation of dinitrotoluene in presence of PdC12 catalyst at approximately 250C 480F and 3000 psi In mixed acid nitration plants for the production of dinitrotoluene the spent acid from the MNT stage is purified reconcentrated and recycled back into the nitration process Thus the consump tion of sulfuric acid is considerably reduced In addition also the sulfuric nitric nitrous acid and MNT and dinitrotoluene plants from the washing of the crude nitroproducts and from the purification and reconcentration of the spent acid from the MNT plants are recovered and recycled back into nitration In this manner not only the nitrate load of the waste water from a dinitrotoluene TABLE 84 Isomers of Toluidine Common name otoluidine mtoluidine ptoluidine Other names omethylaniline mmethylaniline pmethylaniline Chemical name 2methylaniline 3methylaniline 4methylaniline Chemical formula C7H9N Structural formula Molecular mass 10717 gmol Melting point 23C 9F 30C 22F 43C 109F Boiling point 199C200C 203C204C 200C Density 100 gcm3 098 gcm3 105 gcm3 350 Handbook of Petrochemical Processes nitration plant is reduced by 95 but also the consumption figures for nitric acid are considerably improved More than 98 of the nitric acid needed for nitration can thus be converted to dinitro toluene Hermann et al 1996 Finally trinitrotoluene is a wellknown explosive Brown 1998 obtained by further nitration of the dinitrotoluene derivatives In the process for the production of trinitrotoluene the trinitrocompound in is produced in a three step process In the first step toluene is nitrated using a mixture of sulfuric and nitric acids to produce MNT which is then separated and in the second step nitrated to produce dinitrotoluene In the third and final step the dinitrotoluene is nitrated to trinitrotoluene using an anhydrous mixture of nitric acid and oleum fuming sulfuric acid usually represented as H2SO4SO3 The nitric acid is consumed by the manufacturing process but the diluted sulfuric acid can be reconcentrated and reused After nitration the trinitrotoluene is stabilized by a process sometime referred to as sulfitation in which the crude trinitrotoluene is treated with aqueous sodium sulfite Na2SO3 solution to remove less stable isomers of trinitrotoluene and other undesired reaction products The rinse water from sulfitation red water is a significant pollutant and waste product from the manufacture of trinitrotoluene Control of the nitrogen oxide derivative in feed nitric acid is very important because the presence of free nitrogen dioxide NO2 can result in the oxidation of the methyl group of toluene This reac tion is highly exothermic and there is the risk of a runaway reaction leading to an explosion Thus when detonated trinitrotoluene decomposes to gases and carbon 2C H N O 3N 5H O 7CO 7C 2C H N O 3N 5H 12CO 2C 7 5 3 6 2 2 7 5 3 6 2 2 Amatol is a highly explosive material that is a mixture of trinitrotoluene and ammonium nitrate NH4NO3 Amatol was used extensively during World War I and World War II typically as an explosive in military weapons such as aircraft bombs canon shells depth charges and naval mines 836 oxidation Oxidizing toluene in the liquid phase over a cobalt acetate catalyst produces benzoic acid C6H5COOH Kaeding et al 1965 The reaction occurs at temperatures in the order of 165C 330F 150 psi The yield is in excess of 90 ww based on the toluene derivative Benzoic acid benzene carboxylic acid is a white crystalline solid with a characteristic odor It is slightly soluble in water and soluble in most common organic solvents Though much benzoic acid gets used as a mordant in calico printing it also serves to season tobacco preserve food make dentifrices and kill fungus Furthermore it is a precursor for caprolactam phenol and terephthalic acid Caprolactam a white solid that melts at 69C 156F can be obtained either in a fused or flaked form It is soluble in water ligroin and chlorinated hydrocarbon derivatives The predominant use of caprolactam is to produce nylon 6 Other minor uses are as a crosslinking agent for polyure thanes in the plasticizer industry and in the synthesis of lysine The first step in producing caprolactam from benzoic acid is the hydrogenation of benzoic acid to cyclohexane carboxylic acid at approximately 170C 340F and 240 psi over a palladium catalyst Trinitrotoluene 351 Chemicals from Aromatic Hydrocarbons The resulting acid is then converted to caprolactam through a reaction with nitrosylsulfuric acid In the process toluene is first oxidized to benzoic acid Benzoic acid is then hydrogenated to cyclohexane carboxylic acid which reacts with nitrosyl sulfuric acid yielding caprolactam Nitrosyl sulfuric acid comes from reacting nitrogen oxides with oleum Caprolactam comes as an acidic solution that is neutralized with ammonia and gives ammonium sulfate as a byproduct of commer cial value Recovered caprolactam is purified through solvent extraction and fractionation The action of a copper salt converts benzoic acid to phenol The copper reoxidized by air func tions as a real catalyst The Lummus process operates in the vapor phase at approximately 250C 480F and the yield of phenol is in the order of 90 In the Lummus process the reaction occurs in the liquid phase at approximately 220C240C 430F465F over Mg2 Cu2 benzoate Magnesium benzoate is an initiator with the Cu2 copper I ions are reoxidized to copper II ions Phenol can also be produced from chlorobenzene and from cumene the major route for this commodity Terephthalic acid is an important monomer for producing polyesters The main route for obtain ing the acid is the catalyzed oxidation of pxylene The reaction occurs in a liquidphase process at approximately 400C 750F using ZnO or CdO catalysts Terephthalic acid is obtained from an acid treatment the potassium salt is recy cled Terephthalic acid can also be produced from benzoic acid by a disproportionation reaction of potassium benzoate in the presence of carbon dioxide However in the process a high temperature diminishes oxygen solubility in an already oxygenstarved system The oxidation is conducted using acetic acid as solvent and a catalyst composed of cobalt and manganese salts using a bromide promoter The yield is nearly quantitative The most problematic impurity is 4formylbenzoic acid which is removed by hydrogenation of a hot aqueous solution after which the solution is cooled in a stepwise manner to crystallize highly pure terephthalic acid Additionally the corrosive nature of any products at high temperatures requires the reaction be run in expensive titanium reactors Alternatively but not commercially significant is the socalled HenkelRaecke process named after the company and patent holder respectively process involves the rearrangement of phthalic acid to terephthalic acid via the corresponding potassium salts Terephthalic acid can be prepared in the laboratory by oxidizing various paradisubstituted derivatives of benzene including Caraway Oil or a mixture of cymene and cuminaldehyde a liquid C3H7C6H4CHO obtained from oil of carawayalso called cuminic aldehyde with chromic acid 14C6H4CH32 14C6H4CO2H Cuminaldehde 352 Handbook of Petrochemical Processes Oxidizing toluene to benzaldehyde C6H5CHO is a catalyzed reaction in which a selective cata lyst limits further oxidation to benzoic acid In the first step benzyl alcohol is formed and then oxidized to benzaldehyde Further oxidation produces benzoic acid C H CH O C H CH OH C H CH OH O C H CHO 6 5 3 6 5 2 6 5 2 6 5 Depending upon the reaction conditions and the nature of the oxidant Borgaonkar et al 1984 the benzyl alcohol may or may not be isolated However in this reaction each successive oxidation occurs more readily than the preceding one more acidic hydrogens after introducing the oxygen heteroatom which facilitates the oxida tion reaction to occur In addition to using a selective catalyst the reaction can be limited to the production of the aldehyde by employing short residence times and a high toluenetooxygen ratio In one process a mixture of UO2 93 and MnO2 7 is the catalyst A yield of 3050 could be obtained at low conversions of 1020 The reaction temperature is approximately 500C 930F In another process the reaction goes forward in the presence of methanol over a FeBr2 CoBr2 catalyst mixture at approximately 100C140C 212F285F Benzaldehyde has limited uses as a chemical intermediate It is used as a solvent for oils resins cellulose esters and ethers It is also used in flavoring compounds and in synthetic perfumes 84 CHEMICALS FROM XYLENE ISOMERS Xylenes dimethylbenzene derivatives are an aromatic mixture composed of three isomers o m and pxylene They are normally obtained from catalytic reforming and cracking units with other C6 C7 and C8 aromatic derivatives Separating the aromatic mixture from the reformate is done by extractiondistillation and isomerization processes Chapter 2 pXylene is the most important of the three isomers for producing terephthalic acid to manu facture polyesters mXylene is the least used of the three isomers but the equilibrium mixture obtained from catalytic reformers has a higher ratio of the meta isomer mXylene is usually isomer ized to the more valuable pxylene As mentioned earlier xylene chemistry is primarily related to the methyl substituents which are amenable to oxidation Approximately 65 of the isolated xylenes are used to make chemicals The rest are either used as solvents or blended with naphtha for gasoline manufacture The catalyzed oxidation of pxylene produces terephthalic acid pHOOCC6H4COOH Cobalt acetate promoted with either sodium bromide NaBr or hydrogen bromide HBr is used as a cata lyst in an acetic acid medium Reaction conditions are approximately 200C 390F and 220 psi The yield is about 95 Special precautions must be taken so that the reaction does not stop at the ptoluic acid H3CC6H4COOH stage One approach is to esterify toluic acid as it is formed with methanol which facilitates the oxidation of the second methyl group The resulting dimethyl terephthalate DMT may be hydrolyzed to terephthalic acid 353 Chemicals from Aromatic Hydrocarbons Another approach is to use an easily oxidized substance such as acetaldehyde or methyl ethyl ketone which under the reaction conditions forms a hydroperoxide These will accelerate the oxi dation of the second methyl group The DMT process encompasses four major processing steps oxidation esterification distillation and crystallization The main use of terephthalic acid and DMT is to produce polyesters for synthetic fiber and film Currently phthalic anhydride is mainly produced through catalyzed oxidation of oxylene A variety of metal oxides are used as catalysts A typical one is V2O5 TiO2Sb2O3 Approximate conditions for the vaporphase oxidation are 375C435C 705F815F and 10 psi The yield of phthalic anhydride is approximately 85 Liquidphase oxidation of axylene also works at approxi mately 150C 300F Cobalt or manganese acetate in acetic acid medium serves as a catalyst The major byproducts of this process are maleic anhydride benzoic acid and citraconic anhydride methyl maleic anhydride Maleic anhydride could be recovered economically The main use for phthalic anhydride is for producing plasticizers by reactions with C4 to C10 alco hols The most important polyvinyl chloride plasticizer is formed by the reaction of 2ethylhexanol produced via butyraldehyde Chapter 8 and phthalic anhydride Phthalic anhydride is also used to make polyester and alkyd resins It is a precursor for phthalo nitrile by an ammoxidation route used to produce phthalimide and phthalimide The oxidation of mxylene produces isophthalic acid The reaction occurs in the liquid phase in presence of a catalyst such as a cobaltmanganese catalyst The main use of isophthalic acid is in the production of polyesters that are characterized by a higher abrasion resistance than those using other phthalic acids Polyesters from isophthalic acid are used for pressure molding applications Ammoxidation of isophthalic acid produces isophthalo nitrile which serves as a precursor for agricultural chemicals It is readily hydrogenated to the cor responding diamine which can form polyamides or be converted to isocyanates for polyurethane manufacture Similarly phthalonitrilean organic compound with the formula C6H4CN2 which is an off white crystal solid at room temperatureis a derivative of benzene that contains two adjacent nitrile groups The compound has low solubility in water but is soluble in common organic solvents The compound is used as a precursor to phthalocyanine and other pigments fluorescent brighteners and photographic sensitizers Phthalonitrile is produced in a singlestage continuous process by the ammonoxidation of oxylene at 480C 895F in the presence of a vanadium oxideantimony oxide V2O4Sb2O4 catalyst Isophthalic acid 354 Handbook of Petrochemical Processes Phthalonitrile is the precursor to phthalocyanine pigments which are produced by the reaction of phthalonitrile with various metal precursors The reaction is carried out in a solvent at around 180C 355F Ammonolysis of phthalonitrile yields diiminoisoindole which reacts by condensation with active methylene compounds to give pigment yellow 185 and pigment 139 The molecule can exist in different tautomers resulting in different crystalline solids By way of definition a tautomer is each of two or more isomers of a compound that exist together in equi librium and are readily interchanged by migration of an atom or group within the molecule Thus tautomers are constitutional isomers of organic compounds that readily interconvert and the reaction commonly results in the relocation of a proton Tautomerism is for example relevant to the behavior of amino acids and nucleic acids two of the fundamental building blocks of life The TAC9 process is used to selectively convert C9 to C10 aromatics into mixed xylene isomers The process consists of a fixed bed reactor and product separation section The feed is combined with hydrogenrich recycle gas preheated in a combined feed exchanger and heated in a fired heater and the heated feedstock is sent to the reactor The reactor effluent is cooled in a combined feed exchanger and sent to a product separator Hydrogenrich gas is taken off the top of the separator mixed with makeup hydrogen gas and recycled back to the reactor Liquid from the bottom of the separator is sent to a stripper column The stripper overhead gas is exported to the fuel gas system The overhead liquid may be sent to a debutanizer column or a stabilizer The stabilized product is sent to the product fractionation section of the aromatics complex In a modern aromatics complex the transalkylation technologies such as the Tatoray and TAC9 processes are integrated between the aromatics extraction or fractionation and the xylene recovery sections of the plant Fractionated highboiling aromatic derivatives can be fed to the TAC9 unit rather than being blended into the gasoline pool or sold for solvent applications Incorporating transalkylation technology into an aromatics complex for the processing of toluene and C9 to C10 aromatics can more than double the yield of pxylene from a given naphtha feedstock The process provides an efficient means of obtaining additional mixed xylenes from the highestboiling portion of an aromatics fraction thereby producing highervalue products by upgrading byproduct streams Diiminoisoindole 355 Chemicals from Aromatic Hydrocarbons 85 CHEMICALS FROM ETHYLBENZENE Ethylbenzene C6H5CH2CH3 is a highly flammable colorless liquid which is an important chemi cal as an intermediate in the production of styrene the precursor to polystyrene It is one of the C8 aromatic constituents of the products reformates of reforming processes Ethylbenzene can be obtained by intensive fractionation of the aromatic extract but most of the ethylbenzene is obtained by the alkylation of benzene with ethylene C H CH CH C H CH CH 6 6 2 2 6 5 2 3 For example a zeolitebased process using vaporphase alkylation offered a higher purity and yield of ethylbenzene after which a liquidphase process was introduced using zeolite catalysts This liquidphase process offers low benzenetoethylene ratios thereby leading to a reduction in the size of the required equipment and lowering byproduct production Direct dehydrogenation of ethylbenzene to styrene accounts for the majority approximately 85 of the commercial production and the reaction is carried out in the vapor phase with steam over a catalyst consisting primarily of iron oxide The reaction is endothermic and can be accom plished either adiabatically or isothermally Both methods are used in practice The major reaction is the reversible endothermic conversion of ethylbenzene to styrene and hydrogen C H CH CH C H CH CH H 6 5 2 3 6 5 2 2 This reaction proceeds thermally with low yield and catalytically with high yield As it is a revers ible gasphase reaction producing 2 mol of product from 1 mol of starting material low pressure favors the forward reaction In the process ethylbenzene is mixed in the gas phase with 1015 times of its volume of high temperature steam and passed over a solid catalyst bed Most ethylbenzene dehydrogenation catalysts are based on iron oxide Fe2O3 promoted by several percent potassium oxide K2O or potassium carbonate K2CO3 In this reaction steam i is the source of heat for powering the endothermic reaction and ii removes coke that tends to form on the iron oxide catalyst through the water gasshift reaction The potassium promoter enhances this decoking reaction The steam also dilutes the reactant and products shifting the position of chemical equilibrium toward products A typical styrene plant consists of two or three reactors in series which operate under vacuum to enhance the conversion and selectivity The development of commercial processes for the manufacture of styrene based on the dehy drogenation of ethylbenzene was achieved in the 1930s The need for synthetic styrene butadiene rubber ESBR during World War II provided the impetus for largescale production After 1946 this capacity became available for the manufacture of a highpurity monomer that could be polymer ized to a stable clear colorless and cheap plastic polystyrene and styrene copolymers Peacetime uses of styrenebased plastics expanded rapidly and polystyrene is now one of the least expensive thermoplastics on a costpervolume basis However there are competing thermal reactions degrade ethylbenzene to benzene and also to car bon and in addition styrene also reacts catalytically with hydrogen to produce toluene and methane C H CH CH C H CH CH C H CH CH 8C 5H C H CH CH H C H CH CH 6 5 2 3 6 6 2 2 6 5 2 3 2 6 5 2 2 6 5 3 4 356 Handbook of Petrochemical Processes The problem with carbon production is that carbon is a catalyst poison When potassium is incorporated into the iron oxide catalyst the catalyst becomes selfcleaning through enhance ment of the reaction of carbon with steam to give carbon dioxide which is removed in the reactor vent gas Thus C 2H O CO 2H 2 2 2 The typical operating conditions in commercial reactors are in the order of 620640C 1150F640F and at low pressure Improving conversion and so reducing the amount of ethylben zene that must be separated is the chief impetus for researching alternative routes to styrene Styrene is also coproduced commercially in the propylene oxidestyrene monomer POSM pro cess In this process ethylbenzene is treated with oxygen to form the ethylbenzene hydroperoxide This hydroperoxide is then used to oxidize propylene to propylene oxide The resulting 1phenylethanol is dehydrated to give styrene Styrene is a colorless liquid with a distinctive sweetish odor Some physical properties of styrene are summarized on the right Vapor pressure is a key property in the design of styrene distillation equipment Styrene is miscible with most organic solvents in any ratio It is a good solvent for syn thetic rubber polystyrene and other noncrosslinked high polymers Styrene and water are spar ingly soluble in each other The majority of all operating styrene plants carry out the dehydrogenation reaction adiabati cally a process condition in which heat does not enter or leave the system concerned in multiple reactors or reactor beds operated in series The necessary heat of reaction is applied at the inlet to each stage either by injection of superheated steam or by indirect heat transfer Fresh ethylbenzene feed is mixed with recycled ethylbenzene and vaporized Dilution steam must be added to prevent the ethylbenzene from forming coke This stream is further heated by heat exchange superheated steam is added to bring the system up to reaction temperature and the stream is passed through catalyst in the first reactor The adiabatic reaction drops the temperature so the outlet stream is reheated prior to passage through the second reactor Conversion of ethylbenzene can vary with the system but is often about 35 in the first reactor and 65 overall The reactors are run at the low est pressure that is safe and practicable Some units operate under vacuum while others operate at a low positive pressure The steamethylbenzene ratio fed to the reactors is chosen to give optimum yield with mini mum utility cost The reactor effluent is fed through an efficient heat recovery system to minimize energy consumption condensed and separated into vent gas a crude styrene hydrocarbon stream and a steam condensate stream The crude styrene is sent to a distillation system where the steam 357 Chemicals from Aromatic Hydrocarbons condensate is steamstripped treated and reused The vent gas mainly hydrogen and carbon diox ide is treated to recover aromatics after which it can be used as a fuel or a feed stream for chemical hydrogen Isothermal dehydrogenation was pioneered by BASF and has been used for many years using a reactor that is constructed like a shellandtube heat exchanger Ethylbenzene and steam flow through the tubes which are packed with catalyst where the heat of reaction is supplied by hot flue gas on the shell side of the reactorexchanger The steamfeedstock mass ratio can be lowered to approximately 11 and steam temperatures are lower than in the adiabatic process A disadvantage is the practical size limitation on a reactorexchanger which restricts the size of a single train A typical crude styrene mixture from the dehydrogenation process consists of i benzene boiling point 80C 176F ii toluene boiling point 110C 230F ethylbenzene boiling point 136C 277F styrene boiling point 145C 293F The separation of these components is reasonably straightforward but residence time at elevated temperature needs to be minimized to reduce styrene polymerization At least three steps are involved i benzene and toluene are removed and either sent to a toluene dehydrogenation plant or further separated into benzene for recycling and toluene for sale ii ethylbenzene is then separated and recycled to the reactors and iii styrene is distilled away from the tars and polymers under vacuum to keep the temperature as low as possible Ethylbenzene and styrene having similar boiling points require 70100 trays for their separa tion depending on the desired ethylbenzene content of the finished styrene If bubblecap trays are used as in old plants a large pressure drop over the trays means that two columns in series are necessary to keep reboiler temperatures low Most of the modern plants use packing in place of trays which permits this separation to be achieved in one column This results in less pressure drop giving a lower bottom temperature shorter residence time and hence less polymer Sulzer has done pioneering work in the field of packings for distillation A polymerization inhibitor distillation inhibitor is needed throughout the distillation train Today usually aromatic compounds with amino nitro or hydroxy groups are used such as phen ylenediamine derivatives dinitrophenol derivatives and dinitrocresol derivatives The distilla tion inhibitor tends to be colored and is thus unacceptable in the final product and the finished monomer is usually inhibited instead with a chemical such as tertbutylcatechol during storage and transportation Styrene can be produced from toluene and methanol which are cheaper raw materials than those in the conventional process Another route to styrene involves the reaction of benzene and ethane Ethane along with ethylbenzene is fed to a dehydrogenation reactor with a catalyst capable of simul taneously producing styrene and ethylene The dehydrogenation effluent is cooled and separated and the ethylene stream is recycled to the alkylation unit REFERENCES Alotaibi A Hodgkiss S Kozhevnikova EF and Kozhevnikov IV 2017 Selective alkylation of benzene by propane over bifunctional Pdacid catalysts Catalysts 7 303312 Birch AJ 1944 Reduction by dissolving metals Part I Journal of the Chemical Society 430 Birch AJ 1945 Reduction by dissolving metals Part II Journal of the Chemical Society 809 Birch AJ 1946 Reduction by dissolving metals Part III Journal of the Chemical Society 593 Birch AJ 1947a Reduction by dissolving metals Part IV Journal of the Chemical Society 102 Birch AJ 1947b Reduction by dissolving metals Part V Journal of the Chemical Society 1642 Birch AJ and Smith H 1958 Reduction by metalamine solutions Applications in synthesis and determi nation of structure Quarterly Reviews of the Chemical Society 121 17 Borgaonkar HV Raverkar SR and Chandalia SB 1984 Liquid phase oxidation of toluene to benzalde hyde by air Industrial Engineering Chemistry Product Research Development 233 455458 Brown GI 1998 The Big Bang A History of Explosives Sutton Publishing Stroud Doumani T 1958 Dealkylation of organic compounds Benzene from toluene Industrial Engineering Chemistry 5011 16771680 358 Handbook of Petrochemical Processes Gary JG Handwerk GE and Kaiser MJ 2007 Petroleum Refining Technology and Economics 5th Edition CRC Press Taylor Francis Group Boca Raton FL Gosling CD Wilcher FP Sullivan L and Mountiford RA 1999 Process LPG to BTX products Hydrocarbon Processing 69 Hermann H Gebauer J and Konieczny 1996 Chapter 21 Requirements of a modern facility for the production of dinitrotoluene In ACS Symposium Series Vol 623 pp 234249 Hsu CS and Robinson PR Editors 2017 Handbook of Petroleum Technology Springer International Publishing AG Cham Huang X Sun X Zhu S and Liu Z 2007 Benzene alkylation with propane over metal modified HZSM5 Reaction Kinetics and Catalysis Letters 91 385390 Humphrey IW 1916 The nitration of toluene to trinitrotoluene Industrial Engineering Chemistry 811 998999 Kaeding WW Lindblom RO Temple RG and Mahon HI 1965 Oxidation of toluene and other alkylated aromatic hydrocarbons to benzoic acids and phenols Industrial Engineering Chemistry Process Design and Development 41 97101 Kato S Nakagawa K Ikenaga N and Suzuki T 2001 Alkylation of benzene with ethane over platinum loaded zeolite catalyst Catalysis Letters 73 175180 March J 1985 Advanced Organic Chemistry Reactions Mechanisms and Structure 3rd Edition John Wiley Sons Inc Hoboken NJ Noda J Volkamer R and Molina MJ 2009 Dealkylation of alkylbenzenes A significant pathway in the toluene o m pxylene OH reaction Journal of Physical Chemistry 11335 96589666 Ono Y and Ishida H 1981 Amination of phenols with ammonia over palladium supported on alumina Journal of Catalysis 721 121128 Parkash S 2003 Refining Processes Handbook Gulf Professional Publishing Elsevier Amsterdam Rabinovich GL and Maslyanskii GN 1973 A new process for toluene dealkylation Chemistry and Technology of Fuels and Oils 9 8587 Speight JG 2014 The Chemistry and Technology of Petroleum 4th Edition CRCTaylor and Francis Group Boca Raton FL Speight JG 2017 Handbook of Petroleum Refining CRC Press Taylor Francis Group Boca Raton FL Weissermel K and Arpe HJ 2003 Industrial Organic Chemistry WileyVCH Weinheim 359 9 Chemicals from Nonhydrocarbons 91 INTRODUCTION By way of recall a petrochemical is any chemical as distinct from the bulk product which are used for fuels and other petroleum products manufactured from petroleum and natural gas and used for a variety of commercial purposes Petroleum and natural gas are made up of hydrocarbon con stituents which are comprised of one or more carbon atoms to which hydrogen atoms are attached Currently through a variety of intermediates petroleum and natural gas are the main sources of the raw materials because they are the least expensive most readily available and can be processed most easily into the primary petrochemicals An aromatic petrochemical is also an organic chemi cal compound but one that contains or is derived from the basic benzene ring system However the definition of petrochemicals has been broadened and includes with justification not only the whole range of aliphatic aromatic and naphthenic organic chemicals but also nonorganic chemicals such as carbon black sulfur ammonia nitric acid hydrazine and synthesis gas Primary petrochemicals include olefins ethylene propylene and butadiene aromatics benzene toluene and the isomers of xylene and methanol Thus petrochemical feedstocks can be classi fied into three general groups olefins aromatics and methanol a fourth group includes inorganic compounds and synthesis gas mixtures of carbon monoxide and hydrogen In many instances a specific chemical included among the petrochemicals may also be obtained from other sources such as coal coke or vegetable products For example materials such as benzene and naphthalene can be made from either petroleum or coal while ethyl alcohol may be of petrochemical or veg etable origin From natural gas crude oils and other fossil materials such as coal few intermediates are pro duced that are not hydrocarbon compounds Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 The important intermediates discussed here are hydrogen sul fur carbon black and synthesis gas Synthesis gas consists of a nonhydrocarbon mixture carbon monoxide CO and hydrogen H2 that is obtained from any one of several carbonaceous sources Chadeesingh 2011 Speight 2014b It is included in this chapter as a point of acknowledgment but the reaction if synthesis gas are covered in more detail in a later chapter As stated above some of the chemicals and compounds produced in a refinery are destined for further processing and as raw material feedstocks for the fastgrowing petrochemical industry Such nonfuel uses of crude oil products are sometimes referred to as its nonenergy uses Petroleum products and natural gas provide three of the basic starting points for this industry methane from natural gas and naphtha and refinery gases Petrochemical intermediates are generally produced by chemical conversion of primary petro chemicals to form more complicated derivative products Petrochemical derivative products can be made in a variety of ways directly from primary petrochemicals through intermediate prod ucts which still contain only carbon and hydrogen and through intermediates which incorporate chlorine nitrogen or oxygen in the finished derivative In some cases they are finished products in others more steps are needed to arrive at the desired composition Although the focus of this text has been the production of organic petrochemical derivatives mention needs to be made of the inorganic petrochemical products Thus an inorganic petrochem ical is one that does not contain carbon atoms typical examples are sulfur S ammonium sulfate 360 Handbook of Petrochemical Processes NH42SO4 ammonium nitrate NH4NO3 and nitric acid HNO3 Goldstein 1949 Hahn 1970 Lowenheim and Moran 1975 Chemier 1992 Wittcoff and Reuben 1996 Speight 2002 Farhat Ali et al 2005 Speight 2011a 2014a It would be serious omission if other sources of petro chemicals were ignored since the use of these materials can if left unattended in nature cause several damage to the environment Typically these sources are mixed waste polymers which contain a variety of chemical structures and are usually classed as nonhydrocarbonsAn inor ganic compound is typically a chemical compound that lacks carbonhydrogen CH bonds that is a compound that is not an organic compound but the distinction is not defined or even of particular interest Inorganic compounds comprise most of the earths crust although the com position of the deep mantle remains active areas of investigation Inorganic compounds can be defined as any compound that is not organic compound Some simple compounds that contain carbon are often considered inorganic Examples include carbon monoxide carbon dioxide car bonate derivatives cyanide derivatives derivatives carbide derivatives and thiocyanate deriva tives Many of these are normal parts of mostly organic systems including organisms which means that describing a chemical as inorganic does not obligately mean that it does not occur within floral and faunal species Industrial inorganic chemistry includes subdivisions of the chemical industry that manufacture inorganic products on a large scale such as the heavy inorganics chloralkalis sulfuric acid sul fates and fertilizers potassium nitrogen and phosphorus products as well as segments of fine chemicals that are used to produce highpurity inorganics on a much smaller scale Among these are reagents and raw materials used in hightech industries pharmaceuticals or electronics for example as well as in the preparation of inorganic specialties such as catalysts pigments and propellants Metals are chemicals and they are manufactured from ores and purified by many of the same processes as those used in the manufacture of inorganics However if they are commer cialized as alloys or in their pure form such as iron lead copper or tungsten they are considered products of the metallurgical not chemical industry Thus in this book inorganic chemistry is concerned with the properties and behavior of inorganic compounds which include metals minerals and organometallic compounds While organic chem istry is the study of carboncontaining compounds and inorganic chemistry is the study of the remaining subset of compounds other than organic compounds there is overlap between the two fields such as organometallic compounds which usually contain a metal or metalloid bonded directly to carbon Specific examples of inorganic chemicals prepared from petrochemical sources are presented below and included ammonia hydrazine hydrogen nitric acid sulfur and sulfuric acid which are presented below in alphabetical order rather than in any order of preference 92 AMMONIA Ammonia NH3 is a compound of nitrogen and hydrogen that exists as a colorless pungent gas which has a high degree of water solubility where it forms a weakly basic solution Either directly or indirectly ammonia is a building block for the synthesis of many pharmaceutical products and is used in many commercial cleaning products It is mainly collected by downward displacement of both air and water Ammonia boils at 3334C 28012F under ambient pressure so the liquid must be stored under pressure or at low temperature Household ammonia or ammonium hydroxide NH4OH is a solution of NH3 in water Ammonia could be easily liquefied under pressure liquid ammonia and it is an important refrigerant Anhydrous ammonia is a fertilizer by direct application to the soil Ammonia is obtained by the reaction of hydrogen and nitrogen both of which are produced in a refinery and represented simply as N 3H 2NH 2 2 3 361 Chemicals from Nonhydrocarbons Ammonia is one of the most important inorganic chemicals exceeded only by sulfuric acid and lime It is a nitrogen source in fertilizer and it is one of the major inorganic chemicals used in the production of nylons fibers plastics polyurethanes used in tough chemicalresistant coatings adhesives and foams hydrazine used in jet and rocket fuels and explosives 921 Production The production of ammonia is of historical interest because it represents the first important applica tion of thermodynamics to an industrial process Before the start of World War I most ammonia was obtained by the dry distillation of nitrogenous vegetable waste and animal waste products where it was distilled by the reduction of nitrous acid and nitrates with hydrogen In addition ammonia was also produced by the distillation of coal as well as by the decomposition of ammonium salts by alka line hydroxides such as quicklime CaOH2 the salt most generally used is the chloride NH4Cl Hydrogen for ammonia synthesis could also be produced economically by using the watergas reaction followed by the watergas shift reaction produced by passing steam through redhot coke to give a mixture of hydrogen and carbon dioxide gases followed by removal of the carbon dioxide washing the gas mixture with water under pressure or by using other sources like coal or coke gasification Modern ammoniaproducing plants depend on industrial hydrogen production to react with atmospheric nitrogen using a magnetite catalyst Fe3O4 or sometime written as FeO Fe2O3 or over a promoted Fe catalyst under high pressure 1500 psi and temperature 450C 840F to form anhydrous liquid ammonia the HaberBosch process N 3H 2NH 2 2 3 Increasing the temperature increases the reaction rate but decreases the equilibrium Kc at 500C 008 According to the Le Chatelier principle the equilibrium is favored at high pressures and at lower temperatures Much of Habers research was to find a catalyst that favored the forma tion of ammonia at a reasonable rate at lower temperatures Iron oxide promoted with other oxides such as potassium and aluminum oxides is currently used to produce ammonia in good yield at relatively low temperatures In the process a mixture of hydrogen and nitrogen exit gas from the methanator in a ratio of 31 is compressed to the desired pressure 670015000 psi The compressed mixture is then preheated by heat exchange with the product stream before entering the ammonia reactor The reac tion occurs over the catalyst bed at about 450C 840F The exit gas containing ammonia is passed through a cooling chamber where ammonia is condensed to a liquid while unreacted hydrogen and nitrogen are recycled Usually a conversion of approximately 15 per pass is obtained under these conditions The most popular catalysts are based on iron promoted with potassium oxide K2O calcium oxide CaO silica SiO2 and alumina Al2O3 The original HaberBosch reactions contained osmium as the catalyst but it was available in extremely small quantities There is also an iron based catalyst that is still used in modern ammonia production plants Some ammonia production utilizes rutheniumbased catalysts the KAAP process which allow milder operating pressures because of the high activity of the catalyst In industrial practice the iron catalyst is obtained from finely ground iron powder which is usu ally obtained by reduction of highpurity magnetite Fe3O4 The pulverized iron metal is burned oxidized to give magnetite of a defined particle size and the magnetite particles are then partially reduced removing some of the oxygen in the process The resulting catalyst particles consist of a core of magnetite encased in a shell of wűstite FeO ferrous oxide which in turn is surrounded by an outer shell of iron metal The catalyst maintains most of its bulk volume during the reduction resulting in a highly porous high surface area material which enhances its effectiveness as a catalyst 362 Handbook of Petrochemical Processes Other minor components of the catalyst include calcium oxide and aluminum oxide which support the iron catalyst and help it maintain its surface area The oxides of calcium aluminum potassium and silicon are unreactive immune to reduction by the hydrogen As a sustainable alternative to the relatively inefficient and energyintensive electrolysis process hydrogen can be generated from organic wastes such as biomass or foodindustry waste using catalytic reforming This releases hydrogen from carbonaceous substances at only 1020 of energy used by electrolysis and may lead to hydrogen being produced from municipal wastes at below zero cost allowing for the tipping fees and efficient catalytic reforming such as cold plasma Catalytic thermal reforming is possible in small distributed even mobile plants to take advan tage of lowvalue stranded biomassbiowaste or natural gas deposits Conversion of such wastes into ammonia solves the problem of hydrogen storage as hydrogen can be released economically from ammonia on demand without the need for high pressure or cryogenic storage It is also easier to store ammonia onboard vehicles than to store hydrogen as ammonia is less flammable than naphthagasoline or liquefied petroleum gas LPG 922 ProPerties and uses Ammonia is a colorless gas with a distinct odor and is a building block chemical and a key com ponent in the manufacture of many products people use every day It occurs naturally through out the environment in the air soil and water and in plants and animals including humans The human body makes ammonia when the body breaks down foods containing protein into amino acids and ammonia then converting the ammonia into urea H2NCONH2 Ammonium hydroxide NH4OHcommonly known as household ammoniais an ingredient in many everyday house hold cleaning products In the process to produce urea from ammonia NH3 and carbon dioxide CO2 Stamicarbon CO2 stripping Urea 2000 plus Technology ammonia and carbon dioxide are reacted at 2100 psi bar to urea and carbamate a carbamate is an organic compound derived from carbamic acid NH2COOH The conversion of ammonia as well as carbon dioxide in the synthesis section results in a low recycle flow of carbamate Because of the highammonia efficiency no pure ammonia is recycled in this process The synthesis temperature of 185C 365F is low and consequently corrosion is negligible Because of the high conversions in the synthesis the recycle section of the plant is very small An evaporation stage with vacuum condensation system produces urea melt with the required concentration for the Stamicarbon fluidized bed granulation Process water produced in the plant is treated in desorptionhydrolyzer section that produces an effluent which is suitable for use as boiler feedwater One further step although not true a nonorganic step is worthy of men tion here as a follow on from urea production and that is the production ureaformaldehyde resins The chemical structure of the ureaformaldehyde polymer consists of OCNHCH2NHn repeat units Chapter 11 The majority of the ammonia produced is used in fertilizer to help sustain food production The production of food crops naturally depletes soil nutrient supplies In order to maintain healthy crops farmers rely on fertilizers to maintain productivity of the soil and to maintain or increase the levels of essential nutrients such as like zinc selenium and boron in food crops Ammonia is also used in many household cleaning products and can be used to clean a vari ety of household surfacesfrom tubs sinks and toilets to bathroom and kitchen countertops and tiles Ammonia also is effective at breaking down household grime or stains from animal fats or vegetable oils such as cooking grease and wine stains Because ammonia evaporates quickly it is commonly used in glass cleaning solutions to help avoid streaking When used as a refrigerant gas and in airconditioning equipment ammonia can absorb substan tial amounts of heat from its surroundings Ammonia can be used to purify water supplies and as a building block in the manufacture of many products including plastics explosives fabrics pesti cides and dyes Ammonia is also used in the waste and wastewater treatment cold storage rubber 363 Chemicals from Nonhydrocarbons pulp and paper and food and beverage industries as a stabilizer neutralizer and a source of nitrogen as well as in the manufacture of pharmaceutical products In organic chemistry ammonia can act as a nucleophile in substitution reactions and as an example amines RNH2 can be formed by the reaction of ammonia with an alkyl halide RCl although the resulting amino NH2 group is also nucleophilic and secondary and tertiary amines are often formed as byproducts As an example methylamine CH3NH2 is produced commercially by the reaction of ammonia with chloromethane CH3Cl Amide derivatives can be prepared by the reaction of ammonia with carboxylic acid derivatives In addition ammonium salts of carboxylic acids RCO NH 2 4 can be dehydrated to amides so long as there are no thermally sensitive groups present temperatures of 150C200C 300F390F are required Also the hydrogen in ammonia is capable of replacement by metalsas an example magnesium burns in ammonias with the formation of magnesium nitride Mg3N2 and when the gas is passed over heated sodium or potassium sodamide NaNH2 orand potassamide KNH2 are formed 93 CARBON BLACK Carbon black also classed as an inorganic petrochemical is made predominantly by the partial combustion of carbonaceous organic material such as fluid catalytic cracker bottoms and other cracker bottoms in a limited supply of air It has a high surface area to volume ratio and a signifi cantly lower negligible content of polynuclear aromatic hydrocarbon derivative However carbon black is widely used as a model compound for diesel soot for diesel oxidation experiments Carbon black is mainly used as a reinforcing filler in vehicle tires and other rubber products It is also used as a color pigment in plastics paints and inks The carbonaceous sources vary from methane to aromatic petroleum oils to coal tar byproducts The carbon black is used primarily for the production of synthetic rubber Carbon black also classed as an inorganic petrochemical is made predominantly by the partial combustion of carbonaceous organic material in a limited supply of air The carbonaceous sources vary from methane to aro matic petroleum oils to coal tar byproducts The carbon black is used primarily for the production of synthetic rubber Carbon black is an extremely fine powder of great commercial importance especially for the synthetic rubber industry The addition of carbon black to tires lengthens its life extensively by increasing the abrasion and oil resistance of rubber Carbon black consists of elemental carbon with variable amounts of volatile matter and ash There are several types of carbon blacks and their characteristics depend on the particle size which is mainly a function of the production method 931 Production Carbon black is produced by the partial combustion or the thermal decomposition of natural gas or petroleum distillates and residues Petroleum products rich in aromatics such as tars produced from catalytic and thermal cracking units are more suitable feedstocks due to their high carbonhydrogen ratios These feedstocks produce black with a carbon content of approximately 92 ww Coke pro duced from delayed and fluid coking units with low sulfur and ash contents has been investigated as a possible substitute for carbon black Three processes are currently used for the manufacture of carbon blacks i the channel ii the furnace black process and iii the thermal process The channel process is mainly of historical interest because not more than 5 of the carbon black products are manufactures by this route In this process the feedstock eg natural gas is burned in small burners with a limited amount of air Some methane is completely combusted to carbon dioxide and water producing enough heat for the thermal decomposition of the remain ing natural gas The formed soot collects on cooled iron channels from which the carbon black is 364 Handbook of Petrochemical Processes scraped Channel black is characterized by having a lower pH higher volatile matter and smaller average particle size than blacks from other processes The furnace black process is a more advanced partial combustion process The feedstock is first preheated and then combusted in the reactor with a limited amount of air The hot gases containing carbon particles from the reactor are quenched with a water spray and then further cooled by heat exchange with the air used for the partial combustion The type of black produced depends on the feed type and the furnace temperature In the thermal process the feedstock natural gas is pyrolyzed in preheated furnaces lined with a checker work of hot bricks The pyrolysis reaction produces carbon that collects on the bricks The cooled bricks are then reheated after carbon black is collected 932 ProPerties and uses Carbon black subtypes acetylene black channel black furnace black lamp black and thermal black is a material produced by the incomplete combustion of highboiling crude oil products such as the bottoms from a fluid catalytic cracking unit or the bottoms from an ethylene cracking unit Carbon black is a form of crystalline carbon that has a high surface area to volume ratio but lower than the surface area to volume ratio of activated carbon It is dissimilar to soot in that the surface area to volume ratio is higher than the surface area to volume ratio of soot and is also significantly lower negligible in the content of polycyclic aromatic hydrocarbon derivatives PAHs or poly nuclear aromatic hydrocarbon derivatives PNAs Carbon black produced by the channel process was generally acidic while those produced by the furnace process and the thermal process are slightly alkaline The pH of the black has a pronounced influence on the vulcanization time of the rubber Vulcanization is a physicochemical reaction by which rubber changes to a thermosetting mass due to crosslinking of the polymer chains by adding certain agents such as sulfur The basic nature higher pH of furnace blacks is due to the presence of evaporation deposits from the water quench Thermal blacks due to their larger average particle size are not suitable for tire bodies and tread bases but they are used in inner tubes footwear and paint pigment Gas and oil furnace carbon blacks are the most important forms of carbon blacks and are generally used in tire treads and tire bodies Carbon black is also used as a pigment for paints and printing inks as a nucleation agent in weather modifications and as a solar energy absorber About 70 of the worlds consumption of carbon black is used in the production of tires and tire products Approximately 20 goes into other products such as footwear belts and hoses and the rest is used in such items as paints and printing ink The important properties of carbon black are particle size surface area and pH These proper ties are functions of the production process and the feed properties Thus it is widely used as a reinforcing filler in tires and other rubber products Practically all rubber products where tensile and abrasion wear properties are important use carbon black so they are black in color Carbon black is also used as a color pigment in plastics paints and inks 94 CARBON DIOXIDE AND CARBON MONOXIDE Carbon dioxide CO2 is a colorless gas with a density about 60 higher than that of dry air In the current context it is present in reservoirs of crude oil and natural gas and may be isolated from these sources as a usefulsalable product Carbon dioxide is odorless at normally encountered con centrations However at high concentrations it has a sharp and acidic odor Carbon monoxide CO is a colorless odorless and tasteless gas that is slightly less dense than air It is toxic to hemoglobic animals animals with hemoglobin in the blood stream with which carbon monoxide form a complex thereby displacing oxygen from the blood of the hemoglobic animals In the atmosphere it is shortlived having a role in the formation of groundlevel ozone 365 Chemicals from Nonhydrocarbons 941 Production Carbon dioxide is a produced during the production of hydrogen by steam reforming and by the watergas shift reaction in gasification of carbonaceous feedstocks Chapter 5 These processes begin with the reaction of water and natural gas mainly methane In terms of biomass as the source material Chapter 3 carbon dioxide is a byproduct of the fermentation of sugar and starch derivatives C H O 2CO 2C H OH 6 12 6 2 2 5 In addition carbon dioxide is one the byproducts of gas cleaning processesone of the most impor tant aspects of gas processing involves the removal of hydrogen sulfide and carbon dioxide which are generally referred to as contaminants Chapter 4 Natural gas from some wells crude oil wells and gas wells contains significant amounts of hydrogen sulfide and carbon dioxide and is usually referred to as sour gas Sour gas is undesirable because the sulfur compounds it contains can be extremely harmful even lethal to breathe and the gas can also be extremely corrosive The pro cess for removing hydrogen sulfide from sour gas is commonly referred to as sweetening the gas Mokhatab et al 2006 Speight 2007 2014a Also carbon dioxide comprises about 4045 vv of the gas that emanates from decomposi tion in landfills landfill gas Chapter 3most of the remaining 5055 vv of the landfill gas is methane A major industrial source of carbon monoxide is producer gas Chapter 5 a mixture contain ing mostly carbon monoxide and nitrogen formed by gasification of carbonaceous feedstocks Chapter 5 when there is an excess of carbon deficiency of oxygen In the process air is passed through a bed of the carbonaceous feedstock and the initially produced carbon dioxide equilibrates with the remaining hot carbon to yield carbon monoxide the Boudouard reaction Above 800C 1470F carbon monoxide is the predominant product CO C 2CO 2 Another source of carbon monoxide is water gas a mixture of hydrogen and carbon monoxide produced via the endothermic reaction of steam with carbon H O C H CO 2 2 Carbon monoxide is also produced by the direct oxidation of carbon in a limited supply of oxygen or air 2Cs O 2COg 2 942 ProPerties and uses Carbon dioxide is a versatile industrial material used for example as an inert gas in welding and fire extinguishers as a pressurizing gas in air guns and oil recovery as a chemical feedstock and as a supercritical fluid solvent in decaffeination of coffee It is added to drinking water and carbonated beverages including beer and sparkling wine The frozen solid form of carbon dioxide dry ice is used as a refrigerant Carbon monoxide has many applications in the manufacture of bulk chemicals For example aldehydes are produced by the hydroformylation reaction of olefin derivatives carbon monoxide and hydrogen Chapter 7 Phosgene COCl2 is an industrial building block that is used for the production of urethane polymers and polycarbonate polymers Chapter 11 but it is poisonous and 366 Handbook of Petrochemical Processes was used as a chemical weapon during World War I To produce phosgene carbon monoxide and chlorine gas are passed through a bed of porousactivated carbon to form the gas CO Cl COCl 2 2 The phosgene is then reacted with the relevant feedstocks to produce the isocyanate derivatives polyurethane derivative and polycarbonate derivatives Methanol is produced by the hydrogenation of carbon monoxide Furthermore in the Monsanto process carbon monoxide and methanol react in the presence of a homogeneous catalyst typically a rhodium catalyst to produce acetic acid In a related reaction the hydrogenation of carbon mon oxide is coupled to carboncarbon bond formation as in the FischerTropsch process Chapter 10 where carbon monoxide is hydrogenated to liquid hydrocarbon fuels This technology allows non petroleum carbonaceous feedstocks Chapter 3 to be converted to valuable hydrocarbon liquids and solids waxes Carbon monoxide is a strong reductive agent and it has been used in pyrometallurgy to pro duce metals from the corresponding ores In the process carbon monoxide strips oxygen off metal oxides reducing them to pure metal in high temperatures forming carbon dioxide in the process Carbon monoxide is not usually supplied as is but it is formed in high temperature in presence of oxygencarrying ore MO a highly carbonaceous agent such as coke and high temperature MO C CO M As another example in the Mond process also known as the carbonyl process carbon monoxide as a contempt of synthesis gas is used to purify nickel This process is based on the principle that carbon monoxide that readily combines irreversibly with nickel to yield nickel carbonyl NiCO4 Thus NiOs H g Ni s H Og impure nickel Nis 4COg Ni CO g Ni CO g Ni s 4COg pure nickel 2 2 4 4 95 HYDRAZINE Hydrazine N2H4 or H2NNH2 is a colorless fuming liquid miscible with water hydrazine also called diazine is a weak base but a strong reducing agent Hydrazine is a colorless flammable liquid that has an ammonialike odor and is highly toxic and dangerously unstable unless handled in solu tion as eg hydrazine hydrate NH2NH2 xH2O The term hydrazine refers to a class of organic substances which are by replacing one or more hydrogen atoms in hydrazine by an organic group eg RNHNH2 951 Production There are several processes that are available for the production of hydrazinethe essential or key step in each process is the creation of the nitrogennitrogen single bond The many routes can be divided into those that use chlorine oxidants and generate salt and those that do not Hydrazine can be synthesized from ammonia and hydrogen peroxide in the Peroxide process also referred to as PechineyUgineKuhlmann process the AtofinaPCUK cycle or Ketazine process which is often represented simply as 2NH H O H NNH 2H O 3 2 2 2 2 2 367 Chemicals from Nonhydrocarbons However the process is more complex than the above equation suggest and in the process the ketone and ammonia first condense to give the imine which is oxidized by hydrogen peroxide to the oxaziridine a threemembered ring containing carbon oxygen and nitrogen In the next step the oxaziridine gives the hydrazine by treatment with ammonia which creates the nitrogen nitrogen single bond after which the hydrazine derivative condenses with one more equivalent of the ketone The resulting azine is hydrolyzed to give hydrazine and regenerate the ketone methyl ethyl ketone Me Et CNNC Et Me 2H O 2Me Et CO N H 2 2 4 Unlike most other processes this process does not produce a salt as a byproduct In the Olin Raschig process chlorinebased oxidants oxidize ammonia without the presence of a ketonein the peroxide process hydrogen peroxide oxidizes ammonia in the presence of a ketone but the OlinRaschig process relies on the reaction of chloramine with ammonia to create the nitrogennitrogen single bond as well as the hydrogen chloride byproduct NH Cl NH H NNH HCl 2 3 2 2 In a related process urea can be oxidized instead of ammonia with sodium hypochlorite serving as the oxidant H N CO NaOCl 2NaOH N H H O NaCl Na CO 2 2 2 4 2 2 3 Hydrazine is produced by the oxidation of ammonia using the Rashig process Sodium hypochlorite is the oxidizing agent and yields chloramine NH2Cl as an intermediate Chloramine further reacts with ammonia producing hydrazine 2NH NaOCl H NNH NaCl H O 3 2 2 2 Hydrazine is then evaporated from the sodium chloride solution 952 ProPerties and uses Hydrazine is mainly used as a foaming agent in the preparation of polymer foams and other significant uses also include use as a precursor to polymerization catalysts pharmaceuticals and agricultural chemicals Additionally hydrazine is used as a rocket fuel because its combustion is highly exothermic H NNH O N 2H O 2 2 2 2 2 In addition to rocket fuel hydrazine is used as a blowing agent and in the pharmaceutical and fertil izer industries It is used to prepare the gas precursors used in air bags Hydrazine is used within both nuclear and conventional electrical power plant steam cycles as an oxygen scavenger to control concentrations of dissolved oxygen in an effort to reduce corrosion Also because of the weak nitrogennitrogen bond it is used as a polymerization initiator As a reducing agent hydrazine is used as an oxygen scavenger for steam boilers It is also a selective reducing agent for nitro compounds Hydrazine is a good building block for many chemicals espe cially agricultural products which dominates its use Hydrazine is also used as a propellant in space vehicles to reduce the concentration of dissolved oxygen in and to control pH of water used in large industrial boilers 368 Handbook of Petrochemical Processes Hydrazine is a precursor to several pharmaceuticals and pesticides Often these applications involve conversion of hydrazine to heterocyclic ring systems such as pyrazole derivatives and pyr idazine derivatives Hydrazine compounds can be effective as active ingredients in admixture with or in combination with other agricultural chemicals such as insecticides miticides nematicides fungicides antiviral agents attractants herbicides or plant growth regulators Often the use of hydrazine as a precursor to several pharmaceuticals and pesticides involves conversion of hydrazine to heterocyclic ring derivatives such as pyrazole derivaitves and pyridazine derivatives Hydrazine compounds can be effective as active ingredients in admixture with or in combination with other agricultural chemicals such as insecticides miticides nematicides fungicides antiviral agents attractants herbicides or plant growth regulators 96 HYDROGEN Hydrogen is the lightest known element and is only found in the free state in trace amounts but is widely spread in a combined form with other elements Hydrogen is one of the key starting materials used in the chemical industry It is a fundamental building block for the manufacture of ammonia NH3 and hence fertilizers and of methanol CH3OH used in the manufacture of many polymers Hydrogen is used in the manufacture of two of the most important chemical compounds made industrially It is also used in the refining of oil for example in reforming one of the processes for obtaining highoctane naphtha usually called reformate as a blendstock for the production of gasoline and in removing sulfur compounds from petroleum which would otherwise poison the catalytic converters fitted to vehicles 961 Production Water natural gas crude oil hydrocarbons and other organic fossil fuels are major sources of hydrogen 2H O 2H O 2 2 2 Electrolysis and the thermochemical decomposition as well as the photochemical decomposition of water followed by purification through diffusion methods are methods for the production of hydrogen Chemically the electrolysis of water is considered to be a simple method of producing hydrogen In the process a lowvoltage current is run through the water and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage If however the gas is to be burnt onsite oxygen is desirable to assist the combustion and so both electrodes would be made from inert metals For example iron for instance would oxidize and thus decrease the amount of oxygen that is evolved However the electrolysis process is an energyextensive process The most economical way to produce hydrogen is by steam reforming petroleum fractions and natural gas as well as by gasification of carbonaceous feedstocks Speight 2014a In the steam reforming process two major sources of hydrogen water and hydrocarbons such as methane are reacted to produce a mixture of carbon monoxide and hydrogen synthesis gas Hydrogen can then be separated from the mixture after shift converting carbon monoxide to carbon dioxide Carbon oxides are removed by passing the mixture through a pressure swing adsorption PSA system Also hydrogen can be produced by the steam reforming methanol In this process an active catalyst is used to decompose methanol and shift convert carbon monoxide to carbon dioxide The produced gas is cooled and carbon dioxide is removed CH OH H O CO 3H 3 2 2 2 369 Chemicals from Nonhydrocarbons In the petroleum refining industry hydrogen is essentially obtained from catalytic naphtha reform ing Parkash 2003 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 In the petrochemical industry hydrogen is used to hydrogenate benzene to cyclohexane and benzoic acid to cyclohexane carboxylic acid These compounds are precursors for nylon production It is also used to selectively hydrogenate acetylene from C4 olefin mixture As a constituent of synthesis gas hydrogen is a precursor for ammonia methanol Oxo alcohols and hydrocarbons from Fischer Tropsch processes The direct use of hydrogen as a clean fuel for automobiles and buses is currently being evaluated compared to fuel cell vehicles that use hydrocarbon fuels which are converted through onboard reformers to a hydrogenrich gas Thus an important process for the production of hydrogen is by steam reforming The key parts of the process are the conversion of a carboncontaining material to a mixture of carbon monoxide and hydrogen synthesis gas followed by the conversion of carbon monoxide to carbon dioxide and the production of more hydrogen In many refineries the hydrocarbon feedstock is typically methane or other lowboiling hydrocarbon derivatives obtained from natural gas as well as from crude and coal However there is an increasing interest in using biomass as a source of hydrogen Speight 2011b Thus if a hydrocarbon feedstock is employed as the source of hydrogen the hydrocarbon vapor phase is mixed with a large excess of steam and passed through pipes containing nickel oxide which is reduced to nickel during the reaction supported on alumina in a furnace which operates at high temperatures Using methane as the example of the feedstock CH H O 3H CO 4 2 2 The reaction is endothermic and accompanied by an increase in volume 2 volumes to 4 volumes and thus is favored by high temperatures and by low partial pressures The reaction is also favored by a high ration of steam to hydrocarbon which however does increase the yield but also increases operating energy costs The high ratio also helps to reduce the amount of carbon deposited which reduces the efficiency of the catalyst The most effective way to reduce carbon deposition has been found to be impregnation of the catalyst with potassium carbonate In the second part of the process the shift reaction carbon monoxide is converted to carbon dioxide by reacting the carbon monoxide with steam and thus producing more hydrogen CO H O H CH 2 2 2 This reaction is also exothermic and so high conversions to carbon dioxide and hydrogen are favored by low temperatures which may be difficult to control due to the heat evolved and as a result it has been common practice to separate the shift reaction into two stages i the first stage in which the bulk of the reaction being carried out at approximately 377C 710F K over an iron catalyst and the polishing reaction carried out around 450K over a copperzincalumina catalyst The carbon dioxide and any remaining carbon monoxide are then removed by passing the gases through a zeo lite sieve Thus overall 1 mol of methane and 2 mol of steam are theoretically converted into 4 mol of hydrogen although this theoretical yield is not achieved as the reactions do not go to completion CH 2H O 4H CO 4 2 2 2 Due to the increasing demand for hydrogen many separation techniques have been developed to recover it from purge streams vented from certain processing operations such as hydrocracking and hydrotreating In addition to hydrogen these streams contain methane and other light hydrocarbon gases Physical separation techniques such as i adsorption ii diffusion and iii cryogenic phase separation are used to achieve efficient separation 370 Handbook of Petrochemical Processes Adsorption is accomplished using a special solid that preferentially adsorbs hydrocarbon gases not hydrogen The adsorbed hydrocarbons are released by reducing the pressure Cryogenic phase separation on the other hand depends on the difference between the volatilities of the components at the low temperatures and high pressures used The vapor phase is rich in hydrogen and the liquid phase contains the hydrocarbons Hydrogen is separated from the vapor phase at high purity Diffusion separation processes depend on the permeation rate for gas mixtures passing through a special membrane The permeation rate is a function of the type of gas feed the membrane material and the operating conditions Gases having a lower molecular size such as helium and hydrogen permeate membranes more readily than larger molecules such as methane and ethane After the feed gas is preheated and filtered it enters the membrane separation section This is made of a permeater vessel containing 12in diameter bundles resemble filter cartridges and consists of millions of hollow fibers The gas mixture is distributed in the annulus between the fiber bundle and the vessel wall Hydrogen being more permeable diffuses through the wall of the hollow fiber and exits at a lower pressure The less permeable hydrocarbons flow around the fiber walls to a perforated center tube and exit at approximately feed pressure It has been reported that this system can deliver a reliable supply of pure hydrogen 95 vv pure from offgas streams havingas low as 15 vv hydrogen 962 ProPerties and uses The chemical industry is the largest producer and consumer of hydrogen Hydrogen has various applications in the chemical industry Thus once obtained hydrogen is widely used in the produc tion of bulk chemicals intermediates and specialty chemicals Figure 91 Thus hydrogen does form compounds with most elements the bonding of hydrogen to carbon is excluded from this discussion such as the more electronegative elements eg the halogen elementsfluorine chlo rine bromine and iodine and oxygen In these compounds hydrogen takes on a partial positive FIGURE 91 Examples of the use of hydrogen 371 Chemicals from Nonhydrocarbons charge and when bonded to fluorine HF oxygen H2O and nitrogen NH3 hydrogen can par ticipate in a form of mediumstrength noncovalent bonding with the hydrogen of other similar molecules hydrogen bonding that is often reflected in the stability of many biological molecules such as the helix structure of DNA Hydrogen also forms compounds with less electronegative ele ments and forms hydrides with metals and metalloids where it takes on a partial negative charge The key consumers of hydrogen in a petrochemical plant include use as a hydrogenating agent particularly in increasing the level of saturation of unsaturated fats and oils found in items such as margarine It is similarly the source of hydrogen in the manufacture of hydrochloric acid and is a reducing agent for the production of metals from the metallic ores typically the oxide of the metal As an example molybdenum can be produced by passing hydrogen over hot molybdenum oxide 2MoO 6H Mo 6H O 3 2 2 Although hydrides can be formed with almost all main group elements the number and combina tion of possible compounds varies widely for example more than 100 binary borane hydrides are known but there is only 1 binary aluminum hydride In inorganic chemistry hydride derivatives can also serve as bridging ligands that link two metal centers in a coordination complex This function is particularly common in the boranes boron hydride derivatives and aluminum com plexes as well as in clustered carborane derivatives The most important single use of hydrogen is in the manufacture of ammonia NH3 which is produced by combining hydrogen and nitrogen at high pressure and temperature in the presence of a catalyst 3H N 2NH 2 2 3 Hydrogen is also used for a number of similar reactions For example it can be combined with car bon monoxide to make methanol 2H CO CH OH 2 3 Methanol like ammonia has a great many practical uses in a variety of industries The most impor tant use of methanol is in the manufacture of other chemicals such as those from which plastics are made Small amounts are used as additives to gasoline to reduce the amount of pollution released to the environment Methanol is also used widely as a solvent to dissolve other materials in industry Finally one of the most important groups of hydrogen compounds is the acids Common inor ganic acids include hydrochloric acid HCl sulfuric acid H2SO4 nitric acid HNO3 phosphoric acid H3PO4 hydrofluoric acid HF and boric acid H3BO3 Although not a typical hydrogen acid hydrogen peroxide H2O2 is a weak acid but is a strong oxidizing agent used in aqueous solution as a ripening agent bleach and topical antiinfective It is relatively unstable and solutions deteriorate over time unless stabilized by the addition of acetanilide or similar organic materials In keeping with the strong oxidizing properties hydrogen peroxide is a powerful bleaching agent that is mostly used for bleaching paper but has also found use as a disinfectant and as an oxidizer Hydrogen per oxide in the form of carbamide peroxide a solid composed of equal amounts of hydrogen peroxide and urea H2NCONH2 which is a white crystalline solid that dissolves in water to give free hydro gen peroxide is widely used for tooth whitening bleaching both in professionally administered and selfadministered products 97 NITRIC ACID Nitric acid HNO3 is one of the most used chemicals It is a colorless to a yellow liquid which is very corrosive It is a strong oxidizing acid that can attack almost any metal The pure compound is 372 Handbook of Petrochemical Processes colorless but older samples tend to acquire a yellow cast due to decomposition into oxides of nitro gen NOx and water Nitric acid is subject to thermal decomposition or photolytic decomposition decomposition by light and for this reason it was often stored in brown glass bottles 4HNO 2H O 4NO O 3 2 2 2 This reaction may give rise to some nonnegligible variations in the vapor pressure above the liquid because the nitrogen oxides produced dissolve partly or completely in the acid Most commercially available nitric acid has a concentration of 68 vv in water When the solution contains more than 86 vv nitric acid it is fuming nitric acid Depending on the amount of nitrogen dioxide NO2 fuming nitric acid is further characterized as i red fuming nitric acid at concentrations above 86 vv and ii white fuming nitric acid at concentrations above 95 vv Commercially available nitric acid is an azeotrope with water at a concentration of 68 HNO3 which is the ordinary concentrated nitric acid of commerce This solution has a boiling temperature of 1205C760 mm Two solid hydrates are known the monohydrate HNO3 H2O or H3ONO3 and the trihydrate HNO3 3H2O 971 Production Nitric acid is commercially produced by oxidizing ammonia with air over a platinumrhodium wire gauze The following sequence represents the reactions occurring over the heterogeneous catalyst 4NH 5O 4NO 6H O 2NO O 2NO 3NO H O 2HNO NO 3 2 2 2 2 2 2 3 The three reactions are exothermic and the equilibrium constants for the first two reactions fall rapidly with increase of temperature Increasing pressure favors the second reaction but adversely affects the first reaction For this reason operation around atmospheric pressures is typical Space velocity should be high to avoid the reaction of ammonia with oxygen on the reactor walls which produces nitrogen and water and results in lower conversions The concentration of ammonia must be kept below the inflammability limit of the feed gas mixture to avoid explosion Optimum nitric acid production was found to be obtained at approximately 900C 1650F and atmospheric pressure 972 ProPerties and uses Nitric acid has many uses Table 91 but the primary use of nitric acid is for the production of ammonium nitrate NH4NO3 for fertilizers A second major use of nitric acid is in the field of explo sives It is also a nitrating agent for aromatic and paraffin derivatives which are useful intermedi ates in the dye and explosive industries It is also used in steel refining and in uranium extraction In organic chemistry nitric acid is the primary reagent used for nitrationthe addition of a nitro NO2 group to an organic molecule While some resulting nitrocompounds are sensitive to shock and thermal effects such as trinitrotoluene TNT some are sufficiently stable enough to be used in munitions and demolition while others are still more stable and used as pigments in inks and dyes Nitric acid is also commonly used as a strong oxidizing agent The corrosive effects of nitric acid are exploited for a number of specialty applications such as etching in printmaking pickling stainless steel or cleaning silicon wafers in electronics A solu tion of nitric acid water and alcohol is used for etching of metals to reveal the microstructure Commercially available aqueous blends of 530 vv nitric acid and 1540 vv phosphoric 373 Chemicals from Nonhydrocarbons acid are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium and magnesium compounds either deposited from the process stream or resulting from the use of hard water during production and cleaning In a low concentration nitric acid is often used in woodworking to artificially age pine and maple The color produced is a graygold very much like very old wax or oilfinished wood 98 SULFUR Sulfur also called brimstone is one of the few elements found pure in nature And this native sulfur is probably of volcanic origin and after oxidation to sulfur dioxide SO2 or sulfur trioxide SO3 is responsible for the characteristic smell of many volcanoes Sulfur is a reactive nonmetallic ele ment naturally found in nature in a free or combined state Large deposits of elemental sulfur are found in various parts of the world In its combined form sulfur is naturally present in sulfide ores of metals such as iron zinc copper and lead It is also a constituent of natural gas and refinery gas streams in the form of hydrogen sulfide H2S carbonyl sulfide COS and mercaptan derivatives RSH where R is an alkyl group Different processes have been developed for obtaining sulfur and sulfuric acid from these three sources 981 Production The sulfide derivatives form the principal ores of copper zinc nickel cobalt molybdenum as well as several other metals and these materials tend to be darkcolored semiconductors that are not readily attacked by water or even many acids Processing these ores usually by roasting is environ mentally hazardous Also sulfur corrodes many metals through tarnishing Sulfur is now produced as a side product of other industrial processes such as in oil refining in which sulfur is undesired As a mineral native sulfur under salt domes is thought to be a fossil mineral resource produced by the action of ancient bacteria on sulfate deposits Sulfur is produced from natural gas crude oil and related fossil fuel resources from which it is obtained mainly as hydrogen sulfide Organosulfur compounds which are undesirable impurities in such resources may be upgraded by subjecting to hydrodesulfurization in which highpressure hydrogen and high temperatures hydrotreating or hydrocracking are used to cleave the carbon sulfur bonds thereby converting the sulfur to hydrogen sulfide Hydrotreating variously referred to as hydroprocessing to avoid any confusion with those processes that are referred to as hydrotreating processes is a refining process in which the feed stock is treated with hydrogen at temperature and under pressure in which hydrocracking thermal decomposition in the presence of hydrogen is minimized The usual goal of hydrotreating is to TABLE 91 Uses of Nitric Acid Field Use Aerospace engineering Used as an oxidizer in liquidfueled rockets Explosives industry Manufacturing explosives such as trinitrotoluene nitroglycerin Fertilizer Used for manufacturing fertilizers such as ammonium nitrate Metals Used for purification of various precious metals Metallurgy Used in combination with alcohol for etching Woodworking Used to artificially age pine and maple wood Aqueous blends Used for cleaning food and dairy equipment Drugs Used in a colorimetric test to determine the difference between heroin and morphine 374 Handbook of Petrochemical Processes hydrogenate olefins and remove heteroatoms such as sulfur and to saturate aromatic compounds and olefins Parkash 2003 Ancheyta and Speight 2007 Gary et al 2007 Speight 2014a Hsu and Robinson 2017 Speight 2017 On the other hand hydrocracking is a process in which thermal decomposition is extensive and the hydrogen assists in the removal of the heteroatoms as well as mitigating the coke formation that usually accompanies thermal cracking of high molecular weight polar constituents In the process hydrocracking or hydrotreating sulfur in the feedstock is removed under the thermal conditions in the presence of hydrogen represented simply as S H H S feedstock 2 2 The hydrogen sulfide product is isolate in the gas cleaning section of the refinery and converted to sulfur by oxidation H S O H O S 2 2 2 Hydrogen sulfide is a constituent of natural gas and also of the majority of refinery gas streams especially those offgases from hydrodesulfurization processes A large majority of the sulfur is converted to sulfuric acid for the manufacturer of fertilizers and other chemicals Other uses for sul fur include the production of carbon disulfide refined sulfur and pulp and paper industry chemicals The Frasch process developed in 1894 produces sulfur from underground deposits Smelting iron ores produces large amounts of sulfur dioxide which is catalytically oxidized to sulfur trioxide for sulfuric acid production In the process superheated water was pumped into a native sulfur deposit to melt the sulfur and then compressed air returned the 995 pure melted product to the surface Throughout the 20th century this procedure produced elemental sulfur that required no further puri fication However due to a limited number of such sulfur deposits and the high cost of working them this process for mining sulfur has not been employed in a major way anywhere in the world since 2002 Currently sulfur is mainly produced by the partial oxidation of hydrogen sulfide through the Claus process The major sources of hydrogen sulfide are natural gas and petroleum refinery streams treatment operations It has been estimated that 9095 of the worlds recovered sulfur is produced through the Claus process Typical sulfur recovery ranges from 90 for a lean acid gas feed to 97 for a rich acid gas feed This process includes two main sections the burner section with a reaction chamber that does not have a catalyst and a Claus reactor section In the burner section part of the feed containing hydrogen sulfide and some hydrocarbons is burned with a limited amount of air The two main reactions that occur in this section are the complete oxidation of part of the hydrogen sulfide feed to sulfur dioxide and water and the partial oxidation of another part of the hydrogen sulfide to sul fur The two reactions are exothermic 2H S 3O 2SO 2H O 2H S O 2S 2H O 2 2 2 2 2 2 2 In the second section unconverted hydrogen sulfide reacts with the produced sulfur dioxide over a bauxite catalyst in the Claus reactor Normally more than one reactor is available In the SuperClaus process three reactors are used and the final reactor contains a selective oxidation catalyst of high efficiency After each reaction stage sulfur is removed by condensation so that it does not collect on the catalyst The temperature in the catalytic converter should be kept over the dew point of sulfur to prevent condensation on the catalyst surface which reduces activity Due to the presence of hydrocarbons in the gas feed to the burner section some undesirable reactions occur such as the formation of carbon disulfide CS2 and carbonyl sulfide COS A good catalyst has a high activity toward H2S conversion to sulfur and a reconversion of carbonyl sulfide 375 Chemicals from Nonhydrocarbons and carbon disulfide to sulfur and carbon oxides CO CO2 Mercaptans in the acid gas feed results in an increase in the air demand The oxidation of mercaptans could be represented as 2CH SH 3O SO CO C H SH 2H O 3 2 2 2 2 5 2 Sulfur dioxide is then reduced in the Claus reactor to elemental sulfur 982 ProPerties and uses Elemental sulfur is nontoxic as are most of the soluble sulfate SO4 saltsthe soluble sulfate salts are poorly absorbed and laxative When injected parenterally they are freely filtered by the kidneys and eliminated with very little toxicity in multigram amounts Sulfur reacts directly with methane to give carbon disulfide CS2 which is used to manufacture cellophane and rayon One of the uses of elemental sulfur is in vulcanization of rubber where poly sulfide chains crosslink organic polymers Large quantities of sulfite derivatives are used to bleach paper and to preserve dried fruit Many surfactants and detergents are sulfate derivatives Calcium sulfate gypsum CaSO4 2H2O is used in Portland cement and in fertilizers The most important form of sulfur for fertilizer is the mineral calcium sulfate Elemental sulfur is hydrophobic insoluble in water and cannot be used directly by plants Over time soil bacteria can convert it to soluble derivatives which can then be used by plants Sulfur improves the efficiency of other essential plant nutrients particularly nitrogen and phosphorus Biologically produced sulfur particles are naturally hydrophilic due to a biopolymer coating and are easier to disperse over the land in a spray of diluted slurry resulting in a faster uptake Organosulfur compounds are used in pharmaceutical products dyestuffs and agrochemi cals Many drugs contain sulfur early examples being antibacterial sulfonamide drugs sulfa drugs and most βlactam antibiotics including the various penicillin derivatives cephalospo rins and monobactams contain sulfur Mercaptan derivatives also called thiolsthe function group is theSH groupand informally represented as RSH are a family of organosulfur compounds Some are added to natural gas supplies because of their distinctive smell so that gas leaks can be detected easily Others are used in silver polish and in the production of pesticides and herbicides Elemental sulfur is one of the oldest fungicides and pesticides The product known as dusting sulfur which is elemental sulfur in powdered form is a common fungicide for grapes strawberry many vegetables and several other crops It has a strong effect against a wide range of powdery mildew diseases as well as black spot In organic production sulfur is the most important fungicide Standardformulation dusting sulfur is applied to crops with a sulfur duster or from a dusting plane Wettable sulfur is the commercial name for dusting sulfur formulated with additional ingredients to make it miscible with waterit has similar applications and is used as a fungicide to control mildew and other moldrelated problems with plants and soil A diluted solution of lime sulfur which is produced by combining calcium hydroxide CaOH2 with elemental sulfur in water is used as a dip for animals to destroy ringworm fun gus mange and other skin infections and parasite Sulfur dioxide and various sulfites have been used for their antioxidant antibacterial preservative properties in many other parts of the food industry The practice has declined since reports of an allergylike reaction of some persons to sulfites in foods Precipitated sulfur and colloidal sulfur are used in form of lotions creams powders soaps and bath additives for the treatment of some forms of acne and dermatitis Magnesium sulfate also known as epsom salts when in hydrated crystal form can be used as a laxative a bath additive an exfoliant a magnesium supplement for plants or when in dehy drated form as a desiccant Several sulfur halides are important to modern industry For example sulfur hexafluoride SF6 is a dense gas that is used as an insulator in highvoltage transformers Sulfur hexafluoride is also 376 Handbook of Petrochemical Processes a nonreactive and nontoxic propellant for pressurized containers Sulfur dichloride SCl2 and disulfur dichloride S2Cl2 are important industrial chemicals Sulfur reacts with nitrogen to form polymeric sulfur nitrides SNx or polythiazyl derivatives These polymers were found to have the optical and electrical properties of metals An important sulfurnitrogen compound is tetrasulfur tetranitride S4N4 which exists in a cagelike form and when heated yields polymeric sulfur nitride SHn which has metallic properties Thiocyanate derivatives contain the SCN group and oxidation of thiocyanate gives thiocyanogen SCN2 NCSSCN Phosphorus sulfides are also commercially important especially those with the cage structures P4S10 and P4S3 Other uses range from dusting powder for roses to rubber vulcanization to sulfur asphalt pavements Flower sulfur is used in match production and in certain pharmaceuticals Sulfur is also an additive in highpressure lubricants Sulfur can replace 3050 ww of the asphalt in the blends used for road construction Road surfaces made from asphaltsulfur blends have nearly dou ble the strength of conventional pavement and it has been claimed that such roads are more resistant to climatic conditions The impregnation of concrete with molten sulfur is another potential large sulfur use Concretes impregnated with sulfur have better tensile strength and corrosion resistance than conventional concretes Sulfur is also used to produce phosphorous pentasulfide a precursor for zinc dithiophosphate derivative used as corrosion inhibitors The most important use of sulfur is for sulfuric acid production which is the most important and widely used inorganic chemical and is a widely used industrial chemical Sulfuric acid is produced by the contact process where sulfur is burned in an air stream to sulfur dioxide which is catalyti cally converted to sulfur trioxide The catalyst of choice is solid vanadium pentoxide V2O5 The reaction occurs at about 450C 840F increasing the rate at the expense of a higher conversion To increase the yield of sulfur trioxide more than one conversion stage normally three stages is used with cooling between the stages to offset the exothermic reaction heat Absorption of sulfur trioxide from the gas mixture exiting from the reactor favors the conversion of sulfur dioxide The absorbers contain sulfuric acid of 98 concentration which dissolves sulfur trioxide The unreacted sulfur dioxide and oxygen are recycled to the reactor The absorption reaction is exothermic and coolers are used to cool the acid 2SO O SO SO H O H SO 2 2 3 3 2 2 4 99 SULFURIC ACID Sulfuric acid spelled sulphuric acid in many countries and also known as vitriol is a mineral acid composed of the elements hydrogen oxygen and sulfur H2SO4 It is a colorless odorless and syrupy liquid that is soluble in water in a reaction that is highly exothermic The corrosiveness of sulfuric acid can be mainly ascribed to the strong acidic nature of the compound and if at a high concentration it has strong dehydrating and oxidizing properties Sulfuric acid is also a hygro scopic chemical insofar as it readily absorbs water vapor when in contact with the air Sulfuric acid can cause severe burns to the skin and requires cautious handling even at moderatetolow concentration 991 Production The contact process can be divided into five separate stages i combining sulfur and oxygen to form sulfur dioxide ii purifying the sulfur dioxide in a purification unit iii adding an excess of oxygen to sulfur dioxide in the presence of the catalyst iv the sulfur trioxide is added to sulfuric acid to produce oleum and v the oleum is then added to water to form sulfuric acid which is very concentrated 377 Chemicals from Nonhydrocarbons In the first stage sulfur dioxide in converted into sulfur trioxide the reversible reaction at the heart of the process or ion pyrite is used to produce the sulfur dioxide which is then converted into concentrated sulfuric acid Thus S O SO 2 2 or 4FeS 11O 2Fe O 8SO 2 2 2 3 2 In either case an excess of air is used so that the sulfur dioxide produced is already mixed with oxygen for the next stage Conversion of the sulfur dioxide into sulfur trioxide is a reversible reaction and the formation of the sulfur trioxide is exothermic 2SO O 2SO 2 2 3 Conversion of the sulfur trioxide into sulfuric acid cannot be achieved by the simple process of adding water to the sulfur trioxide because of the highly exothermic and uncontrollable nature of the reaction Thus sulfur trioxide is first dissolved in concentrated sulfuric acid to produce fuming sulfuric acid oleum which can then be reacted relatively safely with water to produce concen trated sulfuric acid twice as much as you originally used to produce the fuming sulfuric acid H SO SO H SO SO H S O H SO SO H O 2H SO 2 4 3 2 4 3 2 2 7 2 4 3 2 2 4 The mixture of sulfur dioxide and oxygen going into the reactor is in equal proportions by volume but is in reality an excess of oxygen relative to the proportions demanded by the equation 2SO O 2SO 2 2 3 Increasing the concentration of oxygen in the mixture causes the position of equilibrium to shift towards the right Since the oxygen comes from the air this is a very cheap way of increasing the conversion of sulfur dioxide into sulfur trioxide In order to produce maximum yields of sulfur trioxide a relatively low temperature is required to drive the equilibrium to the right However the lower the temperature the slower the reaction A temperature in the order of 400C450C 750F840F is a compromise temperature producing a high proportion of sulfur trioxide in the equilibrium mixture With an increase in the pressure the system will also help to increase the rate of the reaction However the reaction pressure is maintained at pressures close to atmospheric pres sure at 1530 psi at which there is a 995 vv conversion of sulfur dioxide into sulfur trioxide Adding a catalyst does not produce any greater percentage of sulfur trioxide in the equilibrium mixture but in the absence of a catalyst the reaction rate is so slow that virtually no reaction hap pens in any sensible time The catalyst ensures that the reaction has a sufficiently high rate for a dynamic equilibrium to be set up within the very short time that the gases are actually in the reactor Platinum used to be the catalyst for this reaction however as it is susceptible to reacting with arsenic impurities in the sulfur feedstock vanadium pentoxide V2O5 is now the preferred catalyst and catalyst regeneration is achieved by oxidation of the vanadium V4 to the higher valency V5 Thus V O V 2O 4 2 5 2 378 Handbook of Petrochemical Processes The wet sulfuric acid process is one of the main gas desulfurization processes and is recognized as an efficient process for recovering sulfur from various process gases in the form of sulfuric acid In the current context of refinery operations the process is applied in all industries where removal of sulfur is an issue Examples are the processing of hydrogen sulfide gas from an amine gas treating unit i offgas from sour water stripper gas ii spent acid from an alkylation unit iii Claus unit tail gas and iv offgas from a residfired or cokefired boiler The acid gas coming from any of these operations contains hydrogen sulfide H2S carbonyl sulfide COS and hydrocarbon deriva tives in addition to carbon dioxide CO2 These gases were previously often flared and vented to the atmosphere but now the acid gas requires purification in order not to affect the environment with sulfur dioxide emissions Not only can the process meet environmental demands of sulfur dioxide removal the process also accepts a wide range of feedgas compositions The wet sulfuric acid process plant provides a high sulfur recovery and the process chemistry is reflected in the following reactions Figure 92 Combustion 2H S 3O 2H O 2SO 2 2 2 2 Oxidation 2SO O 2SO 2 2 3 Hydration SO H O H SO g 3 2 2 4 Condensation H SO g H SO l 2 4 2 4 The process can also be used for production of sulfuric acid from sulfur burning or for regenera tion of the spent acid from for example alkylation units Wet catalysis processes differ from other contact sulfuric acid processes in that the feed gas contains excess moisture when it comes into con tact with the catalyst The sulfur trioxide formed by catalytic oxidation of the sulfur dioxide reacts instantly with the moisture to produce sulfuric acid in the vapor phase to an extent determined by the temperature Liquid acid is subsequently formed by condensation of the sulfuric acid vapor and not by absorption of the sulfur trioxide in concentrated sulfuric acid as is the case in the contact process that is based on dry gases FIGURE 92 Flow scheme for the wet sulfuric acid process 379 Chemicals from Nonhydrocarbons The concentration of the product acid depends on the watersulfur trioxide H2OSO3 ratio in the catalytically converted gases and on the condensation temperature The combustion gases are cooled to the converter inlet temperature of about 420C440C 790C825F To process these wet gases in a conventional cold gas contact process would necessitate cooling and drying of the gas to remove all moisture The lead chamber process was an industrial method used to produce sulfuric acid in large quan tities Prior to 1900 most sulfuric acid was manufactured by the lead chamber process and as late as 1940 up to half of the sulfuric acid manufactured in the United States was produced by chamber process plants In the lead chamber process sulfur dioxide and steam was introduced with nitrogen dioxide into large chambers lined with sheet lead where the gases are sprayed down with water and chamber acid 6270 vv sulfuric acid was produced The nitrogen dioxide was necessary for the reaction to proceed at a reasonable rate As might be anticipated the process is highly exothermic and a major consideration of the design of the chambers was to provide a way to dissipate the heat formed in the reactions This chamber process has been largely supplanted by the contact process Another method for the production of sulfuric acid is the less wellknown metabisulfite method in which hydrochloric acid is added to metabisulfite and the gas was bubbled through nitric acid SO HNO H O H SO NO 2 3 2 2 4 992 ProPerties and uses The most common use of sulfuric acid is for fertilizer manufactureother uses include fertilizer manufacture and other mineral processing crude oil refining wastewater processing and chemi cal synthesis Because the hydration reaction of sulfuric acid is highly exothermic dilution should always be performed by adding the acid to the water rather than the water to the acidas anamonic used to alphabetical order atow and not wtoa on a chemical basis because the reaction is in an equi librium that favors the rapid protonation of water addition of acid to the water ensures that the acid is the limiting reagent As a result of the strong affinity of sulfuric acid for water the acid is an excellent dehydrating agent In addition concentrated sulfuric acid has a very powerful dehydrat ing property and is capable of removing the elements of water from chemical compounds such as carbohydrates to produce carbon and steam As an acid sulfuric acid reacts with most bases to produce the corresponding sulfate For example CuOs H SO aq CuSO aq H Ol 2 4 4 2 Sulfuric acid can also be used to displace weaker acids from their salts As an example the reaction of sulfuric acid with sodium acetate displaces acetic acid the weaker acid with the formation of sodium bisulfate H SO CH COONa NaHSO CH COOH 2 4 3 4 3 Similarly reacting sulfuric acid with potassium nitrate KNO3 can be used to produce nitric acid HNO3 and a precipitate of potassium bisulfate When combined with nitric acid sulfuric acid acts both as an acid and dehydrating agent forming the nitronium ion NO2 which is important in nitration reactions involving electrophilic aromatic substitution This type of reaction where pro tonation occurs on an oxygen atom is an important reaction in organic chemistry reactions such as for example the Fischer esterification and dehydration of alcohols 380 Handbook of Petrochemical Processes Dilute sulfuric acid reacts with metals via a single displacement reaction to produce hydrogen gas and metal sulfate salt Thus Fes H SO aq H g FeSO in solution 2 4 2 4 However concentrated sulfuric acid is a strong oxidizing agent and does not react with metals in the same way as other typical acids Sulfur dioxide water and SO4 2 ions are evolved instead of the hydrogen and the formation of the salt 2H SO 2e SO 2H O SO 2 4 2 2 4 2 Sulfuric acid can oxidize nonactive metals such as tin and copper in a reaction that is temperature dependent Cu 2H SO SO 2H O SO Cu 2 4 2 2 4 2 2 Hot concentrated sulfuric acid oxidizes nonmetals such as carbon as bituminous coal and sulfur C 2H SO CO 2SO 2H O S 2H SO 3SO 2H O 2 4 2 2 2 2 4 2 2 Sulfuric acid with sodium chloride to produce hydrogen chloride gas and sodium bisulfate NaCl H SO NaHSO HCl 2 4 4 Benzene undergoes electrophilic aromatic substitution with sulfuric acid to give the corresponding sulfonic acid Finally sulfuric acid is used in large quantities by the ironmaking and steelmaking industries to remove oxidation rust and scaling from rolled sheet and billets prior to sale to the automobile and major appliance industries Used acid is often recycled using a spent acid regeneration SAR plant in which the spent acid is combusted with natural gas refinery gas fuel oil or other fuel sources This combustion process produces gaseous sulfur dioxide and sulfur trioxide which are then used to manufacture fresh sulfuric acid The spent acid regeneration plants are common additions to crude oil refineries metal smelting plants and other industries where sulfuric acid is consumed in bulk As another use for sulfuric acid hydrogen peroxide H2O2 can be added to sulfuric acid to pro duce piranha solution which is a powerful but very toxic cleaning solution with which substrate surfaces can be cleaned Piranha solution is typically used in the microelectronics industry and also in laboratory settings to clean glassware 910 SYNTHESIS GAS Synthesis gas also called syngas is a mixture of carbon monoxide CO and hydrogen H2 that is the beginning of a wide range of chemicals Chapter 10 Chadeesingh 2011 Speight 2013 2014ab Figure 93 The name comes from the use of the gas intermediate in creating synthetic natural gas SNG and for producing ammonia or methanol Synthesis gas is a product the gas ification of carbonaceous feedstocks Chapter 5 Thus synthesis gas can be produced from many sources including natural gas coal biomass or virtually any hydrocarbon feedstock by reaction with steam steam reforming carbon dioxide dry reforming or oxygen partial oxidation 381 Chemicals from Nonhydrocarbons 9101 Production The production of synthesis gas ie mixtures of carbon monoxide and hydrogen has been known for several centuries But it is only with the commercialization of the FischerTropsch reaction that the importance of synthesis gas has been realized The thermal cracking pyrolysis of petro leum or fractions thereof was an important method for producing gas in the years following its use for increasing the heat content of water gas Many watergas set operations converted into oil gasification units some have been used for baseload city gas supply but most find use for peakload situations in the winter In addition to the gases obtained by distillation of crude petroleum further gaseous products are produced during the processing of naphtha and middle distillate to produce gasoline Hydrodesulfurization processes involving treatment of naphtha distillates and residual fuels and from the coking or similar thermal treatment of vacuum gas oils and residual fuel oils also produce gaseous products The chemistry of the oiltogas conversion has been established for several decades and can be described in general terms although the primary and secondary reactions can be truly complex The composition of the gases produced from a wide variety of feedstocks depends not only on the severity of cracking but often to an equal or lesser extent on the feedstock type In general terms gas heating values are in the order of 9501350 Btuft3 3050 MJm3 A second group of refining operations which contribute to gas production are the catalytic cracking processes such as fluidbed catalytic cracking and other variants in which heavy gas oils are converted into gas naphtha fuel oil and coke The catalysts will promote steamreforming reactions that lead to a product gas containing more hydrogen and carbon monoxide and fewer unsaturated hydrocarbon products than the gas product FIGURE 93 Production of chemicals from synthesis gas 382 Handbook of Petrochemical Processes from a noncatalytic process The resulting gas is more suitable for use as a medium heat value gas than the rich gas produced by straight thermal cracking The catalyst also influences the reaction rates in the thermal cracking reactions which can lead to higher gas yields and lower tar and carbon yields Almost all petroleum fractions can be converted into gaseous fuels although conversion pro cesses for the heavier fractions require more elaborate technology to achieve the necessary purity and uniformity of the manufactured gas stream In addition the thermal yield from the gasification of heavier feedstocks is invariably lower than that of gasifying light naphtha or liquefied petroleum gas since in addition to the production of synthesis gas components hydrogen and carbon monoxide and various gaseous hydrocarbons heavy feedstocks also yield some tar and coke Synthesis gas can be produced from heavy oil by partially oxidizing the oil 2CH O 2CO H petroleum 2 2 The initial partial oxidation step consists of the reaction of the feedstock with a quantity of oxygen insufficient to burn it completely making a mixture consisting of carbon monoxide carbon dioxide hydrogen and steam Success in partially oxidizing heavy feedstocks depends mainly on details of the burner design The ratio of hydrogen to carbon monoxide in the product gas is a function of reaction temperature and stoichiometry and can be adjusted if desired by varying the ratio of carrier steam to oil fed to the unit The chemical composition of synthesis gas varies based on the raw materials and the processes Synthesis gas produced by coal gasification generally is a mixture of 3060 vv carbon monoxide 2530 vv hydrogen 515 vv carbon dioxide and 05 vv methane Conversion of biomass to syngas is typically lowyield The University of Minnesota developed a metal catalyst that reduces the biomass reaction time by up to a factor of 100 The catalyst can be operated at atmospheric pressure and reduces char The entire process is autothermic and therefore heating is not required 9102 ProPerties and uses Synthesis gas is a crucial intermediate resource for production of hydrogen ammonia methanol and synthetic hydrocarbon fuels as well as a host other uses Table 92 Syngas is also used as an intermediate in producing synthetic hydrocarbon liquids for use as a fuels and lubricants by the FischerTropsch process Chapter 10 TABLE 92 Uses of Synthesis Gas Steam for use in turbine drivers for electricity generation Nitrogen for use as pressurizing agents and fertilizers Hydrogen for electricity generation and use in refineries Ammonia for use as fertilizers Ammonia for the production of plastics like polyurethane and nylon Methanol for the production of plastics resins pharmaceuticals adhesives and paints Methanol as a component of fuels Carbon monoxide for use in chemical industry feedstock and fuels Sulfur for use as elemental sulfur for chemical industry Minerals and solids for use as slag for roadbeds 383 Chemicals from Nonhydrocarbons When used as an intermediate in the large scale industrial synthesis of hydrogen principally used in the production of ammonia is also produced from natural gas by the steam reforming reaction CH H O CO 3H 4 2 2 In order to produce more hydrogen from this mixture more steam is added and the watergas shift reaction is necessary CO H O CO H 2 2 2 The hydrogen must be separated from the carbon dioxide before use which can be accomplished by pressure swing adsorption amine scrubbing and membrane reactors Mokhatab et al 2006 Speight 2007 2014a REFERENCES Ancheyta J and Speight JG 2007 Hydroprocessing of Heavy Oils and Residua CRCTaylor and Francis Group Boca Raton FL Chadeesingh R 2011 Chapter 5 The FischerTropsch process In The Biofuels Handbook Part 3 JG Speight Editor The Royal Society of Chemistry London Chemier PJ 1992 Survey of Chemical Industry 2nd Revised Edition VCH Publishers Inc New York Farhat Ali M El Ali BM and Speight JG 2005 Handbook of Industrial Chemistry Organic Chemicals McGrawHill New York Gary JG Handwerk GE and Kaiser MJ 2007 Petroleum Refining Technology and Economics 5th Edition CRC Press Taylor Francis Group Boca Raton FL Goldstein RF 1949 The Petrochemical Industry E FN Spon London Hahn AV 1970 The Petrochemical Industry Market and Economics McGrawHill New York Hsu CS and Robinson PR Editors 2017 Handbook of Petroleum Technology Springer International Publishing AG Cham Lowenheim FA and Moran MK 1975 Industrial Chemicals John Wiley Sons New York Mokhatab S Poe WA and Speight JG 2006 Handbook of Natural Gas Transmission and Processing Elsevier Amsterdam Parkash S 2003 Refining Processes Handbook Gulf Professional Publishing Elsevier Amsterdam Speight JG 2002 Chemical Process and Design Handbook McGrawHill Publishers New York Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG 2011a Handbook of Industrial Hydrocarbon Processes Gulf Professional Publishing Elsevier Oxford United Kingdom Speight JG Editor 2011b The Biofuels Handbook The Royal Society of Chemistry London Speight JG 2013 The Chemistry and Technology of Coal 3rd Edition CRC Press Taylor and Francis Group Boca Raton FL Speight JG 2014a The Chemistry and Technology of Petroleum 4th Edition CRC Press Taylor and Francis Group Boca Raton FL Speight JG 2014b Gasification of Unconventional Feedstocks Gulf Professional Publishing Elsevier Oxford United Kingdom Speight JG 2017 Handbook of Petroleum Refining CRC Press Taylor Francis Group Boca Raton FL Wittcoff HA and Reuben BG 1996 Industrial Organic Chemicals John Wiley Sons Inc New York Taylor Francis 385 10 Chemicals from the FischerTropsch Process 101 INTRODUCTION In a previous chapter Chapter 5 there has been mention of the use of the gasification process to convert carbonaceous feedstocks such as crude oil residua tar sand bitumen coal oil shale and biomass into the starting chemicals for the production of petrochemicals The chemistry of the gasification process is based on the thermal decomposition of the feedstock and the reaction of the feedstock carbon and other pyrolysis products with oxygen water and fuel gases such as methane and is represented by a sequence of simple chemical reactions Table 101 However the gasifica tion process is often considered to involve two distinct chemical stages i devolatilization of the feedstock to produce volatile matter and char ii followed by char gasification which is complex and specific to the conditions of the reactionboth processes contribute to the complex kinetics of the gasification process The FischerTropsch process is a catalytic chemical reaction in which carbon monoxide CO and hydrogen H2 in the synthesis are converted into hydrocarbon derivatives of various molecular weights The process can be represented by the simple equation 2 1 H CO C H H O 2 2 2 2 n n n n n In this equation n is an integer Thus for n 1 the reaction represents the formation of methane which in most gastoliquids GTL applications is considered an undesirable byproduct The FischerTropsch process conditions are usually chosen to maximize the formation of higher molecular weight hydrocarbon liquid fuels which are higher value products There are other side reac tions taking place in the process among which the watergas shift reaction WGS is predominant CO H O H CO 2 2 2 TABLE 101 Reactions that Occur During Gasification of a Carbonaceous Feedstock 2C O2 2CO C O2 CO2 C CO2 2CO CO H2O CO2 H2 shift reaction C H2O CO H2 watergas reaction C 2H2 CH4 2H2 O2 2H2O CO 2H2 CH3OH CO 3H2 CH4 H2O methanation reaction CO2 4H2 CH4 2H2O C 2H2O 2H2 CO2 2C H2 C2H2 CH4 2H2O CO2 4H2 386 Handbook of Petrochemical Processes Depending on the catalyst temperature and type of process employed hydrocarbon deriva tives ranging from methane to higher molecular paraffin derivatives and olefin derivatives can be obtained Small amounts of low molecular weight oxygenated derivatives such as alcohol deriva tives and organic acid derivatives are also formed Typically FischerTropsch liquids are unless the process is designed for the production of other products hydrocarbon products which vary from naphthatype liquids to wax and nonhydrocarbon products The production of nonhydrocarbon products requires adjustment of the feedstock composition and the process parameters Briefly synthesis gas is the name given to a gas mixture that contains varying amounts of car bon monoxide CO and hydrogen H2 generated by the gasification of a carbonaceous material Examples include steam reforming of natural gas petroleum residua coal and biomass Synthesis gas is used as an intermediate in producing hydrocarbon derivatives via the FischerTropsch pro cess for use as gaseous and liquids fuels The synthesis gas is produced by the gasification conversion of carbonaceous feedstock such as petroleum residua coal and biomass and production of hydrocarbon products can be represented simply as CH O CO H CO H C H feedstock 2 2 2 2 2 n n n n However before conversion of the carbon monoxide and hydrogen to hydrocarbon products several reactions are employed to adjust the hydrogencarbon monoxide ratio Most important is the water gas shift reaction in which additional hydrogen is produced at the expense of carbon monoxide to satisfy the hydrogencarbon monoxide ratio necessary for the production of hydrocarbon derivatives H O CO H CO 2 2 2 The boiling range of FischerTropsch typically spans the naphtha and kerogen boiling ranges and is suitable for analysis by application of the standard test methods With the suitable choice of a catalyst the preference for products boiling in the naphtha range 200C 390F or for product boiling in the diesel range approximately 150C300C 300F570F can be realized The other product that is worthy of consideration is biooil pyrolysis oil biocrude is the liquid product produced by the thermal decomposition destructive distillation of biomass Chapter 3 at temperatures in the order of 500C 930F The product is a synthetic crude oil and is of interest as a possible complement eventually a substitute to petroleum The product can vary from a light tarry material to a freeflowing liquidboth require further refining to produce specification grade fuels Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 Hydrocarbon moieties are predominant in the product but the presence of varying levels of oxygen depending upon the character of the feedstock requires testament using for example hydrotreating during refining On the other hand the biooil can be used as a feedstock to the FischerTropsch process for the production of lowerboiling products as is the case when naphtha and gas oil are used as feedstocks for the FischerTropsch process In summary the FischerTropsch process produces hydrocarbon products of different molecular weight from a gas mixture of carbon monoxide and hydrogen synthesis gas all of which can find use in various energy scenarios In the current context the most valuable product is synthesis gasthe mixture of carbon mon oxide CO and hydrogen H2 that is the beginning of a wide range of chemicals Figure 101 The production of synthesis gas ie mixtures of carbon monoxide and hydrogen has been known for several centuries But it is only with the commercialization of the FischerTropsch reaction that the importance of synthesis gas has been realized The thermal cracking pyrolysis of petroleum or fractions thereof was an important method for producing gas in the years following its use for increasing the heat content of water gas 387 Chemicals from the FischerTropsch Process In addition to the gases obtained by distillation of crude petroleum further gaseous prod ucts are produced during the processing of naphtha and middle distillate to produce gasoline Hydrodesulfurization processes involving treatment of naphtha distillates and residual fuels and from the coking or similar thermal treatment of vacuum gas oils and residual fuel oils also produce gaseous products The chemistry of the oiltogas conversion has been established for several decades and can be described in general terms although the primary and secondary reactions can be truly complex The composition of the gases produced from a wide variety of feedstocks depends not only on the severity of cracking but often to an equal or lesser extent on the feedstock type In general terms gas heating values are in the order of 9501350 Btuft3 A second group of refining operations which contribute to gas production are the catalytic crack ing processes such as fluid bed catalytic cracking and other variants in which heavy gas oils are converted into gas naphtha fuel oil and coke Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 The catalysts will promote steamreforming reactions that lead to a product gas containing more hydrogen and carbon monoxide and fewer unsaturated hydrocarbon products than the gas product from a noncatalytic process The resulting gas is more suitable for use as a medium heatvalue gas than the rich gas produced by straight thermal cracking The catalyst also influences the reactions rates in the thermal cracking reactions which can lead to higher gas yields and lower tar and carbon yields Almost all petroleum fractions can be converted into gaseous fuels although conversion pro cesses for the heavier fractions require more elaborate technology to achieve the necessary purity and uniformity of the manufactured gas stream In addition the thermal yield from the gasifica tion of heavier feedstocks is invariably lower than that of gasifying light naphtha or liquefied petroleum gas LPG since in addition to the production of synthesis gas components hydrogen and carbon monoxide and various gaseous hydrocarbon derivatives heavy feedstocks also yield some tar and coke Synthesis gas can be produced from heavy oil and other heavy crude feedstocks such as residua by the process known in the industry as partial oxidation POX 2CH O 2CO H crude oil 2 2 FIGURE 101 Routes to chemicals from synthesis gas and methanol 388 Handbook of Petrochemical Processes In this process the step consists of the reaction of the feedstock with a quantity of oxygen insuf ficient to burn it completely making a mixture consisting of carbon monoxide carbon dioxide hydrogen and steam Success in partially oxidizing heavy feedstocks depends mainly on details of the burner design The ratio of hydrogen to carbon monoxide in the product gas is a function of reaction temperature and stoichiometry and can be adjusted if desired by varying the ratio of carrier steam to oil fed to the unit The synthesis of hydrocarbon derivatives from the hydrogenation of carbon monoxide over transition metal catalysts was discovered in 1902 when Sabatier and Sanderens produced methane from hydrogen and carbon monoxide mixtures passed over nickel iron and cobalt catalysts In 1923 Fischer and Tropsch reported the use of alkalized iron catalysts to produce liquid hydrocar bon derivatives rich in oxygenated compounds The FischerTropsch process FischerTropsch synthesis is a series of catalyzed chemical reac tions that convert a mixture of carbon monoxide and hydrogen and into hydrocarbon derivatives The process is a key component of gastoliquids technology that produces liquid and solid hydro carbon derivatives from coal natural gas biomass or other carbonaceous feedstocks Typical cata lysts used are based on iron and cobalt and the hydrocarbon derivatives synthesized in the process are primarily liquid alkanes along with byproducts such as olefin derivatives alcohols and solid paraffin derivatives waxes 102 HISTORY AND DEVELOPMENT OF THE FISCHERTROPSCH PROCESS As originally conceived the function of the FischerTropsch process was to produce liquid trans portation hydrocarbon fuels and various other chemical products Schulz 1999 Since the original conception many refinements and adjustments to the technology have been made including cata lyst development and reactor design Depending on the source of the synthesis gas the technology is often referred to as coaltoliquids CTL andor gastoliquids In the simplest terms the FischerTropsch process is a catalytic chemical reaction in which car bon monoxide CO and hydrogen H2 in the synthesis gas are converted into hydrocarbon deriva tives of various molecular weights according to the following equation 2 1 H CO C H H O is an integer 2 2 2 2 n n n n n n For n 1 the reaction represents the formation of methane which in most coaltoliquids or gas toliquids applications is considered an undesirable byproduct The process conditions are usually chosen to maximize the formation of higher molecular weight hydrocarbon liquid fuels which are higher value products There are other side reactions taking place in the process among which the watergas shift reaction is predominant Thus CO H O H CO 2 2 2 Depending on the catalyst temperature and type of process employed hydrocarbon derivatives ranging from methane to higher molecular paraffin derivatives and olefin derivatives can be obtained Small amounts of low molecular weight oxygenates eg alcohol and organic acids are also formed The FischerTropsch technology has found industrial application since 1938 in Germany where a total of nine plants produced synthetic hydrocarbon derivatives However the history of the com mercial FischerTropsch technology dates back to the early years of the 20th century Table 102 Hence since the turn of the 21st century as indicated in the above summary of the FischerTropsch history there has been significantly renewed interest in FischerTropsch Technology In great part this renaissance has been due to the exploitation of cheaper remote or stranded gas which has the effect of making the economics of FischerTropsch projects increasingly attractive 389 Chemicals from the FischerTropsch Process A FischerTropsch plant incorporates three major process sections i production of synthesis gas which is a mixture of carbon monoxide and hydrogen steam reforming ii conversion of the synthesis gas to aliphatic hydrocarbon derivatives and water FischerTropsch synthesis process and iii hydrocracking the longerchain waxy synthetic hydrocarbon derivatives to fuel grade frac tions Of the above three steps the production of synthesis gas is the most energy intensive as well as expensive A major attraction of the use of synthesis gas is the very wide range of potential uses by con verting synthesis gas into useful downstream products i the FischerTropsch synthesis of hydro carbon derivatives ii methanol synthesis iii mixed alcohol synthesis and iv synthesis gas fermentation By choosing an appropriate catalyst usually based on iron or cobalt and appropriate reaction conditions usually 200C350C 390F650F and pressures in the order of 300600 psi the process with its associated cracking and separation stages can be optimized to produce high molecular weight wax for low molecular weight olefin derivatives and naphtha for petrochemicals production The ideal feedstock for the FischerTropsch process is synthesis gas consisting of a mix ture of hydrogen and carbon monoxide with a molar ratio of 21 Chadeesingh 2011 Methanol synthesis is another attractive conversion route because methanol is one of the top 10 petrochemical commodities insofar as like synthesis gas it can also be a source of chemicals Figure 101 Synthesis gas can be converted into methanol over a copperzinc oxide catalyst at 220C300C 430F570F and 7501500 psi CO 2H CH OH 2 3 Methanol can in turn be used to make acetic acid formaldehyde for resins gasoline additives and petrochemical building blocks such as ethylene and propylene Under slightly more severe process conditions up to 425C 800F and 4500 psi a wider range of mixed alcohols can be produced Chadeesingh 2011 The processes use catalysts modified from either FischerTropsch synthesis or methanol synthesis by addition of alkali metals Finally the fermentation route for the conversion of synthesis gas uses biochemical processes and reaction conditions that are close to ambient temperature and pressure to make ethanol or other alcohols Biochemical processes are addressed below TABLE 102 History and Evolution of the FischerTropsch Process 1902 Methane formed from mixtures of hydrogen and carbon monoxide over a nickel catalyst Sabatier and Sanderens 1923 Fischer and Tropsch report work with cobalt iron and rubidium catalysts at pressure to produce hydrocarbon derivatives 1936 The first four FischerTropsch production plants in Germany began operation 1950 A 5000 bd plant was commissioned and began operation in Brownsville Texas 19501953 The slurry phase reactor pilot unit developed 1950s Decline in construction of new FischerTropsch plants due to sudden availability of cheaper petroleum 1955 First Sasol Plant commissioned in South Africa Iron catalyst was used two further plants were commissioned in 1980 and 1983 19701980s Energy crisis initiated renewed interest in FischerTropsch technology as the price of petroleum increased 1990s Discovery of stranded gas reservoirs renewed interest in FischerTropsch as a viable gastoliquids technology 1992 MossGas plant used Sasol Technology and natural gas as the carbon feedstock 19921993 Shell used cobaltbased catalyst and natural gas as the feedstock 1993 Sasol slurry phase reactor commissioned using Febased catalyst 390 Handbook of Petrochemical Processes There are many options for converting synthesis gas into petrochemical feedstocks For exam ple the olefin derivatives conversion chain in which ethylene and propylene are converted into polymers polyethylene polypropylene polyvinyl chloride glycol derivatives ethylene glycol HOCH2CH2OH propylene glycol CH3CHOHCH2OH and a range of familiar materials such as acetone CH3COCH3 acetic acid CH3CO2H gasoline additives and surfactants The olefin deriv atives can be produced by synthesizing naphtha in a FischerTropsch process and then cracking it in a conventional naphtha cracker to make ethylene and propylene Depending on the source of biomass feedstock and the choice of gasifier technology the raw synthe sis gas can contain varying amounts of particulates eg ash or char which can lead to erosion plug ging or fouling alkali metals which can cause hot corrosion and catalyst poisoning watersoluble trace components eg halides ammonia light oils or tars eg benzene toluene xylene or naphtha lene which can lead to catalyst carbonization and fouling polyaromatic compounds sulfur compo nents phosphorus components as well as methane and carbon dioxide Many of these can be removed if required either using standard chemical industry equipment such as cyclones filters electrostatic precipitators water scrubbers oil scrubbers activated carbon and adsorbents or via cleanup processes such as hydrolysis and various carbon dioxide capture processes Chapter 4 Another important factor is the ratio of hydrogen to carbon dioxide in the synthesis gas Different conversion routes require different ratios eg 171 and 2151 for producing FischerTropsch naphthagasoline and diesel respectively or 31 for methanol synthesis Because biomass molecules contain oxygen within their structure biomassderived synthesis gas often needs to have the hydro gen to carbon monoxide ratio boosted One option for achieving this is to react some of the synthesis gas with steam over a catalyst to produce hydrogen and carbon dioxide in the watergas shift reac tion Chadeesingh 2011 Speight 2013ab as well as accepting a cost for the removal of carbon dioxide unless there is a byproduct hydrogen source readily available The extent to which gas cleanup is required depends on the choice of synthesis gas conversion route Generally the level of particulates will need to be reduced considerably for any chemical synthesis process but the precise extent to which say sulfur or halide levels need to be reduced depends on the catalysts that are going to be used For the methanol synthesis process for example the sulfur content of the synthesis gas has to be below 100 ppb vv For ammonia synthesis process there is a similar sulfur constraint and the carbon dioxide content must be below 10 ppm vv 103 SYNTHESIS GAS Synthesis gas a mixture composed primarily of not only carbon monoxide and hydrogen but also water carbon dioxide nitrogen and methane has been produced on a commercial scale since the early part of the 20th century This section provides a general description of the emerging technolo gies and their potential economic benefits Recent developments in the technology for synthesis production via membrane reactors are also discussed During World War II the Germans obtained synthesis gas by gasifying the carbonaceous feedstock The mixture was used for producing a liquid hydrocarbon mixture in the gasoline range using FischerTropsch technology Although this route was abandoned after the war due to the high production cost of these hydrocarbon derivatives it is currently being used in South Africa where the carbonaceous feedstock coal is relatively inexpen sive SASOL II and SASOL III Almost all carbonaceous materials can be converted into gaseous fuels although conversion processes for the heavier fractions require more elaborate technology to achieve the necessary purity and uniformity of the manufactured gas stream In addition the thermal yield from the gasification of heavier feedstocks is invariably lower than that of gasifying light naphtha or liquefied petroleum gas since in addition to the production of synthesis gas components hydrogen and carbon monoxide and various gaseous hydrocarbon derivatives heavy feedstocks also yield some tar and coke Gasification to produce synthesis gas can proceed from just about any organic material includ ing biomass and plastic waste The resulting synthesis gas burns cleanly into water vapor and carbon 391 Chemicals from the FischerTropsch Process dioxide Alternatively synthesis gas may be converted efficiently to methane via the Sabatier reac tion or to a diesellike synthetic fuel via the FischerTropsch process Inorganic components of the feedstock such as metals and minerals are trapped in an inert and environmentally safe form as char which may have use as a fertilizer In principle synthesis gas can be produced from any hydrocarbon feedstock These include natu ral gas naphtha residual oil petroleum coke coal and biomass The lowest cost routes for synthesis gas production however are based on natural gas The cheapest option is remote or stranded reserves Current economic considerations dictate that the production of liquid fuels from synthesis gas translates into using natural gas as the hydrocarbon source Nevertheless the synthesis gas pro duction operation in a gastoliquids plant amounts to greater than half of the capital cost of the plant The choice of technology for synthesis gas production also depends on the scale of the synthesis operation Synthesis gas production from solid fuels can require an even greater capital investment with the addition of feedstock handling and more complex synthesis gas purification operations The greatest impact on improving gastoliquids plant economics is to decrease capital costs associated with synthesis gas production and improve thermal efficiency through better heat integration and utilization Improved thermal efficiency can be obtained by combining the gastoliquids plant with a power generation plant to take advantage of the availability of lowpressure steam Regardless of the final fuel form gasification itself and subsequent processing neither emits nor traps greenhouse gasses such as carbon dioxide Combustion of synthesis gas or derived fuels does of course emit carbon dioxide However biomass gasification could play a significant role in a renewable energy economy because biomass production removes carbon dioxide from the atmo sphere While other biofuel technologies such as biogas and biodiesel are also reputed to be carbon neutral gasification runs on a wider variety of input materials can be used to produce a wider variety of output fuels and is an extremely efficient method of extracting energy from biomass Biomass gasification is therefore one of the most technically and economically convincing energy possibilities for a carbon neutral economy Synthesis gas consists primarily of carbon monoxide carbon dioxide and hydrogen and has less than half the energy density of natural gas Synthesis gas is combustible and often used as a fuel source or as an intermediate for the production of other chemicals Synthesis gas for use as a fuel is most often produced by gasification of the carbonaceous feedstock or municipal waste mainly by the following paths C O CO CO C 2CO C H O CO H 2 2 2 2 2 When used as an intermediate in the large scale industrial synthesis of hydrogen and ammonia it is also produced from natural gas via the steam reforming reaction as follows CH H O CO 3H 4 2 2 The synthesis gas produced in large wastetoenergy gasification facilities is used as fuel to generate electricity The manufacture of gas mixtures of carbon monoxide and hydrogen has been an important part of chemical technology for about a century Originally such mixtures were obtained by the reaction of steam with incandescent coke and were known as water gas Used first as a fuel water gas soon attracted attention as a source of hydrogen and carbon monoxide for the production of chemicals at which time it gradually became known as synthesis gas Eventually steam reforming processes in which steam is reacted with natural gas methane or petroleum naphtha over a nickel catalyst found wide application for the production of synthesis gas 392 Handbook of Petrochemical Processes A modified version of steam reforming known as autothermal reforming which is a combina tion of partial oxidation near the reactor inlet with conventional steam reforming further along the reactor improves the overall reactor efficiency and increases the flexibility of the process Partial oxidation processes using oxygen instead of steam also found wide application for synthesis gas manufacture with the special feature that they could utilize lowvalue feedstocks such as heavy petroleum residua In recent years catalytic partial oxidation CPOX employing very short reac tion times milliseconds at high temperatures 850C1000C 1560F1830F is providing still another approach to synthesis gas manufacture Nearly complete conversion of methane with close to 100 selectivity to hydrogen and carbon dioxide can be obtained with a rhenium monolith under wellcontrolled conditions Experiments on the catalytic partial oxidation of nhexane conducted with added steam give much higher yields of hydrogen than can be obtained in experiments without steam a result of much interest in obtaining hydrogenrich streams for fuel cell applications The route for a carbonaceous feedstock to synthetic automotive fuels as practiced by SASOL is technically proven and a series of products with favorable environmental characteristics are pro duced Luque and Speight 2015 As is the case in essentially all conversion processes for carbona ceous feedstocks where air or oxygen is used for the utilization or partial conversion of the energy in the coal the carbon dioxide burden is a drawback as compared to crude oil There uses of synthesis gas include use as a chemical feedstock and in gastoliquid processes which use FisherTropsch chemistry to make liquid fuels as feedstock for chemical synthesis as well as being used in the production of fuel additives including diethyl ether and methyl tbutyl ether MTBE acetic acid and its anhydride synthesis gas could also make an important contri bution to chemical synthesis through conversion to methanol There is also the option in which stranded natural gas is converted to synthesis gas production followed by conversion to liquid fuels The chemical train for producing synthesis gas carbon monoxide hydrogen from which a variety of products can be produced can be represented simply as Carbonaceous feedstock partial oxidation synthesis gas Synthesis gas synthetic fuels and petrochemicals The products designated as synthesis fuels include lowtohighboiling hydrocarbon derivatives and methanol Also the highboiling products including wax products can also be used as feedstocks for gas production In addition the actual process described as comprising three components i synthesis gas gen eration ii waste heat recovery and iii gas processing Within each of the above three listed systems are several options For example synthesis gas can be generated to yield a range of compo sitions ranging from highpurity hydrogen to highpurity carbon monoxide Two major routes can be utilized for highpurity gas production i pressure swing adsorption PSA and ii utilization of a cold box where separation is achieved by distillation at low temperatures In fact both processes can also be used in combination as well Unfortunately both processes require high capital expen diture However to address these concerns research and development is ongoing and successes can be measured by the demonstration and commercialization of technologies such as permeable mem brane for the generation of highpurity hydrogen which in itself can be used to adjust the hydrogen carbon monoxide ratio of the synthesis gas produced 104 PRODUCTION OF SYNTHESIS GAS Gasification processes are used to convert a carboncontaining carbonaceous material into a synthesis gas a combustible gas mixture which typically contains carbon monoxide hydrogen nitrogen carbon dioxide and methane Chapter 5 The impure synthesis gas has a relatively low calorific value ranging from 100 to 300 Btuft3 The gasification process can accommodate a wide 393 Chemicals from the FischerTropsch Process variety of gaseous liquid and solid feedstocks and it has been widely used in commercial applica tions for the production of fuels and chemicals Luque and Speight 2015 1041 feedstocks In principle synthesis gas can be produced from any hydrocarbon feedstock which includes natu ral gas naphtha residual oil petroleum coke coal biomass and municipal or industrial waste Chapter 1 The product gas stream is subsequently purified to remove sulfur nitrogen and any particulate matter after which it is catalytically converted to a mixture of liquid hydrocarbon prod ucts In addition synthesis gas may also be used to produce a variety of products including ammo nia and methanol Of all the carbonaceous materials used as feedstocks for gasification process coal represents the most widely used feedstocks and accordingly the feedstock about which most is known In fact gas ification of coal has been a commercially available proven technology Speight 2013ab The modern gasification processes have evolved from three firstgeneration process technologies i Lurgi fixed bed reactor ii hightemperature Winkler fluidized bed reactor and iii KoppersTotzek entrained flow reactor In each case steamairoxygen is passed through heated coal which may either be a fixed bed fluidized bed or entrained in the gas Exit gas temperatures from the reactor are 500C 930F 900C1100C 1650F2010F and 1300C1600C 2370F2910F respectively In addition to the steamairoxygen mixture being used as the feed gases steamoxygen mixtures can also be used in which membrane technology and a compressed oxygencontaining gas is employed In addition lowvalue or negativevalue materials and wastes such as petroleum coke refin ery residua refinery waste municipal sewage sludge biomass hydrocarbon contaminated soils and chlorinated hydrocarbon byproducts have all been used successfully in gasification operations Speight 2008 2013a 2013b In addition synthesis gas is used as a source of hydrogen or as an intermediate in producing a variety of hydrocarbon products by means of the FischerTropsch syn thesis Table 61 Chadeesingh 2011 In fact gasification to produce synthesis gas can proceed from any carbonaceous material including biomass and waste There are different sources for obtaining synthesis gas It can be produced by steam reforming or partial oxidation of any hydrocarbon ranging from natural gas methane to petroleum residua It can also be obtained by gasifying the carbonaceous feedstock to a medium Btu gas medium Btu gas consists of variable amounts of carbon monoxide carbon dioxide and hydrogen and is used principally as a fuel gas A major route for producing synthesis gas is the steam reforming of natural gas over a promoted nickel catalyst at temperatures in the order of 800C 1470F CH H O CO 3H 4 2 2 In some countries synthesis gas is mainly produced by steam reforming naphtha Because naphtha is a mixture of hydrocarbon derivatives ranging approximately from C5 to C10 the steam reforming reaction may be represented using nheptane CH CH CH 7H O 7CO 15H 3 2 5 3 2 2 As the molecular weight of the hydrocarbon increases lower HC feed ratio the hydrogencarbon monoxide H2CO product ratio decreases The hydrogencarbon monoxide product ratio is approx imately 3 for methane 25 for ethane 21 for heptane and less than 2 for heavier hydrocarbon derivatives The noncatalytic partial oxidation of hydrocarbon derivatives is also used to produce synthesis gas but the hydrogencarbon monoxide ratio is lower than from steam reforming In practice this ratio is even lower than what is shown by the stoichiometric equation because part of the methane is oxidized to carbon dioxide and water When resids are partially oxidized by 394 Handbook of Petrochemical Processes oxygen and steam at 1400C1450C 2550F2640F and 800900 atm the gas consists of equal parts of hydrogen and carbon monoxide Synthesis gas is an important intermediate The mixture of carbon monoxide and hydrogen is used for producing methanol It is also used to synthesize a wide variety of hydrocarbon derivatives ranging from gases to naphtha to gas oil using FischerTropsch technology This process may offer an alternative future route for obtaining olefin derivatives and chemicals Synthesis gas is a major source of hydrogen which is used for producing ammonia Ammonia is the host of many chemicals such as urea ammonium nitrate and hydrazine Carbon dioxide a byproduct from synthesis gas reacts with ammonia to produce urea H2NCONH2 Urea also known as carbamide serves an important role in the metabolism of nitrogen containing compounds by animals and is the main nitrogencontaining substance in the urine of mamas It is a colorless odorless solid highly soluble in water and dissolved in water it exhibits neither an acid nor an alkali It is formed in the liver by the combination of two ammonia molecules NH3 with a carbon dioxide CO2 molecule It is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry Most of the production of hydrocarbon derivatives by FischerTropsch method uses synthesis gas produced from sources that yield a relatively low hydrogencarbon monoxide ratio such as typi cal in coal gasifiers This however does not limit this process to low hydrogencarbon monoxide gas feeds The only largescale commercial process using this technology is in South Africa where coal is an abundant energy source The process of obtaining liquid hydrocarbon derivatives from coal through the FischerTropsch process is termed indirect coal liquefaction which was originally intended for obtaining liquid hydrocarbon derivatives from solid fuels However this method may well be applied in the future to the manufacture of chemicals through cracking the liquid products or by directing the reaction to produce more olefin derivatives The reactants in FischerTropsch processes are carbon monoxide and hydrogen The reaction may be considered a hydrogenative oligomerization of carbon monoxide in presence of a heteroge neous catalyst The main reactions occurring in FischerTropsch processes are i Olefin derivatives 2 H CO C H H O 2 2 2 n n n n n ii Paraffin derivatives 2 1 H CO C H H O 2 2 2 2 n n n n n iii Alcohol derivatives 2 H CO C H O 1 H O 2 2 2 2 n n n n n The coproduct water reacts with carbon monoxide the shift reaction yielding hydrogen and carbon dioxide CO H O H CO 2 2 2 Urea 395 Chemicals from the FischerTropsch Process The gained hydrogen from the water shift reaction reduces the hydrogen demand for Fischer Tropsch processes Watergas shift proceeds at about the same rate as the FischerTropsch reaction Another side reaction also occurring in FischerTropsch process reactors is the disproportionation of carbon monoxide to carbon dioxide and carbon 2CO CO C 2 This reaction is responsible for the deposition of carbon in the reactor tubes in fixed bed reactors and reducing heat transfer efficiency FischerTropsch technology is best exemplified by the SASOL projects in South Africa After the carbonaceous feedstock is gasified to a synthesis gas mixture it is purified in a Rectisol unit The purified gas mixture is reacted in a Synthol unit over an ironbased catalyst The main products are gasoline diesel fuel and jet fuels Byproducts are ethylene propylene alpha olefin derivatives sulfur phenol and ammonia which are used for the production of downstream chemicals However the exact mechanism is not fully established One approach assumes a firststep adsorption of car bon monoxide on the catalyst surface followed by a transfer of an adsorbed hydrogen atom from an adjacent site to the metal carbonyl MCO The polymerization continues as in the last three steps shown above until termination occurs and the hydrocarbon is desorbed The last two steps shown above explain the presence of oxygenated derivatives in FischerTropsch products Alternatively an intermediate formation of an adsorbed methylene on the catalyst surface through the dissociative adsorption of carbon monoxide has been considered The formed metal carbide MC is then hydrogenated to a reactive methylene metal species The methylene interme diate abstracts a hydrogen and is converted to an adsorbed methyl Reaction of the methyl with the methylene produces an ethylmetal species Successive reactions of the methylene with the formed ethyl produce a longchain adsorbed alkyl The adsorbed alkyl species can either terminate to a paraffin by a hydrogenation step or to an olefin by a dehydrogenation step The carbide mechanism however does not explain the formation of oxygenate derivatives in FischerTropsch products 1042 Processes 10421 Steam Reforming Steam methane reforming SMR is the benchmark process that has been employed over a period of several decades for hydrogen production The process involves reforming natural gas in a continu ous catalytic process in which the major reaction is the formation of carbon monoxide and hydrogen from methane and steam CH H O CO 3H H 97400 Btulb 4 2 2 298K Higher molecular weight feedstocks can also be reformed to hydrogen C H 3H O 3CO 7H 3 8 2 2 That is C H H O CO 05 H 2 2 n n m n n m In the actual process the feedstock is first desulfurized by passage through activated carbon which may be preceded by caustic and water washes The desulfurized material is then mixed with steam and passed over a nickelbased catalyst 730C845C 1350F1550F and 400 psi Effluent gases are cooled by the addition of steam or condensate to about 370C 700F at which point 396 Handbook of Petrochemical Processes carbon monoxide reacts with steam in the presence of iron oxide in a shift converter to produce carbon dioxide and hydrogen CO H O CO H 2 2 2 The carbon dioxide is removed by amine washing the hydrogen is usually a highpurity 99 material Steam reforming sometimes referred to as steam methane reforming SMR is carried out by passing a preheated mixture comprising essentially methane and steam through catalystfilled tubes Since the reaction is endothermic heat must be provided in order to effect the conversion This is achieved by the use of burners located adjacent to the tubes The products of the process are a mixture of hydrogen carbon monoxide and carbon dioxide Recovery of the heat from the combustion products can be implemented in order to improve the efficiency of the overall process To maximize the conversion of the methane feed both a primary and secondary reformer are gener ally utilized A primary reformer is used to effect 9092 conversion of methane Here the hydro carbon feed is partially reacted with steam over a nickelalumina catalyst to produce a synthesis gas with hydrogencarbon monoxide ratio of approximately 31 This is done in a fired tube furnace at 900C 1650F at a pressure of 225450 psi The unconverted methane is reacted with oxygen at the top of a secondary autothermal reformer ATR containing nickel catalyst in the lower region of the vessel Two watergas shift reactors are used downstream of the secondary reformer to adjust the hydrogencarbon monoxide ratio depending on the end use of the steam reformed products The first of the two watergas shift reactors utilizes an ironbased catalyst which is heated to approximately 400C 750F The second watergas shift reactor operates at approximately 200C 390F and is charged with a copperbased catalyst Steam reforming is an exothermic reaction that is carried out by passing a preheated mixture comprising methane sometimes substituted by natural gas having high methane content and steam through catalystfilled tubes The products of the process are a mixture of hydrogen carbon monox ide and carbon dioxide To maximize the conversion of the methane feed primary and secondary reformers are often usedthe primary reformer effects a 9092 vv conversion of methane In this step the hydrocarbon feed is partially reacted with steam at 900C 1650F at 220500 psi over a nickelalumina catalyst to produce a synthesis gas in which the hydrogencarbon monoxide H2CO ratio is in the order of 31 Any unconverted methane is reacted with oxygen at the top of a secondary autothermal reformer containing nickel catalyst in the lower region of the vessel In autothermal reformers often referred to as secondary reformers the oxidation of methane supplies the necessary energy and carried out either simultaneously or in advance of the reforming reaction The equilibrium of the methane steam reaction and the watergas shift reaction determines the conditions for optimum hydrogen yields The optimum conditions for hydrogen production require high temperature at the exit of the reforming reactor 800C900C 1470F1650F high excess of steam molar steamtocarbon ratio of 253 and relatively low pressures below 450 psi Most commercial plants employ supported nickel catalysts for the process One way of overcoming the thermodynamic limitation of steam reforming is to remove either hydrogen or carbon dioxide as it is produced hence shifting the thermodynamic equilibrium toward the product side The concept for sorptionenhanced methane steam reforming is based on in situ removal of carbon dioxide by a sorbent such as calcium oxide CaO CaO CO CaCO 2 3 Sorption enhancement enables lower reaction temperatures which may reduce catalyst coking and sintering while enabling use of less expensive reactor wall materials In addition heat release by the exothermic carbonation reaction supplies most of the heat required by the endothermic reforming reactions However energy is required to regenerate the sorbent to its oxide form by the energy intensive calcination reaction 397 Chemicals from the FischerTropsch Process CaCO CaO CO 3 2 Use of a sorbent requires either that there be parallel reactors operated alternatively and out of phase in reforming and sorbent regeneration modes or that sorbent be continuously transferred between the reformercarbonator and regeneratorcalciner Balasubramanian et al 1999 Hufton et al 1999 The higher molecular weight hydrocarbon derivatives that are also constituents of natural gas Speight 2007 2014a are converted to methane in an adiabatic prereformer upstream of the steam reformer In the prereformer all higher hydrocarbon derivatives C2 are converted into a mixture of methane hydrogen and carbon oxides C H H O CO 2 H 3H CO CH H O CO H O H CO 2 2 2 4 2 2 2 2 n n n m n m The prereforming process utilizes an adiabatic fixed bed reactor with highly active nickel catalysts and the reactions take place at temperatures of approximately 350C550C 650F1020F and make it possible to preheat the steam reformer feed to higher temperatures without getting problems with olefin formation from the higher hydrocarbon derivatives Olefin derivatives are unwanted in the steam reformer feed as they generally cause coking of the catalyst pellets at high temperatures Preheating of the steam reformer feed is of great advantage because the reformer unit can be scaled down to a minimum size AasbergPetersen et al 2001 2002 Hagh 2004 The reactions are catalyzed by pellets coated with nickel and are highly endothermic overall Effective heat transport to the reactor tubes and further into the center of the catalytic fixed bed is therefore a very important aspect during design and operation of steam reformers The reac tions take place in several tubular fixed bed reactors of low diametertoheight ratio to ensure efficient heat transport in radial direction The process conditions are typically 300600 psi bar with inlet temperature of 300C650C 570F1200F and outlet temperature of 700C950C 1290F1740F There is often an approach to equilibrium of about 5C20C which means that the outlet temperature is slightly higher than the equilibrium temperature calculated from the actual outlet composition In a prereformer whisker carbon can be formed either from methane or higher molecular weight hydrocarbon derivatives The lower limit of the H2OC ratio depends on a number of factors includ ing the feed gas composition the operating temperature and the choice of catalyst In a prereformer operating at low H2OCratio the risk of carbon formation from methane is most pronounced in the reaction zone where the temperature is highest Carbon formation from higher molecular weight hydrocarbon derivatives can only take place in the first part of the reactor with the highest concen trations of higher molecular weight C2 compounds The deposition of carbon can be an acute problem with the use of Nibased catalysts in the pri mary reformer RostrupNielsen 1984 Alstrup 1988 RostrupNielsen 1993 The carbonforming reactions occur in parallel with the reforming reactions and are undesirable as they cause poison ing of the surface of the catalyst pellets This leads to lower catalyst activity and the need for more frequently catalyst reloading The coking reactions are the COreduction methane cracking and Boudouard reaction given by the respective equilibrium reactions CO H H O C H O CH C 2H 2CO C CO 2 2 2 4 2 2 398 Handbook of Petrochemical Processes Thus low steam excess can lead to critical conditions causing coke formationequilibrium calculations of the coking reactions can be a useful tool for predicting the danger for catalyst poi soning but the reaction kinetics may nevertheless be so slow that coking is no concern A complete analysis should therefore also involve kinetic calculations which will be feedstockdependent expressions for these reactions One approach to prevent carbon formation is to use a steamcarbon ratio in the feed gas that does not allow the formation of carbon However this method results in lowering the efficiency of the process Another approach is to utilize sulfur passivation which utilizes the principle that the reac tion leading to the deposition of carbon requires a larger number of adjacent surface Ni atoms than does steam reforming When a fraction of the surface atoms are covered by sulfur the deposition of carbon is thus more greatly inhibited than steam reforming reactions leading to the development of the SPARG process RostrupNielsen 1984 Udengaard et al 1992 A third approach is to use Group VIII metals that do not form carbides eg Pt However due to the high cost of such metals they are unable to compare to the economics associated with Ni A major challenge in steam reforming development is its energyintensive nature due to the high endothermicity of the reactions The trend in development thus is one which seeks higher energy efficiency Improvements in catalysts and metallurgy require adaption to lower steamcarbon ratios and higher heat flux Finally in all reforming processes it is essential that impurities such as sulfur mercury and any other contaminants in the feedstock stream should be removed in order to prevent the poisoning of the reforming catalysts FischerTropsch synthesis takes the requirements for purification to a new level cobalt FischerTropsch catalysts are extremely sensitive to even part per billion ppb levels of contaminants including sulfur compounds and these must be removed typically to levels below 5 ppb The removal of mercury has become increasingly necessary in recent years as compounds of the metal have been found to be present in many gas sources and mercury removal for both environ mental and process reasons is essential Typically the processes are based on fixed beds of absorbents to remove traces of contaminants from hydrocarbon gases and liquids In particular the processes carry out i hydrogen sulfide removal ii carbonyl sulfide COS removal iii mercury Hg removal and iv arsine AsH3 removal The choice of absorbent and the design of the reactor vessel will vary according to the type of feedstock the level of contaminants pressure and temperature conditions as well as the tolerance of the catalyst to the level of impurities 10422 Autothermal Reforming The autothermal reformer was developed in the 1950s and is used in commercial applications to provide synthesis gas for ammonia and methanol synthesis In the case of ammonia production where high hydrogencarbon monoxide ratios are needed the autothermal reformer is operated at high steamcarbon ratios In the case of methanol synthesis the required hydrogencarbon monox ide ratio is provided by manipulating the carbon dioxide recycle In fact development and optimi zation of this technology has led to costeffective operation at very low steamcarbon feed ratios to produce carbon monoxiderich synthesis gas for example which is preferred in FischerTropsch synthesis In the autothermal reforming process the organic feedstock such as natural gas and steam and sometimes carbon dioxide are mixed directly with oxygen and air in the reformer The reformer itself comprises a refractorylined vessel which contains the catalyst together with an injector located at the top of the vessel Partial oxidation reactions occur in a region of the reactor referred to as the combustion zone It is the mixture from this zone which then flows through a catalyst bed where the actual reforming reactions occur Heat generated in the combustion zone from partial oxidation reactions is utilized in the reforming zone so that in the ideal case it is possible that the autothermal reformer can be in complete heat balance 399 Chemicals from the FischerTropsch Process When the autothermal reformer uses carbon dioxide the hydrogencarbon monoxide ratio produced is 11 when the autothermal reformer uses steam the hydrogencarbon monoxide ratio produced is 251 The reactions can be described in the following equations using carbon dioxide 2CH O CO 3H 3CO H O Heat 4 2 2 2 2 Using steam 4CH O 2H O 10H 4CO 4 2 2 2 The reactor itself consists of three zones i the burner in which the feedstock streams are mixed in a turbulent diffusion flame ii the combustion zonewhere partial oxidation reactions produce a mixture of carbon monoxide and hydrogen and iii the catalytic zonewhere the gases leaving the combustion zone reach thermodynamic equilibrium Key elements in the reactor are the burner and the catalyst bedthe burner provides mixing of the feed streams and the natural gas is converted into a turbulent diffusion flame CH 32O CO 2H O 4 2 2 When carbon dioxide is present in the feed the H2CO ratio produced is in the order of 11 but when the process employs steam the H2CO ratio produced is 251 2CH O CO 3H 3CO H O 4CH O 2H O 10H 4CO 4 2 2 2 2 4 2 2 2 The risk of soot formation in an autothermal reformer reactor depends on a number of parameters including feed gas composition temperature pressure and especially burner design Soot precur sors may be formed in the combustion chamber during operation and it is essential that the design of burner catalyst and reactor is such that the precursors are destroyed by the catalyst bed to avoid soot formation Many observers consider the combination of adiabatic prereforming and autothermal reform ing at low H2OC ratios is a preferred layout for production of synthesis gas for large gastoliquids plants The following are the advantages of using the autothermal reformer i compact in design hence less associated footprint ii low investment iii economy of scale iv flexible operationshort startup periods and fast load changes and v sootfree operation 10423 Combined Reforming Combined reforming incorporates a combination of both steam reforming and autothermal reform ing In the process the feedstock is typically a mixture of reformed gas and desulfurized natural gas which is partially converted under mild conditions to synthesis gas in a relatively small steam reformer The offgases from the steam reformer are then sent to an oxygenfired secondary reac tor the autothermal reformer Here the unreacted methane is converted to synthesis gas by partial oxidation followed by steam reforming Another configuration requires the hydrocarbon feed to be split into two streams which are then fed in parallel to the steam reforming and autothermal reactors An example of an efficient version of combined reforming is one which has been developed by Synetix called gasheated reforming 400 Handbook of Petrochemical Processes 10424 Partial Oxidation Partial oxidation reactions occur when a substoichiometric fuelair mixture is partially combusted in a reformer The general reaction equation without catalyst thermal partial oxidation TPOX is of the form C H 2 2O CO 2 H O 2 2 n m n m n m A possible reaction equation is C H 12O 24CO 6H 24 12 2 2 A thermal partial oxidation reactor is similar to the autothermal reformer with the main differ ence being no catalyst is used The feedstock which may include steam is mixed directly with oxygen by an injector which is located near the top of the reaction vessel Both partial oxidation as well as reforming reactions occur in the combustion zone below the burner The principal advan tage of partial oxidation is its ability to process almost any feedstock which can comprise very high molecular weight organics for example petroleum coke Gunardson and Abrardo 1999 Additionally since emission of NOx and SOx are minimal the technology can be considered envi ronmentally benign On the other hand very high temperatures approximately 1300C are required to achieve near complete reaction This necessitates the consumption of some of the hydrogen and a greater than stoichiometric consumption of oxygen ie oxygenrich conditions Capital costs are high on account of the need to remove soot and acid gases from the synthesis gas Operating expenses are also high due to the need for oxygen at high pressure A possible means of improving the efficiency of synthesis gas production is via catalytic partial oxidation technology Although catalytic partial oxidation has not as yet been used commercially it has several advantages over steam reforming especially the higher energy efficiency The reac tion is in fact not endothermic as is the case with steam reforming but rather slightly exothermic Further a hydrogencarbon monoxide ratio close to 20 ie the ideal ratio for the FischerTropsch and methanol synthesis is produced by this technology Catalytic partial oxidation can occur by either of two routes i direct or ii indirect The direct catalytic partial oxidation occurs through a mechanism involving only surface reaction on the catalyst the direct route produces synthesis gas according to the following reaction 2CH O 2CO 4H 4 2 2 On the other hand the indirect catalytic partial oxidation route comprises total combustion of methane to carbon dioxide and water followed by steam reforming and the watergas shift reaction Here equilibrium conversions can be greater than 90 at ambient pressure However in order for an industrial process for this technology to be economically viable an operating pressure of more than 20 atm would be required Unfortunately under such pressures equilibrium conversions are lower Further an operational problem arises on account of the highly exothermic combustion step which makes for problematic temperature control of the process and the possibility of temperature runaways It must be noted that in most studies of catalytic partial oxidation in microreactors in most to nearly all cases the conversion occurred via the indirect route It is apparent that only the direct mechanism is likely to occur at short contact times Interestingly several researchers Choudhary et al 1993 Lapszewicz and Jiang 1992 have observed that yields higher than equilibrium values are obtained with high flow rates through fixed bed reactors 401 Chemicals from the FischerTropsch Process 1043 Product distriBution The product distribution of hydrocarbon derivatives formed during the FischerTropsch process follows an AndersonSchulzFlory distribution 1 2 1 α α W n n n Wn is the weight fraction of hydrocarbon molecules containing n carbon atoms α is the chain growth probability or the probability that a molecule will continue reacting to form a longer chain In general α is largely determined by the catalyst and the specific process conditions According to the above equation methane will always be the largest single product however by increasing α close to 1 the total amount of methane formed can be minimized compared to the sum of all the various longchain products Increasing α increases the formation of longchain hydrocar bon derivativeswaxeswhich are solid at room temperature Therefore for production of liquid transportation fuels it may be necessary to crack the FischerTropsch longerchain products The very longchain hydrocarbon derivatives are waxes which are solid at room temperature Therefore for production of liquid transportation fuels it may be necessary to crack some of the FischerTropsch products In order to avoid this some researchers have proposed using zeolites or other catalyst substrates with fixedsized pores that can restrict the formation of hydrocarbon deriv atives longer than some characteristic size usually n 10 This way they can drive the reaction so as to minimize methane formation without producing lots of longchain hydrocarbon derivatives It has been proposed that zeolites or other catalyst substrates with fixedsized pores that can restrict the formation of hydrocarbon derivatives longer than some characteristic size usually n 10 This would tend to drive the reaction to minimum methane formation without producing the waxy products 105 PROCESS PARAMETERS For largescale commercial FischerTropsch reactors heat removal and temperature control are the most important design features to obtain optimum product selectivity and long catalyst lifetimes Over the years basically four FischerTropsch reactor designs have been used commercially These are the multitubular fixed bed the slurry reactor or the fluidized bed reactor with either a fixed bed or a circulating bed The fixed bed reactor consists of thousands of small tubes with the cata lyst as surfaceactive agent in the tubes Water surrounds the tubes and regulates the temperature by settling the pressure of evaporation The slurry reactor is widely used and consists of fluid and solid elements where the catalyst has no particularly position but flows around as small pieces of catalyst together with the reaction components The slurry and fixed bed reactor are used in the low temperature FischerTropsch process The fluidized bed reactors are diverse but characterized by the fluid behavior of the catalyst The multitubular fixed bed reactors often referred to as Arge reactors were developed jointly by Lurgi and Ruhrchemie and commissioned in the 1955 They were used by Sasol to produce highboiling FischerTropsch liquid hydrocarbon derivatives and waxes in Sasolburg in what Sasol called the lowtemperature FischerTropsch synthesis process aiming for liquid fuels production Most if not all of these types of Arge reactors are now be replaced by slurry bed reactors which is considered the stateoftheart technology for lowtemperature FischerTropsch synthesis Slurry bed FischerTropsch reactors offer better temperature control and higher conversion Fluidized bed FischerTropsch reactors were developed for the hightemperature FischerTropsch synthesis to produce low molecular gaseous hydrocarbon derivatives and naphtha This type of reactor was originally developed in a circulating mode such as the Sasol synthol reactors but has been replaced by a fixed fluidized bed type of reactor advanced synthol reactors which is capable of a high throughput 402 Handbook of Petrochemical Processes Sasol in South Africa uses coal and natural gas as a feedstock and produces a variety of syn thetic petroleum products The process was used in South Africa to meet its energy needs during its isolation under Apartheid This process has received renewed attention in the quest to produce low sulfur diesel fuel in order to minimize the environmental impact from the use of diesel engines The FischerTropsch process as applied at Sasol can be divided into two operating regimes i the hightemperature FischerTropsch process and ii the lowtemperature FischerTropsch process Chadeesingh 2011 The hightemperature FischerTropsch technology uses a fluidized catalyst at 300C330C 570F635F Originally circulating fluidized bed units were used Synthol reactors Since 1989 a commercialscale classical fluidized bed unit has been implemented and improved upon The lowtemperature FischerTropsch technology has originally been used in tubular fixed bed reactors at 200C230C 390F260F This produces a more paraffin derivatives and waxy prod uct spectrum than the hightemperature technology A new type of reactor the Sasol slurry phase distillate reactor has been developed and is in commercial operation This reactor uses a slurry phase system rather than a tubular fixed bed configuration and is currently the favored technology for the commercial production of synfuels The commercial Sasol FischerTropsch reactors all use ironbased catalysts on the basis of the desired product spectrum and operating costs Cobaltbased catalysts have also been known since the early days of this technology and have the advantage of higher conversion for low temperature cases Cobalt is not suitable for high temperature use due to excessive methane formation at such tempera tures For oncethrough maximum diesel production cobalt has despite its high cost advantages and Sasol has also developed cobalt catalysts which perform very well in the slurry phase process However both the iron and cobalt FischerTropsch catalysts are sensitive to the presence of sulfur compounds in the synthesis gas and can be poisoned by the sulfur compounds In addition the sensitivity of the catalyst to sulfur is higher for cobaltbased catalysts than for the ironbased catalysts This is one reason why cobaltbased catalysts are preferred for FischerTropsch synthesis with synthesis gas derived from natural gas where the synthesis gas has a higher hydrogencarbon monoxide ratio and is relatively lower in sulfur content On the other hand ironbased catalysts are preferred for lowerquality feedstocks such as coal The kerosene often referred to as diesel although the product could not be sold as diesel fuel without any further treatment to meet specifications produced by the slurry phase reactor has a highly paraffin derivatives nature giving a cetane number in excess of 70 The aromatic content of the diesel is typically below 3 and it is also sulfurfree and nitrogenfree This makes it an excep tional diesel as such or it can be used to sweeten or to upgrade conventional diesels The FischerTropsch process is an established technology and already applied on a large scale although its popularity is hampered by high capital costs high operation and maintenance costs and the uncertain and volatile price of crude oil In particular the use of natural gas as a feedstock only becomes practical when using stranded gas ie sources of natural gas far from major cities which are impractical to exploit with conventional gas pipelines and liquefied natural gas technology otherwise the direct sale of natural gas to consumers would become much more profitable It is suggested by geologists that supplies of natural gas will peak 515 years after oil does although such predictions are difficult to make and often highly uncertain Hence the increasing interest in a variety of carbonaceous feedstocks as a source of synthesis gas Under most circumstances the production of synthesis gas by reforming natural gas will be more economical than from coal gasification but sitespecific factors need to be considered In fact any technological advance in this field such as better energy integration or the oxygen transfer ceramic membrane reformer concept will speed up the rate at which the synfuels technology will become common practice There are large coal reserves which may increasingly be used as a fuel source during oil deple tion Since there are large coal reserves in the world this technology could be used as an interim transportation fuel if conventional oil were to become more expensive Furthermore combination of 403 Chemicals from the FischerTropsch Process biomass gasification and FischerTropsch synthesis is a very promising route to produce transporta tion fuels from renewable or green resources Often a higher concentration of some sorts of hydrocarbon derivatives is wanted which might be achieved by changed reaction conditions Nevertheless the product range is wide and infected with uncertainties due to lack of knowledge of the details of the process and of the kinetics of the reac tion Since the different products have quite different characteristics such as boiling point physical state at ambient temperature and thereby different use and ways of distribution often only a few of the carbon chains is wanted As an example the lowtemperature FischerTropsch is used when longercarbon chains are wanted because lower temperature increases the portion of longer chains But too low temperature is not wanted because of reduced activity When the wanted products are shorter carbon chains eg petroleum the longer ones might be cracked into shorter chains The yield of kerosene diesel is therefore highly dependent on the chain growth probability which again is dependent on i pressure and temperature ii the composition of the feedstock gas iii the catalyst type iv the catalyst composition and v the reactor design The desire to increase the selectivity of some favorable products leads to a need of understanding the relation between reaction conditions and chain growth probability which in turn request a mathematical expression for the growth probability in order to make a suitable model of the process The different attempts to model the growth probability have resulted in some models that are regarded in literature as appropriate to describe the product distribution Two will be presented here to show the influence of temperature and partial pressure 106 REACTORS AND CATALYSTS Since its discovery the FischerTropsch synthesis has undergone periods of rapid development and periods of inaction Within 10 years of the discovery German companies were building commercial plants The construction of these plants stopped about in 1940 but existing plants continued to oper ate during World War II The synthesis of hydrocarbon derivatives from carbon monoxide hydrogenation was discov ered in 1902 by Sabatier and Sanderens who produced methane by passing carbon monoxide and hydrogen over nickel iron and cobalt catalysts At about the same time the first commercial hydro gen from synthesis gas produced from steam methane reforming was commercialized Haber and Bosch discovered the synthesis of ammonia from hydrogen and N2 in 1910 and the first industrial ammonia synthesis plant was commissioned in 1913 The production of liquid hydrocarbon deriva tives and oxygenated derivatives from synthesis gas conversion over iron catalysts was discovered in 1923 by Fischer and Tropsch Variations on this synthesis pathway were soon to follow for the selective production of methanol mixed alcohols and isosynthesis products Another outgrowth of FischerTropsch synthesis was the hydroformylation of olefin derivatives discovered in 1938 and is based on the reaction of synthesis gas with olefin derivatives for the production of Oxo aldehyde derivatives and alcohol derivatives Chapters 5 7 and 8 1061 reactors Currently two reactor types are used commercially in the FischerTropsch process a fixed bed reactor a fluid bed reactor and a slurry bed reaction The fixed bed reactors usually run at lower temperatures to avoid carbon deposition on the reactor tubes Products from fixed bed reactors are characterized by low olefin content and they are generally heavier than products from fluid beds Heat distribution in fluid beds however is better than fixed bed reactors and fluid beds are gener ally operated at higher temperatures Products are characterized by i having more olefin deriva tives ii a high proportion of lowboiling hydrocarbon derivatives gases and iii lower molecular weight product slate than from fixed bed types 404 Handbook of Petrochemical Processes Originally the FischerTropsch synthesis was carried out in packed bed reactors Gasagitated multiphase reactors sometimes called slurry reactors or slurry bubble columns gained favor however because the circulation of the slurry makes it much easier to control the reaction tempera ture in a slurry bed reactor than in a fixed bed reactor Gasagitated multiphase reactors operate by suspending catalytic particles in liquid and feeding gas reactants into the bottom of the reactor through a gas distributor which produces small gas bubbles As the gas bubbles rise through the reactor the reactants are absorbed into the liquid and diffuse to the catalyst particles where depend ing on the catalyst system they are typically converted to gaseous and liquid products A slurry bed reactor is characterized by having the catalyst in the form of a slurry The feed gas mixture is bubbled through the catalyst suspension Temperature control is easier than the other two reactor types An added advantage to slurry bed reactor is that it can accept a synthesis gas with a lower hydrogencarbon monoxide ratio than either the fixed bed or the fluid bed reactors In the Sasol slurry phase reactor preheated synthesis gas is fed into the bottom of the reactor where it is distributed into slurry consisting of liquid hydrocarbon and catalyst particles As the gas bubbles rise upward through the slurry it diffuses into the slurry and is converted into a range of hydrocarbon derivatives by FischerTropsch reaction The heat generated from this reaction is removed through the reactors cooling coils which generate steam The heavier wax fraction is separated from the slurry containing the catalyst particles in a proprietary process developed by Sasol The lighter more volatile fraction is extracted in a gas stream from the top of the reactor The gas stream is cooled to recover the lighter hydrocarbon derivatives and water The intermediate hydrocarbon streams are sent to the product upgrading unit while the water stream is treated in a water recovery unit The third step upgrades reactor products to diesel and naphtha The reactor products are mainly paraffin derivatives but the lighter products contain some olefin derivatives and oxygenated derivatives that need to be removed for product stabilization Hydrogen is added to hydrotreat the olefin derivatives and oxygenated derivatives converting them to paraffin deriva tives Hydrogen is also added to the mild hydrocracker which breaks the longchain hydrocarbon derivatives into naphtha and diesel The products are separated out in a fractionation section which involves hydrocracking and hydroisomerization As the process evolved other types of reactors have been used and include i the parallel plate reactors ii a variety of fixed bed tubular reactors and iii gasagitated multiphase reactors For the parallel plate type of reactor the catalyst bed is located in tubes fixed between the plates which were cooled by steamwater that passed around the tubes within the catalyst bed In another version the reactor may be regarded as finnedtube in which large fins are penetrated by a large number of parallel or connected catalystfilled tubes Various designs were utilized for the tubular fixed bed reactor with the concentrically paced tubes being the preferred one This type of reactor contained catalyst in the area between the two tubes with cooling watersteam flowing through the inner tube and on the exterior of the outer tube The gaseous products formed enter the gas bubbles and are collected at the top of the reactor Liquid products are recovered from the suspending liquid using different techniques including filtration settling and hydrocyclones Because the FischerTropsch reaction is exothermic temperature control is an important aspect of FischerTropsch reactor operation Gasagitated multiphase reactors or slurry bubblecolumn reactors have very high heat transfer rates and therefore allow good thermal control of the reaction On the other hand because the desired liquid products are mixed with the suspending liquid recov ery of the liquid products can be relatively difficult This difficulty is compounded by the tendency of the catalyst particles to erode in the slurry forming fine catalyst particles that are also relatively difficult to separate from the liquid products Fixed bed reactors generally avoid the issues that arise from liquid separation and catalyst separation but they the fixed bed reactors do not provide the mixing of phases that allows good thermal control in slurry bubblecolumn reactors Furthermore FischerTropsch reactors are typically sized to achieve a desired volume of pro duction When a fixed bed reactor is planned economies of scale tend to result in the use of long tall reactors Because the FischerTropsch reaction is exothermic however a thermal gradient 405 Chemicals from the FischerTropsch Process tends to form along the length of the reactor with the temperature increasing with distance from the reactor inlet In addition for most FischerTropsch catalyst systems each 10 rise in temperature increases the reaction rate approximately 60 which in turn results in the generation of still more heat To absorb the heat generated by the reaction and offset the rise in temperature a cooling liquid is typically circulated through the reactor Thus for a given reactor system having a known amount of catalyst with a certain specific activity and known coolant temperature the maximum flow rate of reactants through the reactor is limited by the need to maintain the catalyst below a predetermined maximum catalyst temperature at all points along the length of the catalyst bed and the need to avoid thermal runaway which can result in catalyst deactivation and possible damage to the physical integrity of the reactor system The net result is that it is unavoidable to operate most of the reactor at temperatures below the maxi mum temperature with the corresponding low volumetric productivities over most of the reactor volume An innovative technology for combining air separation and natural gas reforming processes is being pursued by Sasol BP Praxair and Statoil Dyer and Chen 1999 If successful commer cialized this innovation can reduce the cost of synthesis gas generation by as much as 30 The technology is referred to as oxygen transport membranes OTM and should combine five unit operations currently in use viz oxygen separation oxygen compression partial oxidation steam methane reforming and heat exchange This technology incorporates the use of catalytic compo nents with the membrane to accelerate the reforming reactions Air products have also developed and patented a twostep process for synthesis gas genera tion Nataraj et al 2000 This technology can be utilized to generate synthesis gas from several feedstocks including natural gas associated gas from crude oil production light hydrocarbon gases from refineries and medium molecular weight medium boiling hydrocarbon fractions like naphtha Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 The first stage comprises conventional steam reforming with partial conversion to synthesis gas This is followed by complete conversion in an ion transport ceramic membrane ITM reactor This combination solves the problem associated with steam reforming for feedstocks with hydrocarbon derivatives higherboiling than methane since higher molecular weight C2 hydrocarbon derivatives tend to crack and degrade both the catalyst and membrane By shifting the equilibrium in the steam reforming process through removal of hydrogen from the reaction zone membrane reactors can also be used to increase the equilibriumlimited methane conversion Using palladiumsilver PdAg alloy membrane reactors methane conversion can reach as close to 100 Shu et al 1995 1062 catalysts Of great importance to the FischerTropsch process is the catalyst The catalysts used in the latest generation of FischerTropsch technologies are cobalt based usually carried on alumina supports sometimes with precious metal promoters Coalbased processes including a gasification step use iron catalysts which are better suited to hightemperature processes based on feedstocks containing impurities But iron produces significant quantities of nonparaffin derivatives as byproducts while cobalt catalysts feature high selectivity and are more efficient for making paraffin derivatives from cleaner feedstocks Catalysts play a pivotal role in synthesis gas conversion reactions In fact fuels and chemi cals synthesis from synthesis gas does not occur in the absence of appropriate catalysts The basic concept of a catalytic reaction is that reactants adsorb onto the catalyst surface and rearrange and combine into products that desorb from the surface One of the fundamental functional differences between synthesis catalysts is whether or not the adsorbed carbon monoxide molecule dissociates on the catalyst surface For the FischerTropsch process and higher alcohol synthesis carbon mon oxide dissociation is a necessary reaction condition For methanol synthesis the carbonoxygen 406 Handbook of Petrochemical Processes bond remains intact Hydrogen has two roles in catalytic synthesis gas reactions In addition to serving as a reactant needed for carbon monoxide hydrogenation it is commonly used to reduce the metalized synthesis catalysts and activate the metal surface Generally the FischerTropsch synthesis is catalyzed by a variety of transition metals such as iron nickel and cobalt Ironbased catalysts are relatively low cost and have a higher watergas shift activity and are therefore more suitable for a lower hydrogencarbon monoxide ratio H2CO synthesis gas such as those derived from coal gasification On the other hand nickelbased catalysts tend to promote methane formation as in a methanation process Cobaltbased catalysts are more active and are generally preferred over ruthenium Ru and in comparison to iron Co has much less watergas shift activity Thus in many cases an ironcontaining catalyst is the preferred catalyst due to the higher activ ity but a nickelcontaining catalyst produces large amounts of methane while a cobaltcontaining catalyst has a lower reaction rate and a lower selectivity than the ironcontaining catalyst By com paring cobalt and iron catalysts it was found that cobalt promotes more middledistillate products In the FischerTropsch process a cobaltcontaining catalyst produces hydrocarbon derivatives plus water while iron catalyst produces hydrocarbon derivatives and carbon dioxide It appears that the iron catalyst promotes the shift reaction more than the cobalt catalyst Various metals including but not limited to iron cobalt nickel and ruthenium alone and in conjunction with other metals can serve as FischerTropsch catalysts Cobalt is particularly useful as a catalyst for converting natural gas to heavy hydrocarbon derivatives suitable for the production of diesel fuel Iron has the advantage of being readily available and relatively inexpensive but also has the disadvantage of greater watergas shift activity Ruthenium is highly active but quite expen sive Consequently although ruthenium is not the economically preferred catalyst for commercial FischerTropsch production it is often used in low concentrations as a promoter with one of the other catalytic metals A variety of catalysts can be used for the FischerTropsch process but the most common are the transition metals cobalt iron and ruthenium Nickel can also be used but tends to favor methane formation methanation Cobalt seems to be the most active catalyst although iron may be more suitable for low hydrogen content synthesis gases such as those derived from coal due to its promo tion of the watergas shift reaction In addition to the active metal the catalysts typically contain a number of promoters including potassium and copper Catalysts are supported on high surface area binderssupports such as silica SiO2 alumina Al2O3 or the more complex zeolites Cobalt catalysts are more active for FischerTropsch synthesis when the feedstock is natural gas Natural gas has a high hydrogen to carbon ratio so the watergas shift is not needed for cobalt catalysts Iron catalysts are preferred for lowerquality feedstocks such as petroleum residua coal or biomass Unlike the other metals used for this process Co Ni Ru which remain in the metallic state during synthesis iron catalysts tend to form a number of chemical phases including various oxides and carbides during the reaction Control of these phase transformations can be important in main taining catalytic activity and preventing breakdown of the catalyst particles For synthesis of higher molecular weight alcohols dissociation of carbon monoxide is a necessary reaction condition For methanol synthesis the carbon monoxide molecule remains intact Hydrogen has two roles in cata lytic synthesis gas synthesis reactions In addition to serving as a reactant needed for hydrogenation of carbon monoxide it is commonly used to reduce the metalized synthesis catalysts and activate the metal surface Group 1 alkali metals including potassium are poisons for cobalt catalysts but are promoters for iron catalysts Catalysts are supported on high surface area binderssupports such as silica alumina and zeolites Cobalt catalysts are more active for FischerTropsch synthesis when the feedstock is natural gas Natural gas has a high hydrogen to carbon ratio so the watergas shift is not needed for cobalt catalysts Iron catalysts are preferred for lowerquality feedstocks such as coal or biomass Unlike the other metals used for this process Co Ni Ru which remain in the metallic state dur ing synthesis iron catalysts tend to form a number of phases including various oxides and carbides 407 Chemicals from the FischerTropsch Process during the reaction Control of these phase transformations can be important in maintaining cata lytic activity and preventing breakdown of the catalyst particles FischerTropsch catalysts are sensitive to poisoning by sulfurcontaining compounds The sen sitivity of the catalyst to sulfur is greater for cobaltbased catalysts than for their iron counterparts Promoters also have an important influence on activity Alkali metal oxides and copper are com mon promoters but the formulation depends on the primary metal iron or cobalt Alkali oxides on cobalt catalysts generally cause activity to drop severely even with very low alkali loadings C5 and carbon dioxide selectivity increase while methane and C2 to C4 selectivity decrease In addition the olefin to paraffin ratio increases FischerTropsch catalysts can lose activity as a result of i conversion of the active metal site to an inactive oxide site ii sintering iii loss of active area by carbon deposition and iv chemical poisoning For example FischerTropsch catalysts are notoriously sensitive to poisoning by sulfur containing compounds The sensitivity of the catalyst to sulfur is greater for cobaltbased catalysts than for their iron counterparts Some of these mechanisms are unavoidable and others can be prevented or minimized by controlling the impurity levels in the synthesis gas By far the most abundant important and most studied the FischerTropsch process catalyst poison is sulfur Other catalyst poisons include halides and nitrogen compounds eg NH3 NOx and HCN The hydrocarbon derivatives formed are mainly aliphatic and on a molar basis methane is the most abundant the amount of higher hydrocarbon derivatives usually decreases gradually with increase in molecular weight Isoparaffin formation is more extensive over zinc oxide ZnO or thoria ThO2 at 400C500C 750F930F and at higher pressure Paraffin waxes are formed over ruthenium catalysts at relatively low temperatures 170C200C 340F390F high pressures 1500 psi and with a carbon monoxidehydrogen ratio The more highly branched product made over the iron catalyst is an important factor in a choice for the manufacture of automotive fuels On the other hand a highquality diesel fuel paraffin character can be pre pared over cobalt Secondary reactions play an important part in determining the final structure of the product The olefin derivatives produced are subjected to both hydrogenation and doublebond shifting toward the center of the molecule cis and trans isomers are formed in about equal amounts The proportion of straightchain molecules decreases with rise in molecular weight but even so they are still more abundant than branchedchain compounds up to about C10 The small amount of aromatic hydrocarbon derivatives found in the product covers a wide range of isomer possibilities In the C6 to C9 range benzene toluene ethylbenzene xylene npropyl and isopropylbenzene methyl ethyl benzene derivatives and trimethylbenzene derivatives have been identified naphthalene derivatives and anthracene derivatives are also present Alternatively a methanoltoolefins MTOs option is available Tian et al 2015 The methanol toolefin derivatives reaction is one of the most important reactions in C1 chemistry which provides a viable option for producing basic petrochemicals from nonoil resources such as coal and natural gas As olefinbased petrochemicals and relevant downstream processes have been well developed for many years the methanoltoolefins provide a link between gasification chemistry and the mod ern petrochemical industry In the process olefin derivatives are produced from methanol using a zeolite catalyst The methanol feedstocks vaporized mixed with recovered methanol superheated and sent to the fluidized bed reactor In the reactor methanol is first converted to a dimethyl ether DME CH3OCH3 intermediate and then converted to olefin derivatives with a very high selectivity for ethylene and propylene DME can be produced by any one of several routes Figure 102 but the most common route is using methanol produced from synthesis gas In the process waterfree methanol is vaporized and sent to a reactor with an inlet temperature in the order of 220C250C 430F480F and an outlet temperature in the order of 300C350C 570F660F Thus 2CH OH CH OCH H O 3 3 3 2 408 Handbook of Petrochemical Processes The reactor effluents are sent to a distillation column where the DME is separated from the top and condensed after which the DME is sent to storage Water and methanol are discharged from the bottom and fed to a methanol column for methanol recovery The purified methanol from this column is recycled to the reactor after mixing with feedstock methanol Catalysts considered for FischerTropsch synthesis are based on transition metals of iron cobalt nickel and ruthenium FischerTropsch catalyst development has largely been focused on the preference for high molecular weight linear alkanes and diesel fuels production Among these catalysts it is generally known that i nickel Ni tends to promote methane formation as in a methanation process thus generally it is not desirable ii iron Fe is relatively low cost and has a higher watergas shift activity and is therefore more suitable for a lower hydrogencarbon mon oxide ratio H2CO synthesis gas such as those derived from coal gasification iii cobalt Co is more active and generally preferred over ruthenium Ru because of the prohibitively high cost of Ruthenium and iv in comparison to iron Co has much less watergas shift activity and is much more costly Thus it is not surprising that commercially available FischerTropsch catalysts are either cobalt or iron based In addition to the active metal the ironcontaining catalysts at least typi cally contain a number of promoters including potassium and copper as well as high surface area binderssupports such as silica SiO2 andor alumina Al2O3 Ironbased FischerTropsch catalysts are currently the most popular catalyst for the Fischer Tropsch process for converting synthesis gas into FischerTropsch liquids given Fe catalysts inherent water gasshift capability to increase the hydrogencarbon monoxide ratio of coalderived synthesis gas thereby improving hydrocarbon product yields in the FischerTropsch synthesis Fe catalysts may be operated in both hightemperature regime 300C350C 570F650F and low temperature regime 220C270C 430F520F whereas Co catalysts are only used in the low temperature range This is a consequence of higher temperatures causing more methane formation which is worse for Co compared to Fe Cobaltcontaining catalysts are a useful alternative to ironcontaining catalysts for Fischer Tropsch synthesis because they demonstrate activity at lower synthesis pressures so higher catalyst costs can be offset by lower operating costs Also coke deposition rate is higher for Fe catalyst than Co catalyst consequently Co catalysts have longer lifetimes Co catalysts have a long lifetime greater activity ie Co catalysts are replaced less frequently Although there are differences in the product distribution of cobaltcontaining and iron containing catalysts at similar temperatures and pressures for example 240C 465F and 450 psi a cobaltcontaining catalyst has somewhat higher selectivity for heavier hydrocarbon derivatives FIGURE 102 Routes for the production of dimethyl ether 409 Chemicals from the FischerTropsch Process than an ironcontaining catalyst the product distribution is primarily driven by the choice of oper ating temperature high temperature results in a naphthakerosene ratio of 21 low temperature results in naphthakerosene rat on the order of 12 more or less no matter if the catalyst is an iron containing catalyst or a cobaltcontaining catalyst Higher temperatures shift selectivity toward lower carbon number products and more hydrogenated products branching increases and second ary products such as ketones and aromatic derivatives also increase Thus generally a low temperature favors yielding high molecular mass linear wax derivative while a high temperature favors the production of naphtha and low molecular weight olefin deriva tives In order to maximize production of the naphtha fraction it is best to use an ironcontaining catalyst at a high temperature in a fixed fluid bed reactor On the other hand in order to maximize production of the kerosene fraction a slurry reactor with a cobaltcontaining catalyst is the more appropriate choice Both ironcontaining catalyst and cobaltcontaining are sensitive to the presence of sulfur com pounds in the synthesis gas and can be poisoned by them hence the need for rigorous feedstock prep aration Chapter 4 However the sensitivity of the catalyst to sulfur is higher for cobalt containing catalysts than for iron catalyst and is often the reason why cobaltcontaining catalysts are preferred for FischerTropsch synthesis with natural gasderived synthesis gas where the synthesis gas has a higher hydrogencarbon monoxide ratio and is relatively lower in sulfur content 107 PRODUCTS AND PRODUCT QUALITY The composition of the products from the synthesis gas production processes is varied insofar as the gas composition varies with the type of feedstock and the gasification system employed Speight 2013 ab Luque and Speight 2015 Furthermore the quality of gaseous products must be improved by removal of any pollutants such as particulate matter and sulfur compounds before further use Chapter 4 particularly when the intended use is a watergas shift or methanation reaction 1071 Products Low Btu gas low heat content gas is the product when the oxygen is not separated from the air and as a result the gas product invariably has a low heat content 150300 Btuft3 In medium Btu gas medium heatcontent gas the heating value is in the range 300550 Btuft3 and the composition is much like that of low heat content gas except that there is virtually no nitrogen and the H2CO ratio varies from 23 to approximately 31 and the increased heating value correlates with higher methane and hydrogen contents as well as with lower carbon dioxide content High Btu gas high heat content gas is essentially pure methane and often referred to as synthetic natural gas SNG or substitute natural gas However to qualify as substitute natural gas a product must contain at least 95 methane the energy content of synthetic natural gas is 9801080 Btuft3 The commonly accepted approach to the synthesis of high heat content gas is the catalytic reaction of hydrogen and carbon monoxide Hydrogen is also produced during gasification of carbonaceous feedstocks Although several gasifier types exist Chapter 2 entrained flow gasifiers are considered most appropriate for pro ducing both hydrogen and electricity from coal since they operate at temperatures high enough approximately 1500C 2730F to enable high carbon conversion and prevent downstream foul ing from tars and other residuals There is also a series of products that are called by older even archaic names that evolved from older coal gasification technologies and warrant mention i producer gas ii water gas iii town gas and iv synthetic natural gas These products are typically lowtomedium Btu gases Speight 2013a b 410 Handbook of Petrochemical Processes 1072 Product quality Gas processing although generally simple in chemical andor physical principles is often confusing because of the frequent changes in terminology and often lack of crossreferencing Mokhatab et al 2006 Speight 2007 2008 2013a 2014a Chapter 4 Although gas processing employs different process types there is always overlap between the various concepts And with the variety of possible constituents and process operating conditions a universal purification system cannot be specified for economic application in all cases The processes that have been developed for gas cleaning Mokhatab et al 2006 Speight 2007 2008 vary from a simple oncethrough wash operation to complex multistep systems with options for recycle of the gases Mokhatab et al 2006 In some cases process complexities arise because of the need for recovery of the materials used to remove the contaminants or even recovery of the contaminants in the original or altered form In more general terms gas cleaning is divided into removal of particulate impurities and removal of gaseous impurities For the purposes of this chapter the latter operation includes the removal of hydrogen sulfide carbon dioxide sulfur dioxide and products that are not related to synthesis gas and hydrogen production However there is also a need for subdivision of these two categories as dictated by needs and process capabilities i coarse cleaning whereby substantial amounts of unwanted impurities are removed in the simplest most convenient manner ii fine cleaning for the removal of residual impurities to a degree sufficient for the majority of normal chemical plant operations such as catalysis or preparation of normal commercial products or cleaning to a degree sufficient to discharge an effluent gas to atmosphere through a chimney iii ultrafine cleaning where the extra step as well as the extra expense is justified by the nature of the subsequent opera tions or the need to produce a particularly pure product The products can range from i highpurity hydrogen ii highpurity carbon monoxide iii highpurity carbon dioxide and iv a range of hydrogencarbon monoxide mixtures The plant is often times referred to as a HYCO if it is designed to produce both carbon monoxide and hydrogen at high purity else it is referred to as a synthesis gas or synthesis gas plant In fact the hydrogen carbon monoxide ratio can be selected at will and the plants process scheme chosen in part by the product composition required The hydrogencarbon monoxide ratio will likely vary between 1 and 3 for HYCO and synthesis gas plants However at one end of the scale ie if hydrogen is the desired product then the ratio can approach infinity by shifting all of the carbon monoxide to carbon dioxide By contrast on the other end the ratio cannot be adjusted to zero because hydrogen and water is always produced An interesting general rule of thumb exists in terms of the hydrogen carbon monoxide ratio produced by the different gasification processes It should be noted that in practice however the options are not limited to the ranges shown but rather even greater hydrogencarbon monoxide ratios if adjustments are made like the inclusion of a shift converter to effect nearequilibrium watergas shift conversion or adjusting the amount of steam Throughout the previous section there has of necessity been frequent reference to the produc tion of hydrogen as an integral part of the production of carbon monoxide since the two gases make up the mixture known as synthesis gas Hydrogen is indeed an important commodity in the refining industry because of its use in hydrotreating processes such as desulfurization and in Gasification Process H2CO ratio Steam Methane Reformer 3050 SMR Oxygen Secondary Reforming O2R 2540 Autothermal Reforming 16265 Partial Oxidation 1619 411 Chemicals from the FischerTropsch Process hydroconversion processes such as hydrocracking Part of the hydrogen is produced during reform ing processes but that source once sufficient is now insufficient for the hydrogen needs of a modern refinery Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 In addition optimum hydrogen purity at the reactor inlet extends catalyst life by maintaining desulfurization kinetics at lower operating temperatures and reducing carbon laydown Typical purity increases resulting from hydrogen purification equipment andor increased hydrogen sul fide removal as well as tuning hydrogen circulation and purge rates may extend catalyst life up to about 25 Indeed since hydrogen use has become more widespread in refineries hydrogen production has moved from the status of a hightech specialty operation to an integral feature of most refineries While the gasification of residua and coke to produce hydrogen andor power may increase in use in refineries over the next two decades Speight 2011 several other processes are available for the production of the additional hydrogen that is necessary for the various heavy feedstock hydroprocessing sequences Speight 2014a and it is the purpose of this section to present a general description of these processes Purities in excess of 995 of either the hydrogen or carbon monoxide produced from synthesis gas can be achieved if desired Four of the major process technologies available are i cryogenics plus methanation ii cryogenics plus pressure swing adsorption iii methanewash cryogenic pro cess and iv the Cosorb process Thus i Cryogenics Methanation This process utilizes a cryogenic process occurring in a cold box whereby carbon monoxide is liquefied in a number of steps until hydrogen with a purity of 98 is produced The condensed carbon monoxide product which would con tain methane is then distilled to produce essentially pure carbon monoxide and a mixture of carbon monoxidemethane The latter stream can be used as fuel The hydrogen stream from the cold box is taken to a shift converter where the remaining carbon monoxide is converted to carbon dioxide and hydrogen The carbon dioxide is then removed and any further carbon monoxide or carbon dioxide can be removed by methanation The resulting hydrogen stream can be of purities 997 ii Cryogenics plus Pressure Swing Adsorption This process utilizes the similar sequential liquefaction of carbon monoxide in a cold box until hydrogen of 98 purity is achieved Again the carbon monoxide stream can be further distilled to remove methane until it is essentially pure The hydrogen stream is then allowed to go through multiple swings of pressure swing adsorption cycles until the hydrogen purity of even as high as 99999 is produced iii Methanewash Cryogenic Process In this scheme liquid carbon monoxide is absorbed into a liquid methane stream so that the hydrogen stream produced contains only ppm levels of carbon monoxide but about 58 methane Hence a hydrogen stream purity of only about 95 is possible The liquid carbon monoxidemethane stream however can be distilled to produce an essentially pure carbon monoxide stream and a carbon monoxide methane stream which can be used as fuel iv Cosorb Process This process utilizes copper ions cuprous aluminum chloride CuAlCl4 in toluene to form a chemical complex with the carbon monoxide and in effect separating it from the hydrogen nitrogen carbon dioxide and methane This pro cess can capture about 96 of the carbon monoxide to produce a stream of greater than 99 purity The downside of this process is that water hydrogen sulfide and other trace chemicals which can poison the copper catalyst must be removed prior to the reactor Further a hydrogen stream of only up to 97 purity is obtained However while the efficiency of cryogenic separation decreases with low carbon monoxide content of the feed the Cosorb process is able to process gases with a low carbon monoxide content more efficiently 412 Handbook of Petrochemical Processes 108 FISCHERTROPSCH CHEMISTRY Synthesis gas also called syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide CO and hydrogen H2 generated by the gasification of a carbonaceous mate rial Examples include steam reforming of natural gas petroleum residua coal and biomass 1081 chemical PrinciPles Synthesis gas consists primarily of carbon monoxide carbon dioxide and hydrogen and has less than half the energy density of natural gas Synthesis gas is combustible and often used as a fuel source or as an intermediate for the production of other chemicals Synthesis gas for use as a fuel is most often produced by gasification of the carbonaceous feedstock or municipal waste mainly by the following paths C O CO CO C 2CO C H O CO H 2 2 2 2 2 When used as an intermediate in the largescale industrial synthesis of hydrogen and ammonia it is also produced from natural gas via the steam reforming reaction as follows CH H O CO 3H 4 2 2 The synthesis gas produced in large wastetoenergy gasification facilities is used as fuel to generate electricity Although the focus of this section is the production of hydrocarbon derivatives from synthesis gas it is worthy of note that all or part of the clean synthesis gas can also be used i as chemi cal building blocks to produce a broad range of chemicals using processes well established in the chemical and petrochemical industry ii as a fuel producer for highly efficient fuel cells which run off the hydrogen made in a gasifier or perhaps in the future hydrogen turbines and fuel cellturbine hybrid systems and iii as a source of hydrogen that can be separated from the gas stream and used as a fuel or as a feedstock for refineries which use the hydrogen to upgrade petroleum products Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 However the decreasing availability and increased price of petroleum has renewed the worldwide interest in the production of liquid hydrocarbon derivatives from carbon monoxide and hydrogen using metal catalysts also known as FischerTropsch synthesis or FischerTropsch process Gasification to produce synthesis gas can proceed from just about any organic material includ ing biomass and plastic waste The resulting synthesis gas burns cleanly into water vapor and carbon dioxide Alternatively synthesis gas may be converted efficiently to methane via the Sabatier reac tion or to a diesellike synthetic fuel via the FischerTropsch process Inorganic components of the feedstock such as metals and minerals are trapped in an inert and environmentally safe form as char which may have use as a fertilizer Regardless of the final fuel form gasification itself and subsequent processing neither emits nor traps greenhouse gasses such as carbon dioxide Combustion of synthesis gas or derived fuels does of course emit carbon dioxide However biomass gasification could play a significant role in a renewable energy economy because biomass production removes carbon dioxide from the atmosphere While other biofuel technologies such as biogas and biodiesel are also carbon neutral gasification runs on a wider variety of input materials can be used to produce a wider variety of output fuels and is an extremely efficient method of extracting energy from biomass Biomass gas ification is therefore one of the most technically and economically convincing energy possibilities for a carbon neutral economy 413 Chemicals from the FischerTropsch Process The manufacture of gas mixtures of carbon monoxide and hydrogen has been an important part of chemical technology for about a century Originally such mixtures were obtained by the reaction of steam with incandescent coke and were known as water gas Used first as a fuel water gas soon attracted attention as a source of hydrogen and carbon monoxide for the production of chemicals at which time it gradually became known as synthesis gas Eventually steam reforming processes in which steam is reacted with natural gas methane or petroleum naphtha over a nickel catalyst found wide application for the production of synthesis gas A modified version of steam reforming known as autothermal reforming which is a combina tion of partial oxidation near the reactor inlet with conventional steam reforming further along the reactor improves the overall reactor efficiency and increases the flexibility of the process Partial oxidation processes using oxygen instead of steam also found wide application for synthesis gas manufacture with the special feature that they could utilize lowvalue feedstocks such as heavy petroleum residua In recent years catalytic partial oxidation employing very short reaction times milliseconds at high temperatures 850C1000C 1560F1830F is providing still another approach to synthesis gas manufacture Nearly complete conversion of methane with close to 100 selectivity to hydrogen and carbon monoxide can be obtained with a rhenium monolith under well controlled conditions Experiments on the catalytic partial oxidation of nhexane conducted with added steam give much higher yields of hydrogen than can be obtained in experiments without steam a result of much interest in obtaining hydrogenrich streams for fuel cell applications The route of coal to synthetic automotive fuels as practiced by SASOL is technically proven and products with favorable environmental characteristics are produced As is the case in essentially all the carbonaceous feedstock conversion processes where air or oxygen is used for the utilization or partial conversion of the energy in the carbonaceous feedstock the carbon dioxide burden is a drawback as compared to crude oil The uses of synthesis gas include use as a chemical feedstock and in gastoliquid processes which use FisherTropsch chemistry to make liquid fuels as feedstock for chemical synthesis as well as being used in the production of fuel additives including diethyl ether and methyl tbutyl ether acetic acid and its anhydride synthesis gas could also make an important contribution to chemical synthesis through conversion to methanol There is also the option in which stranded natural gas is converted to synthesis gas production followed by conversion to liquid fuels The hydroformylation synthesis also known as the oxo synthesis or the oxo process is an indus trial process for the production of aldehyde derivatives from alkene derivatives This chemical reac tion entails the addition of a formyl group CHO and a hydrogen atom to a carboncarbon double bond A key consideration of hydroformylation is the production of normal isomers or the produc tion of isoisomers in the products For example the hydroformylation of propylene can yield two isomeric products butyraldehyde and isobutyraldehyde H CO CH CH CH CH CH CH CHO butyraldehyde H CO CH CH CH CH CHCHO butyraldehyde 2 3 2 3 2 2 2 3 2 3 2 n iso These isomers reflect the regiochemistry the preference of one direction of chemical bond forma tion or chemical bond scission over all other possible directions of the insertion of the alkene into the MH bond Generally both products are not equally desirable As an example of the hydroformylation process the Exxon process also Kuhlmannoxo process or the PCUKoxo process is used for the hydroformylation of C6 to C12 olefin derivatives using cobaltbased catalysts In order to recover the catalyst an aqueous sodium hydroxide solution or sodium carbonate is added to the organic phase By extraction with olefin and neutralization by addition of sulfuric acid solution under carbon monoxide pressure the metalcarbonyl hydride can be recovered The recovered hydride is stripped out with synthesis gas absorbed by the olefin and returned to the reactor The Exxon process similar to the BASF process is carried out at a 414 Handbook of Petrochemical Processes temperature in the order of 160C180C 320F355F and a pressure suitable to the reactants and products The FischerTropsch reaction can be described as the synthesis of hydrocarbon derivatives via the hydrogenation of carbon monoxide using transition metal catalysts The major catalysts used industrially are Fe and Co but can also be Ru and Ni From a mechanism perspective the reactions can be regarded as a carbon chain building process where methylene CH2 groups are attached sequentially in a carbon chain Table 103 Thus CO 2 H C H H O 2 2 n n m n n m For example CO 2H CH H O 2 2 2 A common and salient feature of the reactions is the exothermicity of the reactions As a general rule of thumb the reactions which produce water and carbon dioxide as a product tend to be more exothermic on account of the very high heat of formation of these species Some of the reactions proposed are as follows Rauch 2001 CO 3H CH 2H O H 125 kJmol CO 2H CH H O H 165 kJmol 2CO H CH CO H 204 kJmol 3CO H CH 2CO H 244 kJmol 2 2 2 2 2 2 2 2 2 2 2 2 2 There is also the watergas shift reaction CO H O H CO H 39 kJmol 2 2 2 Due to the very high exothermic nature of the FischerTropsch reactions as illustrated in the reactions above an important issue is not surprisingly the need to avoid an increase in temperature TABLE 103 Carbon Chain Groups of the Range of Fischer Tropsch Products Which Can Be Produced Carbon Number Group Name C1C2 Synthetic natural gas C3C4 Liquefied petroleum gas C5C7 Lowboiling naphtha C8C10 Highboiling naphtha C11C16 Middle distillate C17C30 a Lowmelting wax C31C60 Highmelting wax a The C17 nalkane nheptadecane is the first member of the series that is not fully liquid under ambient conditions melting point 21C 70F 415 Chemicals from the FischerTropsch Process The need for cooling is thus of critical importance in order to i maintain stable reaction condi tions ii avoid the tendency to produce lighter hydrocarbon derivatives and iii prevent catalyst sintering and hence reduction in activity Since the total heat of reaction is in the order of approxi mately 25 of the heat of combustion of the synthesis gas ie reactants if the FischerTropsch process a theoretical limit on the maximum efficiency of the FischerTropsch process is imposed Rauch 2001 Two main chemical characteristics of FischerTropsch synthesis are the unavoidable production of a wide range of hydrocarbon products olefin derivatives paraffin derivatives and oxygenated products and the liberation of a large amount of heat from the highly exothermic synthesis reactions Product distributions are influenced by temperature feed gas composition hydrogencarbon monoxide pressure catalyst type and catalyst composition FischerTropsch products are produced in four main steps synthesis gas generation gas purification Fischer Tropsch synthesis and product upgrading Depending on the types and quantities of Fischer Tropsch products desired either low 200C240C 390F465F or hightemperature 300C350C 570F660F synthesis is used with either an iron Fe or cobalt catalyst Co Van Berge 1997 The required gas mixture of carbon monoxide and hydrogen synthesis gas is created through a reaction of coke or the carbonaceous feedstock with water steam and oxygen at temperatures over 900C In the past town gas and gas for lamps were a carbon monoxidehydrogen mixture made by gasifying coke in gas works In the 1970s it was replaced with imported natural gas methane Gasification of carbonaceous feedstocks and FischerTropsch hydrocarbon synthesis together bring about a twostage sequence of reactions which allows the production of liquid fuels like gasoline and diesel out of the solid combustible and the carbonaceous feedstock The FischerTropsch synthesis is in principle a carbon chain building process where methylene groups are attached to the carbon chain The actual reactions that occur have been and remain a matter of controversy as it has been the last century since 1930s 2 1 H CO C H H O 2 2 2 2 n n n n n Even though the overall FischerTropsch process is described by the following chemical equation 2 1 H CO C H H O 2 2 2 2 n n n n n The initial reactants in the above reaction ie carbon monoxide and H2 can be produced by other reactions such as the partial combustion of a hydrocarbon C H O 1 H CO 2 2 12 2 2 n n n n n For example when n 1 methane in the case of gastoliquids applications 2CH O 4H 2CO 4 2 2 Or by the gasification of any carbonaceous source such as biomass C H O H CO 2 2 The energy needed for this endothermic reaction is usually provided by exothermic combustion with air or oxygen 2C O 2CO 2 416 Handbook of Petrochemical Processes These reactions are highly exothermic and to avoid an increase in temperature which results in lighter hydrocarbon derivatives it is important to have sufficient cooling to secure stable reaction conditions The total heat of reaction amounts to approximately 25 of the heat of combustion of the synthesis gas and lays thereby a theoretical limit on the maximal efficiency of the Fischer Tropsch process The reaction is dependent on a catalyst mostly an iron or cobalt catalyst where the reaction takes place There is either a low or hightemperature process lowtemperature FischerTropsch or high temperature FischerTropsch with temperatures ranging between 200C240C 390F465F for lowtemperature FischerTropsch and 300C350C 570F660F for the hightemperature FischerTropsch process The hightemperature FischerTropsch process uses an iron catalyst and the lowtemperature FischerTropsch either an iron or a cobalt catalyst The different catalysts include also nickelbased and rutheniumbased catalysts which also have enough activity for com mercial use in the process But the availability of ruthenium is limited and the nickelbased catalyst has high activity but produces too much methane and additionally the performance at high pres sure is poor due to production of volatile carbonyls This leaves only cobalt and iron as practical catalysts and this study will only consider these two Iron is cheap but cobalt has the advantage of higher activity and longer life though it is on a metal basis 1000 times more expensive than iron catalyst 1082 refininG fischertroPsch Products The FischerTropsch product stream typically contains hydrocarbon derivatives having a range of numbers of carbon atoms including gases liquids and waxes Depending on the molecular weight product distribution different FischerTropsch product mixtures are ideally suited to differ ent uses For example FischerTropsch product mixtures containing liquids may be processed to yield gasoline as well as heavier middle distillates Hydrocarbon waxes may be subjected to addi tional processing steps for conversion to liquid andor gaseous hydrocarbon derivatives Thus in the production of a FischerTropsch product stream for processing to a fuel it is desirable to obtain primarily hydrocarbon derivatives that are liquids and waxes eg C5 hydrocarbon derivatives Initially the light gases in raw product are separated and sent to a gascleaning operation The higherboiling product is distilled to produce separate streams of naphtha distillate and wax The naphtha stream is first hydrotreated which produces a hydrogensaturated liquid product primarily paraffin derivatives a portion of which are converted by isomerization from normal paraffin derivatives to isoparaffin derivatives to boost their octane value Another fraction of the hydrotreated naphtha is catalytically reformed to provide some aromatic content to and further boost the octane value of the final gasoline blend stock The distillate stream is also hydrotreated resulting directly in a finished diesel blend stock The wax fraction is hydrocracked into a finished distillate stream and naphtha streams that augment the hydrotreated naphtha streams sent for isom erization and for catalytic cracking Thus conventional refinery processes Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 can be used for upgrading of FischerTropsch liquid and wax products A number of possible processes for FischerTropsch products are wax hydrocracking distillate hydrotreat ing catalytic reforming naphtha hydrotreating alkylation and isomerization Fuels produced with the FischerTropsch synthesis are of a high quality due to a very low aromaticity and zero sulfur content The diesel fraction has a high cetane number resulting in superior combustion properties and reduced emissions New and stringent regulations may promote replacement or blending of conven tional fuels by sulfur and aromaticfree products Also other products besides fuels can be manu factured with FischerTropsch in combination with upgrading processes for example ethylene 417 Chemicals from the FischerTropsch Process propylene αolefin derivatives alcohols ketones solvents and waxes These valuable byproducts of the process have higher added values resulting in an economically more attractive process econ omy Gary et al 2007 Speight 2011 2014a 2017 Hsu and Robinson 2017 At this point it is necessary to deal once again with the production of chemicals from the carbonaceous feedstock by gasification followed by conversion of the synthesis gas mixture carbon monoxide carbon monoxide and hydrogen H2 to higher molecular weight liquid fuels and other chemicals Chapters 20 and 21 Penner 1987 The production of synthesis gas involves reaction of the carbonaceous feedstock with steam and oxygen The gas stream is subsequently purified to remove sulfur nitrogen and any particulate matter after which it is catalytically converted to a mixture of liquid hydrocarbon products In addition synthesis gas may also be used to produce a variety of products including ammonia and methanol The synthesis of hydrocarbon derivatives from carbon monoxide and hydrogen synthesis gas the FischerTropsch synthesis is a procedure for the indirect liquefaction of coal Storch et al 1951 Batchelder 1962 Jones et al 1992 This process is the only coal liquefaction scheme cur rently in use on a relatively large commercial scale South Africa is currently using the Fischer Tropsch process on a commercial scale in their SASOL complex although Germany produced roughly 156 million barrels of synthetic petroleum annually using the FischerTropsch process during the World War II Briefly in the gasification process the carbonaceous feedstock is converted to gaseous prod ucts at temperatures in excess of 800C 1470F and at moderate pressures to produce synthesis gas C H O CO H 2 2 The gasification may be attained by means of any one of several processes Speight 2013ab 2014ab Luque and Speight 2015 The exothermic nature of the process and the decrease in the total gas volume in going from reactants to products suggest the most suitable experimental condi tions to use in order to maximize product yields The process should be favored by high pressure and relatively low reaction temperature In practice the FischerTropsch reaction is generally carried out at temperatures in the range 200C350C 390F660F and at pressures of 754000 psi the hydrogencarbon monoxide ratio is usually at ca 221 or 251 Since up to three volumes of hydrogen may be required to achieve the next stage of the liquids production the synthesis gas must then be converted by means of the watergas shift reaction to the desired level of hydrogen after which the gas eous mix is purified acid gas removal etc and converted to a wide variety of hydrocarbon derivatives CO H O CO H CO 2 1 H C H H O 2 2 2 2 2 2 2 n n n These reactions result primarily in low and mediumboiling aliphatic compounds present com mercial objectives are focused on the conditions that result in the production of nhydrocarbon derivatives as well as olefin derivatives and oxygenated materials REFERENCES AasbergPetersen K Bak Hansen JH Christiansen TS Dybkjær I Seier Christensen P Stub Nielsen C Winter Madsen SEL and RostrupNielsen JR 2001 Technologies for largescale gas conversion Applied Catalysis A General 221 379387 418 Handbook of Petrochemical Processes AasbergPetersen K Christensen TS Stub Nielsen C and Dybkjaer I 2002 Recent developments in autothermal reforming and prereforming for synthesis gas production in GTL applications Preprints Division of Fuel Chemistry American Chemical Society 471 9697 Alstrup I 1988 A new model explaining carbon filament growth on nickel iron and NiCu alloy catalysts Journal of Catalysis 109 241251 Balasubramanian B Ortiz AL Kaytakoglu S and Harrison DP 1999 Hydrogen from methane in a singlestep process Chemical Engineering Science 54 35433552 Batchelder HR 1962 Chapter 1 Vol V In Advances in Petroleum Chemistry and Refining JJ McKetta Jr Editor Interscience Publishers Inc New York Chadeesingh R 2011 Chapter 5 The FischerTropsch process Part 3 In The Biofuels Handbook JG Speight Editor The Royal Society of Chemistry London pp 476517 Choudhary VR Rajput AM and Prabhakar B 1993 Journal of Catalysis 139 326 Dyer PN and Chen CM 1999 Engineering development of ceramic membrane reactor systems for con verting natural gas to hydrogen and synthesis gas for transportation fuels Proceedings of the Energy Products for the 21st Century Conference September 22 Gary JG Handwerk GE and Kaiser MJ 2007 Petroleum Refining Technology and Economics 5th Edition CRC Press Taylor Francis Group Boca Raton FL Gunardson HH and Abrardo JM April 1999 Hydrocarbon Processing pp 8793 Hagh BF 2004 Comparison of autothermal reforming for hydrocarbon fuels Preprints Division of Fuel Chemistry American Chemical Society 491 144147 Hsu CS and Robinson PR Editors 2017 Handbook of Petroleum Technology Springer International Publishing AG Cham Hufton JR Mayorga S and Sircar S 1999 Sorptionenhanced reaction process for hydrogen production AIChE Journal 45 248256 Jones CJ Jager B and Dry MD 1992 Oil and Gas Journal 903 53 Lapszewicz JA and Jiang X 1992 Preprints ACS Division of Petroleum Chemistry 37 252 Luque R and Speight JG Editors 2015 Gasification for Synthetic Fuel Production Fundamentals Processes and Applications Woodhead Publishing Elsevier Cambridge United Kingdom Mokhatab S Poe WA and Speight JG 2006 Handbook of Natural Gas Transmission and Processing Elsevier Amsterdam Nataraj S Moore RB Russek SL US 6048472 2000 assigned to Air Products and Chemicals Inc Penner SS 1987 Proceedings Fourth Annual Pittsburgh Coal Conference University of Pittsburgh Pittsburgh PA p 493 Rauch R 2001 Biomass gasification to produce synthesis gas for fuel cells liquid fuels and chemicals IEA bioenergy agreement Task 33 Thermal gasification of biomass RostrupNielsen JR 1984 Sulfurpassivated nickel catalysts for carbonfree steam reforming of methane Journal of Catalysis 85 3143 RostrupNielsen JR 1993 Production of synthesis gas Catalysis Today 19 305324 Schulz H 1999 Short history and present trends of FischerTropsch synthesis Applied Catalysis A General 8612 312 Shu J Grandjean BPA and Kaliaguine S 1995 Catalysis Today 25 327332 Speight JG 2007 Natural Gas A Basic Handbook GPC Books Gulf Publishing Company Houston TX Speight JG 2008 Synthetic Fuels Handbook Properties Processes and Performance McGrawHill New York Speight JG 2011 The Refinery of the Future Gulf Professional Publishing Elsevier Oxford United Kingdom Speight JG 2013a The Chemistry and Technology of Coal 3rd Edition CRC Press Taylor Francis Group Boca Raton FL Speight JG 2013b CoalFired Power Generation Handbook Scrivener Publishing Beverly MA Speight JG 2014a The Chemistry and Technology of Petroleum 5th Edition CRC Press Taylor Francis Group Boca Raton FL Speight JG 2014b Gasification of Unconventional Feedstocks Gulf Professional Publishing Elsevier Oxford United Kingdom Speight JG 2017 Handbook of Petroleum Refining Processes CRC Press Taylor Francis Group Boca Raton FL 419 Chemicals from the FischerTropsch Process Storch HH Golumbic N and Anderson RB 1951 The Fischer Tropsch and Related Syntheses John Wiley Sons Inc New York Tian P Wei Y Ye M and Liu Z 2015 Methanol to olefins MTO From fundamentals to commercializa tion ACS Catalysis 53 19221938 Udengaard NR Hansen JHB Hanson DC and Stal JA 1992 Sulfur passivated reforming process lowers syngas H2CO ratio Oil Gas Journal 90 6267 Van Berge PJ 1997 Natural Gas Conversion IV Vol 107 Studies in Surface Science and Catalysis p 207 Watson GH 1980 Methanation Catalysts Report ICTISTR09 International Energy Agency London Taylor Francis 421 11 Monomers Polymers and Plastics 111 INTRODUCTION The list of chemicals produced by the petrochemical industry includes but is not limited to i synthesis gasbased products including ammonia methanol and their derivatives ii ethylene and derivatives iii propylene including onpurpose and methanolbased routes and derivatives iv C4 monomers aromatics oxides glycols and polyols and derivatives v chloralkali ethylene dichloride vinyl chloride monomer and polyvinyl chloride PVC vi polyolefinssolution slurry and gas phase alpha olefins and poly alpha olefins polyethylene terephthalate PETbottles and fiber polystyrene PSgeneral purpose high impact and expandable vii styrene derivatives such as acrylonitrile butadiene styrene acrylonitrilestyrene and acrylonitrile styrene acrylate and viii specialty polymers including polyoxymethylene superabsorbent polymers and poly methylmetacrylate and nylon 6 66 and intermediates Thus the ascent of polymer technology during the 20th century is due in no small part to the availability of starting materials that became available through the evolving and expanding petrochemical industry In fact a high proportion of all petrochemicals are used for the produc tion of polymers the most important building blocks being ethylene propylene and butadiene Table 111 Matar and Hatch 2001 These three petrochemicals can be polymerized directly but an important part of their production is used to create more complex monomers through different ways of information into a polymer Tables 112 and 113 Figure 111 Ethylene is the progenitor of most vinyl monomers and hence the need for an almost endless pressure on ethylene supply is particularly high In fact the C2 and C3 building blocks can be combined with benzene to form another set of monomers and intermediates particularly valuable for constructing the complex repeat units noted in the last section Other chemicals are also produced such as plasticizers which are then added in a subsequent stage to polymers to modify their properties But first the relevant definitions A monomer is the original molecular form from which a polymer and plastic product is pro duced A polymer which may also be referred to as a macromolecule consists of repeating molecu lar units which usually are held together by covalent bonds Ali et al 2005 Polymerization is the TABLE 111 Polymers from Petrochemicals Polyethylene Derived from ethylene CH2CH2 Ethylene is derived from natural gas from overhead gases in refinery and from crackers Polypropylene Derived from propylene CH3CHCH2 Propylene has almost same origin as ethylene Used for making clothes and various other plastics Polyesters Produced from terephthalic acid which is derived from pxylene 14HO2CC6H4CO2H pXylene H3CC6H4CH3 has its origin from various aromatic compounds found in the crude oil Refining separates benzene derivatives Rubber Various synthetic rubbers like polyacrylate rubber and ethyleneacrylate rubber Derived from various petroleumderived chemicals such as 13butadiene CH2CHCHCH2 and acrylic acid CH2CHCO2H 422 Handbook of Petrochemical Processes process of covalently bonding the low molecular weight monomers into a high molecular weight polymer Polymerization is a reaction in which chainlike macromolecules are formed by combining small molecules monomers Monomers are the building blocks of these large molecules called polymers For example in order to depict polymers cellulose and a protein can be considered Cellulose the most abundant organic compound on earth a molecule made of many simple glucose units mono mers joined together through a glycoside linkage TABLE 112 Several Ways in Which Different Monomeric Units Might Be Incorporated in a Polymer Statistical Copolymers Also called random copolymers Here the monomeric units are distributed randomly and sometimes unevenly in the polymer chain ABBAAABAABBBABAABA Alternating Copolymers The monomeric units are distributed in a regular alternating fashion with nearly equimolar amounts of each in the chain ABABABABABABABAB Block Copolymers Instead of a mixed distribution of monomeric units a long sequence or block of one monomer is joined to a block of the second monomer AAAAABBBBBBBAAAAAAABBB Graft Copolymers The side chains of a given monomer are attached to the main chain of the second monomer AAAAAAABBBBBBBAAAAAAABBBBAAA TABLE 113 Selected Hydrocarbon Addition Polymers Names Formula Monomer Properties Uses Polyethylene LDPE CH2CH2n Ethylene CH2CH2 Soft waxy solid Film wrap plastic bags Polyethylene HDPE CH2CH2n Ethylene CH2CH2 Rigid translucent solid Electrical insulation bottles toys Polypropylene CH2CHCH3n Propylene CH2CHCH3 Atactic soft elastic solid Isotactic hard strong solid Similar to LDPE carpet upholstery PS CH2CHC6H5n Styrene CH2CHC6H5 Hard rigid clear solid soluble in organic solvents Toys cabinets Packaging foamed cis Polyisoprene CH2CHCCH3 CH2n Isoprene CH2CHCCH3CH2 Soft sticky solid Requires vulcanization for practical use FIGURE 111 Variations in polymer structure 1 a regular polymer 2 an alternating copolymer 3 a random copolymer 4 a block copolymer and 5 a grafted copolymer 423 Monomers Polymers and Plastics Proteins the material of life are polypeptides made of αamino acids alphaamino acids attached by an amide Several methods exist to synthesize amino acids One of the oldest methods begins with the bromination at the αcarbon of a carboxylic acid For example the Strecker amino acid synthe sis involves the treatment of an aldehyde with potassium cyanide and ammonia this produces an αamino nitrile as an intermediate Hydrolysis of the nitrile in acid then yields an αamino acid Using ammonia or ammonium salts in this reaction gives unsubstituted amino acids whereas substituting primary and secondary amines will yield substituted amino acids Likewise using ketone derivatives instead of aldehydes gives ααdisubstituted amino acids Thus to construct a protein macromolecule the amino acids react to form a link as for example in the cojoining of two amino acids to form a dipeptide In each case the linkage in the structure of the product a dipeptide is known as a peptide link which is chemically speaking an amide link A protein chain with the Nterminal on the left will therefore be of this type Cellulose Aldehyde αamino nitrile amino acid Amino acids Dipeptide Schematic of protein structure 424 Handbook of Petrochemical Processes For a molecule to be a monomer it must be at least bifunctional insofar as it has the capacity to interlink with other monomer molecules While not truly bifunctional in the sense that they contain to functional groups olefin derivatives have the ability to act as bifunctional molecules though the extra pair of electrons in the double bond A polymer may be a natural or synthetic macromolecule comprised of repeating units of a smaller molecule monomers The terms polymer and plastic are often used interchangeably but polymers are a much larger class of molecules which includes plastics plus many other materials such as cellulose amber and natural rubber Examples of hydrocarbon polymers include polyethylene and synthetic rubber Schroeder 1983 In the current context a monomer is a low molecular weight hydrocarbon molecule that has the potential of chemically bonding to other monomers of the same species to form a polymer The lower molecular weight compounds built from monomers are also referred to as dimers two monomer units trimers three monomer units tetramers four monomer units pentamers five monomer units octamers eight monomer units continuing up to very high numbers of monomer units in the product The structure of monomer units in the polymer is retained by the chemical bonds between adja cent atoms thereby conferring upon the polymer the configuration However there can be many dif ferent configurations for a given set of atoms of a particular type Different isomers of the monomer unit which have different properties confer different properties on the polymer This structural configuration of the monomer is an important structural feature and plays a major role as the com plexity of the monomer increase and is a major determinant of the structure and properties of the polymer chains In addition to structural isomerism in the monomer which can be represented simply by the posi tion of the double bond in butylene and is shown below as butylene1 and butylene2 there is also a second type of isomerism This type of isomerism geometrical isomerism occurs with various monomers and is present in polymers such as natural rubber and butadiene rubber In these cases the single double bond in the final polymer can exist in two ways a cis form and a trans form The pendant methyl group appears on the same side as the lone hydrogen atom or on the oppo site side of the lone hydrogen atom Similarly commencing with 2butylene the final polymer may have the methyl group i on the same side of the final product or ii on alternate sides of the final product Thus because of the variations in monomer structure the chemical structure of many polymers is rather complex because the polymerization reaction does not necessarily produce iden tical molecules In fact a polymeric material typically consists of a distribution of molecular sizes and sometimes also of shapes CH3CH2CHCH2 CH3CHCHCH3 butylene1 butylene2 1butene 2butene cis14polyisoprene trans14polyisoprene 425 Monomers Polymers and Plastics The properties of polymers are strongly influenced by details of the chain structure The struc tural parameters that determine properties of a polymer include the overall chemical composition and the sequence of monomer units in the case of copolymers the stereochemistry or the relative stereochemistry of the stereocenters in the polymer chain and geometric isomerization in the case of dienetype polymers The properties of a specific polymer can often be varied by means of controlling molecular weight end groups processing crosslinking Therefore it is possible to classify a single polymer in more than one category For example some polymers nylon can be produced as fibers in the crys talline forms or as plastics in the less crystalline forms Also certain polymers can be processed to act as plastics or elastomers Synthetic fibers are longchain polymers characterized by highly crystalline regions resulting mainly from secondary forces eg hydrogen bonding They have a much lower elasticity than plastics and elastomers They also have high tensile strength a light weight and low moisture absorption 112 PROCESSES AND PROCESS CHEMISTRY Polymerization is the process by which polymers are manufactures and during the polymerization process some chemical groups may be lost from each monomer and the polymer does not always retain the chemical properties or the reactivity of the monomer unit Rudin 1999 Braun et al 2001 Carraher 2003 Odian 2004 The polymer industry dates back to the 19th century when natural polymers such as cotton were modified by chemical treatment to produce artificial silk rayon Work on synthetic polymers did not start until the beginning of the 20th century In 1909 the first synthetic polymeric mate rial was prepared by LH Baekeland who used condensation reaction between formaldehyde and phenol Currently these polymers serve as important thermosetting plastics for example phenol formaldehyde resins Since that time many different polymeric products have been synthesized to respond to the demands of the marketexamples are plastics fibers and synthetic rubber The huge polymer market directly results from extensive work in synthetic organic compounds and catalysts In addition the discovery by Ziegler of a coordination catalyst in the titanium family paved the road for synthesizing many stereoregular polymers with improved properties Polymerization reactions can occur in bulk without solvent in solution in emulsion in suspen sion or in a gasphase process Interfacial polymerization is also used with reactive monomers such as acid chlorides Polymers obtained by the bulk technique are usually pure due to the absence of a solvent The purity of the final polymer depends on the purity of the monomers Heat and viscosity are not easily controlled as in other polymerization techniques due to absence of a solvent suspen sion or emulsion medium This can be overcome by carrying the reaction to low conversion and strong agitation Outside cooling can also control the exothermic heat In solution polymerization an organic solvent dissolves the monomer Solvents should have lowchain transfer activity to minimize chain transfer reactions that produce low molecular weight polymers The presence of a solvent makes heat and viscosity control easier than in bulk polymer ization Removal of the solvent may not be necessary in certain applications such as coatings and adhesives Emulsion polymerization is widely used to produce polymers in the form of emulsions such as paints and floor polishes It is also used to polymerize many waterinsoluble vinyl monomers such as styrene and vinyl chloride In emulsion polymerization an agent emulsifies the monomers Emulsifying agents should have a finite solubility They are either ionic as in the case of alkylben zene sulfonates or nonionic like polyvinyl alcohol Water is extensively used to produce emulsion polymers with a sodium stearate emulsifier The emulsion concentration should allow micelles of large surface areas to form The micelles absorb the monomer molecules activated by an initiator such as a sulfate ion radical Xray and light scattering techniques show that the micelles start to increase in size by absorbing the macromolecules For 426 Handbook of Petrochemical Processes example in the free radical polymerization of styrene the micelles increased to 250 times their original size In suspension polymerization the monomer is first dispersed in a liquid such as water and mechanical agitation keeps the monomer dispersed Initiators should be soluble in the monomer and stabilizers such as talc or polyvinyl alcohol preventing polymer chains from adhering to each other and keep the monomer dispersed in the liquid medium As a result the final polymer appears in a granular form Suspension polymerization produces polymers more pure than those from solution polymerization due to the absence of chain transfer reactions As in a solution polymerization the dispersing liquid helps control the heat of the reaction Interfacial polymerization is mainly used in polycondensation reactions with very reactive mono mers One of the reactants usually an acid chloride dissolves in an organic solvent such as benzene or toluene and the second reactant a diamine or a diacid dissolves in water This technique pro duces polycarbonates PCs polyesters and polyamides The reaction occurs at the interface between the two immiscible liquids and the polymer is continuously removed from the interface Two general reactions form synthetic polymers chain addition and condensation Addition polymerization requires a chain reaction in which one monomer molecule adds to a second then a third and so on to form a macromolecule Addition polymerization monomers are mainly low molecular weight olefinic compounds eg ethylene or styrene or conjugated diolefin derivatives eg butadiene or isoprene Condensation polymerization can occur by reacting with either two similar or two different monomers to form a long polymer This reaction usually releases a small molecule like water as in the case of the esterification of a diol and a diacid In condensation polymerization where ring opening occurs no small molecule is released 1121 addition Polymerization Addition polymerization is employed primarily with substituted or unsubstituted olefin derivatives and conjugated diolefin derivatives Addition polymerization initiators are free radicals anions cations and coordination compounds In addition polymerization a chain grows simply by adding monomer molecules to a propagating chain The first step is to add a free radical a cationic or an anionic initiator to the monomer For example in ethylene polymerization with a special catalyst the chain grows by attaching the ethylene units one after another until the polymer terminates This type of addition produces a linear polymer CH CH CH CH 2 2 2 2 n n Branching occurs especially when free radical initiators are used due to chain transfer reactions For a substituted olefin such as vinyl chloride the addition primarily produces the most stable inter mediate Propagation then occurs by successive monomer molecules additions to the intermediates Three addition modes are possible i head to tail ii head to head and iii tail to tail The headtotail addition mode produces the most stable intermediate For example styrene polymerization mainly produces the headto tail intermediate Headtohead or tailtotail modes of addition are less likely because the intermediates are generally unstable Chain growth continues until the propagating polymer chain terminates Head totail mode 427 Monomers Polymers and Plastics 1122 free radical Polymerization Free radical initiators can polymerize olefinic compounds These chemical compounds have a weak covalent bond that breaks easily into two free radicals when subjected to heat Peroxides hydroper oxides and azo compounds are commonly used For example heating peroxybenzoic acid forms two free radicals which can initiate the polymerization reaction Free radicals are highly reactive shortlived and therefore not selective Chain transfer reactions often occur and result in a highly branched product polymer For example the polymerization of ethylene using an organic peroxide initiator produces highly branched polyethylene The branches result from the abstraction of a hydrogen atom by a propagating polymer intermediate which cre ates a new active center The new center can add more ethylene molecules forming a long branch Intermolecular chain transfer reactions may occur between two propagating polymer chains and result in the termination of one of the chains Alternatively these reactions take place by an intra molecular reaction by the coiling of a long chain Intramolecular chain transfer normally results in short branches Free radical polymers may terminate when two propagating chains combine In this case the tailtotail addition mode is most likely Polymer propagation stops with the addition of a chain transfer agent For example carbon tetra chloride can serve as a chain transfer agent during the production of polyethylene CH CH CCl CH CH Cl CCl 2 2 4 2 2 3 The trichloromethane free radical CCl3 can initiate a new polymerization reaction 1123 cationic Polymerization Strong protonic acids can affect the polymerization of olefin derivatives Chapter 3 Lewis acids such as aluminum chloride AlCl3 or boron trifluoride BF3 can also initiate polymerization In this case a trace amount of a proton donor cocatalyst such as water or methanol is normally required For example water combined with BF3 forms a complex that provides the protons for the polymerization reaction An important difference between free radical and ionic polymerization is that a counter ion only appears in the latter case For example the intermediate formed from the initiation of propene with BF3H2O could be represented as H BF OH CH CH CH CH CH BF OH 3 2 3 3 2 3 The next step is the insertion of the monomer molecules between the ion pair In ionic polymeriza tion reactions reaction rates are faster in solvents with high dielectric constants which promote the separation of the ion pair Cationic polymerizations work better when the monomers possess an electrondonating group that stabilizes the intermediate carbocation For example isobutylene produces a stable carboca tion and usually copolymerizes with a small amount of isoprene using cationic initiators The product polymer is a synthetic rubber widely used for tire inner tubes Cationic initiators can also polymerize aldehydes For example BF3 helps produce commercial poly mers of formaldehyde The resulting polymer a polyacetal is an important thermoplastic Chapter 12 428 Handbook of Petrochemical Processes Because of the low activation energy of the cationic polymerization reaction and anionic polymeriza tion reaction lowtemperature conditions are typically used to reduce any potential side reactions Low temperatures also minimize chain transfer reactions These reactions produce low molecular weight polymers by disproportionation of the propagating polymer chain Cationic polymerization can terminate by adding a hydroxy compound such as water 1124 anionic Polymerization Anionic polymerization is better for vinyl monomers with electron withdrawing groups that sta bilize the intermediates Typical monomers best polymerized by anionic initiators include acrylo nitrile styrene and butadiene As with cationic polymerization a counter ion is present with the propagating chain The propagation and the termination steps are similar to cationic polymeriza tion Many initiators such as alkyl and aryllithium and sodium and lithium suspensions in liq uid ammonia effect the polymerization For example acrylonitrile combined with nbutyllithium forms a carbanion intermediate Chain growth occurs through a nucleophilic attack of the carbanion on the monomer As in cationic polymerizations lower temperatures favor anionic polymerizations by minimizing branching due to chain transfer reactions Solvent polarity is also important in directing the reaction bath and the com position and orientation of the products For example the polymerization of butadiene with lithium in tetrahydrofuran THF a polar solvent gives a high 12 addition polymer Polymerization of either butadiene or isoprene using lithium compounds in nonpolar solvent such as npentane produces a high cis14 addition product However a higher cis14poly isoprene isomer was obtained than when butadiene was used This occurs because butadiene exists mainly in a transoid conformation at room temperature a higher cisoid conformation a form of geometric isomer is anticipated for isoprene 1125 coordination Polymerization In coordination polymerization the bonds are appreciably covalent but with a certain percentage of ionic character Bonding occurs between a transition metal central ion and the ligand perhaps an olefin a diolefin or carbon monoxide to form a coordination complex The complex reacts further with the ligand to be polymerized by an insertion mechanism In recent years much interest has been centered on using late transition metals such as iron and cobalt for polymerization Due to their lower electrophilic character the transition metals have greater tolerance for polar functionality and furthermore that the catalyst activity and the polymer branches could be modified by altering the bulk of the ligand that surrounds the central metal Such a protection reduces chain transfer reactions and results in a high molecular weight polymer An example of these catalysts is pyridine bisimine ligands complexed with iron and cobalt salts ZieglerNatta catalysts currently produce linear polyethylene nonbranched stereoregular poly propylene cispolybutadiene and other stereoregular polymers In the polymerization of these compounds a reaction between αtitanium trichloride and trieth ylaluminum produces a five coordinate titanium III complex arranged octahedrally The catalyst surface has four chloride anions an ethyl group and a vacant catalytic site D with the titanium ion Ti3 in the center of the octahedron A polymerized ligand such as ethylene occupies the vacant site The next step is the cis insertion of the ethyl group leaving a vacant site In another step ethyl ene occupies the vacant site This process continues until the propagating chain terminates When propylene is polymerized with free radicals or some ionic initiators a mixture of three ste reo forms result i the atactic form in which the methyl groups are randomly distributed through out the polymer ii the isotactic form in which all of the methyl groups are located on one side of 429 Monomers Polymers and Plastics the polymer chain and iii the syndiotactic from in which the methyl groups alternate regularly from one side to the other of the polymer chain The isotactic form of polypropylene has better physical and mechanical properties than the three tactic form mixture obtained from free radical polymerization Isotactic polypropylene in which all of the stereo centers of the polymer are the same is a crystalline thermoplastic By contrast atactic polypropylene in which the stereo centers are arranged randomly is an amorphous gum elastomer Polypropylene consisting of blocks of atactic and isotactic stereo sequences are rubbery in nature Polymerizing propylene with ZieglerNatta catalyst produces mainly isotactic polypropyl ene The CosseArlman model explains the formation of the stereoregular type by describing the crystalline structure of αtitanium trichloride αTiCl3 as hexagonal close packing with anion vacan cies This structure allows for cis insertion However due to the difference in the steric requirements one of the vacant sites available for the ligand to link with the titanium catalyst which has a greater affinity for the propagating polymer than the other site The propagating polymer then terminates producing an isotactic polypropylene Linear polyethylene occurs whether the reaction takes place by insertion through this sequence or as explained earlier by ligand occupation of any available vacant site This course however results in a syndiotactic polypropylene when propylene is the ligand Adding hydrogen terminates the propagating polymer The reaction between the polymer com plex and the excess triethylaluminum also terminates the polymer Treatment with alcohol or water releases the polymer A chain transfer reaction between the monomer and the growing polymer pro duces an unsaturated polymer This occurs when the concentration of the monomer is high compared to the catalyst Using ethylene as the monomer the termination reaction has this representation A new generation coordination catalysts are metallocene derivatives The chiral form of metallo cene produces isotactic polypropylene whereas the achiral form produces atactic polypropylene As the ligands rotate the catalyst produces alternating blocks of isotactic and atactic polymer much like a miniature sewing machine which switches back and forth between two different kinds of stitches 1126 condensation Polymerization Though less prevalent than addition polymerization condensation polymerization stepreaction polymerization produces important polymers such as polyesters polyamides nylons polycarbon ates polyurethanes and phenol formaldehyde resins Chapter 12 In general condensation polymerization refers to a reaction between two different monomers Each monomer possesses at least two similar functional groups that can react with the functional groups of the other monomer For example a reaction of a diacid and a dialcohol diol can produce polyesters A similar reaction between a diamine and a diacid can also produce polyamides reac tions between one monomer species with two different functional groups One functional group of one molecule reacts with the other functional group of the second molecule For example polymer ization of an amino acid starts with condensation of two monomer molecules In these examples a small molecule water results from the condensation reaction Ringopening polymerization of lactams can also be considered as a condensation reaction although a small molecule is not eliminated This type is noted later in this chapter under Ring Opening Polymerization Condensation polymerization is also known as stepreaction polymeriza tion because the reactions occur in steps First a dimer forms then a trimer next a tetramer and so on until the polymer terminates Although step polymerizations are generally slower than addition polymerizations with long reaction times required for high conversions the monomers disappear fast The reaction medium contains only dimers trimers tetramers and so on For example the dimer formed from the condensation of a diacid and a diol reaction previously shown has hydroxyl and carboxyl endings that can react with either a diacid or a diol to form a trimer The compounds formed continue condensation as long as the species present have different end ings The polymer terminates by having one of the monomers in excess This produces a polymer with similar endings For example a polyester formed with excess diol could be represented 430 Handbook of Petrochemical Processes In these reactions the monomers have two functional groups whether one or two monomers are used and a linear polymer results With more than two functional groups present cross linking occurs and a thermosetting polymer results Examples of this type are polyurethanes and urea formaldehyde resins The chemical structure of the ureaformaldehyde polymer consists of OCNHCH2NHn repeat units Ureaformaldehyde resins also known as ureamethanal resins are nontransparent thermoset ting resins or polymers They are produced from urea and formaldehyde These resins are used in adhesives finishes and particle board Ureaformaldehyde resins and the related amino resins are in the class of thermosetting resins Examples of amino resins use include in automobile tires to improve the bonding of rubber to tire cord in paper for improving tear strength in products such as molding electrical devices and jar caps Acid catalysts such as metal oxides and sulfonic acids generally catalyze condensation polym erizations However some condensation polymers form under alkaline conditions For example the reaction of formaldehyde with phenol under alkaline conditions produces methylolphenol deriva tives which further condense to a thermosetting polymer 1127 rinGoPeninG Polymerization Ringopening polymerization produces a small number of synthetic commercial polymers Probably the most important ringopening reaction is that of caprolactam for the production of nylon 6 Monomers suitable for polymerization by ringopening condensation normally possess two different functional groups within the ring Examples of suitable monomers are lactams such as caprolactam which produce polyamides and lactone derivatives which produce polyesters Ringopening polymerization may also occur by an addition chain reaction For example a ringopening reaction polymerizes trioxane to a polyacetal in the presence of an acid catalyst Formaldehyde also produces the same polymer Monomers used for ringopening polymerization by addition are cyclic compounds that open easily with the action of a catalyst during the reaction Smallstrained rings are suitable for this type of reaction For example the action of a strong acid or a strong base could polymerize ethylene oxide to a high molecular weight polymer The water soluble polymers are commercially known as carbowax The ring opening of cycloolefin derivatives is also possible with certain coordination catalysts This simplified example shows cyclopentene undergoing a firststep formation of the dimer cyclo decadiene a tencarbon ring with two double bonds and then incorporating additional cyclopen tene monomer units to produce the solid rubbery polypentamer Another example is the metathesis of cyclooctene which produces polyoctenylene an elastomer known as transpolyoctenamer Cyclopentadiene Cyclooctene 431 Monomers Polymers and Plastics 113 POLYMER TYPES To recap a monomer is a reactive molecule that has at least one functional group eg OH COOH NH2 CC A polymer is a large molecular macromolecule composed of repeating structural units monomers typically connected by covalent chemical bonds Rudin 1999 Braun et al 2001 Carraher 2003 Odian 2004 While polymer in the present context refers to hydrocar bon polymers the term actually refers to a large class of natural and synthetic materials with a wide variety of properties many of which are not true hydrocarbon derivatives Monomers may add to themselves as in the case of ethylene or may react with other monomers having different functionalities A monomer initiated or catalyzed with a specific catalyst polymer izes and forms a macromoleculea polymer For example ethylene polymerized in presence of a coordination catalyst produces a linear homopolymer linear polyethylene CH CH X CH CH X 2 2 2 2 linear polyethylene n n The polymer will be terminated by end groups show as X that are dictated by the nature of the reaction and any added reactant Generally polymerization is a relatively simple process but the ways in which monomers are joined together vary and it is more convenient to have more than one system of describing polym erization Polymerization occurs via a variety of reaction mechanisms that vary in complexity due to functional groups present in reacting compounds One system of separating polymerization pro cesses asks the question of how much of the original molecule is left when the monomers bond In addition polymerization monomers are added together with their structure unchanged Table 113 Olefin derivatives which are relatively stable due to σ bonding between carbon atoms form poly mers through relatively simple radical reactions The chain terminating group can be a hydrogen atom H or any nonreactive in this case hydro carbon moiety On the other hand condensation polymerization results in a polymer that is less massive than the two or more monomers that form the polymer because not all of the original monomer is incor porated into the polymer Water is one of the common molecules chemically eliminated during condensation polymerization Polymers such as polyethylene are generally referred to as homopolymers as they consist of repeated long chains or structures of the same monomer unit Polymerization occurs via a variety of reaction mechanisms that vary in complexity due to functional groups present in reacting com pounds and their inherent steric effects In more straightforward polymerization alkene which are relatively stable due to σbonding between carbon atoms form polymers through relatively simple radical reactions For hydrocarbon polymers chain growth polymerization or addition polymerization involves the linking together of molecules incorporating double or triple chemical bonds These unsaturated monomers the identical molecules that make up the polymers have extra internal bonds that are able to break and link up with other monomers to form the repeating chain Chain growth polymerization is involved in the manufacture of polymers such as polyethylene and polypropylene reactive olefin unreactive alkane 432 Handbook of Petrochemical Processes All the monomers from which addition polymers are made are olefin derivatives or function ally substituted olefin derivatives The most common and thermodynamically favored chemical transformations of olefin derivatives are addition reactions and many of these addition reactions are known to proceed in a stepwise fashion by way of a reactive initiator and the formation of reactive intermediates In principle once initiated a radical polymerization might be expected to continue unchecked producing a few extremely longchain polymers In practice larger numbers of moderately sized chains are formed indicating that chainterminating reactions must be taking place The most com mon termination processes are radical combination and disproportionation In both types of termi nation two reactive radical sites are removed by simultaneous conversion to stable products Since the concentration of radical species in a polymerization reaction is small relative to other reactants eg monomers solvents and terminated chains the rate at which these radicalradical termination reactions occurs is very small and most growing chains achieve moderate length before termination The relative importance of these terminations varies with the nature of the monomer undergoing polymerization For acrylonitrile and styrene combination is the major process However methyl methacrylate and vinyl acetate are terminated chiefly by disproportionation Another reaction that diverts radical chain growth polymerizations from producing linear macromolecules is chain trans fer in which a carbon radical from one location is moved to another by an intermolecular or intra molecular hydrogen atom transfer Chain transfer reactions are especially prevalent in the highpressure radical polymerization of ethylene which is the method used to make lowdensity polyethylene LDPE The primary radical at the end of a growing chain is converted to a more stable secondary radical by hydro gen atom transfer Further polymerization at the new radical site generates a side chain radi cal and this may in turn lead to creation of other side chains by chain transfer reactions As a result the morphology of low density polyethylene is an amorphous network of highly branched macromolecules In the radial polymerization of ethylene the Πbond is broken and the two electrons rearrange to create a new propagating center The form this propagating center takes depends on the specific type of addition mechanism There are several mechanisms through which this can be initiated The free radical mechanism was one of the first methods to be used Free radicals are very reac tive atoms or molecules that have unpaired electrons Taking the polymerization of ethylene as an example the free radical mechanism can be divided into three stages i chain initiation ii chain propagation and iii chain termination Polyethylene Polypropylene 433 Monomers Polymers and Plastics The free radical addition polymerization of ethylene must take place at high temperatures and pressures approximately 300C and 29000 psi While most other free radical polymerizations do not require such extreme temperatures and pressures they do tend to lack control One effect of this lack of control is a high degree of branching Also as termination occurs randomly when two chains collide it is impossible to control the length of individual chains A newer method of polym erization similar to free radical but allowing more control involves the ZieglerNatta catalyst especially with respect to polymer branching A ZieglerNatta catalyst is a catalyst used in the synthesis of polymers of αolefins alphaolefins 1alkenes Two general classes of ZieglerNatta catalysts are employed and are distinguished by their solubility i heterogeneous supported catalysts such as those based on titanium compounds which are used in polymerization reactions in combination with cocatalystsorganoaluminum compounds such as triethylaluminum AlC2H53 and ii homogeneous catalysts usually based on complexes of titanium zirconium hafnium which are usually used in combination with a dif ferent organoaluminum cocatalyst methyl aluminoxane or methylalumoxanethese catalysts traditionally contain not only metallocene derivatives but also feature multidentate oxygen and nitrogenbased ligands Finally the use of ZieglerNatta catalysts provides a stereospecific catalytic polymerization procedure discovered by Karl Ziegler and Giulio Natta in the 1950s Their catalysts permit the synthesis of unbranched high molecular weight highdensity polyethylene HDPE which is used predominantly in the manufacture of blowmolded bottles for milk household cleaners injection molded pails bottle caps appliance housings and toys laboratory synthesis of natural rubber from isoprene and configurational control of polymers from terminal olefin derivatives such as propylene eg pure isotactic and syndiotactic polymers In the case of ethylene rapid polymerization occurs at atmospheric pressure and moderate to low temperature giving a stronger more crystalline highdensity polyethylene than that from radical polymerization lowdensity polyethylene ZieglerNatta catalysts are prepared by reacting specific transition metal halides with organometallic reagents such as alkyl aluminum lithium and zinc reagents The catalyst formed by reaction of triethylaluminum with titanium tetrachloride has been widely studied but other metals eg vanadium and zirconium have also proven effective As olefin derivatives can be formed in relatively straightforward reaction mechanisms they form useful compounds such as polyethylene when undergoing radical reactions Polymers such as poly ethylene are generally referred to as homopolymers as they consist of repeated long chains or struc tures of the same monomer unit whereas polymers that consist of more than one type of monomer are referred to as copolymers Polymerization of isobutylene 2methylpropene by traces of strong acids is an example of cat ionic polymerization The polyisobutylene product is a soft rubbery solid Tg 70C 158F which is used for inner tubes This process is similar to radical polymerization and chain growth ceases when the terminal carbocation combines with a nucleophile or loses a proton giving a terminal alkene Hydrocarbon monomers bearing cation stabilizing groups such as alkyl phenyl or vinyl can be polymerized by cationic processes These are normally initiated at low temperature in methylene chloride solution Strong acids such as perchloric acid HClO4 or Lewis acids containing traces of water serve as initiating reagents At low temperatures chain transfer reactions are rare in such polymerizations so the resulting polymers are cleanly linear unbranched An example of anionic chain growth polymerization is the treatment of a cold tetrahydrofuran solution of styrene with 0001 equivalents of nbutyl lithium causes an immediate polymerization Chain growth may be terminated by water or carbon dioxide and chain transfer seldom occurs Only monomers having anion stabilizing substituents such as phenyl cyano or carbonyl are good substrates for this polymerization technique Many of the resulting polymers are largely isotactic in configuration and have high degrees of crystallinity Species that have been used to initiate anionic polymerization include alkali metals alkali amides and alkyl lithium compounds 434 Handbook of Petrochemical Processes In addition to ZieglerNatta catalysts other catalysts have been suggested with changes to accommodate the heterogeneity or homogeneity of the catalyst Polymerization of propylene through action of the titanium catalyst gives an isotactic product whereas vanadiumbased catalyst gives a syndiotactic product The synthetic polymer industry represents the major end use of many petrochemical monomers such as ethylene styrene and vinyl chloride Synthetic polymers have greatly affected our lifestyle Many articles that were previously made from naturally occurring materials such as wood cotton wool iron aluminum and glass are being replaced or partially substituted by synthetic polymers Clothes made from polyester nylon and acrylic fibers or their blends with natural fibers currently dominate the apparel market Plastics are replacing many articles previously made of iron wood porcelain or paper in thousands of diversified applications Polymerization could now be tailored to synthesize materials stronger than steel For example polyethylene fibers with a molecular weight of one million can be treated to be ten times stronger than steel However its melting point is 148C 298F A recently announced thermotropic liquid crystal polymer based on phydroxybenzoic acid terephthalic acid TPA and ppbiphenol has a high melting point of 420C 790F and does not decompose up to 560C 1040F The polymer field is versatile and fast growing and many new polymers are continually being produced or improved The basic chemistry principles involved in polymer synthesis have not changed much since the beginning of polymer production Major changes in the last 70 years have occurred in the catalyst field and in process development These improvements have a great impact on the economy In the elastomer field for example improvements influenced the automobile indus try and also related fields such as mechanical goods and wire and cable insulation Recognition that polymers make up many important natural materials was followed by the cre ation of synthetic analogs having a variety of properties Indeed applications of these materials as fibers flexible films adhesives resistant paints and tough but light solids have transformed mod ern society Polymers are formed by chemical reactions in which a large number of monomers are joined sequentially forming a chain In many polymers only one monomer is used In others two or three different monomers may be combined Polymers are classified by the characteristics of the reactions by which they are formed If all atoms in the monomers are incorporated into the polymer the polymer is called an addition polymer Table 114 If some of the atoms of the monomers are released into small molecules such as water the polymer is called a condensation polymer Most addition polymers are made from monomers containing a double bond between carbon atoms and are typical of polymers formed from olefin derivatives olefin derivatives and most commercial addition polymers are polyolefin derivatives Condensation polymers are made from monomers that have two different groups of atoms which TABLE 114 Glass Transition Temperatures of Various Polymers Material Tg C Tire rubber 70 Polypropylene atactic 20 Polyvinyl acetate 30 Polyethylene terephthalate 70 Polyvinyl alcohol 85 Poly vinyl chloride 80 PS 95 Polypropylene isotactic 0 Poly3hydroxybutyrate 15 Polymethylmethacrylate 105 435 Monomers Polymers and Plastics can join together to form for example ester or amide links Polyesters are an important class of commercial polymers as are polyamides nylon Hydrocarbon derivatives in this case alkene derivatives unsaturated hydrocarbon derivatives are prevalent in the formation of addition polymers but do not usually participate in the formation of condensation polymers The term polymer in popular usage suggests plastic but actually refers to a large class of natural and synthetic materials with a wide range of properties 1131 Polyethylene A simple example of a polymer is polyethylene a polymer composed of a repeating ethylene units CH2CH2n in which the range of properties varies depending upon the number of eth ylene units that make up the polymer The monomer ethylene CH2CH2 is a prime starting material that is readily available through refinery cracking process from which it is sent to the petrochemical side of the refinery The properties of polyethylene depend on the manner in which ethylene is polymerized When catalyzed by organometallic compounds at moderate pressure 220450 psi the product is high density polyethylene Under these conditions the polymer chains grow to very great length and molecular weight on the order of masses average many hundreds of thousands are recorded High density polyethylene is hard tough and resilient Most highdensity polyethylene is used in the manufacture of containers such as milk bottles and laundry detergent jugs When ethylene is polymerized at high pressure 1500030000 psi elevated temperatures 190210C 380410F and catalyzed by peroxides the product is lowdensity polyethylene which is used in film applications due to its toughness flexibility and relative transparency Typically low density polyethylene is used to manufacture flexible films such as those used for plastic retail bags Lowdensity polyethylene is also used to manufacture flexible lids and bottles in wire and cable applications for its stable electrical properties and processing characteristics This form of polyeth ylene has molecular weights in the order of 2000040000 Lowdensity polyethylene is relatively soft and most of it is used in the production of plastic films such as those used in sandwich bags Polyethylene is the most extensively used thermoplastic The ever increasing demand for poly ethylene is partly due to the availability of the monomer from abundant raw materials associated gas LPG naphtha Other factors are i the relative ease of processing the polymer ii resistance of the polymer to chemicals and iii the flexibility of the polymer The two most widely used grades of polyethylene are lowdensity polyethylene and highdensity polyethylene A new grade of low density polyethylene is a linear lowdensity grade produced like the highdensity polymer at low pressures This form of polyethylene is used predominantly in film applications due to its toughness flexibility and relative transparency It is the preferred resin for injection molding because of its superior toughness When ethylene is polymerized the reactor temperature should be well controlled to avoid the endothermic decomposition of ethylene to carbon methane and hydrogen CH CH 2C 2H CH CH C CH 2 2 2 2 2 4 11311 LowDensity Polyethylene Lowdensity polyethylene is produced under high pressure in the presence of a free radical initiator As with many free radical chain addition polymerizations the polymer is highly branched It has a lower crystallinity compared to highdensity polyethylene due to its lower capability of packing Polymerizing ethylene can occur either in a tubular or in a stirred autoclave reactor In the stirred autoclave the heat of the reaction is absorbed by the cold ethylene feed Stirring keeps a uniform temperature throughout the reaction vessel and prevents agglomeration of the 436 Handbook of Petrochemical Processes polymer In the tubular reactor a large amount of reaction heat is removed through the tube walls Reaction conditions for the free radical polymerization of ethylene are 100C200C 212F39F and 15002000 psi Ethylene conversion is kept to a low level 1025 to control the heat and the viscosity but the overall conversion with recycle is in the order of 95 based on ethylene The polymerization rate can be accelerated by increasing the temperature the initiator con centration and the pressure Degree of branching and molecular weight distribution depend on temperature and pressure A higherdensity polymer with a narrower molecular weight distribution could be obtained by increasing the pressure and lowering the temperature The crystallinity of the polymer could be varied to some extent by changing the reaction conditions and by adding como nomers such as vinyl acetate or ethyl acrylate The copolymers have lower crystallinity but better flexibility and the resulting polymer has higher impact strength 11312 HighDensity Polyethylene Highdensity polyethylene is produced by a lowpressure process in a fluid bed reactor Catalysts used for the production of highdensity polyethylene are either of the Zieglertype a complex of triethylaluminum AlC2H53 and αtitanium trichloride αTiCl3 or silica alumina SiO2Al2O3 impregnated with a metal oxide such as chromium oxide Cr2O3 or molybdenum oxide Mo2O3 Reaction conditions are generally mild but they differ from one process to another For example in the Unipol process which is used to produce both highdensity polyethyleneand linear lowdensity polyethylene LLDPE the reaction occurs in the gas phase Ethylene and the comonomers propene 1butene etc are fed to the reactor containing a fluidized bed of grow ing ymer particles Operation temperature and pressure are approximately 100C 212F and 300 psi A singlestage centrifugal compressor circulates unreacted ethylene The circulated gas fluidizes the bed and removes some of the exothermic reaction heat The product from the reac tor is mixed with additives and then pelletized The polymerization of ethylene can also occur in a liquidphase system where a hydrocarbon diluent is added This requires a hydrocarbon recovery system Highdensity polyethylene is characterized by a higher crystallinity and higher melting tem perature than lowdensity polyethylene due to the absence of branching Some branching could be incorporated in the backbone of the polymer by adding variable amounts of comonomers such as hexene These comonomers modify the properties of highdensity polyethylene for specific applications 11313 Linear LowDensity Polyethylene Linear lowdensity polyethylene is produced in the gas phase under low pressure Catalysts used are either Ziegler type or new generation metallocene derivatives The Union Carbide process used to produce HOPE could be used to produce the two polymer grades Terminal olefin derivatives C4 to C6 are the usual comonomers to effect the process 11314 Properties and Uses Polyethylene is an inexpensive thermoplastic that can be molded into almost any shape extruded into fiber or filament and blown or precipitated into film or foil Polyethylene products include packaging largest market bottles irrigation pipes film sheets and insulation materials Because lowdensity polyethylene is flexible and transparent it is mainly used to produce film and sheets Films are usually produced by extrusion Calendaring is mainly used for sheeting and to a lesser extent for film production Highdensity polyethylene is important for producing bottles and hollow objects by blow molding Approximately 64 of all plastic bottles are made from high density polyethylene Injection molding is used to produce solid objects Another important market for highdensity polyethylene is irrigation pipes which when manufactured from highdensity poly ethylene are flexible tough and corrosionresistant 437 Monomers Polymers and Plastics 1132 PolyProPylene Polypropylene is produced by the addition polymerization of propylene CH3CHCH2 The molec ular structure is similar to that of polyethylene but has a methyl group CH3 on alternate carbon atoms of the chain The molecular weight falls in the range 501000200000 Polypropylene is slightly more brittle than polyethylene but softens at a temperature of approximately 40C 104F Propylene like ethylene is a prime starting material that is readily available through refinery crack ing process from which it is sent to the petrochemical side of the refinery Polypropylene is a major thermoplastic polymer that is used extensively in the automotive industry for interior trim such as instrument panels and in food packaging such as yogurt containers It is formed into fibers of very low absorbance and highstain resistance used in clothing and home furnish ings especially carpeting Although polypropylene did not take its position among the largevolume polymers until fairly recently it is currently the third largest thermoplastic after polyvinylchloride The delay in polypropylene development may be attributed to technical reasons related to its polymerization Polypropylene produced by free radical initiation is mainly the atactic form Due to its low crystallinity it is not suitable for thermoplastic or fiber use The turning point in polypropylene production was the development of a Zieglertype catalyst by Natta to produce the stereoregular form isotactic Catalysts developed in the titaniumaluminum alkyl family are highly reactive and stereo selective Very small amounts of the catalyst are needed to achieve polymerization 1 g catalyst300000 g polymer Consequently the catalyst entrained in the polymer is very small and the catalyst removal step is eliminated in many new processes Amoco has intro duced a new gasphase process called absolute gas phase in which polymerization of olefin derivatives ethylene propylene occurs in the total absence of inert solvents such as liquefied propylene in the reactor Titanium residues resulting from the catalyst are less than 1 ppm and aluminum residues are less than those from previous catalysts used in this application Polypropylene could be produced in a liquid or in a gasphase process Until 1980 the vertically stirred bed process of BASF was the only large scale commercial gasphase process In the Union CarbideShell gasphase process a wide range of polypropylenes are made in a fluidized bed gas phase reactor Melt index atactic level and molecular weight distribution are controlled by selecting the proper catalyst adjusting operating conditions and adding molecular weight control agents This process is a modification of the polyethylene process discussed before but a second reactor is added Homopolymers and random copolymers are produced in the first reactor which operates at approximately 70C 158F and 500 psi Impact copolymers are produced in the second reactor impact reactor after transferring the polypropylene resin from the first reactor Gaseous propylene and ethylene are fed to the impact reactor to produce the polymers rubber phase Operation of the impact reactor is similar to the initial one but the second operates at lower pressure approximately 17 atm The granular product is finally pelletized An example of the liquidphase polymerization is the Spheripol process which uses a tubular reactor In the process homopolymer and random copolymer polymerization takes place in liquid propylene within a tubular loop reactor Heterophasic impact copolymerization can be achieved by adding a gasphase reactor in series Removal of catalyst residue and amorphous polymer is not required Any unreacted monomer is flashed in a twostage pressure system and recycled back to the reactors This improves yield and minimizes energy consumption Dissolved monomer is removed from the polymer by a steam sparge The process can use lowerassay chemicalgrade propylene or the typical polymerization grade The process can produce a broad range of propylenebased poly mers including homopolymer various families of random copolymers and terpolymers hetero phasic impact and specialty impact copolymers as well as highstiffness highclarity copolymers New generation metallocene catalysts can polymerize propylene in two different ways Rigid chiral metallocene produce isotactic polypropylene whereas the achiral forms of the catalysts pro duce atactic polypropylene The polymer microstructure is a function of the reaction conditions and the catalyst design However the rate of ligand rotation in some unbridged metallocene derivatives 438 Handbook of Petrochemical Processes can be controlled so that the metallocene oscillates between two stereochemical states One isomer produces isotactic polypropylene and the other produces the atactic polymer As a result alternat ing blocks of rigid isotactic and flexible atactic polypropylene grow within the same polymer chain The properties of commercial polypropylene vary widely according to the percentage of crystal line isotactic polymer and the degree of polymerization Polypropylenes with a 99 isotactic index are currently produced Articles made from polypropylene have good electrical and chemical resis tance and low water absorption The other useful characteristics of polypropylene are i its light weight ie the lowest thermoplastic polymer density ii high abrasion resistance iii dimensional stability iv high impact strength and v no toxicity Polypropylene can be extruded into sheets and thermoformed by solid phase pressure forming into thinwalled containers Due to its light weight and toughness polypropylene and its copolymers are extensively used in automobile parts Improvements in melt spinning techniques and film fila ment processes have made polypropylene accessible for fiber production 1133 Polyvinyl chloride The monomervinyl chloride CH2CHClis not produced directly from a carbonaceous feed stock such as crude oil but it is produced by a variety of processes from ethylene a product produced in the refinery There are several routes to produce vinyl chloride from ethylene and are i direct chlorination ii oxychlorination iii thermal crackingother routes included iv from ethane a petrochemical product and v from acetylene a derived petrochemical One method of producing vinyl chlorides is by the addition of chlorine to ethylene in the pres ence of an iron chloride FeCl3 catalyst followed by dehydrochlorination of the ethylene dichloride CH CH Cl CH ClCH Cl 2 2 2 2 2 Another route to ethylene dichloride is the oxychlorination route that entails the reaction of ethyl ene oxygen and hydrogen chloride over a copper chloride CuCl2 catalyst to produce in a highly exothermic reaction ethylene dichloride 2CH CH 4HCl O ClCH CH Cl H O 2 2 2 2 2 2 Byproducts of the oxychlorination reaction such as ethyl chloride may be recovered as feedstocks for chlorinated solvents production When heated to 500C 930F under pressure 225450 psi ethylene dichloride decomposes to produce vinyl chloride and anhydrous hydrogen chloride ClCH CH Cl CH CHCl HCl 2 2 2 The thermal cracking reaction is highly endothermic and is generally carried out in a fired heater Even though residence time and temperature are carefully controlled it produces significant quanti ties of chlorinated hydrocarbon byproducts In another route the reaction of acetylene with anhydrous hydrogen chloride in the presence of a mercuric chloride HgCl2 catalyst to give vinyl chloride C H HCl CH CHCl 2 2 2 The reaction is exothermic and highly selective Product purity and yields are generally very high This industrial route to vinyl chloride was common before ethylene became widely distributed When the production of vinyl chloride from the thermal cracking of ethylene dichloride became more popular this method the acetylene method fell into disuse 439 Monomers Polymers and Plastics Polyvinyl chloride is one of the most widely used thermoplastic polymers It can be extruded into sheets and film and blow molded into bottles It is used in many common items such as garden hoses shower curtains irrigation pipes and paint formulations Many of these polyvinylchloride products are used every day and include everything from medical devices such as medical tubing and blood bags to footwear electrical cables packaging stationery and toys Polyvinylchloride can be prepolymerized in bulk to approximately 78 conversion It is then transferred to an autoclave where the particles are polymerized to a solid powder Most vinyl chloride however is polymerized in suspension reactors made of stainless steel or glasslined The peroxide used to initiate the reaction is dispersed in about twice its weight of water containing 0011 of a stabilizer such as polyvinyl alcohol In the European Vinyls Corporation process vinyl chloride monomer is dispersed in water and then charged with the additives to the stirred jacketedtype reactor The temperature is maintained between 53C70C 127F158F to obtain a polymer of a particular molecular weight The heat of the reaction is controlled by cooling water in the jacket and by additional reflux condensers for large reactors Conversion could be controlled between 85 and 95 as required by the polymer grade At the end of the reaction the polyvinylchloride and water slurry are channeled to a blowdown vessel from which part of unreacted monomer is recovered The rest of the vinyl chloride monomer is stripped and the slurry is centrifuged to separate the polymer from both water and the initiator Polyvinyl chloride can also be produced in emulsion Water is used as the emulsion medium The particle size of the polymer is controlled using the proper conditions and emulsifier Polymers produced by free radical initiators are highly branched with low crystallinity Vinyl chloride can be copolymerized with many other monomers to improve its properties Examples of monomers used commercially are vinyl acetate propylene ethylene and vinylidine chloride The copolymer with ethylene or propylene Tg 80C which is rigid is used for blow molding objects Copolymers with 620 vinyl acetate Tg C are used for coatings Two types of the homopolymer are available the flexible and the rigid Both types have excel lent chemical and abrasion resistance The flexible types are produced with high porosity to permit plasticizer absorption Articles made from the rigid type are hard and cannot be stretched more than 40 of their original length An important property of polyvinylchloride is that it is self extinguishing due to presence of the chlorine atom Flexible polyvinylchloride grades account for approximately 50 of polyvinylchloride produc tion They go into such items as tablecloths shower curtains furniture automobile upholstery and wire and cable insulation Many additives are used with polyvinylchloride polymers such as plasticizers antioxidants and impact modifiers Heat stabilizers which are particularly important with polyvinylchloride resins extend the useful life of the finished product Plastic additives have been reviewed by Ainsworth Rigid polyvinylchloride is used in many items such as pipes fittings roofing automobile parts siding and bottles 1134 Polystyrene Styrene an important product of the petrochemical section of the refinery is produced by dehydro genation of ethylbenzene which is in turn produced by the alkylation of benzene with ethylene The ethylbenzene is mixed in the gas phase with 1015 times its volume of hightemperature steam and passed over a solid catalyst bed The catalyst is typically ion oxide FeCl3 promoted by potas sium oxide or potassium carbonate The steam serves several roles in this reaction and is the source of heat for the endothermic reaction and it removes coke that tends to form on the iron oxide catalyst through the watergas 440 Handbook of Petrochemical Processes shift reactionthe potassium promoter enhances the decoking reaction The steam also dilutes the reactant and products shifting the position of chemical equilibrium toward products A typical styrene plant consists of two or three reactors in series which operate under vacuum to enhance the conversion and selectivity Polystyrene is the fourth bigvolume thermoplastic Styrene can be polymerized alone or copo lymerized with other monomers It can be polymerized by free radical initiators or using coordina tion catalysts Recent work using group 4 metallocene combined with methyl aluminoxane produce stereoregular polymer When homogeneous titanium catalyst is used the polymer was predomi nantly syndiotactic The heterogeneous titanium catalyst gave predominantly the isotactic Twenty one copolymers with butadiene in a ratio of approximately 13 produces styrenebutadiene rubber SBR the most important synthetic rubber Copolymers of styreneacrylonitrile SAN have higher tensile strength than styrene homopoly mers A copolymer of acrylonitrile butadiene and styrene ABS is an engineering plastic due to its better mechanical properties discussed later in this chapter Polystyrene is produced either by free radical initiators or by use of coordination catalysts Bulk suspension and emulsion techniques are used with free radical initiators and the polymer is atactic In a typical batch suspension process styrene is suspended in water by agitation and use of a stabilizer The polymer forms beads The beadwater slurry is separated by centrifugation dried and blended with additives The polystyrene homopolymer produced by free radical initiators is highly amorphous Tg 100C The general purpose rubber SBR a block copolymer with 75 butadiene is produced by anionic polymerization The most important use of polystyrene is in packaging Molded polysty rene is used in items such as automobile interior parts furniture and home appliances Packaging uses plus specialized food uses such as containers for carryout food are growth areas Expanded polystyrene foams which are produced by polymerizing styrene with a volatile solvent such as pen tane have low densities They are used extensively in insulation and flotation life jackets SAN Tg 105C 221F is stiffer and has better chemical and heat resistance than the homopol ymer However it is not as clear as polystyrene and it is used in articles that do not require optical clarity such as appliances and houseware materials ABS has a specific gravity of 103106 and a tensile strength in the range of 675 103 psi These polymers are tough plastics with outstanding mechanical properties A wide variety of ABS modifications are available with heat resistance comparable to or better than polysulfone derivatives and polycarbonate derivatives Another outstanding property of ABS is its ability to be alloyed with other thermoplastics for improved properties For example ABS is alloyed with rigid polyvinylchlo ride for a product with better flame resistance Among the major applications of ABS are extruded pipes and pipe fittings appliances such as refrigerator door liners and in molded automobile bodies 1135 nylon resins The nylon family of products condensation polymers or copolymers formed by reacting difunc tional monomers containing equal parts of amine and carboxylic acid so that amide derivatives are formed The nylon monomers are manufactured by a variety of routes starting in most cases from crude oil but sometimes from biomass As examples Lactam production Crude oil benzene Benzene cyclohexane Cyclohexane cyclohexanone Cyclohexanone cyclohexanone oxime Cyclohexanone oxime caprolactam 441 Monomers Polymers and Plastics Diacid production Crude oil benzene Benzene cyclohexane Cyclohexane Cyclohexanone Cyclohexane cyclohexanol Cyclohexanol adipic acid Diamine production Crude oil propylene Propylene acrylonitrile Acrylonitrile succinonitrile Succinonitrile tetramethylene diamine Nylon resins are important engineering thermoplastics Nylons are produced by a condensation reaction of amino acids a diacid and a diamine or by ringopening lactams such as caprolactam The polymers however are more important for producing synthetic fibers Important properties of nylons are toughness abrasion and wear resistance chemical resistance and ease of processing Reinforced nylons have higher tensile and impact strengths and lower expan sion coefficients than metals They are replacing metals in many of their applications Objects made from nylons vary from extruded films used for pharmaceutical packaging to bearings and bushings to cable and wire insulation 1136 Polyesters Polyesters are among the largevolume engineering thermoplastics produced by condensation polym erization of terephthalic acid 14HO2CC6H4CHO2H with ethylene glycol CH2OHCH2OH or 14butanediol HOCH2CH2CH2CH2OH all of which are produced within a petrochemical complex Polyester derivatives are used to produce film for magnetic tapes due to their abrasion and chemi cal resistance low water absorption and low gas permeability Polyethylene terephthalate is also used to make plastic bottles approximately 25 of plastic bottles are made from polyethylene tere phthalate Similar to nylons the most important use of polyethylene terephthalate is for producing synthetic fibers discussed later Polybutylene terephthalate is another thermoplastic polyester pro duced by the condensation reaction of terephthalic acid 14HO2CC6H4CO2H and 14butanediol HOCH2CH2CH2CH2OH The polymer is either produced in a bulk or a solution process It is among the fastest growing engineering thermoplastics and leads the market of reinforced plastics with an annual growth rate of 73 1137 PolycarBonates Polycarbonates are another group of condensation thermoplastics used mainly for special engi neering purposes These polymers are considered polyesters of carbonic acid H2CO3 They are produced by the condensation of the sodium salt of bisphenol A with phosgene in the presence of an organic solvent Bisphenol A Phosgene Polymer 442 Handbook of Petrochemical Processes Sodium chloride is precipitated and the solvent is removed by distillation Another method for producing polycarbonate products is by an exchange reaction between bisphenol A or a similar bisphenol with diphenyl carbonate Bisphenol A is synthesized by the condensation of acetone with two phenolsthe reaction is catalyzed by a strong acid such as hydrochloric acidall of which are available within the petro chemical complex Typically a large excess of phenol is used to ensure full condensation The product mixture from the cumene process acetone and phenol may also be used as starting material Diphenyl carbonate is produced by the reaction of phosgene and phenol Thus 2C H OH COCl C H OCO C H 2HCl 6 5 2 6 5 2 6 5 Dimethyl carbonate can also be transesterified with phenol CH OCO CH 2C H OH C H OCO C H 2MeOH 3 2 3 6 5 6 5 2 6 5 Another approach to the synthesis of diphenyl carbonate by the reaction of CO and methyl nitrite using Pdalumina 2C H OH CO O C H OCO C H H O 6 5 6 5 2 6 5 2 Dimethyl carbonate is formed which is further reacted with phenol in presence of tetraphenox tita nium catalyst Decarbonylation in the liquid phase yields diphenyl carbonate Polycarbonates known for their toughness in molded parts typify the class of polymers known as engineering thermoplastics These materials designed to replace metals and glass in applica tions demanding strength and temperature resistance and offer additional advantages of light weight and ease of fabrication Materials made from polycarbonates are transparent strong and heat and breakresistant However these materials are subject to stress cracking and can be attacked by weak alkalis and acids Polycarbonates are used in a variety of articles such as laboratory safety shields street light globes and safety helmets The maximum usage temperature for polycarbonate objects is 125C 257F 1138 Polyether sulfones Polyether sulfones PESs are another class of engineering thermoplastics generally used for objects that require continuous use of temperatures around 200C 390F Polyether sulfones can be pre pared by the reaction of the sodium or potassium salt of bisphenol A and 44 dichlorodiphenyl sulfone Bisphenol A acts as a nucleophile in the presence of the deactivated aromatic ring of the dichlorophenyl sulfone The reaction may also be catalyzed with FriedelCrafts catalysts the dichlorophenyl sulfone acts as an electrophile In the process polyether sulfone derivatives are prepared by a polycondensation reaction of the sodium salt of an aromatic diphenol derivative and bis4chlorophenylsulfone The aromatic diphenol of which there are three isomers and also known as dihydroxybenzene or benzenediol or Bisphenol A 443 Monomers Polymers and Plastics commonly produced within the petrochemical complex of refinery Also the 44dichlorodiphenyl sulfone is synthesized by sulfonation of chlorobenzene with sulfuric acid often in the presence of various additives to optimize the formation of the 44isomer ClC H SO ClC H SO H O 6 5 3 6 4 2 2 2 It can also be produced by chlorination of diphenyl sulfone In the process the sodium salt of the diphenol is formed in situ by reaction with a stoichiometric amount of sodium hydroxide NaOH The water formed in the reaction must be removed with an azeotropic solvent after which the polymerization is carried out at 130C160C 265F320F under inert conditions in a polar aprotic solvent such as dimethyl sulfoxide and a polyether is formed by the elimination of sodium chloride Through the use of chain terminators the chain length of the polymer can be regulated in a range that a technical melt processing is possible Typically the product has endgroups that are capable of further reaction and to prevent further condensation in the melt the endgroups can be con verted to an ether by reaction with chloromethane CH3Cl The diphenol is typically bisphenol A or 14 dihydroxybenzene 14HOC6H4OH also known as hydroquinone benzene14diol or quinol Written simply the general polymerization reaction is ClC H SO NaO aromatic center ONa OC H SO C H Oaromatic center 6 4 2 2 6 4 2 4 4 n Some of the commercial products include 44 Dichlorodiphenyl sulfone 444 Handbook of Petrochemical Processes In general the properties of polyether sulfone derivatives are similar to those of polycarbonate derivatives but they can be used at higher temperatures 1139 PolyPhenylene oxide Polyphenylene oxide PPO also known as polyphenylene ether PPE is produced by the condensa tion of 26dimethylphenol This compound can be synthesized by the alkylation of phenol with methanol Grabowska et al 1989 The polymers are formed by oxidative coupling of substituted phenols at the paraposition Although many different choices of monomer exist only 26dimethylphenol has any practical importance In the process reaction occurs by passing oxygen in the phenol solution in presence of cuprous chloride CuCl or Cu2Cl2 and pyridine The monomer is synthesized by reacting phenol with methanol in the vapor phase in the pres ence of a metal oxide catalyst Naturally it important that the phenol used in this reaction be very pure Impurities in the monomer with blocked para and ortho positions are chain terminators while impurities with open ortho positions can cause chain branching or crosslinking The final polymer is a stiff tough white plastic with a glass transition temperature Tg of 205C 400F Polyphenylene oxide is a thermoplastic linear noncrystalline polyether that is one of the most important engineering plastics due to its high strength high heat distortion temperature and high chemical resistance Because of its unique combination of high mechanical property low moisture absorption excellent electrical insulation property excellent dimension stability and inherent flame resistance polyphenylene oxide has been widely used for a broad range of appli cations However the high melting temperature high melt viscosity poor formability and poor resistance to organic solvent can hinder the applications of the polymer To achieve desired prop erties a series of polyphenylene nanocomposites has been introduced by physical or chemical modification in the past decades An example is the blends of poly26dimenthy14phenylene oxide with polystyrene which are the first commercially available alloy of polyphenylene oxide in the early 11310 Polyacetal Polyacetal also known as polyoxymethylene polyformaldehyde is among the aliphatic polyether family and is produced by the polymerization of formaldehyde 26dimethyl phenol 445 Monomers Polymers and Plastics These polymers are termed polyacetals to distinguish them from polyether derivatives pro duced by polymerizing ethylene oxide which has two methylene CH2 groups between the ether groups The polymerization reaction occurs in the presence of a Lewis acid and a small amount of water at room temperature Formaldehyde is produced industrially by the catalytic oxidation of methanol a com mon petrochemical starting material using catalysts such as solver metal or a mixture of an ion oxide and molybdenum oxide or vanadium oxide In the commonly Formox process methanol and oxygen react at a temperature in the order of 250C400C 480F750F in presence of iron oxide in combination with molybdenum andor vanadium to produce formal dehyde Thus 2CH OH O 2CH O 2H O 3 2 2 2 The silverbased catalyst usually operates at a higher temperature approximately 650C 1200F Two chemical reactions occur simultaneously produce formaldehyde 2CH OH O 2CH O 2H O CH OH CH O H 3 2 2 2 3 2 2 In principle formaldehyde could be generated by oxidation of methane but this route is not indus trially viable due to the more facile oxidation of methanol relative to the moredifficulttooxide methane In the process to produce polyacetal the formaldehyde is generated by the reaction of the form aldehyde solution with an alcohol to create a hemiformal dehydration of the hemiformalwater mixture either by extraction or vacuum distillation and release of the formaldehyde by heating the hemiformal The formaldehyde is then polymerized by anionic catalysis and the resulting polymer stabilized by reaction with acetic anhydride Polyacetals are highly crystalline polymers The number of repeating units ranges from 500 to 3000 They are characterized by high impact resistance strength and a low friction coefficient Articles made from polyacetals vary from door handles to gears and bushings carburetor parts to aerosol containers The major use of polyacetals is for molded grades 11311 Butadiene Polymers and coPolymers Butadiene an extremely important multifunctional petrochemical can be produced by the cata lytic dehydrogenation of nbutane CH3CH2CH2CH3 by the Houdry Catadiene process which was developed during World War II and involves treating butane over an aluminachromia Al2O3 Cr2O3 catalyst at high temperatures Butadiene can also be produced from ethanol and two processes are available i at 400C450C 700F840F using a variety of metal oxide catalysts Polyacetal polyoxymethylene 446 Handbook of Petrochemical Processes Thus 2CH3CH2OH CH2CHCHCH2 2H2O H2 In the alternate process ethanol is oxidized to acetaldehyde which reacts with additional ethanol over a porous silica catalyst which is promoted by tantalum 325C350C 615F660F to yield butadiene Thus CH3CH2OH CH3CHO CH2CHCHCH2 2 H2O Butadiene could be polymerized using free radical initiators or ionic or coordination catalysts When butadiene is polymerized in emulsion using a free radical initiator such as cumene hydroper oxide a random polymer is obtained with three isomeric configurations the 14addition configura tion dominating Polymerization of butadiene using anionic initiators alkyl lithium in a nonpolar solvent produces a polymer with a high cis configuration A high cispolybutadiene is also obtained when coordination catalysts are used cis14Polybutadiene is characterized by high elasticity low heat buildup high abrasion resis tance and resistance to oxidation However it has a relatively low mechanical strength This is improved by incorporating a cis trans block copolymer or 12vinyl block copolymer in the poly butadiene matrix Also a small amount of natural rubber may be mixed with polybutadiene to improve its properties Trans14polybutadiene is characterized by a higher glass transition tem perature Tg 14C 7F than the cis form Tg 108C 162F The polymer has the toughness resilience and abrasion resistance of natural rubber Tg 14C 7F While on the issue of diene derivatives it is worthy of note that a transpolypentamer TPR is pro duced by the ring cleavage of cyclopentene Cyclopentene is obtained from cracked naphtha or gas oil which contain small amounts of cyclopentene cyclopentadiene and dicyclopentadiene Polymerization using organometallic catalysts produce a stereoregular product trans 15polypentamer Due to the presence of residual double bonds the polymer could be crosslinked with regular agents The transpolypentamer is a linear polymer with a high trans configuration It is highly amorphous at normal temperatures and has a Tg of about 90C 194F and a density of 085 114 PLASTICS AND THERMOPLASTICS Plastic is the general common term for a wide range of synthetic organic usually solid materials produced and used in the manufacture of industrial products Jones and Simon 1983 Austin 1984 447 Monomers Polymers and Plastics Lokensgard 2010 A plastic is a type of polymerall plastics are polymers but not all polymers are plastics Polymers can be fibers elastomers or adhesives and plastics are a wide group of solid composite materials that are largely organic usually based on synthetic resins or modified polymers of natural origin and possess appreciable mechanical strength A plastic exhibits plasticity and the ability to be deformed or undergo change of shape under pressure temperature or both At a suit able stage in their manufacture plastics can be cast molded or polymerized directly Plastic mate rial is any of a wide range of synthetic or semisynthetic organic solids used in the manufacture of industrial products Plastics are typically polymers of high molecular mass and may contain other substances to improve performance Plastics are produced from chemicals sourced almost entirely from fossil fuels and because fossil fuel production is highly localized plastic production is also concentrated in specific regions where fossil fuel development is present including notably the US Gulf Coast Natural gas liquids NGLs a key input for plastic production are hard to transport and petrochemical producers rely ing on natural gas liquids or ethane as a feedstock typically cluster geographically near sources of natural gas Naphtha another key input for plastic production is a product of oil refining and its production is concentrated among major oil companies with refining capacity Thus because of the need to colocate fossil fuel and plastic production there is a high degree of vertical integration between the industries Major oil and gas producers own plastics companies and major plastic producers own oil and gas companies As example listed alphabetically BP Chevron ExxonMobil Shell and Chevron are all integrated companies Plastics are available in the form of bars tubes sheets coils and blocks and these can be fabri cated to specification However plastic articles are commonly manufactured from plastic powders in which desired shapes are fashioned by compression transfer injection or extrusion molding In compression molding materials are generally placed immediately in mold cavities where the application of heat and pressure makes them first plastic then hard The transfer method in which the compound is plasticized by outside heating and then poured into a mold to harden is used for designs with intricate shapes and great variations in wall thickness Injectionmolding machinery dissolves the plastic powder in a heating chamber and by plunger action forces it into cold molds where the product sets The operations take place at rigidly controlled temperatures and intervals Extrusion molding employs a heating cylinder pressure and an extrusion die through which the molten plastic is sent and from which it exits in continuous form to be cut in lengths or coiled Thermoplastics are elastic and flexible above a glass transition temperature Tg which is spe cific to each plastic specific for each one Below a second higher melting temperature Tm most thermoplastics have crystalline regions alternating with amorphous regions in which the chains approximate random coils The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity Above Tm all crystalline structure disappears and the chains become randomly interdispersed As the temperature increases above Tm the viscosity gradually decreases without any distinct phase change Some thermoplastics normally do not crystallize they are termed amorphous plastics and are useful at temperatures below the glass transition temperature Generally amorphous thermoplastics are less chemically resistant and can be subject to stress cracking Thermoplastics will crystallize to a certain extent and are called semicrystalline The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain Semicrystalline thermoplastics are more resistant to solvents and other chemicals If the crystal lites are larger than the wavelength of light the thermoplastic is hazy or opaque Semicrystalline thermoplastics become less brittle above the glass transition temperature If a plastic with otherwise desirable properties has too high a glass transition temperature it can often be lowered by adding a low molecular weight plasticizer to the melt before forming and cooling A similar result can some times be achieved by adding nonreactive side chains to the monomers before polymerization Both methods make the polymer chains stand off a bit from one another Another method of lowering the glass transition temperature or raising the melting temperature is to incorporate the original plastic 448 Handbook of Petrochemical Processes into a copolymer as with graft copolymers of polystyrene Lowering the glass transition tempera ture is not the only way to reduce brittleness Drawing and similar processes that stretch or orient the molecules or increasing the length of the polymer chains also decrease brittleness Thermoplastics can go through meltingfreezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name This quality makes thermoplastics recyclable The processes required for recycling vary with the thermoplastic Although modestly vulcanized natu ral and synthetic rubbers are stretchy they are elastomeric thermosets not thermoplastics Each has its own glass transition temperature and will crack and shatter when cold enough so that the crosslinked polymer chains can no longer move relative to one another But they have no melting temperature and will decompose at high temperatures rather than melt Ethylene CH2CH2 is a critical feedstock for the production of polyethylene polyvinyl chlo ride polyethylene terephthalate and polystyrene Propylene CH3CHCH2 is the basic chemical for the manufacture of polypropylene Therefore the overwhelming majority of plastics can be traced to the product streams of just two industrial chemicals ethylene and propylene Ethylene and propylene are particularly critical in the production of plastic packaging the largest and fastest growing category of plastic products and the biggest though by no means only contributor to the accelerating crisis of plastics pollution In addition moreover plastic packag ing is comprised nearly exclusively of the five major thermoplastics discussed above primarily polyethylene polypropylene and polyethylene terephthalate In addition the abundant supply of natural gas in the United States has made natural gas liquids the preferred input for ethylene pro duction Nearly 90 of US ethylene production is sourced from ethanerich natural gas liquids Moreover virtually all ethane in the United States and onethird of propane is used in ethylene production Plastics are relatively tough substances with high molecular weight that can be molded with or without the application of heat In general plastics are subclassified into thermoplastics polymers that can be softened by heat and thermosets which cannot be softened by heat Thermoplastics have moderate crystallinity They can undergo large elongation but this elongation is not as revers ible as it is for elastomers Examples of thermoplastics are polyethylene and polypropylene Thermosetting plastics are usually rigid due to high crosslinking between the polymer chains Examples of this type are phenol fomaldehyde and polyurethanes Crosslinking may also be pro moted by using chemical agents such as sulfur or by heat treatment or irradiation with gamma rays ultraviolet light or energetic electrons Recently highenergy ion beams were found to increase the hardness of the treated polymer drastically In addition thermoplastics are plastics that do not undergo chemical change in their composition when heated and therefore can be molded again and again examples are polyethylene polypropylene polystyrene polyvinyl chloride and polytetra fluoroethylene The raw materials needed to make most of these plastics come from petroleum and natural gas Plastics are the polymeric materials with properties in chemical structure the demarcation between fibers and plastics may sometimes be blurred Polymers such as polypropylene and poly amides can be used as fibers and plastics by a proper choice of processing conditions Plastics can be extruded as sheets or pipes painted on surfaces or molded to form countless objects A typi cal commercial plastic resin may contain two or more polymers in addition to various additives and fillers Additives and fillers are used to improve some property such as the processability thermal or environmental stability and mechanical properties of the final product A plastic is also any organic material with the ability to flow into a desired shape when heat and pressure are applied to it and to retain the shape when they are withdrawn Plastics are typically polymers of high molecular weight and may contain other substances to improve performance Because of their relative ease of manufacture versatility and imperviousness to water plastics are used in a wide range of products from paper clips to space vehicles However these same properties make them persist beyond their usefulness and the focus is on making polycarbonates environmentally friendly 449 Monomers Polymers and Plastics Thermoplastics are important polymeric materials that have replaced or substituted many natu rally derived products such as paper wood and steel Plastics possess certain favorable proper ties such as light weight corrosion resistance toughness and ease of handling They are also less expensive The major use of the plastics is in the packaging field Many other uses include con struction electrical and mechanical goods and insulation One growing market that evolved fairly recently is engineering thermoplastics This field includes polymers with special properties such as high thermal stability toughness and chemical and weather resistance Nylons polycarbonates polyether sulfones and polyacetals are examples of this group Resins are basic building materials that constitute the greater bulk of plastics Resins undergo polymerization reactions during the development of plastics Plastics are formed when polymers are blended with specific external materials in a process known as compounding The important com pounding ingredients include plasticizers stabilizers chelating agents and antioxidants Hydrocarbon plastics are plastics based on resins made by the polymerization of monomers com posed of carbon and hydrogen only A plastic is made up principally of a binder together with plasticizers fillers pigments and other additives The binder gives a plastic its main characteristics and usually its name Binders may be natural materials eg cellulose derivatives casein or milk protein but are more commonly synthetic resins In either case the binder materials consist of polymers Cellulose derivatives are made from cellulose a naturally occurring polymer casein is also a naturally occur ring polymer Synthetic resins are polymerized or built up from small simple molecules called monomers Plasticizers are added to a binder to increase flexibility and toughness Fillers are added to improve particular properties eg hardness or resistance to shock Pigments are used to impart various colors Virtually any desired color or shape and many combinations of the properties of hardness dura bility elasticity and resistance to heat cold and acid can be obtained in a plastic Plastic deformation is observed in most materials including metals soils rocks concrete and plastics However the physical mechanisms that cause plastic deformation can vary widely At the crystal scale plasticity in metals is usually a consequence of dislocations and although in most crystalline materials such defects are relatively rare are also materials where defects are numer ous and are part of the very crystal structure in such cases plastic crystallinity can result In brittle materials plasticity is caused predominantly by slippage at microcracks Plastics are so durable that they will not rot or decay as do natural products such as those made of wood As a result great amounts of discarded plastic products accumulate in the environment as waste It has been suggested that plastics could be made to decompose slowly when exposed to sun light by adding certain chemicals to them Plastics present the additional problem of being difficult to burn When placed in an incinerator they tend to melt quickly and flow downward clogging the incinerators grate they also emit harmful fumes 1141 classification There are two types of plastics thermoplastics and thermosetting polymers Thermoplastics will soften and melt if enough heat is applied examples among the truly hydrocarbon derivatives poly mers are polyethylene and polystyrene Thermosetting polymers can melt and take shape once after they have solidified they remain solid Thermoset plastics harden during the molding process and do not soften after solidifying During molding these resins acquire threedimensional crosslinked structure with predominantly strong covalent bonds that retain their strength and structure even on heating However on prolonged heating thermoset plastics get charred In the softened state these resins harden quickly with pres sure assisting the curing process Thermoset plastics are usually harder stronger and more brittle than thermoplastics and cannot be reclaimed from wastes These resins are insoluble in almost all inorganic solvents 450 Handbook of Petrochemical Processes Thermoplastics when compounded with appropriate ingredients can usually withstand several heating and cooling cycles without suffering any structural breakdown Examples of commercial thermoplastics are polystyrene polyolefin derivatives eg polyethylene and polypropylene nylon polyvinyl chloride and polyethylene terephthalate Thermoplastics are used for a wide range of applications such as film for packaging photographic magnetic tape beverage and trash contain ers and a variety of automotive parts and upholstery Advantageously waste thermoplastics can be recovered and refabricated by application of heat and pressure Thermosets are polymers whose individual chains have been chemically linked by covalent bonds during polymerization or by subsequent chemical or thermal treatment during fabrication The thermosets usually exist initially as liquids called prepolymers they can be shaped into desired forms by the application of heat and pressure Once formed these crosslinked networks resist heat softening creep and solvent attack and cannot be thermally processed or recycled Such properties make thermosets suitable materials for composites coatings and adhesive appli cations Principal examples of thermosets include epoxies phenolformaldehyde resins and unsaturated polyesters Vulcanized rubber used in the tire industry is also an example of thermo setting polymers Thermosetting polymers are usually insoluble because the crosslinking causes a tremendous increase in molecular weight At most thermosetting polymers only swell in the presence of solvents as solvent molecules penetrate the network The designation of a material as thermoplastic reflects the fact that above the glass transition temperature the material may be shaped or pressed into molds spun or cast from melts or dissolved in suitable solvents for later fashioning The polymers that are characterized by a high degree of crosslinking resist deformation and solution once their final morphology is achieved Such polymers thermosets are usually prepared in molds that yield the desired object and these polymers once formed cannot be reshaped by heating Plastics can be classified by chemical structure namely the molecular units the monomers that make up the polymers backbone and side chains Plastics can also be classified by the chemical process used in their synthesis such as condensation polyaddition and crosslinking Other clas sifications are based on qualities that are relevant for manufacturing or product design and include classes such as the thermoplastic and thermoset elastomers structural conductive and biodegrad able Plastics can also be classified by various physical properties such as density tensile strength glass transition temperature and resistance to various chemical products The use of plastics is constrained chiefly by their organic chemistry which seriously limits their hardness density and their ability to resist heat organic solvents oxidation and ionizing radiation In particular most plastics will melt or decompose when heated above 200C 390F 1142 chemical structure Common thermoplastics range in molecular weight from 20000 to 500000 while thermosets have higher almost indefinable molecular weights The molecular chains are made up of many repeating monomer units and each plastic will have several thousand repeating units In the current context the plastics are composed of polymers of hydrocarbon units with hydro carbon moieties attached to the hydrocarbon backbone which is that part of the chain in which a large number of repeat units together are linked together To customize the properties of a plastic different molecular groups are attached to the backbone This finetuning of the properties of the polymer by repeating units molecular structure has allowed plastics to become such an indispens able part of 21stcentury world Some plastics are partially crystalline and partially amorphous giving them both a melting point and one or more glass transitions temperatures above which the extent of localized molecular flexibility is substantially increased The socalled semicrystalline hydrocarbon plastics include 451 Monomers Polymers and Plastics polyethylene and polypropylene Many plastics are completely amorphous such as polystyrene and its copolymers and all thermosets 1143 ProPerties A thermoplastic thermosoftening plastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently Most hydrocarbonbased thermoplastics are high molecular weight polymers whose chains associate through weak van der Waals forces polyethylene or even stacking of aromatic rings polystyrene Thermoplastic polymers differ from thermosetting polymers since they can unlike thermosetting polymers be remelted and remolded Many thermoplastic materials are additional polymers which result from vinyl chain growth poly mers such as polyethylene and polypropylene 11431 Mechanical Properties Plastics have the characteristics of a viscous liquid and a springlike elastomer traits known as a viscoelasticity These characteristics are responsible for many of the characteristic material prop erties displayed by plastics Under mild loading conditions such as shortterm loading with low deflection and small loads at room temperature plastics usually react like springs returning to their original shape after the load is removed Under longterm heavy loads or elevated temperatures many plastics deform and flow similar to high viscous liquids although still solid Creep is the deformation that occurs over time when a material is subjected to constant stress at constant temperature This is the result of the viscoelastic behavior of plastics Stress relaxation is another viscoelastic phenomenon It is defined as a gradual decrease in stress at constant temperature Recovery is the degree to which a plastic returns to its original shape after a load is removed Specific gravity is the ratio of the weight of any volume to the weight of an equal volume of some other substance taken as the standard at a stated temperature For plastics the standard is water Water absorption is the ratio of the weight of water absorbed by a material to the weight of the dry material Many plastics are hygroscopic meaning that over time they absorb water Tensile strength at break is a measure of the stress required to deform a material prior to break age It is calculated by dividing the maximum load applied to the material before its breaking point by the original crosssectional area of the test piece Tensile modulus modulus of elasticity is the slope of the line that represents the elastic portion of the stressstrain graph Elongation at break is the increase in the length of a tension specimen usually expressed as a percentage of the original length of the specimen Compressive strength is the maximum compressive stress a material is capable of sustaining For materials that do not fail by a shattering fracture the value depends on the maximum allowed distortion Flexural strength is the strength of a material in bending expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure Flexural modulus is the ratio within the elastic limit of stress to the corresponding strain Impact is one of the most common ASTM tests for testing the impact strength of plastic materi als It gives data to compare the relative ability of materials to resist brittle fracture as the service temperature decreases The coefficient of thermal expansion is the change in unit length or volume resulting from a unit change in temperature Commonly used unit is 106 cmcmC Thermal conductivity is the ability of a material to conduct heat a physical constant for the quantity of heat that passes through a unit cube of a material in a unit of time when the difference in temperature of two faces is 1C 452 Handbook of Petrochemical Processes The limiting oxygen index is a measure of the minimum oxygen level required to support com bustion of the polymer 11432 Chemical Properties Many applications require that plastics retain critical properties such as strength toughness or appearance during and after exposure to natural environmental conditions Furthermore the rapid growth of the use of plastics in major appliances has forced an exami nation of how best to manage this material once these products have reached the end of service Integrated resource management requires that alternatives be developed to best utilize the material value of this postconsumer plastic Since the value of recovered materials will be determined by composition the value over time changes as the composition of refrigerators changes Any recycling process developed for plastics recovered should not only accommodate materials used 1520 years ago but also be adaptable for the effective reclamation of the recovery of plastics Some of the environmental effects that may damage plastic materials are as follows Corrosion of metallic materials takes place via an electrochemical reaction at a specific corro sion rate However plastics do not have such specific rates They are usually completely resistant to a specific corroding chemical or they deteriorate rapidly Polymers are attacked either by chemical reaction or solvation Solvation is the penetration of the polymer by a corroding chemical which causes softening swelling and ultimate failure Corrosion of plastics can be classified in the follow ing ways as to attack mechanism Disintegration or degradation of a physical nature due to absorption permeation solvent action or other factors Oxidation where chemical bonds are attacked Hydrolysis where ester linkages are attacked Radiation Thermal degradation involving depolymerization and possibly repolymerization Dehydration less common The absorption of UV light mainly from sunlight degrades polymers in two ways First the UV light adds thermal energy to the polymer as in heating causing thermal degradation Second the UV light excites the electrons in the covalent bonds of the polymer and weakens the bonds Hence the plastic becomes more brittle Some plastics that are originated from natural products or plastics that have natural products mixed with them are potentially susceptible to degradation by microorganisms This is not a desired property in the use stage of the plastic product However at the end of their life cycle disposal of plastics become an important issue Oxidation is a degradation phenomenon when the electrons in a polymeric bond are so strongly attracted to another atom or molecule here oxygen outside the bond that the polymer bond breaks The results of oxidation are loss of mechanical and physical properties embrittlement and discoloration Environmental stress cracking occurs when the plastic is exposed to hostile environment condi tions and mechanical stresses at the same time It is different from polymer degradation because stress cracking does not break polymer bonds Instead it breaks the secondary linkages between polymers These are broken when the mechanical stresses cause minute cracks in the polymer and they propa gate rapidly under harsh environmental conditions Nevertheless the plastic material would not fail that fast if exposed to either the damaging environment or the mechanical stresses separately Crazing In some cases an environmental chemical embrittles the plastic material even when there is no mechanical stress applied Cracks may also appear when the plastic part is stresses usu ally in tensile with no apparent environmental solvent present These phenomena are called crazing 453 Monomers Polymers and Plastics and differ from environmental stress cracking in both the direction of the cracks and the extent of the cracking The crack direction in environmental stress cracking is in the direction of molecular orientation in the part while in crazing the cracks are much more numerous in a small area but are much shorter than environmental stress cracks Permeation is molecular migration through microvoids either in the polymer or between poly mer molecules Permeability is a measure of how easily gases or liquids can pass through a material All materials are somewhat permeable to chemical molecules but plastic materials tend to be an order of magnitude greater in their permeability than metals However not all polymers have the same rate of permeation In fact some polymers are not affected by permeation 11433 Electrical Properties Resistivity of a material is the resistance that a material presents to the flow of electrical charge Dielectric strength is the voltage that an insulating material can withstand before breakdown occurs It usually depends on the thickness of the material and on the method and conditions of the test Arc resistance is the property that measures the ease of formation of a conductive path along the sur face of a material rather than through the thickness of the material as is done with dielectric strength Dielectric constant or permittivity is a measure of how well the insulating material will act as a dielectric capacitor This constant is defined as the capacitance of the material in question compared by ratio with the capacitance of a vacuum A high dielectric constant indicates that the material is highly insulating Dissipation factor of a material measures the tendency of the material to dissipate internally generated thermal energy ie heat resulting from an applied alternating electric field 11434 Optical Properties Light transmission Plastics differ greatly in their ability to transmit light The materials that allow light to pass through them are called transparent Many plastics do not allow any light to pass through These are called opaque materials Some plastic materials have light transmission proper ties between transparent and opaque These are called translucent Surface reflectance The reflection of light off the surface of a plastic part determines the amount of gloss on the surface The reflectance is dependent upon a property of materials called the index of refraction which is a measure of the change in direction of an incident ray of light as it passes through a surface boundary If the index of refraction of the plastic is near the index of air light will pass through the boundary without significant change in direction If the index of refraction between the air and the plastic is large the ray of light will significantly change direction causing some of the light to be reflected back toward its source 115 THERMOSETTING PLASTICS This group includes many plastics produced by condensation polymerization Among the important thermosets are the polyurethanes epoxy resins phenolic resins and urea and melamine formalde hyde resins 1151 Polyurethanes Polyurethanes are produced by the condensation reaction of a polyol and a diisocyanate OCNRNCO HO OHCNRNCOR O R No byproduct is formed from this reaction Toluene diisocyanate Chapter 10 is a widely used monomer Dials and trials produced from the reaction of glycerol and ethylene oxide or propylene oxide are suitable for producing polyurethanes 454 Handbook of Petrochemical Processes Polyurethane polymers are either rigid or flexible depending on the type of the polyol used For example triol derivatives derived from glycerol and propylene oxide are used for produc ing block slab foams These polyols have moderate reactivity because the hydroxy groups are predominantly secondary More reactive polyols used to produce molding polyurethane foams are formed by the reaction of polyglycols with ethylene oxide to give the more reactive primary group Other polyhydric compounds with higher functionality than glycerol threeOH are commonly used Examples are sorbitol sixOH and sucrose eightOH Triethanolamine with three OH groups is also used Diisocyanate derivatives generally employed with polyols to produce polyurethane derivatives are 24and 26toluene diisocyanate derivatives prepared from dinitro toluene derivatives Chapter 10 A different diisocyanate used in polyurethane synthesis is methylene diisocyanate MDI which is prepared from aniline and formaldehyde The diamine product is reacted with phosgene to get methylene diisocyanate The physical properties of polyurethanes vary with the ratio of the polyol to the diisocyanate For example tensile strength can be adjusted within a range of 1200600 psi elongation between 150 and 800 Improved polyurethane can be produced by copolymerization Block copolymers of polyure thanes connected with segments of isobutylene derivatives exhibit hightemperature properties hydrolytic stability and barrier characteristics The hard segments of polyurethane block polymers consist of RNHCOOH where R usually contains an aromatic moiety The major use of polyurethanes is to produce foam The density as well as the mechanical strength of the rigid and the flexible types varies widely with polyol type and reaction conditions For example polyurethanes could have densities ranging between 1 lbft3 and 6 lbft3 for the flex ible types and 1 lbft3 and 50 lbft3 for the rigid types Polyurethane foams have good abrasion resistance low thermal conductance and good load bearing characteristics However they have moderate resistance to organic solvents and are attacked by strong acids The ability of polyure thanes to acts as flame retardants can be improved by using special additives spraying a coating material such as magnesium oxychloride or by grafting a halogen phosphorous moiety to the polyol Trichloro butylene oxide is sometimes copolymerized with ethylene and propylene oxides to produce the polyol Major markets for polyurethanes are furniture transportation and building and construction Other uses include carpet underlay textural laminates and coatings footwear packaging toys and fibers The largest use for rigid polyurethane is in construction and industrial insulation due to its high insulating property Molded urethanes are used in items such as bumpers steering wheels instrument panels and body panels Elastomers from polyurethanes are characterized by toughness and resistance to oils oxidation and abrasion They are produced using shortchain polyols such as polytetramethylene glycol from 14butanediol Polyurethanes are also used to produce fibers Spandex trade name is a copolymer of polyurethane 85 and polyesters Polyurethane networks based on triisocyante and diisocyanate connected by segments consisting of polyisobutylene are rubbery and exhibit hightemperature properties hydrolytic stability and barrier characteristics 455 Monomers Polymers and Plastics 1152 ePoxy resins Epoxy resins are produced by reacting epichlorohydrin and a diphenol Bisphenol A is the diphenol generally used The reaction a ringopening polymerization of the epoxide ring is catalyzed with strong bases such as sodium hydroxide A nucleophilic attack of the phenoxy ion displaces a chlo ride ion and opens the ring The linear polymer formed is cured by crosslinking either with an acid anhydride which reacts with the OH groups or by an amine which opens the terminal epoxide rings Cresols and other bisphenols are also used for producing epoxy resins Epoxy resins have a wide range of molecular weights approximately l00010000 Those with higher molecular weight termed phenoxy are hydrolyzed to transparent resins that do not have the epoxide groups These could be used in molding purposes or crosslinked by diisocyanate deriva tives or by cyclic anhydride derivatives Important properties of epoxy resins include their ability to adhere strongly to metal surfaces their resistance to chemicals and their high dimensional stability They can also withstand tem peratures up to 500C Epoxy resins with improved stress cracking properties can be made by using toughening agents such as carboxylterminated butadieneacrylonitrile liquid polymers The carboxyl group reacts with the terminal epoxy ring to form an ester The ester with its pendant hydroxyl groups reacts with the remaining epoxide rings then more crosslinking occurs by form ing ether linkages This material is tougher than epoxy resins and suitable for encapsulating electri cal units Other uses of epoxy resins are coatings for appliance finishes auto primers adhesive and in coatings for cans and drums Interior coatings of drums used for chemicals and solvents manifest its chemical resistance 1153 unsaturated Polyesters Unsaturated polyesters are a group of polymers and resins used in coatings or for castings with sty rene These polymers normally have maleic anhydride moiety or an unsaturated fatty acid to impart the required unsaturation A typical example is the reaction between maleic anhydride and ethylene glycol Also phthalic anhydride a polyol and an unsaturated fatty acid are usually copolymerized to unsaturated polyesters for coating purposes Many other combinations in variable ratios are pos sible for preparing these resins 1154 Phenolformaldehyde resins Phenolformaldehyde resins are the oldest thermosetting polymers They are produced by a conden sation reaction between phenol and formaldehyde Although many attempts were made to use the product and control the conditions for the acidcatalyzed reaction described by Bayer in 1872 there was no commercial production of the resin until the exhaustive work by Baekeland was published in 1909 In this paper he describes the product as far superior to amber for pipe stem and similar articles less flexible but more durable than celluloid odorless and fireresistant The reaction between phenol and formaldehyde is either base or acid catalyzed and the poly mers are termed resols for the base catalyzed and novalacs for the acid catalyzed The first step in the basecatalyzed reaction is an attack by the phenoxide ion on the carbonyl carbon of formaldehyde giving a mixture of orthosubstituted and parasubstituted monomethylolphenol plus di and trisubstituted methylol phenol derivatives The second step is the condensation reac tion between the methylol phenol derivatives with the elimination of water and the formation of the polymer Crosslinking occurs by a reaction between the methylol groups and results in the formation of ether bridges It occurs also by the reaction of the methylol groups and the aro matic ring which forms methylene bridges The formed polymer is a threedimensional network thermoset 456 Handbook of Petrochemical Processes The acidcatalyzed reaction occurs by an electrophilic substitution where formaldehyde is the electrophile Condensation between the methylol groups and the benzene rings results in the forma tion of methylene bridges Usually the ratio of formaldehyde to phenol is kept less than unity to produce a linear fusible polymer in the first stage Crosslinking of the formed polymer can occur by adding more formaldehyde and a small amount of hexamethylene tetramine hexamine CH26N4 Hexamine decomposes in the presence of traces of moisture to formaldehyde and ammonia This results in crosslinking and formation of a thermoset resin Important properties of phenolic resins are their hardness corrosion resistance rigidity and resistance to water hydrolysis They are also less expensive than many other polymers Many additives are used with phenolic resins such as wood flour oils asbestos and fiberglass Fiberglass piping made with phenolic resins can operate at 150C and pressure up to 150 psi Molding applications dominate the market of phenolic resins Articles produced by injection mold ing have outstanding heat resistance and dimensional stability Compressionmolded glassfilled phenolic disk brake pistons are replacing the steel ones in many automobiles because of their light weight and corrosion resistance Phenol derivatives are also used in a variety of other applications such as adhesives paints lami nates for building automobile parts and ionexchange resins 1155 amino resins Amino resins aminoplasts are condensation thermosetting polymers of formaldehyde with either urea or melamine Melamine is a condensation product of three urea molecules It is also prepared from cyanimide at high pressure and high temperature The nucleophilic addition reaction of urea to formaldehyde produces mainly monomethylol urea and some dimethylol urea When the mixture is heated in presence of an acid condensation occurs and water is released This is accompanied by the formation of a crosslinked polymer A similar reaction occurs between melamine and formal dehyde and produces methylolmelamine derivatives A variety of methylol derivatives are possible due to the availability of six hydrogens in melamine As with urea formaldehyde resins polymerization occurs by a condensation reaction and the release of water Amino resins are characterized by being more clear and harder tensile strength than phenol derivatives However their impact strength breakability and heat resistance are lower Melamine resins have better heat and moisture resistance and better hardness than their urea analogs 457 Monomers Polymers and Plastics The most important use of amino resins is the production of adhesives for particleboard and hardwood plywood Compression and injection molding are used with amino resins to produce articles such as radio cabinets buttons and cover plates Because melamine resins have lower water absorption and better chemical and heat resistance than urea resins they are used to produce din nerware and laminates used to cover furniture Almost all molded objects use fillers such as cel lulose asbestos glass wood flour glass fiber and paper 1156 Polycyanurates A new polymer type that emerged as an important material for circuit boards are polycyan urate derivatives The simplest monomer is the dicyanate ester of bisphenol A When polymer ized it forms threedimensional densely cross linked structures through threeway cyanuric acid 246 triazinetriol The cyanurate ring is formed by the trimerization of the cyanate ester Other monomers such as hexaflurobisphenol A and tetramethyl bisphenol F are also used These poly mers are characterized by high glass transition temperatures ranging between 192C and 350C 377F and 660F The largest application of polycyanurate derivatives is in circuit boards Their transparency to microwave and radar energy makes them useful for manufacturing the housing of radar antennas of military and reconnaissance planes Their impact resistance makes them ideal for aircraft struc tures and engine pistons Thermoplastic elastomers as the name indicates are plastic polymers with the physical proper ties of rubbers They are soft flexible and possess the resilience needed of rubbers However they are processed like thermoplastics by extrusion and injection molding Thermoplastic elastomers are more economical to produce than traditional thermoset materials because fewer steps are required to manufacture them than to manufacture and vulcanize thermoset rubber An important property of these polymers is that they are recyclable Thermoplastic elastomers are multiphase composites in which the phases are intimately depressed In many cases the phases are chemically bonded by block or graft copolymerization At least one of the phases consists of a material that is hard at room temperature Currently important thermoplastic elastomers include blends of semicrystalline thermoplastic polyolefin derivatives such as propylene copolymers with ethylenepropylene terepolymer EPT elastomer Block copolymers of styrene with other monomers such as butadiene isoprene and eth ylene or ethylenepropylene are the most widely used thermoplastic elastomers Polyurethane thermoplastic elastomers are relatively more expensive than other thermoplas tic elastomers However they are noted for their flexibility strength toughness and abrasion and chemical resistance Blends of polyvinyl chloride with elastomers such as butyl are widely used in Japan Random block copolymers such as polyesters hard segments and amorphous glycol soft segments alloys of ethylene interpolymers and chlorinated polyolefin derivatives are among the evolving thermoplastic elastomers Important properties of thermoplastic elastomers are the flexibility softness and resilience However compared to vulcanizable rubbers they are inferior in resistance to deformation and sol vents Important markets for thermoplastic elastomers include shoe soles pressuresensitive adhe sives insulation and recyclable bumpers 116 SYNTHETIC FIBERS Briefly and by way of explanation a fiber is often is as a polymer with a lengthtodiameter ratio of at least 100 Browne and Work 1983 Fibers synthetic or natural are polymers with high molecular symmetry and strong cohesive energies between chains that result usually from the pres ence of polar groups Fibers possess a high degree of crystallinity characterized by the presence of stiffening groups in the polymer backbone and of intermolecular hydrogen bonds Also they 458 Handbook of Petrochemical Processes are characterized by the absence of branching or irregularly spacedependent groups that will oth erwise disrupt the crystalline formation Fibers are normally linear and drawn in one direction to make them long thin and threadlike with great strength along the fiber These characteristics permit formation of this type of polymers into long fibers suitable for textile applications Typical examples of fibers include polyesters nylons and acrylic polymers such as polyacrylonitrile and naturally occurring polymers such as cotton wool and silk Fibers fall into a class of materials that are continuous filaments or are in discrete elongated pieces similar to lengths of thread Fiber classification in reinforced plastics falls into two classes i short fibers also known as discontinuous fibers with a general aspect ratio defined as the ratio of fiber length to diameter between 20 and 60 and ii long fibers also known as continuous fibers the general aspect ratio is between 200 and 500 Thus fibers are materials that are continuous filaments or discrete elongated pieces similar to lengths of thread and are characterized by a high ratio of length to diameter They are important for a variety of applications including holding tissues together in both plants and animals There are many different kinds of fibers including textile fiber natural fibers and synthetic or humanmade fibers such as cellulose mineral polymer and microfibers Fibers can be manufactured from a natu ral origin such as silk wool and cotton or derived from a natural fiber such as rayon They may also be synthesized from certain monomers by polymerization synthetic fibers In general polymers with high melting points high crystallinity and moderate thermal stability and tensile strengths are suitable for fiber production Fibers can be spun into filaments string or rope used as a component of composite material or matted into sheets to make products such as paper and are often used in the manufacture of other materials The strongest engineering materials are generally made of fibers for example carbon fiber and ultrahigh molecular weight polyethylene Synthetic fibers can often be produced cheaply and in large amounts as compared to natural fibers but natural fibers have benefit in some applica tions especially for clothing Manmade fibers include in addition to synthetic fibers those derived from cellulose cotton wood but modified by chemical treatment such as rayon cellophane and cellulose acetate These are sometimes termed regenerated cellulose fibers Rayon and cellophane have shorter chains than the original cellulose due to degradation by alkaline treatment Cellulose acetates produced by reacting cellulose with acetic acid and modified or regenerated fibers are excluded from this book because they are derived from a plant source Fibers produced by drawing metals or glass SiO2 such as glass wool are also excluded Major fibermaking polymers are those of polyesters polyamides nylons polyacrylic deriva tives and polyolefin derivatives Polyesters and polyamides are produced by step polymerization reactions while polyacrylic derivatives and polyolefin derivatives are synthesized by chainaddition polymerization 1161 Polyester fiBers Polyesters are the most important class of synthetic fibers In general polyesters are produced by an esterification reaction of a diol and a diacid Carothers was the first to try to synthesize a polyester fiber by reacting an aliphatic diacid with a diol The polymers were not suitable because of their low melting points However he was successful in preparing the first synthetic fiber nylon 66 Polyesters can be produced by an esterification of a dicarboxylic acid and a diol a transesterifica tion of an ester of a dicarboxylic acid and a diol or by the reaction between an acid dichloride and a diol Less important methods are the selfcondensation of whydroxy acid and the ring opening of lactones and cyclic esters In selfcondensation of w hydroxy acids cyclization might compete seri ously with linear polymerization especially when the hydroxyl group is in a position to give five or sixmembered lactones 459 Monomers Polymers and Plastics Polyethylene terephthalate is produced by esterifying terephthalic acid and ethylene glycol or more commonly by the transesterification of dimethyl terephthalate and ethylene glycol The reac tion occurs in two stages i in the first stage methanol is released in at approximately 200C 370F with the formation of bis2hydroxyethyl terephthalate and ii in the second stage poly condensation occurs and excess ethylene glycol is driven away at approximately 280C 535F and at lower pressures Using excess ethylene glycol is the usual practice because it drives the equilibrium to near com pletion and terminates the acid end groups This results in a polymer with terminal OH When the free acid is used esterification the reaction is selfcatalyzed However an acid catalyst is used to compensate for the decrease in terephthalic acid as the esterification nears completion In addition to the catalyst and terminator other additives are used such as color improvers and dulling agents The molecular weight of the polymer is a function of the extent of polymerization and could be monitored through the melt viscosity The final polymer may be directly extruded or transformed into chips which are stored Batch polymerization is still used However most new processes use continuous polymerization and direct spinning An alternative route to polyethylene terephthalate is by the direct reaction of terephthalic acid and ethylene oxide The product bis2hydroxyethylterephthalate reacts in a sec ond step with terephthalic acid to form a dimer and ethylene glycol which is released under reduced pressure at approximately 300C 570F This process differs from the direct esterification and the transesterification routes in that only ethylene glycol is released In the former two routes water or methanol is coproduced and the excess glycol released Polyethylene terephthalate is an important thermoplastic However most polyethylene tere phthalate is consumed in the production of fibers Polyester fibers contain crystalline as well as noncrystalline regions The degree of crystallinity and molecular orientation are important in deter mining the tensile strength of the fiber between 18 and 22 denier and its shrinkage The degree of crystallinity and molecular orientation can be determined by Xray diffraction techniques Important properties of polyesters are the relatively high melting temperatures 265C 510F high resistance to weather conditions and sunlight and moderate tensile strength Due to the hydro phobic nature of the fiber sulfonated terephthalic acid may be used as a comonomer to provide anionic sites for cationic dyes Small amounts of aliphatic diacid derivatives such as adipic acid may also be used to increase the ability of the fibers to dyes by disturbing the crystallinity of the fiber Polyester fibers can be blended with natural fibers such as cotton and wool The products have better qualities and are used for mens and womens wear pillow cases and bedspreads Fiberfill made from polyesters is used in mattresses pillows and sleeping bags Hightenacity polymers for tire cord reinforcement are equivalent in strength to nylon tire cords and are superior because they do not flat spot Vbelts and fire hoses made from industrial filaments are another market for polyesters 1162 Polyamides Polyamides nylon fibers are the second largest group of synthetic fibers after polyesters Numbers that follow the word nylon denote the number of carbons present within a repeating unit and whether one or two monomers are being used in polymer formation For nylons using a single mono mer such as nylon 6 or nylon 12 the numbers 6 and 12 denote the number of carbons in caprolactam and laurolactam respectively For nylons using two monomers such as nylon 610 the first number 6 indicates the number of carbons in the hexamethylene diamine and the other number 10 is for the second monomer sebacic acid Polyamides are produced by the reaction between a dicarboxylic acid and a diamine eg nylon 66 ring openings of a lactam eg nylon 6 or by the polymerization of wamino acids eg nylon 11 The production of some important nylons is discussed in the following sections 460 Handbook of Petrochemical Processes 11621 Nylon 66 Nylon 66 polyhexamethyleneadipate is produced by the reaction of hexamethylenediamine and adipic acid see Chapters 9 and 10 for the production of the two monomers This produces hexa methylene diammonium adipate salt The product is a dilute salt solution concentrated to approxi mately 60 and charged with acetic acid to a reactor where water is continuously removed The presence of a small amount of acetic acid limits the degree of polymerization to the desired level The temperature is then increased to 270C300C and the pressure to approximately 16 atm which favors the formation of the polymer The pressure is finally reduced to atmospheric to permit further water removal After a total of 3 h nylon 66 is extruded under nitrogen pressure 11622 Nylon 6 Nylon 6 polycaproamide is produced by the polymerization of caprolactam The monomer is first mixed with water which opens the lactam ring and gives wamino acid The formed amino acid reacts with itself or with caprolactam at approximately 250C280C to form the polymer Temperature control is important especially for depolymerization which is directly propor tional to reaction temperature and water content 11623 Nylon 12 Nylon 12 polylaurylamide is produced in a similar way to nylon 6 by the ringopening polymeriza tion of laurolactam The polymer has a lower water capacity than nylon 6 due to its higher hydro phobic properties The polymerization reaction is slower than for caprolactam Higher temperatures are used to increase the rate of the reaction The monomer laurolactam could be produced from 159cyclododecatriene a trimer of buta diene Chapter 9 The trimer is epoxidized with peracetic acid or acetaldehyde peracetate and then hydrogenated The saturated epoxide is rearranged to the ketone with magnesium iodide MgI2 at 100C 212F This is then changed to the oxime and rearranged to laurolactam 11624 Nylon 4 Nylon 4 polybutyramide is produced by ringopening 2pyrrolidone Anionic polymerization is used to polymerize the lactam Cocatalysts are used to increase the yield of the polymer Carbon dioxide is reported to be an excellent polymerization activator Nylon 4 has a higher water absorption capacity than other nylons due to its lower hydrophobic property Caprolactam wAmino acid 461 Monomers Polymers and Plastics 11625 Nylon 11 Nylon 11 polyundecanylamide is produced by the condensation reaction of 11aminoundecanoic acid This is an example of the selfcondensation of an amino acid where only one monomer is used The monomer is first suspended in water then heated to melt the monomer and to start the reaction Water is continuously removed to drive the equilibrium to the right The polymer is finally withdrawn for storage 11626 Other Nylon Polymers Many other nylons could be produced such as nylon 5 nylon 7 nylon 610 and nylon 612 Nylon polymers are generally characterized by relatively high melting points due to the presence of the amide linkage They are also highly crystalline and the degree of crystallinity depends upon fac tors such as the polymer structure and the distance between the amide linkages An increase in polymer crystallinity increases its tensile strength abrasion resistance and modulus of elasticity Hydrogen bonding in polyamides is fairly strong and has a pronounced effect on the physical properties of the polymer such as the crystallinity melting point and water absorption For exam ple nylon 6 with six carbon atoms has a melting point of 223C 433F while it is only 190C 374F for nylon 11 This reflects the higher hydrogen bonding in nylon 6 than in nylon 11 Moisture absorption of nylons differs according to the distance between the amide groups For example nylon 4 has a higher moisture absorption than most other nylons and it is approximately similar to that of cotton This is a result of the higher hydrophilic character of nylon Nylons how ever are to some extent subject to deterioration by light This has been explained on the basis of chain breaking and crosslinking Nylons are liable to attack by mineral acids but are resistant to alkalis They are difficult to ignite and are selfextinguishing In general most nylons have remarkably similar properties and the preference of using one nylon over the other is usually dictated by economic considerations except for specialized uses Nylons have a variety of uses ranging from tire cord to carpet to hosiery The most important application is cord followed by apparel Nylon staple and filaments are extensively used in the carpet industry Nylon fiber is also used for a variety of other articles such as seat belts monofilament finishes and knitwear Because of its high tenacity and elasticity it is a valuable fiber for ropes parachutes and underwear 1163 acrylic and modacrylic fiBers Acrylic fibers are a major synthetic fiber class developed about the same time as polyesters Modacrylic fibers are copolymers containing between 35 and 85 acrylonitrile Acrylic fibers contain at least 85 acrylonitrile Orlon is an acrylic fiber developed by DuPont in 1949 Dynel is a modacrylic fiber developed by Union Carbide in 1951 Polyacrylics are produced by copolymerizing acrylonitrile with other monomers such as vinyl acetate vinyl chloride and acrylamide Solution polymerization may be used where water is the solvent in the presence of a redox catalyst Free radical or anionic initiators may also be used The produced polymer is insoluble in water and forms a precipitate Copolymers of acrylonitrile are sen sitive to heat and melt spinning is not used Solution spinning wet or dry is the preferred process where a polar solvent such as dimethylformamide is used In dry spinning the solvent is evaporated and recovered Dynel a modacrylic fiber is produced by copolymerizing vinyl chloride with acrylonitrile Solution spinning is also used where the polymer is dissolved in a solvent such as acetone After the solvent is evaporated the fibers are washed and subjected to stretching which extends the fiber 410 times of the original length 462 Handbook of Petrochemical Processes Acrylic fibers are characterized by having properties similar to wool and have replaced wool in many markets such as blankets carpets and sweaters Important properties of acrylics are resis tance to solvents and sunlight resistance to creasing and quick drying Acrylic fiber breaking strength ranges between 22000 and 39000 psi and they have a water absorption of approximately 5 Dynel due to the presence of chlorine is less flammable than many other synthetic fibers Major uses of acrylic fibers are woven and knitted clothing fabrics for apparel carpets and upholstery 1164 GraPhite fiBers Carbon fibers are special reinforcement types having a carbon content of 9299 ww They are prepared by controlled pyrolysis of organic materials in fibrous forms at temperatures ranging from 1000C to 3000C 1800F5400F The commercial fibers are produced from rayon polyacrylonitrile and petroleum pitch When acrylonitrile is heated in air at moderate temperatures 220C 430F hydrogen cyanide HCN is emanated Further heating above 1700C 3100F in the presence of nitrogen for a period of 24 h produces carbon fiber Carbon fibers are characterized by high strength stiffness low thermal expansion and thermal and electrical conductivity which makes them an attractive substitute for various metals and alloys 1165 PolyProPylene fiBers Polypropylene fibers represent a small percent of the total polypropylene production Most polypropylene is used as a thermoplastic The fibers are usually manufactured from isotac tic polypropylene Important characteristics of polypropylene are high abrasion resistance strength low static buildup and resistance to chemicals Crystallinity of fibergrade polypropylene is mod erate and when heated it starts to soften at approximately 145C 293F and then melts at 170C 338F The high melting points of polypropylene polymers are attributed to low entropy of fusion arising from stiffening of the chain Polyethylene fiber properties depend markedly on the crystallinity or density of the polymer although highstrength fibers can be made from linear polyethylene resiliency properties are poor tensile properties are highly timedependent and endurance under sustained loading is very poor On the other hand polypropylene fibers have good stressendurance properties excellent recov ery from high extensions and fairtogood recovery properties at low strains recovery at low strains is shown to depend on the extent of fiber orientation and annealing Anomalies in the change of the sonic modulus of polypropylene yarns during extension and relaxation are noted and interpreted in terms of structure changes in the crystalline phase The high melting temperature of 235C 455F for poly4methyl1pentene appears to be due to its low entropy of melting and fibers from this polymer are characterized by low tenacity when tested at elevated temperatures Crystalline polystyrene fibers have relatively good retention of tenacity at elevated temperatures and are characterized by excellent resiliency at low strains good washwear characteristics in cotton blends and low abrasion resistance 117 SYNTHETIC RUBBER Synthetic rubber an elastomer is a longchain polymer with special chemical and physical as well as mechanical properties These materials have chemical stability high abrasion resistance strength and good dimensional stability Many of these properties are imparted to the original polymer through crosslinking agents and additives An important property of elastomeric materi als is their ability to be stretched at least twice their original length and to return back to nearly their original length when released 463 Monomers Polymers and Plastics Natural rubber is a polymer of isoprenemost often cis14polyisoprenewith a molecular weight of 1000001000000 Typically a few percent of other materials such as proteins fatty acids resins and inorganic materials are found in highquality natural rubber Some natural rub ber sources called gutta percha ie trees of the genus Palaquium in the family Sapotaceae and the rigid natural latex produced from the sap of these trees particularly from Palaquium gutta are composed of trans14polyisoprene a structural isomer that has similar but not identical properties Isoprene 2methyl13butadiene is a common organic compound with the formula CH2CCH3 CHCH2 Under standard conditions isoprene is a colorless liquid and is the monomer of natural rubber as well as a precursor to an immense variety of other naturally occurring compounds Synthetic rubber is any type of artificial elastomer invariably a polymer An elastomer is a mate rial with the mechanical or material property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation Synthetic rubber serves as a substitute for natural rubber in many cases especially when improved material properties are required Synthetic rubber can be made from the polymerization of a variety of monomers including iso prene 2methyl13butadiene 13butadiene and isobutylene methylpropene with a small per centage of isoprene for crosslinking These and other monomers can be mixed in various desirable proportions to be copolymerized for a wide range of physical mechanical and chemical properties The monomers can be produced pure and the addition of impurities or additives can be controlled by design to give optimal properties Polymerization of pure monomers can be better controlled to give a desired proportion of cis and trans double bonds Natural rubber is an elastomer constituted of isoprene units These units are linked in a cis14configuration that gives natural rubber the outstanding properties of high resilience and strength Natural rubber occurs as a latex water emulsion and is obtained from Hevea brasiliensis a tree that grows in Malaysia Indonesia and Brazil Charles Goodyear was the first to discover that the latex could be vulcanized crosslinked by heating with sulfur or other agents Vulcanization of rubber is a chemical reaction by which elastomer chains are linked together The longchain mol ecules impart elasticity and the crosslinks give load supporting strength Synthetic rubbers include elastomers that could be crosslinked such as polybutadiene polyiso prene and ethylenepropylenediene terepolymer It also includes thermoplastic elastomers that are not crosslinked and are adapted for special purposes such as automobile bumpers and wire and cable coatings These materials could be scraped and reused However they cannot replace all tra ditional rubber since they do not have the wide temperature performance range of thermoset rubber The major use of rubber is for tire production Nontire consumption includes hoses footwear molded and extruded materials and plasticizers 1171 styreneButadiene ruBBer Styrenebutadiene rubber is the most widely used synthetic rubber It can be produced by the copolymerization of butadiene 75 and styrene 25 using free radical initiators A random copolymer is obtained The microstructure of the polymer is 6068 trans polymer 1419 cis polymer and 1721 12 configuration Wet methods are normally used to characterize Isoprene 464 Handbook of Petrochemical Processes polybutadiene polymers and copolymers Solidstate nuclear magnetic resonance spectroscopy provides a more convenient way to determine the polymer microstructure Currently more styrenebutadiene rubber is produced by copolymerizing the two monomers with anionic or coordination catalysts The formed copolymer has better mechanical properties and a narrower molecular weight distribution A random copolymer with ordered sequence can also be made in solution using butyllithium provided that the two monomers are charged slowly Block copo lymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts Butadiene polymerizes first until it is consumed then styrene starts to polymerize Styrenebutadiene rubber produced by coordination catalysts has better tensile strength than that produced by free radical initiators The main use of styrenebutadiene rubber is for tire production Other uses include footwear coatings carpet backing and adhesives 1172 nitrile ruBBer Nitrile rubber NBR is a copolymer of butadiene and acrylonitrile It has the special property of being resistant to hydrocarbon liquids The copolymerization occurs in an aqueous emulsion When free radicals are used a random copolymer is obtained Alternating copolymers are produced when a ZieglerNatta catalyst is employed Molecular weight can be controlled by adding modifiers and inhibitors When the polymerization reaches approximately 65 the reaction mixture is vacuum distilled in presence of steam to recover the monomer The ratio of acrylonitrilebutadiene could be adjusted to obtain a polymer with specific properties Increasing the acrylonitrile ratio increases oil resistance of the rubber but decreases its plasticizer compatibility Nitrile rubber is produced in different grades depending on the end use of the polymer Low acrylonitrile rubber is flexible at low temperatures and is generally used in gaskets 0rings and adhesives The medium type is used in less flexible articles such as kitchen mats and shoe soles High acrylonitrile polymers are more rigid and highly resistant to hydrocarbon derivatives and oils and are used in fuel tanks and hoses hydraulic equipment and gaskets 1173 PolyisoPrene Natural rubber is a stereoregular polymer composed of isoprene units attached in a cis con figuration This arrangement gives the rubber high resilience and strength Isoprene can be polymerized using free radical initiators but a random polymer is obtained As with butadiene polymerization of isoprene can produce a mixture of isomers However because the isoprene molecule is asymmetrical the addition can occur in 12 14 and 34 positions Six tactic forms are possible from both 12 and 34 addition and two geometrical isomers from 14 addition cis and trans Stereoregular polyisoprene is obtained when ZieglerNatta catalysts or anionic initiators are used The most important coordination catalyst is αtitanium trichloride cocatalyzed with alumi num alkyl derivatives The polymerization rate and cis content depends upon AlTi ratio which should be greater than one Lower ratios predominantly produce the trans structure Polyisoprene is a synthetic polymer elastomer that can be vulcanized by the addition of sulfur cisPolyisoprene has properties similar to that of natural rubber It is characterized by high tensile strength and insensitivity to temperature changes but it has low abrasion resistance It is attacked by oxygen and hydrocarbon derivatives transPolyisoprene is similar to Gutta percha which is pro duced from the leaves and bark of the Sapotaceae tree It has different properties from the cis form and cannot be vulcanized Few commercial uses are based on transpolyisoprene Important uses of cispolyisoprene include the production of tires specialized mechanical prod ucts conveyor belts footwear and insulation 465 Monomers Polymers and Plastics 1174 PolychloroPrene Polychloroprene neoprene rubber is the oldest synthetic rubber It is produced by the polymeriza tion of 2chloro13butadiene in a water emulsion with potassium sulfate as a catalyst The product is a random polymer that is vulcanized with sulfur or with metal oxides zinc oxide magnesium oxide etc Vulcanization with sulfur is very slow and an accelerator is usually required Neoprene vulcanizates have a high tensile strength excellent oil resistance better than natural rubber and heat resistance Neoprene rubber could be used for tire production but it is expensive Major uses include cable coatings mechanical goods gaskets conveyor belts and cables 1175 Butyl ruBBer Butyl rubber is a copolymer of isobutylene 975 and isoprene 25 The polymerization is car ried out at low temperature below 95C 139F using aluminum chloride AlCl3 co catalyzed with a small amount of water The cocatalyst furnishes the protons needed for the cationic polymerization AlCl H O H AlCl OH 3 2 3 The product is a linear random copolymer that can be cured to a thermosetting polymer This is made possible through the presence of some unsaturation from isoprene Butyl rubber vulcanizates have tensile strengths up to 2000 psi and are characterized by low permeability to air and a high resistance to many chemicals and to oxidation These properties make it a suitable rubber for the production of tire inner tubes and inner liners of tubeless tires The major use of butyl rubber is for inner tubes Other uses include wire and cable insulation steam hoses mechanical goods and adhesives Chlorinated butyl is a low molecular weight polymer used as an adhesive and a sealant 1176 ethyleneProPylene ruBBer Ethylenepropylene rubber EPR is a stereoregular copolymer of ethylene and propylene Elastomers of this type do not possess the double bonds necessary for crosslinking A third monomer usually a monoconjugated diene is used to provide the residual double bonds needed for crosslinking The 14hexadiene and ethylidene norbornene are examples of these dienes The main polymer chain is completely saturated while the unsaturated part is pending from the main chain The product elastomer termed ethylenepropylene terepolymer can be crosslinked using sulfur Crosslinking ethylenepropylene rubber is also possible without using a third component a diene This can be done with peroxides Important properties of vulcanized ethylenepropylene rubber and ethylenepropylene terepoly mer include resistance to abrasion oxidation and heat and ozone but they are susceptible to hydro carbon derivatives The main use of ethylenepropylene rubber is to produce automotive parts such as gaskets mechanical goods wire and cable coating It may also be used to produce tires REFERENCES Ali MF El Ali BM and Speight JG 2005 Handbook of Industrial Chemistry Organic Chemicals McGrawHill New York Austin GT 1984 Chapters 34 35 and 36 Shreves Chemical Process Industries 5th Edition McGraw Hill New York Braun D Cherdron H and Ritter H 2001 Polymer Synthesis Theory and Practice Fundamentals Methods Experiments SpringerVerlag Berlin 466 Handbook of Petrochemical Processes Browne CL and Work RW 1983 Chapter 11 ManMade Textile Fibers In Riegels Handbook of Industrial Chemistry JA Kent Editor 8th Edition Van Nostrand Reinhold New York Carraher CE Jr 2003 Polymer Chemistry 6th Edition Revised and Expanded Marcel Dekker Inc New York Grabowska H Kaczmarczyk W and Wrzyszcz J 1989 Synthesis of 26xylenol by alkylation of phenol with methanol Applied Catalysis 472 351355 Jones RW and Simon RHM 1983 Chapter 10 Synthetic plastics In Riegels Handbook of Industrial Chemistry 8th Edition JA Kent Editor Van Nostrand Reinhold New York Lokensgard E 2010 Industrial Plastics Theory and Applications Delmar Cengage Learning Clifton Park NY Matar S and Hatch LF 2001 Chemistry of Petrochemical Process 2nd Edition Gulf Professional Publishing Elsevier BV Amsterdam Odian G 2004 Principles of Polymerization 4th Edition John Wiley Sons Inc New York Rudin A 1999 The Elements of Polymer Science and Engineering 2nd Edition Academic Press Inc New York Schroeder EE 1983 Chapter 9 Rubber In Riegels Handbook of Industrial Chemistry 8th Edition JA Kent Editor Van Nostrand Reinhold New York 467 12 Pharmaceuticals 121 INTRODUCTION The modern pharmaceutical industry can trace its beginnings to two sources i local apothecaries now called chemists in the United Kingdom and pharmacists in the United Statesthat expanded from their traditional role distributing botanical drugs such as morphine and quinine to wholesale manufacture in the mid1800s By the late 1880s German dye manufacturers had perfected the purification of individual organic compounds from coal tar and other mineral sources and had also established fundamental methods in organic chemical synthesis The development of synthetic chemical methods allowed scientists to systematically vary the structure of chemical substances and growth in the emerging science of pharmacology expanded their ability to evaluate the biologi cal effects of these structural changes It is from these early beginning and the recognition of the wealth of chemical that could be produced from crude oil that led to the rapid expansion of the medicinesfromcrudeoil industry as an extension of the petrochemical industry From the previous chapters it is obvious that petrochemicals play many roles in modern life because they are used to create resins films and plastics In addition petrochemicals also play a major role in the production of medicines because they are used to produce chemicals such as i phenol and cumene that are used to create a substance that is essential for manufacturing of penicillinan extremely important antibioticand aspirin ii petrochemical resins are used to purify medicines speeding up the manufacturing process iii resins made from petrochemi cals are used in the manufacture of medicines including treatments for aids arthritis and cancer iv plastics and resins which are used to make devices such as artificial limbs and skin v and plastics are used to make a wide range of medical equipment including bottles disposable syringes and much more Hess et al 2011 Thus it would be remiss not to mention the role of petrochemical intermediates in the manufac ture of pharmaceutical products Petrochemical solutions and petrochemicals are the secondphase products and solutions that originate from crude oil following a number of refining methods Crude oil works as the fundamental portal ingredient which offers petrochemical products and byproducts after an extensive procedure of refining which takes place in various oil refineries Petrochemicals play an important role in the production of medicines For example most medi cines contain two types of ingredients i the active ingredient which is composed of one or more compounds manufactured synthetically or extracted and purified from plant or animal sources and the active ingredient is the chemical that reacts with your body to produce a therapeutic effect and ii the inactive ingredients which are typically the additives present in the medication which are normally inactiveinert and which may have been added as preservatives flavoring agents coloring sweeteners and sorbents Also for the purposes of this chapter there are two general definitions that are used i a medi cine or medication which is a chemical that is available as an overthecounter OTC purchase at a pharmacy and ii a drug which is available only by prescription from an authorized person Over thecounter medicine is also known as overthecounter or nonprescription medicine All of these terms refer to medicine that you can buy without a prescription They are safe and effective when you follow the directions on the label and as directed by your health care professional Examples of the former overthecounter medicines are the subject of this chapter Table 121 through pub lished synthesis while the latter ie medicines that are available only by prescription are not included in the subject of this chapter 468 Handbook of Petrochemical Processes In addition many synthetic routes to medicines are not published because of proprietary issues as well as dangeroustohealth issues There are also the questions of nomenclature which can be troublesome as well as confusing Because of proprietary issues even overthecounter medications have names that often bear no relationship to the actual chemical for industrial usage In all cases where possible the trade name and the chemical name of the medication are presented A word of caution should be added here Although relatively easy to obtain overthecounter medications can still carry a risk even though they do not require a prescription There is the pos sibility of side effects interactions with other medications or harm due to excessive doses All patients should consult with their doctor pharmacist or other healthcare provider if they have additional questions concerning use of overthecounter medications Thus medications usually referred to as drugs that change behavior patterns are not included in this chapter It is not the purpose of this chapter to produce methods by which drugs especially harmful medications often referred to as drugs can be synthesized but to present to the reader a section of the published synthetic methods that results in the production of commonly used medica tions For this it will also be pointed out the starting materials or other constituents that originated from petrochemical processes A medicine is a chemical substance that has known biological effects on humans or other ani mals used in the treatment cure mitigation prevention or diagnosis of disease or used to enhance physical or mental wellbeing Medicines may be used for a limited duration or on a regular basis for chronic disorders and are generally taken to cure andor relieve any symptoms of an illness or medical condition or may be used as prophylactic medicines One or more of the constituents of the medicine usually interacts with either normal or abnormal physiological process in a biological sys tem and produces a desired and positive biological action However if the effect causes harm to the body the medicine is classified as a poison and is no longer a medication The medications can treat different types of diseases such as infectious diseases noninfectious diseases and nondiseases alleviation of pain prevention of pregnancy and anesthesia Many of the modern medications are prepared from petrochemical starting materials Table 122 TABLE 121 Examples of Readily Available OvertheCounter Medications 469 Pharmaceuticals Petrochemicals have contributed to the development of many medications for diverse indications While most US pharmaceutical companies have reduced or eliminated inhouse natural product groups new paradigms and new enterprises have evolved to carry on a role for natural products in the pharmaceutical industry Many of the reasons for the decline in popularity of natural products are being addressed by the development of new techniques for screening and production This chap ter aims to inform pharmacologists of current strategies and techniques that make petrochemicals a continuing and viable strategic choice for use in medication synthesis programs The use of petroleum products in not new As early as 1500 BC the use of asphalt for medicinal purposes and when mixed with beer as a sedative for the stomach has been recorded It is also recorded in the code of Hammurabi that hot asphalt was to be poured over the head of a miscreant as a form of punishment In more modern times medicinal oil sometimes referred to as paraffin oil distilled from crude oil was prescribed to lubricate the alimentary tract where coal dust was likely to collect From these humble beginnings crude oil has through the production of petrochemicals become a major contributor to the pharmaceutical industry For example the first analgesics and antipyretics exemplified by phenacetin and acetanilide were simple chemical derivatives of ani line and pnitrophenol both of which were byproducts from coal tar and nor from crude oil An extract from the bark of the white willow tree had been used for centuries to treat various fevers and inflammation The active principle in white willow Salicin or salicylic acid had a bitter taste TABLE 122 Selection of Common Petrochemical Products Used in the Pharmaceutical Industry Chemical Processes Ammonia aqueous C F B Aniline C Benzene C nButyl acetate C F nButyl alcohol C F B Chloroform C F B Chloromethane C Cyclohexane C 12Dichloroethane C B Diethyl ether C B Ethanol C F B Ethyl acetate C F B Ethylene glycol C B Formaldehyde C F B nHeptane C F B nHexane C F B Methanol C F B Methylene chloride C F B 2Methylpyridine C Phenol C F B nPropanol C B Pyridine C B Toluene C F B Xylenes C C chemical synthesis F fermentation B biological or natural extraction 470 Handbook of Petrochemical Processes and irritated the gastric mucosa but a simple chemical modification was much more palatable This was acetylsalicylic acid better known as aspirin the first drug that could be generally administered for a variety of ailments At the start of the 20th century the first of the barbiturate family of drugs entered the pharmacopeia leading to the start of the evolution of the modern pharmaceutical indus try Mahdi et al 2006 Fuster and Sweeny 2011 Jones 2011 Wick 2012 Aronson 2013 The pharmaceutical industry includes the manufacture extraction processing purification and packaging of chemical materials to be used as medications for humans or animals Gad 2008 Pharmaceutical manufacturing is divided into two major stages the production of the active ingre dient or medicine primary processing or manufacture and secondary processing the conversion of the active medicines into products suitable for administration The products are available as tablets capsules liquids in the form of solutions suspensions emulsions gels or injectables creams usually oilinwater emulsions ointments usually water in oil emulsions and aerosols which contain inhalable products or products suitable for external use Propellants used in aerosols include chlorofluorocarbons which are being phased out Recently butane has been used as a propellant in externally applied products The major manufactured groups include i antibiotics such as penicillin streptomycin tetracyclines chloramphenicol and antifungals ii other synthetic drugs including sulfa drugs antituberculosis drugs antileprotic drugs analgesics anesthetics and antimalarials iii vitamins iv synthetic hormones v glandular products vi drugs of vegetable origin such as quinine strychnine and brucine emetine and digitalis vii glycosides and viii vaccines Other pharmaceutical chemicals such as calcium gluconate ferrous salts nikethamide glycerophosphates chloral hydrate saccharin antihistamines including meclozine and buclozine tranquilizers including meprobamate and chloropromoazine antifilarials diethyl carbamazine citrate and oral antidiabetics including tolbutamide chloropropamide and surgical sutures and dressings The principal manufacturing steps are i preparation of process intermediates ii introduction of functional groups iii coupling and esterification iv separation processes such as washing and stripping and v purification of the final product Additional product preparation steps include granulation drying tablet pressing printing and coating filling and packaging The main pharmaceutical groups manufactured include i proprietary ethical products or pre scription only medicines which are usually patented products ii general ethical products which are basically standard prescriptiononly medicines made to a recognized formula that may be specified in standard industry reference books and iii overthe counter or nonprescription prod ucts For those readers interested in the synthesis of medications available by prescription there are citations available for example Karaman 2015 Flick et al 2017 and references cited therein Finally it is not the purpose of this chapter to show preference for any type of medication but it is the purpose to show the methods by which selected overthecounter medicines can be produced from crude oil 122 MEDICINAL OILS FROM PETROLEUM This section deals with the synthesis of the bulk fractions that have been used and in some coun tries continue to be used as medications as well the individual molecular active ingredients of medications and their usage in drug formulations to deliver the prescribed dosage Formulation is also referred to as galenical production A galenical is a simple cure in the form of a vegetable or herbal remedy as prescribed by Galen Aelius Galenus or Claudius Galenus or better known to the Western world as Galen of Pergamon 129217 AD a Greek physician surgeon and philosopher in the Roman Empire The petroleum industry is first encountered in the archaeological record near Hit Tuttul in what is now Iraq Hit is on the banks of the Euphrates River and is the site of an oil seep known locally as The Fountains of Pitch There the bitumen was quarried for use as mortar between building stones as early as 6000 years ago and was also used as a waterproofing agent for baths pottery and boats 471 Pharmaceuticals The Babylonians caulked their ships with bitumen and in Mesopotamia around 4000 BC bitumen was used as caulking for ships a setting for jewels and mosaics and an adhesive to secure weapon handles On the human side of bitumen use the Egyptians used it for embalming while the ancient Persians the 10thcentury Sumatrans and preColumbian natives of the Americas believed that crude oil had medicinal benefits From that time the ancient literature acts as a record of the use of petroleum In fact it was the Persian scientist Ibn Sina c9801037 who was known in the West as Avicenna discussed medicinal petroleum in his enormously influential encyclopedia of medicine The translation of this work into Latin spread that knowledge into Europe where it reached Constantinus Africanus c10201087 who may have been the first Latin writer to use the word petroleumthe word was also used by Georgius Agricola Georg Bauer in his work entitled De Natura Fossilium published 1546 From that time there was a tradition of employing petroleum in medicine which included concoctions recommended for eye diseases reptile bites respiratory problems hysteria and epi lepsy Mixing petroleum and the ashes of cabbage stalks was recommended for the treatment of scabies and a preparation of petroleum was prescribed to warm the brain by applying it to the forehead Marco Polo 12541324 reported that bitumen was used in the Caspian Sea region to treat camels for mange and the first oil exported from Venezuela in 1539 was intended as a gout treatment for the Holy Roman Emperor Charles V reigned 15191556 The native North Americans collected oil for medicines and European settlers found its pres ence in the water supplies a contamination but they learned to collect it to use as fuel in their lamps Native Americans also traded crude oil that they obtained from oil seeps in upstate New York among other places The Seneca tribe traded oil for so long that all crude oil was referred to as Seneca Oil which was reputed to have great medicinal value In fact in 1901 a petroleum technology text was published in which it was noted that petroleum was an excellent remedy for diphtheria Purdy 1957 The members of the Seneca tribe also used crude oil for body paint and for ceremonial fires Several historical factors evolved to change the use of crude oil The kerosene lamp invented in 1854 ultimately created the first largescale demand for petroleum Kerosene was first made from coal but by the late 1880s most was derived from crude oil In 1859 at Titusville Penn Col Edwin Drake drilled the first successful well through rock and produced crude oil However bulk oil products from petroleum still find a variety of uses in health and human service roles ie cos metics and because of the imperative of these products a brief discussion of the various types of products and their roles within the various human communities is also included herethe oil products being considered to be bulk petrochemical products In fact mineral oil and petrolatum are petroleum byproducts used in many creams and topical pharmaceuticals Tar also called resid asphalt pitch for psoriasis and dandruff is also produced from petroleum Most pharmaceuticals are complex organic compounds which have their basis in smaller simpler precursor organic molecules that are petroleum byproducts 1221 mineral oilwhite oil Some of the imprecision in the definition of the names such as mineral oil and white oil reflect the use of the oil by the buyers and by the sellers In fact mineral oils have numerous definitions and are substances by nature also complex being derived from crude oil The term mineral oil includes many petroleum products and applications including fuel and medicinal white oils and can range from less refined only straightrun to highly refined severely hydrotreated with a composition and toxicity that depend on the refining history The first use of the term mineral oil was in 1771 and prior to the late 19th century the chemi cal science to determine such makeup was unavailable White oils are highly refined odorless tasteless and have excellent color stability They are chemically and biologically stable and do not support bacterial growth The inert nature of mineral makes it easy to work with as they lubricate 472 Handbook of Petrochemical Processes sooth soften and hold in moisture formulations These oils are used in a variety of product lines such as antibiotics baby oils lotions creams shampoos sunscreens and tissues White oils are manufactured from highly refined base oils and consist of saturated paraffin deriv atives and cycloparaffin derivatives The refinement process ensures complete removal of aromat ics sulfur and nitrogen compounds The technologies employed result in products that are highly stable over time besides being hydrophobic colorless odorless and tasteless White mineral oils are extensively used as bases for pharmaceuticals and personal care products The inertness of the prod uct offers properties such as good lubricity smoothness and softness and resistance to moisture in the formulations The products are also used in the polymer processing and plastic industry such as polystyrene polyolefin and thermoplastic elastomers The oil controls the melt flow behavior of the finished polymer besides providing release properties Very often the oils also impart improvement in physical characteristics of the finished product In the refining process the feedstock is hydrotreated and the hydrotreated feedstock exits hydrotreater and conducted to fractionating column Lowboiling constituents especially hydrogen sulfide and ammonia are removed and the hydrotreated product is then conducted to a second hydrotreater where it is hydrotreated using process parameters that may be the same or different from the hydrotreating conditions in the first hydrotreater The product from the second hydrotreater is sent to a catalytic dewaxing unit after which the dewaxed product exits dewaxing unit and is sent to a hydrofinishing unit The product is analyzed for the CnCp naphthene carbonparaffin carbon ratio When the desired CnCp ratio is attained typically in the range 045065 the medicinal white product is finished Mineral oil sold widely and cheaply in the United States is not sold as such in Britain but is sold under the trade names paraffinum perliquidum for light mineral oil and paraffinum liquidum or paraffinum subliquidum for the higher density more viscous types of the oil The term Paraffinum Liquidum is often seen on the ingredient lists of baby oil and cosmeticsBritish aromatherapists commonly use the term white mineral oil In lubricating oil technology mineral oil is termed from groups 12 worldwide and group 3 in certain regions because the high end of group 3 mineral lubri cating oils are of high purity and exhibit properties similar to polyalphaolefin derivatives which constitute the group 4 synthetic oils Speight and Exall 2014 Mineral oil is any of various colorless odorless light mixtures of higher molecular weight alkane derivatives from a mineral source particularly as a distillate from petroleum The name mineral oil by itself is imprecise having been used for many specific types of oils over the past several centuries Other names similarly imprecise include white oil paraffin oil liquid paraffin a highly refined medical grade paraffinum liquidum Latin and liquid petroleum The product popularly called baby oil is a mineral oil to which scented ingredients perfumes have been added Most often mineral oil is a liquid byproduct of refining crude oil to produce an array of various petroleum products Parkash 2003 Gary et al 2007 Speight 2011 2014 2017 Hsu and Robinson 2017 This type of mineral oil is a transparent colorless waterwhere lowdensity oil approxi mately 08 gcm3 composed mainly of alkane derivatives and cycloalkane derivatives related to petroleum jelly White oil is highly refined oil which is colorless tasteless and odorless It is espe cially refined to obtain the highest degree of purity for their use in those applications requiring direct contact with food The purified oil is recommended for use in the manufacture of pharmaceutical and cosmetic preparations such as ointments complexion creams haircare products laxatives baby oils and as carriers in the preparation of many curative drugs It is also used to coat eggs and fruit to make them shinier It is also used to lubricate baking equipment so that food does not stick to it 1222 Petroleum Jelly Petroleum jelly is a mixture of hydrocarbons having a melting point usually close to human body temperature approximately 37C 99F Petroleum jelly is typically composed of paraffin wax microcrystalline wax and mineral oil in varying amounts The composition of highly refined 473 Pharmaceuticals constituents and their physical properties vary considerably according to the origin of the raw mate rial and the refining methods The solid or liquid elements of the hydrocarbons may contain 1660 carbon atoms with significantly different molecular weights therefore the possible structures are extremely varied and their number practically infinite Vaseline is a brand name for petroleum jellybased products which include plain unaltered petro leum jelly and a selection of skin creams soaps lotions cleansers and deodorants to provide various types of skincare and protection by minimizing friction or reducing moisture loss or by functioning as a grooming aid It is believed that the use of petroleum jelly comes from a product known as rod wax that was used by early oil workers in Titusville Pennsylvania to heal cuts and burns In many countries the word vaseline vasenol in some countries is used as generic for petroleum jelly Petrolatum a related product to petroleum jelly although the names are often used interchange ably is a byproduct of petroleum refining with a melting point close to body temperaturebody temperature ranges from 361C 97F to 372C 99F in older adults the typical body tempera ture is lower than 362C 986F Petrolatum softens upon application and forms a waterrepellant film around the applied area creating an effective barrier against the evaporation of the skins natural moisture and foreign particles or microorganisms that may cause infection Petrolatum is odorless and colorless and it has an inherently long shelf life These qualities make petrolatum a popular ingredient in skincare products and cosmetics Petroleum jelly has been and continues to be manufactured from the highestboiling crude oil refinery fraction resid However because of the occurrence of cancerforming polynuclear aro matic derivatives as well as other constituents that are risky to health in resids number of cleanup purification steps are required to meet the stringent requirements of a product used for direct skin and mouth contact Although not a comprehensive list these cleanup steps can include propane deas phalting hydrogenation solvent dewaxing and fixed bed adsorption using adsorbents such as baux ite and carbon In the simplest process paraffin wax is introduced into a reaction vessel after which microcrystalline wax ie wax with a very fine crystalline structure is added The mixture is melted with continuous mixing and the temperature is maintained between 120C and 130C 248F and 266F Liquid paraffin is added with continuous stirring 150200 rpm at constant temperature so that ingredients are mixed together to form emulsion or gel after which the mass is cooled Briefly bauxite is a complex mineral that is often claimed to be alumina Al2O3 but which in reality consists mostly the aluminum minerals gibbsite AlOH3 boehmite γAlOOH and dia spore αAlOOH mixed with the two oxides of iron namely goethite and hematite as well as the aluminum clay mineral kaolinite as well as small amounts of anatase TiO2 and ilmenite FeTiO3 or FeOTiO2 Petroleum jelly can also be produced by way of synthesis gas in which the process for conversion of synthesis gas to hydrocarbon products is adapted to produce higher molecular weight paraffin derivatives Abhari 2010 Thus petroleum jelly is a subtle balance of liquid and solid hydrocarbons The crystalline struc ture of the substances in its composition is one of the basic qualitative elements The role of the amorphous solid hydrocarbons is in fact to retain in a sufficiently dense fibrous mesh oily hydro carbons of a generally high molecular weight Petroleum jelly is flammable only when heated to the liquid state at which point the fumes will combust but the liquid does not combust not the liquid itself so a wick material like leaves bark or small twigs is needed to ignite petroleum jelly Petroleum jelly is colorless or has a pale yellow color when not highly distilled translucent and devoid of taste and smell when pure It does not oxidize on exposure to the air and is not readily acted on by chemical reagents and is insoluble in water It is soluble in dichloromethane CH2Cl2 chloroform CHCl3 benzene C6H6 diethyl ether CH3CH2OCH2CH3 and carbon disulfide CS2 Petroleum products generally defined collectively as petrolatum have a long history in medical applications and that heritage continues as pharmaceutical grade petrolatum constituents are com mon components in a variety of balms ointments creams moisturizers haircare products and other products where a virtually odorless additive that helps retain and even lockin moisture is desired 474 Handbook of Petrochemical Processes According to the requirements of the International Nomenclature of Cosmetic Ingredients which lists and assigns the INCI names of cosmetic ingredients there are two possible designations depending on the manufacturing method of the petroleum jelly i if the product is manufactured by blending paraffin oil wax and mineral paraffin the INCI name of the mixture is composed of all the INCI names of the ingredients paraffinum liquidum and cera microcristallina and paraffin or ii if the product is manufactured by directly refining the crude oil or its derivatives of crude oil the INCI name is petrolatum 1223 Paraffin wax Paraffin wax is a white or colorless soft solid wax that is composed of a complex mixture of hydrocarbons with the following general properties i nonreactive ii nontoxic iii water bar rier and iv colorless Paraffin wax is characterized by a clearly defined crystal structure and has the tendency to be hard and brittle with a melting point typically in the range 50C70C 122F158F On a more specific basis petroleum wax is of two general types i paraffin wax in petroleum distillates and ii microcrystalline wax in petroleum residua The melting point of wax is not directly related to its boiling point because waxes contain hydrocarbons of different chemical nature Nevertheless waxes are graded according to their melting point and oil content In the process for wax manufacture known as wax sweating Parkash 2003 Gary et al 2007 Speight 2011 2014 2017 Hsu and Robinson 2017 a cake of slack wax paraffin wax from a solvent dewaxing operation is slowly warmed to a temperature at which the oil in the wax and the lower melting waxes become fluid and drip or sweat from the bottom of the cake leaving a residue of higher melting wax However wax sweating can be carried out only when the residual wax con sists of large crystals that have spaces between them through which the oil and lower melting waxes can percolate it is therefore limited to wax obtained from light paraffin distillate Wax recrystallization like wax sweating separates slack wax into fractions but instead of using the differences in melting points it makes use of the different solubility of the wax fractions in a solvent such as the ketone used in the dewaxing process When a mixture of ketone and slack wax is heated the slack wax usually dissolves completely and if the solution is cooled slowly a tem perature is reached at which a crop of wax crystals is formed These crystals will all be of the same melting point and if they are removed by filtration a wax fraction with a specific melting point is obtained If the clear filtrate is further cooled a second crop of wax crystals with a lower melting point is obtained Thus by alternate cooling and filtration the slack wax can be subdivided into a large number of wax fractions each with different melting points Microcrystalline wax sometimes also called micro wax or microwax is produced from a com bination of heavy lube distillates and residual oils and differs from paraffin wax in that the micro crystalline has a less welldefined crystalline structure and is darker color The physical properties of microcrystalline wax is affected significantly by the oil content Kumar et al 2007 and by achieving the desired level of oil content wax of the desired physical properties and specifications can be produced Deep deoiling of microcrystalline wax is comparatively difficult compared to paraffin wax macrocrystalline wax as the oil remains occluded in these and is difficult to separate by sweating Also since wax and residual oil have similar boiling ranges separation by distillation is difficult However these waxes can be deoiled by treatment with solvents at lower temperature that have high oil miscibility and poor wax solubility and these have been used extensively to separate Paraffin wax is mostly used for relief of discomfort and pain in following conditions such as bur sitis eczema psoriasis dry flaky skin stiff joints fibromyalgia tired sore muscles inflammation and arthritis Paraffin wax is often used in skinsoftening salon and spa treatments on the hands cuticles and feet because it is colorless tasteless and odorless It can also be used to provide pain relief to sore joints and muscles Paraffin wax is often used as lubrication electrical insulation and to make candles and crayons Cosmetically paraffin wax is often applied to the hands and feet The wax is a natural emollient helping make skin supple and soft When applied to the skin it adds 475 Pharmaceuticals moisture and continues to boost the moisture levels of the skin after the treatment is complete It can also help open pores and remove dead skin cells That may help make the skin look fresher and feel smoother and give comfort to the user 1224 Bitumen The bitumen in the Bible it is referenced as slime is not the same as the refinery product known as asphalt Speight 2008 2014 2015 2016 Bitumen is a naturaloccurring material that occurs in tar sand formations and that has seeped from crude oil formation Typically the bitumen that has been referenced in ancient texts unless recovered from a tar sand formation is equivalent to an atmospheric residuum insofar as it is found as a seepage on the surface and is crude oil from which the more volatile constituents have escaped by evaporation The bitumen obtained from the area of Hit Tuttul in Iraq Mesopotamia or as blocks floating on the Dead Sea are examples of such occurrences Abraham 1945 Forbes 1958ab 1959 Nissenbaum 1999 Typically asphalt is produced from crude oil as the treated usually airblown vacuum residuum Parkash 2003 Gary et al 2007 Speight 2011 2014 2017 Hsu and Robinson 2017 Surface manifestations of bitumen are found in Middle Eastern countries as seepages from rocks This bitumen has been extensively employed for a variety of uses including in medicine The historical evidence on the medicinal uses of bitumen spans at least 3000 years and while many of the attributes of bitumen as a drug in antiquity are not based on medical evidence certain treat ments using bitumen may have been confirmed by modern medicine For example the application of bitumen and asphalt as a therapy for skin diseases in humans and in animals has been borne out in modern times by extensive experimentation The nature of the active ingredient or ingredients in the bitumen has not been investigated as yet not have the constituents been identified with any degree of certainty Also it has long been recorded that bitumen from what is now Iraq and Syria was exported to Egypt for embalming purposes from at least the early Ptolemaic periodthe acces sion of Soter after the death of Alexander the Great in 323 BC and which ended with the death of Cleopatra and the Roman conquest of Egypt in 30 BC Furthermore when going further back into history it has become evident that bitumen was used widely in the Middle East especially in the Zagros Mountains of Iran Connan 1999 Ancient peo ple from northern Iraq southwest Iran and the Dead Sea area extensively used this ubiquitous natu ral resource until the Neolithic period 70006000 BC Evidence of earlier use has been recently documented in the Syrian Desert near El Kown where bitumencoated flint implements dated to 40000 BC Mousterian period have been unearthed This discovery at least proves that bitumen was used by Neanderthal populations as hafting material to fix handles to their flint tools Numerous testimonies proving the importance of this petroleumbased material in ancient civilizations were brought to light by the excavations conducted in the Near East as of the beginning of the century The early records show that bitumen was largely used in Mesopotamia and Elam as mortar in the construction of palaces eg the Darius Palace in Susa temples ziggurats eg the socalled Tower of Babel in Babylon terraces eg the famous Hanging Gardens of Babylon and exceptionally for roadway coating eg the processional way of Babylon Since Neolithic times bitumen served to waterproof containers baskets earthenware jars storage pits wooden posts palace grounds eg in Mari and Haradum reserves of lustral waters bathrooms palm roofs etc Mats sarcophagi coffins and jars used for funeral practices were often covered and sealed with bitumen Reed and wood boats were also caulked with bitumen Bitumen was also a widespread adhesive in antiquity and served to repair broken ceramics fix eyes and horns on statues eg at Tell alUbaid around 2500 BC Decorations with stones shells mother of pearl on palm trees cups ostrich eggs musi cal instruments eg the Queens lyre and other items such as rings jewelry and games have been excavated from the Royal tombs in Ur Connan 1999 Bitumen was also considered as a powerful remedy in medical practice especially as a disin fectant and insecticide and was used by the ancient Egyptians to prepare mixtures to embalm the 476 Handbook of Petrochemical Processes corpses of their dead Recent geochemical studies on more than 20 balms from Egyptian mummies from the Intermediate Ptolemaic and Roman periods have revealed that these balms are composed of various mixtures of bitumen conifer resins grease and beeswax The physician Ibn alBaitar described as a preservative for embalming the dead in order that the dead bodies might remain in the state in which they were buried and neither decay nor change In addition the historical records show that bitumen was used since ancient times for cosmetic art and the caulk of boats and was reputed to be useful to cure varying pulmonary digestive earnosethroat troubles and even to set fractured bones Bourée et al 2011 In medicine Muslim physicians used petroleum and bitumen for pleurisy and dropsythe patient was given bitumenous water to drinkand for various skin ailments and wounds There is also frag mentary evidence that hot bitumen was used to cauterize the wound resulting from a severed limbas a side note medieval physicians used fire as the cauterizing agent Whether or not the bitumentreated patients survived is not clear Another law of the time suggests that the use of hot bitumen as a cura tive agentnot in the sense of a medicinal cure but as a punishment The hot bitumen was to be poured over the head of the miscreant The record do not show if the miscreant survived as a bald person after the bitumen was removed or if the miscreant actually survived the treatment For example an early mention of the use of bitumen as a punishment appears in orders that Richard I of England also known as Richard the Lionheart issued to his navy when he set out of the Holy Land in 1189 Concerning the lawes and ordinances appointed by King Richard for his navie the forme thereof was this item a thiefe or felon that hath stolen being lawfully convicted shal have his head shorne and boyling pitch poured upon his head and feathers or downe strawed upon the same whereby he may be knowen and so at the first landingplace they shall come to there to be cast up Hakluyt 1582 In other literature the name shilajit occurs frequently and is the Sanskrit name for Asphaltum bitumen also called mineral pitch vegetable asphalt shilajita guj kalmadam perangyum rel yahudi and silaras refers to a curative agent as an analgesic antiinflammatory antibacterial cholagogic diuretic wound cleaner expectorant respiratory stimulant general health medicine amongst a host of other effects Jonas 2005 1225 solvents Finally for this section it would be remiss if mention was not made of the solvents produced from crude oil that are used by the pharmaceutical industry many of which are derived from crude oil Table 123 TABLE 123 Example of Solvents Used in the Pharmaceutical Industry Solvent Use Acetone C F B Acetonitrile C F B Ammonia aqueous C F B nAmyl acetate C F B Amyl alcohol C F B Aniline C Benzene C 2Butanone methyl ethyl ketone MEK C nButyl acetate C F nButyl alcohol C F B Continued 477 Pharmaceuticals TABLE 123 Continued Example of Solvents Used in the Pharmaceutical Industry Solvent Use Chlorobenzene C Chloroform C F B Chloromethane C Cyclohexane C oDichlorobenzene 12Dichlorobenzene C 12Dichloroethane C B Diethylamine C B Diethyl ether C B NNDimethyl acetamide C Dimethylamine C NNdimethylaniline C NNdimethylformamide C F B Dimethyl sulphoxide C B 14Dioxane C B Ethanol C F B Ethyl acetate C F B Ethylene glycol C B Formaldehyde C F B Formamide C Furfural C nHeptane C F B nHexane C F B Isobutyraldehyde C Isopropanol C F B Isopropyl acetate C F B Isopropyl ether C B Methanol C F B Methylamine C Methyl cellosolve C F Methylene chloride C F B Methyl formate C Methyl isobutyl ketone MIBK C F B 2Methylpyridine C Petroleum naphtha C F B Phenol C F B Polyethylene glycol 600 C nPropanol C B Pyridine C B Tetrahydrofuran C Toluene C F B Trichlorofluoromethane C Triethylamine C F Xylenes C C chemical synthesis F fermentation B biological or natural extraction 478 Handbook of Petrochemical Processes Briefly a solvent is a substance that dissolves a solute a chemically distinct liquid solid or gas resulting in a solution A solvent is usually a liquid but can also be a solid a gas or a supercritical fluid The quantity of solute that can dissolve in a specific volume of solvent varies with temperature In the current context solvents are used for production isolation andor purification and have found wide use in the pharmaceutical industry including in synthetic processes and purification processes The term petroleum solvent describes the liquid hydrocarbon fractions obtained from petroleum and used in industrial processes and formulations These fractions are also referred to naphtha or as industrial naphtha By definition the solvents obtained from the petrochemical industry such as alcohols ethers and the like are not included in this chapter A refinery is capable of producing hydrocarbons of a high degree of purity and at the present time petroleum solvents are available covering a wide range of solvent properties including both volatile and highboiling qualities Naphtha has been available since the early days of the petroleum industry Indeed the infamous Greek fire documented as being used in warfare during the last three millennia is a petroleum deriv ative Chapter 1 It was produced either by distillation of crude oil isolated from a surface seep age or more likely by destructive distillation of the bituminous material obtained from bitumen seepages of which there arewere many known during the heyday of the civilizations of the Fertile Crescent Chapter 1 The bitumen obtained from the area of Hit Tuttul in Iraq Mesopotamia is an example of such an occurrence Abraham 1945 Forbes 1958a Other petroleum products boiling within the naphtha boiling range include i industrial Spirit and white spirit Industrial spirit comprises liquids distilling between 30C and 200C 1F390F with a temperature difference between 5 volume and 90 volume distillation points including losses of not more than 60C 140F There are several up to eight grades of industrial spirit depending on the position of the cut in the distillation range defined above On the other hand white spirit is an industrial spirit with a flash point above 30C 99F and has a distillation range from 135C to 200C 275F390F Solvents used for extracting the product from a natural product source such as biomass or from a reaction mixture are to many scientists engineers and technologists as equally important as the product of the medicine Generally the solvent can be recovered but small portions remain in the process wastewater depending upon their solubility and the design of the process equipment Precipitation from a solvent is a method to separate the medicine or a precursor chemical from the reaction mixture after which the medicinal product precursor is filtered and extracted from say any solid the solid residues The medicinal product is then recovered from the solvent phase by evaporation and recovery of the solvent 123 PHARMACEUTICAL PRODUCTS Petrochemical compounds are necessary for many of the things we depend upon but unfortunately the process to make them is costly energy intensive and very harmful to the environment The pet rochemical manufacturing process is particularly energy intensive and harmful to the environment The complex mixture of hydrocarbons compounds made of hydrogen and carbon that comprises oils are separated into various fractions by distillation a process that separates various compounds based on their boiling points Lowboiling fractions of petroleum including propane and butane are separated from the crude oil at low temperatures 300C 570F Manufacturers then apply various chemical processes to generate a variety of petrochemicals These chemicals are the starting points for the manufacture of plastics the polyester used in carpet and clothing and industrial solvents oils and acids used in cleaning products Many pharmaceuticals are also derived from petrochemicals as are food addi tives dyes and explosives Simply put modern life would not be possible without petrochemicals Petrochemicals play a major role in the manufacture of many pharmaceutical products and many advances in health care and sanitation have been made possible by the use of petrochemicals and there is a long history of their use with oils first being used in medicines at least 1000 years ago 479 Pharmaceuticals The petrochemicals are used in pharmaceutical products from the most commonplace to the highly specialized An everyday example is ASAor Acetylsalicylic acidan important part of many overthecounter pain medications While penicillin a drug that has saved countless lives since its discovery by Alexander Fleming in 1928 and subsequent development by Howard Florey and Ernst Chain in the 1940s is manufac tured via fungi and microbes phenol and cumene are used as preparatory substances These chemi cals are also used in the production of aspirin with acetylsalicylic acid being the main metabolite of aspirin Other common medical products some available by prescription some overthecounter that use petrochemicals include antihistamine medications antibacterial medications supposito ries cough syrups lubricants creams ointments salves analgesics and gels Petrochemical resins have also been used in drug purification These resins simplify mass pro duction of medicine thus making them more affordable to produce and then distribute The resins have been used in the production of a wide range of medications including those for treating AIDS arthritis and cancer Plastics play an important role in health care too Resins and plastics from petrochemicals are used to make artificial limbs and joints They are also a familiar sight in hospitals and other medical facilities for storing blood and vaccines for use in disposable syringes and other items of medical equipment that are used once to prevent the threat of contagion Specially created polymers are used extensively in health care most notably during cardiac surgery or for auditory and visual stimula tors Eyeglasses have benefitted from the use of plastics in frames and lenses and contact lenses are also made of plastic Even safety has improved thanks to the introduction of childproof caps and tamperproof seals for medication containers all made using plastics Surgical gloves are often made from pliable plastics plastic petri dishes are essential to laboratories and at a larger level for the housing of large diagnostic medical machinery As well as petrochemicals playing an important role in the manufacture of pharmaceuticals and medical equipment petroleum use through transport is a major cost to healthcare systems glob ally including ambulances staff transport and transportation of supplies Indeed in the United States according to US Bureau of Labor Statistics figures it is estimated that the use of petroleum products in transport for health care is far greater than that used for drugs and plastics The ongoing supply of the fossil fuels required to make all these relevant healthcare products may become a bigger issue as time goes on and if healthcare systems are placed under further financial pressure Finding alternatives to using petrochemicals for many medications and items of medical equip ment may become important if health care is to remain accessible or for some regions to become more accessible In the United States the Center for Disease Control is investigating the impact of dwindling petroleum reserves on the provision of health care Going forward the healthcare industry may have to look at alternatives to using petrochemicals for pharmaceuticals and plastics although currently there are few alternatives However as only a tiny proportion of petrochemicals is used to produce specialized products for the healthcare industry the supply chain for such prod ucts is currently considered to be secure 124 PRODUCTION OF PHARMACEUTICALS The pharmaceutical industry includes the manufacture extraction processing purification and packaging of chemical materials to be used as medications for humans or animals Pharmaceutical manufacturing is divided into two major stages i the production of the active ingredient or drug primary processing or manufacture and ii secondary processing the conversion of the active medicines into products suitable for administration However before a medication can be manu factured at any scale much work goes into the actual formulation of the medicine Formulation development scientists must evaluate a compound for uniformity stability and many other factors After the evaluation phase a solution must be developed to deliver the medication in its required form such as solid semisolid immediate or controlled release tablet and capsule 480 Handbook of Petrochemical Processes In the pharmaceutical industry a wide range of excipients may be blended together to create the final blend used to manufacture the solid dosage form The range of materials that may be blended excipients API presents a number of variables which must be addressed to achieve products of acceptable blend uniformity These variables may include the particle size distribution including aggregates or lumps of material particle shape spheres rods cubes plates and irregular presence of moisture or other volatile compounds and particle surface properties roughness cohesiveness The following sections present the published synthetic routs for several overthecounter non prescription medications These are list alphabetically rather than by preference or by stated use or effect 1241 acetaminoPhen Acetaminophen paracetamol is an analgesic and feverreducing medicine similar in effect to aspirin It is an active ingredient in many overthecounter medicines including Tylenol and Midol Introduced in the early 1900s acetaminophen is a coal tar derivative that acts by interfering with the synthesis of prostaglandins and other substances necessary for the transmission of pain impulses The starting material paminophenol 4aminophenol is produced from phenol by nitration followed by reduction with iron Alternatively the partial hydrogenation of nitrobenzene affords phenylhydroxylamine which rearranges primarily to 4aminophenol C H NO 2H C H NHOH H O C H NHOH HOC H NH 6 5 2 2 6 5 2 6 5 6 4 2 The paminophenol can also be produced from nitrobenzene by electrolytic conversion to phenyl hydroxylamine which under the reaction conditions spontaneously rearranges to 4aminophenol pAminophenol is a white powder that is moderately soluble in alcohols and can be recrystal lized from hot water Also it is the final intermediate in the industrial synthesis of paracetamol by treatment with acetic anhydride 1242 aleve The active constituent of Aleve is Naproxen sodium which is an antiinflammatory compound Naproxen is used to treat a variety of inflammatory conditions and symptoms that are due to exces sive inflammation such as pain and fevernaproxen has feverreducing antipyretic properties in addition to its antiinflammatory activity Naproxen has been produced starting from 2naphthol βnaphthola constituent of coal tar or which can be prepared from naphthalene that is isolated from gas oil 2Naphthol is not a product that is isolated from crude oil more likely it is isolated from the prod ucts of the thermal decomposition of coal and some types of biomass Traditionally 2naphthol is produced by a twostep process that begins with the sulfonation of naphthalene in sulfuric acid The sulfonic acid group is then cleaved in molten sodium hydroxide C H H SO C H SO H H O C H SO H 3NaOH C H ONa Na SO 2H O 10 8 2 4 10 7 3 2 10 7 3 10 7 2 3 2 Neutralization of the sodium salt with acid gives 2naphthol 2Naphthol can also be produced by a method analogous to the cumene process 2Naphthol is also the base from which certain dyestuffs Table 124 can be manufactured 481 Pharmaceuticals 1243 asPirin Acetylsalicylic acid commonly known as aspirin is a widely used drug The analgesic antipyretic and antiinflammatory properties make it a powerful and effective drug to relive symptoms of pain fever and inflammation Historically aspirin has been known for some time In the North American context it was extracted by the Native Americans from willow and poplar tree bark about 2500 years ago Native Americans used willow bark in teas to reduce fever In 1763 Reverend Edward isolated and identified one of the compounds used to synthesize aspirin which came to be known as salicylic acid Large quantities of salicylic acid became available however it caused severe stomach irritation In 1893 German chemist Felix Hoffman synthesized an ester derivative of salicylic acid acetylsalicylic acid aspirin The acetyl group cloaks the acidity when ingested The drug then passes through the small intestine where it gets converted back to salicylic acid and enters the bloodstream Although TABLE 124 Example of Dyestuffs Based on 2Naphthol Sudan I Sudan II Sudan III Sudan IV Oil Red O Naphthol 482 Handbook of Petrochemical Processes weaker than salicylic acid aspirin had medicinal properties without the bitter taste and harsh stom ach irritation The company Bayer patented aspirin in 1899 which has made aspirin one of the most widely used and modern commerciallyavailable drugs The synthesis of aspirin may be achieved in one simple step Oacetylation of salicylic acid which is incorporated into many undergraduate synthetic chemistry laboratory courses The purity of the product as a pharmaceutical is crucial An additional step may be added to the synthesis of aspirin conversion of oil of wintergreen methyl salicylate to salicylic acid This serves as an introduction to multistep synthesis and the concept of converting a naturally occurring substance into one with therapeutic value Salicylic acid 12HOC6H4COOH C8H8O3 is produced by the basecatalyzed hydrolysis reac tion conversion of oil of wintergreen methyl salicylate 12HOC6H4CO2CH3 to salicylic acid C H O 2NaOH H SO C H O Na SO CH OH H O 8 8 3 2 4 4 6 3 2 4 3 2 In terms of a petrochemical precursor salicylic acid can be synthesized from phenol by a threestep process 1244 cePacol The main ingredient of Cepacol is benzocaine which is commonly used as a topical pain reliever or in cough drops It is the active ingredient in many overthecounter anesthetic ointments such as products for oral ulcers Benzocaine is the ethyl ester of paminobenzoic acid PABA and can be prepared by the reac tion of paminobenzoic acid with ethanol or via the reduction of ethyl pnitrobenzoate Benzocaine is sparingly soluble in water it is more soluble in dilute acids and very soluble in ethanol chloro form and ethyl ether It can be synthesized from toluene by a threestep process 1245 excedrin Excedrin is an extrastrength pain reliever that is available as an overthecounter medicine for pain Excedrin combines three medications i acetaminophen also known as paracetamol ii aspirin and iii caffeine Caffeine has its origins in biomass such as the seeds nuts or leaves of a number of plants native to Africa East Asia and South America and helps to protect them against predator insects and to prevent germination of nearby seeds To the Western world the most wellknown source of caffeine is the coffee bean a misnomer for the seed of Coffea plants 1246 Gaviscon Gaviscon is an antacid medication that reduced stomach acid and the typical uncomfortable side effects that accompany acid reflux The active ingredients of Gaviscon are i aluminum hydroxide AlOH3 and ii magnesium carbonate MgCO3 While not a true petrochemical in the general sense aluminum hydroxide is often used in a refinery and is available as a product It is however found in nature as the mineral gibbsite also known as hydrargillite and its three much rarer polymorphs occurring in several different forms bayerite doyleite and nordstrandite Aluminum hydroxide is amphoterichaving both basic and acidic properties Like aluminum hydroxide magnesium carbonate is also not a true petrochemical Magnesium carbonate is often found in use in refineries It is ordinarily obtained by mining the mineral 483 Pharmaceuticals magnesote and can also be prepared by reaction between any soluble magnesium salt and sodium bicarbonate MgCl 2NaHCO MgCO 2NaCl H O CO 2 3 3 2 2 If magnesium chloride or sulfate is treated with aqueous sodium carbonate a precipitate of basic magnesium carbonate a hydrated complex of magnesium carbonate and magnesium hydroxide is formed 5MgCl 5Na CO 5H O Mg OH 3MgCO 3H O Mg HCO 10NaCl 2 2 3 2 2 3 2 3 2 Highpurity industrial routes include a path through magnesium bicarbonate which can be formed by combining a slurry of magnesium hydroxide and carbon dioxide at high pressure and moderate temperature The bicarbonate is then vacuum dried causing it to lose carbon dioxide and a molecule of water Mg OH 2CO Mg HCO Mg HCO MgCO CO H O 2 2 3 2 3 2 3 2 2 1247 iBuProfen Ibuprofen is a medication in the nonsteroidal antiinflammatory drug NSAID class NSAID class that is used for treating pain fever and inflammation Since the introduction of the drug in 1969 ibuprofen has become one of the most common painkillers in the world Ibuprofen in an NSAID and like other drugs of its class it possesses analgesic antipyretic and antiinflammatory proper ties While ibuprofen is a relatively simple molecule there is still sufficient structural complexity to ensure that a large number of different synthetic approaches are possible Ibuprofen is typically found in many overthecounter drugs such as Motrin Advil Potrin and Nuprin In other words it often comes in capsules tablets or powder form Comparing to that of aspirin for example Ibuprofen is somewhat shortlived and relatively mild However it is known to have an antiplatelet nonblood clotting effect Since the introduction of pharmaceutical products containing ibuprofen industrial and academic scientists developed many potential production processes Two of the most popular ways to obtain Ibuprofen are the Boot process and the Hoechst process The Boot process is an older commercial process and the Hoechst process is a newer process Most of these routes to Ibuprofen begin with isobutyl benzene and use FriedelCrafts acylation The Boot process requires six steps while the Hoechst process with the assistance of catalysts is completed in only three steps The starting material cumene isopropyl benzene 2phenylpropane or 1methylethyl benzene for both of these processes is produced by the gasphase reaction FriedelCrafts alkylation of benzene by propylene In the process benzene and propylene are compressed together to a pressure in the order of 450 psi 250C 482F in presence of a Lewis acid catalyst such as an aluminum halidea phosphoric acid H3PO4 catalyst is often favored over an aluminum halide catalyst Cumene is a colorless volatile liquid with a gasolinelike odor It is a natural component of coal tar and crude oil and also can be used as a blending component in gasoline 1248 kaoPectate Kaopectate is an orally taken medication used for the treatment of mild indigestion nausea and stomach ulcers The active ingredients have varied over time and are different between the United States and Canada The original active ingredients were kaolinite a layered clay mineral which has 484 Handbook of Petrochemical Processes the approximate chemical composition Al2Si2O5OH4 and pectin a structural heteropolysaccha ride contained in the primary cell walls of terrestrial plants In the United States the active ingredi ent is now bismuth subsalicylate which has the empirical chemical formula of C7H5BiO4 and it is a colloidal substance obtained by hydrolysis of bismuth salicylate BiC6H4OHCO23 Bismuth subsalicylate is also the active ingredient in PeptoBismol and displays anti inflammatory action due to salicylic acid and is used to relieve the discomfort that arises from an upset stomach due to overindulgence in food and drink including heartburn indigestion nausea gas and fullness As stated previously salicylic acid or as a precursor to the acid sodium salicylate is produced commercially by treating sodium phenate the sodium salt of phenolphenol is a wellknown pet rochemical starting material with carbon dioxide at high pressure 1500 psi and high temperature 117C 242F the KolbeSchmitt reaction after which acidification of the product with sulfuric acid yield gives salicylic acid Salicylic acid can also be prepared by the hydrolysis of acetylsalicylic acid aspirin or by the hydrolysis of methyl salicylate oil of wintergreen with a strong acid or base Another method for the production of salicylic acid involves biosynthesis from phenylalanine Salicylic acid is also used in the production of other pharmaceuticals including 4aminosalicylic acid and sandulpiridethe latter is an antipsychotic of the benzamide class which is used mainly in the treatment of psychosis associated with schizophrenia and depressive disorders Other deriva tives include methyl salicylate that is used as a liniment to soothe joint and muscle pain and choline salicylate that is used topically to relieve the pain of mouth ulcers 1249 lmenthol LMenthol laevomenthol or laevorotary menthol is an organic compound that occurs naturally from corn mint peppermint and other mint oils The main form of menthol occurring in nature is laevomenthol which is a waxy crystalline solid that is clear sometimes referred to as white or waterwhite in color and which melts slightly above room temperature Natural menthol is obtained by freezing peppermint oil and the resultant crystals of menthol are then separated by filtration Briefly and by way of clarification dextrorotation and laevorotation also spelled levorotation are terms used to describe the rotation of planepolarized Looking at the molecule headon dextro rotation refers to clockwise rotation while levorotation refers to counterclockwise rotation A chem ical that causes dextrorotation is referred to as being dextrorotatory dextrorotary often abbreviated to dextro while a compound that causes levorotation is called levorotatory or levorotary often abbreviated to laevo Also a dextrorotary compound is often prefixed or d Likewise a levorotary compound is often prefixed or l Solomons and Fryhle 2004 Compounds with these properties have varying degrees of optical activity and consist of chiral mileages that often react differently with other chemicals or with organs within the human body because of spatial effects If a chiral molecule is dextrorotary the enantiomer one of a pair of molecules that are mirror images of each other of the molecule will be levorotary and other enantiomer will be dextrorotatory This means that each of the enantiomers will rotate the plane polarized light the same number of degrees but in opposite directions As an illustration of the two forms of menthol in the formulas below with the ring in the plane of the paper in the laevomenthol lmenthol the methyl group and the hydroxyl group are above the plane of the paper while the isopropyl group is below the plane of the paper The converse is true for the dextromenthol dmentholthe methyl group and the hydroxyl group are below the plane of the paper while the isopropyl group is above the plane of the paper In the current context menthol is produced by the HaarmannReimer process which starts from mcresol a simple petrochemical which is alkylated with propene to yield thymol which is then hydrogenated and the racemic menthol is isolated by fractional distillation The enantiomers are 485 Pharmaceuticals separated by chiral resolution in a reaction with methyl benzoate selective crystallization followed by hydrolysis Menthol is included in many products for a variety of reasons which include i nonprescrip tion products for shortterm relief of minor sore throat and minor mouth or throat irritation such as lip balms and cough medicines ii as an antipruritic medicine to reduce itching iii as a topical analgesic to relieve minor aches and pains such as muscle cramps sprains headaches and simi lar conditions alone or combined with chemicals such as camphor eucalyptus or capsaicin and iv in firstaid products such as mineral ice to produce a cooling effect as a substitute for real ice in the absence of water or electricity pouch body patchsleeve or cream A further established application of LMenthol is in form of inhalations for the symptomatic relief of sinusitis rhinitis bronchitis and similar conditions 12410 oraJel Orajel is another pain reliever especially when the pain is due to toothache The active ingredient is benzocaine which is the ethyl ester of paminobenzoic acid Benzocaine can be prepared from paminobenzoic acid and ethanol by the Fischer esterification reaction or by the reduction of ethyl pnitrobenzoate In the Fischer esterification reaction a carboxylic acid R1CO2H is treated with an alcohol R2OH in the presence of a mineral inorganic acid catalyst to form the ester R1COOR2 Benzocaine is sparingly soluble in water it is more soluble in dilute acids and very soluble in ethanol chloroform and ethyl ether Benzocaine is a local anesthetic used in medical applications to reduce pain and increase com fort of painful drugs Such applications are administered with the leprosy drug chaulmoogra oil and even reducing the pain from needle injections It is the active ingredient in many overthe counter painrelieving ointments such as products for oral ulcers It is also used in aerosol spray lotions to relieve the discomfort of sunburn 12411 tylenol The active constituent of Tylenol is acetaminophen which is an analgesic and feverreducing medi cine similar in effect to aspirin It is an active ingredient in many overthecounter medicines including Tylenol and Midol Introduced in the early 1900s acetaminophen is a coal tar derivative that acts by interfering with the synthesis of prostaglandins and other substances necessary for the transmission of pain impulses The preparation of acetaminophen involves treating an amine with an acid anhydride to form an amide In this case paminophenol the amine is treated with acetic anhydride to form acetamino phen pacetamidophenol the amide 12412 zantac Ranitidine sold under the trade name Zantac among others is a medication which decreases acid production in the stomach Rather than being derived from petroleum the starting material is derived from biomass Chapter 3 which is also a source of pharmaceutical derivative Thus the biomassderived chemical furfural is converted into ranitidine in four steps with an overall 68 isolated yield Mascal and Dutta 2011 Xylose C5H10O5 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Fuels Handbook Properties Processes and Performance McGrawHill New York 487 Pharmaceuticals Speight JG 2014 The Chemistry and Technology of Petroleum 5th Edition CRCTaylor and Francis Group Boca Raton FL Speight JG and Exall DI 2014 Refining Used Lubricating Oils CRC Press Taylor and Francis Group Boca Raton FL Speight JG 2015 Asphalt Materials Science and Technology ButterworthHeinemann Elsevier Oxford United Kingdom Speight JG 2016 Introduction to Enhanced Recovery Methods for Heavy Oil and Tar Sands 2nd Edition Gulf Professional Publishing Elsevier Oxford United Kingdom Speight JG 2017 Handbook of Petroleum Refining CRC Press Taylor Francis Group Boca Raton FL Wick JY 2012 Aspirin A history a love story The Consultant Pharmacist 275 322329 Taylor Francis 489 Conversion Tables 1 Area 1 square centimeter 1 cm2 01550 square inches 1 square meter 1 m2 11960 square yards 1 hectare 24711 acres 1 square kilometer 1 km2 03861 square miles 1 square inch 1 in2 64516 square centimeters 1 square foot 1 ft2 00929 square meters 1 square yard 1 yd2 08361 square meters 1 acre 40469 square meters 1 square mile 1 mi2 259 square kilometers 2 Concentration Conversions 1 part per million 1 ppm 1 microgram per liter 1 μgL 1 microgram per liter 1 μgL 1 milligram per kilogram 1 mgkg 1 microgram per liter μgL 6243 108 1 lb per cubic foot 1 lbft3 1 microgram per liter 1 μgL 103 1 milligram per liter 1 mgL 1 milligram per liter 1 mgL 6243 105 1 pound per cubic foot 1 lbft3 I gram mole per cubic meter 1 g molm3 6243 105 1 pound per cubic foot 1 lbft3 10000 ppm 1 ww 1 ppm hydrocarbon in soil 0002 1 lb of hydrocarbons per ton of contaminated soil 3 Nutrient Conversion Factor 1 pound phosphorus 23 1 lb P 23 1 pound phosphorous pentoxide 1 lb P2O5 1 pound potassium 12 1 lb K 12 1 pound potassium oxide 1 lb K2O 4 Temperature Conversions F C 18 32 C F 3218 F 32 0555 C Absolute zero 27315C Absolute zero 45967F 5 Sludge Conversions 1700 lbs wet sludge 1 yd3 wet sludge 1 yd3 sludge wet tons085 Wet tons sludge 240 gallons sludge 1 wet ton sludge dry solids100 1 dry ton of sludge 6 Various Constants Atomic mass µ 16605402 1027 Avogadros number N 60221367 1023 mol1 Boltzmanns constant k 1380658 1023 JK Elementary charge e 160217733 1019 C Faradays constant F 96485309 104 Cmol Gas molar constant R k N 8314510 Jmol K 008205783 L atmmol K Gravitational acceleration g 980665 ms2 Molar volume of an ideal gas at 1 atm and 25C Videal gas 24465 Lmol1 Plancks constant h 66260755 1034 J s Zero Celsius scale 0C 27315K 490 Conversion Tables 7 Volume Conversion Barrels petroleum U S to Cu feet multiply by 56146 Barrels petroleum U S to Gallons U S multiply by 42 Barrels petroleum U S to Liters multiply by 15898 Barrels US liq to Cu feet multiply by 42109 Barrels US liq to Cu inches multiply by 72765 103 Barrels US liq to Cu meters multiply by 01192 Barrels US liq to Gallons multiply by U S liq 315 Barrels US liq to Liters multiply by 11924 Cubic centimeters to Cu feet multiply by 35315 105 Cubic centimeters to Cu inches multiply by 006102 Cubic centimeters to Cu meters multiply by 10 106 Cubic centimeters to Cu yards multiply by 1308 106 Cubic centimeters to Gallons US liq multiply by 2642 104 Cubic centimeters to Quarts US liq multiply by 10567 103 Cubic feet to Cu centimeters multiply by 28317 104 Cubic feet to Cu meters multiply by 0028317 Cubic feet to Gallons US liq multiply by 74805 Cubic feet to Liters multiply by 28317 Cubic inches to Cu cm multiply by 16387 Cubic inches to Cu feet multiply by 5787 104 Cubic inches to Cu meters multiply by 16387 105 Cubic inches to Cu yards multiply by 21433 105 Cubic inches to Gallons US liq multiply by 4329 103 Cubic inches to Liters multiply by 001639 Cubic inches to Quarts US liq multiply by 001732 Cubic meters to Barrels US liq multiply by 83864 Cubic meters to Cu cm multiply by 10 106 Cubic meters to Cu feet multiply by 35315 Cubic meters to Cu inches multiply by 61024 104 Cubic meters to Cu yards multiply by 1308 Cubic meters to Gallons US liq multiply by 26417 Cubic meters to Liters multiply by 1000 Cubic yards to Bushels Brit multiply by 21022 Cubic yards to Bushels US multiply by 21696 Cubic yards to Cu cm multiply by 76455 105 Cubic yards to Cu feet multiply by 27 Cubic yards to Cu inches multiply by 46656 104 Cubic yards to Cu meters multiply by 076455 Cubic yards to Gallons multiply by 16818 Cubic yards to Gallons multiply by 17357 Cubic yards to Gallons multiply by 20197 Cubic yards to Liters multiply by 76455 Cubic yards to Quarts multiply by 67271 Cubic yards to Quarts multiply by 69428 Cubic yards to Quarts multiply by 80790 Gallons US liq to Barrels US liq multiply by 003175 Gallons US liq to Barrels petroleum US multiply by 002381 Gallons US liq to Bushels US multiply by 010742 Gallons US liq to Cu centimeters multiply by 37854 103 Gallons US liq to Cu feet multiply by 013368 491 Conversion Tables Gallons US liq to Cu inches multiply by 231 Gallons US liq to Cu meters multiply by 37854 103 Gallons US liq to Cu yards multiply by 4951 103 Gallons US liq to Gallons wine multiply by 10 Gallons US liq to Liters multiply by 37854 Gallons US liq to Ounces US fluid multiply by 1280 Gallons US liq to Pints US liq multiply by 80 Gallons US liq to Quarts US liq multiply by 40 Liters to Cu centimeters multiply by 1000 Liters to Cu feet multiply by 0035315 Liters to Cu inches multiply by 61024 Liters to Cu meters multiply by 0001 Liters to Gallons US liq multiply by 02642 Liters to Ounces US fluid multiply by 33814 8 Weight Conversion 1 ounce 1 ounce 283495 grams 182495 g 1 pound 1 lb 0454 kilogram 1 pound 1 lb 454 grams 454 g 1 kilogram 1 kg 220462 pounds 220462 lb 1 stone English 14 pounds 14 lb 1 ton US 1 short ton 2000 lbs 1 ton English 1 long ton 2240 lbs 1 metric ton 220462262 pounds 1 tonne 220462262 pounds 9 Other Approximations 147 pounds per square inch 147 psi 1 atmosphere 1 atm 1 kilopascal kPa 98692 103 147 pounds per square inch 147 psi 1 yd3 27 ft3 1 US gallon of water 834 lbs 1 imperial gallon of water 10 lbs 1 ft3 75 gallon 1728 cubic inches 625 lbs 1 yd3 0765 m3 1 acreinch of liquid 27150 gallons 3630 ft3 1foot depth in 1 acre insitu 1613 20 to 25 excavation factor 2000 yd3 1 yd3 clayey soilsexcavated 11 to 12 tons US 1 yd3 sandy soilsexcavated 12 to 13 tons US Pressure of a column of water in psi height of the column in feet by 0434 Taylor Francis Taylor Francis Group httptaylorandfranciscom 493 Glossary The following list represents a selection of definitions that are commonly used in reference to petro chemical operations processes equipment and products which will be of use to the reader Older names as may occur in many books are also included for clarification Abiotic Not associated with living organisms synonymous with abiological Abiotic transformation The process in which a substance in the environment is modified by non biological mechanisms ABN separation A method of fractionation by which petroleum is separated into acidic basic and neutral constituents Absorber See Absorption tower Absorption The penetration of atoms ions or molecules into the bulk mass of a substance Absorption gasoline Gasoline extracted from natural gas or refinery gas by contacting the absorbed gas with an oil and subsequently distilling the gasoline from the higherboiling components Absorption gasoline Gasoline extracted from natural gas or refinery gas by contacting the absorbed gas with an oil and subsequently distilling the gasoline from the higherboiling components Absorption oil Oil used to separate the heavier components from a vapor mixture by absorption of the heavier components during intimate contacting of the oil and vapor used to recover natural gasoline from wet gas Absorption plant A plant for recovering the condensable portion of natural or refinery gas by absorbing the higherboiling hydrocarbons in an absorption oil followed by separation and fractionation of the absorbed material Absorption tower A tower or column which promotes contact between a rising gas and a falling liquid so that part of the gas may be dissolved in the liquid Abyssal zone The portion of the ocean floor below 32816561 ft where light does not penetrate and where temperatures are cold and pressures are intense this zone lies seaward of the continental slope and covers approximately 75 of the ocean floor the temperature does not rise above 4C 39F since oxygen is present a diverse community of invertebrates and fishes do exist and some have adapted to harsh environments such as hydrothermal vents of volcanic creation Acceleration A measure of how fast velocity is changing so we can think of it as the change in velocity over change in time The most common use of acceleration is acceleration due to gravity which can also appear as the gravitational constant 98 ms2 Acetic acid CH3CO2H Trivial name for ethanoic acid formed by the oxidation of ethanol with potassium permanganate Acetone CH3COCH3 Trivial name for propanone formed by the oxidation of 2propanol with potassium permanganate Acetonebenzol process A dewaxing process in which acetone and benzol benzene or aromatic naphtha are used as solvents Acetylene A chemical compound with the formula C2H2 a colorless gas widely used as a fuel and chemical building block Acetyl A functional group with the formula CH3CO Achiral molecule A molecule that does not contain a stereogenic carbon an achiral molecule has a plane of symmetry and is superimposable on its mirror image Acid A chemical containing the carboxyl group and capable of donating a positively charged hydro gen atom proton H or capable of forming a covalent bond with an electron pair an acid increases the hydrogen ion concentration in a solution and it can react with certain metals 494 Glossary Acid anhydride An organic compound that react with water to form an acid Acidbase partitioning The tendency for acids to accumulate in basic fluid compartments and bases to accumulate in acidic regions also called pH partitioning Acidbase reaction A reaction in which an acidic hydrogen atom is transferred from one molecule to another Acid catalyst A catalyst having acidic character the alumina minerals are examples of such catalysts Acid deposition Acid rain a form of pollution depletion in which pollutants such as nitrogen oxides and sulfur oxides are transferred from the atmosphere to soil or water often referred to as atmospheric selfcleaning The pollutants usually arise from the use of fossil fuels Acidic A solution with a high concentration of H ions Acidity The capacity of the water to neutralize OH Acid number A measure of the reactivity of petroleum with a caustic solution and given in terms of milligrams of potassium hydroxide that are neutralized by one gram of petroleum Acidophiles Metabolically active in highly acidic environments and often have a high heavy metal resistance Acid rain The precipitation phenomenon that incorporates anthropogenic acids and other acidic chemicals from the atmosphere to the land and water see Acid deposition Acids bases and salts Many inorganic compounds are available as acids bases or salts Acid sludge The residue left after treating petroleum oil with sulfuric acid for the removal of impu rities a black viscous substance containing the spent acid and impurities Acid treating A process in which unfinished petroleum products such as gasoline kerosene and lubricatingoil stocks are contacted with sulfuric acid to improve their color odor and other properties Acrylic fibers Fibers where the major raw material is acrylonitrile a derivative of propylene Active ingredients One or more compounds in a medicine that has been manufactured syntheti cally or extracted and purified from plant or animal sources the active ingredients react with your body to produce a therapeutic effect See Inactive ingredients Acyclic A compound with straight or branched carboncarbon linkages but without cyclic ring structures Addition reaction A reaction where a reagent is added across a double or triple bond in an organic compound to produce the corresponding saturated compound Additive A material added to another usually in small amounts in order to enhance desirable properties or to suppress undesirable properties Additivity The effect of the combination equals the sum of individual effects Addon control methods The use of devices that remove refinery process emissions after they are generated but before they are discharged to the atmosphere Adhesion The degree to which oil will coat a surface expressed as the mass of oil adhering per unit area A test has been developed for a standard surface that gives a semiquantitative measure of this property Adsorbent sorbent The solid phase or substrate onto which the sorbate adsorbs Adsorption The retention of atoms ions or molecules onto the surface of another substance the twodimensional accumulation of an adsorbate at a solid surface In the case of surface precipitation also used when there is diffusion of the sorbate into the solid phase Adsorption gasoline Natural gasoline obtained by adsorption from wet gas Advection A process due to the bulk largescale movement of air or water as seen in blowing wind and flowing streams Aerobe An organism that needs oxygen for respiration and hence for growth Aerobic In the presence of or requiring oxygen an environment or process that sustains biologi cal life and growth or occurs only when free molecular oxygen is present Aerobic bacteria Any bacteria requiring free oxygen for growth and cell division 495 Glossary Aerobic conditions Conditions for growth or metabolism in which the organism is sufficiently supplied with oxygen Aerobic respiration The process whereby microorganisms use oxygen as an electron acceptor Aerosol A colloidalsized atmospheric particle Airblown asphalt Asphalt produced by blowing air through residua at elevated temperatures Airlift thermofor catalytic cracking A moving bed continuous catalytic process for conversion of heavy gas oils into lighter products the catalyst is moved by a stream of air Air pollution The discharge of toxic gases and particulate matter introduced into the atmosphere principally as a result of human activity Air sweetening A process in which air or oxygen is used to oxidize lead mercaptide derivatives to disulfide derivatives instead of using elemental sulfur Air toxics Hazardous air pollutants Alcohol An organic compound with a carbon bound to a hydroxyl OH group a hydroxyl group attached to an aromatic ring is called a phenol rather than an alcohol a compound in which a hydroxy group OH is attached to a saturated carbon atom eg ethyl alcohol C2H5OH Aldehyde An organic compound with a carbon bound to a COH group a compound in which a carbonyl group is bonded to one hydrogen atom and to one alkyl group RCOH Algae Microscopic organisms that subsist on inorganic nutrients and produce organic matter from carbon dioxide by photosynthesis Alicyclic hydrocarbon A compound containing carbon and hydrogen only which has a cyclic structure eg cyclohexane also collectively called naphthenes Aliphatic compound Any organic compound of hydrogen and carbon characterized by a linear chain or branchedchain of carbon atoms three subgroups of such compounds are alkanes alkenes and alkynes Aliphatic hydrocarbon A compound containing carbon and hydrogen only which has an openchain structure eg as ethane butane octane butene or a cyclic structure eg cyclohexane Aliquot That quantity of material of proper size for measurement of the property of interest test portions may be taken from the gross sample directly but often preliminary operations such as mixing or further reduction in particle size are necessary Alkali metal A metal in Group IA on the periodic table an active metal which may be used to react with an alcohol to produce the corresponding metal alkoxide and hydrogen gas Alkaline A high pH usually of an aqueous solution aqueous solutions of sodium hydroxide sodium orthosilicate and sodium carbonate are typical alkaline materials used in enhanced oil recovery Alkalinity The capacity of water to accept H ions protons Alkaliphiles Organisms that have their optimum growth rate at least 2 pH units above neutrality Alkalitolerants Organisms that are able to grow or survive at pH values above 9 but their opti mum growth rate is around neutrality or less Alkali treatment See Caustic wash Alkali wash See Caustic wash Alkane paraffin A group of hydrocarbons composed of only carbon and hydrogen with no dou ble bonds or aromaticity They are said to be saturated with hydrogen They may by straight chain normal branched or cyclic The smallest alkane is methane CH4 the next ethane CH3CH3 then propane CH3CH2CH3 and so on Alkanes The homologous group of linear acyclic aliphatic hydrocarbons having the general for mula CnH2n2 alkanes can be straight chains linear branched chains or ring structures often referred to as paraffins Alkene olefin An unsaturated hydrocarbon containing only hydrogen and carbon with one or more double bonds but having no aromaticity Alkenes are not typically found in crude oils but can occur as a result of heating 496 Glossary Alkenes Acyclic branched or unbranched hydrocarbons having one carboncarbon double bond CC and the general formula CnH2n often referred to as olefins Alphascission The rupture of the aromatic carbonaliphatic carbon bond that joins an alkyl group to an aromatic ring Aliphatic compounds A broad category of hydrocarbon compounds distinguished by a straight or branched openchain arrangement of the constituent carbon atoms excluding aromatic compounds the carboncarbon bonds may be either single or multiple bondsalkanes alkenes and alkynes are aliphatic hydrocarbons Alkoxide An ionic compound formed by removal of hydrogen ions from the hydroxyl group in an alcohol using a reactive metal such as sodium or potassium Alkoxy group RO A substituent containing an alkyl group linked to an oxygen Alkyl A molecular fragment derived from an alkane by dropping a hydrogen atom from the for mula examples are methyl CH3 and ethyl CH2CH3 Alkylate The product of an alkylation process Alkylate bottoms Residua from fractionation of alkylate the alkylate product which boils higher than the aviation gasoline range sometimes called heavy alkylate or alkylate polymer Alkylation In the petroleum industry a process by which an olefin eg ethylene is combined with a branchedchain hydrocarbon eg isobutane alkylation may be accomplished as a thermal or as a catalytic reaction Alkyl groups A group of carbon and hydrogen atoms that branch from the main carbon chain or ring in a hydrocarbon molecule The simplest alkyl group a methyl group is a carbon atom attached to three hydrogen atoms Alkyne A compound that consists of only carbon and hydrogen that contains at least one carbon carbon triple bond alkyne names end with yne Alkyl benzene C6H5R A benzene ring that has one alkyl group attached the alkyl group except quaternary alkyl groups is susceptible to oxidation with hot KMnO4 to yield benzoic acid C6H5CO2H Alkyl groups A hydrocarbon functional group CnH2n1 obtained by dropping one hydrogen from fully saturated compound eg methyl CH3 ethyl CH2CH3 propyl CH2CH2CH3 or isopropyl CH32CH Alkyl radicals Carboncentered radicals derived formally by removal of one hydrogen atom from an alkane for example the ethyl radical CH3CH2 Alkynes The group of acyclic branched or unbranched hydrocarbons having a carboncarbon triple bond CC Alumina Al2O3 Used in separation methods as an adsorbent and in refining as a catalyst Ambient The surrounding environment and prevailing conditions American Society for Testing and Materials See ASTM International Amide An organic compound that contains a carbonyl group bound to nitrogen the simplest amides are formamide HCONH2 and acetamide CH3CONH2 Amine An organic compound that contains a nitrogen atom bound only to carbon and possibly hydrogen atoms examples are methylamine CH3NH2 dimethylamine CH3NHCH3 and trimethylamine CH33N Amine washing A method of gas cleaning whereby acidic impurities such as hydrogen sulfide and carbon dioxide are removed from the gas stream by washing with an amine usually an alkanolamine Amino acid A molecule that contains at least one amine group NH2 and at least one carboxylic acid group COOH when these groups are both attached to the same carbon the acid is an αamino acida αamino acids are the basic building blocks of proteins Amorphous solid A noncrystalline solid having no welldefined ordered structure Ammonia A pungent colorless gas with the formula NH3 often used to manufacture fertilizers and a range of nitrogencontaining organic and inorganic chemicals 497 Glossary Amphoteric molecule A molecule that behaves both as an acid and as a base such as hydroxy pyridine Anaerobe An organism that does not need freeform oxygen for growth Many anaerobes are even sensitive to free oxygen Anaerobic A biologically mediated process or condition not requiring molecular or free oxygen relating to a process that occurs with little or no oxygen present Anaerobic bacteria Any bacteria that can grow and divide in the partial or complete absence of oxygen Anaerobic respiration The process whereby microorganisms use a chemical other than oxygen as an electron acceptor common substitutes for oxygen are nitrate sulfate and iron Analyte The component of a system to be analyzedfor example chemical elements or ions in groundwater sample Analytical equivalence The acceptability of the results obtained from the different laboratories a range of acceptable results Aniline point The temperature usually expressed in oF above which equal volumes of a petroleum product are completely miscible a qualitative indication of the relative proportions of par affins in a petroleum product which are miscible with aniline only at higher temperatures a high aniline point indicates low aromatics Anion An atom or molecule that has a negative charge a negatively charged ion Anode The electrode where electrons are lost oxidized in redox reactions Anoxic An environment without oxygen Antagonism The effect of the combination is less than the sum of individual effects Anticline Structural configuration of a package of folding rocks in which the rocks are tilted in different directions from the crest Antiknock Resistance to detonation or pinging in sparkignition engines Antiknock agent A chemical compound such as tetraethyl lead which when added in small amount to the fuel charge of an internalcombustion engine tends to lessen knocking Antistripping agent An additive used in an asphaltic binder to overcome the natural affinity of an aggregate for water instead of asphalt Aphotic zone The deeper part of the ocean beneath the photic zone where light does not penetrate sufficiently for photosynthesis to occur API gravity An American Petroleum Institute measure of density for petroleum API Gravity 1415specific gravity at 156C 1315 fresh water has a gravity of 10API The scale is commercially important for ranking oil quality heavy oils are typi cally 20API medium oils are 2035API light oils are 3545API Apparent bulk density The density of a catalyst as measured usually loosely compacted in a container Apparent viscosity The viscosity of a fluid or several fluids flowing simultaneously measured in a porous medium rock and subject to both viscosity and permeability effects also called effective viscosity Aquasphere The water areas of the earth also called the hydrosphere Aquatic chemistry The branch of environmental chemistry that deals with chemical phenomena in water Aquifer A waterbearing layer of soil sand gravel rock or other geologic formation that will yield usable quantities of water to a well under normal hydraulic gradients or by pumping Arene A hydrocarbon that contains at least one aromatic ring OH Acidic function N Basic function 498 Glossary Aromatic An organic cyclic compound that contains one or more benzene rings these can be monocyclic bicyclic or polycyclic hydrocarbons and their substituted derivatives In aro matic ring structures every ring carbon atom possesses one double bond Aromatic hydrocarbon A hydrocarbon characterized by the presence of an aromatic ring or condensed aromatic rings benzene and substituted benzene naphthalene and substituted naphthalene phenanthrene and substituted phenanthrene as well as the higher condensed ring systems compounds that are distinct from those of aliphatic compounds or alicyclic compounds Aromatic ring An exceptionally stable planar ring of atoms with resonance structures that consist of alternating double and single bonds such as benzene Aromatic compound A compound containing an aromatic ring aromatic compounds have strong characteristic odors Aromatization The conversion of nonaromatic hydrocarbons to aromatic hydrocarbons by 1 rearrangement of aliphatic noncyclic hydrocarbons into aromatic ring structures and 2 dehydrogenation of alicyclic hydrocarbons naphthenes Arosorb process A process for the separation of aromatic derivatives from nonaromatic deriva tives by adsorption on a gel from which they are recovered by desorption Aryl A molecular fragment or group attached to a molecule by an atom that is on an aromatic ring Asphalt The nonvolatile product obtained by distillation and treatment of an asphaltic crude oil a manufactured product Asphalt cement Asphalt especially prepared as to quality and consistency for direct use in the manufacture of bituminous pavements Asphalt emulsion An emulsion of asphalt cement in water containing a small amount of emulsify ing agent Asphalt flux An oil used to reduce the consistency or viscosity of hard asphalt to the point required for use Asphalt primer A liquid asphaltic material of low viscosity which upon application to a non bituminous surface to waterproof the surface and prepare it for further construction Asphaltene association factor The number of individual asphaltene species which associate in nonpolar solvents as measured by molecular weight methods the molecular weight of asphaltenes in toluene divided by the molecular weight in a polar nonassociating solvent such as dichlorobenzene pyridine or nitrobenzene Asphaltene fraction A complex mixture of heavy organic compounds precipitated from crude oil and bitumen by natural processes or in laboratory by addition of excess npentane or nheptane after precipitation of the asphaltene fraction the remaining oil or bitumen consists of saturates aromatics and resins Asphaltic pyrobitumen See Asphaltoid Asphaltic road oil A thick fluid solution of asphalt usually a residual oil See also nonasphaltic road oil Asphaltite A variety of naturally occurring dark brown to black solid nonvolatile bituminous material that is differentiated from bitumen primarily by a high content of material insol uble in npentane asphaltene or other liquid hydrocarbons Asphaltoid A group of brown to black solid bituminous materials of which the members are dif ferentiated from asphaltites by their infusibility and low solubility in carbon disulfide Asphaltum See Asphalt Assay Qualitative or more usually quantitative determination of the components of a material or system 499 Glossary Associated gas Natural gas that is in contact with andor dissolved in the crude oil of the reservoir It may be classified as gas cap free gas or gas in solution dissolved gas Associated gas in solution or dissolved gas Natural gas dissolved in the crude oil of the reser voir under the prevailing pressure and temperature conditions Associated molecular weight The molecular weight of asphaltenes in an associating nonpolar solvent such as toluene Association colloids Colloids which consist of special aggregates of ions and molecules micelles ASTM International An international organization headquartered in the United States that provides standard test methods that are used to assert the quality of products including materials processes and services and personnel for industries that desire an independent thirdparty demonstration of compliance to standards andor are facing regulatory pres sures to prove compliance to standards formerly called the American Society for Testing and Materials Asymmetric carbon A carbon atom covalently bonded to four different atoms or groups of atoms Atmosphere The thin layer of gases that cover surface of the earth composed of two major com ponents nitrogen 7808 and oxygen 20955 with smaller amounts of argon 0934 car bon dioxide 0035 neon 1818 103 krypton 114 104 helium 524 104 and xenon 87 106 may also contain 015 water by volume with a normal range of 13 the reservoir of gases moderates the temperature of the earth absorbs energy and damaging ultraviolet radiation from the sun transports energy away from equatorial regions and serves as a pathway for vaporphase movement of water in the hydrologic cycle Atmospheric residuum A residuum obtained by distillation of a crude oil under atmospheric pres sure and which boils above 350C 660F Atmospheric equivalent boiling point AEBP A mathematical method of estimating the boiling point at atmospheric pressure of nonvolatile fractions of petroleum Atomic number The atomic number is equal to the number of positively charged protons in the nucleus of an atom which determines the identity of the element Atomic radius The relative size of an atom among the main group of elements atomic radii mostly decrease from left to right across rows in the periodic table metal ions are smaller than their neutral atoms and nonmetallic anions are larger than the atoms from which they are formed atomic radii are expressed in angstrom units of length Å ATSDR Agency for Toxic Substances and Disease Registry Attainment area A geographical area that meets NAAQS for criteria air pollutants See also Non attainment area Attapulgus clay See Fullers earth Attenuation The set of humanmade or natural processes that either reduce or appear to reduce the amount of a chemical compound as it migrates away or is disposed from one specific point toward another point in space or time for example the apparent reduction in the amount of a chemical in a groundwater plume as it migrates away from its source degradation dilu tion dispersion sorption or volatilization are common processes of attenuation Autofining A catalytic process for desulfurizing distillates Autoignition Temperature AIT A fixed temperature above which a flammable mixture is capa ble of extracting sufficient energy from the environment to selfignite Autotrophs Organisms or chemicals that use carbon dioxide and ionic carbonates for the carbon that they require Average particle size The weighted average particle diameter of a catalyst Aviation gasoline Any of the special grades of gasoline suitable for use in certain airplane engines Aviation turbine fuel See Jet fuel Avogadros number The number of molecules 6023 1023 in one grammole of a substance Bacteria Singlecelled prokaryotic microorganisms that may be shaped as rods bacillus spheres coccus or spirals vibrios spirilla spirochetes 500 Glossary Baghouse A filter system for the removal of particulate matter from gas streams socalled because of the similarity of the filters to coal bags Bank The concentration of oil oil bank in a reservoir that moves cohesively through the reservoir BariSol process A dewaxing process which employs a mixture of ethylene dichloride and benzol as the solvent Barrel The unit of measurement of liquids in the petroleum industry equivalent to 42 US stan dard gallons or 336 imperial gallons Barrel of oil equivalent BOE A measure used to aggregate oil and gas resources or production with one BOE being approximately equal to 6000 ft3 of natural gas Base A substance which gives off hydroxide ions OH in solution Basement The foot or base of a sedimentary sequence composed of igneous or metamorphic rocks Base number The quantity of acid expressed in milligrams of potassium hydroxide per gram of sample that is required to titrate a sample to a specified end point Base stock A primary refined petroleum fraction into which other oils and additives are added blended to produce the finished product Basic Having the characteristics of a base Basic nitrogen Nitrogen in petroleum which occurs in pyridine form Basic sediment and water BSW BSW The material which collects in the bottom of storage tanks usually composed of oil water and foreign matter also called bottoms bottom settlings Battery A series of stills or other refinery equipment operated as a unit Baumé gravity The specific gravity of liquids expressed as degrees on the Baumé oBé scale for liquids lighter than water Spgr60 F 140 130 Bé For liquids heavier than water Spgr60 F 145 145 Bé Bauxite Mineral matter used as a treating agent hydrated aluminum oxide formed by the chemical weathering of igneous rock Bbl See Barrel Bell cap A hemispherical or triangular cover placed over the riser in a distillation tower to direct the vapors through the liquid layer on the tray see Bubble cap Bender process A chemical treating process using lead sulfide catalyst for sweetening light distil lates by which mercaptans are converted to disulfides by oxidation Benthic zone The ecological region at the lowest level of a body of water such as an ocean or a lake including the sediment surface and some subsurface layers organisms living in this zone benthos or benthic organisms generally live in close relationship with the substrate bottom many such organisms are permanently attached to the bottom because light does not penetrate very deep ocean water the energy source for the ben thic ecosystem is often organic matter from higher up in the water column which sinks to the depths Benzene A colorless liquid formed from both anthropogenic activities and natural processes widely used in the United States and ranks in the top 20 chemicals used a natural part of crude oil gasoline and cigarette smoke one of the major components of JP8 fuel Benzin A refined light naphtha used for extraction purposes Benzine An obsolete term for light petroleum distillates covering the gasoline and naphtha range see Ligroine Benzoic acid C6H5CO2H The simplest aromatic carboxylic acid formed by the vigorous oxida tion of alkyl benzene benzyl alcohol and benzaldehyde 501 Glossary Benzol The general term which refers to commercial or technical not necessarily pure benzene also the term used for aromatic naphtha Betascission The rupture of a carboncarbon bond two bonds removed from an aromatic ring Billion 1 109 Bimolecular reaction The collision and combination of two reactants involved in the ratelimiting step Bioaccumulation The accumulation of substances such as pesticides or other chemicals in an organism occurs when an organism absorbs a chemicalpossibly a toxic chemicalat a rate faster than that at which the substance is lost by catabolism and excretion the longer the biological halflife of a toxic substance the greater the risk of chronic poisoning even if environmental levels of the toxin are not very high see Biomagnification Bioaugmentation A process in which acclimated microorganisms are added to soil and ground water to increase biological activity Spray irrigation is typically used for shallow contami nated soils and injection wells are used for deeper contaminated soils Biochemical oxygen demand BOD An important water quality parameter refers to the amount of oxygen utilized when the organic matter in a given volume of water is degraded biologically Biocide A chemical substance or microorganism intended to destroy deter render harmless or exert a controlling effect on any harmful organism by chemical or biological means Biodegradation The natural process whereby bacteria or other microorganisms chemically alter and breakdown organic molecules the breakdown or transformation of a chemical sub stance or substances by microorganisms using the substance as a carbon andor energy source Biogeochemical cycle The pathway by which a chemical moves through biotic biosphere and abiotic atmosphere aquasphere lithosphere compartments of the earth Bioinorganic compounds Natural and synthetic compounds that include metallic elements bonded to proteins and other biological chemistries Biological marker biomarker Complex organic compounds composed of carbon hydrogen and other elements which are found in oil bitumen rocks and sediments and which have undergone little or no change in structure from their parent organic molecules in living organisms typically biomarkers are isoprenoids composed of isoprene subunits biomarkers include compounds such as pristane phytane triterpane derivatives sterane derivatives and porphyrin derivatives Biomagnification The increase in the concentration of heavy metals ie mercury or organic contaminants such as chlorinated hydrocarbons in organisms as a result of their consump tion within a food chainweb an example is the process by which contaminants such as polychlorobiphenyl derivatives PCBs accumulate or magnify as they move up the food chainPCBs concentrate in tissue and internal organs and as big fish eat little fish they accumulate all the PCBs that have been eaten by everyone below them in the food chain can occur as a result of i persistence in which the chemical cannot be broken down by environmental processes ii food chain energetics in which the concentration of the chem ical increases progressively as it moves up a food chain and iii a low or nonexistent rate of internal degradation or excretion of the substance that is often due to waterinsolubility Biomass Biological organic matter Biopolymer A high molecular weight carbohydrate produced by bacteria Bioremediation A treatment technology that uses biological activity to reduce the concentration or toxicity of contaminants materials are added to contaminated environments to accelerate natural biodegradation Biosphere A term representing all of the living entities on the earth Biota Living organisms that constitute the plant and animal life of a region arctic region temper ate region subtropical region or tropical region 502 Glossary Bitumen A complex mixture of hydrocarbonaceous constituents of natural or pyrogenous origin or a combination of both Bituminous Containing bitumen or constituting the source of bitumen Bituminous rock See Bituminous sand Bituminous sand A formation in which the bituminous material see Bitumen is found as a filling in veins and fissures in fractured rock or impregnating relatively shallow sand sandstone and limestone strata a sandstone reservoir that is impregnated with a heavy viscous black petroleumlike material that cannot be retrieved through a well by conventional production techniques Black acids A mixture of the sulfonates found in acid sludge which are insoluble in naphtha ben zene and carbon tetrachloride very soluble in water but insoluble in 30 sulfuric acid in the dry oilfree state the sodium soaps are black powders Black oil Any of the darkcolored oils that does not give any measure of the quality of the oil a term now often applied to heavy oil Black soap See Black acid Black strap The black material mainly lead sulfide formed in the treatment of sour light oils with doctor solution and found at the interface between the oil and the solution Blown asphalt The asphalt prepared by air blowing a residuum or an asphalt BOE See Barrel of oil equivalent BOED Barrels of oil equivalent per day Bogging A condition that occurs in a coking reactor when the conversion to coke and light ends is too slow causing the coke particles to agglomerate Boiling liquid expanding vapor explosion BLEVE An event which occurs when a vessel rup tures which contains a liquid at a temperature above its atmospheric pressure boiling point the explosive vaporization of a large fraction of the vessel contents possibly followed by the combustion or explosion of the vaporized cloud if it is combustible similar to a rocket Boiling point The temperature at which a liquid begins to boilthat is it is the temperature at which the vapor pressure of a liquid is equal to the atmospheric or external pressure The boiling point distributions of crude oils and petroleum products may be in a range from 30C to in excess of 700C 86F1290F Boiling range The range of temperature usually determined at atmospheric pressure in stan dard laboratory apparatus over which the distillation of an oil commences proceeds and finishes Bottled gas Usually butane or propane or butanepropane mixtures liquefied and stored under pressure for domestic use see also liquefied petroleum gas Bottoms The liquid which collects in the bottom of a vessel tower bottoms tank bottoms either during distillation also the deposit or sediment formed during storage of petroleum or a petroleum product see also Residuum and Basic sediment and water Breakdown product A compound derived by chemical biological or physical action on a chemi cal compound the breakdown is a process which may result in a more toxic or a less toxic compound and a more persistent or less persistent compound than the original compound Bright stock Refined highviscosity lubricating oils usually made from residual stocks by pro cesses such as a combination of acid treatment or solvent extraction with dewaxing or clay finishing British thermal unit See Btu Bromine number The number of grams of bromine absorbed by 100 g of oil which indicates the percentage of double bonds in the material Brown acid Oilsoluble petroleum sulfonates found in acid sludge which can be recovered by extraction with naphtha solvent Brownacid sulfonates are somewhat similar to mahogany sulfonates but are more watersoluble In the dry oilfree state the sodium soaps are light colored powders 503 Glossary Brown soap See Brown acid Brønsted acid A chemical species which can act as a source of protons Brønsted base A chemical species which can accept protons BSW See Basic sediment and water BTEX The collective name given to benzene toluene ethylbenzene and the xylene isomers p m and oxylene a group of volatile organic compounds VOCs found in petroleum hydrocarbons such as gasoline and other common environmental contaminants Btu British thermal unit The energy required to raise the temperature of one pound of water one degree Fahrenheit BTU See British thermal unit BTX The collective name given to benzene toluene and the xylene isomers p m and oxylene a group of volatile organic compounds VOCs found in petroleum hydrocarbons such as gasoline and other common environmental contaminants Bubble cap An inverted cup with a notched or slotted periphery to disperse the vapor in small bubbles beneath the surface of the liquid on the bubble plate in a distillation tower Bubble plate A tray in a distillation tower Bubble point The temperature at which incipient vaporization of a liquid in a liquid mixture occurs corresponding with the equilibrium point of 0 vaporization or 100 condensation Bubble tower A fractionating tower so constructed that the vapors rising pass up through lay ers of condensate on a series of plates or trays see Bubble plate the vapor passes from one plate to the next above by bubbling under one or more caps see Bubble cap and out through the liquid on the plate where the less volatile portions of vapor condense in bub bling through the liquid on the plate overflow to the next lower plate and ultimately back into the reboiler thereby effecting fractionation Bubble tray A circular perforated plates having the internal diameter of a bubble tower set at specified distances in a tower to collect the various fractions produced during distillation BuckleyLeverett method A theoretical method of determining frontal advance rates and satura tions from a fractional flow curve Buffer solution A solution that resists change in the pH even when small amounts of acid or base are added Bumping The knocking against the walls of a still occurring during distillation of petroleum or a petroleum product which usually contains water Bunker C oil See No 6 Fuel oil Burner fuel oil Any petroleum liquid suitable for combustion Burning oil An illuminating oil such as kerosene suitable for burning in a wick lamp Burning point See Fire point Burningquality index An empirical numerical indication of the likely burning performance of a furnace or heater oil derived from the distillation profile and the API gravity and gener ally recognizing the factors of paraffin character and volatility 504 Glossary Burton process An older thermal cracking process in which oil was cracked in a pressure still and any condensation of the products of cracking also took place under pressure Butadiene A colorless flammable hydrocarbon obtained from petroleum with the chemical for mula C4H6 CH2CHCHCH2 often used to make synthetic rubber Butane Either of two isomers of a gaseous hydrocarbon with the chemical formula C4HIO pro duced synthetically from petroleum uses include household fuel as a refrigerant aerosol propellant and in the manufacture of synthetic rubber Butane dehydrogenation A process for removing hydrogen from butane to produce butenes and on occasion butadiene Butane vaporphase isomerization A process for isomerizing nbutane to isobutane using alu minum chloride catalyst on a granular alumina support and with hydrogen chloride as a promoter Butylene A colorless flammable liquid gas with a detectable odor the butylene isomers have a chemical formula of C4H8 and are formed during the cracking of petroleum fractions used in the production of highoctane gasoline butyl alcohols and synthetic rubber Butylene isomers C1 C2 C3 C4 C5 fractions A common way of representing fractions containing a preponderance of hydrocarbons having 1 2 3 4 or 5 carbon atoms respectively and without reference to hydrocarbon type Calorific equivalence of dry gas to liquid factor The factor used to relate dry gas to its liquid equivalent It is obtained from the molar composition of the reservoir gas considering the unit heat value of each component and the heat value of the equivalence liquid often abbreviated to CEDGLF Carbenium ion A generic name for carbocation that has at least one important contributing struc ture containing a tervalent carbon atom with a vacant p orbital Carbanion The generic name for anions containing an even number of electrons and having an unshared pair of electrons on a carbon atom eg Cl3C Carbene The pentane or heptaneinsoluble material that is insoluble in benzene or toluene but which is soluble in carbon disulfide or pyridine a type of rifle used for hunting bison Carboid The pentane or heptaneinsoluble material that is insoluble in benzene or toluene and which is also insoluble in carbon disulfide or pyridine Carbon Element number 6 in the periodic table of elements IUPAC Name Common Name Structure Skeletal Formula But1ene αbutylene 2Zbut2ene cisβbutylene 2Ebut2ene transβbutylene 2methylprop1ene Isobutylene 505 Glossary Carbonate washing Processing using a mild alkali eg potassium carbonate process for emis sion control by the removal of acid gases from gas streams Carbon dioxideaugmented water flooding Injection of carbonated water or water and carbon dioxide to increase water flood efficiency see immiscible carbon dioxide displacement Carbonforming propensity See Carbon residue Carbonization The conversion of an organic compound into char or coke by heat in the substantial absence of air often used in reference to the destructive distillation with simultaneous removal of distillate of coal Carbon preference index CPI The ratio of odd to even nalkanes oddeven CPI alkanes are equally abundant in petroleum but not in biological materiala CPI near 1 is an indication of petroleum Carbon rejection Upgrading processes in which coke is produced eg coking Carbon residue The amount of carbonaceous residue remaining after thermal decomposition of petroleum a petroleum fraction or a petroleum product in a limited amount of air also called the coke or carbonforming propensity often prefixed by the terms Conradson or Ramsbottom in reference to the inventor of the respective tests Carbon tetrachloride A manufactured compound that does not occur naturally produced in large quantities to make refrigeration fluid and propellants for aerosol cans in the past carbon tetrachloride was widely used as a cleaning fluid in industry and dry cleaning businesses and in the household also used in fire extinguishers and as a fumigant to kill insects in grainthese uses were stopped in the mid1960s Carbonyl group A divalent group consisting of a carbon atom with a doublebond to oxygen for example acetone CH3COCH3 is a carbonyl group linking two methyl groups Carboxy group CO2H or COOH A carbonyl group to which a hydroxyl group is attached carboxylic acids have this functional group Carboxylic acid An organic molecule with a CO2H group hydrogen atom on the CO2H group ionizes in water the simplest carboxylic acids are formic acid HCOOH and acetic acid CH3COOH Cascade tray A fractionating device consisting of a series of parallel troughs arranged on stair step fashion in which liquid frown the tray above enters the uppermost trough and liquid thrown from this trough by vapor rising from the tray below impinges against a plate and a perforated baffle and liquid passing through the baffle enters the next longer of the troughs Casing Hickwalled steel pipe placed in wells to isolate formation fluids such as fresh water and to prevent borehole collapse Casinghead gas Natural gas which issues from the casinghead the mouth or opening of an oil well Casinghead gasoline The liquid hydrocarbon product extracted from casinghead gabby one of three methods compression absorption or refrigeration see also Natural gasoline Catabolism The breakdown of complex molecules into simpler ones through the oxidation of organic substrates to provide biologically available energyATP adenosine triphosphate is an example of such a molecule Catalysis The process where a catalyst increases the rate of a chemical reaction without modifying the overall standard Gibbs energy change in the reaction Catalyst A substance that alters the rate of a chemical reaction and may be recovered essentially unaltered in form or amount at the end of the reaction Catalyst selectivity The relative activity of a catalyst with respect to a particular compound in a mixture or the relative rate in competing reactions of a single reactant Catalyst stripping The introduction of steam at a point where spent catalyst leaves the reactor in order to strip ie remove deposits retained on the catalyst Catalytic activity The ratio of the space velocity of the catalyst under test to the space velocity required for the standard catalyst to give the same conversion as the catalyst being tested usually multiplied by 100 before being reported 506 Glossary Catalytic conversion The catalytic of or relating to a catalyst oxidation of carbon monoxide and hydrocarbons especially in automotive exhaust gas to carbon dioxide and water Catalytic cracking The conversion of highboiling feedstocks into lowerboiling products by means of a catalyst which may be used in a fixed bed or fluid bed Cat cracking See Catalytic cracking Catalytic reforming A chemical process which is used to convert lowoctane petroleum refinery naphtha into highoctane liquid products the product reformates are components of high octane gasoline rearranging hydrocarbon molecules in a gasoline boiling range feedstock to produce other hydrocarbons having a higher antiknock quality isomerization of paraf fins cyclization of paraffins to naphthenes dehydrocyclization of paraffins to aromatics Catforming A process for reforming naphtha using a platinumsilicaalumina catalyst which per mits relatively high space velocities and results in the production of highpurity hydrogen Cathode The electrode where electrons are gained reduction in redox reactions Cation exchange The interchange between a cation in solution and another cation in the boundary layer between the solution and surface of negatively charged material such as clay or organic matter Cationexchange capacity CEC The sum of the exchangeable bases plus total soil acidity at a specific pH usually 70 or 80 When acidity is expressed as salt extractable acidity the cationexchange capacity is called the effective cationexchange capacity ECEC because this is considered to be the CEC of the exchanger at the native pH value usually expressed in centimoles of charge per kilogram of exchanger cmolkg or millimoles of charge per kilogram of exchanger Caustic consumption The amount of caustic lost from reacting chemically with the minerals in the rock the oil and the brine Caustic wash The process of treating a product with a solution of caustic soda to remove minor impurities often used in reference to the solution itself Cellulose A polysaccharide polymer of glucose that is found in the cell walls of plants a fiber that is used in many commercial products notably paper CERCLA Comprehensive Environmental Response Compensation and Liability Act This law created a tax on the chemical and petroleum industries and provided broad federal author ity to respond directly to releases or threatened releases of hazardous substances that may endanger public health or the environment Cetane index An approximation of the cetane number calculated from the density and midboiling point temperature see also Diesel index Cetane number A number indicating the ignition quality of diesel fuel a high cetane number represents a short ignition delay time Chain reaction A reaction in which one or more reactive reaction intermediates frequently radi cals are continuously regenerated usually through a repetitive cycle of elementary steps the propagation step for example in the chlorination of methane by a radical mecha nism Cl is continuously regenerated in the chain propagation steps Cl CH HCl H C 4 3 H3C Cl CH Cl Cl 2 3 In chain polymerization reactions reactive intermediates of the same types generated in successive steps or cycles of steps differ in relative molecular mass Characterization factor The UOP characterization factor K defined as the ratio of the cube root of the molal average boiling point TB in degrees Rankine R F 460 to the specific gravity at 60F60F K T sp gr B 13 507 Glossary The value ranges from 125 for paraffin stocks to 100 for the highly aromatic stocks also called the Watson characterization factor Check standard An analyte with a wellcharacterized property of interest eg concentration density and other properties that is used to verify method instrument and operator per formance during regular operation check standards may be obtained from a certified supplier may be a pure substance with properties obtained from the literature or may be developed inhouse Chelating agents Complexforming agents having the ability to solubilize heavy metals Chemical bond The forces acting among two atoms or groups of atoms that lead to the forma tion of an aggregate with sufficient stability to be considered as an independent molecular species Chemical change Processes or events that alter the fundamental structure of a chemical Chemical dispersion In relation to oil spills this term refers to the creation of oilinwater emul sions by the use of chemical dispersants made for this purpose Chemical induction coupling When one reaction accelerates another in a chemical system there is said to be chemical induction or coupling Coupling is caused by an intermediate or byproduct of the inducing reaction that participates in a second reaction chemical induc tion is often observed in oxidationreduction reactions Chemical octane number The octane number added to gasoline by refinery processes or by the use of octane number improvers such as tetraethyl lead Chemical reaction A process that results in the interconversion of chemical species Chemical species An ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on the time scale of the experiment the term is applied equally to a set of chemically identical atomic or molecular structural units in a solid array Chemical waste Any solid liquid or gaseous waste material that if improperly managed or disposed may pose substantial hazards to human health and the environment Chemical weight The weight of a molar sample as determined by the weight of the molecules the molecular weight calculated from the weights of the atoms in the molecule Chemistry The science that studies matter and all of the possible transformations of matter Chemotrophs Organisms or chemicals that use chemical energy derived from oxidationreduction reactions for their energy needs Chirality The ability of an object or a compound to exist in right and lefthanded forms a chiral compound will rotate the plane of planepolarized light Chlorex process A process for extracting lubricatingoil stocks in which the solvent used is Chlorex ß ß dichlorodiethyl ether Chlorinated solvent A volatile organic compound containing chlorine common solvents are tri chloroethylene tetrachloroethylene and carbon tetrachloride Chlorofluorocarbon Gases formed of chlorine fluorine and carbon whose molecules normally do not react with other substances formerly used as spray can propellants they are known to destroy the protective ozone layer of the earth Chromatographic adsorption Selective adsorption on materials such as activated carbon alu mina or silica gel liquid or gaseous mixtures of hydrocarbons are passed through the adsorbent in a stream of diluent and certain components are preferentially adsorbed Chromatographic separation The separation of different species of compounds according to their size and interaction with the rock as they flow through a porous medium Chromatography A method of chemical analysis where compounds are separated by passing a mixture in a suitable carrier over an absorbent material compounds with different absorp tion coefficients move at different rates and are separated Cistrans isomers The difference in the positions of atoms or groups of atoms relative to a refer ence plane in an organic molecule in a cisisomer the atoms are on the same side of the 508 Glossary molecule but are on opposite sides in the transisomer sometimes called stereoisomers these arrangements are common in alkenes and cycloalkanes Clarified oil The heavy oil which has been taken from the bottom of a fractionator in a catalytic cracking process and from which residual catalyst has been removed Clarifier Equipment for removing the color or cloudiness of an oil or water by separating the foreign material through mechanical or chemical means may involve centrifugal action filtration heating or treatment with acid or alkali Clastic Composed of pieces of preexisting rock Clay A very finegrained soil that is plastic when wet but hard when fired typical clay minerals consist of silicate and aluminosilicate minerals that are the products of weathering reactions of other minerals the term is also used to refer to any mineral of very small particle size Clay contact process See Contact filtration Clay refining A treating process in which vaporized gasoline or other light petroleum product is passed through a bed of granular clay such as fullers earth Clay regeneration A process in which spent coarsegrained adsorbent clays from percolation pro cesses are cleaned for reuse by deoiling them with naphtha steaming out the excess naph tha and then roasting in a stream of air to remove carbonaceous matter Clay treating See Gray clay treating Clay wash Light oil such as naphtha or kerosene used to clean fullers earth after it has been used in a filter Clean water act The Clean Water Act establishes the basic structure for regulating discharges of pollutants into the waters of the United States It gives EPA the authority to implement pollution control programs such as setting wastewater standards for industry also con tinued requirements to set water quality standards for all contaminants in surface waters and makes it unlawful for any person to discharge any pollutant from a point source into navigable waters unless a permit was obtained under its provisions Cloud point The temperature at which paraffin wax or other solid substances begin to crystallize or separate from the solution imparting a cloudy appearance to the oil when the oil is chilled under prescribed conditions Cluster compounds Ensembles of bound atoms typically larger than a molecule yet more defined than a bulk solid Coal An organic rock Coalescence The union of two or more droplets to form a larger droplet and ultimately a continu ous phase Coal tar The specific name for the tar produced from coal Coal tar pitch The specific name for the pitch produced from coal Code of Federal Regulations CFR For example Title 40 40 CFR contains the regulations for protection of the environment Coefficient of linear thermal expansion The ratio of the change in length per degree C to the length at 0C Cofferdam also called a coffer A temporary enclosure built within or in pairs across a body of water and constructed to allow the enclosed area to be pumped out Coke A hard dry substance containing carbon that is produced by heating bituminous coal or other carbonaceous materials to a very high temperature in the absence of air used as a fuel Coke drum A vessel in which coke is formed and which can be cut oil from the process for cleaning Coke number Used particularly in Great Britain to report the results of the Ramsbottom carbon residue test which is also referred to as a coke test Coker The processing unit in which coking takes place Coking A process for the thermal conversion of petroleum in which gaseous liquid and solid coke products are formed 509 Glossary Cold pressing The process of separating wax from oil by first chilling to help form wax crystals and then filtering under pressure in a plate and frame press Cold production The use of operation and specialized exploitation techniques in order to rapidly produce heavy oils without using thermal recovery methods Cold settling Processing for the removal of wax from highviscosity stocks wherein a naphtha solution of the waxy oil is chilled and the wax crystallizes out of the solution Colligative properties The properties of a solution that depend only on the number of particles dissolved in it not the properties of the particles themselves the main colligative proper ties addressed at this website are boiling point elevation and freezing point depression Colloidal particles Particles which have some characteristics of both species in solution and larger particles in suspension which range in diameter form about 0001 micrometer μm to approximately 1 μm and which scatter white light as a light blue hue observed at right angles to the incident light Color stability The resistance of a petroleum product to color change for example due to exposure to light and aging Combination reactions Reactions where two substances combine to form a third substance an exam ple is two elements reacting to form a compound of the elements and is shown in the general form A B AB examples include 2Nas Cl2g 2NaCls and 8Fe S8 8FeS Combustible liquid A liquid with a flash point in excess of 378C 100F but below 933C 200F Combustion zone The volume of reservoir rock wherein petroleum is undergoing combustion dur ing enhanced oil recovery Cometabolism cometabolism The process by which compounds in petroleum may be enzymat ically attacked by microorganisms without furnishing carbon for cell growth and division a variation on biodegradation in which microbes transform a contaminant even though the contaminant cannot serve as the primary energy source for the organisms To degrade the contaminant the microbes require the presence of other compounds primary substrates that can support their growth Complex modulus A measure of the overall resistance of a material to flow under an applied stress in units of force per unit area It combines viscosity and elasticity elements to pro vide a measure of stiffness or resistance to flow The complex modulus is more useful than viscosity for assessing the physical behavior of very nonNewtonian materials such as emulsions Complex inorganic chemicals Molecules that consist of different types of atoms atoms of differ ent chemical elements which in chemical reactions are decomposed with the formation several other chemicals Composition The general chemical makeup of petroleum Completion interval The portion of the reservoir formation placed in fluid communication with the well by selectively perforating the wellbore casing Composition map A means of illustrating the chemical makeup of petroleum using chemical and or physical property data Compound The combination of two or more different elements held together by chemical bonds the elements in each compound are always combined in the same proportion by mass law of definite proportion Con carbon See Carbon residue Concentration Composition of a mixture characterized in terms of mass amount volume or number concentration with respect to the volume of the mixture Condensate A mixture of light hydrocarbon liquids obtained by condensation of hydrocarbon vapors predominately butane propane and pentane with some heavier hydrocarbons and relatively little methane or ethane see also Natural gas liquids Condensate recovery factor CRF The factor used to obtain liquid fractions recovered from natural gas in the surface distribution and transportation facilities It is obtained from the 510 Glossary gas and condensate handling statistics of the last annual period in the area corresponding to the field being studied Condensation aerosol Formed by condensation of vapors or reactions of gases Conjugate acid A substance which can lose an H ion to form a base Conjugate base A substance which can gain an H ion to form an acid Conradson carbon residue See Carbon residue Conservative constituent or compound One that does not degrade is unreactive and its move ment is not retarded within a given environment aquifer stream contaminant plume Constituent An essential part or component of a system or group that is an ingredient of a chemi cal mixture for example benzene is one constituent of gasoline Contact filtration A process in which finely divided adsorbent clay is used to remove color bodies from petroleum products Contaminant A pollutant unless it has some detrimental effect can cause deviation from the normal composition of an environment a pollutant that causes deviations from the normal composition of an environment Are not classified as pollutants unless they have some detrimental effect Continuous contact coking A thermal conversion process in which petroleumwetted coke par ticles move downward into the reactor in which cracking coking and drying take place to produce coke gas gasoline and gas oil Continuous contact filtration A process to finish lubricants waxes or special oils after acid treat ing solvent extraction or distillation Conventional recovery Primary andor secondary recovery Conversion The thermal treatment of petroleum which results in the formation of new products by the alteration of the original constituents Conversion cost The cost of changing a production well to an injection well or some other change in the function of an oilfield installation Conversion factor The percentage of feedstock converted to light ends gasoline other liquid fuels and coke Coordination compounds Compounds where the central ion typically a transition metal is sur rounded by a group of anions or molecules Copper sweetening Processes involving the oxidation of mercaptans to disulfides by oxygen in the presence of cupric chloride Corrosion Oxidation of a metal in the presence of air and moisture Covalent bond A region of relatively high electron density between atomic nuclei that results from sharing of electrons and that gives rise to an attractive force and a characteristic inter nuclear distance carbonhydrogen bonds are covalent bonds Cp centipoise A unit of viscosity Cracked residua Residua that have been subjected to temperatures above 350C 660F during the distillation process Cracking temperature The temperature 350C 660F at which the rate of thermal decomposi tion of petroleum constituents becomes significant Cracking The process in which large molecules are broken down thermally decomposed into smaller molecules used especially in the petroleum refining industry Critical point The combination of critical temperature and critical pressure the temperature and pressure at which two phases of a substance in equilibrium become identical and form a single phase Critical pressure The pressure required to liquefy a gas at its critical temperature the minimum pressure required to condense gas to liquid at the critical temperature a substance is still a fluid above the critical point neither a gas nor a liquid and is referred to as a supercritical fluid expressed in atmosphere or psi Critical temperature The temperature above which a gas cannot be liquefied regardless of the amount of pressure applied the temperature at the critical point end of the vapor pressure 511 Glossary curve in phase diagram at temperatures above critical temperature a substance cannot be liquefied no matter how great the pressure expressed in C Crosslinking Combining of two or polymer molecules by use of a chemical that mutually bonds with a part of the chemical structure of the polymer molecules Crude assay A procedure for determining the general distillation characteristics eg distillation profile and other quality information of crude oil Crude oil See Petroleum Cryogenic plant A processing plant capable of producing liquid natural gas products including ethane at very low operating temperatures Cryogenics The study production and use of low temperatures Culture The growth of cells or microorganisms in a controlled artificial environment Cumene A colorless liquid C6H5CHCH32 used as an aviation gasoline blending component and as an intermediate in the manufacture of chemicals Cut point The boiling temperature division between distillation fractions of petroleum Cutback The term applied to the products from blending heavier feedstocks or products with lighter oils to bring the heavier materials to the desired specifications Cutback asphalt Asphalt liquefied by the addition of a volatile liquid such as naphtha or kerosene which after application and on exposure to the atmosphere evaporates leaving the asphalt Cutting oil An oil to lubricate and cool metalcutting tools also called cutting fluid cutting lubricant Cycle stock The product taken from some later stage of a process and recharged recycled to the process at some earlier stage Cyclic compound A molecule which has the two ends of the carbon chain connected to form a ring Cyclization The process by which an openchain hydrocarbon structure is converted to a ring structure eg hexane to benzene Cyclo The prefix used to indicate the presence of a ring Cycloalkanes naphthene cycloparaffin A saturated cyclic compound containing only carbon and hydrogen One of the simplest cycloalkanes is cyclohexane C6H12 sterane derivatives and triterpane derivatives are branched naphthene derivatives consisting of multiple con densed five or sixcarbon rings Cyclone A device for extracting dust from industrial waste gases It is in the form of an inverted cone into which the contaminated gas enters tangential from the top the gas is propelled down a helical pathway and the dust particles are deposited by means of centrifugal force onto the wall of the scrubber Daughter product A compound that results directly from the degradation of another chemical Deactivation The reduction in catalyst activity by the deposition of contaminants eg coke metals during a process Dealkylation The removal of an alkyl group from aromatic compounds Deasphalted oil Typically the soluble material after the insoluble asphaltic constituents have been removed commonly but often incorrectly used in place of deasphaltened oil see Deasphalting Deasphaltened oil The fraction of petroleum after only the asphaltene constituents have been removed Deasphaltening The removal of a solid powdery asphaltene fraction from petroleum by the addi tion of the lowboiling liquid hydrocarbons such as npentane or nheptane under ambient conditions Deasphalting The removal of the asphaltene fraction from petroleum by the addition of a low boiling hydrocarbon liquid such as npentane or nheptane more correctly the removal asphalt tacky semisolid from petroleum as occurs in a refinery asphalt plant by the addition of liquid propane or liquid butane under pressure 512 Glossary Debutanization Distillation to separate butane and lighter components from higherboiling components Decant oil The highestboiling product from a catalytic cracker also referred to as slurry oil clari fied oil or bottoms Decarbonizing A thermal conversion process designed to maximize coker gasoil production and minimize coke and gasoline yields operated at essentially lower temperatures and pres sures than delayed coking Decoking Removal of petroleum coke from equipment such as coking drums hydraulic decoking uses highvelocity water streams Decolorizing Removal of suspended colloidal and dissolved impurities from liquid petroleum products by filtering adsorption chemical treatment distillation bleaching etc Decomposition reactions Reactions in which a single compound reacts to give two or more prod ucts an example of a decomposition reaction is the decomposition of mercury II oxide into mercury and oxygen when the compound is heated a compound can also decompose into a compound and an element or two compounds Deethanization Distillation to separate ethane and lighter components from propane and higher boiling components also called deethanation Deflagration An explosion with a flame front moving in the unburned gas at a speed below the speed of sound 1250 fts Degradation The breakdown or transformation of a compound into byproducts andor end products Degree of completion The percentage or fraction of the limiting reactant that has been converted to products Dehydrating agents Substances capable of removing water drying or the elements of water from another substance Dehydration reaction condensation reaction A chemical reaction in which two organic mol ecules become linked to each other via covalent bonds with the removal of a molecule of water common in synthesis reactions of organic chemicals Dehydrocyclization Any process by which both dehydrogenation and cyclization reactions occur Dehydrogenation The removal of hydrogen from a chemical compound for example the removal of two hydrogen atoms from butane to make butenes as well as the removal of additional hydrogen to produce butadiene Dehydrohalogenation Removal of hydrogen and halide ions from an alkane resulting in the for mation of an alkene Denitrification Bacterial reduction of nitrate to nitrite to gaseous nitrogen or nitrous oxides under anaerobic conditions Delayed coking A coking process in which the thermal reactions are allowed to proceed to com pletion to produce gaseous liquid and solid coke products Delimitation An exploration activity that increases or decreases reserves by means of drilling delimiting wells Demethanization The process of distillation in which methane is separated from the higher boiling components also called demethanation Density The mass per unit volume of a substance Density is temperaturedependent generally decreasing with temperature The density of oil relative to water its specific gravity gov erns whether a particular oil will float on water Most fresh crude oils and fuels will float on water Bitumen and certain residual fuel oils however may have densities greater than water at some temperature ranges and may submerge in water The density of a spilled oil will also increase with time as components are lost due to weathering Deoiling Reduction in quantity of liquid oil entrained in solid wax by draining sweating or by a selective solvent see MEK deoiling Depentanizer A fractionating column for the removal of pentane and lighter fractions from a mixture of hydrocarbons 513 Glossary Depropanization Distillation in which lighter components are separated from butanes and higher boiling material also called depropanation Derivative products Petrochemical derivative products which can be made in a number of differ ent ways via intermediates which still contain only carbon and hydrogen through inter mediates that incorporate chlorine nitrogen or oxygen in the finished derivative some derivatives are finished products while further steps are required for others to arrive at the desired composition Desalting Removal of mineral salts mostly chlorides from crude oils Desulfurization The removal of sulfur or sulfur compounds from a feedstock Desorption The release of ions or molecules from solids into solution Detection limit in analysis The minimum single result that with a stated probability can be dis tinguished from a representative blank value during the laboratory analysis of substances such as water soil air rock and biota Detergent A cleansing agent especially a surfaceactive chemical such as an alkyl sulfonate Detergent oil Lubricating oil possessing special sludgedispersing properties for use in internal combustion engines Detonation An explosion with a shock wave moving at a speed greater than the speed of sound in the unreacted medium Dewaxing See Solvent dewaxing Dew point pressure The pressure at which the first drop of liquid is formed when it goes from the vapor phase to the twophase region Devolatilized fuel Smokeless fuel coke that has been reheated to remove all of the volatile material 14Dichlorobenzene A chemical used to control moths molds and mildew and to deodorize restrooms and waste containers does not occur naturally but is produced by chemical companies to make products for home use and other chemicals such as resins most of the 14dichlorobenzene enters the environment as a result of its use in mothrepellant products and in toiletdeodorizer blocks Because it changes from a solid to a gas easily sublimes almost all 14dichlorobenzene produced is released into the air Dichloroelimination Removal of two chlorine atoms from an alkane compound and the formation of an alkene compound within a reducing environment Dichloromethane CH2Cl2 An organic solvent often used to extract organic substances from sam ples toxic but much less so than chloroform or carbon tetrachloride which were previ ously used for this purpose Diene A hydrocarbon with two double bonds Diesel fuel Fuel used for internal combustion in diesel engines usually that fraction which distills after kerosene Diesel cycle A repeated succession of operations representing the idealized working behavior of the fluids in a diesel engine Dieselindex anilinepoint F APIgravity 100 Diesel knock The result of a delayed period of ignition is long and the accumulated of diesel fuel in the engine Differential thermal analysis DTA and thermogravimetric analysis TGA Techniques that may be used to measure the water of crystallization of a salt and the thermal decomposi tion of hydrates Diffuse layer The region of ion adsorption near a sorbent surface that is subject to diffusion with the bulk solution diffuse layer ions are not immediately adjacent to the surface but rather are distributed between the inner Stern layer ions and the bulk solution by balance of electrostatic attraction to the sorbent and diffusion away from the sorbent see Stern layer 514 Glossary Dihaloelimination Removal of two halide atoms from an alkane compound and the formation of an alkene compound within a reducing environment Dilution The process of decreasing the concentration for example of a solute in a solution usually by mixing the solution with more solvent without the addition of more solute Dilution capacity of a waterbased ecosystem The effective volume of receiving water available for the dilution of the discharged chemical Diols Chemical compounds that contain two hydroxy OH groups generally assumed to be but not necessarily alcoholic aliphatic diols are also called glycols Dipoledipole forces Intermolecular forces that exist between polar molecules Active only when the molecules are close together The strengths of intermolecular attractions increase when polarity increases Dispersion Is an intermolecular attraction force that exists between all molecules These forces are the result of the movement of electrons which cause slight polar moments Dispersion forces are generally very weak but as the molecular mass increases so does their strength Dispersion forces also called London dispersion forces Direct emissions Emissions from sources that are owned or controlled by the reporting entity Dispersant chemical dispersant A chemical that reduces the surface tension between water and a hydrophobic substance such as oil In the case of an oil spill dispersants facilitate the breakup and dispersal of an oil slick throughout the water column in the form of an oilin water emulsion chemical dispersants can only be used in areas where biological damage will not occur and must be approved for use by government regulatory agencies Dispersion aerosol Formed by grinding of solids atomization of liquids or dispersion of dusts a colloidalsized particle in the atmosphere formed Dissolved oxygen DO The key substance in determining the extent and kinds of life in a body of water Distillation A process for separating liquids with different boiling points Distillation curve See Distillation profile Distillation loss The difference in a laboratory distillation between the volume of liquid originally introduced into the distilling flask and the sum of the residue and the condensate recovered Distillation range The difference between the temperature at the initial boiling point and at the end point as obtained by the distillation test Distillation profile The distillation characteristics of petroleum or petroleum products showing the temperature and the percent distilled Doctor solution A solution of sodium plumbite used to treat gasoline or other light petroleum dis tillates to remove mercaptan sulfur see also Doctor test Doctor sweetening A process for sweetening gasoline solvents and kerosene by converting mer captans to disulfides using sodium plumbite and sulfur Doctor test A test used for the detection of compounds in light petroleum distillates which react with sodium plumbite see also Doctor solution Domestic heating oil See No 2 Fuel Oil Donor solvent process A conversion process in which hydrogen donor solvent is used in place of or to augment hydrogen Double bond A covalent bond resulting from the sharing of two pairs of electrons four electrons between two atoms Double displacement reactions Reactions where the anions and cations of two different mol ecules switch places to form two entirely different compounds These reactions are in the general form AB CD AD CB An example is the reaction of lead II nitrate with potassium iodide to form lead II iodide and potassium nitrate Pb NO 2KI PbI 2KNO 3 2 2 3 515 Glossary A special kind of double displacement reaction takes place when an acid and base react with each other the hydrogen ion in the acid reacts with the hydroxyl ion in the base caus ing the formation of water Generally the product of this reaction is some ionic salt and water HA BOH H O BA 2 An example is the reaction of hydrobromic acid HBr with sodium hydroxide HBr NaOH NaBr H O 2 Downgradient In the direction of decreasing static hydraulic head Downstream The oil and gas industry is usually divided into three major parts upstream mid stream and downstream Downstream commonly referred to as petrochemical is the refining of petroleum crude oil and the processing and purifying of raw natural gas as well as the marketing and distribution of products made from crude oil and natural gas Drug Any substance presented for treating curing or preventing disease in human beings or in animals a drug may also be used for making a medical diagnosis managing pain or for restoring correcting or modifying physiological functions Dry gas equivalent to liquid DGEL The volume of crude oil that because of its heat rate is equivalent to the volume of dry gas Dry gas Natural gas containing negligible amounts of hydrocarbons heavier than methane Dry gas is also obtained from the processing complexes Drying Removal of a solvent or water from a chemical substance also referred to as the removal of solvent from a liquid or suspension Dropping point The temperature at which grease passes from a semisolid to a liquid state under prescribed conditions Dry gas A gas which does not contain fractions that may easily condense under normal atmo spheric conditions Dry point The temperature at which the last drop of petroleum fluid evaporates in a distillation test Dualayer distillate process A process for removing mercaptans and oxygenated compounds from distillate fuel oils and similar products using a combination of treatment with concentrated caustic solution and electrical precipitation of the impurities Dualayer gasoline process A process for extracting mercaptans and other objectionable acidic compounds from petroleum distillates see also Dualayer solution Dualayer solution A solution which consists of concentrated potassium or sodium hydroxide containing a solubilizer see also Dualayer gasoline process Dubbs cracking An older continuous liquidphase thermal cracking process formerly used Dye A substance either natural or chemical used to color materials Ebullated bed A process in which the catalyst bed is in a suspended state in the reactor by means of a feedstock recirculation pump which pumps the feedstock upwards at sufficient speed to expand the catalyst bed at approximately 35 above the settled level Ecology The scientific study of the relationships between organisms and their environments Ecological chemistry The study of the interactions between organisms and their environment that are mediated by naturally occurring chemicals Ecology The study of environmental factors that affect organisms and how organisms interact with these factors and with each other Ecosystem A community of organisms together with their physical environment which can be viewed as a system of interacting and interdependent relationships this can also include processes such as the flow of energy through trophic levels as well as the cycling of chemi cal elements and compounds through living and nonliving components of the system the 516 Glossary trophic level of an organism is the position it occupies in a food chain Ecosystem a term representing an assembly of mutually interacting organisms and their environment in which materials are interchanged in a largely cyclical manner Edeleanu process A process for refining oils at low temperature with liquid sulfur dioxide SO2 or with liquid sulfur dioxide and benzene applicable to the recovery of aromatic concen trates from naphtha and heavier petroleum distillates Effective viscosity See Apparent viscosity Elastomer A material that can resume its original shape when a deforming force is removed such as natural or synthetic rubber Electric desalting A continuous process to remove inorganic salts and other impurities from crude oil by settling out in an electrostatic field Electrical precipitation A process using an electrical field to improve the separation of hydrocar bon reagent dispersions May be used in chemical treating processes on a wide variety of refinery stocks Electrofining A process for contacting a light hydrocarbon stream with a treating agent acid caustic doctor etc then assisting the action of separation of the chemical phase from the hydrocarbon phase by an electrostatic field Electrolytic mercaptan process A process in which aqueous caustic solution is used to extract mercaptans from refinery streams Electron acceptor The atom molecule or compound that receives electrons and therefore is reduced in the energyproducing oxidationreduction reactions that are essential for the growth of microorganisms and bioremediationcommon electron acceptors in bioreme diation are oxygen nitrate sulfate and iron Electron affinity The electron affinity of an atom or molecule is the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion Electron configuration of an atom The extranuclear structure the arrangement of electrons in shells and subshells chemical properties of elements their valence states and reactivity can be predicted from the electron configuration Electron donor The atom molecule or compound that donates electrons and therefore is oxi dized in bioremediation the organic contaminant often serves as an electron donor Electronegativity The tendency of an atom to attract electrons in a chemical bond nonmetals have high electronegativity fluorine being the most electronegative while alkali metals possess least electronegativity the electronegativity difference indicates polarity in the molecule Electrostatic precipitators Devices used to trap fine dust particles usually in the size range 3060 microns that operate on the principle of imparting an electric charge to particles in an incoming air stream and which are then collected on an oppositely charged plate across a highvoltage field Elimination A reaction where two groups such as chlorine and hydrogen are lost from adjacent carbon atoms and a double bond is formed in their place Empirical formula The simplest wholenumber ratio of atoms in a compound Emulsan Is a polyanionic heteropolysaccharide bioemulsifier produced by Acinetobacter calco aceticus RAG1 used to stabilize oilinwater emulsions Emulsion A stable mixture of two immiscible liquids consisting of a continuous phase and a dispersed phase Oil and water can form both oilinwater and waterinoil emulsions The former is termed a dispersion while emulsion implies the latter Waterinoil emulsions formed from petroleum and brine can be grouped into four stability classes stable a formal emulsion that will persist indefinitely mesostable which gradually degrade over time due to a lack of one or more stabilizing factors entrained water a mechanical mixture char acterized by high viscosity of the petroleum component which impedes separation of the two phases and unstable which are mixtures that rapidly separate into immiscible layers 517 Glossary Emulsion stability Generally accompanied by a marked increase in viscosity and elasticity over that of the parent oil which significantly changes behavior Coupled with the increased volume due to the introduction of brine emulsion formation has a large effect on the choice of countermeasures employed to combat a spill Emulsification The process of emulsion formation typically by mechanical mixing In the envi ronment emulsions are most often formed as a result of wave action Chemical agents can be used to prevent the formation of emulsions or to break the emulsions to their compo nent oil and water phases Endergonic reaction A chemical reaction that requires energy to proceed A chemical reaction is endergonic when the change in free energy is positive Endothermic reaction A chemical reaction in which heat is absorbed Engineered bioremediation A type of remediation that increases the growth and degradative activity of microorganisms by using engineered systems that supply nutrients electron acceptors andor other growthstimulating materials Engler distillation A standard test for determining the volatility characteristics of a gasoline by measuring the percent distilled at various specified temperatures Enhanced bioremediation A process which involves the addition of microorganisms eg fungi bacteria and other microbes or nutrients eg oxygen nitrates to the subsurface environ ment to accelerate the natural biodegradation process Entering group An atom or group that forms a bond to what is considered to be the main part of the substrate during a reaction for example the attacking nucleophile in a bimolecular nucleophilic substitution reaction Enthalpy of formation ΔHf The energy change or the heat of reaction in which a compound is formed from its elements energy cannot be created or destroyed but is converted from one form to another the enthalpy change or heat of reaction is ΔH H2 H1 H1 is the enthalpy of reactants and H2 the enthalpy of the products or heat of reaction when H2 is less than H1 the reaction is exothermic and ΔH is negative ie temperature increases when H2 is greater than H1 the reaction is endothermic and the temperature falls Entrained bed A bed of solid particles suspended in a fluid liquid or gas at such a rate that some of the solid is carried over entrained by the fluid Entropy A thermodynamic quantity that is a measure of disorder or randomness in a system the total entropy of a system and its surroundings always increases for a spontaneous process the total entropy of a system and its surroundings always increases for a spontaneous pro cess the standard entropies are entropy values for the standard states of substances Environment The total living and nonliving conditions of an organisms internal and external surroundings that affect an organisms complete life span the conditions that surround someone or something the conditions and influences that affect the growth health prog ress etc of someone or something the total living and nonliving conditions internal and external surroundings that are an influence on the existence and complete life span of the organism Environmental analytical chemistry The application of analytical chemical techniques to the analysis of environmental samplein a regulatory setting Environmental biochemistry The discipline that deals specifically with the effects of environ mental chemical species on life Environmental chemistry The study of the sources reactions transport effects and fates of chemical species in water soil and air environments and the effects of technology thereon Environmentalist A person working to solve environmental problems such as air and water pol lution the exhaustion of natural resources and uncontrolled population growth Environmental pollution The contamination of the physical and biological components of the earth system atmosphere aquasphere and geosphere to such an extent that normal envi ronmental processes are adversely affected 518 Glossary Environmental science The study of the environment its living and nonliving components and the interactions of these components Environmental studies The discipline dealing with the social political philosophical and ethical issues concerning mans interactions with the environment Enzyme A macromolecule mostly proteins or conjugated proteins produced by living organisms that facilitate the degradation of a chemical compound catalyst in general an enzyme catalyzes only one reaction type reaction specificity and operates on only one type of substrate substrate specificity any of a group of catalytic proteins that are produced by cells and that mediate or promote the chemical processes of life without themselves being altered or destroyed Epoxidation A reaction wherein an oxygen molecule is inserted in a carboncarbon double bond and an epoxide is formed Epoxides A subclass of epoxy compounds containing a saturated threemembered cyclic ether See Epoxy compounds Epoxy compounds Compounds in which an oxygen atom is directly attached to two adjacent or nonadjacent carbon atoms in a carbon chain or ring system thus cyclic ethers Equilibrium A state when the reactants and products are in a constant ratio The forward reaction and the reverse reactions occur at the same rate when a system is in equilibrium Equilibrium constant A value that expresses how far the reaction proceeds before reaching equi librium A small number means that the equilibrium is toward the reactants side while a large number means that the equilibrium is toward the products side Equilibrium expression The expression giving the ratio between the products and reactants The equilibrium expression is equal to the concentration of each product raised to its coefficient in a balanced chemical equation and multiplied together divided by the concentration of the product of reactants to the power of their coefficients Equipment blank A sample of analytefree media which has been used to rinse the sampling equipment It is collected after completion of decontamination and prior to sampling This blank is useful in documenting and controlling the preparation of the sampling and labora tory equipment Ester A compound formed from an acid and an alcohol in esters of carboxylic acids the COOH group and the OH group lose a moleculeof water and form a COO bond R1 and R2 represent organic groups R COOH R OH R COOR H O 1 2 1 2 2 Ethane A colorless odorless flammable gaseous alkane with the formula C2H6 used as a fuel and also in the manufacture of organic chemicals Ethanol See Ethyl alcohol Ether A compound with an oxygen atom attached to two hydrocarbon groups Any carbon com pound containing the functional group COC such as diethyl ether C2H5O C2H5 Ethoxy group CH3CH2O A twocarbon alkoxy substituent Ethyl alcohol ethanol or grain alcohol An inflammable organic compound C2H5OH formed during fermentation of sugars used as an intoxicant and as a fuel Ethylbenzene A colorless flammable liquid found in natural products such as coal tar and crude oil it is also found in manufactured products such as inks insecticides and paints a minor component of JP8 fuel Ethylene A colorless flammable gas containing only two carbons that are double bonded to one another CH2CH2 an olefin that is used extensively in chemical synthesis and to make many different plastics such as plastic used for water bottles Ethyl group CH3CH2 A twocarbon alkyl substituent Eurkaryotes Microorganisms that have welldefined cell nuclei enclosed by a nuclear membrane 519 Glossary Eutrophication The growth of algae may become quite high in very productive water with the result that the concurrent decomposition of dead algae reduces oxygen levels in the water to very low values Evaporation A process for concentrating nonvolatile solids in a solution by boiling off the liquid portion of the waste stream Excess reactant The excess of a reactant over the stoichiometric amount with the exception of the limiting reactant the term may refer to more than one reactant Exergy A combination property of a system and its environment because it depends on the state of both the system and environment the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir when the surroundings are the reservoir exergy is the potential of a system to cause a change as it achieves equilibrium with its environment and after the system and surroundings reach equilibrium the exergy is zero determining exergy is a prime goal of thermodynamics Exothermic reaction A reaction that produces heat and absorbs heat from the surroundings Explosive limits The limits of percentage composition of mixtures of gases and air within which an explosion takes place when the mixture is ignited Exsitu bioremediation A process which involves removing the contaminated soil or water to another location before treatment Extent of reaction The extent to which a reaction proceeds and the material actually reacting can be expressed by the extent of reaction in molesconventionally relates the feed quanti ties to the amount of each component present in the product stream after the reaction has proceeded to equilibrium through the stoichiometry of the reaction to a term that appears in all reactions Extractive distillation The separation of different components of mixtures which have similar vapor pressures by flowing a relatively highboiling solvent which is selective for one of the components in the feed down a distillation column as the distillation proceeds the selective solvent scrubs the soluble component from the vapor Extra heavy oil Crude oil with relatively high fractions of heavy components high specific grav ity low API density and high viscosity but mobile at reservoir conditions thermal recov ery methods are the most common form of commercially exploiting this kind of oil Facultative anaerobes Microorganisms that use and prefer oxygen when it is available but can also use alternate electron acceptors such as nitrate under anaerobic conditions when necessary Fate The ultimate disposition of the inorganic chemical in the ecosystem either by chemical or biological transformation to a new form which hopefully is nontoxic degradation or in the case of an ultimately persistent inorganic pollutants by conversion to a less offensive chemicals or even by sequestration in a sediment or other location which is expected to remain undisturbed Fat oil The bottom or enriched oil drawn from the absorber as opposed to lean oil Fatty acids Carboxylic acids with long hydrocarbon side chains most natural fatty acids have hydrocarbon chains that dont branch any double bonds occurring in the chain are cis isomersthe side chains are attached on the same side of the double bond FCC Fluid catalytic cracking FCCU Fluid catalytic cracking unit Feedstock Petroleum as it is fed to the refinery a refinery product that is used as the raw mate rial for another process the term is also generally applied to raw materials used in other industrial processes 520 Glossary Fauna All of the animal life of any particular region ecosystem or environment generally the naturally occurring or indigenous animal life native animal life Fermentation The process whereby microorganisms use an organic compound as both electron donor and electron acceptor converting the compound to fermentation products such as organic acids alcohols hydrogen and carbon dioxide microbial metabolism in which a particular compound is used both as an electron donor and an electron acceptor resulting in the production of oxidized and reduced daughter products Ferrocyanide process A regenerative chemical treatment for mercaptan removal using caustic sodium ferrocyanide reagent Field capacity or in situ field water capacity The water content on a mass or volume basis remaining in soil 2 or 3 days after having been wetted with water and after free drainage is negligible Fingerprint A chromatographic signature of relative intensities used in oiloil or oilsource rock correlations mass chromatograms of sterane derivatives or terpane derivatives are examples of fingerprints that can be used for qualitative or quantitative comparison of crude oil Fire point The lowest temperature at which under specified conditions in standardized apparatus a petroleum product vaporizes sufficiently rapidly to form above its surface an airvapor mixture which burns continuously when ignited by a small flame FischerTropsch process A process for synthesizing hydrocarbons and oxygenated chemicals from a mixture of hydrogen and carbon monoxide Fixed bed A stationary bed of catalyst to accomplish a process see Fluid bed Flammability limits A gas mixture will not burn when the composition is lower than the lower flammable limit LFL the mixture is also not combustible when the composition is above the upper flammability limit UFL Flammability range The range of temperature over which a chemical is flammable Flammable chemical flammable substance A chemical or substance is usually termed flam mable if the flash point of the chemical or substance is below 38C 100F Flammable liquid A liquid having a flash point below 378C 100F Flammable solid A solid that can ignite from friction or from heat remaining from its manufac ture or which may cause a serious hazard if ignited Flaring The burning of natural gas for safety reasons or when there is no way to transport the gas to market or use the gas for other beneficial purposes such as enhanced oil recovery or res ervoir pressure maintenance the practice of flaring is being steadily reduced as pipelines are completed and in response to environmental concerns Flash point The temperature at which the vapor over a liquid will ignite when exposed to an igni tion source A liquid is considered to be flammable if its flash point is less than 60C Flash point is an extremely important factor in relation to the safety of spill cleanup operations Gasoline and other light fuels can ignite under most ambient conditions and therefore are a serious hazard when spilled Many freshly spilled crude oils also have low flash points until the lighter components have evaporated or dispersed Flexicoking A modification of the fluid coking process insofar as the process also includes a gas ifier adjoining the burnerregenerator to convert excess coke to a clean fuel gas Flocculation threshold The point at which constituents of a solution eg asphaltene constituents or coke precursors will separate from the solution as a separate solid phase Floc point The temperature at which wax or solids separate as a definite floc Flora The plant life occurring in a particular region or time generally the naturally occurring or indigenous plant life native plant life Flue gas Gas from the combustion of fuel the heating value of which has been substantially spent and which is therefore discarded to the flue or stack 521 Glossary Fluid bed Use of an agitated bed of inert granular material to accomplish a process in which the agitated bed resembles the motion of a fluid a bed of catalyst that is agitated by an upward passing gas in such a manner that the particles of the bed simulate the movement of a fluid and has the characteristics associated with a true liquid see Fixed bed Fluid catalytic cracking Cracking in the presence of a fluidized bed of catalyst Fluid coking A continuous fluidized solids process that cracks feed thermally over heated coke particles in a reactor vessel to gas liquid products and coke Fluidized bed combustion A process used to burn lowquality solid fuels in a bed of small par ticles suspended by a gas stream usually air that will lift the particles but not blow them out of the vessel Rapid burning removes some of the offensive byproducts of combustion from the gases and vapors that result from the combustion process Fluids Liquids also a generic term applied to all substances that flow freely such as gases and liquids Fly ash Particulate matter produced from mineral matter in coal that is converted during combus tion to finely divided inorganic material and which emerges from the combustor in the gases Foam A colloidal suspension of a gas in a liquid Fog A term denoting high level of water droplets Foots oil The oil sweated out of slack wax named from the fact that the oil goes to the foot or bottom of the pan during the sweating operation Fossil fuel A fuel source such as oil condensate natural gas natural gas liquids or coal formed in the earth from plant or animal remains Fossil fuel resources A gaseous liquid or solid fuel material formed in the ground by chemical and physical changes diagenesis in plant and animal residues over geological time natu ral gas petroleum coal and oil shale Fraction One of the portions of a chemical mixture separated by chemical or physical means from the remainder Fractional composition The composition of petroleum as determined by fractionation separation methods Fractional distillation The separation of the components of a liquid mixture by vaporizing and collecting the fractions or cuts which condense in different temperature ranges Fractional flow The ratio of the volumetric flow rate of one fluid phase to the total fluid volumetric flow rate within a volume of rock Fractional flow curve The relationship between the fractional flow of one fluid and its saturator during simultaneous flow of fluids through rock Fractionating column A column arranged to separate various fractions of petroleum by a single distillation and which may be tapped at different points along its length to separate various fractions in the order of their boiling points Fractionation The separation of petroleum into the constituent fractions using solvent or adsorbent methods chemical agents such as sulfuric acid may also be used Frasch process A process formerly used for removing sulfur by distilling oil in the presence of copper oxide Free associated gas Natural gas that overlies and is in contact with the crude oil of the reservoir it may be gas cap Free radical A molecule with an odd number of electronsthey do not have a completed octet and often undergo vigorous redox reactions Fuel oil Also called heating oil is a distillate product that covers a wide range of properties see also No 1 to No 4 Fuel oils Fugacity of a real gas An effective partial pressure which replaces the mechanical partial pres sure in an accurate computation of the chemical equilibrium constant 522 Glossary Fugitive emissions Emissions that include losses from equipment leaks or evaporative losses from impoundments spills or leaks Fullers earth A clay mineral which has high adsorptive capacity for removing color from oils Attapulgus clay is a widely used as fullers earth Functional group An atom or a group of atoms attached to the base structure of a compound that has similar chemical properties irrespective of the compound to which it is a part a means of defining the characteristic physical and chemical properties of families of organic compounds Functional isomers Compounds which have the same molecular formula that possess different functional groups Fungi Nonphotosynthetic organisms larger than bacteria aerobic and can thrive in more acidic media than bacteria Important function is the breakdown of cellulose in wood and other plant materials Furfural extraction A singlesolvent process in which furfural is used to remove aromatic naph thene olefin and unstable hydrocarbons from a lubricatingoil charge stock Furnace oil A distillate fuel primarily intended for use in domestic heating equipment Gas Matter that has no definite volume or definite shape and always fills any space given in which it exists Gas cap A part of a hydrocarbon reservoir at the top that will produce only gas Gas chromatography GC A separation technique involving passage of a gaseous moving phase through a column containing a fixed liquid phase it is used principally as a quantitative analytical technique for compounds that are volatile or can be converted to volatile forms Gaseous nutrient injection A process in which nutrients are fed to contaminated groundwater and soil via wells to encourage and feed naturally occurring microorganismsthe most com mon added gas is air in the presence of sufficient oxygen microorganisms convert many organic contaminants to carbon dioxide water and microbial cell mass In the absence of oxygen organic contaminants are metabolized to methane limited amounts of carbon diox ide and trace amounts of hydrogen gas Another gas that is added is methane It enhances degradation by cometabolism in which as bacteria consume the methane they produce enzymes that react with the organic contaminant and degrade it to harmless minerals Gasohol A term for motor vehicle fuel comprising between 8090 unleaded gasoline and 1020 ethanol see also Ethyl alcohol Gas oil A petroleum distillate with a viscosity and boiling range between those of kerosene and lubricating oil GCMS Gas chromatographymass spectrometry GCTPH GC detectable total petroleum hydrocarbons that is the sum of all GCresolved and unre solved hydrocarbons The resolvable hydrocarbons appear as peaks and the unresolvable hydrocarbons appear as the area between the lower baseline and the curve defining the base of resolvable peaks Geological time The span of time that has passed since the creation of the earth and its compo nents a scale used to measure geological events millions of years ago Geometric isomers Stereoisomers which differ in the geometry around either a carboncarbon double bond or ring Geosphere A term representing the solid earth including soil which supports most plant life Gibbs free energy The energy of a system that is available to do work at constant temperature and pressure Girbotol process A continuous regenerative process to separate hydrogen sulfide carbon dioxide and other acid impurities from natural gas refinery gas etc using mono di or trietha nolamine as the reagent Grahams law The rate of diffusion of a gas is inversely proportional to the square root of the molar mass 523 Glossary Glycerol A small molecule with three alcohol groups HOCH2CHOHCH2OH basic building block of fats and oils Glycolamine gas treating A continuous regenerative process to simultaneously dehydrate and remove acid gases from natural gas or refinery gas Grain alcohol See Ethyl alcohol Gram equivalent weight nonredox reaction The mass in grams of a substance equivalent to 1 gatom of hydrogen 05 gatom of oxygen or 1 gion of the hydroxyl ion can be deter mined by dividing the molecular weight by the number of hydrogen atoms or hydroxyl ions or their equivalent supplied or required by the molecule in a reaction Gram equivalent weight redox reaction The molecular weight in grams divided by the change in oxidation state Gravimetric analysis A technique of quantitative analytical chemistry in which a desired con stituent is efficiently recovered and weighed Gravity See API gravity Gray clay treating A fixed bed usually fullers earth vaporphase treating process to selec tively polymerize unsaturated gumforming constituents diolefins in thermally cracked gasoline Greenhouse effect The warming of an atmosphere by its absorption of infrared radiation while shortwave radiation is allowed to pass through Greenhouse gas Any gas whose absorption of solar radiation is responsible for the greenhouse effect including carbon dioxide ozone methane and the fluorocarbons Guard bed A bed of an adsorbent such as bauxite that protects a catalyst bed by adsorbing spe cies detrimental to the catalyst Guest molecule or ion An organic or inorganic ion or molecule that occupies a cavity cleft or pocket within the molecular structure of a host molecular entity and forms a complex with the host entity or that is trapped in a cavity within the crystal structure of a host Gulf HDS process A fixed bed process for the catalytic hydrocracking of heavy stocks to lower boiling distillates with accompanying desulfurization Gulfining A catalytic hydrogen treating process for cracked and straightrun distillates and fuel oils to reduce sulfur content improve carbon residue color and general stability and effect a slight increase in gravity Gum An insoluble tacky semisolid material formed as a result of the storage instability andor the thermal instability of petroleum and petroleum products Halflife abbreviated to t12 The time required to reduce the concentration of a chemical to 50 of its initial concentration units are typically in hours or days the term is com monly used in nuclear physics to describe how quickly radioactive decay unstable atoms undergo radioactive decay or how long stable atoms survive the potential for radioactive decay Halide An element from the halogen group which include fluorine chlorine bromine iodine and astatine Halogen Group 17 in the periodic table of the elements these elements are the reactive nonmetals and are electronegative Halogenation The addition of a halogen molecule to an alkene to produce an alkyl dihalide or alkyne to produce an alkyl tetrahalide Halo group X A substituent which is one of the four halogens fluorine F chlorine Cl bromine Br or iodine I 524 Glossary Hardness scale Mhos scale A measure of the ability of a substance to abrade or indent one another the Mohs hardness is based on a scale from 1 to 10 units in which diamond the hardest substance is given a value of 10 Mohs and talc given a value of 05 Hazardous waste A potentially dangerous chemical substance that has been discarded aban doned neglected released or designated as a waste material or one that may interact with other substances to pose a threat Haze A term denoting decreased visibility due to the presence of particles Heat capacity Cρ The quantity of thermal energy needed to raise the temperature of an object by 1C the heat capacity is the product of mass of the object and its specific heat Cρ mass specific heat Heating oil See Fuel oil Heat of fusion ΔHfus The amount of thermal energy required to melt one mole of the substance at the melting point also termed as latent heat of fusion and expressed in kcalmol or kJmol Heat of vaporization ΔHvap The amount of thermal energy needed to convert one mole of a sub stance to vapor at boiling point also known as latent heat of vaporization and expressed kcalmol or kJmol Heat value The amount of heat released per unit of mass or per unit of volume when a substance is completely burned The heat power of solid and liquid fuels is expressed in calories per gram or in Btu per pound For gases this parameter is generally expressed in kilocalories per cubic meter or in Btu per cubic foot Heavy ends The highestboiling portion of a petroleum fraction see also Light ends Heavy fuel oil Fuel oil having a high density and viscosity generally residual fuel oil such as No 5 and No 6 fuel oil Heavy oil Typically petroleum having an API gravity of less than 20 Heavy petroleum See Heavy oil Henrys law The relation between the partial pressure of a compound and the equilibrium con centration in the liquid through a proportionality constant known as the Henrys Law constant Henrys law constant The concentration ratio between a compound in air or vapor and the con centration of the compound in water under equilibrium conditions Herbicide A chemical that controls or destroys unwanted plants weeds or grasses Heteroatom compounds Chemical compounds which contain nitrogen andor oxygen andor sul fur and or metals bound within their molecular structures Heteroatoms Elements other than carbon and hydrogen that are commonly found in organic mol ecules such as nitrogen oxygen and the halogens Heterocyclic An organic group or molecule containing rings with at least one noncarbon atom in the ring Heterogeneous Varying in structure or composition at different locations in space Heterotroph An organism that cannot synthesize its own food and is dependent on complex organic substances for nutrition Heterotrophic bacteria Bacteria that utilize organic carbon as a source of energy organisms that derive carbon from organic matter for cell growth Heterotrophs Organisms or chemicals that obtain their carbon from other organisms HF alkylation An alkylation process whereby olefins C3 C4 C5 are combined with isobutane in the presence of hydrofluoric acid catalyst Homogeneous Having uniform structure or composition at all locations in space Homolog A compound belonging to a series of compounds that differ by a repeating group for example propanol CH3CH2CH2OH nbutanol CH3CH2CH2CH2OH and npentanol CH3CH2CH2CH2CH2OH are homologs they belong to the homologous series of alco hols CH3CH2nOH Homologous series Compounds which differ only by the number of CH2 units present 525 Glossary Hopane A pentacyclic hydrocarbon of the triterpane group believed to be derived primarily from bacteriohopanoids in bacterial membranes Hot filtration test A test for the stability of a petroleum product Houdresid catalytic cracking A continuous moving bed process for catalytically cracking reduced crude oil to produce highoctane gasoline and light distillate fuels Houdriflow catalytic cracking A continuous moving bed catalytic cracking process employing an integrated single vessel for the reactor and regenerator kiln Houdriforming A continuous catalytic reforming process for producing aromatic concentrates and highoctane gasoline from lowoctane straight naphtha Houdry butane dehydrogenation A catalytic process for dehydrogenating light hydrocarbons to their corresponding mono or diolefins Houdry fixed bed catalytic cracking A cyclic regenerable process for cracking of distillates Houdry hydrocracking A catalytic process combining cracking and desulfurization in the pres ence of hydrogen Humic substances Dark complex heterogeneous mixtures of organic materials that form in the geological systems of the earth from microbial transformations and chemical reactions that occur during the decay of organic biomolecules polymers and resides Hydration The addition of a water molecule to a compound within an aerobic degradation pathway Hydration sphere Shell of water molecules surrounding an ion in solution Hydraulic fracturing The opening of fractures in a reservoir by highpressure highvolume injec tion of liquids through an injection well Hydrocarbon One of a very large and diverse group of chemical compounds composed only of carbon and hydrogen the largest source of hydrocarbons is petroleum crude oil the prin cipal constituents of crude oils and refined petroleum products Hydroconversion A term often applied to hydrocracking Hydrocracking A catalytic highpressure hightemperature process for the conversion of petro leum feedstocks in the presence of fresh and recycled hydrogen carboncarbon bonds are cleaved in addition to the removal of heteroatomic species Hydrocracking catalyst A catalyst used for hydrocracking which typically contains separate hydrogenation and cracking functions Hydrodenitrogenation The removal of nitrogen by hydrotreating Hydrodesulfurization The removal of sulfur by hydrotreating Hydrofining A fixed bed catalytic process to desulfurize and hydrogenate a wide range of charge stocks from gases through waxes Hydroforming A process in which naphtha is passed over a catalyst at elevated temperatures and moderate pressures in the presence of added hydrogen or hydrogencontaining gases to form highoctane motor fuel or aromatics Hydrogen A flammable colorless gas with the chemical symbol formula H2 the lightest and most abundant element in the universe As petrochemicals are produced from hydrogen containing hydrocarbons hydrogen is involved in nearly all petrochemical processes the most common application of hydrogen is as a reducing agent in catalytic hydrogenation and hydrorefining Hydrogen addition An upgrading process in the presence of hydrogen eg hydrocracking see Hydrogenation Hydrogenation The chemical addition of hydrogen to a material In nondestructive hydrogenation hydrogen is added to a molecule only if and where unsaturation with respect to hydrogen exists Hydrogen bond A form of association between an electronegative atom and a hydrogen atom attached to a second relatively electronegative atom best considered as an electrostatic interaction heightened by the small size of hydrogen which permits close proximity of the interacting dipoles or charges 526 Glossary Hydrogenation A reaction where hydrogen is added across a double or triple bond usually with the assistance of a catalyst a process whereby an enzyme in certain microorganisms cata lyzes the hydrolysis or reduction of a substrate by molecular hydrogen Hydrogenolysis A reductive reaction in which a carbonhalogen bond is broken and hydrogen replaces the halogen substituent Hydrogen transfer The transfer of inherent hydrogen within the feedstock constituents and prod ucts during processing Hydrology The scientific study of water Hydrolysis A chemical transformation process in which a chemical reacts with water in the process a new carbonoxygen bond is formed with oxygen derived from the water mol ecule and a bond is cleaved within the chemical between carbon and some functional group Hydrophilic Water loving the capacity of a molecular entity or of a substituent to interact with polar solvents in particular with water or with other polar groups hydrophilic molecules dissolve easily in water but not in fats or oils Hydrophilic colloids Generally macromolecules such as proteins and synthetic polymers that are characterized by strong interaction with water resulting in spontaneous formation of colloids when they are placed in water Hydrophilicity The tendency of a molecule to be solvated by water Hydrophobic Fear of water the tendency to repel water Hydrophobic colloids Colloids that interact to a lesser extent with water and are stable because of their positive or negative electrical charges Hydrophobic effect The attraction of nonionic nonpolar compounds to surfaces that occurs due to the thermodynamic drive of these molecules to minimize interactions with water molecules Hydrophobic interaction The tendency of hydrocarbons or of lipophilic hydrocarbonlike groups in solutes to form intermolecular aggregates in an aqueous medium and analogous intra molecular interactions Hydroprocessing A term often equally applied to hydrotreating and to hydrocracking often col lectively applied to both hydrotreating and to hydrocracking Hydropyrolysis A short residence time hightemperature process using hydrogen Hydrorefining A refining process for treating petroleum in the presence of catalysts and sub stantial quantities of hydrogen the process includes desulfurization and the removal of substances that deactivate catalysts such as nitrogen compounds The process is used in the conversion of olefins to paraffins to reduce gum formation in gasoline and in other processes to upgrade the quality of a fraction Hydrosphere The water areas of the earth also called the aquasphere Hydrovisbreaking A noncatalytic process conducted under similar conditions to visbreaking which involves treatment with hydrogen to reduce the viscosity of the feedstock and pro duce more stable products than is possible with visbreaking Hydroxylation Addition of a hydroxyl group to a chlorinated aliphatic hydrocarbon Hydroxyl group A functional group that has a hydrogen atom joined to an oxygen atom by a polar covalent bond OH Hydroxyl ion One atom each of oxygen and hydrogen bonded into an ion OH that carries a negative charge Hydroxyl radical A radical consisting of one hydrogen atom and one oxygen atom normally does not exist in a stable form Hyperforming A catalytic hydrogenation process for improving the octane number of naphtha through removal of sulfur and nitrogen compounds Hypochlorite sweetening The oxidation of mercaptans in a sour stock by agitation with aqueous alkaline hypochlorite solution used where avoidance of freesulfur addition is desired 527 Glossary because of a stringent copper strip requirements and minimum expense is not the pri mary object Ideal gas law A law which describes the relationship between pressure P temperature T vol ume V and moles of gas n This equation expresses behavior approached by real gases at low pressure and high temperature PV nRT Ignitability A characteristic of liquids whose vapors are likely to ignite in the presence of ignition source also characteristic of nonliquids that may catch fire from friction or contact with water and that burn vigorously Illuminating oil Oil used for lighting purposes Immiscibility The inability of two or more fluids to have complete mutual solubility they coexist as separate phases Immiscible Two or more fluids that do not have complete mutual solubility and coexist as separate phases Inactive ingredients also called excipients The additives present in a medicine along with active ingredients which are normally inactiveinert these ingredients are not intended to have therapeutic effect but are added as preservatives flavoring agents coloring sweeten ers and sorbents See Active ingredientss Incompatibility The immiscibility of petroleum products and also of different crude oils which is often reflected in the formation of a separate phase after mixing andor storage Indirect emissions Emissions that are a consequence of the activities of the reporting entity but occur at sources owned or controlled by another entity Infiltration rate The time required for water at a given depth to soak into the ground Inhibition The decrease in rate of reaction brought about by the addition of a substance inhibitor by virtue of its effect on the concentration of a reactant catalyst or reaction intermediate a component having no effect reduces the effect of another component Inhibitor A substance the presence of which in small amounts in a petroleum product prevents or retards undesirable chemical changes from taking place in the product or in the condition of the equipment in which the product is used Inhibitor sweetening A treating process to sweeten gasoline of low mercaptan content using a phenylenediamine type of inhibitor air and caustic Initial boiling point The recorded temperature when the first drop of liquid falls from the end of the condenser Initial vapor pressure The vapor pressure of a liquid of a specified temperature and 0 evaporated Innersphere adsorption complex Sorption of an ion or molecule to a solid surface where waters of hydration are distorted during the sorption process and no water molecules remain inter posed between the sorbate and sorbent Inoculum A small amount of material either liquid or solid containing bacteria removed from a culture in order to start a new culture Inorganic Pertaining to or composed of chemical compounds that are not organic that is chemi cal compounds that contain no carbonhydrogen bonds examples include chemicals with no carbon and those with carbon in nonhydrogenlinked forms Inorganic acid An inorganic compound that elevates the hydrogen concentration in an aqueous solution alphabetically examples are Carbonic acid HCO3 An inorganic acid Hydrochloric acid HCl A highly corrosive strong inorganic acid with many uses Hydrofluoric acid HF An inorganic acid that is highly reactive with silicate glass met als and semimetals Nitric acid HNO3 A highly corrosive and toxic strong inorganic acid 528 Glossary Phosphoric acid Not considered a strong inorganic acid found in solid form as a mineral and has many industrial uses Sulfuric acid A highly corrosive inorganic acid It is soluble in water and widely used Inorganic base An inorganic compound that elevates the hydroxide concentration in an aqueous solution alphabetically examples are Ammonium hydroxide ammonia water A solution of ammonia in water Calcium hydroxide lime water A weak base with many industrial uses Magnesium hydroxide Referred to as brucite when found in its solid mineral form Sodium bicarbonate baking soda A mild alkali Sodium hydroxide caustic soda A strong inorganic base used widely in industrial and laboratory environments Inorganic chemistry The study of inorganic compounds specifically the structure reactions catalysis and mechanism of action Inorganic compound A compound that consists of an ionic component an element from the peri odic table and an anionic component a compound that does not contain carbon chemically bound to hydrogen carbonates bicarbonates carbides and carbon oxides are considered inorganic compounds even though they contain carbon a large number of compounds occur naturally while others may be synthesized in all cases charge neutrality of the compound is key to the structure and properties of the compound Inorganic reaction chemistry Inorganic chemical reactions fall into four broad categories com bination reactions decomposition reactions single displacement reactions and double displacement reactions Inorganic salts Inorganic salts are neutral ionically bound molecules and do not affect the con centration of hydrogen in an aqueous solution Inorganic synthesis The process of synthesizing inorganic chemical compounds is used to pro duce many basic inorganic chemical compounds In situ In its original place unmoved unexcavated remaining in the subsurface In situ bioremediation A process which treats the contaminated water or soil where it was found Instability The inability of a petroleum product to exist for periods of time without change to the product Interfacial Tension The net energy per unit area at the interface of two substances such as oil and water or oil and air The airliquid interfacial tension is often referred to as surface ten sion the SI units for interfacial tension are milliNewtons per meter mNm The higher the interfacial tension the less attractive the two surfaces are to each other and the more size of the interface will be minimized Low surface tensions can drive the spreading of one fluid on another The surface tension of an oil together its viscosity affects the rate at which spilled oil will spread over a water surface or into the ground Intermediates Petrochemical intermediates are generally produced by chemical conversion of pri mary petrochemicals to form more complicated derivative products common petrochemi cal intermediate products include vinyl acetate for paint paper and textile coatings vinyl chloride for polyvinyl chloride PVC resin manufacturing ethylene glycol for polyester textile fibers and styrene which is used in rubber and plastic manufacturing Intermolecular forces Force of attraction that exist between particles atoms molecules ions in a compound Internal Standard IS A pure analyte added to a sample extract in a known amount which is used to measure the relative responses of other analytes and surrogates that are compo nents of the same solution The internal standard must be an analyte that is not a sample component Intramolecular i Descriptive of any process that involves a transfer of atoms groups electrons etc or interactions such as forces between different parts of the same molecular entity ii relating to a comparison between atoms or groups within the same molecular entity 529 Glossary Intrinsic bioremediation A type of bioremediation that manages the innate capabilities of natu rally occurring microbes to degrade contaminants without taking any engineering steps to enhance the process Inversions Conditions characterized by high atmospheric stability which limit the vertical circula tion of air resulting in air stagnation and the trapping of air pollutants in localized areas Iodine number A measure of the iodine absorption by oil under standard conditions used to indi cate the quantity of unsaturated compounds present also called iodine value Ionic bond A chemical bond or link between two atoms due to an attraction between oppositely charged positivenegative ions Ionic bonding Chemical bonding that results when one or more electrons from one atom or a group of atoms is transferred to another Ionic bonding occurs between charged particles Ionic compounds Compounds where two or more ions are held next to each other by electrical attraction Ionic liquids An ionic liquid is a salt in the liquid state or a salt with a melting point lower than 100C 212F variously called liquid electrolytes ionic melts ionic fluids fused salts liquid salts or ionic glasses powerful solvents and electrically conducting fluids electrolytes Ionic radius A measure of ion size in a crystal lattice for a given coordination number CN metal ions are smaller than their neutral atoms and nonmetallic anions are larger than the atoms from which they are formed ionic radii depend on the element its charge and its coordination number in the crystal lattice ionic radii are expressed in angstrom units of length Å Ionization energy The ionization energy is the energy required to remove an electron completely from its atom molecule or radical Ionization potential The energy required to remove a given electron from its atomic orbital the values are given in electron volts eV Irreversible reaction A reaction in which the reactants proceed to products but there is no significant backward reaction nA mB Products In this reaction the products do not recombine or change to form reactants in any appre ciable amount Isobutylene A fourcarbon branched olefin one of the four isomers of butane with the chemical formula C4H8 Isocracking A hydrocracking process for conversion of hydrocarbons which operates at relatively low temperatures and pressures in the presence of hydrogen and a catalyst to produce more valuable lowerboiling products Isoforming A process in which olefinic naphtha is contacted with an alumina catalyst at high tem perature and low pressure to produce isomers of higher octane number IsoKel process A fixed bed vaporphase isomerization process using a precious metal catalyst and external hydrogen Isomate process A continuous nonregenerative process for isomerizing C5C8 normal paraffin hydrocarbons using aluminum chloridehydrocarbon catalyst with anhydrous hydrochlo ric acid as a promoter Isomerate process A fixed bed isomerization process to convert pentane hexane and heptane to highoctane blending stocks Isomerization The conversion of a normal straightchain paraffin hydrocarbon into an iso branchedchain paraffin hydrocarbon having the same atomic composition Isopach A line on a map designating points of equal formation thickness 530 Glossary Isomers Compounds that have the same number and types of atomsthe same molecular formulabut differ in the structural formula ie the manner in which the atoms are combined with each other Isoplus Houdriforming A combination process using a conventional Houdriformer operated at moderate severity in conjunction with one of three possible alternatives including the use of an aromatic recovery unit or a thermal reformer see Houdriforming Isotope A variant of a chemical element which differs in the number of neutrons in the atom of the element all isotopes of a given element have the same number of protons in each atom and different isotopes of a single element occupy the same position on the periodic table of the elements IUPAC International Union of Pure and Applied Chemistry the organization that establishes the system of nomenclature for organic and inorganic compounds using prefixes and suffixes developed in the late 19th century Jet fuel Fuel meeting the required properties for use in jet engines and aircraft turbine engines Kaolinite A clay mineral formed by hydrothermal activity at the time of rock formation or by chemical weathering of rock with high feldspar content usually associated with intrusive granite rock with high feldspar content Katacondensed aromatic compounds Compounds based on linear condensed aromatic hydro carbon systems eg anthracene and naphthacene tetracene Kauri butanol number A measurement of solvent strength for hydrocarbon solvents the higher the kauributanol KB value the stronger the solvency the test method ASTM D1133 is based on the principle that kauri resin is readily soluble in butyl alcohol but not in hydro carbon solvents and the resin solution will tolerate only a certain amount of dilution and is reflected as a cloudiness when the resin starts to come out of solution solvents such as toluene can be added in a greater amount and thus have a higher KB value than weaker solvents like hexane Kelvin The SI unit of temperature It is the temperature in degrees Celsius plus 27315 Kerogen A complex carbonaceous organic material that occurs in sedimentary rock and shale generally insoluble in common organic solvents Kerosene A fraction of petroleum that was initially sought as an illuminant in lamps a precursor to diesel fuel Ketone An organic compound that contains a carbonyl group R1COR2 Kfactor See Characterization factor Kinematic viscosity The ratio of viscosity to density both measured at the same temperature Knock The noise associated with selfignition of a portion of the fuelair mixture ahead of the advancing flame front Lag phase The growth interval adaption phase between microbial inoculation and the start of the exponential growth phase during which there is little or no microbial growth Lamp burning A test of burning oils in which the oil is burned in a standard lamp under specified conditions in order to observe the steadiness of the flame the degree of encrustation of the wick and the rate of consumption of the kerosene Lamp oil See Kerosene Latex A polymer of cis14 isoprene milky sap from the rubber tree Hevea brasiliensis Law A system of rules that are enforced through social institutions to govern behavior can be made by a collective legislature or by a single legislator resulting in statutes by the execu tive through decrees and regulations or by judges through binding precedent the forma tion of laws themselves may be influenced by a constitution written or tacit and the rights encoded therein the law shapes politics economics history and society in various ways and serves as a mediator of relations between people See also Regulation Layer silicate clay Clay minerals composed of planes of aluminum Al3 or magnesium Mg2 in octahedral coordination with oxygen and planes of silica Si4 in tetrahedral coordination 531 Glossary to oxygen Substitution of Al3 for Si4 in the tetrahedral plane or substitution of Mg2 or Fe2 for Al3 in the octahedral plane isomorphic substitution results in a permanent charge imbalance ie structural charge that must be satisfied through cation adsorption Leaded gasoline Gasoline containing tetraethyl lead or other organometallic lead antiknock compounds Lean gas The residual gas from the absorber after the condensable gasoline has been removed from the wet gas Lean oil Absorption oil from which gasoline fractions have been removed oil leaving the stripper in a naturalgasoline plant Leaving group An atom or group charged or uncharged that becomes detached from an atom in what is considered to be the residual or main part of the substrate in a specified reaction Le Chateliers principle The principle that states that a system at equilibrium will oppose any change in the equilibrium conditions Lewis acid A chemical species which can accept an electron pair from a base Lewis base A chemical species which can donate an electron pair Light ends The lowerboiling components of a mixture of hydrocarbons see also Heavy ends Light hydrocarbons Light hydrocarbons Hydrocarbons with molecular weights less than that of heptane C7H16 Light oil The products distilled or processed from crude oil up to but not including the first lubricatingoil distillate Light petroleum Petroleum having an API gravity greater than 20 Lignin A complex amorphous polymer in the secondary cell wall middle lamella of woody plant cells that cements or naturally binds cell walls to help make them rigid highly resistant to decomposition by chemical or enzymatic action also acts as support for cellulose fibers Ligroine Ligroin A saturated petroleum naphtha boiling in the range of 20C135C 68C275F and suitable for general use as a solvent also called benzine or petroleum ether Limiting reactant The reactant that is present in the smallest stoichiometric amount and which deter mines the maximum extent to which a reaction can proceed if the reaction is 100 complete then all of the limiting reactant is consumed and the reaction can proceed no further Limnology The branch of science dealing with characteristics of freshwater including biological properties as well as chemical and physical properties Linde copper sweetening A process for treating gasoline and distillates with a slurry of clay and cupric chloride Lipophilic Floving applied to molecular entities or parts of molecular entities tending to dis solve in fatlike eg hydrocarbon solvents Lipophilicity The affinity of a molecule or a moiety portion of a molecular structure for a lipo philic fat soluble environment It is commonly measured by its distribution behavior in a biphasic system either liquidliquid eg partition coefficient in octanolwater Liquid petrolatum See White oil Liquefied petroleum gas Propane butane or mixtures thereof gaseous at atmospheric tempera ture and pressure held in the liquid state by pressure to facilitate storage transport and handling Liquid chromatography A chromatographic technique that employs a liquid mobile phase Liquidliquid extraction An extraction technique in which one liquid is shaken with or contacted by an extraction solvent to transfer molecules of interest into the solvent phase Liquid sulfur dioxidebenzene process A mixedsolvent process for treating lubricatingoil stocks to improve viscosity index also used for dewaxing Lithosphere The part of the geosphere consisting of the outer mantle and the crust that is directly involved with environmental processes through contact with the atmosphere the hydro sphere and living things varies from approximately 40 to 60 miles in thickness also called the terrestrial biosphere 532 Glossary Loading rate The amount of a chemical that can be absorbed on soil on a per volume of soil basis LTU Land Treatment Unit a physically delimited area where contaminated land is treated to removeminimize contaminants and where parameters such as moisture pH salinity tem perature and nutrient content can be controlled Lube See Lubricating oil Lube cut A fraction of crude oil of suitable boiling range and viscosity to yield lubricating oil when completely refined also referred to as lube oil distillates or lube stock Lubricating oil A fluid lubricant used to reduce friction between bearing surfaces Macromolecule A large molecule of high molecular mass composed of more than 100 repeated monomers single chemical units of lower relative mass a large complex molecule formed from many simpler molecules Mahogany acids Oilsoluble sulfonic acids formed by the action of sulfuric acid on petroleum distillates They may be converted to their sodium soaps mahogany soaps and extracted from the oil with alcohol for use in the manufacture of soluble oils rust preventives and special greases The calcium and barium soaps of these acids are used as detergent addi tives in motor oils see also Brown acids and Sulfonic acids Maltenes That fraction of petroleum that is soluble in for example pentane or heptane deas phaltened oil also the term arbitrarily assigned to the pentanesoluble portion of petro leum that is relatively high boiling 300C 760 mm see also Petrolenes Marine engine oil Oil used as a crankcase oil in marine engines Marine gasoline Fuel for motors in marine service Marine sediment The organic biomass from which petroleum is derived Masking Occurs when two components have opposite cancelling effects such that no effect is observed from the combination Mass number The number of protons plus the number of neutrons in the nucleus of an atom Matter Any substance that has inertia and occupies physical space can exist as solid liquid gas plasma or foam Mayonnaise Lowtemperature sludge a black brown or gray deposit having a soft mayonnaise like consistency not recommended as a food additive Measurement A description of a property of a system by means of a set of specified rules that maps the property on to a scale of specified values by direct or mathematical comparison with specified references Mechanical explosion An explosion due to the sudden failure of a vessel containing a nonreactive gas at a high pressure Medicinal oil Highly refined colorless tasteless and odorless petroleum oil used as a medicine in the nature of an internal lubricant sometimes called liquid paraffin MEK methyl ethyl ketone A colorless liquid CH3COCH2CH3 used as a solvent as a chemical intermediate and in the manufacture of lacquers celluloid and varnish removers MEK deoiling A waxdeoiling process in which the solvent is generally a mixture of methyl ethyl ketone and toluene MEK dewaxing A continuous solvent dewaxing process in which the solvent is generally a mix ture of methyl ethyl ketone and toluene Melting point The temperature when matter is converted from solid to liquid Membrane technology Gas separation processes utilizing membranes that permit different com ponents of a gas to diffuse through the membrane at significantly different rates Mesosphere The portion of the atmosphere of the earth where molecules exist as charged ions caused by interaction of gas molecules with intense ultraviolet UV light Metabolic byproduct A product of the reaction between an electron donor and an electron accep tor metabolic byproducts include volatile fatty acids daughter products of chlorinated aliphatic hydrocarbons methane and chloride 533 Glossary Metabolism The physical and chemical processes by which foodstuffs are synthesized into complex elements complex substances are transformed into simple ones and energy is made available for use by an organism thus all biochemical reactions of a cell or tissue both synthetic and degradative are included the sum of all of the enzyme catalyzed reactions in living cells that transform organic molecules into simpler com pounds used in biosynthesis of cellular components or in extraction of energy used in cellular processes Metabolize A product of metabolism Metal oxyhydroxide Minerals composed of various structural arrangements of metal cations principally Al3 Fe3 and Mn4in octahedral coordination with oxygen or hydroxide anions These minerals are dissolution byproducts of mineral weathering and they are often found as coatings on layer silicates and other soil particles Methanogens Strictly anaerobic archaebacteria able to use only a very limited spectrum of sub strates for example molecular hydrogen formate methanol methylamine carbon mon oxide or acetate as electron donors for the reduction of carbon dioxide to methane Methanogenic The formation of methane by certain anaerobic bacteria methanogens during the process of anaerobic fermentation Methanol See Methyl alcohol Methyl A group CH3 derived from methane for example CH3Cl is methyl chloride systematic name chloromethane and CH3OH is methyl alcohol systematic name methanol Methyl tbutyl ether An ether added to gasoline to improve its octane rating and to decrease gas eous emissions see Oxygenate Mercapsol process A regenerative process for extracting mercaptans utilizing aqueous sodium or potassium hydroxide containing mixed cresols as solubility promoters Mercaptans Organic compounds having the general formula RSH Methyl alcohol methanol wood alcohol A colorless volatile inflammable and poisonous alco hol CH3OH traditionally formed by destructive distillation of wood or more recently as a result of synthetic distillation in chemical plants Methyl ethyl ketone See MEK Micelle The name given to the structural entity by which asphaltene constituents are dispersed in petroleum Microcarbon residue The carbon residue determined using a themogravimetric method See also Carbon residue Microclimate A highly localized climatic conditions the climate that organisms and objects on the surface are exposed to being close to ground under rocks and surrounded by vegeta tion and it is often quite different from the surrounding macroclimate Microcosm A diminutive representative system analogous to a larger system in composition development or configuration Microorganism microorganism An organism of microscopic size that is capable of growth and reproduction through biodegradation of food sources which can include hazardous contaminants microscopic organisms including bacteria yeasts filamentous fungi algae and protozoa a living organism too small to be seen with the naked eye includes bacteria fungi protozoans microscopic algae and viruses Microbe The shortened term for microorganism Microcrystalline wax Wax extracted from certain petroleum residua and having a finer and less apparent crystalline structure than paraffin wax Microemulsion A stable finely dispersed mixture of oil water and chemicals surfactants and alcohols Midboiling point The temperature at which approximately 50 of a material has distilled under specific conditions Middle distillate Distillate boiling between the kerosene and lubricating oil fractions 534 Glossary Middlephase microemulsion A microemulsion phase containing a high concentration of both oil and water that when viewed in a test tube resides in the middle with the oil phase above it and the water phase below it Mineral hydrocarbons Petroleum hydrocarbons considered mineral because they come from the earth rather than from plants or animals Mineralization The biological process of complete breakdown of organic compounds whereby organic materials are converted to inorganic products eg the conversion of hydrocarbons to carbon dioxide and water the release of inorganic chemicals from organic matter in the process of aerobic or anaerobic decay Mineral oil The older term for petroleum the term was introduced in the 19th century as a means of differentiating petroleum rock oil from whale oil which at the time was the predomi nant illuminant for oil lamps Minerals Naturally occurring inorganic solids with welldefined crystalline structures Mineral seal oil A distillate fraction boiling between kerosene and gas oil Mineral wax Yellow to dark brown solid substances that occur naturally and are composed largely of paraffins usually found associated with considerable mineral matter as a filling in veins and fissures or as an interstitial material in porous rocks Miscibility An equilibrium condition achieved after mixing two or more fluids which is characterized by the absence of interfaces between the fluids i firstcontact miscibility miscibility in the usual sense whereby two fluids can be mixed in all proportions without any interfaces forming Example At room temperature and pressure ethyl alcohol and water are firstcontact miscible ii multiplecontact miscibility dynamic miscibility miscibility that is developed by repeated enrichment of one fluid phase with components from a second fluid phase with which it comes into contact iii minimum miscibility pressure the minimum pressure above which two fluids become miscible at a given temperature or can become miscible by dynamic processes Mist Liquid particles Mixedphase cracking The thermal decomposition of higherboiling hydrocarbons to gasoline components Mixed waste Any combination of waste types with different properties or any waste that contains both hazardous waste and source specially nuclear or byproduct material as defined by the US EPA mixed waste contains both hazardous waste as defined by RCRA and its amendments and radioactive waste as defined by AEA and its amendments Modified naphtha insolubles MNI An insoluble fraction obtained by adding naphtha to petro leum usually the naphtha is modified by adding paraffin constituents the fraction might be equated to asphaltenes if the naphtha is equivalent to nheptane but usually it is not Modulus of elasticity The stress required to produce unit strain to cause a change of length Youngs modulus or a twist or shear shear modulus or a change of volume bulk modu lus expressed as dynescm2 Moiety A term generally used to signify part of a molecule eg in an ester R1COOR2 the alcohol moiety is R2O Molality m The gram moles of solute divided by the kilograms of solvent Molar A term expressing molarity the number of moles of solute per liters of solution Molarity M The gram moles of solute divided by the liters of solution Mole A collection of 6022 1023 number of objects Usually used to mean molecules Molecular sieve A synthetic zeolite mineral having pores of uniform size it is capable of separat ing molecules on the basis of their size structure or both by absorption or sieving Mole fraction The number of moles of a particular substance expressed as a fraction of the total number of moles Molecular weight The mass of one mole of molecules of a substance Molecule The smallest unit in a chemical element or compound that contains the chemical proper ties of the element or compound 535 Glossary Mole fraction The number of moles of a component of a mixture divided by the total number of moles in the mixture Monoaromatic Aromatic hydrocarbons containing a single benzene ring Monosaccharide A simple sugar such as fructose or glucose that cannot be decomposed by hydro lysis colorless crystalline substances with a sweet taste that have the same general for mula CnH2nOn Motor octane method A test for determining the knock rating of fuels for use in sparkignition engines see also Research Octane Method Moving bed catalytic cracking A cracking process in which the catalyst is continuously cycled between the reactor and the regenerator MSDS Material safety data sheet MTBE See Methyl tbutyl ether MTBE Methyl tbutyl ether Is a fuel additive which has been used in the United States since 1979 Its use began as a replacement for lead in gasoline because of health hazards associ ated with lead MTBE has distinctive physical properties that result in it being highly solu ble persistent in the environment and able to migrate through the ground Environmental regulations have required the monitoring and cleanup of MTBE at petroleum contaminated sites since February 1990 the program continues to monitor studies focusing on the poten tial health effects of MTBE and other fuel additives Naft PreChristian era Greek term for naphtha Napalm A thickened gasoline used as an incendiary medium that adheres to the surface it strikes Naphtha A generic term applied to refined partly refined or unrefined petroleum products and liquid products of natural gas the majority of which distills below 240C 464F the volatile fraction of petroleum which is used as a solvent or as a precursor to gasoline Naphthenes Cycloparaffins any of various volatile often flammable liquid hydrocarbon mixtures characterized by saturated ring structures that are used chiefly as solvents and diluents Native asphalt See Bitumen Native fauna The native and indigenous animal of an area Native flora The native and indigenous plant life of an area Natural asphalt See Bitumen Natural gas The naturally occurring gaseous constituents that are found in many petroleum reser voirs also there are those reservoirs in which natural gas may be the sole occupant Natural gas liquids NGL The hydrocarbon liquids that condense during the processing of hydrocarbon gases that are produced from oil or gas reservoir see also Natural gasoline Natural gasoline A mixture of liquid hydrocarbons extracted from natural gas suitable for blending with refinery gasoline Natural gasoline plant A plant for the extraction of fluid hydrocarbon such as gasoline and liquefied petroleum gas from natural gas Natural organic matter NOM An inherently complex mixture of polyfunctional organic mol ecules that occurs naturally in the environment and is typically derived from the decay of floral and faunal remains although they do occur naturally the fossil fuels coal crude oil and natal gas are usually not included in the term natural organic matter NCP National Contingency Planalso called the National Oil and Hazardous Substances Pollution Contingency Plan provides a comprehensive system of accident reporting spill contain ment and cleanup and established response headquarters National Response Team and Regional Response Teams Nernst Equation An equation that is used to account for the effect of different activities upon electrode potential E E 2303RT nF log Reactants Products E 00591 n log Reactants Products 0 0 536 Glossary Neutralization A process for reducing the acidity or alkalinity of a waste stream by mixing acids and bases to produce a neutral solution also known as pH adjustment Neutral oil A distillate lubricating oil with viscosity usually not above 200 s at 100F Neutralization number The weight in milligrams of potassium hydroxide needed to neutralize the acid in 1 g of oil an indication of the acidity of an oil Nitrate enhancement A process in which a solution of nitrate is sometimes added to groundwater to enhance anaerobic biodegradation Nonasphaltic road oil Any of the nonhardening petroleum distillates or residual oils used as dust layers They have sufficiently low viscosity to be applied without heating and together with asphaltic road oils are sometimes referred to as dust palliatives Nonassociated gas Natural gas found in reservoirs that do not contain crude oil at the original pressure and temperature conditions Nonionic surfactant A surfactant molecule containing no ionic charge NonNewtonian A fluid that exhibits a change of viscosity with flow rate Nonpoint source pollution Pollution that does not originate from a specific source Examples of nonpoint sources of pollution include the following i sediments from construction forestry operations and agricultural lands ii bacteria and microorganisms from failing septic systems and pet wastes iii nutrients from fertilizers and yard debris iv pesticides from agricultural areas golf courses athletic fields and residential yards oil grease anti freeze and metals washed from roads parking lots and driveways v toxic chemicals and cleaners that were not disposed of correctly and vi litter thrown onto streets sidewalks and beaches or directly into the water by individuals See Point Source Pollution Normality N The gram equivalents of solute divided by the liters of solution NOx Oxides of nitrogen Nucleophile A chemical reagent that reacts by forming covalent bonds with electronegative atoms and compounds Nuclide A nucleus rather than to an atomisotope the older term it is better known than the term nuclide and is still sometimes used in contexts where the use of the term nuclide might be more appropriate identical nuclei belong to one nuclide for example each nucleus of the carbon13 nuclide is composed of six protons and seven neutrons Number 1 Fuel oil No 1 Fuel oil Very similar to kerosene and is used in burners where vapor ization before burning is usually required and a clean flame is specified Number 2 Fuel oil No 2 Fuel oil Also called domestic heating oil has properties similar to diesel fuel and heavy jet fuel used in burners where complete vaporization is not required before burning Number 4 Fuel oil No 4 Fuel oil A light industrial heating oil and is used where preheating is not required for handling or burning there are two grades of No 4 fuel oil differing in safety flash point and flow viscosity properties Number 5 Fuel oil No 5 Fuel oil A heavy industrial fuel oil which requires preheating before burning Number 6 Fuel oil No 6 Fuel oil A heavy fuel oil and is more commonly known as Bunker C oil when it is used to fuel oceangoing vessels preheating is always required for burning this oil Nutrients Major elements for example nitrogen and phosphorus and trace elements including sulfur potassium calcium and magnesium that are essential for the growth of organisms Oceanography The science of the ocean and its physical and chemical characteristics Octane A flammable liquid C8H18 found in petroleum and natural gas there are 18 different octane isomers which have different structural formulas but share the molecular formula C8H18 used as a fuel and as a raw material for building more complex organic molecules Octane barrel yield A measure used to evaluate fluid catalytic cracking processes defined as RON MONtwo times the gasoline yield where RON is the research octane number and MON is the motor octane number 537 Glossary Octane number A number indicating the antiknock characteristics of gasoline Octanolwater partition coefficient Kow The equilibrium ratio of a chemicals concentration in octanol an alcoholic compound to its concentration in the aqueous phase of a twophase octanol water system typically expressed in log units log Kow Kow provides an indication of a chemicals solubility in fats lipophilicity its tendency to bioconcentrate in aquatic organisms or sorb to soil or sediment Oils fraction That portion of the maltenes that is not adsorbed by a surfaceactive material such as clay or alumina Oil sand See Tar sand Oil shale A finegrained impervious sedimentary rock which contains an organic material called kerogen Olefin Synonymous with alkene a hydrocarbon characterized by having at least one carbon carbon double bond CC specifically any of a series of openchain hydrocarbons such as ethylene Oleophilic Oil seeking or oil loving eg nutrients that stick to or dissolve in oil Order of reaction A chemical rate process occurring in systems for which concentration changes and hence the rate of reaction are not themselves measurable provided it is possible to measure a chemical flux Organic Compounds that contain carbon chemically bound to hydrogen often containing other elements particularly O N halogens or S chemical compounds based on carbon that also contain hydrogen with or without oxygen nitrogen and other elements Organic carbon soil partition coefficient Koc The proportion of a chemical sorbed to the solid phase at equilibrium in a twophase watersoil or watersediment system expressed on an organic carbon basis chemicals with higher Koc values are more strongly sorbed to organic carbon and therefore tend to be less mobile in the environment Organic chemistry The study of compounds that contain carbon chemically bound to hydrogen including synthesis identification modeling and reactions of those compounds Organic liquid nutrient injection An enhanced bioremediation process in which an organic liq uid which can be naturally degraded and fermented in the subsurface to result in the gen eration of hydrogen The most commonly added for enhanced anaerobic bioremediation include lactate molasses hydrogen release compounds HRCs and vegetable oils Organochlorine compounds chlorinated hydrocarbons Organic pesticides that contain chlo rine carbon and hydrogen such as DDT these pesticides affect the central nervous system Organometallic compounds Compounds that include carbon atoms directly bonded to a metal ion Organophosphorus compound A compound containing phosphorus and carbon many pesticides and most nerve agents are organophosphorus compounds such as malathion Osmotic potential Expressed as a negative value or zero indicates the ability of the soil to dis solve salts and organic molecules the reduction of soil water osmotic potential is caused by the presence of dissolved solutes Outersphere adsorption complex Sorption of an ion or molecule to a solid surface where waters of hydration are interposed between the sorbate and sorbent Oven dry The weight of a soil after all water has been removed by heating in an oven at a specified temperature usually in excess of 100C 212F for water temperatures will vary if other solvents have been used Overhead That portion of the feedstock which is vaporized and removed during distillation Oxidation The transfer of electrons away from a compound such as an organic contaminant the coupling of oxidation to reduction see below usually supplies energy that microorganisms use for growth and reproduction Often but not always oxidation results in the addition of an oxygen atom andor the loss of a hydrogen atom Oxidation number A number assigned to each atom to help keep track of the electrons during a redox reaction 538 Glossary Oxidation reaction A reaction where a substance loses electrons Oxidationreduction reactions redox reactions Reactions that involve oxidation of one reactant and reduction of another a reaction involving the transfer of electrons Oxidize The transfer of electrons away from a compound such as an organic contaminant The coupling of oxidation to reduction see below usually supplies energy that microorganisms use for growth and reproduction Often but not always oxidation results in the addition of an oxygen atom andor the loss of a hydrogen atom Oxygen enhancement with hydrogen peroxide An alternative process to pumping oxygen gas into groundwater involves injecting a dilute solution of hydrogen peroxide Its chemical formula is H2O2 and it easily releases the extra oxygen atom to form water and free oxy gen This circulates through the contaminated groundwater zone to enhance the rate of aerobic biodegradation of organic contaminants by naturally occurring microbes A solid peroxide product eg oxygenreleasing compound ORC can also be used to increase the rate of biodegradation Ozone O3 A form of oxygen containing three atoms instead of the common two O2 formed by highenergy ultraviolet radiation reacting with oxygen PAHs Polycyclic aromatic hydrocarbons Alkylated PAHs are alkyl group derivatives of the parent PAHs The five target alkylated PAHs referred to in this report are the alkylated naphtha lene phenanthrene dibenzothiophene fluorene and chrysene series Pale oil A lubricating oil or a process oil refined until its color by transmitted light is straw to pale yellow Paraffinum liquidum See Liquid petrolatum Paraffin An alkane Paraffinbase crude oil Crude oil with a high content of waxes and lubricating oil fractions hav ing small amounts of naphthenes or asphalts and low in sulfur nitrogen and oxygen Paraffin wax The colorless translucent highly crystalline material obtained from the light lubri cating fractions of paraffin crude oils wax distillates Particulate matter particulates Particles in the atmosphere or on a gas stream that may be organic or inorganic and originate from a wide variety of sources and processes Partition coefficient A partition coefficient is used describe how a solute is distributed between two immiscible solvents used in environmental science as a measure of a hydrophobicity of a solute and a proxy for transportation of a chemical through an ecosystem Partitioning The distribution of a solute S between two immiscible solvents such as aque ous phase and organic phase important aspect of the transportation of a chemical into through and out of an ecosystem Partitioning equilibrium The equilibrium distribution of a chemical that is established between the phases the distribution of a chemical between the different phases Partition ratio K The ratio of total analytical concentration of a solute in the stationary phase CS to its concentration in the mobile phase CM Pathogen An organism that causes disease eg some bacteria or viruses Penex process A continuous nonregenerative process for isomerization of C5 andor C6 fractions in the presence of hydrogen from reforming and a platinum catalyst Pentafining A pentane isomerization process using a regenerable platinum catalyst on a silica alumina support and requiring outside hydrogen Pepper sludge The fine particles of sludge produced in acid treating which may remain in suspension Percentage excess The excess of a reactant t based on the quantity of excess reactant above the amount required to react with the total quantity of limiting reactant Percent conversion The percentage of any reactant that has been converted to products Perfluorocarbon PFC A derivative of hydrocarbons in which all of the hydrogens have been replaced by fluorine 539 Glossary Pericondensed aromatic compounds Compounds based on angular condensed aromatic hydro carbon systems eg phenanthrene chrysene picene etc Periodic table Grouping of the known elements by their number of protons there are many other trends such as size of elements and electronegativity that are easily expressed in terms of the periodic table Permeability The ease of flow of the water through the rock Petrol A term commonly used in some countries for gasoline Petrolatum A semisolid product ranging from white to yellow in color produced during refining of residual stocks see Petroleum jelly Petrolenes The term applied to that part of the pentanesoluble or heptanesoluble material that is low boiling 300C 570F 760 mm and can be distilled without thermal decomposition see also Maltenes Petroleum crude oil A naturally occurring mixture of gaseous liquid and solid hydrocarbon compounds usually found trapped deep underground beneath impermeable cap rock and above a lower dome of sedimentary rock such as shale most petroleum reservoirs occur in sedimentary rocks of marine deltaic or estuarine origin Petroleum asphalt See Asphalt Petroleum ether See Ligroine Petroleum jelly A translucent yellowish to amber or white hydrocarbon substance melting point 38C54C having almost no odor or taste derived from petroleum and used principally in medicine and pharmacy as a protective dressing and as a substitute for fats in ointments and cosmetics also used in many types of polishes and in lubricating greases rust preven tives and modeling clay obtained by dewaxing heavy lubricatingoil stocks Petroleum refinery See Refinery Petroleum refining A complex sequence of events that result in the production of a variety of products Petroleum sulfonate A surfactant used in chemical flooding prepared by sulfonating selected crude oil fractions Petroporphyrins See Porphyrins Permeability The capability of the soil to allow water or air movement through it The quality of the soil that enables water to move downward through the profile measured as the number of inches per hour that water moves downward through the saturated soil Permeable reactive barrier PRB A subsurface emplacement of reactive materials through which a dissolved contaminant plume must move as it flows typically under natural gradi ent and treated water exits the other side of the permeable reactive barrier Pesticide A chemical that is designed and produced to control for pest control including weed control pH A measure of the acidity or basicity of a solution the negative logarithm base 10 of the hydro gen ion concentration in gram ions per liter a number between 0 and 14 that describes the acidity of an aqueous solution mathematically the pH is equal to the negative logarithm of the concentration of H3O in solution pH adjustment Neutralization Phase A separate fluid that coexists with other fluids gas oil water and other stable fluids such as microemulsions are all called phases in EOR research Phase behavior The tendency of a fluid system to form phases as a result of changing temperature pressure or the bulk composition of the fluids or of individual fluid phases Phase diagram A graph of phase behavior In chemical flooding a graph showing the relative volume of oil brine and sometimes one or more microemulsion phases In carbon dioxide flooding conditions for formation of various liquid vapor and solid phases Phase properties Types of fluids compositions densities viscosities and relative amounts of oil microemulsion or solvent and water formed when a micellar fluid surfactant slug or miscible solvent eg CO2 is mixed with oil 540 Glossary Phase separation The formation of a separate phase that is usually the prelude to coke formation during a thermal process the formation of a separate phase as a result of the instability incompatibility of petroleum and petroleum products Phenol A molecule containing a benzene ring that has a hydroxyl group substituted for a ring hydrogen Phenyl A molecular group or fragment formed by abstracting or substituting one of the hydrogen atoms attached to a benzene ring Phosphoric acid polymerization A process using a phosphoric acid catalyst to convert propene butene or both to gasoline or petrochemical polymers Photic zone The upper layer within bodies of water reaching down to about 200 m where sunlight penetrates and promotes the production of photosynthesis the richest and most diverse area of the ocean Photocatalysis The acceleration of a photoreaction in the presence of a catalyst in which light is absorbed by a substrate that is typically adsorbed on a solid catalyst Photocatalyst A material that can absorb light producing electronhole pairs that enable chemical transformations of the reaction participants and regenerate its chemical composition after each cycle of such interactions Phototrophs Organisms or chemicals that utilize light energy from photosynthesis Physical change Refers to the change that occurs when a material changes from one physical state to another without formation of intermediate substances of different composition in the process such as the change from gas to liquid Phytodegradation The process in which some plant species can metabolize VOC contaminants The resulting metabolic products include trichloroethanol trichloroacetic acid and dichloracetic acid mineralization products are probably incorporated into insoluble prod ucts such as components of plant cell walls Phytovolatilization The process in which VOCs are taken up by plants and discharged into the atmosphere during transpiration PINA analysis A method of analysis for paraffins isoparaffins naphthenes and aromatics PIONA analysis A method of analysis for paraffins isoparaffins olefins naphthenes and aromatics Pipe still A still in which heat is applied to the oil while being pumped through a coil or pipe arranged in a suitable firebox Pipestill gas The most volatile fraction that contains most of the gases that are generally dissolved in the crude Also known as pipestill light ends Pipestill light ends See Pipestill gas Pitch The nonvolatile brown to black semisolid to solid viscous product from the destructive dis tillation of many bituminous or other organic materials especially coal Platforming A reforming process using a platinumcontaining catalyst on an alumina base PM10 Particulate matter below 10 microns in diameter this corresponds to the particles inhalable into the human respiratory system and its measurement uses a sizeselective inlet PM25 Particulate matter below 25 microns in diameter this is closer to but slightly finer than the definitions of respirable dust that have been used for many years in industrial hygiene to identify dusts which will penetrate the lungs PNA A polynuclear aromatic compound PNA analysis A method of analysis for paraffins naphthenes and aromatics pOH A measure of the basicity of a solution the negative log of the concentration of the hydroxide ions Point emissions Emissions that occur through confined air streams as found in stacks ducts or pipes Point source pollution Any single identifiable source of pollution from which pollutants are dis charged such as a pipe Examples of point sources include i discharges from wastewater 541 Glossary treatment plants ii operational wastes from industries and iii combined sewer outfalls See Nonpoint Source Pollution Polar aromatics Resins the constituents of petroleum that are predominantly aromatic in character and contain polar nitrogen oxygen and sulfur functions in their molecular structures Polar compound An organic compound with distinct regions of positive and negative charge Polar compounds include alcohols such as sterols and some aromatics such as monoaromatic steroids Because of their polarity these compounds are more soluble in polar solvents including water compared to nonpolar compounds of similar molecular structure Pollutant Either i a nonindigenous chemical that is present in the environment or ii an indig enous chemical that is present in the environment in greater than the natural concentration Both types of pollutants are the result of human activity and have an overall detrimental effect upon the environment or upon something of value in that environment Polycyclic aromatic hydrocarbons PAHs Polycyclic aromatic hydrocarbons are a suite of com pounds comprised of two or more condensed aromatic rings They are found in many petroleum mixtures and they are predominantly introduced to the environment through natural and anthropogenic combustion processes Polyforming A process charging both C3 and C4 gases with naphtha or gas oil under thermal con ditions to produce gasoline Polymer A large molecule made by linking smaller molecules monomers together Polymerization The combination of two olefin molecules to form a higher molecular weight paraffin Polymer gasoline The product of polymerization of gaseous hydrocarbons to hydrocarbons boil ing in the gasoline range Polynuclear aromatic compound An aromatic compound having two or more fused benzene rings eg naphthalene and phenanthrene Polysulfide treating A chemical treatment used to remove elemental sulfur from refinery liquids by contacting them with a nonregenerable solution of sodium polysulfide PONA analysis A method of analysis for paraffins P olefins O naphthenes N and aromatics A Porphyrins Organometallic constituents of petroleum that contain vanadium or nickel the degra dation products of chlorophyll that became included in the protopetroleum Positional isomers Compounds which differ only in the position of a functional group 2pentanol and 3pentanol are positional isomers Potentiation A component having no effect increases the effect of another component Pour point The lowest temperature at which an oil will appear to flow under ambient pressure over a period of five seconds The pour point of crude oils generally varies from 60C to 30C Lighter oils with low viscosities generally have lower pour points Powerforming A fixed bed naphthareforming process using a regenerable platinum catalyst Precipitation Formation of an insoluble product that occurs via reactions between ions or mol ecules in solution Precipitation number The number of milliliters of precipitate formed when 10 mL of lubricating oil is mixed with 90 mL of petroleum naphtha of a definite quality and centrifuged under definitely prescribed conditions Primary oil recovery Oil recovery utilizing only naturally occurring forces Primary structure The chemical sequence of atoms in a molecule Primary substrates The electron donor and electron acceptor that are essential to ensure the growth of microorganism these compounds can be viewed as analogous to the food and oxygen that are required for human growth and reproduction Producers Organisms or chemicals that utilize light energy and store it as chemical energy Prokaryotes Microorganisms that lack a nuclear membrane so that their nuclear genetic material is more diffuse in the cell 542 Glossary Propagule Any part of a plant eg bud that facilitates dispersal of the species and from which a new plant may form Propane A colorless odorless flammable gas C3H8 found in petroleum and natural gas used as a fuel and as a raw material for building more complex organic molecules Propane asphalt See Solvent asphalt Propane deasphalting Solvent deasphalting using propane as the solvent Propane decarbonizing A solvent extraction process used to recover catalytic cracking feed from heavy fuel residues Propane dewaxing A process for dewaxing lubricating oils in which propane serves as solvent Propane fractionation A continuous extraction process employing liquid propane as the solvent a variant of propane deasphalting Propylene A threecarbon flammable gaseous molecule containing a doublebond CH3CHCH2 another important olefin used in organic synthesis also a base chemical to make polypro pylene fibers which are used in highperformance clothing carpeting and other products Protopetroleum A generic term used to indicate the initial productformed changes have occurred to the precursors of petroleum Protozoa Microscopic animals consisting of single eukaryotic cells Purge and trap A chromatographic sample introduction technique in volatile components that are purged from a liquid medium by bubbling gas through it The components are then concen trated by trapping them on a short intermediate column which is subsequently heated to drive the components on to the analytical column for separation Pyrobitumen See Asphaltoid Pyrolysis Exposure of a feedstock to high temperatures in an oxygenpoor environment Pyrophoric Substances that catch fire spontaneously in air without an ignition source Quadrillion 1 1015 Quench The sudden cooling of hot material discharging from a thermal reactor Radical free radical A molecular entity such asCH3 Cl possessing an unpaired electron Radioactive decay The process by which the nucleus of an unstable atom loses energy by emitting radiation Raffinate That portion of the oil which remains undissolved in a solvent refining process Ramsbottom carbon residue See Carbon residue Rate A derived quantity in which time is a denominator quantity so that the progress of a reaction is measured with time Rate constant k See Order of reaction Ratecontrolling step ratelimiting step ratedetermining step The elementary reaction hav ing the largest control factor exerts the strongest influence on the rate a step having a control factor much larger than any other step is said to be ratecontrolling Raw materials Minerals extracted from the earth prior to any refining or treating Reactants Substances initially present in a chemical reaction Reaction rate The change in concentration of the starting chemical in given time interval Reaction irreversible A reaction in which the reactants proceed to products but there is no significant backward reaction nA mB Products In this reaction the products do not recombine or change to form reactants in any appre ciable amount Reaction reversible A reaction in which the products can revert to the starting materials A and B Thus nA mB Products 543 Glossary Recalcitrant Unreactive nondegradable refractory Receptor An object animal vegetable or mineral or a locale that is affected by the pollutant Recycle ratio The volume of recycle stock per volume of fresh feed often expressed as the volume of recycle divided by the total charge Recycle stock The portion of a feedstock which has passed through a refining process and is recir culated through the process Recycling The use or reuse of chemical waste as an effective substitute for a commercial product or as an ingredient or feedstock in an industrial process Redox reductionoxidation reactions Oxidation and reduction occur simultaneously in general the oxidizing agent gains electrons in the process and is reduced while the reducing agent donates electrons and is oxidized Reduce The transfer of electrons to a compound such as oxygen that occurs when another com pound is oxidized Reduced crude A residual product remaining after the removal by distillation or other means of an appreciable quantity of the more volatile components of crude oil Reducers Organisms or chemicals that break down chemical compounds to more simple species and thereby extract the energy needed for their growth and metabolism Reduction The transfer of electrons to a compound such as oxygen that occurs when another compound is oxidized Reductive dehalogenation A variation on biodegradation in which microbially catalyzed reac tions cause the replacement of a halogen atom on an organic compound with a hydrogen atom The reactions result in the net addition of two electrons to the organic compound Refinery A series of integrated unit processes by which petroleum can be converted to a slate of useful salable products Refinery gas A gas or a gaseous mixture produced as a result of refining operations Refining The processes by which petroleum is distilled andor converted by application of a physi cal and chemical processes to form a variety of products are generated Reformate The liquid product of a reforming process Reformed gasoline Gasoline made by a reforming process Reforming The conversion of hydrocarbons with low octane numbers into hydrocarbons having higher octane numbers eg the conversion of a nparaffin into a isoparaffin Reformulated gasoline RFG Gasoline designed to mitigate smog production and to improve air quality by limiting the emission levels of certain chemical compounds such as benzene and other aromatic derivatives often contains oxygenates Refractive index index of refraction The ratio of wavelength or phase velocity of an electromag netic wave in a vacuum to that in the substance a measure of the amount of refraction a ray of light undergoes as it passes through a refraction interface a useful physical property to identify a pure compound Regulation A concept of management of complex systems according to a set of rules laws and trends can take many forms legal restrictions promulgated by a government authority contractual obligations such as contracts between insurers and their insureds social regu lation coregulation thirdparty regulation certification accreditation or market regula tion See Law Reid vapor pressure A measure of the volatility of liquid fuels especially gasoline Regeneration The reactivation of a catalyst by burning off the coke deposits Regenerator A reactor for catalyst reactivation Releases Onsite discharge of a toxic chemical to the surrounding environment includes emissions to the air discharges to bodies of water releases at the facility to land as well as contained disposal into underground injection wells Releases to air point and fugitive air emissions All air emissions from industry activity point emissions occur through confined air streams as found in stacks ducts or pipes fugitive 544 Glossary emissions include losses from equipment leaks or evaporative losses from impoundments spills or leaks Releases to land Disposal of toxic chemicals in waste to onsite landfills land treated or incorpo ration into soil surface impoundments spills leaks or waste piles These activities must occur within the boundaries of the facility for inclusion in this category Release to underground injection A contained release of a fluid into a subsurface well for the purpose of waste disposal Releases to water surface water discharges Any releases going directly to streams rivers lakes oceans or other bodies of water any estimates for storm water runoff and nonpoint losses must also be included Rerunning The distillation of an oil which has already been distilled Research octane method A test for determining the knock rating in terms octane numbers of fuels for use in sparkignition engines see also Motor Octane Method Reservoir Rock Highly permeable sedimentary rock limestone sand or shale through which petroleum may migrate and given their structural and stratigraphic characteristics it forms a trap that is surrounded by a seal layer that will avoid the hydrocarbons escape Residual asphalt See Straightrun asphalt Residual fuel oil Obtained by blending the residual products from various refining processes with suitable diluents usually middle distillates to obtain the required fuel oil grades Residual oil See Residuum petroleum remaining in situ after oil recovery Residuum resid pl residua The residue obtained from petroleum after nondestructive distil lation has removed all the volatile materials from crude oil eg an atmospheric 345C 650F residuum Resins The name given to a large group of polar compounds in oil These include hetero substituted aromatics acids ketones alcohols and monoaromatic steroids Because of their polarity these compounds are more soluble in polar solvents including water than the nonpolar compounds such as waxes and aromatics of similar molecular weight They are largely responsible for oil adhesion Respiration The process of coupling oxidation of organic compounds with the reduction of inor ganic compounds such as oxygen nitrate iron III manganese IV and sulfate Retention time The time it takes for an eluate to move through a chromatographic system and reach the detector Retention times are reproducible and can therefore be compared to a standard for analyte identification Reversible reaction A reaction in which the products can revert to the starting materials A and B Thus nA mB Products Rexforming A process combining platforming with aromatics extraction wherein lowoctane raf finate is recycled to the platformer Rhizodegradation The process whereby plants modify the environment of the root zone soil by releasing root exudates and secondary plant metabolites Root exudates are typically photo synthetic carbon low molecular weight molecules and high molecular weight organic acids This complex mixture modifies and promotes the development of a microbial community in the rhizosphere These secondary metabolites have a potential role in the development of naturally occurring contaminantdegrading enzymes Rhizosphere The soil environment encompassing the root zone of the plant Rich oil Absorption oil containing dissolved natural gasoline fractions Riser The part of the bubbleplate assembly which channels the vapor and causes it to flow down ward to escape through the liquid also the vertical pipe where fluid catalytic cracking reactions occur 545 Glossary Rock asphalt Bitumen which occurs in formations that have a limiting ratio of bitumentorock matrix RRF Relative response factor SARA analysis A method of fractionation by which petroleum is separated into saturates aromat ics resins and asphaltene fractions SARA separation See SARA analysis Saturated hydrocarbon A saturated carbonhydrogen compound with all carbon bonds filled that is there are no double or triple bonds as in olefins or acetylenes Saturated solution A solution in which no more solute will dissolve a solution in equilibrium with the dissolved material Saturates Paraffins and cycloparaffins naphthenes Saturation The maximum amount of solute that can be dissolved or absorbed under prescribed conditions Saybolt Furol viscosity The time in seconds Saybolt Furol Seconds SFS for 60 mL of fluid to flow through a capillary tube in a Saybolt Furol viscometer at specified temperatures between 70F and 210F the method is appropriate for highviscosity oils such as trans mission gear and heavy fuel oils Saybolt Universal viscosity The time in seconds Saybolt Universal Seconds SUS for 60 mL of fluid to flow through a capillary tube in a Saybolt Universal viscometer at a given temperature Scale wax The paraffin derived by removing the greater part of the oil from slack wax by sweating or solvent deoiling Scrubber A device that uses water and chemicals to clean air pollutants from combustion exhaust Scrubbing Purifying a gas by washing with water or chemical less frequently the removal of entrained materials Secondary pollutants A pollutant chemical species produced by interaction of a primary pol lutant with another chemical or by dissociation of a primary pollutant or by other effects within a particular ecosystem Secondary recovery Oil recovery resulting from injection of water or an immiscible gas at moder ate pressure into a petroleum reservoir after primary depletion Secondary structure The ordering of the atoms of a molecule in space relative to each other Secondary tracer The product of the chemical reaction between reservoir fluids and an injected primary tracer Sediment An insoluble solid formed as a result of the storage instability andor the thermal insta bility of petroleum and petroleum products Sedimentary Formed by or from deposits of sediments especially from sand grains or silts trans ported from their source and deposited in water as sandstone and shale or from calcare ous remains of organisms as limestone Sedimentary strata Typically consist of mixtures of clay silt sand organic matter and various minerals formed by or from deposits of sediments especially from sand grains or silts transported from their source and deposited in water such as sandstone and shale or from calcareous remains of organisms such as limestone Seismic section A seismic profile that uses the reflection of seismic waves to determine the geo logical subsurface Selective solvent A solvent which at certain temperatures and ratios will preferentially dis solve more of one component of a mixture than of another and thereby permitting partial separation Separation process An upgrading process in which the constituents of petroleum are separated usually without thermal decomposition eg distillation and deasphalting SeparatorNobel dewaxing A solvent tricholoethylene dewaxing process Separatory funnel Glassware shaped like a funnel with a stoppered rounded top and a valve at the tapered bottom used for liquidliquid separations 546 Glossary Shale A very finegrained sedimentary rock that is formed by the consolidation of clay mud or silt and that usually has a finely stratified or laminated structure Certain shale formations such as the Eagle Ford and the Barnett contain large amounts of oil and natural gas Shear Mechanical deformation or distortion or partial destruction of a polymer molecule as it flows at a high rate Shear rate A measure of the rate of deformation of a liquid under mechanical stress Shearthinning The characteristic of a fluid whose viscosity decreases as the shear rate increases Shell fluid catalytic cracking A twostage fluid catalytic cracking process in which the catalyst is regenerated Shell still A still formerly used in which the oil was charged into a closed cylindrical shell and the heat required for distillation was applied to the outside of the bottom from a firebox Side chain A chain of atoms which is attached to a longer chain of atoms examples of side chains would be methyl ethyl and propyl groups among others Sidestream A liquid stream taken from any one of the intermediate plates of a bubble tower Sidestream stripper A device used to perform further distillation on a liquid stream from any one of the plates of a bubble tower usually by the use of steam SIM Selecting Ion Monitoring Mass spectrometric monitoring of a specific masscharge mz ratio The SIM mode offers better sensitivity than can be obtained using the full scan mode Simple inorganic chemicals Molecules that consist of onetype atoms atoms of one element which in chemical reactions cannot be decomposed to form other chemicals Single displacement reactions Reactions where one element trades places with another element in a compound These reactions come in the general form of A BC AC B Examples include i magnesium replacing hydrogen in water to make magnesium hydrox ide and hydrogen gas Mg 2H O Mg OH H 2 2 2 ii the production of silver crystals when a copper metal strip is dipped into silver nitrate Cu s 2AgNO aq 2Ag s Cu NO aq 3 3 2 Slack wax The soft oily crude wax obtained from the pressing of paraffin distillate or wax distillate Slime A name used for petroleum in ancient texts Slim tube testing Laboratory procedure for the determination of minimum miscibility pressure using long small diameter sandpacked oilsaturated stainless steel tube Sludge A semisolid to solid product which results from the storage instability andor the thermal instability of petroleum and petroleum products Slug A quantity of fluid injected into a reservoir during enhanced oil recovery Slurry hydroconversion process A process in which the feedstock is contacted with hydrogen under pressure in the presence of a catalytic cokeinhibiting additive Slurry phase reactors Tanks into which wastes nutrients and microorganisms are placed Smoke The particulate material assessed in terms of its blackness or reflectance when collected on a filter as opposed to its mass this is the historical method of measurement of particulate pollution particles formed by incomplete combustion of fuel Smoke point A measure of the burning cleanliness of jet fuel and kerosene Sodium hydroxide treatment See Caustic wash 547 Glossary Sodium plumbite A solution prepared front a mixture of sodium hydroxide lead oxide and dis tilled water used in making the doctor test for light oils such as gasoline and kerosene Soil organic matter Living and partially decayed nonliving materials as well as assemblages of biomolecules and transformation products of organic residue decay known as humic substances Solid state compounds A diverse class of compounds that are solid at standard temperature and pressure and exhibit unique properties as semiconductors etc Solubility The amount of a substance solute that dissolves in a given amount of another sub stance solvent a measure of the solubility of an inorganic chemical in a solvent such as water generally ionic substances are soluble in water and other polar solvents while the nonpolar covalent compounds are more soluble in the nonpolar solvents in sparingly soluble slightly soluble or practically insoluble salts degree of solubility in water and occurrence of any precipitation process may be determined from the solubility product Ksp of the saltthe smaller the Ksp value the lower the solubility of the salt in water Solubility parameter A measure of the solvent power and polarity of a solvent Soluble Capable of being dissolved in a solvent Solute Any dissolved substance in a solution Solution Any liquid mixture of two or more substances that is homogeneous Solutizersteam regenerative process A chemical treating process for extracting mercaptans from gasoline or naphtha using solutizers potassium isobutyrate potassium alkyl pheno late in strong potassium hydroxide solution Solvent A liquid in which certain kinds of molecules dissolve While they typically are liquids with lowboiling points they may include highboiling liquids supercritical fluids or gases Solvent asphalt The asphalt produced by solvent extraction of residua or by light hydrocarbon propane treatment of a residuum or an asphaltic crude oil Solvent deasphalting A process for removing asphaltic and resinous materials from reduced crude oils lubricatingoil stocks gas oils or middle distillates through the extraction or precipi tant action of low molecular weight hydrocarbon solvents see also Propane deasphalting Solvent decarbonizing See Propane decarbonizing Solvent deresining See Solvent deasphalting Solvent dewaxing A process for removing wax from oils by means of solvents usually by chilling a mixture of solvent and waxy oil filtration or by centrifuging the wax which precipitates and solvent recovery Solvent extraction A process for separating liquids by mixing the stream with a solvent that is immiscible with part of the waste but that will extract certain components of the waste stream Solvent gas An injected gaseous fluid that becomes miscible with oil under reservoir conditions and improves oil displacement Solvent naphtha A refined naphtha of restricted boiling range used as a solvent also called petro leum naphtha petroleum spirits Solvent refining See Solvent extraction Solvolysis Generally a reaction with a solvent involving the rupture of one or more bonds in the reacting solute more specifically the term is used for substitution elimination or fragmen tation reactions in which a solvent species is the nucleophile hydrolysis if the solvent is water or alcoholysis if the solvent is an alcohol Sorbate Sometimes referred to as adsorbate is the solute that adsorbs on the solid phase Sorbent adsorbent The solid phase or substrate onto which the sorbate sorbs the solid phase may be more specifically referred to as an absorbent or adsorbent if the mechanism of removal is known to be absorption or adsorption respectively Sorption A general term that describes removal of a solute from solution to a contiguous solid phase and is used when the specific removal mechanism is not known 548 Glossary Sorption isotherm Graphical representation of surface excess ie the amount of substance sorbed to a solid relative to sorptive concentration in solution after reaction at fixed temperature pressure ionic strength pH and solidtosolution ratio Sorptive Ions or molecules in solution that could potentially participate in a sorption reaction Source Rock Sedimentary rock formed by very fine grain and with an abundant content of organic carbon which is deposited under reducing and lowenergy conditions generating hydro carbons over time Sour crude oil Crude oil containing an abnormally large amount of sulfur compounds see also Sweet crude oil Sour gas Natural gas or any other gas containing significant amounts of hydrogen sulfide H2S SOx Oxides of sulfur Soxhlet extraction An extraction technique for solids in which the sample is repeatedly contacted with solvent over several hours increasing extraction efficiency Specific gravity The mass or weight of a unit volume of any substance at a specified temperature compared to the mass of an equal volume of pure water at a standard temperature see also Density Specific heat The amount of heat required to raise the temperature of one gram of a substance by 1C the specific heat of water is 1 calorie or 4184 Joule Spent catalyst Catalyst that has lost much of its activity due to the deposition of coke and metals Spontaneous ignition Ignition of a fuel such as coal under normal atmospheric conditions usu ally induced by climatic conditions Stabilization The removal of volatile constituents from a higher boiling fraction or product strip ping the production of a product which to all intents and purposes does not undergo any further reaction when exposed to the air Stabilizer A fractionating tower for removing light hydrocarbons from an oil to reduce vapor pres sure particularly applied to gasoline Stable As applied to chemical species the term expresses a thermodynamic property which is quantitatively measured by relative molar standard Gibbs energies a chemical species A is more stable than its isomer B under the same standard conditions Standard conditions The reference amounts for pressure and temperaturein the English system they are 1473 pounds per square inch for the pressure and 60F for temperature Standard potential Used to predict if a species will be oxidized or reduced in solution under acidic or basic conditions and whether any oxidationreduction reaction will take place Starch A polysaccharide containing glucose longchain polymer of amylose and amylopectin that is the energy storage reserve in plants Stationary phase In chromatography the porous solid or liquid phase through which an intro duced sample passes The different affinities the stationary phase has for a sample allow the components in the sample to be separated or resolved Steam cracking A conversion process in which the feedstock is treated with superheated steam Steam distillation Distillation in which vaporization of the volatile constituents is effected at a lower temperature by introduction of steam open steam directly into the charge Stereochemistry The branch of organic chemistry that deals with the threedimensional structure of molecules Stereogenic carbon asymmetric carbon A carbon atom which is bonded to four different groups or atoms a chiral molecule must contain a stereogenic carbon and therefore has no plane of symmetry and is not superimposable on its mirror image Stereoisomers Isomers which have the same bonding connectivity but have a different three dimensional structure examples would be cis2butene and trans2butene geometric iso mers and the left and righthanded forms of 2butanol enantiomers Stern layer The layer of ions adsorbed immediately adjacent to a charged sorbent surface Ions in the Stern layer can be directly bonded to the sorbent through covalent and ionic bonds 549 Glossary innersphere complexes or held adjacent to a sorbent through strictly electrostatic forces in outersphere complexes Stoichiometry The calculation of the quantities of reactants and products among elements and compounds involved in a chemical reaction Stokes Law ρ ρ η v gd 18 2 1 2 Storage stability or storage instability the ability inability of a liquid to remain in storage over extended periods of time without appreciable deterioration as measured by gum formation and the depositions of insoluble material sediment Straightrun asphalt The asphalt produced by the distillation of asphaltic crude oil Straightrun products Obtained from a distillation unit and used without further treatment Stratosphere The portion of the atmosphere of the earth where ozone is formed by the reaction of ultraviolet light on dioxygen molecules Straw oil Pale paraffin oil of straw color used for many process applications Stripping A means of separating volatile components from less volatile ones in a liquid mix ture by the partitioning of the more volatile materials to a gas phase of air or steam see Stabilization Strong acid An acid that releases H ions easilyexamples are hydrochloric acid and sulfuric acid Strong base A basic chemical that accept and hold proton tightlyan example is the hydroxide ion Structural formula A convention used to represent the structures of organic molecules in which not all the valence electrons of the atoms are shown Structural isomerism The relationship between two compounds which have the same molecular formula but different structures they may be further classified as functional positional or skeletal isomers This relation is also called constitutional isomerism Styrene A humanmade chemical used mostly to make rubber and plastics present in combustion products such as cigarette smoke and automobile exhaust Sublimation The direct vaporization or transition of a solid directly to a vapor without passing through the liquid state Substitution reaction The process in which one group or atom in a molecule is replaced by another group or atom Substrate A chemical species of particular interest of which the reaction with some other chemi cal reagent is under observation eg a compound that is transformed under the influence of a catalyst also the component in a nutrient medium supplying microorganisms with carbon Csubstrate nitrogen Nsubstrate as food needed to grow Sulfonic acids Acids obtained by petroleum or a petroleum product with strong sulfuric acid Sulfuric acid alkylation An alkylation process in which olefins C3 C4 and C5 combine with isobutane in the presence of a catalyst sulfuric acid to form branched chain hydrocarbons used especially in gasoline blending stock Supercritical fluid An extraction method where the extraction fluid is present at a pressure and temperature above its critical point Superlight oil Oil with a specific gravity typically higher than 38 API Surfaceactive agent A compound that reduces the surface tension of liquids or reduces interfa cial tension between two liquids or a liquid and a solid also known as surfactant wetting agent or detergent Surface tension Caused by molecular attractions between the molecules of two liquids at the sur face of separation Surfactant A type of chemical characterized as one that reduces interfacial resistance to mixing between oil and water or changes the degree to which water wets reservoir rock 550 Glossary Suspensoid catalytic cracking A nonregenerative cracking process in which cracking stock is mixed with slurry of catalyst usually clay and cycle oil and passed through the coils of a heater Sustainable development Development and economic growth that meets the requirements of the present generation without compromising the ability of future generations to meet their needs a strategy seeking a balance between development and conservation of natural resources Sustainable enhancement An intervention action that continues until such time that the enhance ment is no longer required to reduce contaminant concentrations or fluxes Steranes A class of tetracyclic saturated biomarkers constructed from six isoprene subunits C30 Steranes are derived from sterols which are important membrane and hormone compo nents in eukaryotic organisms Most commonly used steranes are in the range of C26C30 and are detected using mz 217 mass chromatograms Surrogate analyte A pure analyte that is extremely unlikely to be found in any sample which is added to a sample aliquot in a known amount and is measured with the same procedures used to measure other components The purpose of a surrogate analyte is to monitor the method performance with each sample Sweated wax A crude wax that was freed from oil by having been passed through a heater sweater Sweating The separation of paraffin oil and low melting wax from paraffin wax Sweep efficiency The ratio of the pore volume of reservoir rock contacted by injected fluids to the total pore volume of reservoir rock in the project area See aso areal sweep efficiency and vertical sweep efficiency Sweet crude oil Crude oil containing little sulfur see also Sour crude oil Sweetening The process by which petroleum products are improved in odor and color by oxidizing or removing the sulfurcontaining and unsaturated compounds Swelling Increase in the volume of crude oil caused by absorption of EOR fluids especially carbon dioxide Also increase in volume of clays when exposed to brine Synthesis gas A mixture of carbon monoxide and hydrogen used especially in chemical synthesis to make hydrocarbon derivatives Synthetic crude oil syncrude A hydrocarbon product produced by the conversion of coal oil shale or tar sand bitumen that resembles conventional crude oil can be refined in a petro leum refinery Synergism The effect of the combination is greater than the sum of individual effects Tar The volatile brown to black oily viscous product from the destructive distillation of many bituminous or other organic materials especially coal a name used for petroleum in ancient texts Target analyte Target analytes are compounds that are required analytes in US EPA analytical methods BTEX and PAHs are examples of petroleumrelated compounds that are target analytes in US EPA Methods Tar sand See Bituminous sand Terminal electron acceptor TEA A compound or molecule that accepts an electron is reduced during metabolism oxidation of a carbon source under aerobic conditions molecular oxy gen is the terminal electron acceptor under anaerobic conditions a variety of terminal electron acceptors may be used In order of decreasing redox potential these terminal elec tron acceptors include nitrate manganese Mn3 Mn6 iron Fe3 sulfate and carbon dioxide microorganisms preferentially utilize electron acceptors that provide the maxi mum free energy during respiration of the common terminal electron acceptors listed above oxygen has the highest redox potential and provides the most free energy during electron transfer Terpanes A class of branched cyclic alkane biomarkers including hopanes and tricyclic compounds 551 Glossary Terpenes Hydrocarbon solvents compounds composed of molecules of hydrogen and carbon they form the primary constituents in the aromatic fractions of scented plants eg pine oil as well as turpentine and camphor oil Terrestrial biosphere The part of the geosphere consisting of the outer mantle and the crust that is directly involved with environmental processes through contact with the atmosphere the hydrosphere and living things varies from approximately 40 to 60 miles in thickness also called the lithosphere Tertiary structure The threedimensional structure of a molecule Tetrachloroethylene perchloroethylene A humanmade chemical that is widely used for dry cleaning of fabrics and for metaldegreasing operations also used as a starting material building block for making other chemicals and is used in some consumer products such as water repellents silicone lubricants fabric finishers spot removers adhesives and wood cleaners can stay in the air for a long time before breaking down into other chemicals or coming back to the soil and water in rain much of the tetrachloroethylene that gets into water and soil will evaporate because tetrachloroethylene can travel easily through soils it can get into underground drinking water supplies Thermal coke The carbonaceous residue formed as a result of a noncatalytic thermal process the Conradson carbon residue the Ramsbottom carbon residue Thermal conductivity A measure of the rate of transfer of heat by conduction through unit thick ness across unit area for unit difference of temperature measured as calories per second per square centimeter for a thickness of one centimeter and a temperature difference of 1C units are calcm secK or WcmK Thermal cracking A process which decomposes rearranges or combines hydrocarbon molecules by the application of heat without the aid of catalysts Thermal polymerization A thermal process to convert light hydrocarbon gases into liquid fuels Thermal process Any refining process which utilizes heat without the aid of a catalyst Thermal recovery See EOR process Thermal reforming A process using heat but no catalyst to effect molecular rearrangement of lowoctane naphtha into gasoline of higher antiknock quality Thermal stability thermal instability The ability inability of a liquid to withstand relatively high temperatures for short periods of time without the formation of carbonaceous deposits sediment or coke Thermodynamic equilibrium The thermodynamic state that is characterized by absence of flow of matter or energy Thermodynamics The study of the energy transfers or conversion of energy in physical and chem ical processes defines the energy required to start a reaction or the energy given out during the process Thermofor catalytic cracking A continuous moving bed catalytic cracking process Thermofor catalytic reforming A reforming process in which the synthetic beadtype catalyst of coprecipitated chromia Cr2O3 and alumina Al2O3 flows down through the reactor concurrent with the feedstock Thermofor continuous percolation A continuous clay treating process to stabilize and decolorize lubricants or waxes Thermogravimetric analysis TGA and differential thermal analysis DTA Techniques that may be used to measure the water of crystallization of a salt and the thermal decomposi tion of hydrates Thin layer chromatography TLC A chromatographic technique employing a porous medium of glass coated with a stationary phase An extract is spotted near the bottom of the medium and placed in a chamber with solvent mobile phase The solvent moves up the medium and separates the components of the extract based on affinities for the medium and solvent 552 Glossary Tight gas Natural gas produced from relatively impermeable rock Getting tight gas out usually requires enhanced technology applications like hydraulic fracturing the term is generally used for reservoirs other than shale when the gas is referred to as shale gas Toluene A clear colorless aromatic liquid also called methyl benzene C6H5CH3 occurs naturally in crude oil and in the tolu tree produced in the process of making gasoline and other fuels from crude oil used in making paints paint thinners fingernail polish lacquers adhe sives and rubber and in some printing and leather tanning processes a major component of JP8 fuel Topped crude Petroleum that has had volatile constituents removed up to a certain temperature eg 250C 480F topped crude not always the same as a residuum Topping The distillation of crude oil to remove light fractions only Total nalkanes The sum of all resolved nalkanes from C8 to C40 plus pristane and phytane Total 5 alkylated PAH homologs The sum of the 5 target PAHs naphthalene phenanthrene dibenzothiophene fluorene chrysene and their alkylated C1C4 homologues as deter mined by GCMS These 5 target alkylated PAH homologous series are oilcharacteristic aromatic compounds Total aromatics The sum of all resolved and unresolved aromatic hydrocarbons including the total of BTEX and other alkyl benzene compounds total 5 target alkylated PAH homologues and other EPA priority PAHs Total saturates The sum of all resolved and unresolved aliphatic hydrocarbons including the total nalkanes branched alkanes and cyclic saturates Total suspended particulate matter The mass concentration determined by filter weighing usu ally using a specified sampler which collects all particles up to approximately 20 microns depending on wind speed Tower Equipment for increasing the degree of separation obtained during the distillation of crude oil in a still Toxicity A measure of the toxic nature of a chemical usually expressed quantitatively as LD50 median lethal dose or LC50 median lethal concentration in airthe latter refers to inha lation toxicity of gaseous substances in air both terms refer to the calculated concentration of a chemical that can kill 50 of test animals when administered Toxicological chemistry The chemistry of toxic substances with emphasis upon their interactions with biologic tissue and living organisms TPH Total petroleum hydrocarbons the total measurable amount of petroleumbased hydrocar bons present in a medium as determined by gravimetric or chromatographic means Transfers A transfer of toxic organic chemicals in wastes to a facility that is geographically or physically separate from the facility reporting under the toxic release inventory the quanti ties reported represent a movement of the chemical away from the reporting facility except for offsite transfers for disposal these quantities do not necessarily represent entry of the chemical into the environment Transfers POTWs Waste waters transferred through pipes or sewers to a publicly owned treat ment works POTW treatment and chemical removal depend on the chemicals nature and treatment methods used chemicals not treated or destroyed by the publicly owned treatment works are generally released to surface waters or land filled within the sludge Transfers to disposal Wastes that are taken to another facility for disposal generally as a release to land or as an injection underground Transfers to energy recovery Wastes combusted offsite in industrial furnaces for energy recovery treatment of an organic chemical by incineration is not considered to be energy recovery Transfers to recycling Wastes that are sent offsite for the purposes of regenerating or recovering still valuable materials once these chemicals have been recycled they may be returned to the originating facility or sold commercially 553 Glossary Transfers to treatment Wastes moved offsite for either neutralization incineration biological destruction or physical separation in some cases the chemicals are not destroyed but prepared for further waste management Treatment Any method technique or process that changes the physical andor chemical character of petroleum 111Trichloroethane Does not occur naturally in the environment used in commercial products mostly to dissolve other chemicals beginning in 1996 111trichloroethane was no longer made in the United States because of its effects on the ozone layer because of its tendency to evaporate easily the vapor form is usually found in the environment 111 trichloroethane also can be found in soil and water particularly at hazardous waste sites Trichloroethylene A colorless liquid that does not occur naturally mainly used as a solvent to remove grease from metal parts and is found in some household products including type writer correction fluid paint removers adhesives and spot removers Trickle hydrodesulfurization A fixed bed process for desulfurizing middle distillates Triglyceride An ester of glycerol and three fatty acids the fatty acids represented by R can be the same or different Trillion 1 1012 Triterpanes A class of cyclic saturated biomarkers constructed from six isoprene subunits cyclic terpane compounds containing two four and six isoprene subunits are called monoter pane C10 diterpane C20 and triterpane C30 respectively Trophic The trophic level of an organism is the position it occupies in a food chain Troposphere The portion of the atmosphere of the earth that is closest to the surface True boiling point True boiling range The boiling point boiling range of a crude oil fraction or a crude oil product under standard conditions of temperature and pressure Tubeandtank cracking An older liquidphase thermal cracking process Tyndall effect The characteristic light scattering phenomenon of colloids results from those being the same order of size as the wavelength of light UCM Unresolved complex mixture of hydrocarbons on for example a gas chromatographic trac ing the UCM appear as the envelope or hump area between the solvent baseline and the curve defining the base of resolvable peaks Ultimate analysis Elemental composition Ultrafining A fixed bed catalytic hydrogenation process to desulfurize naphtha and upgrade distil lates by essentially removing sulfur nitrogen and other materials Ultraforming A lowpressure naphthareforming process employing onstream regeneration of a platinumonalumina catalyst and producing high yields of hydrogen and highoctane number reformate Ultraviolet radiation UV radiation An electromagnetic radiation with a wavelength from 10 to 400 nm shorter than the wavelength of visible light but longer than the wavelength of Xrays UV radiation is present in sunlight constituting about 10 of the total light output of the Sun Unassociated molecular weight The molecular weight of asphaltenes in an nonassociating polar solvent such as dichlorobenzene pyridine or nitrobenzene Underground storage tank A storage tank that is partially or completely buried in the earth Unifining A fixed bed catalytic process to desulfurize and hydrogenate refinery distillates Unisol process A chemical process for extracting mercaptan sulfur and certain nitrogen com pounds from sour gasoline or distillates using regenerable aqueous solutions of sodium or potassium hydroxide containing methanol 554 Glossary Universal viscosity See Saybolt Universal viscosity Unresolved complex The thousands of compounds that a gas chromatograph mixture UCM is unable to fully separate Unsaturated compound An organic compound with molecules containing one or more double bonds Unsaturated zone The zone between land surface and the capillary fringe within which the mois ture content is less than saturation and pressure is less than atmospheric soil pore spaces also typically contain air or other gases the capillary fringe is not included in the unsatu rated zone See Vadose zone Unstable Usually refers to a petroleum product that has more volatile constituents present or refers to the presence of olefin and other unsaturated constituents UOP alkylation A process using hydrofluoric acid which can be regenerated as a catalyst to unite olefins with isobutane UOP copper sweetening A fixed bed process for sweetening gasoline by converting mercaptans to disulfides by contact with ammonium chloride and copper sulfate in a bed UOP fluid catalytic cracking A fluid process of using a reactoroverregenerator design Upgradient In the direction of increasing potentiometric piezometric head See also Downgradient Upgrading The conversion of petroleum to valueadded salable products Upperphase microemulsion A microemulsion phase containing a high concentration of oil that when viewed in a test tube resides on top of a water phase Urea dewaxing A continuous dewaxing process for producing lowpourpoint oils and using urea which forms a solid complex adduct with the straightchain wax paraffins in the stock the complex is readily separated by filtration US EPA United States Environmental Protection Agency USGS United States Geological Survey Vacuum distillation Distillation under reduced pressure Vacuum residuum A residuum obtained by distillation of a crude oil under vacuum reduced pres sure that portion of petroleum which boils above a selected temperature such as 510C 950F or 565oC 1050oF Vadose zone The zone between land surface and the water table within which the moisture content is less than saturation except in the capillary fringe and pressure is less than atmospheric soil pore spaces also typically contain air or other gases the capillary fringe is included in the vadose zone Valence state of an atom The power of an atom to combine to form compounds determines the chemical properties Van der Waals forces Intermolecular attractive forces that arise between nonionic nonpolar mol ecules due to dipoledipole interactions and instantaneous dipole interactions London dispersion forces Van der Waals interaction The cohesive interaction attraction between like or the adhesive interaction attraction between unlike andor repulsive forces between molecules Vaporphase cracking A hightemperature lowpressure conversion process Vaporphase hydrodesulfurization A fixed bed process for desulfurization and hydrogenation of naphtha Vapor pressure The pressure exerted by a solid or liquid in equilibrium with its own vapor depends on temperature and is characteristic of each substance the higher the vapor pres sure at ambient temperature the more volatile the substance VGC viscositygravity constant An index of the chemical composition of crude oil defined by the general relation between specific gravity sg at 60F and Saybolt Universal viscosity SUV at 100F a 10sg 10752log SUV 38 10sg log SUV 38 555 Glossary The constant a is low for the paraffin crude oils and high for the naphthenic crude oils VI Viscosity index An arbitrary scale used to show the magnitude of viscosity changes in lubri cating oils with changes in temperature Visbreaking A process for reducing the viscosity of heavy feedstocks by controlled thermal decomposition Viscosity The resistance of a fluid to shear movement or flow a function of the composition of a fluid the viscosity of an ideal noninteracting fluid does not change with shear ratesuch fluids are called Newtonian expressed as gcm sec or Poise 1 Poise 100 centipoise Viscositygravity constant See VGC Viscosity index See VI VOC VOCs Volatile organic compounds volatile organic compounds are regulated because they are precursors to ozone carboncontaining gases and vapors from incomplete gaso line combustion and from the evaporation of solvents Volatile Readily dissipating by evaporation Volatile compounds A relative term that may mean i any compound that will purge ii any com pound that will elute before the solvent peak usually those C6 or iii any compound that will not evaporate during a solvent removal step Volatile organic compounds VOC Organic compounds with high vapor pressures at normal temperatures VOCs include light saturates and aromatics such as pentane hexane BTEX and other lighter substituted benzene compounds which can make up to a few percent of the total mass of some crude oils Water solubility The maximum amount of a chemical that can be dissolved in a given amount of pure water at standard conditions of temperature and pressure typical units are milligrams per liter mgL gallons per liter gL or pounds per gallon lbsgal Watson characterization factor See Characterization factor Wax See Mineral wax and Paraffin wax Wax distillate A neutral distillate containing a high percentage of crystallizable paraffin wax obtained on the distillation of paraffin or mixedbase crude and on reducing neutral lubricating stocks Waxes Waxes are predominately straightchain saturates with melting points above 20C gener ally the nalkanes C18 and higher molecular weight Wax fractionation A continuous process for producing waxes of low oil content from wax concen trates see also MEK deoiling Wax manufacturing A process for producing oilfree waxes Weak Acid An acid that does not release H ions easilyan example is acetic acid CH3CO2H Weak base A basic chemical that has little affinity for a protonan example is the chloride ion Weathered crude oil Crude oil which due to natural causes during storage and handling has lost an appreciable quantity of its more volatile components also indicates uptake of oxygen Weathering Processes related to the physical and chemical actions of air water and organisms after oil spill The major weathering processes include evaporation dissolution dispersion photochemical oxidation waterinoil emulsification microbial degradation adsorption onto suspended particulate materials interaction with mineral fines sinking sedimenta tion and formation of tar balls Wellbore A hole drilled by a drilling rig to explore for or develop oil andor natural gas also referred to as a well or borehole Wellhead The control equipment adjusted to the wellhead which is used to control the flow and prevent explosions and it consists of piping valves power outlets and blowup preventers Wet Deposition The term used to describe pollutants brought to ground either by rainfall or by snow this mechanism can be further subdivided depending on the point at which the pol lutant was absorbed into the water droplets Wet gas Gas containing a relatively high proportion of hydrocarbons which are recoverable as liquids see also Lean gas 556 Glossary Wet scrubbers Devices in which a countercurrent spray liquid is used to remove impurities and particulate matter from a gas stream Wettability The relative degree to which a fluid will spread on or coat a solid surface in the pres ence of other immiscible fluids Wettability number A measure of the degree to which a reservoir rock is waterwet or oilwet based on capillary pressure curves Wettability reversal The reversal of the preferred fluid wettability of a rock eg from waterwet to oilwet or vice versa White oil A generic tame applied to highly refined colorless hydrocarbon oils of low volatility and covering a wide range of viscosity Wilting point The largest water content of a soil at which indicator plants growing in that soil wilt and fail to recover when placed in a humid chamber Wobbe Index or Wobbe Number The calorific value of a gas divided by the specific gravity Wood alcohol See Methyl alcohol Xylenes The term that refers to all three types of xylene isomers metaxylene orthoxylene and paraxylene produced from crude oil used as a solvent and in the printing rubber and leather industries as well as a cleaning agent and a thinner for paint and varnishes a major component of JP8 fuel Yield The mass or moles of a chosen final product divided by the mass or moles of one of the initial reactants Zeolite A crystalline aluminosilicate used as a catalyst and having a particular chemical and physi cal structure Zwitterion A particle that contains both positively charged and negatively charged groups for example amino acids H2NHCHRCO2H can form zwitterions H3NCHRCOO 557 Index A Acetaminophen 480 Acetylene 316 chemicals from 319 properties 317 Acid gas removal 128 Acrylic and modacrylic fibers 461 Adipic acid 314 Adiponitrile 314 Aleve 480 Amino resins 456 Ammonia 360 production 361 properties and uses 362 Anaerobic digestion 107 chemistry 107 Aromatic compounds formulas 323 Aspirin 481 Autothermal reforming 398 B Benzene 14 331 Biogas 47 161 composition 48 Bioliquids 161 Biomass 79 94 111 161 chemicals from 190 feedstocks 97 gaseous products 111 gasification 96 103 165 172 liquid products 112 products 95 114 pyrolysis 96 103 waste 114 Biorefining 100 Butadiene 313 polymers and copolymers 445 properties 313 Butanediol 315 Butyl rubber 465 Butane 248 250 Butane isomers 247 chemical properties 249 physical properties 249 Butylene 16 17 304 butylene isomers 55 56 isomers 305 properties 305 C C4 olefins 303 Carbohydrates 99 Carbon black 363 production 363 properties and uses 364 Carbon dioxide 364 gasification 177 production 365 properties and uses 365 Carbon monoxide 364 production 365 properties and uses 365 Catalytic cracking processes 152 153 Cepacol 482 Chemicals from acetylene 316 319 hydrocarbons 323 Chemicals from benzene 14 324 331 332 alkylation 334 chlorination 339 hydrogenation 340 nitration 342 oxidation 343 Chemicals from biomass 95 96 111 190 Chemicals from butadiene 313 adipic acid 314 adiponitrile 314 butanediol 315 chloroprene 315 cyclic oligomers 316 hexamethylenediamine 314 Chemicals from butane 250 aromatics 252 isomerization 252 oxidation 250 Chemicals from butylene 16 304 hydration 308 isomerization 309 metathesis 309 oligomerization 310 oxidation 306 Chemicals from C4 olefins 303 Chemicals from diolefins 313 Chemicals from ethane 237 Chemicals from ethylbenzene 355 Chemicals from ethylene 15 271 273 acetaldehyde 283 alcohols 273 alkylation 275 1butylene 290 carbonylation 285 chlorination 286 ethanolamines 282 ethoxylates 281 ethylene glycol 279 halogen derivatives 276 hydration 287 oligomerization 288 oxygen derivatives 277 perchloroethylene 287 polymerization 289 290 558 Index Chemicals from ethylene cont 13propanediol 282 trichloroethylene 287 vinyl chloride 286 Chemicals from fuel oil 262 Chemicals from gas oil 259 Chemicals from isobutane 252 Chemicals from isobutylene 16 310 addition of alcohols 312 carbonylation 312 dimerization 312 epoxidation 311 hydration 312 oxidation 311 Chemicals from kerosene 258 Chemicals from liquid petroleum fractions and resids 264 266 chlorination 265 oxidation 265 sulfonation 265 Chemicals from methane 13 211 215 aldehyde derivatives 229 alkylation 231 carbon disulfide 216 chloromethane derivatives 218 ethylene 217 ethylene glycol 229 formaldehyde 226 hydrogen cyanide 218 methyl alcohol 223 nitration 230 oxidation 230 oxidative coupling 233 substitution reactions 38 synthesis gas 18 220 thermolysis 232 urea 223 Chemicals from naphtha 256 Chemicals from nonhydrocarbons 359 Chemicals from olefins 269 Chemicals from paraffins 209 Chemicals from propane 240 chlorination 240 dehydrogenation 241 nitration 247 oxidation 240 Chemicals from propylene 16 291 293 addition of organic acids 302 alkylation 303 ammoxidation 296 chlorination 300 disproportionation 303 hydration 300 hydroformylation 302 oxidation 294 oxyacylation 299 Chemicals from synthesis gas 381 Chemicals from toluene 14 324 343 carbonylation 345 chlorination 345 dealkylation 347 disproportionation 348 nitration 348 oxidation 350 Chemicals from xylene isomers 324 352 Chloroprene 315 Claus process 145 146 Coal 79 81 carbonization products 85 coalbed methane 48 coal gas 49 50 158 coal liquids 158 coal tar chemicals 85 composition 83 conversion 83 creosote 90 feedstocks 82 product streams 158 properties 82 Coalbed methane 48 Coal carbonization products 85 Coal gas 49 158 composition 50 Coal liquids 158 Coal tar creosote composition 90 Combined reforming 399 Combustion chemistry 37 Condensable hydrocarbon derivatives 137 Cracking processes 150 Creosote composition 90 Cyclic oligomers 316 Cycloparaffins 209 D Dehydrocyclization processes 157 Dehydrogenation processes 155 Dimethyl ether 408 Diolefins 313 Distillation fractions of petroleum 1 E Epoxy resins 455 Ethane 235 237 chemical properties 236 physical properties 235 Ethylbenzene 355 Ethylene 271 chemicals from 273 production 270 properties 272 Ethylene glycol 272 Ethylenepropylene rubber 465 Excedrin 482 Ethylbenzene 355 Ethylene 271 Extra heavy oil 68 69 60 72 F Feedstock preparation 119 composition 31 gasification 165 properties 31 Fermentation 110 559 Index FischerTropsch reaction chemical principles 412 chemicals from 387 chemistry 385 412 development 388 history 389 process 385 process history 388 products 414 refining FischerTropsch products 416 synthesis 181 Foamy oil 62 Fuel oil 65 260 261 chemical properties 261 physical properties 261 G Gas cleaning 123 124 127 see also Gas processing Gas condensate 43 Gaseous products 199 Gas hydrates 44 composition 45 Gasification 165 asphalt 184 biomass 189 black liquor 193 chemistry 168 169 coal 188 deasphalter bottoms 184 feedstock pretreatment 170 heavy feedstocks 183 195 with biomass 196 with coal 195 with waste 198 hydrogasification 178 petroleum coke 186 processes 179 products 167 198 solid waste 191 Gasification chemistry 168 169 feedstocks 183 187 reactions 171 refinery 166 193 Gasification processes 165 179 Gasification products high BTU gas 201 liquid products 201 low BTU gas 200 medium BTU gas 200 solid products 202 Gasifiers 171 180 Gas oil 67 258 chemical properties 259 physical properties 258 Gas processing 123 124 127 acid gas removal 128 130 condensable hydrocarbon derivatives 137 nitrogen removal 145 water removal 142 Gas production 198 Gas streams 120 121 122 from crude oil 124 from natural gas 121 Gaviscon 482 Geopressurized gas 51 Glycol refrigeration process 142 H Heavy oil 68 69 Hexamethylenediamine 314 High acid crude oil 61 High BTU gas 201 Highdensity polyethylene 436 Hydrazine 366 production 366 properties and uses 367 Hydrocarbons from petroleum 2 Hydrogasification 178 Hydrogen 368 production 368 properties and uses 370 I Ibuprofen 483 Iron oxide process 132 Isobutane 248 Isobutylene 16 properties 310 Isoprene 316 K Kaopectate 483 Kerosene 64 257 258 chemical properties 257 physical properties 257 L Landfill gas 51 Liquefied petroleum gas 123 Liquid petroleum fractions and resids 252 LMenthol 484 Low BTU gas 200 Lowdensity polyethylene 435 M Medicinal oils from bitumen 475 from mineral oilwhite oil 471 from paraffin wax 474 from petroleum 470 from petroleum jelly 472 from petroleum solvents 476 Medium BTU gas 200 Methanation 178 chemical properties 213 physical properties 212 Methane 211 215 substitution reactions 38 Molecular sieve process 138 Monomers polymers and plastics 421 addition polymerization 426 anionic polymerization 428 560 Index Monomers polymers and plastics cont cationic polymerization 427 condensation polymerization 429 coordination polymerization 428 free radical polymerization 427 processes and process chemistry 425 ringopening polymerization 430 N Naphtha 63 254 256 chemical properties 255 physical properties 254 production 7 Naphthenic acids 263 Natural gas 31 associated 32 composition 32 33 39 120 270 liquids 42 123 properties 33 refined and unrefined 34 Nitric acid 371 production 372 properties and uses 372 Nitrile rubber 464 Nitrogen removal 145 Nonhydrocarbons 359 Nylon 4 460 Nylon 6 460 Nylon 11 461 Nylon 12 460 Nylon 66 460 Nylon resins 440 O Oil shale 79 90 159 Oil shale gas 159 Olamine process 130 Opportunity crude oil 61 Olefins 269 Orajel 485 P Paraffins 209 Partial oxidation 400 Petrochemical industry 11 Petrochemicals 3 17 253 feedstocks 9 10 Petroleum 59 composition 59 distillation fractions 1 hydrocarbons 2 pour point 73 properties 59 streams 147 types 70 72 73 Pharmaceutical products 478 Acetaminophen 480 Aleve 480 Aspirin 481 Cepacol 482 Excedrin 482 Gaviscon 482 Ibuprofen 483 Kaopectate 483 LMenthol 484 Orajel 485 Tylenol 485 Zantac 485 Pharmaceuticals 467 production 479 Phenolformaldehyde resins 455 Plant fibers 99 Plastics and thermoplastics 421 446 chemical properties 452 chemical structure 450 classification 449 electrical properties 453 mechanical properties 451 optical properties 453 properties 451 Polyacetals 444 Polyamides 459 Polycarbonates 441 Polychloroprene 465 Polycyanurates 457 Polyester fibers 458 Polyesters 441 Polyether sulfones 442 Polyethylene 435 highdensity polyethylene 436 lowdensity polyethylene 435 Polyisoprene 464 Polymers 421 422 Polymer types 431 butadiene polymers and copolymers 445 glass transitions temperatures 434 highdensity polyethylene 436 lowdensity polyethylene 435 nylon resins 440 polyacetals 444 polycarbonates 441 polyesters 441 polyether sulfones 442 polyethylene 435 polyphenylene oxide 444 polypropylene 437 polystyrene 439 polyvinyl chloride 438 properties and uses 436 Polyphenylene oxide 444 Polypropylene 437 Polypropylene fibers 462 Polystyrene 439 Polyurethanes 453 Polyvinyl chloride 438 Primary gasification 174 Primary petrochemicals 4 19 Production of petrochemicals 20 Product quality 410 Propane 238 240 chemical properties 239 physical properties 238 Propylene 16 291 production 292 561 Index R Refinery configuration 5 148 149 Refinery gas 39 composition 53 54 270 Reforming catalysts 405 Reforming reactors 403 Resids 67 262 264 266 physical properties 263 Rubber 462 S Secondary gasification 174 Shale permeability 58 Shale oil 160 compound types 93 hydrocarbon products 92 nitrogencontaining compounds 93 oxygencontaining compounds 94 production 90 properties 91 sulfurcontaining compounds 94 Steam cracking 7 Steam reforming 395 Styrenebutadiene rubber 463 Sulfur 373 production 373 properties and uses 375 recovery processes 147 Sulfuric acid 376 production 376 properties and uses 379 manufacture wet process 378 Synthesis gas 18 57 199 380 390 uses 382 Synthesis gas feedstocks 393 Synthesis gas processes autothermal reforming 398 catalysts 405 combined reforming 399 feedstocks 393 partial oxidation 400 process parameters 401 product distribution 401 409 reactors 403 steam reforming 395 Synthesis gas production 381 392 395 Synthetic fibers 457 acrylic and modacrylic fibers 461 nylon 4 460 nylon 6 460 nylon 11 461 nylon 12 460 nylon 66 460 polyamides 459 polyester fibers 458 polypropylene fibers 462 Synthetic rubber 462 butyl rubber 465 ethylenepropylene rubber 465 nitrile rubber 464 polychloroprene 465 polyisoprene 464 styrenebutadiene rubber 463 T Tail gas treating processes 146 Tar sand bitumen 68 70 71 Terephthalic acid 9 Thermal cracking processes 150 Thermoplastics 446 Thermosetting plastics 453 amino resins 456 epoxy resins 455 phenolformaldehyde resins 455 polycyanurates 457 polyurethanes 453 unsaturated polyesters 455 Tight gas 58 Tight oil 62 Toluene 14 343 Toluidine isomers 349 Tylenol 485 U Unsaturated polyesters 455 Used lubricating oil 68 263 V Vegetable oils 99 W Watergas shift reaction 176 Water removal from gas streams 142 X Xylene isomers 5 14 352 properties 328 Z Zantac 485 REQUEST A FREE TRIAL supporttaylorfranciscom Taylor Francis eBooks wwwtaylorfranciscom A single destination for eBooks from Taylor Francis with increased functionality and an improved user experience to meet the needs of our customers 90000 eBooks of awardwinning academic content in Humanities Social Science Science Technology Engineering and Medical written by a global network of editors and authors TAYLOR FRANCIS EBOOKS OFFERS A streamlined experience for our library customers A single point of discovery for all of our eBook content Improved search and discovery of content at both book and chapter level