Chemistry of Petrochemical Processes - 2nd Edition

Copyright 1994 2000 by Gulf Publishing Company Houston Texas All rights reserved Printed in the United States of America This book or parts thereof may not be reproduced in any form without permission of the publisher Gulf Publishing Company Book Division PO Box 2608 Houston Texas 772522608 Library of Congress CataloginginPublication Data Printed on acidfree paper Chemistry oof PETROCHEMICAL PROCESSES 2nd Edition This book is dedicated to the memory of Professor Lewis Hatch 19121991 a scholar an educator and a sincere friend Frontmatter 12201 1054 AM Page iv v Contents Preface to Second Edition xi Preface to First Edition xiii CHAPTER ONE Primary Raw Materials for Petrochemicals 1 Introduction 1 Natural Gas 1 Natural Gas Treatment Processes 3 Natural Gas Liquids 8 Properties of Natural Gas 10 Crude Oils 11 Composition of Crude Oils 12 Properties of Crude Oils 19 Crude Oil Classification 21 Coal Oil Shale Tar Sand and Gas Hydrates 22 References 26 CHAPTER TWO Hydrocarbon Intermediates 29 Introduction 29 Paraffinic Hydrocarbons 29 Methane 30 Ethane 30 Propane 31 Butanes 31 Olefinic Hydrocarbons 32 Ethylene 32 Propylene 33 Butylenes 34 Dienes 36 Butadiene 37 Isoprene 37 Aromatic Hydrocarbons 37 Extraction of Aromatics 38 Liquid Petroleum Fractions and Residues 42 Naphtha 43 Kerosine 45 Gas Oil 46 Residual Fuel Oil 47 References 47 Frontmatter 12201 1054 AM Page v CHAPTER THREE Crude Oil Processing and Production of Hydrocarbon Intermediates 49 Introduction 49 Physical Separation Processes 49 Atmospheric Distillation 50 Vacuum Distillation 51 Absorption Process 52 Adsorption Process 52 Solvent Extraction 53 Conversion Processes 54 Thermal Conversion Processes 55 Catalytic Conversion Processes 60 Production of Olefins 91 Steam Cracking of Hydrocarbons 91 Production of Diolefins 101 References 107 CHAPTER FOUR Nonhydrocarbon Intermediates 111 Introduction 111 Hydrogen 111 Sulfur 114 Uses of Sulfur 116 The Claus Process 116 Sulfuric Acid 117 Carbon Black 118 The Channel Process 119 The Furnace Black Process 119 The Thermal Process 119 Properties and Uses of Carbon Black 120 Synthesis Gas 121 Uses of Synthesis Gas 123 Naphthenic Acids 130 Uses of Naphthenic Acid and Its Salts 130 Cresylic Acid 131 Uses of Cresylic Acid 133 References 133 CHAPTER FIVE Chemicals Based on Methane 135 Introduction 135 Chemicals Based on Direct Reactions of Methane 136 Carbon Disulfide 136 Hydrogen Cyanide 137 Chloromethanes 138 vi Frontmatter 12201 1054 AM Page vi Chemicals Based on Synthesis Gas 143 Ammonia 144 Methyl Alcohol 149 Oxo Aldehydes and Alcohols 163 Ethylene Glycol 166 References 167 CHAPTER SIX Ethane and Higher ParaffinsBased Chemicals 169 Introduction 169 Ethane Chemicals 169 Propane Chemicals 171 Oxidation of Propane 171 Chlorination of Propane 172 Dehydrogenation of Propane 172 Nitration of Propane 173 nButane Chemicals 174 Oxidation of nButane 175 Aromatics Production 177 Isomerization of nButane 180 Isobutane Chemicals 180 NaphthaBased Chemicals 181 Chemicals from High Molecular Weight nParaffins 182 Oxidation of Paraffins 183 Chlorination of nParaffins 184 Sulfonation of nParaffins 185 Fermentation Using nParaffins 185 References 186 CHAPTER SEVEN Chemicals Based on Ethylene 188 Introduction 188 Oxidation of Ethylene 189 Derivatives of Ethylene Oxide 192 Acetaldehyde 198 Oxidative Carbonylation of Ethylene 201 Chlorination of Ethylene 201 Vinyl Chloride 202 Perchloro and Trichloroethylene 203 Hydration of Ethylene 204 Oligomerization of Ethylene 205 Alpha Olefins Production 206 Linear Alcohols 207 Butenel 209 Alkylation Using Ethylene 210 References 211 vii Frontmatter 12201 1054 AM Page vii CHAPTER EIGHT Chemicals Based on Propylene 213 Introduction 213 Oxidation of Propylene 214 Acrolein 215 Mechanism of Propene Oxidation 215 Acrylic Acid 217 Ammoxidation of Propylene 218 Propylene Oxide 221 Oxyacylation of Propylene 226 Chlorination of Propylene 226 Hydration of Propylene 227 Properties and Uses of Isopropanol 228 Addition of Organic Acids to Propene 232 Hydroformylation of Propylene The Oxo Reaction 232 Disproportionation of Propylene Metathesis 234 Alkylation Using Propylene 235 References 236 CHAPTER NINE C4 Olefins and DiolefinsBased Chemicals 238 Introduction 238 Chemicals from nButenes 238 Oxidation of Butenes 239 Oligomerization of Butenes 248 Chemicals from Isobutylene 249 Oxidation of Isobutylene 250 Epoxidation of Isobutylene 251 Addition of Alcohols to Isobutylene 252 Hydration of Isobutylene 253 Carbonylation of Isobutylene 255 Dimerization of Isobutylene 255 Chemicals from Butadiene 255 Adiponitrile 256 Hexamethylenediamine 257 Adipic Acid 257 Butanediol 258 Chloroprene 258 Cyclic Oligomers of Butadiene 259 References 260 CHAPTER TEN Chemicals Based on Benzene Toluene and Xylenes 262 Introduction 262 Reactions and Chemicals of Benzene 262 viii Frontmatter 12201 1054 AM Page viii Alkylation of Benzene 263 Chlorination of Benzene 276 Nitration of Benzene 278 Oxidation of Benzene 280 Hydrogenation of Benzene 281 Reactions and Chemicals of Toluene 284 Dealkylation of Toluene 284 Disproportionation of Toluene 285 Oxidation of Toluene 286 Chlorination of Toluene 291 Nitration of Toluene 292 Carbonylation of Toluene 294 Chemicals from Xylenes 294 Terephthalic Acid 295 Phthalic Anhydride 296 Isophthalic Acid 297 References 299 CHAPTER ELEVEN Polymerization 301 Introduction 301 Monomers Polymers and Copolymers 302 Polymerization Reactions 303 Addition Polymerization 304 Condensation Polymerization 312 Ring Opening Polymerization 314 Polymerization Techniques 315 Physical Properties of Polymers 317 Crystallinity 317 Melting Point 317 Viscosity 317 Molecular Weight 318 Classification of Polymers 320 References 321 CHAPTER TWELVE Synthetic PetroleumBased Polymers 323 Introduction 323 Thermoplastics 324 Polyethylene 324 Polypropylene 329 Polyvinyl Chloride 332 Polystyrene 334 Nylon Resins 336 Thermoplastic Polyesters 336 Polycarbonates 337 Polyether Sulfones 339 Polyphenylene Oxide 340 Polyacetals 341 Thermosetting Plastics 342 Polyurethanes 342 Epoxy Resins 344 Unsaturated Polyesters 346 PhenolFormaldehyde Resins 346 Amino Resins 348 ix Frontmatter 12201 1054 AM Page ix Synthetic Rubber 350 Butadiene Polymers and Copolymers 352 Nitrile Rubber 353 Polyisoprene 354 Polychloroprene 356 Butyl Rubber 356 Ethylene Propylene Rubber 357 Thermoplastic Elastomers 358 Synthetic Fibers 359 Polyester Fibers 359 Polyamides 362 Acrylic and Modacrylic Fibers 368 Carbon Fibers 369 Polypropylene Fibers 370 References 371 Appendix One Conversion Factors 374 Appendix Two Selected Properties of Hydrogen Important C1C10 Paraffins Methylcyclopentane and Cyclohexane 376 Index 378 About the Authors 392 x Frontmatter 12201 1054 AM Page x Preface to Second Edition When the first edition of Chemistry of Petrochemical Processes was written the intention was to introduce to the users a simplified approach to a diversified subject dealing with the chemistry and technology of var ious petroleum and petrochemical process It reviewed the mechanisms of many reactions as well as the operational parameters temperature pressure residence times etc that directly effect products yields and composition To enable the readers to follow the flow of the reactants and products the processes were illustrated with simplified flow diagrams Although the basic concept and the arrangement of the chapters is this second edition are the same as the first this new edition includes many minor additions and updates related to the advances in processing and catalysis The petrochemical industry is a huge field that encompasses many commercial chemicals and polymers As an example of the magnitude of the petrochemical market the current global production of polyolefins alone is more than 80 billion tons per year and is expected to grow at a rate of 45 per year Such growth necessitates much work be invested to improve processing technique and catalyst design and ensure good product qualities This is primarily achieved by the search for new cata lysts that are active and selective The following are some of the impor tant additions to the text Because ethylene and propylene are the major building blocks for petro chemicals alternative ways for their production have always been sought The main route for producing ethylene and propylene is steam cracking which is an energy extensive process Fluid catalytic cracking FCC is also used to supplement the demand for these light olefins A new process that produces a higher percentage of light olefins than FCC is deep catalytic cracking DCC and it is described in Chapter 3 xi Frontmatter 12201 1054 AM Page xi xii The search for alternative ways to produce monomers and chemicals from sources other than oil such as coal has revived working using Fisher Tropseh technology which produces in addition to fuels light olefins sulfur phenols etc These could be used as feedstocks for petrochemicals as indicated in Chapter 4 Catalysts for many petroleum and petrochemical processes represent a substantial fraction of capital and operation costs Heterogeneous catalysts are more commonly used due to the ease of separating the products Homogeneous catalysts on the other hand are normally more selective and operate under milder conditions than heteroge neous types but lack the simplicity and ease of product separation This problem has successfully been solved for the oxo reaction by using rhodium modified with triphenylphosphine ligands that are water soluble Thus lyophilic products could be easily separated from the catalyst in the aqueous phase A water soluble cobalt cluster can effectively hydroformylate higher olefins in a twophase system using polyethylene glycol as the polar medium This approach is described in Chapter 5 In the polymer filed newgeneration metallocenes which are cur rently used in many polyethylene and polypropylene processes can polymerize proplylene in two different modes alternating blocks of rigid isotactic and flexible atactic These new developments and other changes and approaches related to polymerization are noted in Chapters 11 and 12 I hope the new additions that I felt necessary for updating this book are satisfactory to the readers Sami Matar PhD Frontmatter 12201 1054 AM Page xii Preface to First Edition Petrochemicals in general are compounds and polymers derived direct ly or indirectly from petroleum and used in the chemical market Among the major petrochemical products are plastics synthetic fibers synthetic rubber detergents and nitrogen fertilizers Many other important chem ical industries such as paints adhesives aerosols insecticides and phar maceuticals may involve one or more petrochemical products within their manufacturing steps The primary raw materials for the production of petrochemicals are natural gas and crude oil However other carbonaceous substances such as coal oil shale and tar sand can be processed expensively to produce these chemicals The petrochemical industry is mainly based on three types of interme diates which are derived from the primary raw materials These are the C2C4 olefins the C6C8 aromatic hydrocarbons and synthesis gas an H2CO2 mixture In general crude oils and natural gases are composed of a mixture of relatively unreactive hydrocarbons with variable amounts of nonhydro carbon compounds This mixture is essentially free from olefins However the C2 and heavier hydrocarbons from these two sources nat ural gas and crude oil can be converted to light olefins suitable as start ing materials for petrochemicals production The C6C8 aromatic hydrocarbonsthough present in crude oilare generally so low in concentration that it is not technically or economical ly feasible to separate them However an aromaticrich mixture can be obtained from catalytic reforming and cracking processes which can be further extracted to obtain the required aromatics for petrochemical use Liquefied petroleum gases C3C4 from natural gas and refinery gas streams can also be catalytically converted into a liquid hydrocarbon mixture rich in C6C8 aromatics xiii Frontmatter 12201 1054 AM Page xiii Synthesis gas the third important intermediate for petrochemicals is generated by steam reforming of either natural gas or crude oil fractions Synthesis gas is the precursor of two bigvolume chemicals ammonia and methanol From these simple intermediates many important chemicals and poly mers are derived through different conversion reactions The objec tive of this book is not merely to present the reactions involved in such conversions but also to relate them to the different process variables and to the type of catalysts used to get a desired product When plausi ble discussions pertinent to mechanisms of important reactions are included The book however is an attempt to offer a simplified treatise for diversified subjects dealing with chemistry process technology poly mers and catalysis As a starting point the book reviews the general properties of the raw materials This is followed by the different techniques used to convert these raw materials to the intermediates which are further reacted to pro duce the petrochemicals The first chapter deals with the composition and the treatment techniques of natural gas It also reviews the proper ties composition and classification of various crude oils Properties of some naturally occurring carbonaceous substances such as coal and tar sand are briefly noted at the end of the chapter These materials are tar geted as future energy and chemical sources when oil and natural gas are depleted Chapter 2 summarizes the important properties of hydrocarbon intermediates and petroleum fractions obtained from natural gas and crude oils Crude oil processing is mainly aimed towards the production of fuels so only a small fraction of the products is used for the synthesis of olefins and aromatics In Chapter 3 the different crude oil processes are reviewed with special emphasis on those conversion techniques employed for the dual purpose of obtaining fuels as well as olefinic and aromatic base stocks Included also in this chapter are the steam crack ing processes geared specially for producing olefins and diolefins In addition to being major sources of hydrocarbonbased petrochemi cals crude oils and natural gases are precursors of a special group of compounds or mixtures that are classified as nonhydrocarbon intermedi ates Among these are the synthesis gas mixture hydrogen sulfur and carbon black These materials are of great economic importance and are discussed in Chapter 4 Chapter 5 discusses chemicals derived directly or indirectly from methane Because synthesis gas is the main intermediate from methane xiv Frontmatter 12201 1054 AM Page xiv it is again further discussed in this chapter in conjunction with the major chemicals based on it Higher paraffinic hydrocarbons than methane are not generally used for producing chemicals by direct reaction with chemical reagents due to their lower reactivities relative to olefins and aromatics Nevertheless a few derivatives can be obtained from these hydrocarbons through oxida tion nitration and chlorination reactions These are noted in Chapter 6 The heart of the petrochemical industry lies with the C2C4 olefins butadiene and C6C8 aromatics Chemicals and monomers derived from these intermediates are successively discussed in Chapters 710 The use of light olefins diolefins and aromaticbased monomers for producing commercial polymers is dealt with in the last two chapters Chapter 11 reviews the chemistry involved in the synthesis of polymers their classification and their general properties This book does not dis cuss the kinetics of polymer reactions More specialized polymer chem istry texts may be consulted for this purpose Chapter 12 discusses the use of the various monomers obtained from a petroleum origin for producing commercial polymers Not only does it cover the chemical reactions involved in the synthesis of these polymers but it also presents their chemical physical and mechanical properties These properties are well related to the applicability of a polymer as a plastic an elastomer or as a fiber As an additional aid to readers seeking further information of a specif ic subject references are included at the end of each chapter Throughout the text different units are used interchangeably as they are in the indus try However in most cases temperatures are in degrees celsius pressures in atmospheres and energy in kilo joules The book chapters have been arranged in a way more or less similar to From Hydrocarbons to Petrochemicals a book I coauthored with the late Professor Hatch and published with Gulf Publishing Company in 1981 Although the book was more addressed to technical personnel and to researchers in the petroleum field it has been used by many colleges and universities as a reference or as a text for senior and special topics courses This book is also meant to serve the dual purpose of being a ref erence as well as a text for chemistry and chemical engineering majors In recent years many learning institutions felt the benefits of one or more technicallyrelated courses such as petrochemicals in their chem istry and chemical engineering curricula More than forty years ago Lewis Hatch pioneered such an effort by offering a course in Chemicals from Petroleum at the University of Texas Shortly thereafter the ter xv Frontmatter 12201 1054 AM Page xv petrochemicals was coined to describe chemicals obtained from crude oil or natural gas I hope that publishing this book will partially fulfill the objective of continuing the effort of the late Professor Hatch in presenting the state of the art in a simple scientific approach At this point I wish to express my appreciation to the staff of Gulf Publishing Co for their useful comments I wish also to acknowledge the cooperation and assistance I received from my colleagues the administration of KFUPM with special mention of Dr A AlArfaj chairman of the chemistry department Dr M Z El Faer dean of sciences and Dr A AlZakary vicerector for graduate studies and research for their encouragement in completing this work Sami Matar PhD xvi Frontmatter 12201 1054 AM Page xvi CHAPTER ONE Primary Raw Materials for Petrochemicals INTRODUCTION In general primary raw materials are naturally occurring substances that have not been subjected to chemical changes after being recovered Natural gas and crude oils are the basic raw materials for the manufac ture of petrochemicals The first part of this chapter deals with natural gas The second part discusses crude oils and their properties Secondary raw materials or intermediates are obtained from natural gas and crude oils through different processing schemes The intermedi ates may be light hydrocarbon compounds such as methane and ethane or heavier hydrocarbon mixtures such as naphtha or gas oil Both naph tha and gas oil are crude oil fractions with different boiling ranges The properties of these intermediates are discussed in Chapter 2 Coal oil shale and tar sand 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 tar sand and oil shale These materials are discussed briefly at the end of this chapter NATURAL GAS Nonassociated and Associated Natural Gases Natural gas is a naturally occurring mixture of light hydrocarbons accompanied by some nonhydrocarbon compounds Nonassociated nat ural 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 1 Chapter 1 12201 1055 AM Page 1 natural gases is methane Higher molecular weight paraffinic hydrocar bons C2C7 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 asso ciated gas while the latter contains a higher ratio of heavier hydrocar bons Table 11 shows the analyses of some selected nonassociated and associated gases1 In our discussion both nonassociated and associated gases will be referred to as natural gas However important differences will be noted The nonhydrocarbon constituents in natural gas vary appreciably from one gas field to another Some of these compounds are weak acids such as hydrogen sulfide and carbon dioxide Others are inert such as nitrogen helium and argon Some natural gas reservoirs contain enough helium for commercial production Higher molecular weight hydrocarbons present in natural gases are important fuels as well as chemical feedstocks and are normally recov ered as natural gas liquids For example ethane may be separated for use as a feedstock for steam cracking for the production of ethylene Propane and butane are recovered from natural gas and sold as liquefied petro leum gas LPG Before natural gas is used it must be processed or treated to remove the impurities and to recover the heavier hydrocarbons heavier than methane The 1998 US gas consumption was approxi mately 225 trillion ft3 2 Chemistry of Petrochemical Processes Table 11 Composition of nonassociated and associated natural gases1 Nonassociated gas Associated gas Salt Lake Kliffside Abqaiq North Sea Component US US Saudi Arabia UK Methane 950 658 622 859 Ethane 08 38 151 81 Propane 02 17 66 27 Butanes 08 24 09 Pentane and Heavier 05 11 03 Hydrogen sulfide 28 Carbon dioxide 36 92 16 Nitrogen 04 256 05 Helium 18 Chapter 1 12201 1055 AM Page 2 NATURAL GAS TREATMENT PROCESSES Raw natural gases contain variable amounts of carbon dioxide hydro gen sulfide and water vapor The presence of hydrogen sulfide in natural gas for domestic consumption cannot be tolerated because it is poison ous It also corrodes metallic equipment Carbon dioxide is undesirable because it reduces the heating value of the gas and solidifies under the high pressure and low temperatures used for transporting natural gas For obtaining a sweet dry natural gas acid gases must be removed and water vapor reduced In addition natural gas with appreciable amounts of heavy hydrocarbons should be treated for their recovery as natural gas liquids Acid Gas Treatment Acid gases can be reduced or removed by one or more of the follow ing methods 1 Physical absorption using a selective absorption solvent 2 Physical adsorption using a solid adsorbent 3 Chemical absorption where a solvent a chemical capable of react ing reversibly with the acid gases is used Physical Absorption Important processes commercially 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 hydro carbons 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 Figure 11 shows the Selexol process2 Physical Adsorption In these processes a solid with a high surface area is used Molecular sieves zeolites are widely used and are capable of adsorbing large amounts of gases In practice more than one adsorption bed is used for continuous operation One bed is in use while the other is being regenerated Primary Raw Materials for Petrochemicals 3 Chapter 1 12201 1055 AM Page 3 Regeneration is accomplished by passing hot dry fuel gas through the bed Molecular sieves are competitive only when the quantities of hydro gen sulfide and carbon disulfide are low Molecular sieves are also capable of adsorbing water in addition to the acid gases Chemical Absorption Chemisorption These 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 monoethanolamine The acid gas forms a weak bond with the base which can be regenerated easily Mono and diethanolamines are frequently used for this purpose The amine concentration 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 needs3 Diethanolamine also reacts reversibly with 75 of carbonyl sulfides COS while the mono reacts irreversibly with 95 of the COS and forms a degradation product that must be disposed of Diglycolamine DGA is another amine solvent used in the Econamine process Fig 124 Absorption of acid gases occurs in an absorber containing an aqueous solution of DGA and the heated rich 4 Chemistry of Petrochemical Processes Figure 11 The Selexol process for acid gas removal2 1 absorber 2 flash drum 3 compressor 4 lowpressure drum 5 stripper 6 cooler Chapter 1 12201 1055 AM Page 4 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 Strong basic solutions are effective solvents for acid gases However these solutions are not normally used for treating large volumes of natu ral 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 CO2 2NaOH aq r Na2 CO3 H2O H2S 2 NaOH aq r Na2S 2 H2O However a strong caustic solution is used to remove mercaptans from gas and liquid streams In the Merox Process for example a caustic sol vent 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 Fig 13 is mainly used for treatment of refinery gas streams5 Primary Raw Materials for Petrochemicals 5 Figure 12 The Econamine process4 1 absorption tower 2 regenera tion tower Chapter 1 12201 1055 AM Page 5 Water Removal Moisture must be removed from natural gas to reduce corrosion prob lems and to prevent hydrate formation Hydrates are solid white com pounds formed from a physicalchemical reaction between hydrocarbons and water under the high pressures and low temperatures used to trans port natural gas via pipeline Hydrates reduce pipeline efficiency 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 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 TEG absorber normally contains 6 to 12 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 inter action between TEG and water vapor in natural gas over a broad range allows the designs for ultralow dew point applications to be made6 A computer program was developed by Grandhidsan et al to estimate the number of trays and the circulation rate of lean TEG needed to dry nat ual gas It was found that more accurate predictions of the rate could be achieved using this program than using hand calculation7 Figure 14 shows the Dehydrate process where EG DEG or TEG could be used as an absorbent8 One alternative to using bubblecap trays 6 Chemistry of Petrochemical Processes Figure 13 The Merox process5 1 extractor 2 oxidation reactor Chapter 1 12201 1055 AM Page 6 is structural packing which improves control of mass transfer Flow pas sages direct the gas and liquid flows countercurrent to each other The use of structural packing in TEG operations has been reviewed by Kean et al9 Another way to dehydrate natural gas is by injecting methanol into gas lines to lower the hydrateformation temperature below ambient10 Water can also be reduced or removed from natural gas by using solid adsor bents such as molecular sieves or silica gel Condensable Hydrocarbon Recovery Hydrocarbons heavier than methane that are present in natural gases are valuable raw materials and important fuels They can be recovered by lean oil extraction 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 hydro carbons The uncondensed gas is dry natural gas and is composed mainly of methane with small amounts of ethane and heavier hydrocarbons The condensed hydrocarbons or natural gas liquids NGL are stripped from the rich solvent which is recycled Table 12 compares the analysis of natural gas before and after treatment11 Dry natural gas may then be used either as a fuel or as a chemical feedstock Another way to recover NGL is through cryogenic cooling to very low temperatures 150 to 180F which are achieved primarily through Primary Raw Materials for Petrochemicals 7 Figure 14 Flow diagram of the Dehydrate process8 1 absorption column 2 glycol sill 3 vacuum drum Chapter 1 12201 1055 AM Page 7 adiabatic expansion of the inlet gas The inlet gas is first treated to remove water and acid gases then cooled via heat exchange and refrig eration Further cooling of the gas is accomplished through turbo expanders and the gas is sent to a demethanizer to separate methane from NGL Improved NGL recovery could be achieved through better control strategies and use of online gas chromatographic analysis12 NATURAL GAS LIQUIDS NGL Natural gas liquids condensable hydrocarbons are those hydrocarbons heavier than methane that are recovered from natural gas The amount of NGL depends mainly on the percentage of the heavier hydrocarbons pres ent in the gas and on the efficiency of the process used to recover them A high percentage is normally expected from associated gas Natural gas liquids are normally fractionated to separate them into three streams 1 An ethanerich stream which is used for producing ethylene 2 Liquefied petroleum gas LPG which is a propanebutane mix ture It is mainly used as a fuel or a chemical feedstock Liquefied petroleum gas is evolving into an important feedstock for olefin production It has been predicted that the world LPG market for chemicals will grow from 231 million tons consumed in 1988 to 360 million tons by the year 2000l3 3 Natural gasoline NG is mainly constituted of C5 hydrocarbons and is added to gasoline to raise its vapor pressure Natural gaso line is usually sold according to its vapor pressure 8 Chemistry of Petrochemical Processes Table 12 Typical analysis of natural gas before and after treatment11 Component Pipeline mole Feed gas N2 045 062 CO2 2785 350 H2S 00013 Cl 7035 9485 C2 083 099 C3 022 0003 C4 0 13 0004 C5 006 0004 C6 011 0014 Chapter 1 12201 1055 AM Page 8 Natural gas liquids may contain significant amounts of cyclohexane a precursor for nylon 6 Chapter 10 Recovery of cyclohexane from NGL by conventional distillation is difficult and not economical because hep tane isomers are also present which boil at temperatures nearly identical to that of cyclohexane An extractive distillation process has been recently developed by Phillips Petroleum Co to separate cyclohexanel4 Liquefied Natural Gas LNG After the recovery of natural gas liquids sweet dry natural gas 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 respectively 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 temperature of methane is reached Figure 15 is a flow diagram for the expander cycle for liquefying natural gasl5 In mechanical refrigeration a multicomponent refrigerant consisting of nitrogen methane ethane and propane is used through a cascade cycle When these liquids evaporate the heat required is obtained from Primary Raw Materials for Petrochemicals 9 Figure 15 Flow diagram of the expander cycle for liquefying natural gas15 1 pretreatment molsieve 2 heat exchanger 3 turboexpander Chapter 1 12201 1055 AM Page 9 natural gas which loses energytemperature till it is liquefied The refrig erant gases are recompressed and recycled Figure 16 shows the MCR natural gas liquefaction process15 Table 13 lists important properties of a representative liquefied natural gas mixture PROPERTIES OF NATURAL GAS Treated natural gas consists mainly of methane the properties of both gases natural gas and methane are nearly similar However natural gas is not pure methane and its properties are modified by the presence of impurities such as N2 and CO2 and small amounts of unrecovered heav ier hydrocarbons 10 Chemistry of Petrochemical Processes Figure 16 The MCR process for liquefying natural gas15 1 coolers 2 heat exchangers 34 two stage compressors 5 liquidvapor phase separator Table 13 Important properties of a representative liquefied natural gas mixture Density lbcf 2700 Boiling point C 158 Calorific value Btulb 21200 Specific volume cflb 0037 Critical temperature C 823 Critical pressure psi 673 Critical temperature and pressure for pure liquid methane Chapter 1 12201 1055 AM Page 10 An important property of natural gas is its heating value Relatively 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 approximately 900 Btuft3 if the gas contains about 10 N2 and CO2 The 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 highermolecular weight hydrocarbons which have higher heating values For example ethanes heating value is 1800 Btuft3 compared to 1009 Btuft3 for methane Heating values of hydrocarbons normally present in natural gas are shown in Table 14 Natural gas is usually sold according to its heating values The heating value of a product gas is a function of the constituents present in the mix ture In the natural gas trade a heating value of one million Btu is approximately equivalent to 1000 ft3 of natural gas CRUDE OILS Crude oil petroleum is a naturally occurring brown to black flamma ble liquid Crude oils are principally found in oil reservoirs associated with sedimentary rocks beneath the earths surface Although exactly how crude oils originated is not established it is generally agreed that crude oils derived from marine animal and plant debris subjected to high temperatures and pressures It is also suspected that the transformation may have been catalyzed by rock constituents Regardless of their origins Primary Raw Materials for Petrochemicals 11 Table 14 Heating values of methane and heavier hydrocarbons present in natural gas Heating value Hydrocarbon Formula Btuft3 Methane CH4 1009 Ethane C2H6 1800 Propane C3H8 2300 Isobutane C4H10 3253 nButane C4H10 3262 Isopentane C5H12 4000 nPentane C5H12 4010 nHexane C6H14 4750 nHeptane C7H16 5502 Chapter 1 12201 1055 AM Page 11 all crude oils are mainly constituted of hydrocarbons mixed with variable amounts of sulfur nitrogen and oxygen compounds Metals in the forms of inorganic salts or organometallic compounds are present in the crude mixture in trace amounts The ratio of the differ ent constituents in crude oils however vary appreciably from one reser voir to another Normally crude oils are not used directly as fuels or as feedstocks for the production of chemicals This is due to the complex nature of the crude oil mixture and the presence of some impurities that are corrosive or poisonous to processing catalysts Crude oils are refined to separate the mixture into simpler fractions that can be used as fuels lubricants or as intermediate feedstock to the petrochemical industries A general knowledge of this composite mixture is essential for establishing a processing strategy COMPOSITION OF CRUDE OILS The crude oil mixture is composed of the following groups 1 Hydrocarbon compounds compounds made of carbon and hydrogen 2 Nonhydrocarbon compounds 3 Organometallic compounds and inorganic salts metallic com pounds Hydrocarbon Compounds The principal constituents of most crude oils are hydrocarbon com pounds All hydrocarbon classes are present in the crude mixture except alkenes and alkynes This may indicate that crude oils originated under a reducing atmosphere The following is a brief description of the different hydrocarbon classes found in all crude oils Alkanes Paraffins Alkanes are saturated hydrocarbons having the general formula CnH2n2 The simplest alkane methane CH4 is the principal con stituent of natural gas Methane ethane propane and butane are gaseous hydrocarbons at ambient temperatures and atmospheric pressure They are usually found associated with crude oils in a dissolved state Normal alkanes nalkanes nparaffins are straightchain hydrocar bons having no branches Branched alkanes are saturated hydrocarbons with an alkyl substituent or a side branch from the main chain A branched 12 Chemistry of Petrochemical Processes Chapter 1 12201 1055 AM Page 12 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 hydro carbon increases the number of isomers also increases Pentane C5C12 has three isomers hexane C6H14 has five The following shows the isomers of hexane An isoparaffin is an isomer having a methyl group branching from car bon number 2 of the main chain Crude oils contain many short medium and longchain normal and branched paraffins A naphtha fraction obtained as a light liquid stream from crude fractionation with a narrow boiling range may contain a limited but still large number of isomers Cycloparaffins Naphthenes Saturated cyclic hydrocarbons normally known as naphthenes are also part of the hydrocarbon constituents of crude oils Their ratio how ever depends on the crude type The lower members of naphthenes are cyclopentane cyclohexane and their monosubstituted compounds They are normally present in the light and the heavy naphtha fractions Cyclohexanes substituted cyclopentanes and substituted cyclohexanes are important precursors for aromatic hydrocarbons Primary Raw Materials for Petrochemicals 13 Methylcyclopentane Cyclohexane Methylcyclohexane Chapter 1 12201 1055 AM Page 13 The examples shown here are for three naphthenes of special importance If a naphtha fraction contains these compounds the first two can be con verted to benzene and the last compound can dehydrogenate to toluene during processing Dimethylcyclohexanes are also important precursors for xylenes see Xylenes later in this section Heavier petroleum fractions such as kerosine and gas oil may contain two or more cyclohexane rings fused through two vicinal carbons Aromatic Compounds Lower members of aromatic compounds are present in small amounts in crude oils and light petroleum fractions The simplest mononuclear aromatic compound is benzene C6H6 Toluene C7H8 and xylene C8H10 are also mononuclear aromatic compounds found in variable amounts in crude oils Benzene toluene and xylenes BTX are impor tant petrochemical intermediates as well as valuable gasoline compo nents Separating BTX aromatics from crude oil distillates is not feasible because they are present in low concentrations Enriching a naphtha frac tion with these aromatics is possible through a catalytic reforming process Chapter 3 discusses catalytic reforming Binuclear aromatic hydrocarbons are found in heavier fractions than naphtha Trinuclear and polynuclear aromatic hydrocarbons in com bination with heterocyclic compounds are major constituents of heavy crudes and crude residues Asphaltenes are a complex mixture of aro matic and heterocyclic compounds The nature and structure of some of these compounds have been investigated16 The following are represen tative examples of some aromatic compounds found in crude oils 14 Chemistry of Petrochemical Processes Chapter 1 12201 1055 AM Page 14 Only a few aromaticcycloparaffin compounds have been isolated and identified Tetralin is an example of this class Nonhydrocarbon Compounds 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 compounds are also found in all crudes The presence of these impurities is harmful and may cause prob lems to certain catalytic processes Fuels having high sulfur and nitrogen levels cause pollution problems in addition to the corrosive nature of their oxidization products Sulfur Compounds Sulfur in crude oils is mainly present in the form of organosulfur com pounds Hydrogen sulfide is the only important inorganic sulfur com pound found in crude oil Its presence however is harmful because of its corrosive nature Organosulfur compounds may generally be classified as acidic and nonacidic Acidic sulfur compounds are the thiols mercap tans Thiophene sulfides and disulfides are examples of nonacidic sul fur compounds found in crude fractions Extensive research has been carried out to identify some sulfur compounds in a narrow light petroleum fraction17 Examples of some sulfur compounds from the two types are Acidic Sulfur Compounds Primary Raw Materials for Petrochemicals 15 Nonacidic Sulfur Compounds Chapter 1 12201 1055 AM Page 15 Sour crudes contain a high percentage of hydrogen sulfide Because many organic sulfur compounds are not thermally stable hydrogen sul fide is often produced during crude processing Highsulfur crudes are less desirable because treating the different refinery streams for acidic hydrogen sulfide increases production costs Most sulfur compounds can be removed from petroleum streams through hydrotreatment processes where hydrogen sulfide is produced and the corresponding hydrocarbon released Hydrogen sulfide is then absorbed in a suitable absorbent and recovered as sulfur Chapter 4 Nitrogen Compounds Organic nitrogen compounds occur in crude oils either in a simple het erocyclic form as in pyridine C5H5N and pyrrole C4H5N or in a com plex structure as in porphyrin The nitrogen content in most crudes is very low and does not exceed 01 wt In some heavy crudes however the nitrogen content may reach up to 09 wt l8 Nitrogen compounds are more thermally stable than sulfur compounds and accordingly are con centrated in heavier petroleum fractions and residues Light petroleum streams may contain trace amounts of nitrogen compounds which should be removed because they poison many processing catalysts During hydrotreatment of petroleum fractions nitrogen compounds are hydro denitrogenated to ammonia and the corresponding hydrocarbon For example pyridine is denitrogenated to ammonia and pentane Nitrogen compounds in crudes 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 The following are examples of organic nitrogen compounds Basic Nitrogen Compounds 16 Chemistry of Petrochemical Processes Chapter 1 12201 1055 AM Page 16 NonBasic Nitrogen Compounds Porphyrins are nonbasic nitrogen compounds The porphyrin ring system is composed of four pyrrole rings joined by CHgroups The entire ring system is aromatic 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 metal19 Almost all crude oils and bitumens contain detectable amounts of vanadyl and nickel porphyrins The following shows a por phyrin structure 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 Oxygen compounds in crude oils are more complex than the sulfur types However their presence in petroleum streams is not poisonous to processing catalysts Many of the oxygen compounds found in crude oils are weakly acidic They are carboxylic acids cresylic acid phenol and naphthenic acid Naphthenic acids are mainly cyclopentane and cyclo hexane derivatives having a carboxyalkyl side chain Naphthenic acids in the naphtha fraction have a special commercial importance 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 as in some California crudes Primary Raw Materials for Petrochemicals 17 Chapter 1 12201 1055 AM Page 17 Nonacidic oxygen compounds such as esters ketones and amides are less abundant than acidic compounds They are of no commercial value The following shows some of the oxygen compounds commonly found in crude oils Acidic Oxygen Compounds 18 Chemistry of Petrochemical Processes NonAcidic Oxygen Compounds Chapter 1 12201 1055 AM Page 18 Metallic Compounds Many metals occur in crude oils Some of the more abundant are sodium calcium magnesium aluminium 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 porphyrins Calcium and magnesium can form salts or soaps with carboxylic acids These compounds act as emul sifiers 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 cor rosive 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 heavy residues Solvent extraction processes are used to reduce the concentration of heavy metals in petroleum residues PROPERTIES OF CRUDE OILS Crude oils differ appreciably in their properties according to origin and the ratio of the different components in the mixture Lighter crudes generally yield more valuable light and middle distillates and are sold at higher prices Crudes containing a high percent of impurities such as sul fur compounds are less desirable than lowsulfur crudes because of their corrosivity and the extra treating cost Corrosivity of crude oils is a func tion of many parameters among which are the type of sulfur compounds and their decomposition temperatures the total acid number the type of carboxylic and naphthenic acids in the crude and their decomposition temperatures It was found that naphthenic acids begin to decompose at 600F Refinery experience has shown that above 750F there is no naph thenic acid corrosion The subject has been reviewed by Kane and Cayard20 For a refiner it is necessary to establish certain criteria to relate one crude to another to be able to assess crude quality and choose the best processing scheme The following are some of the important tests used to determine the properties of crude oils Density Specific Gravity and API Gravity Density is defined as the mass of unit volume of a material at a spe cific temperature A more useful unit used by the petroleum industry is Primary Raw Materials for Petrochemicals 19 Chapter 1 12201 1055 AM Page 19 20 Chemistry of Petrochemical Processes specific gravity which is the ratio of the weight of a given volume of a material to the weight of the same volume of water measured at the same temperature Specific gravity is used to calculate the mass of crude oils and its prod ucts Usually crude oils and their liquid products are first measured on a volume basis then changed to the corresponding masses using the spe cific gravity The API American Petroleum Institute gravity is another way to express the relative masses of crude oils The API gravity could be cal culated mathematically using the following equation API i415 1315 Spgr 6060 A low API gravity indicates a heavier crude oil or a petroleum product while a higher API gravity means a lighter crude or product Specific gravities of crude oils roughly range from 082 for lighter crudes to over 10 for heavier crudes 41 10 API scale Salt Content The salt content expressed in milligrams of sodium chloride per liter oil or in poundsbarrel indicates the amount of salt dissolved in water Water in crudes is mainly present in an emulsified form A high salt con tent in a crude oil presents serious corrosion problems during the refin ing process In addition high salt content is a major cause of plugging heat exchangers and heater pipes A salt content higher than 10 1b1000 barrels expressed as NaCl requires desalting Sulfur Content Determining the sulfur content in crudes is important because the amount of sulfur indicates the type of treatment required for the distil lates To determine sulfur content a weighed crude sample or fraction is burned in an air stream All sulfur compounds are oxidized to sulfur dioxide which is further oxidized to sulfur trioxide and finally titrated with a standard alkali Identifying sulfur compounds in crude oils and their products is of lit tle use to a refiner because all sulfur compounds can easily be hydro desulfurized to hydrogen sulfide and the corresponding hydrocarbon The sulfur content of crudes however is important and is usually con sidered when determining commercial values Pour Point The pour point of a crude oil or product is the lowest temperature at which an oil is observed to flow under the conditions of the test Pour point data indicates the amount of longchain paraffins petroleum wax found in a crude oil Paraffinic crudes usually have higher wax content than other crude types Handling and transporting crude oils and heavy fuels is difficult at temperatures below their pour points Often chemical additives known as pour point depressants are used to improve the flow properties of the fuel Longchain nparaffins ranging from 1660 carbon atoms in particular are responsible for nearambient temperature precip itation In middle distillates less than 1 wax can be sufficient to cause solidification of the fuel21 Ash Content This test indicates the amount of metallic constituents in a crude oil The ash left after completely burning an oil sample usually consists of stable metallic salts metal oxides and silicon oxide The ash could be further analyzed for individual elements using spectroscopic techniques CRUDE OIL CLASSIFICATION Appreciable property differences appear between crude oils as a result of the variable ratios of the crude oil components For a refiner dealing with crudes of different origins a simple criterion may be established to group crudes with similar characteristics Crude oils can be arbitrarily classified into three or four groups depending on the relative ratio of the hydrocarbon classes that predominates in the mixture The following describes three types of crudes 1 Paraffinicthe ratio of paraffinic hydrocarbons is high compared to aromatics and naphthenes 2 Naphthenicthe ratios of naphthenic and aromatic hydrocarbons are relatively higher than in paraffinic crudes 3 Asphalticcontain relatively a large amount of polynuclear aro matics a high asphaltene content and relatively less paraffins than paraffinic crudes Primary Raw Materials for Petrochemicals 21 Chapter 1 12201 1055 AM Page 21 22 Chemistry of Petrochemical Processes A correlation index is a useful criterion for indicating the crude class or type The following relationship between the midboiling point in Kelvin degrees K and the specific gravity of a crude oil or a fraction yields the correlation index Bureau of Mines Correlation index BMCI 48640 K 4736d 4568 K midboiling point in Kelvin degrees Midboiling point is the temperature at which 50 vol of the crude is distilled d specific gravity at 6060F A zero value has been assumed for nparaffins 100 for aromatics A low BMCI value indicates a higher paraffin concentration in a petro leum fraction Another relationship used to indicate the crude type is the Watson characterization factor The factor also relates the midboiling point of the crude or a fraction to the specific gravity T3 Watson characterization factor a where T midboiling point in R R is the absolute F and equals F 460 A value higher than 10 indicates a predominance of paraffins while a value around 10 means a predominance of aromatics Table 15 Typical analysis of some crude oils Arab Extra Alameen Arab Bakr9 Light Egypt Heavy Egypt Gravity API 385 334 280 209 Carbon residue wt 20 51 68 117 Sulfur content wt 11 086 28 38 Nitrogen content wt 004 012 015 Ash content wt 0002 0004 0012 004 Iron ppm 04 00 10 Nickel ppm 06 00 90 108 Vanadium ppm 22 15 400 150 Pour point F Zero 35 110 55 Paraffin wax content wt 33 Ali M F et al Hydrocarbon Processing Vol 64 No 2 1985 p 83 Properties of crude oils vary considerably according to their types Table 15 lists the analyses of some crudes from different origins COAL OIL SHALE TAR SAND AND GAS HYDRATES Coal oil shale and tar sand are carbonaceous materials that can serve as future energy and chemical sources when oil and gas are consumed The HC ratio of these materials is lower than in most crude oils As solids or semisolids they are not easy to handle or to use as fuels com pared to crude oils In addition most of these materials have high sulfur andor nitrogen contents which require extensive processing Changing these materials into hydrocarbon liquids or gaseous fuels is possible but expensive The following briefly discusses these alternative energy and chemical sources COAL Coal is a natural combustible rock composed of an organic heteroge neous substance contaminated with variable amounts of inorganic com pounds Most coal reserves are concentrated in North America Europe and China Coal is classified into different 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 a high fixed carbon content are considered to have been sub jected 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 chemi cal change and is mostly carbon bituminous coal subbituminous coal and lignite Table 16 compares the analysis of some coals with crude oil23 During the late seventies and early eighties when oil prices rose after the 1973 war extensive research was done to change coal to liquid hydrocarbons However coalderived hydrocarbons were more expen sive than crude oils Another way to use coal is through gasification to a fuel gas mixture of CO and H2 medium Btu gas This gas mixture could be used as a fuel or as a synthesis gas mixture for the production of fuels and chemicals via a Fischer Tropsch synthesis route This process is Primary Raw Materials for Petrochemicals 23 Chapter 1 12201 1055 AM Page 23 operative in South Africa for the production of hydrocarbon fuels Fischer Tropsch synthesis is discussed in Chapter 4 OIL SHALE Oil shale is a lowpermeable rock made of inorganic material inter spersed with a highmolecular weight organic substance called Kerogen Heating the shale rock produces an oily substance with a complex structure The composition of oil shales differs greatly from one shale to another For example the amount of oil obtained from one ton of eastern US shale deposit is only 10 gallons compared to 30 gallons from western US shale deposits Retorting is a process used to convert the shale to a high molecular weight oily material In this process crushed shale is heated to high temperatures to pyrolyze Kerogen The product oil is a viscous high molecular weight material Further processing is required to change the oil into a liquid fuel Major obstacles to largescale production are the disposal of the spent shale and the vast earthmoving operations Table 17 is a typical analy sis of a raw shale oil produced from retorting oil shale TAR SAND Tar sands oil sands are large deposits of sand saturated with bitumen and water Tar sand deposits are commonly found at or near the earths surface entrapped in large sedimentary basins Large accumulations of tar sand deposits are few About 98 of all world tar sand is found in 24 Chemistry of Petrochemical Processes Table 16 Typical element analysis of some coals compared with a crude oil23 Weight HC mol C H S N O ratio Crude oil 846 128 15 04 05 182 Peat 568 56 03 27 346 118 Lignite 688 49 07 11 245 086 Bitumenous Coal 818 56 15 14 97 082 Anthracite 917 35 27 046 Chapter 1 12201 1055 AM Page 24 seven large tar deposits The oil sands resources in Western Canada sed imentary basin is the largest in the world In 1997 it produced 99 of Canadas crude oil It is estimated to hold 1725 trillon barrels of bitu men in place This makes it one of the largest hydrocarbon deposits in the world24 Tar sand deposits are covered by a semifloating mass of partially decayed vegetation approximately 6 meters thick Tar sand is difficult to handle During summer it is soft and sticky and during the winter it changes to a hard solid material Recovering the bitumen is not easy and the deposits are either strip mined if they are near the surface or recovered in situ if they are in deeper beds The bitumen could be extracted by using hot water and steam and adding some alkali to disperse it The produced bitumen is a very thick material having a density of approximately 105 gcm3 It is then subjected to a cracking process to produce distillate fuels and coke The distillates are hydrotreated to saturate olefinic components Table 18 is a typical analysis of Athabasca bitumen25 GAS HYDRATES Gas hydrates are an icelike material which is constituted of methane molecules encaged in a cluster 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 Primary Raw Materials for Petrochemicals 25 Table 17 Typical analysis of shale oil Test Result Gravity 197 Nitrogen wt 218 Conradson Carbon wt 45 Sulfur wt 074 Ash wt 006 Chapter 1 12201 1055 AM Page 25 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 evaluated26 REFERENCES 1 Hatch L F and Matar S From Hydrocarbons to Petrochemicals Gulf Publishing Company 1981 p 5 2 Gas Processing Handbook Hydrocarbon Processing Vol 69 No4 1990 p 91 3 Tuttle R and Allen K Oil and Gas Journal Aug 9 1976 pp 7882 4 Gas Processing Handbook Hydrocarbon Processing Vol 69 No 4 1990 p 77 26 Chemistry of Petrochemical Processes Table 18 Properties of Athabasca bitumen25 Gravity at 60F 156C 60API UOP characterization factor 1118 Pour point 50F 10C Specific heat 035 calgC Calorific value 17900 Btulb Viscosity at 60F 156C 3000300000 poise Carbonhydrogen ratio 81 Components asphaltenes 200 resins 250 oils 550 Ultimate analysis carbon 836 hydrogen 103 sulfur 55 nitrogen 04 oxygen 02 Heavy metals ppm nickel 100 vanadium 250 copper 5 Chapter 1 12201 1055 AM Page 26 5 Gas Processing Handbook Hydrocarbon Processing Vol 77 No 4 1998 p 113 6 Hicks R L and Senules E A New Gas WaterTEG Equilibria Hydrocarbon Processing Vol 70 No 4 1991 pp 5558 7 Gandhidasan P AlFarayedhi A and AlMubarak A A review of types of dessicant dehydrates solid and liquid Oil and Gas Journal June 21 1999 pp 3640 8 Gas Processing Handbook Hydrocarbon Processing Vol 69 No 4 1990 p 76 9 Kean J A Turner H M and Price B C How Packing Works in Dehydrators Hydrocarbon Processing Vol 70 No 4 1991 pp 4752 10 Aggour M Petroleum Economics and Engineering edited by Abdel Aal H K Bakr B A and AlSahlawi M Marcel Dekker Inc 1992 p 309 11 Hydrocarbon Processing Vol 57 No 4 1978 p 122 12 Jesnen B A Improve Control of Cryogenic Gas Plants Hydro carbon Processing Vol 70 No 5 1991 pp 109111 13 Watters P R New Partnerships Emerge in LPG and Petrochem icals Trade Hydrocarbon Processing Vol 69 No 6 1990 pp 100B100N 14 Brown R E and Lee F M Way to Purify Cyclohexane Hydro carbon Processing Vol 70 No 5 1991 pp 8384 15 Gas Processing Handbook Hydrocarbon Processing Vol 71 No 4 1992 p 115 16 Speight J G Applied Spectroscopy Reviews 5 1972 17 Rall H C et al Proc Am Petrol Inst Vol 42 Sec VIII 1962 p 19 18 Speight J G The Chemistry and Technology of Petroleum Marcel Dekker Inc 2nd Ed 1991 pp 242243 19 Fessenden R and Fessenden J Organic Chemistry 4th Ed BrooksCole Publishing Company 1991 p 793 20 Kane R D and Cayard M S Assess crude oil corrosivity Hydro carbon Processing Vol 77 No 10 1998 pp 97103 21 Wang S L Flamberg A and Kikabhai T Select the optimum pour point depressant Hydrocarbon Processing Vol 78 No 2 1999 pp 5962 22 Smith H M Bureau of Mines Technical Paper 610 1940 23 Matar S Synfuels Hydrocarbons of the Future PennWell Publishing Company 1982 p 38 Primary Raw Materials for Petrochemicals 27 Chapter 1 12201 1055 AM Page 27 24 Newell E P Oil and Gas Journal June 28 1999 pp 4446 25 Considine D M Energy Technology Handbook McGraw Hill Book Co New York 1977 pp 3163 26 Dagani R Gas hydrates eyed as future energy source Chemical and Engineering News March 6 1995 p 39 28 Chemistry of Petrochemical Processes Chapter 1 12201 1055 AM Page 28 CHAPTER TWO Hydrocarbon Intermediates INTRODUCTION Natural gas and crude oils are the main sources for hydrocarbon inter mediates or secondary raw materials for the production of petro chemicals From natural gas ethane and LPG are recovered for use as intermediates in the production of olefins and diolefins Important chem icals such as methanol and ammonia are also based on methane via syn thesis gas On the other hand refinery gases from different crude oil processing schemes are important sources for olefins and LPG Crude oil distillates and residues are precursors for olefins and aromatics via cracking and reforming processes This chapter reviews the properties of the different hydrocarbon intermediatesparaffins olefins diolefins and aromatics Petroleum fractions and residues as mixtures of different hydrocarbon classes and hydrocarbon derivatives are discussed sepa rately at the end of the chapter PARAFFINIC HYDROCARBONS Paraffinic hydrocarbons used for producing petrochemicals range from the simplest hydrocarbon methane to heavier hydrocarbon gases and liquid mixtures present in crude oil fractions and residues Paraffins are relatively inactive compared to olefins diolefins and aromatics Few chemicals could be obtained from the direct reaction of paraffins with other reagents However these compounds are the precur sors for olefins through cracking processes The C6C9 paraffins and cycloparaffins are especially important for the production of aromatics through reforming This section reviews some of the physical and chem ical properties of C1C4 paraffins Longchain paraffins normally present as mixtures with other hydrocarbon types in different petroleum fractions are discussed later in this chapter 29 Chapter 2 12201 1056 AM Page 29 METHANE CH4 Methane is the first member of the alkane series and is the main com ponent of natural gas It is also a byproduct in all gas streams from pro cessing crude oils It is a colorless odorless gas that is lighter than air Table 21 shows selected physical properties of C1C4 paraffinic hydro carbon gases As a chemical compound methane is not very reactive It does not react with acids or bases under normal conditions It reacts however with a limited number of reagents such as oxygen and chlorine under specific conditions For example it is partially oxidized with a limited amount of oxygen to a carbon monoxidehydrogen mixture at high tem peratures in presence of a catalyst The mixture synthesis gas is an important building block for many chemicals Chapter 5 Methane is mainly used as a clean fuel gas Approximately one mil lion BTU are obtained by burning 1000 ft3 of dry natural gas methane It is also an important source for carbon black Methane may be liquefied under very high pressures and low temper atures Liquefaction of natural gas methane allows its transportation to long distances through cryogenic tankers ETHANE CH3CH3 Ethane is an important paraffinic hydrocarbon intermediate for the production of olefins especially ethylene It is the second member of the alkanes and is mainly recovered from natural gas liquids Ethane like methane is a colorless gas that is insoluble in water It does not react with acids and bases and is not very reactive toward many reagents It can also be partially oxidized to a carbon monoxide and hydrogen mixture or chlorinated under conditions similar to those used 30 Chemistry of Petrochemical Processes Table 21 Selected physical properties of C1C4 paraffins Specific Boiling Calorific value Name Formula gravity point C Btuft3 Methane CH4 0554 1615 1009 Ethane CH3CH3 1049 886 1800 Propane CH3CH2CH3 1562 421 2300 nButane CH3CH22CH3 0579 05 3262 Isobutane CH32CHCH3 0557 111 3253 Air 1000 Chapter 2 12201 1056 AM Page 30 for methane 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 natural gas ethane is normally burned with methane as a fuel gas Ethanes relation with petrochemicals is mainly through its cracking to ethylene Ethylene is the largest end use of ethane in the US while it is only 5 in Western Europe1 Chapter 3 discusses steam cracking of ethane PROPANE CH3CH2CH3 Propane is a more reactive paraffin than ethane and methane This is due to the presence of two secondary hydrogens that could be easily sub stituted 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 LPG is currently an important feedstock for the production of olefins for petrochemical use 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 hydrocarbons from natural gas Chemicals directly based on propane are few although as mentioned propane and LPG are important feedstocks for the production of olefins Chapter 6 discusses a new process recently developed for the dehydro genation of propane to propylene for petrochemical use Propylene has always been obtained as a coproduct with ethylene from steam cracking processes Chapter 6 also discusses the production of aromatics from LPG through the Cyclar process2 BUTANES C4H10 Like propane butanes are obtained from natural gas liquids and from refinery gas streams The C4 acyclic paraffin consists of two isomers n butane and isobutane 2methylpropane The physical as well as the chemical properties of the two isomers are quite different due to structural differences For example the vapor pressure Reid method for nbutane is 52 lbin2 while it is 71 lbin2 for isobutane This makes the former a more favorable gasoline additive to adjust its vapor pressure However this use is declining in the United States due to new regulations that reduce the volatility of gasolines to 9 psi primarily by removing butane3 Hydrocarbon Intermediates 31 Chapter 2 12201 1056 AM Page 31 Isobutane on the other hand is a much more reactive compound due to the presence of a tertiary hydrogen CH3CH2CH2CH3 CH32CHCH3 nButane Isobutane Butane is primarily used as a fuel gas within the LPG mixture 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 production of synthetic rubber nButane is also a starting material for acetic acid and maleic anhydride production Chapter 6 Due to its higher reactivity isobutane is an alkylating agent of light olefins for the production of alkylates Alkylates are a mixture of branched hydrocarbons in the gasoline range having high octane ratings Chapter 3 Dehydrogenation of isobutane produces isobutene which is a reactant for the synthesis of methyl tertiary butyl ether MTBE This compound is currently in high demand for preparing unleaded gasoline due to its high octane rating and clean burning properties Octane ratings of hydrocarbons are noted later in this chapter OLEFINIC HYDROCARBONS The most important olefins used for the production of petrochemicals are ethylene propylene the butylenes and isoprene These olefins are usually coproduced with ethylene by steam cracking ethane LPG liquid petroleum fractions and residues Olefins are characterized by their higher reactivities compared to paraffinic hydrocarbons They can easily react with inexpensive reagents such as water oxygen hydrochloric acid and chlorine to form valuable chemicals Olefins can even add to them selves to produce important polymers such as polyethylene and polypropy lene Ethylene is the most important olefin for producing petrochemicals and therefore many sources have been sought for its production The fol lowing discusses briefly the properties of these olefinic intermediates ETHYLENE CH2CH2 Ethylene ethene the first member of the alkenes is a colorless gas with a sweet odor It is slightly soluble in water and alcohol It is a highly 32 Chemistry of Petrochemical Processes Chapter 2 12201 1056 AM Page 32 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 ethylene dichloride 12dichloro ethane which is cracked to vinyl chloride Vinyl chloride is an impor tant plastic precursor Ethylene is also an active alkylating agent Alkylation of benzene with ethylene produces ethyl benzene which is dehydrogenated to styrene Styrene is a monomer used in the manufac ture of many commercial polymers and copolymers Ethylene can be polymerized to different grades of polyethylenes or copolymerized with other olefins Catalytic oxidation of ethylene produces ethylene oxide which is hydrolyzed to ethylene glycol Ethylene glycol is a monomer for the pro duction of synthetic fibers Chapter 7 discusses chemicals based on eth ylene and Chapter 12 covers polymers and copolymers of ethylene Ethylene is a constituent of refinery gases especially those produced from catalytic cracking units The main source for ethylene is the steam cracking of hydrocarbons Chapter 3 Table 22 shows the world ethyl ene production by source until the year 20004 US production of ethylene was approximately 51 billion lbs in 19975 PROPYLENE CH3CHCH2 Like ethylene propylene propene 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 cracking of hydrocarbons where it is coproduced with ethylene There is no special process for propylene production except the dehydrogenation of propane Catalyst CH3CH2CH3 r CH3CHCH2H2 Hydrocarbon Intermediates 33 Table 22 World ethylene production by feedstock4 MMtpd Feedstock 1990 1995 2000 Ethanerefinery gas 16 18 20 LPG 6 9 12 Naphthacondensates 30 36 40 Gasoilothers 4 5 6 Total 56 68 78 Chapter 2 12201 1056 AM Page 33 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 Chapter 8 discusses the production of these chemicals US production of proplylene was approximately 275 billion lbs in 19975 BUTYLENES C4H8 Butylenes butenes are byproducts of refinery cracking processes and steam cracking units for ethylene production Dehydrogenation of butanes is a second source of butenes However this source is becoming more important because isobutylene a butene isomer is currently highly demanded for the production of oxygenates as gasoline additives There are four butene isomers three unbranched normal butenes nbutenes and a branched isobutene 2methylpropene The three n butenes are 1butene and cis and trans 2butene The following shows the four butylene isomers 34 Chemistry of Petrochemical Processes The industrial reactions involving cis and trans2butene are the same and produce the same products There are also addition reactions where both lbutene and 2butene give the same product For this reason it is economically feasible to isomerize 1butene to 2butene cis and trans and then separate the mixture The isomerization reaction yields two streams one of 2butene and the other of isobutene which are separated by fractional distillation each with a purity of 8090 Table 236 shows the boiling points of the different butene isomers Chapter 2 12201 1056 AM Page 34 An alternative method for separating the butenes is by extracting isobutene due to its higher reactivity in cold sulfuric acid which poly merizes it to di and triisobutylene The dimer and trimer of isobutene have high octane ratings and are added to the gasoline pool Figure 21 shows the two processes for the separation of nbutenes from isobutene7 Chemicals based on butenes are discussed in Chapter 9 Hydrocarbon Intermediates 35 Table 23 Structure and boiling points of C4 olefins6 Name Structure Boiling PointC 1Butene CH2CHCH2CH3 63 cis2Butene 37 trans2Butene 09 Isobutene 66 Figure 21 The two processes for separating nbutenes and isobutylene7 Chapter 2 12201 1056 AM Page 35 THE DIENES 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 diolefins 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 independently and reacts as if the other is not pres ent8 Examples of nonconjugated dienes are 14pentadiene and 14 cyclohexadiene Examples of conjugated dienes are 13butadiene and 13cyclohexadiene 36 Chemistry of Petrochemical Processes An important difference between conjugated and nonconjugated dienes is that the former compounds can react with reagents such as chlorine yielding 12 and 14addition products For example the reaction between chlorine and 13butadiene produces a mixture of 14dichloro 2butene and 34dichloro 1butene 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 follow ing reviews some of the physical and chemical properties of butadiene and isoprene Chapter 2 12201 1056 AM Page 36 BUTADIENE CH2CHCHCH2 Butadiene is by far the most important monomer for synthetic rubber production It can be polymerized to polybutadiene or copolymerized with styrene to styrenebutadiene rubber SBR Butadiene is an impor tant 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 The unique role of butadiene among other conjugated diolefins lies in its high reactivity as well as its low cost Butadiene is obtained mainly as a coproduct with other light olefins from steam cracking units for ethylene production Other sources of buta diene are the catalytic dehydrogenation of butanes and butenes and dehydration of 14butanediol Butadiene is a colorless gas with a mild aromatic odor Its specific gravity is 06211 at 20C and its boiling tem perature is 44C The US production of butadiene reached 41 billion pounds in 1997 and it was the 36th highestvolume chemical5 Hydrocarbon Intermediates 37 Isoprene 2methyl13butadiene is a colorless liquid soluble in alcohol but not in water Its boiling temperature is 341C Isoprene is the second important conjugated diene for synthetic rub ber production The main source for isoprene is the dehydrogenation of C5 olefins tertiary amylenes 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 isobutene formalde hyde and propene Chapter 3 The main use of isoprene is the production of polyisoprene It is also a comonomer with isobutene for butyl rubber production AROMATIC HYDROCARBONS Benzene toluene xylenes BTX and ethylbenzene are the aromatic hydrocarbons with a widespread use as petrochemicals They are impor tant precursors for many commercial chemicals and polymers such as Chapter 2 12201 1056 AM Page 37 phenol trinitrotoluene TNT nylons and plastics 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 hydrocarbons are susceptible however to electrophilic substitution reactions in presence of a catalyst Aromatic hydrocarbons are generally nonpolar They are not soluble in water but they dissolve in organic solvents such as hexane diethyl ether and carbon tetrachloride EXTRACTION OF AROMATICS Benzene toluene xylenes BTX and ethylbenzene are obtained mainly from the catalytic reforming of heavy naphtha The product refor mate is rich in C6 C7 and C8 aromatics which could be extracted by a suitable solvent such as sulfolane or ethylene glycol These solvents are characterized by a high affinity for aromatics good thermal stability and rapid phase separation The Tetra extraction process by Union Carbide Figure 22 uses tetraethylene glycol as a solvent9 The feed reformate which contains a mixture of aromatics paraffins 38 Chemistry of Petrochemical Processes Figure 22 The Union Carbide aromatics extraction process using tetraethyl ene glycol9 Chapter 2 12201 1056 AM Page 38 and naphthenes after heat exchange with hot raffinate is countercurrentIy contacted with an aqueous tetraethylene lycol solution in the extraction column The hot rich solvent containing BTX aromatics is cooled and introduced into the top of a stripper column The aromatics extract is then purified by extractive distillation and recovered from the solvent by steam stripping Extractive distillation has been reviewed by Gentry and Kumar10 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 BTX and ethylbenzene is then fractionated Benzene and toluene are recovered separately and ethyl benzene and xylenes are obtained as a mixture C8 aromatics Due to the narrow range of the boiling points of C8 aromatics Table 24 separation by fractional distillation is difficult 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 crys tallization used to be the method for separating the isomers but the yield was only 60 Currently industry uses continuous liquidphase adsorp tion separation processes11 The overall yield of pxylene is increased Hydrocarbon Intermediates 39 Table 24 Boiling and freezing points of C8 aromatics Boiling Freezing Name Structure point C point C oXylene 1444 252 pXylene 1384 133 mXylene 1391 468 Ethylbenzene 1362 949 Chapter 2 12201 1056 AM Page 39 by incorporating an isomerization unit to isomerize o and mxylenes to pxylene An overall yield of 90 pxylene could be achieved Figure 23 is a flow diagram of the Mobil isomerization process In this process partial conversion of ethylbenzene to benzene also occurs The catalyst used is shape selective and contains ZSM5 zeolite12 Benzene Benzene C6H6 is the simplest aromatic hydrocarbon and by far the most widely used one Before 1940 the main source of benzene and sub stituted benzene was coal tar Currently it is mainly obtained from cat alytic reforming Other sources are pyrolysis gasolines and coal liquids Benzene has a unique structure due to the presence of six delocalized π electrons that encompass the six carbon atoms of the hexagonal ring 40 Chemistry of Petrochemical Processes Figure 23 Flow diagram of the Mobil xylene isomerization process12 Benzene could be represented by two resonating Kekule structures It may also be represented as a hexagon with a circle in the middle The circle is a symbol of the π cloud encircling the benzene ring The delocalized electrons associated with the benzene ring impart very spe cial properties to aromatic hydrocarbons They have chemical properties of singlebond compounds such as paraffin hydrocarbons and double bond compounds such as olefins as well as many properties of their own Chapter 2 12201 1056 AM Page 40 Aromatic hydrocarbons like paraffin hydrocarbons react by substitu tion but by a different reaction mechanism and under milder conditions Aromatic compounds react by addition only under severe 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 Hydrocarbon Intermediates 41 give cyclohexane Monosubstitution can occur at any one of the six equivalent carbons of the ring Most of the monosubstituted benzenes have common names such as toluene methylbenzene phenol hydroxybenzene 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 location of the substituents in 12 13 or 14positions For example there are three xylene isomers Benzene is an important chemical intermediate and is the precursor for many commercial chemicals and polymers such as phenol styrene for poly Chapter 2 12201 1057 AM Page 41 styrenics and caprolactom for nylon 6 Chapter 10 discusses chemicals based on benzene The US production of benzene was approximately 15 billion pounds in 1994 Ethylbenzene Ethylbenzene C6H5CH2CH3 is one of the C8 aromatic constituents in reformates and pyrolysis gasolines It can be obtained by intensive frac tionation of the aromatic extract but only a small quantity of the demanded ethylbenzene is produced by this route Most ethylbenzene is obtained by the alkylation of benzene with ethylene Chapter 10 dis cusses conditions for producing ethylbenzene with benzene chemicals The US production of ethylbenzene was approximately 127 billion pounds in 1997 Essentially all of it was directed for the production of styrene Methylbenzenes Toluene and Xylenes Methylbenzenes occur in small quantities in naphtha and higher boil ing 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 xylenes are reformates from catalytic reforming units gasoline from catcracking and pyrolysis gasoline from steam reforming of naphtha and gas oils As mentioned earlier solvent extraction is used to separate these aromatics from the reformate mixture Only a small amount of the total toluene and xylenes available from these sources is separated and used to produce petrochemicals Toluene and xylenes have chemical characteristics similar to benzene but these characteristics 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 benzene Currently the largest single use of toluene is to convert it to benzene paraXylene is mainly used to produce terephthalic acid for polyesters oXylene is mainly used to produce phthalic anhydride for plasticizers In 1997 the US produced approximately 78 billion pounds of p xylene and only one billion pounds of oxylene5 LIQUID PETROLEUM FRACTIONS AND RESIDUES Liquid Petroleum fractions are light naphtha heavy naphtha kerosine and gas oil The bottom product from distillation units is the residue These 42 Chemistry of Petrochemical Processes Chapter 2 12201 1057 AM Page 42 mixtures are intermediates through which other reactive intermediates are obtained Heavy naphtha is a source of aromatics via catalytic reforming and of olefins from steam cracking units Gas oils and residues are sources of olefins through cracking and pyrolysis processes The composition and the properties of these mixtures are reviewed in the following sections Naphtha Naphtha is a generic term normally used in the petroleum refining industry for the overhead liquid fraction obtained from atmospheric dis tillation units The approximate boiling range of light straightrun naph tha LSR is 3590C while it is about 80200C for heavy straightrun naphtha HSR Naphtha is also obtained from other refinery processing units such as cat alytic cracking hydrocracking and coking units The composition of naph tha which varies appreciably depends mainly on the crude type and whether it is obtained from atmospheric distillation or other processing units Naphtha from atmospheric distillation is characterized by an absence of olefinic compounds Its main constituents are straight and branched chain paraffins cycloparaffins naphthenes and aromatics and the ratios of these components are mainly a function of the crude origin Naphthas obtained from cracking units generally contain variable amounts of olefins higher ratios of aromatics and branched paraffins Due to presence of unsaturated compounds they are less stable than straightrun naphthas On the other hand the absence of olefins 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 paraffinicbase naphtha is a better feedstock for steam cracking units because paraffins are cracked at relatively lower tempera tures than cycloparaffins Alternately a naphtha rich in cycloparaffins would be a better feedstock to catalytic reforming units because cyclo paraffins are easily dehydrogenated to aromatic compounds Table 25 is a typical analysis of naphtha from two crude oil types The main use of naphtha in the petroleum industry is in gasoline pro duction Light naphtha is normally blended with reformed gasoline from catalytic reforming units to increase its volatility and to reduce the aro matic content of the product gasoline Heavy naphtha from atmospheric distillation units or hydrocracking Hydrocarbon Intermediates 43 Chapter 2 12201 1057 AM Page 43 units has a low octane rating 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 aromatics and branched paraffins 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 low octane rating produces a strong knock while a fuel with a high octane rating burns smoothly without detonation Octane rating is measured by an arbitrary scale in which isooctane 224trimethylpentane is given a value of 100 and n heptane a value of zero A fuels octane number equals the percentage of isooctane in a blend with nheptane13 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 constituents present In general aromatics and branched paraffins have higher octane ratings than straightchain paraffins and cycloparaffins Table 26 shows the octane rating of different hydrocarbons in the gasoline range Chapter 3 discusses the reforming process Reformates are the main source for extracting C6C8 aromatics used for petrochemicals Chapter 10 discusses aromaticsbased chemicals Naphtha is also a major feedstock to steam cracking units for the pro duction of olefins This route to olefins 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 Naphtha could also serve as a feedstock for steam reforming units for 44 Chemistry of Petrochemical Processes Table 25 Typical analyses of two straightrun naphtha fractions from two crude types Marine Balayem Bakr9 Test Egypt Egypt Boiling range C 58170 71182 Specific gravity 6060F 07485 07350 API 5755 Sulfur content wt 0055 026 Hydrocarbon types vol Paraffins 627 802 Naphthenes 291 110 Aromatics 82 88 Chapter 2 12201 1057 AM Page 44 the production of synthesis gas for methanol Chapter 4 KEROSINE Kerosine a distillate fraction heavier than naphtha is normally a product from distilling crude oils under atmospheric pressures It may also be obtained as a product from thermal and catalytic cracking or hydrocracking units Kerosines from cracking units are usually less sta ble than those produced from atmospheric distillation and hydrocracking units due to presence of variable amounts of olefinic constituents Kerosine is usually a clear colorless liquid which does not stop flow ing except at very low temperature normally below 30C However kerosine containing high olefin and nitrogen contents may develop some color pale yellow after being produced The main constituents of kerosines obtained from atmospheric and Hydrocarbon Intermediates 45 Table 26 Boiling points and octane ratings of different hydrocarbons in the gasoline range Octane number clear Boiling Research Motor Hydrocarbon point F method F1 method F2 nButane 05 nPentane 97 617 619 2Methylbutane 82 923 903 22Dimethylbutane 122 918 934 23 Dimethylbutane 137 1035 943 nHexane 156 248 260 2Methylpentane 146 734 735 3Methylpentane 140 745 743 nHeptane 208 00 00 2Methylhexane 194 424 464 nOctane 258 190 150 224Trimethyl pentane isooctane 211 1000 1000 Benzene 176 1148 Toluene 231 1201 1035 Ethylbenzene 278 1074 979 Isopropylbenzene 306 oXylene 292 1200 1030 mXylene 283 1450 1240 pXylene 281 1460 1270 Blending value of 20 in 60 octane number reference fuel Chapter 2 12201 1057 AM Page 45 hydrocracking units are paraffins cycloparaffins and aromatics Kero sines with a high normalparaffin content are suitable feedstocks for extracting C12C14 nparaffins which are used for producing biodegrad able detergents Chapter 6 Currently kerosine is mainly used to pro duce jet fuels after it is treated to adjust its burning quality and freezing point Before the widespread use of electricity kerosine 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 Gas Oil Gas oil is a heavier petroleum fraction than kerosine 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 Atmospheric gas oil has a relatively lower density and sulfur content than vacuum gas oil produced 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 aromatic content is approximately 10 for light gas oil and may reach up to 50 for vacuum and cracked gas oil Table 27 is a typical analysis of atmos pheric and vacuum gas oils14 A major use of gas oil is as a fuel for diesel engines Another impor tant use is as a feedstock to cracking and hydrocracking units Gases pro duced from these units are suitable sources for light olefins and LPG Liquefied petroleum gas LPG may be used as a fuel as a feedstock to 46 Chemistry of Petrochemical Processes Table 27 Characteristics of typical atmospheric gas oil AGO and vacuum gas oil VGO14 Gas oil Atmospheric Vacuum Properties AGO VGO Specific gravity API 386 300 Specific gravity 1515C 0832 0876 Boiling range C 232327 299538 Hydrogen wt 137 130 Aromatics wt 240 280 Chapter 2 12201 1057 AM Page 46 steam cracking units for olefin production or as a feedstock for a Cyclar unit for the production of aromatics Residual Fuel Oil Residual fuel oil is generally known as the bottom product from atmospheric distillation units 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 Residues containing high levels of heavy metals are not suitable for cat alytic 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 an oil with a low metal and asphaltene content and asphalt with high metal con tent Demetallized oils could be processed by direct hydrocatalysis15 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 cat alytic activity of these metals in promoting coke and gas formation Metal passivation is especially important in fluid catalytic cracking FCC processes Additives that improve FCC processes were found to increase catalyst life and improve the yield and quality of products16 Residual fuels with high heavy metal content can serve as feedstocks for thermal 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 olefins and LPG for petrochemical production Residual fuel oils are also feedstocks for steam cracking units for the production of olefins REFERENCES Hydrocarbon Intermediates 47 Chapter 2 12201 1057 AM Page 47 1 Chemical Industries Newsletter OctoberDecember 1998 pp 910 2 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 142 3 Yepsen G and Witoshkin T Refiners Have Options to Deal with Reformulated Gasoline Oil and Gas Journal April 8 1991 pp 6871 4 DiCintio R et al Separate Ethylene Efficiently Hydrocarbon Processing Vol 70 No 7 1991 pp 8386 5 Chemical and Engineering News June 29 1998 pp 4347 6 Hatch L F and Matar S Chemicals from C4 Hydrocarbon Processing Vol 57 No 8 1978 pp 153165 7 Chemical Week Nov 16 1977 p 49 8 Fessenden R J and Fessenden J S Organic Chemistry 4th Ed BrooksCole Publishing Co Pacific Grove California 1991 p 70 9 Petrochemical Handbook Hydrocarbon Processing Vol 61 No 11 1982 p 195 10 Gentry J C and Kumar C S Improve BTX Processing Economics Hydrocarbon Processing Vol 77 No 3 1998 pp 6982 11 Biesser H J and Winter G R Oil and Gas Journal Aug 11 1975 pp 7475 12 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 pp 166 13 Matar S Synfuels Hydrocarbons of the Future PennWell Publishing Co Tulsa Okla 1982 p 10 14 Barwell J and Martin S R International Seminar on Petrochemical Industries No 9 P2 Iraq Oct 2530 1975 15 Oil and Gas Journal March 20 1978 p 94 16 Krishna A S et al Additives Improve FCC Process Hydrocarbon Processing Vol 70 No 11 1991 pp 5966 48 Chemistry of Petrochemical Processes Chapter 2 12201 1057 AM Page 48 CHAPTER THREE Crude Oil Processing and Production of Hydrocarbon Intermediates INTRODUCTION The hydrocarbon intermediates referred to in the previous chapter are produced by subjecting crude oils to various processing schemes These include a primary distillation step to separate the crude oil complex mix ture into simpler fractions These fractions are primarily used as fuels However a small percentage of these streams are used as secondary raw materials or intermediates for obtaining olefins diolefins and aromatics for petrochemicals production Further processing of these fractions may be required to change their chemical composition to the required prod ucts These new products may also be used as fuels of improved qualities or as chemical feedstocks For example reforming a naphtha fraction catalytically produces a reformate rich in aromatics The major use of the reformate is to supplement the gasoline pool due to its high octane rating However the reformate is also used to extract the aromatics for petrochemicals use At this point the production of intermediates for petrochemicals is not separable from the production of fuels In this chapter the production of hydrocarbon intermediates is discussed in con junction with different crude oil processing schemes These include physical separation techniques and chemical conversion processes The production of olefins is also discussed in the last section PHYSICAL SEPARATION PROCESSES Physical separation techniques separate a mixture such as a crude oil without changing the chemical characteristics of the components The 49 Chapter 3 12201 1058 AM Page 49 separation is based on differences of certain physical properties of the constituents such as the boiling and melting points adsorption affinities on a certain solid and diffusion through certain membranes The important physical separation processes discussed here are dis tillation absorption adsorption and solvent extraction ATMOSPHERIC DISTILLATION Atmospheric distillation separates the crude oil complex mixture into different fractions with relatively narrow boiling ranges In general sep aration of a mixture into fractions is based primarily on the difference in the boiling points of the components In atmospheric distillation units one or more fractionating columns are used Distilling a crude oil starts by preheating the feed by exchange with the hot product streams The feed is further heated to about 320C as it passes through the heater pipe pipe still heater The hot feed enters the fractionator which normally contains 3050 fractionation trays Steam is introduced at the bottom of the fractionator to strip off light components The efficiency of separation is a function of the number of theoretical plates of the fractionating tower and the reflux ratio Reflux is provided by condensing part of the tower overhead vapors Reflux ratio is the ratio of vapors condensing back to the still to vapors condensing out of the still distillate The higher the reflux ratio the better the separation of the mixture Products are withdrawn from the distillation tower as side streams while the reflux is provided by returning a portion of the cooled vapors from the tower overhead condenser Additional reflux could be obtained by returning part of the cold side stream products to the tower In prac tice the reflux ratio varies over a wide range according to the specific separations desired From the overhead condenser the uncondensed gases are separated and the condensed light naphtha liquid is withdrawn to storage Heavy naphtha kerosine and gas oil are withdrawn as side stream products Table 31 shows the approximate boiling ranges for crude oil fractions The residue topped crude is removed from the bot tom of the distillation tower and may be used as a fuel oil It may also be charged to a vacuum distillation unit a catalytic cracking or steam crack ing process Figure 31 is a flow diagram for atmospheric and vacuum distillation units1 50 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 50 VACUUM DISTILLATION Vacuum distillation increases the amount of the middle distillates and produces lubricating oil base stocks and asphalt The feed to the unit is the residue from atmospheric distillation In vacuum distillation reduced pressures are applied to avoid cracking longchain hydrocarbons present in the feed The feed is first preheated by exchange with the products charged to the vacuum unit heater and then passed to the vacuum tower in an atmos phere of superheated steam Using superheated steam is important it Crude Oil Processing and Production of Hydrocarbon Intermediates 51 Table 31 Approximate ASTM boiling point ranges for crude oil fractions Boiling range Fractions F C Light naphtha 85210 3099 Heavy naphtha 190400 88204 Kerosine 340520 171271 Atmospheric gas oil 540820 288438 Vacuum gas oil 7501050 399566 Vacuum residue 1000 538 Figure 31 Flow diagram of atmospheric and vacuum distillation units1 13 heat exchangers 2 desalter 34 heater 5 distillation column 6 overhead condenser 710 pump around streams 11 vacuum distillation heater 12 vacuum tower Chapter 3 12201 1058 AM Page 51 decreases the partial pressure of the hydrocarbons and reduces coke formation in the furnace tubes Distillation normally occurs at a tem perature range of 400440C and an absolute pressure of 2540 mmHg The top tower temperature is adjusted by refluxing part of the gas oil product top product The size diameter of the vacuum dis tillation tower is much larger than atmospheric towers because the volume of the vaporunitvolume of the feed is much larger than in atmospheric distillation2 Products obtained as side streams are vacuum gas oil VGO lube oil base stocks and asphalt Asphalt may be used for paving roads or may be charged to a delayed coking unit ABSORPTION PROCESS This process selectively removes a certain gas from a gas mixture using a liquid absorbent In the refining industry this process is used extensively to free the product gas streams from acid gases mainly H2S either by using a physical or a chemical absorbent Absorption of acid gases from natural gas are discussed in Chapter 1 ADSORPTION PROCESS Adsorption processes use a solid material adsorbent possessing a large surface area and the ability to selectively adsorb a gas or a liquid on its surface Examples of adsorbents are silica SiO2 anhydrous alumina Al2O3 and molecular sieves crystalline silicaalumina Adsorption processes may be used to remove acid gases from natural gas and gas streams For example molecular sieves are used to dehydrate natural gas and to reduce its acid gases Adsorption processes are also used to separate liquid mixtures For example molecular sieve 5A selectively adsorbs nparaffins from a low octane naphtha fraction Branched paraffins and aromatics in the mixture are not adsorbed on the solid surface The collected fraction containing mainly aromatics and branched paraffins have a higher octane number than the feed Desorbing nparaffins is effected by displacement with another solvent or by using heat The recovered nparaffins in this range are good steam cracking feedstocks for olefin production Adsorption of nparaffins C10C14 from a kerosine or a gas oil frac tion can be achieved in a liquid or a vapor phase adsorption process 52 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 52 Normal paraffins in this range are important intermediates for alkylating benzene for synthetic detergents production Chapter 10 They are also good feedstocks for singlecell protein SCP The IsoSiv process is an isobaric isothermal adsorption technique used to separate nparaffins from gas oils The operation conditions are approximately 370C and 100 psi3 Desorption is achieved using n pentane or nhexane The solvent is easily distilled from the heavier nparaffins and then recycled SOLVENT EXTRACTION Liquid solvents are used to extract either desirable or undesirable com pounds from a liquid mixture Solvent extraction processes use a liquid solvent that has a high solvolytic power for certain compounds in the feed mixture For example ethylene glycol has a greater affinity for aro matic hydrocarbons and extracts them preferentially from a reformate mixture a liquid paraffinic and aromatic product from catalytic reform ing The raffinate which is mainly paraffins is freed from traces of eth ylene glycol by distillation Other solvents that could be used for this purpose are liquid sulfur dioxide and sulfolane tetramethylene sulfone The sulfolane process is a versatile extractant for producing high purity BTX aromatics benzene toluene and xylenes It also extracts aromatics from kerosines to produce lowaromatic jet fuels On the other hand liquid propane also has a high affinity for paraffinic hydrocarbons Propane deasphalting removes asphaltic materials from heavy lube oil base stocks These materials reduce the viscosity index of lube oils In this process liquid propane dissolves mainly paraffinic hydrocarbons and leaves out asphaltic materials Higher extraction tem peratures favor better separation of the asphaltic components Deas phalted oil is stripped to recover propane which is recycled Solvent extraction may also be used to reduce asphaltenes and metals from heavy fractions and residues before using them in catalytic crack ing The organic solvent separates the resids into demetallized oil with lower metal and asphaltene content than the feed and asphalt with high metal content Figure 32 shows the IFP deasphalting process and Table 32 shows the analysis of feed before and after solvent treatment4 Solvent extraction is used extensively in the petroleum refining indus try Each process uses its selective solvent but the basic principle is the same as above Crude Oil Processing and Production of Hydrocarbon Intermediates 53 Chapter 3 12201 1058 AM Page 53 CONVERSION PROCESSES Conversion processes in the petroleum industry are generally used to 1 Upgrade lowervalue materials such as heavy residues to more valuable products such as naphtha and LPG Naphtha is mainly used to supplement the gasoline pool while LPG is used as a fuel or as a petrochemical feedstock 54 Chemistry of Petrochemical Processes Figure 32 The IFP deasphalting process4 12 extractor 36 solvent recovery towers Table 32 Typical analysis of light Arabian vacuum resid before and after solvent treatment using once C4 and another C5 hydrocarbon solvent4 Feed DAO Solvent C4 C5 Yield wt 701 855 Sp gr 1003 0959 0974 Visc cSt 210F 345 63 105 Conradson carbon wt 164 53 79 Asphaltenes C7 insol wt 420 005 005 Ni ppm 19 20 70 V ppm 61 26 155 S wt 405 33 365 N2 ppm 2875 1950 2170 Chapter 3 12201 1058 AM Page 54 2 Improve the characteristics of a fuel For example a lower octane naphtha fraction is reformed to a higher octane reformate product The reformate is mainly blended with naphtha for gasoline formu lation or extracted for obtaining aromatics needed for petrochemi cals production 3 Reduce harmful impurities in petroleum fractions and residues to control pollution and to avoid poisoning certain processing cata lysts For example hydrotreatment of naphtha feeds to catalytic reformers is essential because sulfur and nitrogen impurities poison the catalyst Conversion processes are either thermal where only heat is used to effect the required change or catalytic where a catalyst lowers the reac tion activation energy The catalyst also directs the reaction toward a desired product or products selective catalyst THERMAL CONVERSION PROCESSES Thermal cracking was the first process used to increase gasoline pro duction After the development of catalytic cracking which improved yields and product quality thermal cracking was given other roles in refinery operations The three important thermal cracking techniques are coking viscosity breaking and steam cracking Steam cracking is of special importance as a major process designed specifically for producing light olefins It is discussed separately later in this chapter Coking Processes Coking is a severe thermal cracking process designed to handle heavy residues with high asphaltene and metal contents These residues cannot be fed to catalytic cracking units because their impurities deactivate and poison the catalysts Products from coking processes vary considerably with feed type and process conditions These products are hydrocarbon gases cracked naph tha middle distillates and coke The gas and liquid products are charac terized by a high percentage of unsaturation Hydrotreatment is usually required to saturate olefinic compounds and to desulfurize products from coking units Crude Oil Processing and Production of Hydrocarbon Intermediates 55 Chapter 3 12201 1058 AM Page 55 Thermal Cracking Reactions The first step in cracking is the thermal decomposition of hydrocarbon molecules to two free radical fragments This initiation step can occur by a homolytic carboncarbon bond scission at any position along the hydro carbon chain The following represents the initiation reaction RCH2CH2CH2Rv r RCH2CH2 RvCH2 The radicals may further crack yielding an olefin and a new free rad ical Cracking usually occurs at a bond beta to the carbon carrying the unpaired electron RCH2CH2 r R CH2CH2 Further β bond scission of the new free radical R can continue to pro duce ethylene until the radical is terminated Free radicals may also react with a hydrocarbon molecule from the feed by abstracting a hydrogen atom In this case the attacking radical is terminated and a new free radical is formed Abstraction of a hydrogen atom can occur at any position along the chain However the rate of hydrogen abstraction is faster from a tertiary position than from a sec ondary which is faster than from a primary position R RCH2CH2CH2Rv r RCH2CHCH2Rv RH The secondary free radical can crack on either side of the carbon car rying the unpaired electron according to the beta scission rule and a ter minal olefin is produced 56 Chemistry of Petrochemical Processes Free radicals unlike carbocations do not normally undergo isomeriza tion by methyl or hydrogen migration However hydrogen transfer chain transfer occurs when a free radical reacts with other hydrocarbons There are two major commercial thermal cracking processes delayed coking and fluid coking Flexicoking is a fluid coking process in which the coke is gasified with air and steam The resulting gas mixture par tially provides process heat Chapter 3 12201 1058 AM Page 56 Delayed Coking In delayed coking the reactor system consists of a short contacttime heater coupled to a large drum in which the preheated feed soaks on a batch basis Coke gradually forms in the drum A delayed coking unit has at least a pair of drums When the coke reaches a predetermined level in one drum flow is diverted to the other so that the process is continuous Vapors from the top of the drum are directed to the fractionator where they are separated into gases naphtha kerosine and gas oil Table 33 shows products from a delayed coker using different feeds5 Decoking the filled drum can be accomplished by a hydraulic system using several water jets under at least 3000 pounds per square inch gauge Operating conditions for delayed coking are 2530 psi at 480500C with a recycle ratio of about 025 based on equivalent feed Improved liquid yields could be obtained by operating at lower pressures Coking at approximately 15 psi with ultra low recycle produced about 10 more gas oil6 Operating at toolow temperature produces soft spongy coke On the other hand operating at a higher temperature produces more coke and gas but less liquid products Mochida et al reviewed the chemistry and different options for the production of delayed coke7 It is the chem istry of the pyrolysis system which controls the properties of the semi Crude Oil Processing and Production of Hydrocarbon Intermediates 57 Table 33 Feeds and products from a delayed coker unit using different feeds5 Operating conditions Heater outlet temperature F 900950 Coke drum pressure psig 1590 Recycle ratio volvol feed 10100 Yields Vacuum residue Middle East of hydrotreated Coal tar Feedstock vac residue bottoms pitch Gravity ºAPI 74 13 110 Sulfur wt 42 23 05 Conradson carbon wt 200 276 Products wt Gas LPG 79 90 39 Naphtha 126 111 Gas oil 508 440 310 Coke 287 359 651 Chapter 3 12201 1058 AM Page 57 and final coke structure Factors that govern the reactions are the coke drum size the heating rate the soak time the pressure and the final reac tion temperature8 However if everything is equal temperature pres sure soak time etc the quality of coke produced by delayed coking is primarily a function of the feed quality Figure 33 shows a delayed cok ing unit5 Coke produced from delayed coking is described as delayed sponge shot or needle coke depending on its physical structure Shot coke is the most common when running the unit under severe conditions with sour crude residues Needle coke is produced from selected aromatic feed stocks Sponge coke is more porous and has a high surface area The properties and markets for petroleum cokes have been reviewed by Dymond9 Table 34 shows the types of petroleum cokes and their uses9 Fluid Coking In the fluid coking process part of the coke produced is used to pro vide the process heat Cracking reactions occur inside the heater and the fluidizedbed reactor The fluid coke is partially formed in the heater Hot coke slurry from the heater is recycled to the fluid reactor to provide the heat required for the cracking reactions Fluid coke is formed by spray ing the hot feed on the alreadyformed coke particles Reactor tempera ture is about 520C and the conversion into coke is immediate with 58 Chemistry of Petrochemical Processes Figure 33 Flow diagram of a delayed coking unit5 1 coker fractionator 2 coker heater 3 coke drum 4 vapor recovery column Chapter 3 12201 1058 AM Page 58 complete disorientation of the crystallites of product coke The burning process in fluid coking tends to concentrate the metals but it does not reduce the sulfur content of the coke Fluid coking has several characteristics that make it undesirable for most petroleum coke markets These characteristics are high sulfur con tent low volatility poor crystalline structure and low grindability index10 Flexicoking on the other hand integrates fluid coking with coke gasi fication Most of the coke is gasified Flexicoking gasification produces a substantial concentration of the metals in the coke product Figure 34 shows an Exxon flexicoking process5 Viscosity Breaking Visbreaking Viscosity breaking aims to thermally crack longchain feed molecules to shorter ones thus reducing the viscosity and the pour point of the product In this process the feed is usually a high viscosity high pour point fuel oil that cannot be used or transported especially in cold climates due to the presence of waxy materials Wax is a complex mixture of longchain paraffins mixed with aromatic compounds having long paraffinic side chains Visbreaking is a mild cracking process that operates at approxi mately 450C using short residence times Long paraffinic chains break to Crude Oil Processing and Production of Hydrocarbon Intermediates 59 Table 34 Types of petroleum cokes and their end uses9 Application Type coke State End use Carbon source Needle Calcined Electrodes Synthetic graphite Sponge Calcined Aluminum anodes TiO2 pigments Carbon raiser Sponge Green Silicon carbide Foundries Coke ovens Fuel use Sponge Green lump EuropeJapan space heating Sponge Green Industrial boilers Shot Green Utilities Fluid Green Cogeneration Flexicoke Green Lime Cement Chapter 3 12201 1058 AM Page 59 shorter ones and dealkylation of the aromatic side chains occurs Table 35 shows the analysis of feed and products from a visbreaking unit11 CATALYTIC CONVERSION PROCESSES Catalytic conversion processes include naphtha catalytic reforming cat alytic cracking hydrocracking hydrodealkylation isomerization alkyla tion and polymerization In these processes one or more catalyst is used A common factor among these processes is that most of the reactions are initiated by an acidtype catalyst that promotes carbonium ion formation Other important catalytic processes are those directed toward improv ing the product quality through hydrotreatment These processes use heterogeneous hydrogenation catalysts Catalytic Reforming The aim of this process is to improve the octane number of a naphtha feedstock by changing its chemical composition Hydrocarbon com pounds differ greatly in their octane ratings due to differences in struc ture In general aromatics have higher octane ratings than paraffins and cycloparaffins Similar to aromatics branched paraffins have high octane ratings The octane number of a hydrocarbon mixture is a function of the octane numbers of the different components and their ratio in the mix ture See octane ratings of different hydrocarbons in Chapter 2 60 Chemistry of Petrochemical Processes Figure 34 Flow diagram of an Exxon flexicoking unit5 1 reactor 2 scrubber 3 heater 4 gasifier 5 coke fines removal 6 H2S removal Chapter 3 12201 1058 AM Page 60 Increasing the octane number of a lowoctane naphtha fraction is achieved by changing the molecular structure of the low octane number components Many reactions are responsible for this change such as the dehydrogenation of naphthenes and the dehydrocyclization of paraffins to aromatics Catalytic reforming is considered the key process for obtaining benzene toluene and xylenes BTX These aromatics are important intermediates for the production of many chemicals12 Reformer Feeds The feed to a catalytic reformer is normally a heavy naphtha fraction produced from atmospheric distillation units Naphtha from other sources such as those produced from cracking and delayed coking may also be used Before using naphtha as feed for a catalytic reforming unit it must be hydrotreated to saturate the olefins and to hydrodesulfurize Crude Oil Processing and Production of Hydrocarbon Intermediates 61 Table 35 Analysis of feed and products from viscosity breaking11 Charge inspections Libyan residue Gravity API 244 Vacuum Engler corrected F IBP 510 5 583 10 608 20 650 Pour point max F 75 Visc SUS 122F 1758 Product yield vol Gasoline 100 C4 330 EP 108 Furnace oil 805F EP 427 Fuel oil 463 Gas C3 Lighter wt 21 Properties of products Furnace oil Pour point max F 5 Flash PMCO F 150 Fuel oil Pour point max F 40 Flash PMCC F 150 Visc SFS 122F 675 Stability ASTM D1661 No 1 Chapter 3 12201 1058 AM Page 61 and hydrodenitrogenate sulfur and nitrogen compounds Olefinic com pounds are undesirable because they are precursors for coke which deac tivates the catalyst Sulfur and nitrogen compounds poison the reforming catalyst The reducing atmosphere in catalytic reforming promotes form ing of hydrogen sulfide and ammonia Ammonia reduces the acid sites of the catalyst while platinum becomes sulfided with H2S Types of hydrocarbons in the feed have significant effects on the oper ation severity Feeds with a high naphthene content are easier to aroma tize than feeds with a high ratio of paraffins see Reforming reactions The boiling range of the feeds is also an effective parameter Feeds with higher end points 200C are favorable because some of the longchain molecules are hydrocracked to molecules in the gasoline range These molecules can isomerize and dehydrocyclize to branched paraffins and to aromatics respectively Reforming Catalysts The catalysts generally used in catalytic reforming are dual functional to provide two types of catalytic sites hydrogenationdehydrogenation sites and acid sites The former sites are provided by platinum which is the best known hydrogenationdehydrogenation catalyst and the latter acid sites promote carbonium ion formation and are provided by an alu mina carrier The two types of sites are necessary for aromatization and isomerization reactions Bimetallic catalysts such as PtRe were found to have better stability increased catalyst activity and selectivity Trimetallic catalysts of noble metal alloys are also used for the same purpose The increased stability of these catalysts allowed operation at lower pressures A review of reforming catalysts by AlKabbani manifests the effect of the ratio of the metallic components of the catalyst A ratio of 05 or less for PtRe in the new generation catalysts versus 10 for the older ones can tolerate much higher coke levels Reforming units can perform similarly with higher coke levels 2025 versus 1520 These catalysts can tolerate higher sulfer naphtha feeds 1 ppm Higher profitability may be realized by increasing the cycle length13 Reforming Reactions Many reactions occur in the reactor under reforming conditions These are aromatization reactions which produce aromatics isomeriza tion reactions which produce branched paraffins and other reactions 62 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 62 which are not directly involved in aromatics formation hydrocracking and hydrodealkylation Aromatization The two reactions directly responsible for enriching naphtha with aromatics are the dehydrogenation of naphthenes and the dehydrocyclization of paraffins The first reaction can be represented by the dehydrogenation of cyclohexane to benzene Crude Oil Processing and Production of Hydrocarbon Intermediates 63 This reaction is fast it reaches equilibrium quickly The reaction is also reversible highly endothermic and the equilibrium constant is quite large 6 l05 500C It is evident that the yield of aromatics benzene is favored at higher temperatures and lower pressures The effect of decreasing H2 partial pressure is even more pronounced in shifting the equilibrium to the right The second aromatization reaction is the dehydrocyclization of paraf fins to aromatics For example if nhexane represents this reaction the first step would be to dehydrogenate the hexane molecule over the plat inum surface giving 1hexene 2 or 3hexenes are also possible isomers but cyclization to a cyclohexane ring may occur through a different mechanism Cyclohexane then dehydrogenates to benzene H 266 KJmol Kp 78 104 500C This is also an endothermic reaction and the equilibrium production of aromatics is favored at higher temperatures and lower pressures However the relative rate of this reaction is much lower than the dehy drogenation of cyclohexanes Table 36 shows the effect of temperature on the selectivity to benzene when reforming nhexane using a plat inum catalyst14 Chapter 3 12201 1058 AM Page 63 More often than what has been mentioned above regarding the cyclization of paraffins over the platinum catalyst the formed olefin species reacts with the acid catalyst forming a carbocation Carbocation formation may occur by abstraction of a hydride ion from any position along the hydrocarbon chain However if the carbocation intermediate has the right configuration cyclization occurs For example cyclization of 1heptene over the alumina catalyst can occur by the following suc cessive steps 64 Chemistry of Petrochemical Processes Table 36 Selectivity to benzene from reforming nhexane over a platinum catalyst14 Selectivity Selectivity to to LHSV TempF Conversion Benzene Isohexane 2 885 802 166 580 2 932 868 241 369 2 977 904 274 234 The formed methylcyclohexane carbocation eliminates a proton yielding 3methylcyclohexene 3Methylcyclohexene can either dehy drogenate over the platinum surface or form a new carbocation by losing H over the acid catalyst surface This step is fast because an allylic car bonium ion is formed Losing a proton on a Lewis base site produces methyl cyclohexadiene This sequence of carbocation formation fol lowed by loss of a proton continues till the final formation of toluene Chapter 3 12201 1058 AM Page 64 It should be noted that both reactions leading to aromatics dehydro genation of naphthenes and dehydrocyclization of paraffins produce hydrogen and are favored at lower hydrogen partial pressure Isomerization Reactions leading to skeletal rearrangement of paraf fins and cycloparaffins in a catalytic reactor are also important in raising the octane number of the reformate product Isomerization reactions may occur on the platinum catalyst surface or on the acid catalyst sites In the former case the reaction is slow Most isomerization reactions however occur through formation of a carbocation The formed carbocation could rearrange through a hydridemethide shift that would lead to branched isomers The following example illustrates the steps for the isomerization of nheptane to 2methylhexane through 12methidehydride shifts Carbocation Formation Crude Oil Processing and Production of Hydrocarbon Intermediates 65 Chapter 3 12201 1058 AM Page 65 Isomerization of alkylcyclopentanes may also occur on the platinum catalyst surface or on the silicaalumina For example methylcyclopen tane isomerizes to cyclohexane 66 Chemistry of Petrochemical Processes The formed cyclohexane can dehydrogenate to benzene Hydrocracking Hydrocracking is a hydrogenconsuming reaction that leads to higher gas production and lower liquid yield This reaction is favored at high temperatures and high hydrogen partial pressure The following represents a hydrocracking reaction RCH2CH2CH2Rv H2 r RCH2CH3 RvCH3 Bond breaking can occur at any position along the hydrocarbon chain Because the aromatization reactions mentioned earlier produce hydrogen and are favored at high temperatures some hydrocracking occurs also under these conditions However hydrocracking longchain molecules can produce C6 C7 and C8 hydrocarbons that are suitable for hydrode cyclization to aromatics For more aromatics yield the end point of the feed may be raised to include higher molecular weight hydrocarbons in favor of hydrocracking and dehydrocyclization However excessive hydrocracking is not desir able because it lowers liquid yields Hydrodealkylation Hydrodealkylation is a cracking reaction of an aromatic side chain in presence of hydrogen Like hydrocracking the Chapter 3 12201 1058 AM Page 66 reaction consumes hydrogen and is favored at a higher hydrogen partial pressure This reaction is particularly important for increasing benzene yield when methylbenzenes and ethylbenzene are dealkylated Although the overall reaction is slightly exothermic the cracking step is favored at higher temperatures Hydrodealkylation may be represented by the reac tion of toluene and hydrogen Crude Oil Processing and Production of Hydrocarbon Intermediates 67 As in hydrocracking this reaction increases the gas yield and changes the relative equilibrium distribution of the aromatics in favor of benzene Table 37 shows the properties of feed and products from Chevron Rheiniforming process15 Table 37 Properties of feed and products from Chevron Rheiniforming process15 Yields Typical yields for severe reforming Naphtha Feed Hydrotreated Hydrocracked Feed type Paraffinic Naphthenic Boiling range F 200330 200390 Paraffins LV 686 326 Naphthenes LV 234 555 Aromatics LV 80 119 Sulfur ppm 02 02 Nitrogen ppm 05 05 Reactor outlet press psig 90 200 200 Products Hydrogen scfbbl feed 1510 1205 1400 C1C3 scfbbl feed 160 355 160 C5 reformate Yield LV 801 735 847 Research octane clear 98 99 100 Paraffins LV 324 312 275 Naphthenes LV 11 09 26 Aromatics LV 665 679 699 Chapter 3 12201 1058 AM Page 67 Reforming Process Catalytic reformers are normally designed to have a series of catalyst beds typically three beds The first bed usually contains less catalyst than the other beds This arrangement is important because the dehydro genation of naphthenes to aromatics can reach equilibrium faster than the other reforming reactions Dehydrocyclization is a slower reaction and may only reach equilibrium at the exit of the third reactor Isomerization and hydrocracking reactions are slow They have low equilibrium con stants and may not reach equilibrium before exiting the reactor The second and third reactors contain more catalyst than the first one to enhance the slow reactions and allow more time in favor of a higher yield of aromatics and branched paraffins Because the dehydrogenation of naphthenes and the dehydrocyclization of paraffins are highly endothermic the reactor outlet temperature is lower than the inlet tem perature The effluent from the first and second reactors are reheated to compensate for the heat loss Normally catalytic reformers operate at approximately 500525C and 100300 psig and a liquid hourly space velocity range of 24 hr1 Liquid hourly space velocity LHSV is an important operation parame ter expressed as the volume of hydrocarbon feed per hour per unit vol ume of the catalyst Operating at lower LHSV gives the feed more contact with the catalyst Regeneration of the catalyst may be continuous for certain processes that are designed to permit the removal and replacement of the catalyst during operation In certain other processes an additional reactor is used Swing reactor When the activity of the catalyst is decreased in one of the reactors on stream it is replaced with the standby Swing reactor In many processes regeneration occurs by shutting down the unit and regenerating the catalyst Semiregenerative Figure 35 shows a Chevron Rheiniforming semiregenerative fixed threebed process15 Products from catalytic reformers the reformate is a mixture of aro matics paraffins and cycloparaffins ranging from C6C8 The mixture has a high octane rating due to presence of a high percentage of aromatics and branched paraffins Extraction of the mixture with a suitable solvent produces an aromaticrich extract which is further fractionated to sepa rate the BTX components Extraction and extractive distillation of refor mate have been reviewed by Gentray and Kumar16 68 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 68 Catalytic Cracking Catalytic cracking Catcracking is a remarkably versatile and flexi ble process Its principal aim is to crack lowervalue stocks and produce highervalue light and middle distillates The process also produces light hydrocarbon gases which are important feedstocks for petrochemicals Catalytic cracking produces more gasoline of higher octane than thermal cracking This is due to the effect of the catalyst which promotes iso merization and dehydrocyclization reactions Products from catalytic cracking units are also more stable due to a lower olefin content in the liquid products This reflects a higher hydro gen transfer activity which leads to more saturated hydrocarbons than in thermally cracked products from delayed coking units for example The feeds to catalytic cracking units vary from gas oils to crude residues Heavier feeds contain higher concentrations of basic and polar molecules as well as asphaltenes Examples are basic nitrogen com pounds which are readily adsorbed on the catalyst acid sites and lead to instantaneous albeit temporary deactivation Polycyclic aromatics and asphaltenes contribute strongly to coke formation FCC fluid catalytic cracking catalyst deactivation in resid processing have been reviewed by OConnor et al17 and Occelli18 These feedstocks are often pretreated to decrease the metallic and asphaltene contents Hydrotreatment solvent extraction and propane deasphalting are important treatment processes Crude Oil Processing and Production of Hydrocarbon Intermediates 69 Figure 35 Flow diagram of a Chevron Rheiniforming unit15 1 sulfur sorber 24 reactors 5 separator 6 stabilizer Chapter 3 12201 1058 AM Page 69 Excessive asphaltene and aromatics in the feed are precursors to carbon formation on the catalyst surface which substantially reduces its activity and produces gasolines of lower quality Residium fluid catalytic cracking RFCC has gained wide acceptance due to a larger production of gasoline with only small amounts of low value products Pretreating the feed in a lowseverity residue desulfur ization RDS increased the gasoline yield by 7419 Table 38 compares the effect of RDS pretreatment on product yields from RFCC with and without RDS19 Other resid treatment approaches to passivate heavy metals in catalytic cracking feeds are noted in the following sec tion Cracking Catalysts Cracking Catalysts Acidtreated clays were the first catalysts used in catalytic cracking processes but have been replaced by synthetic amorphous silicaalumina which is more active and stable Incorporating zeolites crystalline alu minasilica with the silicaalumina catalyst improves selectivity towards aromatics These catalysts have both Lewis and Bronsted acid sites that promote carbonium ion formation An important structural feature of zeolites is the presence of holes in the crystal lattice which are formed by the silicaalumina tetrahedra Each tetrahedron is made of four oxy gen anions with either an aluminum or a silicon cation in the center Each oxygen anion with a 2 oxidation state is shared between either two sili con two aluminum or an aluminum and a silicon cation The four oxygen anions in the tetrahedron are balanced by the 4 oxi dation state of the silicon cation while the four oxygen anions connect ing the aluminum cation are not balanced This results in 1 net charge which should be balanced Metal cations such as Na Mg2 or protons H balance the charge of the alumina tetrahedra A twodimensional representation of an Hzeolite tetrahedra is shown 70 Chemistry of Petrochemical Processes Bronsted acid sites in HYzeolites mainly originate from protons that neutralize the alumina tetrahedra When HYzeolite X and Yzeolites Chapter 3 12201 1058 AM Page 70 are cracking catalysts is heated to temperatures in the range of 400500C Lewis acid sites are formed Crude Oil Processing and Production of Hydrocarbon Intermediates 71 Table 38 Effect of RDS pretreatment on product yields from RFCC with and without RDS19 Arabian light Arabian light RDS feed RDS product RFCC feed properties Boiling range C 370 370 API 151 201 CCR wt 89 49 Sulfur wt 330 048 Nitrogen wt 017 013 Nickel vanadium ppm 51 7 RFCC yields H2S wt 17 02 C2 wt 40 40 C3 LV 84 101 C4 LV 124 152 Gasoline C5221C LV 506 580 LCO 221C to 360C LV 214 182 Bottoms 360C LV 97 72 Coke wt 103 70 Catalyst makeup lbbbl 172 023 Catalyst cooler required Yes No A Lewis acid site Zeolites as cracking catalysts are characterized by higher activity and better selectivity toward middle distillates than amorphous silicaalumina catalysts This is attributed to a greater acid sites density and a higher adsorption power for the reactants on the catalyst surface The higher selectivity of zeolites is attributed to its smaller pores which allow diffusion of only smaller molecules through their pores and Chapter 3 12201 1058 AM Page 71 to the higher rate of hydrogen transfer reactions However the silica alumina matrix has the ability to crack larger molecules Hayward and Winkler have recently demonstrated the importance of the interaction of the zeolite with the silicaalumina matrix In a set of experiments using gas oil and rare earth zeolitesilicaalumina the yield of gasoline increased when the matrix was used before the zeolite This was explained by the mechanism of initial matrix cracking of large feedstock molecules to smaller ones and subsequent zeolite cracking of the smaller molecules to products20 Aluminum distribution in zeolites is also important to the catalytic activity An inbalance in charge between the silicon atoms in the zeolite framework creates active sites which determine the predominant reac tivity and selectivity of FCC catalyst Selectivity and octane performance are correlated with unit cell size which in turn can be correlated with the number of aluminum atoms in the zeolite framework21 Deactivation of zeolite catalysts occurs due to coke formation and to poisoning by heavy metals In general there are two types of catalyst deactivation that occur in a FCC system reversible and irreversible Reversible deactivation occurs due to coke deposition This is reversed by burning coke in the regenerator Irreversible deactivation results as a combination of four separate but interrelated mechanisms zeolite dealu mination zeolite decomposition matrix surface collapse and contami nation by metals such as vanadium and sodium22 Pretreating the feedstocks with hydrogen is not always effective in reducing heavy metals and it is expensive Other means that proved suc cessful are modifying the composition and the microporous structure of the catalyst or adding metals like Sb Bi or Sn or SbSn combination23 Antimony organics have been shown to reduce by 50 gas formation due to metal contaminants especially nickel24 Cracking Reactions A major difference between thermal and catalytic cracking is that reac tions through catalytic cracking occur via carbocation intermediate com pared to the free radical intermediate in thermal cracking Carbocations are longer lived and accordingly more selective than free radicals Acid cat alysts such as amorphous silicaalumina and crystalline zeolites promote the formation of carbocations The following illustrates the different ways by which carbocations may be generated in the reactor 72 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 72 1 Abstraction of a hydride ion by a Lewis acid site from a hydrocarbon Crude Oil Processing and Production of Hydrocarbon Intermediates 73 2 Reaction between a Bronsted acid site H and an olefin 3 Reaction of a carbonium ion formed from step 1 or 2 with another hydrocarbon by abstraction of a hydride ion R RCH2CH3 r RH RC HCH3 Abstraction of a hydride ion from a tertiary carbon is easier than from a secondary which is easier than from a primary position The formed car bocation can rearrange through a methidehydride shift similar to what has been explained in catalytic reforming This isomerization reaction is responsible for a high ratio of branched isomers in the products The most important cracking reaction however is the carboncarbon beta bond scission A bond at a position beta to the positivelycharged carbon breaks heterolytically yielding an olefin and another carbocation This can be represented by the following example RCH2C HCH3 r R CH2CHCH3 The new carbocation may experience another beta scission rearrange to a more stable carbonium ion or react with a hydrocarbon molecule in the mixture and produce a paraffin The carboncarbon beta scission may occur on either side of the car bocation with the smallest fragment usually containing at least three carbon atoms For example cracking a secondary carbocation formed from a long chain paraffin could be represented as follows Lewis Acid Site Chapter 3 12201 1058 AM Page 73 If R H in the above example then according to the beta scission rule an empirical rule only route b becomes possible and propylene would be a product CH3C HCH2CH2Rv r RvC H2 CH3CHCH2 The propene may be protonated to an isopropyl carbocation CH2CHCH3 H r CH3C HCH3 An isopropyl carbocation cannot experience a beta fission no CC bond beta to the carbon with the positive charge25 It may either abstract a hydride ion from another hydrocarbon yielding propane or revert back to propene by eliminating a proton This could explain the relatively higher yield of propene from catalytic cracking units than from thermal cracking units Aromatization of paraffins can occur through a dehydrocyclization reaction Olefinic compounds formed by the beta scission can form a car bocation intermediate with the configuration conducive to cyclization For example if a carbocation such as that shown below is formed by any of the methods mentioned earlier cyclization is likely to occur 74 Chemistry of Petrochemical Processes Once cyclization has occurred the formed carbocation can lose a proton and a cyclohexene derivative is obtained This reaction is aided by the presence of an olefin in the vicinity RCHCH2 Chapter 3 12201 1058 AM Page 74 The next step is the abstraction of a hydride ion by a Lewis acid site from the zeolite surface to form the more stable allylic carbocation This is again followed by a proton elimination to form a cyclohexadiene intermediate The same sequence is followed until the ring is completely aromatized Crude Oil Processing and Production of Hydrocarbon Intermediates 75 During the cracking process fragmentation of complex polynuclear cyclic compounds may occur leading to formation of simple cycloparaf fins These compounds can be a source of C6 C7 and C8 aromatics through isomerization and hydrogen transfer reactions Coke formed on the catalyst surface is thought to be due to polycon densation of aromatic nuclei The reaction can also occur through a car bonium ion intermediate of the benzene ring The polynuclear aromatic structure has a high CH ratio Cracking Process Most catalytic cracking reactors are either fluid bed or moving bed In the more common fluidized bed process FCC the catalyst is an extremely porous powder with an average particle size of 60 microns Catalyst size is important because it acts as a liquid with the reacting hydrocarbon mixture In the process the preheated feed enters the reac tor section with hot regenerated catalyst through one or more risers where cracking occurs A riser is a fluidized bed where a concurrent upward flow of the reactant gases and the catalyst particles occurs The reactor temperature is usually held at about 450520C and the pressure is approximately 1020 psig Gases leave the reactor through cyclones to remove the powdered catalyst and pass to a fractionator for separation of the product streams Catalyst regeneration occurs by combusting carbon deposits to carbon dioxide and the regenerated catalyst is then returned Chapter 3 12201 1058 AM Page 75 to the bottom of the riser Figure 36 is a typical FCC reactorregenera tion system26 Fluid catalytic cracking produces unsaturates especially in the light hydrocarbon range C3C5 which are used as petrochemical feedstocks and for alkylate production In addition to hydrocarbon gases FCC units produce gasolines with high octane numbers due to the high aromatic content branched paraffins and olefins gas oils and tar The ratio of these products depends greatly on the different process variables In gen eral higher conversions increase gas and gasoline yields Higher conver sion also increases coke formation Process variables that increase conversion are higher temperatures longer residence times and higher catalystoil ratio Table 39 shows the analysis of the feed and the prod ucts from an FCC unit27 In the moving bed processes the preheated feed meets the hot catalyst which is in the form of beads that descend by gravity to the regeneration zone As in fluidized bed cracking conversion of aromatics is low and a mixture of saturated and unsaturated light hydrocarbon gases is produced The gasoline product is also rich in aromatics and branched paraffins 76 Chemistry of Petrochemical Processes Figure 36 Typical FCC reactorregenerator26 Chapter 3 12201 1058 AM Page 76 Deep Catalytic Cracking Deep catalytic cracking DCC is a catalytic cracking process which selectively cracks a wide variety of feedstocks into light olefins The reactor and the regenerator systems are similar to FCC However inno vation in the catalyst development severity and process variable selec tion enables DCC to produce more olefins than FCC In this mode of operation propylene plus ethylene yields could reach over 25 In addi tion a high yield of amylenes C5 olefins is possible Figure 37 shows the DCC process and Table 310 compares olefins produced from DCC and FCC processes28 Crude Oil Processing and Production of Hydrocarbon Intermediates 77 Table 39 Analysis of feed and products from a fluid catalytic cracking process27 Yields Typical examples North slope Maya PR Springs vac resid crude bitumen Feed Gravity API 107 235 21 Sulfur wt 20 30 10 Nitrogen wt 048 03 076 Con carb resid wt 118 112 180 Ni V ppm 73 264 89 Product yields H2S wt 03 03 08 LightC2 wt 51 29 16 LPG vol 78 42 30 Naphtha whole vol 187 265 140 Light gas oil vol 137 291 179 Heavy gas oil vol 543 3349 554 Coke burned wt 95 87 171 Heavy gas oil cut Gravity API 115 170 149 Sulfur wt 22 31 05 Nitogren wt 044 022 048 Ni V ppm 30 207 120 Visc cSt 210F 18 12 Chapter 3 12201 1058 AM Page 77 Hydrocracking Process Hydrocracking is essentially catalytic cracking in the presence of hydrogen It is one of the most versatile petroleum refining schemes adapted to process low value stocks Generally the feedstocks are not suitable for catalytic cracking because of their high metal sulfur nitro gen and asphaltene contents The process can also use feeds with high aromatic content Products from hydrocracking processes lack olefinic hydrocarbons The product slate ranges from light hydrocarbon gases to gasolines to residues Depending on the operation variables the process could 78 Chemistry of Petrochemical Processes Figure 37 Deep catalytic cracking process28 Table 310 Comparison of products from DCC with those from FCC28 Products wt FF DCC Type I DCC Type II FCC Ethylene 61 23 09 Propylene 205 143 68 Butylene 143 146 110 in which IC4 54 61 33 Amylene 98 85 in which IC5 65 43 Chapter 3 12201 1058 AM Page 78 be adapted for maximizing gasoline jet fuel or diesel production Table 311 shows the feed and the products from a hydrocracking unit29 Hydrocracking Catalysts and Reactions The dualfunction catalysts used in hydrocracking provide high surface area cracking sites and hydrogenationdehydrogenation sites Amorphous silicaalumina zeolites or a mixture of them promote carbonium ion formation Catalysts with strong acidic activity promote isomerization leading to a high isonormal ratios30 The hydrogenationdehydrogenation activity on the other hand is provided by catalysts such as cobalt molyb denum tungsten vanadium palladium or rare earth elements As with catalytic cracking the main reactions occur by carbonium ion and beta scission yielding two fragments that could be hydrogenated on the cata lyst surface The main hydrocracking reaction could be illustrated by the firststep formation of a carbocation over the catalyst surface Crude Oil Processing and Production of Hydrocarbon Intermediates 79 Table 311 Analysis of feed and products from hydrocracking process29 Yields Typical from various feeds Feed Naphtha LCCO VGO VGO Catalyst stages 1 2 2 2 Gravity API 725 246 258 216 Aniline pt F 145 92 180 180 ASTM 10EP F 154290 478632 7401050 7401100 Sulfur wt 0005 06 10 25 Nitrogen ppm 01 500 1000 900 Yields vol Propane 55 34 isoButane 29 91 30 25 nButane 19 45 30 25 Light naphtha 23 300 119 70 Heavy naphtha 787 142 70 Kerosine 868 480 Diesel 500 Product quality Lt naphtha RON cl 85 76 77 76 Hv naphtha RON cl 65 61 61 Kerosine freeze pt F 65 75 Diesel pour pt F 10 Chapter 3 12201 1058 AM Page 79 The carbocation may rearrange eliminate a proton to produce an olefin or crack at a beta position to yield an olefin and a new carbocation Under an atmosphere of hydrogen and in the presence of a catalyst with hydrogenationdehydrogenation activity the olefins are hydrogenated to paraffinic compounds This reaction sequence could be represented as follows 80 Chemistry of Petrochemical Processes As can be anticipated most products from hydrocracking are saturated For this reason gasolines from hydrocracking units have lower octane rat ings than those produced by catalytic cracking units they have a lower aromatic content due to high hydrogenation activity Products from hydro cracking units are suitable for jet fuel use Hydrocracking also produces light hydrocarbon gases LPG suitable as petrochemical feedstocks Other reactions that occur during hydrocracking are the fragmentation followed by hydrogenation hydrogenolysis of the complex asphaltenes and heterocyclic compounds normally present in the feeds Dealkylation fragmentation and hydrogenation of substituted poly nuclear aromatics may also occur The following is a representative example of hydrocracking of a substituted anthracene Chapter 3 12201 1058 AM Page 80 It should be noted however that this reaction sequence may be dif ferent from what may actually be occurring in the reactor The reactions proceed at different rates depending on the process variables Hydro desulfurization of complex sulfur compounds such as dibenzothiophene also occurs under these conditions The desulfurized product may crack to give two benzene molecules Crude Oil Processing and Production of Hydrocarbon Intermediates 81 Process Most commercial hydrocracking operations use a single stage for maximum middledistillate optimization despite the flexibility gained by having more than one reactor In the single stage process two operation modes are possible a oncethrough mode and a total conversion of the fractionator bottoms through recycling In the oncethrough operation low sulfur fuels are produced and the fractionator bottoms are not recycled In the total conversion mode the fractionator bottoms are recycled to the inlet of the reactor to obtain more middle distillates In the twostage operation the feed is hydrodesulfurized in the first reactor with partial hydrocracking Reactor effluent goes to a highpressure separator to separate the hydrogenrich gas which is recycled and mixed with the fresh feed The liquid portion from the separator is fractionated and the bottoms of the fractionator are sent to the second stage reactor Hydrocracking reaction conditions vary widely depending on the feed and the required products Temperature and pressure range from 400 to 480C and 35 to 170 atmospheres Space velocities in the range of 05 to 20 hr1 are applied Figure 38 shows the Chevron twostage hydro cracking process29 Hydrodealkylation Process This process is designed to hydrodealkylate methylbenzenes ethyl benzene and C9 aromatics to benzene The petrochemical demand for benzene is greater than for toluene and xylenes After separating benzene Chapter 3 12201 1058 AM Page 81 from the reformate the higher aromatics are charged to a hydrodealkyla tion unit The reaction is a hydrocracking one where the alkyl side chain breaks and is simultaneously hydrogenated For example toluene dealkylates to methane and benzene while ethylbenzene produces ethane and benzene In each case one mole of H2 is consumed 82 Chemistry of Petrochemical Processes Figure 38 Flow diagram of a Cheveron hydocracking unit29 14 reactors 25 HP separators 3 recycle scrubber optional 6 LP separator 7 fractionator Consuming hydrogen is mainly a function of the number of benzene sub stituents Dealkylation of polysubstituted benzene increases hydrogen consumption and gas production methane For example dealkylating one mole xylene mixture produces two methane moles and one mole of benzene it consumes two moles of hydrogen Chapter 3 12201 1058 AM Page 82 Unconverted toluene and xylenes are recycled Hydrotreatment Processes Hydrotreating is a hydrogenconsuming process primarily used to reduce or remove impurities such as sulfur nitrogen and some trace metals from the feeds It also stabilizes the feed by saturating olefinic compounds Feeds to hydrotreatment units vary widely they could be any petro leum fraction from naphtha to crude residues The process is relatively simple choosing the desulfurization process depends largely on the feed type the level of impurities present and the extent of treatment needed to suit the market requirement Table 312 shows the feed and product properties from a hydrotreatment unit31 In this process the feed is mixed with hydrogen heated to the proper temperature and introduced to the reactor containing the catalyst The Crude Oil Processing and Production of Hydrocarbon Intermediates 83 Table 312 Products from hydrodesulfurization of feeds with different sulfur levels31 VGO Process VGO VRDS VRDS RDS Feed sulfur wt 23 41 29 29 Product sulfur wt 01 128 05 05 Product yields C1C4 wt 059 056 058 058 H2S NH3 wt 244 300 255 255 C5 wt 9751 9734 9746 9767 C5 LV 1006 1020 1010 1015 Hydrogen consumption scfbbl 330 720 450 550 scflb sulfur 47 71 56 69 Vacuum gas oil hydrotreater Vacuum residuum hydrotreater Atmospheric residuum desulfurization hydrotreating Chapter 3 12201 1058 AM Page 83 conditions are usually adjusted to minimize hydrocracking Typical reac tor temperatures range from 260 to 425C Hydrogen partial pressure and space velocity are important process variables Increasing the tempera ture and hydrogen partial pressure increases the hydrogenation and hydrodesulfurization reactions Lower space velocities are used with feeds rich in polyaromatics Total pressure varies widelyfrom 100 to 3000 psidepending on the type of feed level of impurities and the extent of hydrotreatment required Figure 39 shows an Exxon hydrotreatment unit32 Hydrotreatment Catalysts and Reactions Catalysts used in hydrotreatment hydrodesulfurization HDS processes are the same as those developed in Germany for coal hydro genation during World War II The catalysts should be sulfurresistant The cobaltmolybdenum system supported on alumina was found to be an effective catalyst The catalyst should be reduced and sulfided during the initial stages of operation before use Other catalyst systems used in HDS are NiOMoO3 and NiOWO3 Because mass transfer has a significant influence on the reaction rates catalyst performance is significantly affected by the parti cle size and pore diameter Reactions occurring in hydrotreatment units are mainly hydrodesulfu rization and hydrodenitrogenation of sulfur and nitrogen compounds In 84 Chemistry of Petrochemical Processes Figure 39 Flow diagram of an Exxon hydrotreating unit32 1 filter 2 guard ves sel to protect reactor 3 main reactor 4 gas treatment 5 fractionator Chapter 3 12201 1058 AM Page 84 the first case H2S is produced along with the hydrocarbon In the latter case ammonia is released The following examples are hydrodesulfur ization reactions of some representative sulfur compounds present in petroleum fractions and coal liquids RSH H2 r RH H2S RSR 2H2 r 2RH H2S RSSR 3H2 r 2RH 2H2S Crude Oil Processing and Production of Hydrocarbon Intermediates 85 Examples of hydrodenitrogenation of two types of nitrogen com pounds normally present in some light and middle crude distillates are shown as follows More complex sulfur and nitrogen compounds are present in heavy residues These are hyrodesulfurized and hydrodenitrogenated but under more severe conditions than normally used for lighter distillates For example for light petroleum distillates the approximate temperature and pressure ranges of 300400C and 3570 atm are used versus 340425C and 55170 atm for heavy petroleum residua Liquid hourly space velocities LHSV in the range of 210 hr1 are used for light prod ucts while it is 0210 hr1 for heavy residues33 Alkylation Process Alkylation in petroleum processing produces larger hydrocarbon mol ecules in the gasoline range from smaller molecules The products are branched hydrocarbons having high octane ratings Chapter 3 12201 1058 AM Page 85 The term alkylation generally is applied to the acid catalyzed reaction between isobutane and various light olefins and the product is known as the alkylate Alkylates are the best of all possible motor fuels having both excellent stability and a high octane number Either concentrated sulfuric acid or anhydrous hydrofluoric acid is used as a catalyst for the alkylation reaction These acid catalysts are capable of providing a proton which reacts with the olefin to form a carbocation For example when propene is used with isobutane a mixture of C5 iso mers is produced The following represents the reaction steps 86 Chemistry of Petrochemical Processes The formed carbocation from the last step may abstract a hydride ion from an isobutane molecule and produce 22dimethylpentane or it may rearrange to another carbocation through a hydride shift The new carbocation can rearrange again through a methidehydride shift as shown in the following equation Chapter 3 12201 1058 AM Page 86 The rearranged carbocation finally reacts with isobutane to form 223 trimethylbutane Crude Oil Processing and Production of Hydrocarbon Intermediates 87 The final product contains approximately 6080 22dimethylpen tane and varying amounts of 223trimethylbutane and 2methylhexane The primary process variables affecting the economics of sulfuric acid alkylation are the reaction temperature isobutane recycle rate reactor space velocity and spent acid strength To control fresh acid makeup spent acid could be monitored by continuously measuring its density the flow rate and its temperature This can reduce the acid usage in alkyla tion units34 The presence of impurities such as butadiene affects the product yield and properties Butadiene tends to polymerize and form acidsoluble oils which increases acid makeup requirements For every pound of butadi ene in the feed ten pounds of additional makeup acid will be required35 Other olefins that are commercially alkylated are isobutene and 1 and 2butenes Alkylation of isobutene produces mainly 224trimethylpen tane isooctane Both sulfuric acid and hydrofluoric acid catalyzed alkylations are low temperature processes Table 313 gives the alkylation conditions for HF and H2SO4 processes36 One drawback of using H2SO4 and HF in alky lation is the hazards associated with it Many attempts have been tried to use solid catalysts such as zeolites alumina and ion exchange resins Also strong solid acids such as sulfated zirconia and SbF5sulfonic acid resins were tried Although they were active nevertheless they lack sta bility37 No process yet proved successful due to the fast deactivation of the catalyst A new process which may have commercial possibility uses Chapter 3 12201 1058 AM Page 87 liquid trifilic acid CF3SO2OH on a porous solid bed Using isobutane and light olefins the intermediates are isopropyl secbutyl 2pentyl and 3pentyl esters of trifilic acid38 Isomerization Process Isomerization is a smallvolume but important refinery process Like alkylation it is acid catalyzed and intended to produce highlybranched hydrocarbon mixtures The low octane C5C6 fraction obtained from nat ural gasoline or from a light naphtha fraction may be isomerized to a high octane product Dualfunction catalysts activated by either inorganic or organic chlo rides are the preferred isomerization catalysts A typical catalyst is plat inum with a zeolite base These catalysts serve the dual purpose of promoting carbonium ion formation and hydrogenationdehydrogenation reactions The reaction may start by forming a carbocation via abstrac tion of a hydride ion by a catalyst acid site Alternatively an olefin formed on the catalyst surface could be protonated to form the carboca tion The carbocation isomerizes by a 12hydridemethide shift as men tioned earlier see this chapter Reforming Reactions Figure 310 shows the vapor phase equilibrium of hexane isomers39 Oligomerization of Olefins Dimerization This process produces polymer gasoline with a high octane Dimeri zation was first used 1935 to dimerize isobutylene to diisobutylene constituted of 244trimethyl1pentene 80 and 244trimethyl2 pentene 20 Both phosphoric and sulfuric acid were used as catalysts At present the feedstock is either a propylenepropane mixture or propylenebutane mixture where propane and butane are diluents The 88 Chemistry of Petrochemical Processes Table 313 Ranges of operating conditions for H2SO4 and HF alkylation36 Process catalysts H2SO4 HF Temperature C 216 1652 Isobutaneolefin feed 312 312 Olefin space velocity vohrvo 0106 Olefin contact time min 2030 820 Catalysts acidity wt 8895 8095 Acid in emulsion vol 4060 2580 Chapter 3 12201 1058 AM Page 88 product is an olefin having a high octane number When propylene is used a trimer or a tetramer is formed The polymerization reaction is highly exothermic so the temperature has to be controlled The presence of propane and butane in the mixture acts as a heat sink to absorb part of the reaction heat Typical reaction conditions are 170250C and 25100 atm The polymerization reaction starts by protonating the olefin and form ing a carbocation For example protonating propene gives isopropyl car bocation The proton is provided by the ionization of phosphoric acid Crude Oil Processing and Production of Hydrocarbon Intermediates 89 Figure 310 Vapor phase equilibrium for hexanes39 The next step is the reaction of the carbocation with the olefin propene or butene The newlyformed carbocation either eliminates a proton and forms a dimer or attacks another propene molecule and eliminates a proton giv ing the trimer Chapter 3 12201 1058 AM Page 89 Further protonation of the trimer produces a C9 carbocation which may further react with another propene molecule and eventually produce propylene tetramer The product is a mixture of dimers trimers tetramers and pentamers having an average RON Research Octane Number 95 Table 314 shows the analysis of feed and products from dimerization of propylene40 90 Chemistry of Petrochemical Processes Table 314 Typical feed and products from the dimerization of propylene40 Vol Total wt Total Feed Propylene 71 Propane 29 100 Products LPG Propylene 42 Propane 346 Isohexanes 612 100 Isohexenes 920 Isononenes 65 Heavier 15 100 ASTM distillation F IBP 133 10 136 50 140 90 160 95 320 EP 370 Dimersol isohexenes A trimer Chapter 3 12201 1058 AM Page 90 PRODUCTION OF OLEFINS The most important olefins and diolefins used to manufacture petro chemicals are ethylene propylene butylenes and butadiene Butadiene a conjugated diolefin is normally coproduced with C2C4 olefins from different cracking processes Separation of these olefins from catalytic and thermal cracking gas streams could be achieved using physical and chemical separation methods However the petrochemical demand for olefins is much greater than the amounts these operations produce Most olefins and butadienes are produced by steam cracking hydrocarbons Butadiene can be alternatively produced by other synthetic routes dis cussed with the synthesis of isoprene the second major diolefin for rub ber production STEAM CRACKING OF HYDROCARBONS Production of Olefins The main route for producing light olefins especially ethylene is the steam cracking of hydrocarbons The feedstocks for steam cracking units range from light paraffinic hydrocarbon gases to various petroleum frac tions and residues The properties of these feedstocks are discussed in Chapter 2 The cracking reactions are principally bond breaking and a substantial amount of energy is needed to drive the reaction toward olefin production The simplest paraffin alkane and the most widely used feedstock for producing ethylene is ethane As mentioned earlier ethane is obtained from natural gas liquids Cracking ethane can be visualized as a free rad ical dehydrogenation reaction where hydrogen is a coproduct CH3CH3 r CH2CH2 H2 H590C 143 KJ The reaction is highly endothermic so it is favored at higher tempera tures and lower pressures Superheated steam is used to reduce the par tial pressure of the reacting hydrocarbons in this reaction ethane Superheated steam also reduces carbon deposits that are formed by the pyrolysis of hydrocarbons at high temperatures For example pyrolysis of ethane produces carbon and hydrogen CH3CH3 r 2C 3H2 Ethylene can also pyrolyse in the same way Additionally the presence of steam as a diluent reduces the hydrocarbons chances of being in contact Crude Oil Processing and Production of Hydrocarbon Intermediates 91 Chapter 3 12201 1058 AM Page 91 with the reactor tubewall Deposits reduce heat transfer through the reactor tubes but steam reduces this effect by reacting with the carbon deposits steam reforming reaction C H2O r CO H2 Many side reactions occur when ethane is cracked A probable sequence of reactions between ethylene and a formed methyl or an ethyl free radical could be represented CH2 CH2 CH3 r CH3CH2CH2 r CH3CH CH2 H CH2CH2 CH3CH2 r CH3CH2CH2CH2 r CH3CH2CHCH2 H Propene and lbutene respectively are produced in this free radical reac tion Higher hydrocarbons found in steam cracking products are proba bly formed through similar reactions When liquid hydrocarbons such as a naphtha fraction or a gas oil are used to produce olefins many other reactions occur The main reaction the cracking reaction occurs by a free radical and beta scission of the CC bonds This could be represented as RCH2CH2CH2R r RCH2CH2CH2 R RCH2CH2CH2 r RCH2 CH2CH2 The newly formed free radical may terminate by abstraction of a hydro gen atom or it may continue cracking to give ethylene and a free radical Aromatic compounds with side chains are usually dealkylated The pro duced free radicals further crack to yield more olefins In the furnace and in the transfer line exchanger coking is a signifi cant problem Catalytic coking occurs on clean metal surfaces when nickel and other transition metals used in radiant tube alloys catalyze dehydrogenation and formation of coke Coke formation reduces product yields increases energy consumption and shortens coil service life Coking is related to feedstock temperature and steam dilution The radi ant tubes gradually become coated with an internal layer of coke thus raizing the tube metal temperature and increasing pressure drop through the radiant coils When coke reaches an allowable limit as indicated by a high pressure drop it should be removed41 Coke could be reduced by adding antifoulants which passivate the catalytic coking mechanism 92 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 92 The subject has been reviewed by Burns et al42 Over the past 20 years significant improvements have been made in the design and operation of high severity pyrolysis furnances Using better alloys for tubing has enabled raising the temperature shortening residence time and lowering pressure drop in the cracking coils The use of cast alloys with a higher alloy content increases their longterm strength Figure 311 shows the effect of alloy content on the longterm rupture stress for modified Ni CrFe alloys41 Steam Cracking Process A typical ethane cracker has several identical pyrolysis furnaces in which fresh ethane feed and recycled ethane are cracked with steam as a diluent Figure 312 is a block diagram for ethylene from ethane The outlet temperature is usually in the 800C range The furnace effluent is quenched in a heat exchanger and further cooled by direct contact in a water quench tower where steam is condensed and recycled to the pyrol ysis furnace After the cracked gas is treated to remove acid gases hydro gen and methane are separated from the pyrolysis products in the demethanizer The effluent is then treated to remove acetylene and eth ylene is separated from ethane and heavier in the ethylene fractionator The bottom fraction is separated in the deethanizer into ethane and C3 fraction Ethane is then recycled to the pyrolysis furnace Crude Oil Processing and Production of Hydrocarbon Intermediates 93 Figure 311 Effect of alloy content on longterm rupture stress for cast modified NiCrFe alloys41 Chapter 3 12201 1058 AM Page 93 94 Chemistry of Petrochemical Processes Figure 312 Block diagram for producing ethylene from ethane Chapter 3 12201 1058 AM Page 94 An olefin plant that uses liquid feeds requires an additional pyrolysis furnace an effluent quench exchanger and a primary fractionator for fuel oil separation Process Variables The important process variables are reactor temperature residence time and steamhydrocarbon ratio Feed characteristics are also consid ered since they influence the process severity Temperature Steam cracking reactions are highly endothermic Increasing tempera ture favors the formation of olefins high molecular weight olefins and aromatics Optimum temperatures are usually selected to maximize olefin production and minimize formation of carbon deposits Reactor temperature is also a function of the feedstock used Higher molecular weight hydrocarbons generally crack at lower temperatures than lower molecular weight compounds For example a typical furnace outlet temperature for cracking ethane is approximately 800C while the temperature for cracking naphtha or gas oil is about 675700C Residence Time In steam cracking processes olefins are formed as primary products Aromatics and higher hydrocarbon compounds result from secondary reactions of the formed olefins Accordingly short residence times are required for high olefin yield When ethane and light hydrocarbon gases are used as feeds shorter residence times are used to maximize olefin production and minimize BTX and liquid yields residence times of 0512 sec are typical Cracking liquid feedstocks for the dual purpose of producing olefins plus BTX aromatics requires relatively longer resi dence times than for ethane However residence time is a compromise between the reaction temperature and other variables A fairly new development in cracking liquid feeds that improves eth ylene yield is the Millisecond furnace which operates between 00301 sec with an outlet temperature range of 870925C The Millisecond furnace probably represents the last step that can be taken with respect to this critical variable because contact times below the 01 sec range lead to production of acetylenes in large quantities43 Crude Oil Processing and Production of Hydrocarbon Intermediates 95 Chapter 3 12201 1058 AM Page 95 SteamHydrocarbon Ratio A higher steamhydrocarbon ratio favors olefin formation Steam reduces the partial pressure of the hydrocarbon mixture and increases the yield of olefins Heavier hydrocarbon feeds require more steam than gaseous feeds to additionally reduce coke deposition in the furnace tubes Liquid feeds such as gas oils and petroleum residues have complex polynuclear aromatic compounds which are coke precursors Steam to hydrocarbon weight ratios range between 021 for ethane and approxi mately 112 for liquid feeds Feedstocks Feeds to steam cracking units vary appreciably from light hydrocarbon gases to petroleum residues Due to the difference in the cracking rates of the various hydrocarbons the reactor temperature and residence time vary As mentioned before long chain hydrocarbons crack more easily than shorter chain compounds and require lower cracking temperatures For example it was found that the temperature and residence time that gave 60 conversion for ethane yielded 90 conversion for propane44 Feedstock composition also determines operation parameters The rates of cracking hydrocarbons differ according to structure Paraffinic hydrocarbons are easier to crack than cycloparaffins and aromatics tend to pass through unaffected Isoparaffins such as isobutane and isopentane give high yields of propylene This is expected because cracking at a ter tiary carbon is easier 96 Chemistry of Petrochemical Processes As feedstocks progress from ethane to heavier fractions with lower HC ratios the yield of ethylene decreases and the feed per pound ethylene product ratio increases markedly Table 315 shows yields from steam cracking of different feedstocks45 and how the liquid byproducts and BTX aromatics increase dramatically with heavier feeds Cracking Gas Feeds The main gas feedstock for ethylene production is ethane Propane and butane or their mixture LPG are also used but to a lesser extent They Chapter 3 12201 1058 AM Page 96 are specially used when coproduct propylene butadiene and the butenes are needed The advantage of using ethane as a feed to cracking units is a high ethylene yield with minimal coproducts For example at 60 per pass conversion level the ultimate yield of ethylene is 80 based on ethane being recycled to extinction The following are typical operating conditions for an ethane cracking unit and the products obtained Conditions Temperature C 750850 Pressure Kgcm2 112 SteamHC 05 Yield wt Hydrogen methane 129 Ethylene 809 Propylene 18 Butadiene 19 Other 25 Other Propane 03 butanes 04 butenes 04 C5 14 Propane cracking is similar to ethane except for the furnace tempera ture which is relatively lower longer chain hydrocarbons crack easier However more byproducts are formed than with ethane and the sepa ration section is more complex Propane gives lower ethylene yield higher propylene and butadiene yields and significantly more aromatic pyrolysis gasoline Residual gas mainly H2 and methane is about two and half times that produced when ethane is used Increasing the severity Crude Oil Processing and Production of Hydrocarbon Intermediates 97 Table 315 Ultimate yields from steam cracking various feedstocks45 Feedstock Yield wt Ethane Propane Butane Naphtha Gas oil Saudi NGL H2 CH4 13 28 24 26 18 23 Ethylene 80 45 37 30 25 50 Propylene 24 15 18 13 14 12 Butadiene 14 2 2 45 5 25 Mixed butenes 16 1 64 8 6 35 C5 16 9 126 185 32 9 Chapter 3 12201 1058 AM Page 97 of a propane cracking unit increases ethylene and residual gas yields and decreases propylene yield Figure 313 shows the influence of conversion severity on the theoretical product yield for cracking propane46 Cracking nbutane is also similar to ethane and propane but the yield of ethylene is even lower It has been noted that cracking either propane or butanes at nearly similar severity produced approximately equal liquid yields Mixtures of propane and butane LPG are becoming important steam cracker feedstocks for C2C4 olefin production It has been fore casted that world LPG markets will grow from 1147 million metric tonsday in 1988 to 1369 MMtpd in the year 2000 and the largest por tion of growth will be in the chemicals field47 Cracking Liquid Feeds Liquid feedstocks for olefin production are light naphtha full range naphtha reformer raffinate atmospheric gas oil vacuum gas oil resi dues and crude oils The ratio of olefins produced from steam cracking of these feeds depends mainly on the feed type and to a lesser extent on the operation variables For example steam cracking light naphtha pro duces about twice the amount of ethylene obtained from steam cracking vacuum gas oil under nearly similar conditions Liquid feeds are usually 98 Chemistry of Petrochemical Processes Figure 313 The influence of conversion severity on the theoretical product yield for the cracking of propane Acetylene methyl acetylene and propadiene are hydrogenated and both ethane and propane are recycled to extinction wt46 Chapter 3 12201 1058 AM Page 98 cracked with lower residence times and higher steam dilution ratios than those used for gas feedstocks The reaction section of the plant is essen tially the same as with gas feeds but the design of the convection and the quenching sections are different This is necessitated by the greater vari ety and quantity of coproducts An additional pyrolysis furnace for crack ing coproduct ethane and propane and an effluent quench exchanger are required for liquid feeds Also a propylene separation tower and a methyl acetylene removal unit are incorporated in the process Figure 314 is a flow diagram for cracking naphtha or gas oil for ethylene production42 As with gas feeds maximum olefin yields are obtained at lower hydrocarbon partial pressures pressure drops and residence times These variables may be adjusted to obtain higher BTX at the expense of higher olefin yield One advantage of using liquid feeds over gas feedstocks for olefin pro duction is the wider spectrum of coproducts For example steam crack ing naphtha produces in addition to olefins and diolefins pyrolysis gasoline rich in BTX Table 316 shows products from steam cracking naphtha at low and at high severities44 48 It should be noted that opera tion at a higher severity increased ethylene product and byproduct methane and decreased propylene and butenes The following conditions are typical for naphtha cracking Temperature C 800 Pressure Atm Atmospheric SteamHC KgKg 0608 Residence time sec 035 Steam cracking raffinate from aromatic extraction units is similar to naphtha cracking However because raffinates have more isoparaffins relatively less ethylene and more propylene is produced Cracking gas oils for olefin production has been practiced since 1930 However due to the simplicity of cracking gas feeds the use of gas oil declined Depending on gas feed availability and its price which is increasing relative to crude prices gas oil cracking may return as a poten tial source for olefins Gas oils in general are not as desirable feeds for olefin production as naphtha because they have higher sulfur and aromatic contents The presence of a high aromatic content in the feed affects the running time of the system and the olefin yield gas oils generally produce less ethylene and more heavy fuel oil Although high sulfur gas oils could be directly cracked it is preferable to hydrodesulfurize these feeds before cracking to avoid separate treatment schemes for each product Crude Oil Processing and Production of Hydrocarbon Intermediates 99 Chapter 3 12201 1058 AM Page 99 100 Chemistry of Petrochemical Processes Figure 314 Flow diagram of an ethylene plant using liquid feeds42 Chapter 3 12201 1058 AM Page 100 Processes used to crack gas oils are similar to those for naphtha However gas oil throughput is about 2025 higher than that for naph tha The ethylene cracking capacity for AGO is about 15 lower than for naphtha There must be a careful balance between furnace residence time hydrocarbon partial pressure and other factors to avoid problems inherent in cracking gas oils49 Table 317 shows the product composi tion from cracking AGO and VGO at low and high severities444850 Figure 315 shows the effect of cracking severity when using gas oil on the product composition51 PRODUCTION OF DIOLEFINS Diolefins are hydrocarbon compounds that have two double bonds Conjugated diolefins have two double bonds separated by one single bond Due to conjugation these compounds are more stable than mono olefins and diolefins with isolated double bonds Conjugated diolefins also have different reactivities than monoolefins The most important industrial diolefinic hydrocarbons are butadiene and isoprene Crude Oil Processing and Production of Hydrocarbon Intermediates 101 Table 316 Products from steam cracking naphtha at high severities4448 Cracking severity Products Low High Methane 103 15 Ethylene 258 313 Propylene 160 121 Butadiene 45 42 Butenes 79 28 BTX 10 13 C5 17 9 Fuel oil 3 6 Other 55 66 Feed Sp gr 6060F 0713 Boiling range C 32170 Aromatics 7 Weight percent Ethane 33 and 34 acetylene methylacetylene propane hydrogen Chapter 3 12201 1058 AM Page 101 102 Chemistry of Petrochemical Processes Figure 315 Component yields vs cracking severity for a typical gas oil51 Table 317 Product composition from cracking atmospheric gas oil and vacuum gas oil444850 AGO VGO Severity Severity Products Low High Low High Methane 80 137 66 94 Ethylene 195 260 194 230 Ethane 33 30 28 30 Propylene 140 90 139 137 Butadiene 45 42 50 63 Butenes 64 20 70 49 BTX 107 126 C5205C 100 80 189 169 Fuel oil 218 190 250 210 Other 18 25 14 18 Weight Other than BTX Acetylene methylacetylene propane hydrogen Chapter 3 12201 1058 AM Page 102 Butadiene CH2 CHCH CH2 Butadiene is the raw material for the most widely used synthetic rub ber a copolymer of butadiene and styrene SBR In addition to its util ity in the synthetic rubber and plastic industries over 90 of butadiene produced many chemicals could also be synthesized from butadiene Production Butadiene is obtained as a byproduct from ethylene production It is then separated from the C4 fraction by extractive distillation using furfural Butadiene could also be produced by the catalytic dehydrogenation of butanes or a butanebutene mixture CH3CH2CH2CH3 r CH2CHCHCH2 2H2 The first step involves dehydrogenation of the butanes to a mixture of butenes which are then separated recycled and converted to butadiene Figure 316 is the Lummus fixedbed dehydrogenation of C4 mixture to butadiene52 The process may also be used for the dehydrogenation of mixed amylenes to isoprene In the process the hot reactor effluent is quenched compressed and cooled The product mixture is extracted un reacted butanes are separated and recycled and butadiene is recovered Crude Oil Processing and Production of Hydrocarbon Intermediates 103 Figure 316 Flow diagram of the Lummus process for producing butadiene52 1 reactor 2 quenching 3 compressor 4 cryogenic recovery 5 stabilizer 6 extraction Chapter 3 12201 1058 AM Page 103 The Phillips process uses an oxidativedehydrogenation catalyst in the presence of air and steam The C4 mixture is passed over the catalyst bed at 900 to 1100C Hydrogen released from dehydrogenation reacts with oxygen thus removing it from the equilibrium mixture and shifting the reaction toward the formation of more butadiene An indepth study of the oxidative dehydrogenation process was made by Welch et al They concluded that conversion and overall energy costs are favorable for butadiene production via this route53 In some parts of the world as in Russia fermented alcohol can serve as a cheap source for butadiene The reaction occurs in the vapor phase under normal or reduced pressures over a zinc oxidealumina or magne sia catalyst promoted with chromium or cobalt Acetaldehyde has been suggested as an intermediate two moles of acetaldehyde condense and form crotonaldehyde which reacts with ethyl alcohol to give butadiene and acetaldehyde Butadiene could also be obtained by the reaction of acetylene and formaldehyde in the vapor phase over a copper acetylide catalyst The produced 14butynediol is hydrogenated to 14butanediol Dehydration of 14butanediol yields butadiene 104 Chemistry of Petrochemical Processes Isoprene 2methyl 13butadiene is the second most important con jugated diolefin after butadiene Most isoprene production is used for the manufacture of cispolyisoprene which has a similar structure to natural rubber It is also used as a copolymer in butyl rubber formulations Chapter 3 12201 1058 AM Page 104 Production There are several different routes for producing isoprene The choice of one process over the other depends on the availability of the raw mate rials and the economics of the selected process While most isoprene produced today comes from the dehydrogenation of C5 olefin fractions from cracking processes several schemes are used for its manufacture via synthetic routes The following reviews the important approaches for isoprene production Dehydrogenation of Tertiary Amylenes Shell Process tAmylenes 2methyl1butene and 2methyl2butene are produced in small amounts with olefins from steam cracking units The amylenes are extracted from a C5 fraction with aqueous sulfuric acid Dehydrogenation of tamylenes over a dehydrogenation catalyst pro duces isoprene The overall conversion and recovery of tamylenes is approximately 70 The C5 olefin mixture can also be produced by the reaction of ethyl ene and propene using an acid catalyst Crude Oil Processing and Production of Hydrocarbon Intermediates 105 The C5 olefin mixture is then dehydrogenated to isoprene From Acetylene and Acetone A threestep process developed by Snamprogetti is based on the reac tion of acetylene and acetone in liquid ammonia in the presence of an alkali metal hydroxide The product methylbutynol is then hydro genated to methylbutenol followed by dehydration at 250300C over an acidic heterogeneous catalyst Chapter 3 12201 1058 AM Page 105 From Isobutylene and Formaldehyde IFP Process The reaction between isobutylene separated from C4 fractions from cracking units or from cracking isobutane to isobutene and formalde hyde produces a cyclic ether dimethyl dioxane Pyrolysis of dioxane gives isoprene and formaldehyde The formaldehyde is recovered and recycled to the reactor 106 Chemistry of Petrochemical Processes From Isobutylene and Methylal Sun Oil Process In this process methylal dimethoxymethane is used instead of formaldehyde The advantage of using methylal over formaldehyde is its lower reactivity toward 1butene than formaldehyde thus allowing mixed feedstocks to be used Also unlike formaldehyde methylal does not decompose to CO and H2 The first step in this process is to produce methylal by the reaction of methanol and formaldehyde using an acid catalyst Chapter 3 12201 1058 AM Page 106 The second step is the vapor phase reaction of methylal with isobutene to produce isoprene 2Butene in the C4 mixture also reacts with methylal but at a slower rate to give isoprene 1Butene reacts slowly to give 13pentadiene From Propylene Goodyear Process Another approach for producing isoprene is the dimerization of propy lene to 2methyl1pentene The reaction occurs at 200C and about 200 atmospheres in the presence of a tripropyl aluminum catalyst combined with nickel or platinum Crude Oil Processing and Production of Hydrocarbon Intermediates 107 The next step is the isomerization of 2methyl1pentene to 2methyl2 pentene using an acid catalyst 2Methyl2pentene is finally pyrolyzed to isoprene REFERENCES 1 Refining Handbook Hydrocarbon Processing Vol 59 No 11 1990 p 86 2 Gary J H and Handwerk G E Petroleum Refining Technology and Economics Second Edition Marcell Dekker Inc 1984 p 45 3 Reber R A and Symoniak M F Ind Eng Chem Div 169th ACS National Meeting paper 75 April 1975 4 Refining Handbook Hydrocarbon Processing Vol 77 No 11 1998 p 68 Chapter 3 12201 1058 AM Page 107 5 Refining Handbook Hydrocarbon Processing Vol 69 No 11 1990 p l06 6 Elliot J D Maximize Distillate Liquid Products Hydrocarbon Processing Vol 71 No 1 1992 pp 7582 7 Mochida I Fugimato K and Oyama T Thrower P A editor Chemistry and Physics of Carbon Vol 24 Marcell Dekker 1994 8 MartinezEscandell M et al Pyrolysis of Petroleum Residues Carbon Vol 37 No 10 1999 pp 15671582 9 Dymond R E World Markets for Petroleum Coke Hydrocarbon Processing Vol 70 No 9 1991 pp 162C162J 10 Gotshall W W Reprints Division of Petroleum Chemistry ACS No 20 Nov 3 1975 11 Refining Handbook Hydrocarbon Processing Vol 53 No 11 1974 p 123 12 Matar S Aromatics Production and Chemicals The Arabian Journal for Science and Engineering Vol 11 No11986 pp 2332 13 AlKabbani A S Reforming Catalyst Optimization Hydrocarbon Processing Vol 78 No 7 1999 pp 6167 14 Pollitzer E L Hayes J C and Haensel V The Chemistry of Aromatics Production via Catalytic Reforming Refining Petroleum for Chemicals Advances in Chemistry Series No 97 American Chemical Society 1970 pp 2023 15 Refining Handbook Hydrocarbon Processing Vol 69 No 11 1990 p 118 16 Gentry J C and Kumar C S Improve BTX Processing Economics Hydrocarbon Processing Vol 77 No 3 1998 pp 6982 17 OConnor P et al Improve Resid Processing Hydrocarbon Processing Vol 70 No 11 1991 pp 7684 18 Ocelli M L MetalResistant Fluid Cracking Catalyst Thirty Years Of Research ACS Symposium Series No 52 Washington DC 1990 p 343 19 Reynolds B E Brown E C and Silverman M A Clean Gasoline via VRDSRFCC Hydrocarbon Processing Vol 71 No 4 1992 pp 4351 20 Hayward C M and Winkler W S FCC Matrixzeolite Interactions Hydrocarbon Processing Vol 69 No 2 1990 pp 5556 21 Humphries A et al Catalyst Helps Reformulation Hydrocarbon Processing Vol 70 No 4 1991 pp 6972 108 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 108 22 McLean J B and Moorehead E L Steaming Affects FCC Catalyst Hydrocarbon Processing Vol 70 No 2 1991 pp 4145 23 Occelli M L ed Fluid Catalytic Cracking Role in Modern Refining ACS Symposium Series American Chemical Society Washington DC 1988 pp 116 24 Gall J W et al NPRA Annual Meeting AM 8250 5 1982 25 Hatch L F and Matar S Refining Processes and Petrochemicals Part I Hydrocarbon Processing Vol 56 No 7 1977 pp 191201 26 Jazayeri B Optimize FCC Riser Design Hydrocarbon Process ing Vol 70 No 5 1991 pp 9395 27 Refining Handbook Hydrocarbon Processing Vol 75 No 11 1996 p 121 28 Petrochemical Handbook Hydrocarbon Processing Vol 78 No 3 1999 p 124 29 Refining Handbook Hydrocarbon Processing Vol 69 No 11 1990 p 1 00 30 Scott J W and Bridge A G Origin and Refining of Petroleum No 7 Washington DC American Chemical Society 1971 p 116 31 Bridge A G Scott J W and Reed A M Hydrocarbon Processing Vol 54 No 5 1975 pp 7481 32 Refining Handbook Hydrocarbon Processing Vol 69 No 11 1990 p 116 33 Gates B C Katzer J R and Schuit G C Chemistry of Catalytic Processes McGrawHill Book Company 1979 p 394 34 Jensen B et al Reduce Acid Usage on Alkylation Hydrocarbon Processing Vol 77 No 7 1998 p 101 35 Lerner H and Citarella V A Improve Alkylation Efficiency Hydrocarbon Processing Vol 70 No 11 1991 pp 8992 36 Lafferty W L and Stokeld R W Origin and Refining of Petroleum Advances in Chemistry Series 103 ACS Washington DC 1971 p 134 37 Cheung T and Gates B Strong Acid Catalyst for Paraffin Conversion CHEMTECH Vol 27 No 9 1997 pp 2834 38 Albright L F Improving Alkylate Gasoline Technology CHEMTECH Vol 28 No 7 1998 pp 4653 39 Lawrance P A and Rawlings A A Proceedings 7th World Pet Congress 1967 p 137 40 Andrews J W et al Hydrocarbon Processing Vol 54 No 5 1975 pp 6973 Crude Oil Processing and Production of Hydrocarbon Intermediates 109 Chapter 3 12201 1058 AM Page 109 41 Wysiekierski A G et al Control Coking for Olefin Production Hydrocarbon Processing Vol 78 No 1 1999 pp 97100 42 Burns K G et al Chemicals Increase Ethylene Plant Efficiency Hydrocarbon Processing Vol 70 No 1 1991 pp 8387 43 Belgian Patent 840343 to Continental Oil Houston 44 Barwell J and Martin S R International Seminar on Petro chemicals paper No 9 p 2 Baghdad Oct 2530 1975 45 Lee A K K and Aitani A M Saudi Ethylene Plants Move Toward More Feed Flexibility Oil and Gas Journal Special Sept 10 1990 pp 6064 46 Nahas R S and Nahas M R Second Arab Conference on Petrochemicals paper No 6 P1 Abu Dhabi March 1522 1976 47 Watters P R New Partnership Emerge in LPG and Petrochemicals trade Hydrocarbon Processing Vol 69 No 6 1990 pp 100B100N 48 ElEnany N M and Abdel Rahman O F Second Arab Conference on Petrochemicals paper No 9 p2 Abu Dhabi March 1523 1976 49 Smith J Chemical Engineering Sept 15 1975 pp 131136 50 Bassler E J Oil and Gas Journal March 17 1975 pp 9396 51 Zdonik S B Potter W S and Hayward G L Hydrocarbon Processing Vol 55 No 4 1976 pp 161166 52 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 141 53 Welch L M Croce L J and Christmann H F Hydrocarbon Processing Vol 57 No 11 1978 pp 131136 110 Chemistry of Petrochemical Processes Chapter 3 12201 1058 AM Page 110 CHAPTER FOUR Nonhydrocarbon Intermediates INTRODUCTION From natural gas crude oils and other fossil materials such as coal few intermediates are produced that are not hydrocarbon compounds The important intermediates discussed here are hydrogen sulfur carbon black and synthesis gas Synthesis gas consists of a nonhydrocarbon mixture H2CO obtain able from more than one source It is included in this chapter and is fur ther noted in Chapter 5 in relation to methane as a major feedstock for this mixture This chapter discusses the use of synthesis gas obtained from coal gasification and from different petroleum sources for produc ing gaseous as well as liquid hydrocarbons Fischer Tropsch synthesis Naphthenic acids and cresylic acid which are extracted from certain crude oil fractions are briefly reviewed at the end of the chapter HYDROGEN Hydrogen is the lightest known element Although only found in the free state in trace amounts it is the most abundant element in the uni verse and is present in a combined form with other elements Water nat ural gas crude oils hydrocarbons and other organic fossil materials are major sources of hydrogen Hydrogen has been of great use to theoretical investigation The struc ture of the atom developed by Bohr Nobel Prize Winner 1922 was based on a model of the hydrogen atom Chemically hydrogen is a very reactive element Obtaining hydrogen from its compounds is an energy extensive process To decompose water into hydrogen and oxygen an energy input equal to an enthalpy change of 286 KJmol is required1 111 Chapter 4 12201 1100 AM Page 111 H2O r H2 12O2 H 286 KJmol Electrolysis and thermochemical and photochemical decomposition of water followed by purification through diffusion methods are expensive processes to produce hydrogen The most economical way to produce hydrogen is by steam reforming petroleum fractions and natural gas Figure 412 In this process two major sources of hydrogen water and hydrocarbons are reacted to pro duce 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 pass ing the mixture through a pressure swing adsorption system The shift conversion reaction is discussed in relation to ammonia synthesis in Chapter 5 The production of synthesis gas by steam reforming liquid hydrocarbons is noted later in this chapter Recently a new process has been developed to manufacture hydrogen by 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 CH3OHg H2Og r CO2g 3 H2g 112 Chemistry of Petrochemical Processes Figure 41 A process for producing hydrogen by steam reforming of hydrocar bons2 1 reforming furnace 23 purification section 4 shift converter 5 pres sure swing adsorption Chapter 4 12201 1100 AM Page 112 This process is used to produce relatively small quantities 01818 MMscfd of highly pure hydrogen when methanol is available at a rea sonable price In the petroleum refining industry hydrogen is essentially obtained from catalytic naphtha reforming where it is a coproduct with reformed gasoline The use of hydrogen in the chemical and petroleum refining industries is of prime importance Hydrogen is essentially a hydrogenating agent For example it is used with vegetable oils and fats to reduce unsaturated esters triglycerides It is also a reducing agent for sulfide ores such as zinc and iron sulfides to get the metals from their ores Hydrogen use in the petroleum refining includes many processing schemes such as hydrocracking hydrofinishing of lube oils hydrodealkyla tion and hydrodesulfurization of petroleum fractions and residues Hydro cracking of petroleum resids is becoming more important to produce lighter petroleum distillates of low sulfur and nitrogen content to meet stringent governmentmandated product specifications to control pollution In the petrochemical field hydrogen is used to hydrogenate benzene to cyclohexane and benzoic acid to cyclohexane carboxylic acid These compounds are precursors for nylon production Chapter 10 It is also used to selectively hydrogenate acetylene from C4 olefin mixture As a constituent of synthesis gas hydrogen is a precursor for ammo nia 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 Direct use of H2 provides greater efficiency and envi ronmental benefits3 Due to the increasing demand for hydrogen many separation tech niques 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 adsorption diffusion and cryogenic phase separation are used to achieve this goal 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 com ponents at the low temperatures and high pressures used The vapor phase is rich in hydrogen and the liquid phase contains the hydrocar bons Hydrogen is separated from the vapor phase at high purity Nonhydrocarbon Intermediates 113 Chapter 4 12201 1100 AM Page 113 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 operat ing conditions Gases with smaller molecular sizes such as helium and hydrogen permeate membranes more readily than larger molecules such as methane and ethane4 An example of membrane separator is the hol low fiber type shown in Figure 42 After the feed gas is preheated and filtered it enters the membrane separation section This is made of a per meater vessel containing 12inch diameter bundles resemble filter car tridges 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 hol low fiber and exits at a lower pressure The less permeable hydrocarbons flow around the fiber walls to a perforated center tube and exit at approx imately feed pressure It has been reported that this system can deliver a reliable supply of 95 pure hydrogen from offgas streams having as low as 15 H25 SULFUR Sulfur is a reactive nonmetallic element naturally found in nature in a free or combined state Large deposits of elemental sulfur are found in various parts of the world with some of the largest being along the coastal plains of Louisiana In its combined form sulfur is naturally pres ent 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 hydro gen sulfide Different processes have been developed for obtaining sul fur and sulfuric acid from these three sources The Frasch process developed in 1894 produces sulfur from under ground deposits Smelting iron ores produces large amounts of sulfur dioxide which is catalytically oxidized to sulfur trioxide for sulfuric acid production This process is declining due to pollution control measures and the presence of some impurities in the product acid Currently sulfur is mainly produced by the partial oxidation of hydro gen sulfide through the Claus process The major sources of hydrogen sulfide are natural gas and petroleum refinery streams treatment opera tions It has been estimated that 9095 of the worlds recovered sulfur is produced through the Claus process6 Typical sulfur recovery ranges from 90 for a lean acid gas feed to 97 for a rich acid gas feed7 114 Chemistry of Petrochemical Processes Chapter 4 12201 1100 AM Page 114 Nonhydrocarbon Intermediates 115 Figure 42 Permeator for gas separation5 Chapter 4 12201 1100 AM Page 115 USES OF SULFUR The most important use of sulfur is for sulfuric acid production Other uses range from dusting powder for roses to rubber vulcanization to sulfur asphalt pavements Flower sulfur is used in match production and in cer tain pharmaceuticals Sulfur is also an additive in high pressure lubricants Sulfur can replace 3050 of the asphalt in the blends used for road construction Road surfaces made from asphaltsulfur blends have nearly double the strength of conventional pavement and it has been claimed that such roads are more resistant to climatic conditions The impregna tion of concrete with molten sulfur is another potential large sulfur use Concretes impregnated with sulfur have better tensile strength and cor rosion resistance than conventional concretes Sulfur is also used to pro duce phosphorous pentasulfide a precursor for zinc dithiophosphates used as corrosion inhibitors Sulfur reacts with nitrogen to form polymeric sulfur nitrides SNx or polythiazyls These polymers were found to have the optical and electri cal properties of metals8 THE CLAUS PROCESS This process includes two main sections the burner section with a reaction chamber that does not have a catalyst and a Claus reactor sec tion 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 sulfur The two reactions are exothermic H2S 32O2 r SO2 H2O H 519 to 577 KJ 3H2S 32O2 r 3x Sx 3H2O H 607 to 724 KJ 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 Figure 43 three reactors are used9 The last reactor contains a selective oxidation catalyst of high efficiency The reaction is slightly exothermic 2H2S SO2 r 3x Sx 2H2O H 88 to 146 KJ 116 Chemistry of Petrochemical Processes Chapter 4 12201 1100 AM Page 116 After each reaction stage sulfur is removed by condensation so that it does not collect on the catalyst The temperature in the catalytic con verter should be kept over the dew point of sulfur to prevent condensa tion on the catalyst surface which reduces activity Due to the presence of hydrocarbons in the gas feed to the burner sec tion 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 COS and CS2 to sulfur and carbon oxides Mercaptans in the acid gas feed results in an increase in the air demand For example approximately 513 increase in the air required is anticipated if about 2 mol mercaptans are present7 The increase in the air requirement is essentially a function of the type of mercaptans present The oxidation of mercaptans could be represented as CH3 SH 3O2 r SO2 CO2 2H2O C2H5SH 92O2 r SO2 2CO2 3H2O Sulfur dioxide is then reduced in the Claus reactor to elemental sulfur SULFURIC ACID H2SO4 Sulfuric acid is the most important and widely used inorganic chemi cal The 1994 US production of sulfuric acid was 892 billion pounds Nonhydrocarbon Intermediates 117 Figure 43 The Super Claus process for producing sulfur9 1 main burner 24 68 condensers 35 Claus reactors 7 reactor with selective oxidation catalyst Chapter 4 12201 1100 AM Page 117 most used industrial chemical10 Sulfuric acid is produced by the con tact process where sulfur is burned in an air stream to sulfur dioxide which is catalytically converted to sulfur trioxide The catalyst of choice is solid vanadium pentoxide V2O5 The oxidation reaction is exother mic and the yield is favored at lower temperatures SO2 g 12O2 g r SO3 g H 989 KJ The reaction occurs at about 450C 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 SO3 from the gas mixture exiting from the reactor favors the conversion of SO2 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 spe cial coolers are used to cool the acid SO3g H2O1 r H2SO4l Uses of Sulfuric Acid Sulfuric acid is primarily used to make fertilizers It is also used in other major industries such as detergents paints pigments and pharmaceuticals CARBON BLACK Carbon black is an extremely fine powder of great commercial impor tance 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 func tion of the production method 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 cat alytic and thermal cracking units are more suitable feedstocks due to their high carbonhydrogen ratios These feeds produce blacks with a 118 Chemistry of Petrochemical Processes Chapter 4 12201 1100 AM Page 118 carbon content of approximately 92 wt Coke produced from delayed and fluid coking units with low sulfur and ash contents has been investi gated as a possible substitute for carbon black11 Three processes are cur rently used for the manufacture of carbon blacks These are the channel the furnace and the thermal processes THE CHANNEL PROCESS This process is only of historical interest because not more than 5 of the blacks are produced via this route In this process the feed eg natural gas is burned in small burners with a limited amount of air Some methane is completely combusted to carbon dioxide and water produc ing enough heat for the thermal decomposition of the remaining natural gas The two main reactions could be represented as CH4 2O2 r CO2 2H2O H 799 KJ CH4 r C H2 H 92KJ The formed soot collects on cooled iron channels from which the carbon black is 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 This is a more advanced partial combustion process The feed 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 The average particle diameter of the blacks from the oil furnace process ranges between 200500 Å while it ranges between 400700 Å from the gas furnace process Figure 44 shows the oil furnace black process12 THE THERMAL PROCESS In this process the feed natural gas is pyrolyzed in preheated fur naces lined with a checker work of hot bricks The pyrolysis reaction pro duces carbon which collects on the bricks The cooled bricks are then Nonhydrocarbon Intermediates 119 Chapter 4 12201 1100 AM Page 119 reheated after carbon black is collected The average particle diameter from this process is large and ranges between 1800 Å for the fine ther mal and 5000 Å for medium thermal black PROPERTIES AND USES OF CARBON BLACK The important properties of carbon black are particle size surface area and pH These properties are functions of the production process and the feed properties Channel blacks are generally acidic while those produced by the Furnace and Thermal processes 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 aver age particle size are not suitable for tire bodies and tread bases but they 120 Chemistry of Petrochemical Processes Figure 44 Carbon black oil black by furnace process of Ashland Chemical Co12 Chapter 4 12201 1100 AM Page 120 are used in inner tubes footwear and paint pigment Gas and oil fur nace blacks are the most important forms of carbon blacks and are gen erally used in tire treads and tire bodies Table 41 shows a typical analysis of carbon black from an oil furnace process 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 hoses etc and the rest is used in such items as paints printing ink etc The world capacity of carbon black was approximately 17 billion pounds in 199813 US projected con sumption for the year 2003 is approximately 39 billion pounds SYNTHESIS GAS Synthesis gas generally refers to a mixture of carbon monoxide and hydrogen The ratio of hydrogen to carbon monoxide varies according to the type of feed the method of production and the end use of the gas During World War II the Germans obtained synthesis gas by gasify ing coal The mixture was used for producing a liquid hydrocarbon mix ture in the gasoline range using FischerTropsch technology Although this route was abandoned after the war due to the high production cost of these hydrocarbons it is currently being used in South Africa where coal is inexpensive SASOL II and III There are different sources for obtaining synthesis gas It can be pro duced by steam reforming or partial oxidation of any hydrocarbon rang ing from natural gas methane to heavy petroleum residues It can also Nonhydrocarbon Intermediates 121 Table 41 Selected properties of carbon black from an oil furnace process General High Analysis purpose abrasion Conductive Volatile matter wt 09 16 16 pH 91 90 80 Average particle diameter Å 550 280 190 Surface area m2g electron microscope method 40 75 120 Surface area m2g nitrogen adsorption method 25 75 220 Chapter 4 12201 1100 AM Page 121 be obtained by gasifying coal to a medium Btu gas medium Btu gas con sists of variable amounts of CO CO2 and H2 and is used principally as a fuel gas Figure 45 shows the different sources of synthesis gas A major route for producing synthesis gas is the steam reforming of natural gas over a promoted nickel catalyst at about 800C CH4g H2Og r COg 3H2g This route is used when natural gas is abundant and inexpensive as it is in Saudi Arabia and the USA In Europe synthesis gas is mainly produced by steam reforming naph tha Because naphtha is a mixture of hydrocarbons ranging approxi mately from C5C10 the steam reforming reaction may be represented using nheptane CH3CH25CH3 7H2Og r 7COg 15H2g As the molecular weight of the hydrocarbon increases lower HC feed ratio the H2CO product ratio decreases The H2CO product ratio is approximately 3 for methane 25 for ethane 21 for heptane and less than 2 for heavier hydrocarbons Noncatalytic partial oxidation of hydro carbons is also used to produce synthesis gas but the H2CO ratio is lower than from steam reforming 122 Chemistry of Petrochemical Processes Figure 45 The different sources and routes to synthesis gas Chapter 4 12201 1100 AM Page 122 CH4g 12O2 g r CO g 2H2 g In practice this ratio is even lower than what is shown by the stoi chiometric equation because part of the methane is oxidized to carbon dioxide and water When resids are partially oxidized by oxygen and steam at 14001450C and 5560 atmospheres the gas consists of equal parts of hydrogen and carbon monoxide Table 42 compares products from steam reforming natural gas with products from partial oxidation of heavy fuel oil14 USES OF SYNTHESIS GAS 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 hydrocarbons ranging from gases to naph tha to gas oil using Fischer Tropsch technology This process may offer an alternative future route for obtaining olefins and chemicals The hydroformylation reaction Oxo synthesis is based on the reaction of synthesis gas with olefins for the production of Oxo aldehydes and alco hols Chapters 5 7 and 8 Synthesis gas is a major source of hydrogen which is used for pro ducing 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 The production of synthesis gas from methane and the major chemi cals based on it are noted in Chapter 5 Hydrocarbons from Synthesis Gas Fischer Tropsch Synthesis FTS Most of the production of hydrocarbons by Fischer Tropsch method uses synthesis gas produced from sources that yield a relatively low Nonhydrocarbon Intermediates 123 Table 42 Composition of synthesis gas from steam reforming natural gas and partial oxidation of fuel oil14 Volume dry sulfur free Process CO H2 CO2 N2A CH4 Steam reforming natural gas 155 757 81 02 05 Partial oxidationheavy fuel oil 475 467 43 14 03 Chapter 4 12201 1100 AM Page 123 H2CO ratio such as coal gasifiers This however does not limit this process to low H2CO gas feeds The only largescale commercial process using this technology is in South Africa where coal is an abun dant energy source The process of obtaining liquid hydrocarbons from coal through FTS is termed indirect coal liquefaction It was originally intended for obtaining liquid hydrocarbons from solid fuels15 However this method may well be applied in the future to the manufacture of chemicals through cracking the liquid products or by directing the reac tion to produce more olefins The reactants in FTS are carbon monoxide and hydrogen The reaction may be considered a hydrogenative oligomerization of carbon monoxide in presence of a heterogeneous catalyst The main reactions occurring in FTS are represented as16 2nH2 nCO r CnH2n nH2O olefins 2n 1 H2 nCO r CnH2n2 nH2O paraffins 2nH2 nCO r CnH2n2 O nl H2O alcohols The coproduct water reacts with carbon monoxide the shift reaction yielding hydrogen and carbon dioxide CO H2O r CO2 H2 The gained hydrogen from the water shift reaction reduces the hydrogen demand for FTS Water gas shift proceeds at about the same rate as the FT reaction Studies of the overall water shift reaction in FT synthesis have been reviewed by Rofer Deporter17 Another side reaction also occurring in FTS reactors is the disproportionation of carbon monoxide to carbon dioxide and carbon 2CO r CO2 C This reaction is responsible for the deposition of carbon in the reactor tubes in fixedbed reactors and reducing heat transfer efficiency Fischer Tropsch synthesis is catalyzed by a variety of transition met als such as iron nickel and cobalt Iron is the preferred catalyst due to its higher activity and lower cost Nickel produces large amounts of methane while cobalt has a lower reaction rate and lower selectivity than iron By comparing cobalt and iron catalysts it was found that cobalt promotes more middledistillate products In FTS cobalt produces 124 Chemistry of Petrochemical Processes Chapter 4 12201 1100 AM Page 124 hydrocarbons plus water while iron catalyst produces hydrocarbons and carbon dioxide18 It appears that the iron catalyst promotes the shift reac tion more than the cobalt catalyst Dry19 reviewed types of catalysts used in FT processes and their preparation Two reactor types are used commercially in FTS a fixed bed and a fluidbed The fixedbed reactors usually run at lower temperatures to avoid carbon deposition on the reactor tubes Products from fixedbed reactors are characterized by low olefin content and they are generally heavier than products from fluidbeds Heat distribution in fluidbeds however is better than fixedbed reactors and fluidbeds are generally operated at higher temperatures Figure 46 shows the Synthol fluidbed reactor20 Products are characterized by having more olefins a high per cent of light hydrocarbon gases and lower molecular weight product slate than from fixed bed types Table 43 compares the feed the reaction conditions and the products from the two reactor systems Fischer Tropsch technology is best exemplified by the SASOL proj ects in South Africa After coal is gasified to a synthesis gas mixture it is purified in a rectisol unit The purified gas mixture is reacted in a syn thol unit over an ironbased catalyst The main products are gasoline diesel fuel and jet fuels Byproducts are ethylene propylene alpha olefins sulfur phenol and ammonia which are used for the production of downstream chemicals21 Nonhydrocarbon Intermediates 125 Figure 46 A flow chart of the Synthol process20 Chapter 4 12201 1100 AM Page 125 A slurry bed reactor is in a pilot stage investigation This type is char acterized by having the catalyst in the form of a slurry The feed gas mix ture is bubbled through the catalyst suspension Temperature control is easier than the other two reactor types An added advantage to slurrybed reactor is that it can accept a synthesis gas with a lower H2CO ratio than either the fixedbed or the fluidbed reactors Reactions occurring in FTS are essentially bond forming and they release a large amount of heat This requires an efficient heat removal system The FTS mechanism could be considered a simple polymerization reaction the monomer being a C1 species derived from carbon monox ide16 This polymerization follows an AndersonSchulzFlory distribu tion of molecular weights This distribution gives a linear plot of the logarithm of yield of product in moles versus carbon number22 Under the assumptions of this model the entire product distribution is deter mined by one parameter α the probability of the addition of a carbon atom to a chain Figure 4716 Much work has been undertaken to understand the steps and interme diates by which the reaction occurs on the heterogeneous catalyst sur face However the exact mechanism is not fully established One approach assumes a firststep adsorption of carbon monoxide on the cat alyst surface followed by a transfer of an adsorbed hydrogen atom from an adjacent site to the metal carbonyl MCO 126 Chemistry of Petrochemical Processes Table 43 Typical analysis of products from FischerTropsch fixed and fluidbed reactors Conditions FixedBed FluidBed Temperature range F 425450 625650 Conversion 65 85 H2CO ratio 17 28 Products Hydrocarbon Gases C1C4 211 510 C5Cl2 190 310 C13C18 150 50 C19C31 Heavy oil 410 60 Oxygenates 39 70 Chapter 4 12201 1100 AM Page 126 Note M represents a catalyst surface adsorption site Successive hydrogenation produces a metalmethyl species accompanied by the release of water Nonhydrocarbon Intermediates 127 Figure 47 Yields of various products from FTS16 Chapter 4 12201 1100 AM Page 127 In a subsequent step the insertion of CO between the metal and the adsorbed methyl group occurs followed by hydrogenation and elimina tion of water 128 Chemistry of Petrochemical Processes 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 oxygenates in FTS products Chapter 4 12201 1100 AM Page 128 Alternatively an intermediate formation of an adsorbed methylene on the catalyst surface through the dissociative adsorption of carbon monox ide has been considered Nonhydrocarbon Intermediates 129 The formed metal carbide MC is then hydrogenated to a reactive methylene metal species The methylene intermediate 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 produces a long chain adsorbed alkyl The adsorbed alkyl species can either terminate to a paraffin by a hydro genation step or to an olefin by a dehydrogenation step The carbide mechanism however does not explain the formation of oxy genates in FTS products23 Chapter 4 12201 1100 AM Page 129 NAPHTHENIC ACIDS Naphthenic acids are a mixture of cycloparaffins with alkyl side chains ending with a carboxylic group The lowmolecularweight naph thenic acids 812 carbons are compounds having either a cyclopentane or a cyclohexane ring with a carboxyalkyl side chain These compounds are normally found in middle distillates such as kerosine and gas oil High boiling napthenic acids from the lube oils are monocarboxylic acids Cl4Cl9 with an average of 26 rings Naphthenic acids constitute about 50 wt of the total acidic com pounds in crude oils Naphthenicbased crudes contain a higher percent age of naphthenic acids Consequently it is more economical to isolate these acids from naphthenicbased crudes24 The production of naphthenic acids from middle distillates occurs by extraction with 710 caustic solution 130 Chemistry of Petrochemical Processes The formed sodium salts which are soluble in the lower aqueous layer are separated from the hydrocarbon 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 Properties of two naphthenic acid types are shown in Table 4425 USES OF NAPHTHENIC ACIDS AND ITS SALTS Free naphthenic acids are corrosive and are mainly used as their salts and esters The sodium salts are emulsifying agents for preparing agri cultural 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 antioxidant Lead zinc and barium naphthenates are wetting agents used as dispersion agents for paints Some oil soluble metal naphthenates such as those of zinc cobalt and lead are used as Chapter 4 12201 1100 AM Page 130 driers in oilbased paints Among the diversified uses of naphthenates is the use of aluminum naphthenates as gelling agents for gasoline flame throw ers napalm Manganese naphthenates are wellknown oxidation catalysts CRESYLIC ACID Cresylic acid is a commercial mixture of phenolic compounds includ ing phenol cresols and xylenols This mixture varies widely according to its source Properties of phenol cresols and xylenols are shown in Table 4526 Cresylic acid constitutes 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 aque ous 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 petro leum fractions especially cracked gasolines which contain higher per centages of phenols It is also extracted from coal liquids Strong alkaline solutions are used to extract cresylic acid The aque ous layer contains in addition to sodium phenate and cresylate a small amount of sodium naphthenates and sodium mercaptides The reaction between cresols and sodium hydroxide gives sodium cresylate Nonhydrocarbon Intermediates 131 Table 44 Properties of two types of naphthenic acids25 Test Type A Type B Density d4 20 0972 0987 Viscosity SU210 F 401 1590 Pour point F 30 40 Refractive index d4 20 1476 1503 Average molecular weight of deoiled acids 206 330 Unsaponifiable matter wt 125 63 Acid number mg KOHg 235 Used to produce driers Used to produce inhibitors and emulsifiers Chapter 4 12201 1100 AM Page 131 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 12O2 r RSSR H2O Free cresylic acid is obtained by treating the solution with a weak acid or dilute sulfuric acid Refinery flue gases containing CO2 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 solution27 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 132 Chemistry of Petrochemical Processes Table 45 Properties of Phenol Cresols and Xylenols26 Name Formula MPC BPC 204C pKa Ka 1010 Phenol 425 182 10722 100 11 Cresols oCresol 31 191 102734 102 063 mCresol 11 202 10336 1001 098 pCresol 355 202 10178 1017 067 Xylenols 24Dimethylphenol 26 211 09650 25Dimethylphenol 75 212 34Dimethylphenol 625 225 09830 35Dimethylphenol 68 2195 09680 Chapter 4 12201 1100 AM Page 132 Uses of Cresylic Acid 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 phosphates are produced from a mixture of cresols and phosphorous oxychloride The esters are plasticizers for vinyl chloride polymers They are also gasoline additives for reducing carbon deposits in the combustion chamber REFERENCES 1 Ohta T Solar Energy Pergamon Press Oxford England 1979 p 9 2 Gas Processing Handbook Hydrocarbon Processing Vol 71 No 4 1992 p 110 3 Raman V Oil and Gas Journal July 12 1999 p 5 4 Chiu C H Advances in Gas Separation Hydrocarbon Processing Vol 69 No 1 1990 pp 6972 5 Shaver K G Poffenbarger G L and Grotewold D R Membranes Recover Hydrogen Hydrocarbon Processing Vol 70 No 6 1991 pp 7779 6 Chou J S et al Mercaptans Affect Claus Units Hydrocarbon Processing Vol 70 No 4 1991 pp 3942 7 Yen C Chen D H and Maddox R N Chemical Engineering Communications Vol 52 1987 p 237 8 Chemical and Engineering News May 26 1976 pp 1819 9 Gas Processing Handbook Hydrocarbon Processing Vol 69 No 4 1990 p 97 10 Chemical and Engineering News April 10 1995 p 17 11 Gotshall W W Reprints Division of Petroleum Chemistry ACS Vol 20 No 2 1975 12 Petrochemical Handbook Hydrocarbon Processing Vol 58 No 11 1979 p 162 13 Chemical Industries Newsletter JanMar 1999 p 5 14 Foo K W and Shortland I Hydrocarbon Processing Vol 55 No 5 1976 pp 149152 15 Bukur D B Lang X Patel S A Zimmerman W H Rosynek M P and Withers H P Texas A M Univ TAMU Proc 8th Indirect Liquefaction Contractors Review Meeting Pittsburgh 1988 16 Srivastava R D et al Catalysts for Fischer Tropsch Hydrocarbon Processing Vol 69 No 2 1990 pp 5968 Nonhydrocarbon Intermediates 133 Chapter 4 12201 1100 AM Page 133 17 RoferDepoorter C K Water Gas Shift from Fischer Tropsch in Catalytic Conversions of Synthesis Gas and Alcohols to Chemicals edited by R G Herman Plenum New York 1984 18 Lingung Xu et al Dont Rule Out Iron Catalysts for FischerTropsch Synthesis CHEMTECH Vol 29 No 1 1998 pp 4753 19 Dry M E The Fischer Tropsch Synthesis in Catalysis Science and Technology edited by J R Anderson and M Boudart Springer Verlag 1981 20 Deckwer W D FT Process Alternatives Hold Promise Oil and Gas Journal Vol 78 10 Nov 1980 pp 198208 21 Layman P L Chemical and Engineering News Aug 8 1994 pp 1224 22 Anderson R B The Fischer Tropsch Synthesis Academic Press Orlando Fla 1984 23 Rober M FischerTropsch Synthesis in Catalysis in C1 Chemistry edited by W Keim D Reidel Publishing Company Dordrecht The Netherlands 1983 pp 4187 24 Lochte H L and Littman E R Petroleum Acids and Bases Chemical Publishing Company Inc 1955 p 124 25 Matson J A Oil and Gas Journal March 24 1980 pp 9394 26 Hatch L F and Matar S From Hydrocarbons to Petrochemicals Gulf Publishing Co 1981 p 46 27 Fox C R Hydrocarbon Processing Vol 54 No 7 1975 pp 109111 134 Chemistry of Petrochemical Processes Chapter 4 12201 1100 AM Page 134 CHAPTER FIVE Chemicals Based on Methane INTRODUCTION As mentioned in Chapter 2 methane is a onecarbon paraffinic hydro carbon that is not very reactive under normal conditions Only a few chemicals can be produced directly from methane under relatively severe conditions Chlorination of methane is only possible by thermal or photo chemical 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 is the precursor for two major chem icals ammonia and methanol Both compounds are the hosts for many important petrochemical products Figure 51 shows the important chem icals based on methane synthesis gas methanol and ammonia1 135 Figure 51 Important chemicals based on methane synthesis gas ammonia and methanol1 Chapter 5 12201 1101 AM Page 135 CHEMICALS BASED ON DIRECT REACTIONS OF METHANE A few chemicals are based on the direct reaction of methane with other reagents These are carbon disulfide hydrogen cyanide chloromethanes and synthesis gas mixture Currently a redox fuel cell based on methane is being developed2 CARBON DISULFIDE CS2 Methane reacts with sulfur an active nonmetal element of group 6A at high temperatures to produce carbon disulfide The reaction is endothermic and an activation energy of approximately 160 KJ is required3 Activated alumina or clay is used as the catalyst at approxi mately 675C and 2 atmospheres The process starts by vaporizing pure sulfur mixing it with methane and passing the mixture over the alumina catalyst The reaction could be represented as CH4g 2S2g r CS2g 2H2Sg H298 150 KJmol Hydrogen sulfide a coproduct is used to recover sulfur by the Claus reaction A CS2 yield of 8590 based on methane is anticipated An alternative route for CS2 is by the reaction of liquid sulfur with charcoal However this method is not used very much Uses of Carbon Disulfide Carbon disulfide is primarily used to produce rayon and cellophane regenerated cellulose CS2 is also used to produce carbon tetrachloride using iron powder as a catalyst at 30C CS2 3Cl2 r CCl4 S2Cl2 Sulfur monochloride is an intermediate that is then reacted with carbon disulfide to produce more carbon tetrachloride and sulfur 2S2Cl2 CS2 r CCl4 6S The net reaction is CS2 2Cl2 r CCl4 2S 136 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 136 Carbon disulfide is also used to produce xanthates ROCSSNa as an ore flotation agent and ammonium thiocyanate as a corrosion inhibitor in ammonia handling systems HYDROGEN CYANIDE HCN Hydrogen cyanide hydrocyanic acid is a colorless liquid bp 256C 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 via the Andrussaw process using ammonia and methane in presence of air The reaction is exothermic and the released heat is used to supplement the required catalystbed energy 2CH4 2NH3 3O2 r 2HCN 6H2O A platinumrhodium alloy is used as a catalyst at 1100C 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 The Degussa process on the other hand reacts ammonia with methane in absence of air using a platinum aluminumruthenium alloy as a cata lyst at approximately 1200C The reaction produces hydrogen cyanide and hydrogen and the yield is over 90 The reaction is endothermic and requires 251 KJmol CH4 NH3 251 KJ r HCN 3H2 Hydrogen cyanide may also be produced by the reaction of ammonia and methanol in presence of oxygen NH3 CH3OH O2 r HCN 3H2O 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 nitro gen 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 and atmospheric pressure Chemicals Based on Methane 137 Chapter 5 12201 1101 AM Page 137 CHLOROMETHANES The successive substitution of methane hydrogens with chlorine pro duces a mixture of four chloromethanes Monochloromethane methyl chloride CH3Cl Dichloromethane methylene chloride CH2Cl2 Trichloromethane chloroform CHCl3 Tetrachloromethane carbon tetrachloride CCl4 Each of these four compounds has many industrial applications that will be dealt with separately Production of Chloromethanes Methane is the most difficult alkane to chlorinate The reaction is ini tiated by chlorine free radicals obtained via the application of heat ther mal or light hv Thermal chlorination more widely used industrially occurs at approximately 350370C and atmospheric pressure A typical product distribution for a CH4Cl2 feed ratio of 17 is mono 587 di 293 tri 97 and tetra 23 chloromethanes The highly exothermic chlorination reaction produces approximately 95 KJmol of HCI The first step is the breaking of the ClCl bond bond energy 5842 KJ which forms two chlorine free radicals Cl atoms hv Cl2 r 2Cl The Cl atom attacks methane and forms a methyl free radical plus HCI The methyl radical reacts in a subsequent step with a chlorine molecule forming methyl chloride and a Cl atom Cl CH4 r CH3 HCl CH3 Cl2 r CH3Cl Cl The new 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 and HCl 138 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 138 Cl CH3Cl r CH2Cl HCl The chloromethyl free radical then attacks another chlorine molecule and produces dichloromethane along with a Cl atom CH2CI Cl2 r CH2Cl2 Cl This formation of Cl free radicals continues until all chlorine is con sumed Chloroform and carbon tetrachloride are formed in a similar way by reaction of CHCl2 and CCl3 free radicals with chlorine Product distribution among the chloromethanes depends primarily on the mole ratio of the reactants For example the yield of mono chloromethane could be increased to 80 by increasing the CH4Cl2 mole ratio to 101 at 450C If dichloromethane is desired the CH4Cl2 ratio is lowered and the monochloromethane recycled Decreasing the CH4Cl2 ratio generally increases polysubstitution and the chloroform and carbon tetrachloride yield An alternative way to produce methyl chloride monochloromethane is the reaction of methanol with HCl see later in this chapter Chemicals from Methanol Methyl chloride could be further chlori nated to give a mixture of chloromethanes dichloromethane chloro form and carbon tetrachloride Uses of Chloromethanes 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 production a solvent and a refrigerant Methylene chloride has a wide variety of markets One major use is a paint remover It is also used as a degreasing solvent a blowing agent for polyurethane foams and a solvent for cellulose acetate Chloroform is mainly used to produce chlorodifluoromethane Fluoro carbon 22 by the reaction with hydrogen fluoride CHCl3 2 HF r CHClF2Cl 2HCl This compound is used as a refrigerant and as an aerosol propellent It is also used to synthesize tetrafluoroethylene which is polymerized to a heat resistant polymer Teflon 2CHClF2 r CF2CF2 2HCl Chemicals Based on Methane 139 Chapter 5 12201 1101 AM Page 139 Carbon tetrachloride is used to produce chlorofluorocarbons by the reaction with hydrogen fluoride using an antimony pentachloride SbCl5 catalyst CCl4 HF r CCl3F HCl CCl4 2HF r CCl2F2 2HCl The formed mixture is composed of trichlorofluoromethane Freon11 and dichlorodifluoromethane Freon12 These compounds are used as aerosols and as refrigerants Due to the depleting effect of chlorofluoro carbons CFCs on the ozone layer the production of these compounds may be reduced appreciably Much research is being conducted to find alternatives to CFCs with lit tle or no effect on the ozone layer Among these are HCFC123 HCCl2CF3 to replace Freon11 and HCFC22 CHClF2 to replace Freon12 in such uses as air conditioning refrigeration aerosol and foam These compounds have a much lower ozone depletion value com pared to Freon11 which was assigned a value of 1 Ozone depletion values for HCFC123 and HCFC22 relative to Freon11 equals 002 and 0055 respectively4 SYNTHESIS GAS STEAM REFORMING OF NATURAL GAS As mentioned in Chapter 4 synthesis gas may be produced from a vari ety of feedstocks Natural gas is the preferred feedstock when it is avail able from gas fields nonassociated gas or from oil wells associated gas The first step in the production of synthesis gas is to treat natural gas to remove hydrogen sulfide The purified gas is then mixed with steam and introduced to the first reactor primary reformer The reactor is con structed from vertical stainless steel tubes lined in a refractory furnace The steam to natural gas ratio varies from 45 depending on natural gas composition natural gas may contain ethane and heavier hydrocarbons and the pressure used A promoted nickel type catalyst contained in the reactor tubes is used at temperature and pressure ranges of 700800C and 3050 atmos pheres 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 equilibrium mixture that is rich in hydrogen5 140 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 140 The product gas from the primary reformer is a mixture of H2 CO CO2 unreacted CH4 and steam The main steam reforming reactions are CH4g H2Og r CO g 3H2 g H 206 KJ H800C 226 KJ CH4g 2H2Og r CO2g 4H2g H 1648 KJ For the production of methanol this mixture could be used directly with no further treatment except adjusting the H2CO CO2 ratio to approx imately 21 For producing 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 done by par tially oxidizing 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 oxi dation 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 The reaction is represented as follows CH4 12 O2 376 N2 r CO 2H2 188 N2 H 321 KJ The reactor temperature can reach over 900C in the secondary reformer due to the exothermic reaction heat Typical analysis of the exit gas from the primary and the secondary reformers is shown in Table 51 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 shift conversion carbon dioxide removal and methanation of the remaining CO and CO2 Chemicals Based on Methane 141 Table 51 Typical analysis of effluent from primary and secondary reformers Constituent Primary reformer Secondary reformer H2 47 390 CO 102 122 CO2 63 42 CH4 70 06 H2O 294 270 N2 002 170 Chapter 5 12201 1101 AM Page 141 Shift Conversion The product gas mixture from the secondary reformer is cooled then subjected to shift conversion In the shift converter carbon monoxide is reacted with steam to give carbon dioxide and hydrogen The reaction is exothermic and independ ent of pressure COg H2O g r CO2g H2g H 41 KJ 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 425500C to enhance the oxidation 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 byproduct 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 Methanation Catalytic methanation is the reverse of the steam reforming reaction Hydrogen reacts with carbon monoxide and carbon dioxide converting them to methane Methanation reactions are exothermic and methane yield is favored at lower temperatures 3H2g COg r CH4g H2Og H 206 KJ 4H2g CO2 g r CH4g 2H2Og H 1648 KJ 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 Rany nickel is the preferred catalyst Typical methanation reactor operating conditions are 200300C and approximately 10 atmospheres The product is a gas mixture of hydrogen and nitrogen hav ing an approximate ratio of 31 for ammonia production Figure 52 142 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 142 shows the ICI process for the production of synthesis gas for the manu facture of ammonia6 CHEMICALS BASED ON SYNTHESIS GAS Many chemicals are produced from synthesis gas This is a conse quence of the high reactivity associated with hydrogen and carbon monoxide gases the two constituents of synthesis gas The reactivity of this mixture was demonstrated during World War II when it was used to produce alternative hydrocarbon fuels using Fischer Tropsch technology The synthesis gas mixture was produced then by gasifying coal Fischer Tropsch synthesis of hydrocarbons is discussed in Chapter 4 Synthesis gas is also an important building block for aldehydes from olefins The catalytic hydroformylation reaction Oxo reaction is used with many olefins 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 ammonia urea nitric acid hydrazine acrylonitrile methylamines and many other minor chemicals are produced see Figure 51 Each of these chemicals is also a precursor of more chemicals Methanol the second major product from synthesis gas is a unique compound of high chemical reactivity as well as good fuel properties It Chemicals Based on Methane 143 Figure 52 The ICI process for producing synthesis gas and ammonia6 1 desul furization 2 feed gas saturator 3 primary reformer 4 secondary reformer 5 shift converter 6 methanator 7 ammonia reactor Chapter 5 12201 1101 AM Page 143 is a building block for many reactive compounds such as formaldehyde acetic acid and methylamine It also offers an alternative way to pro duce hydrocarbons in the gasoline range Mobil to gasoline MTG process It may prove to be a competitive source for producing light olefins in the future AMMONIA NH3 Ammonia is one of the most important inorganic chemicals exceeded only by sulfuric acid and lime This colorless gas has an irritating odor and is very soluble in water forming a weakly basic solution Ammonia could be easily liquefied under pressure liquid ammonia and it is an important refrigerant Anhydrous ammonia is a fertilizer by direct appli cation to the soil Ammonia is obtained by the reaction of hydrogen and atmospheric nitrogen the synthesis gas for ammonia The 1994 US ammonia production was approximately 40 billion pounds sixth highest volume chemical Ammonia Production Haber Process The production of ammonia is of historical interest because it repre sents the first important application of thermodynamics to an industrial process Considering the synthesis reaction of ammonia from its ele ments the calculated reaction heat H and free energy change G at room temperature are approximately 46 and 165 KJmol respectively Although the calculated equilibrium constant Kc 36 108 at room temperature is substantially high no reaction occurs under these condi tions and the rate is practically zero The ammonia synthesis reaction could be represented as follows N2 g 3H2 g r 2NH3 g H 461 KJmol Increasing the temperature increases the reaction rate but decreases the equilibrium Kc 500C 008 According to LeChatliers princi ple the equilibrium is favored at high pressures and at lower tempera tures Much of Habers research was to find a catalyst that favored the formation 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 144 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 144 In a commercial process a mixture of hydrogen and nitrogen exit gas from the methanator in a ratio of 31 is compressed to the desired pres sure 1501000 atmospheres The compressed mixture is then pre heated by heat exchange with the product stream before entering the ammonia reactor The reaction occurs over the catalyst bed at about 450C 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 see Figure 52 Usually a conver sion of approximately 15 per pass is obtained under these conditions Uses of Ammonia 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 Compared with hydrogen anhydrous ammonia is more manageable It is stored in iron or steel con tainers and could be transported commercially via pipeline railroad tanker cars and highway tanker trucks7 The oxidation reaction could be represented as 4NH3 3O2 r 2N2 6H2O H 3169 KJmol 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 following describes the important chemicals based on ammonia Chemicals Based on Methane 145 The highest fixed nitrogencontaining fertilizer 467 wt 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 Chapter 5 12201 1101 AM Page 145 substances such as phenol and salicylic acid By reacting with formalde hyde it produces an important commercial polymer urea formaldehyde resins that is used as glue for particle board and plywood Production The technical production of urea is based on the reaction of ammonia with carbon dioxide 146 Chemistry of Petrochemical Processes 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 stoichio metric is used to compensate for the ammonia that dissolves in the melt The reactor temperature ranges between 170220C at a pressure of about 200 atmospheres The second reaction represents the decomposition of the carbamate The reaction conditions are 200C and 30 atmospheres Decomposition in presence of excess ammonia limits corrosion problems and inhibits the decomposition 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 Figure 53 shows the Snamprogetti process for urea production8 Uses of Urea The major use of urea is the fertilizer field which accounts for approximately 80 of its production about 162 billion pounds were produced during 1994 in US About 10 of urea is used for the production of adhesives and plastics urea formaldehyde and melamine formaldehyde resins Animal feed accounts for about 5 of the urea produced Chapter 5 12201 1101 AM Page 146 Urea possesses a unique property of forming adducts with nparaffins This is used in separating C12C14 nparaffins from kerosines for deter gent production Chapter 6 Nitric Acid HNO3 Nitric acid is one of the most used chemicals The 1994 US produc tion was approximately 1765 billion pounds 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 most important use of nitric acid is to pro duce ammonium nitrate fertilizer 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 4NH3g 5O2g r 4NOg 6H2Og H 2264 KJmol 2NOg O2g r 2NO2g H 565 KJmol 3NO2g H2O1 r 2HNO3aq NOg H 334 KJmol 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 Chemicals Based on Methane 147 Figure 53 The Snamprogetti process for producing urea8 1 reactor 234 car bonate decomposers 56 crystallizing and prilling Chapter 5 12201 1101 AM Page 147 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 Opti mum nitric acid production was found to be obtained at approximately 900C and atmospheric pressure Uses of Nitric Acid The primary use of nitric acid is for the production of ammonium nitrate for fertilizers A second major use of nitric acid is in the field of explosives It is also a nitrating agent for aromatic and paraf finic compounds which are useful intermediates in the dye and explosive industries It is also used in steel refining and in uranium extraction Hydrazine H2NNH2 A colorless fuming liquid miscible with water hydrazine diazine is a weak base but a strong reducing agent Hydrazine is used as a rocket fuel because its combustion is highly exothermic and produces 620 KJmol H2NNH2 O2 r N2 2H2O 620 KJ Hydrazine is produced by the oxidation of ammonia using the Rashig process Sodium hypochlorite is the oxidizing agent and yields chlo ramine NH2Cl as an intermediate Chloramine further reacts with ammo nia producing hydrazine 2NH3 NaOCl r H2NNH2 NaCl H2O Hydrazine is then evaporated from the sodium chloride solution Hydrazine can also be produced by the Puck process The oxidizing agent is hydrogen peroxide 2NH3 H2O2 r H2NNH2 2H2O Uses of Hydrazine In addition to rocket fuel hydrazine is used as a blowing agent and in the pharmaceutical and fertilizer industries Due to the weak NN bond it is used as a polymerization initiator As a reduc ing agent hydrazine is used as an oxygen scavenger for steam boilers It is also a selective reducing agent for nitro compounds Hydrazine is a 148 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 148 good building block for many chemicals especially agricultural prod ucts which dominates its use METHYL ALCOHOL CH3OH Methyl alcohol methanol is the first member of the aliphatic alcohol family It ranks among the top twenty organic chemicals consumed in the US The current world demand for methanol is approximately 255 mil lion tonsyear 1998 and is expected to reach 30 million tons by the year 20029 The 1994 US production was 108 billion pounds Methanol was originally produced by the destructive distillation of wood wood alcohol for charcoal production Currently it is mainly pro duced from synthesis gas As a chemical compound methanol is highly polar and hydrogen bond ing is evidenced by its relatively high boiling temperature 65C its high heat of vaporization and its low volatility Due to the high oxygen content of methanol 50 wt it is being considered as a gasoline blending com pound to reduce carbon monoxide and hydrocarbon emissions in automo bile exhaust gases It was also tested for blending with gasolines due to its high octane RON 112 During the late seventies and early eighties 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 the cold engine startability due to its high vaporization heat heat of vaporization is 37 times that for gasoline its lower heating value which is approximately half that of gasoline and its corrosive properties The subject has been reviewed by Keller10 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 hydrocarbons in the gasoline range MTG process Methanol reacts almost quantitatively with isobutene and isoamylenes producing methyl tbutylether MTBE and tertiary amyl methyl ether TAME respectively Both are important gasoline additives for raising the octane number and reducing carbon monoxide and hydrocarbon exhaust emissions Additionally much of the current work is centered on the use of shapeselective catalysts to convert methanol to light olefins as a possible future source of ethylene and propylene The subject has been reviewed by Chang11 Chemicals Based on Methane 149 Chapter 5 12201 1101 AM Page 149 Production of Methanol 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 stoichiometric ratio required for methanol synthesis is 12 carbon dioxide is added to reduce the surplus hydrogen An energyefficient alternative to adjusting the COH2 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 Figure 54 is a combined reforming diagram12 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 150 Chemistry of Petrochemical Processes Figure 54 A block flow diagram showing the combined reforming for methanol synthesis12 Chapter 5 12201 1101 AM Page 150 An added advantage of combined reforming is the decrease in NOx emis sion However a capital cost increase for air separation unit of roughly 15 is anticipated when using combined reforming in comparison to plants using a single train steam reformer The process scheme is viable and is commercially proven13 The following reactions are representative for methanol synthesis COg 2H2g CH3OH1 H 128 KJmol CO2 3H2 CH3OHl H2O Old processes use a zincchromium oxide catalyst at a highpressure range of approximately 270420 atmospheres for methanol production A lowpressure process has been developed by ICI operating at about 50 atm 700 psi using a new active copperbased catalyst at 240C 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 to condense product methanol and the unreacted gases are recy cled Crude methanol from the separator contains water and low levels of byproducts which are removed using a twocolumn distillation system Figure 55 shows the ICI methanol synthesis process14 Methanol synthesis over the heterogeneous catalyst is thought to occur by a successive hydrogenation of chemisorbed carbon monoxide Chemicals Based on Methane 151 Other mechanisms have been also proposedl5 Uses of Methanol Methanol has many important uses as a chemical a fuel and a build ing block Approximately 50 of methanol production is oxidized to Chapter 5 12201 1101 AM Page 151 formaldehyde As a methylating agent it is used with many organic acids to produce the methyl esters such as methyl acrylate methylmethacry late methyl acetate and methyl terephthalate Methanol is also used to produce dimethyl carbonate and methyltbutyl ether an important gaso line additive It is also used to produce synthetic gasoline using a shape selective catalyst MTG process Olefins from methanol may be a future route for ethylene and propylene in competition with steam cracking of hydrocarbons The use of methanol in fuel cells is being investigated Fuel cells are theoretically capable of converting the free energy of oxi dation 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 H2SO416 The benefits of low emission may be offest by the high cost The following describes the major chemicals based on methanol 152 Chemistry of Petrochemical Processes Figure 55 The ICI lowpressure process for producing methanol14 1 desulfu rization 2 saturator for producing process steam 3 synthesis loop circulator 4 reactor 5 heat exchanger and separator 6 column for light ends recovery 7 column for water removal The main industrial route for producing formaldehyde is the catalyzed air oxidation of methanol Chapter 5 12201 1101 AM Page 152 A silvergauze catalyst is still used in some older processes that oper ate at a relatively higher temperature about 500C New processes use an ironmolybdenum oxide catalyst Chromium or cobalt oxides are sometimes used to dope the catalyst The oxidation reaction is exother mic and occurs at approximately 400425C and atmospheric pressure Excess air is used to keep the methanol air ratio below the explosion lim its Figure 56 shows the Haldor Topsoe ironmolybdenum oxide cat alyzed process17 Uses of Formaldehyde Formaldehyde is the simplest and most reac tive aldehyde Condensation polymerization of formaldehyde 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 Condensation of formaldehyde with acetaldehyde in presence of a strong alkali produces pentaerythritol a polyhydric alcohol for alkyd resin production Chemicals Based on Methane 153 Figure 56 The Haldor Topsoe and Nippon Kasei process for producing formalde hyde17 1 blower 2 heat exchanger 3 reactor 4 steam boiler 5 absorber 67 coolers 8 incinerator 9 heat recovery 10 methanol evaporator 11 boiler feed water Chapter 5 12201 1101 AM Page 153 Formaldehyde reacts with ammonia and produces hexamethylenete tramine hexamine 154 Chemistry of Petrochemical Processes Hexamine is a crosslinking agent for phenolic resins Methyl Chloride CH3CI Methyl chloride is produced by the vapor phase reaction of methanol and hydrogen chloride CH3OH HCI r CH3CI H2O Many catalysts are used to effect the reaction such as zinc chloride on pumice cuprous chloride and ignited alumina gel The reaction condi tions are 350C at nearly atmospheric pressure The yield is approxi mately 95 Zinc chloride is also a catalyst for a liquidphase process using con centrated hydrochloric acid at 100150C Hydrochloric acid may be generated in situ by reacting sodium chloride with sulfuric acid As men tioned earlier methyl chloride may also be produced directly from methane with other chloromethanes However methyl chloride from methanol may be further chlorinated to produce dichloromethane chlo roform and carbon tetrachloride Methyl chloride is primarily an intermediate for the production of other chemicals Other uses of methyl chloride have been mentioned with chloromethanes Acetic Acid CH3COOH 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 Chapter 5 12201 1101 AM Page 154 atmospheres The newer process uses a rhodium complex catalyst in presence of CH3I which acts as a promoter The reaction occurs at 150C and atmospheric pressure A 99 selectivity is claimed with this catalyst CH3OH CO r CH3COOH The mechanism of the carbonylation reaction is thought to involve a firststep oxidative addition of the methyl iodide promotor to the RhI complex followed by a carbonyl cis insersion step Chemicals Based on Methane 155 Carbonylation followed by reductive elimination produces back the RhI catalyst The final step is the reaction between acetyl iodide and methyl alcohol yielding acetic acid and the promotor Figure 57 is a flow diagram showing the Monsanto carbonylation process18 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 Uses of Acetic Acid 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 Chapter 5 12201 1101 AM Page 155 156 Chemistry of Petrochemical Processes Figure 57 The Monsanto methanol carbonylation process for producing acetic acid18 Chapter 5 12201 1101 AM Page 156 and textiles Terephthalic acid consumes 12 of acetic acid demand19 Acetic acid is also used to produce pharmaceuticals dyes and insecticides Chloroacetic acid from acetic acid is a reactive intermediate used to man ufacture many chemicals such as glycine and carboxymethyl cellulose Methyl Tertiary Butyl Ether CH33COCH3 MTBE is produced by the reaction of methanol and isobutene Chemicals Based on Methane 157 The reaction occurs in the liquid phase at relatively low temperatures about 50C in the presence of a solid acid catalyst Few side reactions occur such as the hydration of isobutene to tertiary butyl alcohol and methanol dehydration and formation of dimethyl ether and water However only small amounts of these compounds are produced Figure 58 is a simplified flow diagram of the BP Etherol process20 The MTBE reaction is equilibrium limited Higher temperatures increase the reaction rate but the conversion level is lower Lower tem peratures shift the equilibrium toward ether production but more catalyst Figure 58 Simplified flow diagram of the British Petroleum Etherol process20 Chapter 5 12201 1101 AM Page 157 inventory is required Therefore conventional MTBE units are designed with two reactors in series Most of the etherification reaction is achieved at an elevated temperature in the first reactor and then finished at a ther modynamically favorable lower temperature in the second reactor21 An alternative way for the production of MTBE is by using isobutane propene and methanol This process coproduces propylene oxide In this process isobutane reacts with oxygen giving tbutyl hydroperoxide The epoxide reacts with propene yielding tbutyl alcohol and propylene oxide tButyl alcohol loses water giving isobutene which reacts with methanol yielding MTBE22 The following shows the sequence of the reactions 158 Chemistry of Petrochemical Processes MTBE is an important gasoline additive because of its high octane rat ing Currently it is gaining more importance for the production of lead free gasolines It reduces carbon monoxide and hydrocarbon exhaust emissions probably the exact means is not known by reducing the aromatics in gasolines In the past few years many arguments existed regarding the use of MTBE as a gasoline additive It was found that leak age from old gasoline storage tanks pollutes underground water Compared to other constituents of gasoline MTBE is up to 10 times more soluble in water It also has little affinity for soil and unlike other gasoline components it passes through the soil and is carried by the water23 Many recommendations are being thought to reduce pollution effects of MTBE One way is to use alternative oxygenates which are not as soluble in water as MTBE Another way is by phasing out the 2 oxy gen by weight required in reformulated gasoline These changes will affect the future demand for MTBE Currently the worldwide con sumption of MTBE reached 66 billion gallons of which 65 is con sumed in the US23 CH3 CH3 CH3CH 12O2 r CH3COOH CH3 CH3 CH33COOH CH2CHCH3 r CH2CHCH3 CH33COH O CH33COH CH3OH r CH33COCH3 H2O Chapter 5 12201 1101 AM Page 158 Tertiary Amyl Methyl Ether CH3CH2CCH32OCH3 TAME can also be produced by the reaction of methanol with iso amylenes The reaction conditions are similar to those used with MTBE except the temperature is a little higher Chemicals Based on Methane 159 Similar to MTBE TAME is used as gasoline additive for its high octane rating and its ability to reduce carbon monoxide and hydrocarbon exhaust emissions Properties of oxygenates used as gasoline additives are shown in Table 5220 Dimethyl Carbonate COOCH32 Dimethyl carbonate DMC is a colorless liquid with a pleasant odor It is soluble in most organic solvents but insoluble in water The classi cal synthesis of DMC is the reaction of methanol with phosgene Because phosgene is toxic a nonphosgeneroute 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 yield24 Dimethyl carbonate is used as a specialty solvent It could be used as an oxygenate to replace MTBE It has almost three times the oxygen con tent as MTBE It has also a high octane rating However it must be eval uated in regard to economics and toxicity O O H2NCNH2 2CH3OH r CH3OCOCH3 2NH3 Methylamines Methylamines can be synthesized by alkylating ammonia with methyl halides or with methyl alcohol The reaction with methanol usually occurs at approximately 500C and 20 atmospheres in the presence of an Chapter 5 12201 1101 AM Page 159 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 MMA 43 dimethylamine DMA 24 and trimethylamine TMA 33 CH3OH NH3 r CH3NH2 H2O CH3OH CH3NH2 r CH32NH H2O CH3OH CH32NH r CH33N H2O 160 Chemistry of Petrochemical Processes Table 52 Properties of oxygenates MTBE TAME and ETBE20 Property MTBE ETBE TAME Blending octane 110 111 105 R M2 Blending octane 112 120 105 RON 130 115 Blending octane 97115 102 95105 MON Reid vapor pressure 78 40 25 psi Boiling point C 55 72 88 F 131 161 187 Density kgl 742 743 788 lbgal 619 620 841 Energy density kcall 893 925 980 kBtugal 935 969 1008 Heat of vaporization kcall 082 079 086 kBtugal nbp 086 083 090 Oxygenate requirement 150 172 167 vol 27 wt ox Solubility in water 43 12 12 wt Water pickup 14 05 06 wt Heat of reaction kcalmol 94 66 11 kBtulb mol 17 12 20 Chapter 5 12201 1101 AM Page 160 To improve the yield of mono and dimethylamines a shape selective catalyst has been tried Carbogenic sieves are microporous materials similar to zeolites which have catalytic as well as shape selective prop erties Combining the amorphous aluminum silicate catalyst used for producing the amines with carbogenic sieves gave higher yeilds of the more valuable MMA and DMA25 Uses of Methylamines 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 insec ticide Trimethylamine has only one major use the synthesis of choline a highenergy additive for poultry feed Hydrocarbons from Methanol Methanol to Gasoline MTG Process Methanol may have a more important role as a basic building block in the future because of the multisources of synthesis gas When oil and gas are depleted coal and other fossil energy sources could be converted to synthesis gas then to methanol from which hydrocarbon fuels and chemicals could be obtained During the early seventies oil prices esca lated as a result of 1973 ArabIsraeli War and much research was directed toward alternative energy sources In 1975 a Mobil research group discovered that methanol could be converted to hydrocarbons in the gasoline range with a special type of zeolite ZSM5 catalyst26 The reaction of methanol over a ZSM5 catalyst could be considered a dehydration oligomerization reaction It may be simply represented as nCH3OH r CH2n nH2O where CH2n represents the hydrocarbons paraffins olefins aromat ics The hydrocarbons obtained are in the gasoline range Table 53 shows the analysis of hydrocarbons obtained from the conversion of methanol to gasoline MTG Process27 The MTG process has been oper ating in New Zealand since 1985 The story of the discovery of the MTG process has been reviewed by Meisel28 Converting methanol to hydrocarbons is not as simple as it looks from the previous equation Many reaction mechanisms have been proposed Chemicals Based on Methane 161 Chapter 5 12201 1101 AM Page 161 and most of them are centered around the intermediate formation of dimethyl ether followed by olefin formation Olefins are thought to be the precursors for paraffins and aromatics 162 Chemistry of Petrochemical Processes Table 53 Analysis of gasoline from MTG process27 Components wt Butanes 1132 Alkylates 1286 C5 gasoline 682 1000 Components wt Paraffins 156 Olefins 117 Naphthenes 114 Aromatics 33 100 Octane Research Motor Clear 1968 874 Leaded 3 cc TELUS gal 1026 958 Reid vapor pressure psi 9 kPa 62 Specific gravity 0730 Sulfur wt Nil Nitrogen wt Nil Durene wt 38 Corrosion copper strip 1A ASTM distillation C 10 147 30 170 50 103 90 169 The product distribution is influenced by the catalyst properties as well as the various reaction parameters The catalyst activity and selec tivity are functions of acidity crystalline size silicaalumina ratio and even the synthetic procedure Since the discovery of the MTG process Chapter 5 12201 1101 AM Page 162 much work has been done on other catalyst types to maximize light olefins production The important property of ZSM5 and similar zeolites is the intercrys talline catalyst sites which allow one type of reactant molecule to dif fuse 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 catalyst is called shape selectivity Chen and Garwood document investigations regarding the various aspects of ZSM5 shape selectivity in relation to its intercrystalline and pore structure29 In general two approaches have been found that enhance selectivity toward light olefin formation One approach is to use catalysts with smaller pore sizes such as crionite chabazite and 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 lowering its acidity by decreasing the Al2OSiO3 ratio This latter approach is used to stop the reaction at the olefin stage thus limiting the steps up to the formation of olefins and suppressing the formation of higher hydrocarbons Methanol conversion to light olefins has been reviewed by Chang30 Table 54 shows the product distribution when methanol was reacted over different catalysts for maximizing olefin yield11 Chemicals Based on Methane 163 Table 54 Methanol conversion to hydrocarbons over various zeolites11 370C 1 atm 1 LHSV Hydrocarbon distribution wt in Erionite ZSM5 ZSM11 ZSM4 Mordenite C1 55 10 01 85 45 C2 04 06 01 18 03 C2 2 363 05 04 112 110 C3 18 162 60 191 59 C3 2 391 10 24 87 157 C4 57 242 250 88 138 C4 2 90 13 50 32 98 C5 aliphatic 22 140 327 48 186 A6 17 08 01 04 A7 105 53 05 09 A8 180 124 13 10 A9 75 84 22 10 A10 33 15 32 20 A11 02 266 151 Chapter 5 12201 1101 AM Page 163 OXO ALDEHYDES AND ALCOHOLS Hydroformylation Reaction Hydroformylation of olefins 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 hydrogenated to the corresponding alcohols The reaction is catalyzed with cobalt or rhodium complexes Olefins with terminal double bonds are more reac tive and produce aldehydes which are hydrogenated to the corresponding primary alcohols With olefins 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 164 Chemistry of Petrochemical Processes The largest commercial process is the hydroformylation of propene which yields nbutyraldehyde and isobutyraldehyde nButyraldehyde nbutanal is either hydrogenated to nbutanol or transformed to 2 ethylhexanol via aldol condensation and subsequent hydrogenation 2 Ethylhexanol is an important plasticizer for polyvinyl chloride This reaction is noted in Chapter 8 Other olefins applied in the hydroformylation process with subse quent hydrogenation are propylene trimer and tetramer for the produc tion of decyl and tridecyl alcohols respectively and C7 olefins from copolymers of C3 and C4 olefins for isodecyl alcohol production Several commercial processes are currently operative Some use a rhodium catalyst complex incorporating phosphine ligands HRhCOPPh32 at relatively lower temperatures and pressures and produce less branched aldehydes Older processes use a cobalt carbonyl complex HCoCO4 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 anti cipated in aqueous media than in hydrocarbons Selectivity is also higher Having more than one phase allows for complete separation of the catalyst and the products Chapter 5 12201 1101 AM Page 164 In order to make the catalysts soluble in water ionic ligands are attached to the catalyst The RhurchemieRhonePoulenc process for the production of butyraldehyde from propylene is based on this technol ogy31 Hydroformylation of higher olefins using ionic phosphine cata lysts that are solubilized in both reactants and products was investigated by Union Carbide researchers This yields a onephase homogeneous system The catalyst is recovered outside the reaction zone Although this is a singlephase system these catalysts could be induced to sepa rate into a nonpolar product and polar catalyst phases This technology provides an effective means of catalyst recovery32 Cobalt catalysts have also been investigated Hoechest researchers have developed a water soluble cobalt cluster compound that can hydroformylate olefins in a twophase system Hydroformylation of higher olefins is possible when polyethylene glycol is used as a solvent Higher olefins have greater affinity for ethylene glycol than for water therefore allowing greater reaction rates To facilitate the separation of the products pentane is added to the system The reaction takes place at 120C and 70 KPa When 1hexene is used the ratio of nheptanal to the iso was 07337533 Table 55 shows the hydroformylation conditions of some commercial processes A simplified mechanism for the hydroformylation reaction using the rhodium complex starts by the addition of the olefin to the catalyst A to form complex B The latter rearranges probably through a four centered intermediate to the alkyl complex C A carbon monoxide insertion gives the squareplanar complex D Successive H2 and CO addition produces the original catalyst and the product34 Chemicals Based on Methane 165 Table 55 Catalysts used in some commerical oxo processes and approximate conditions for propylene hydroformylation Process Catalyst Conditions Normal Ruhrchemie Co2 Co0 150C 300 atm 70 BASF HCOCO4 150C 30 MPa 70 ICI Co2 high pressure 70 Shell COPR3 180 50 atm 88 UCC HRhCOPPh33 100 30 atm 94 Chapter 5 12201 1101 AM Page 165 PPh3 is triphenyl phosphine ETHYLENE GLYCOL Ethylene glycol could be produced directly from synthesis gas using an Rh catalyst at 230C at very high pressure 3400 atm In theory five moles synthesis gas mixture are needed to produce one mole ethylene glycol35 3H2 2CO r HOCH2CH2OH Other routes have been tried starting from formaldehyde or paraformaldehyde One process reacts formaldehyde with carbon monoxide and H2 hydroformylation at approximately 4000 psi and 110C using a rhodium triphenyl phosphine catalyst with the intermedi ate formation of glycolaldehyde Glycolaldehyde is then reduced to eth ylene glycol 166 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 166 The DuPont process the oldest syngas process to produce ethylene gly col reacts formaldehyde with CO in the presence of a strong mineral acid The intermediate is glycolic acid which is esterified with methanol The ester is then hydrogenated to ethylene glycol and methanol which is recovered The net reaction from either process could be represented as Chemicals Based on Methane 167 REFERENCES 1 Hatch L F and Matar S Petrochemicals from Methane From Hydrocarbons to Petrochemicals Gulf Publishing Co Houston 1981 p 49 2 Chemical and Engineering News Aug 16 1999 p 7 3 Stevenson R M Introduction to the Chemical Process lndustries Reinhold Publishing Corporation 1966 p 293 4 AlNajjar I M CFCs Symposium Phase out Chlorofluorocarbons Chamber of Commerce and Industry Dammam Saudi Arabia No 24 1992 pp 398441 5 Shahani G H et al Hydrogen and Utility Optimization Hydrocarbon Processing Vol 77 No 9 1998 pp 143150 6 Petrochemicals Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 134 7 Steele R B A Proposal for an Ammonia Economy CHEMTECH Vol 29 No 8 1999 p 28 8 Petrochemicals Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 191 9 Hydrocarbon Processing Vol 78 No 1 1999 p 29 10 Keller J L Alcohols as Motor Fuel Hydrocarbon Processing Vol 58 No 5 1979 pp 127137 11 Chang C D Hydrocarbons from Methanol Catal Rev Sci Eng Vol 25 No 1 1983 pp 1118 and Chang C D Lang W H and Bell K Catalysis of Organic Reactions Dekker New York 1981 12 Farina G L and Supp E Produce Syngas from Methanol Hydrocarbon Processing Vol 71 No 3 1992 pp 7779 Chapter 5 12201 1101 AM Page 167 13 Schneider R V and LeBlanc J R Jr Choose Optional Syngas Route Hydrocarbon Processing Vol 71 No 3 1992 pp 5157 14 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 164 15 Matar S Mirbach M and Tayim H Catalysis in Petrochemical Processes Kluwer Publishing Company 1989 p 158 16 Chemical and Engineering News September 5 1994 p 21 17 Petrochemical Handbook Hydrocarbon Processing Vol 69 No 3 1991 p 158 18 Grove H D Hydrocarbon Processing Vol 51 No 11 1972 pp 7678 19 Hydrocarbon Processing Vol 76 No 2 1997 p 29 20 Rock K TAME Technology Merits Hydrocarbon Processing Vol 71 No 5 1992 p 87 21 Chang E J and Leiby S M Ethers Help Gasoline Quality Hydrocarbon Processing Vol 71 No 2 1992 pp 4144 22 Morse P M Producers brace for MTBE Phaseout Chemical and Engineering News April 12 1999 p 26 23 Nakamura D N HP in Processing Hydrocarbon Processing Vol 77 No 1 1998 p 15 24 CHEMTECH Vol 29 No 8 1999 p 26 US patent 5902894 11 May 1999 25 Haggin J Carbogenic Sieves Chemical and Engineering News Dec 19 1994 pp 3637 26 Chang C D and Silverstri A J MTG Origin Evolution Operation CHEMTECH Oct 1987 pp 624631 27 Oil and Gas Journal New Zealand Methanol to Gasoline Jan 14 1980 pp 9596 28 Meisel S L Catalysis Research Bears Fruit CHEMTECH Vol 18 No 1 1988 pp 3237 29 Chen N Y and Garwood W E Some Catalytic Properties of ZSM 5 a New ShapeSelective Zeolite J Cat Vol 52 1978 pp 453458 30 Chang C D Methanol Conversion To Light Olefins Catal Rev Sci Eng 26 No 344 1984 pp 323345 31 Chemical and Engineering News October 10 1994 p 28 32 Chemical and Engineering News April 17 1995 pp 2526 33 CHEMTECH Vol 29 No 3 1999 p 32 34 Gates B Katzer J and Schuit G C Chemistry of Catalytic Processes McGrawHill Book Company 1979 p 144 35 Kollar J Ethylene Glycol From Syngas CHEMTECH August 1984 pp 504510 168 Chemistry of Petrochemical Processes Chapter 5 12201 1101 AM Page 168 CHAPTER SIX Ethane and Higher ParaffinsBased Chemicals INTRODUCTION As discussed in Chapter 2 paraffinic hydrocarbons are less reactive than olefins only a few chemicals are directly based on them Neverthe less paraffinic hydrocarbons are the starting materials for the production of olefins Methanes relation with petrochemicals is primarily through synthesis gas Chapter 5 Ethane on the other hand is a major feedstock for steam crackers for the production of ethylene Few chemicals could be obtained from the direct reaction of ethane with other reagents The higher paraffinspropane butanes pentanes and heavieralso have limited direct use in the chemical industry except for the production of light olefins through steam cracking This chapter reviews the petro chemicals directly produced from ethane and higher paraffins ETHANE CHEMICALS The main source for ethane is natural gas liquids Approximately 40 of the available ethane is recovered for chemical use The only large con sumer of ethane is the steam cracking process for ethylene production A minor use of ethane is its chlorination to ethyl chloride CH3CH3 Cl2 r CH3CH2Cl HCl Byproduct HCl 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 CH2 CH2 HCl r CH3CH2Cl 169 Chapter 6 12201 1102 AM Page 169 170 Chemistry of Petrochemical Processes Figure 61 The Transcat process for producing vinyl chloride from ethane1 Chapter 6 12201 1102 AM Page 170 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 via the Transcat process In this process a combination of chlorination oxychlo rination and dehydrochlorination reactions occur in a molten salt reactor The reaction occurs over a copper oxychloride catalyst at a wide temper ature range of 310640C During the reaction the copper oxychloride is converted to copperI and copperII chlorides which are air oxidized to regenerate the catalyst Figure 61 is a flow diagram of the Transcat process for producing vinyl chloride from ethanel Vinyl chloride is an important monomer for polyvinyl chloride PVC The main route for obtaining this monomer however is via ethylene Chapter 7 A new approach to utilize ethane as an inexpensive chemi cal intermediate is to ammoxidize it to acetonitrile The reaction takes place in presence of a cobaltBzeolite CH3CH3 NH3 32O2 r CH3CN 3H2O However the process is not yet commercial2 PROPANE CHEMICALS A major use of propane recovered from natural gas is the production of light olefins 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 reactiv ity of propane than ethane due to presence of two secondary hydrogens which are easily substituted The following reviews some of the important reactions and chemicals based on propane OXIDATION OF PROPANE The noncatalytic oxidation of propane in the vapor phase is nonselec tive and produces a mixture of oxygenated products Oxidation at tem peratures below 400C produces a mixture of aldehydes acetaldehyde and formaldehyde and alcohols methyl and ethyl alcohols At higher temperatures propylene and ethylene are obtained in addition to hydro gen peroxide Due to the nonselectivity of this reaction separation of the products is complex and the process is not industrially attractive Ethane and Higher ParaffinsBased Chemicals 171 Chapter 6 12201 1102 AM Page 171 CHLORINATION OF PROPANE Production of Perchloroethylene Chlorination of propane with chlorine at 480640C yields a mixture of perchloroethylene Perchlor and carbon tetrachloride CH3CH2CH3 8Cl2 r CCl2CCl2 CCl4 8HCl Perchlor Carbon tetrachloride is usually recycled to produce more perchloroethylene 2CCl4 r CCl2CCl2 2Cl2 Perchlor may also be produced from ethylene dichloride 12 dichloroethane through an oxychlorinationoxyhydrochlorination process Trichloroethylene trichlor is coproduced Chapter 7 Perchlor and trichlor are used as metal degreasing agents and as sol vents in dry cleaning Perchlor is also used as a cleaning and drying agent for electronic equipment and as a fumigant DEHYDROGENATION OF PROPANE Propene Production The catalytic dehydrogenation of propane is a selective reaction that produces mainly propene CH3CH2CH3 r CH2CHCH3 H2 H ve The process could also be used to dehydrogenate butane isobutane or mixed LPG feeds It is a singlestage system operating at a temperature range of 540680C and 520 absolute pressures Conversions in the range of 5565 are attainable and selectivities may reach up to 95 Figure 62 shows the LummusCrest Catofin dehydrogenation process3 For a given dehydrogenation system ie operating temperature and pressure thermodynamic theory provides a limit to the per pass conver sion that can be achieved4 A general formula is Kp X2P IX2 Kp equilibrium constant at a given temperature X fraction paraffin converted to monoolefins P reaction pressure in atmospheres 172 Chemistry of Petrochemical Processes Chapter 6 12201 1102 AM Page 172 According to Le Chateliers principle conversion is increased by increas ing the temperature and decreasing the pressure Figure 63 shows the effect of temperature on the dehydrogenation of different light paraffins4 NITRATION OF PROPANE Production of Nitroparaffins Nitrating propane produces a complex mixture of nitro compounds ranging from nitromethane to nitropropanes The presence of lower nitroparaffins is attributed to carboncarbon bond fission occurring at the temperature used Temperatures and pressures are in the range of 390440C and 100125 psig respectively Increasing the mole ratio of propane to nitric acid increases the yield of nitropropanes Typical prod uct composition for 251 propaneacid ratio is5 Ethane and Higher ParaffinsBased Chemicals 173 Figure 62 The Lummus Crest Catofin dehydrogenation process3 1 reactor 2 compressor 3 liquid product recovery 4 product purification Nitropropanes are good solvents for vinyl and epoxy resins They are also used to manufacture rocket propellants Nitromethane is a fuel addi tive for racing cars Chapter 6 12201 1102 AM Page 173 Nitropropane reacts with formaldehyde producing nitroalcohols CH3CH2CH2NO2 HCHO r CH3CH2CHNO2CH2OH These difunctional compounds are versatile solvents but they are expensive nBUTANE CHEMICALS 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 gaso lines 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 which are important octane number boosters6 Another alternative outlet for surplus nbutane is its oxidation to maleic anhydride Almost all new maleic anhydride processes are based on butane oxidation 174 Chemistry of Petrochemical Processes Figure 63 Effect of temperature on the dehydrogenation of light paraffins at one atmosphere4 Chapter 6 12201 1102 AM Page 174 nButane has been the main feedstock for the production of butadiene However this process has been replaced by steam cracking hydrocar bons which produce considerable amounts of byproduct butadiene The chemistry of nbutane is more varied than that of propane partly because nbutane has four secondary hydrogen atoms available for substitu tion and three carboncarbon bonds that can be cracked at high temperatures Ethane and Higher ParaffinsBased Chemicals 175 Like propane the noncatalytic oxidation of butane yields a variety of prod ucts including organic acids alcohols aldehydes ketones and olefins Although the noncatalytic oxidation of butane produces mainly alde hydes and alcohols the catalyzed oxidation yields predominantly acids OXIDATION OF nBUTANE Acetic Acid and Acetaldehyde The oxidation of nbutane represents a good example illustrating the effect of a catalyst on the selectivity 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 Typical weight yields when nbutane is oxidized in the vapor phase at a temperature range of 360450C and approximately 7 atmospheres are formaldehyde 33 acetaldehyde 31 methanol 20 acetone 4 and mixed solvents 12 On the other hand the catalytic oxidation of a nbutane using either 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 150225C and a pressure of approximately 55 atmospheres7 CH3CH2CH2CH3 O2 r CH3COOH byproducts H2O The main byproducts are formic acid ethanol methanol acetaldehyde acetone and methylethyl ketone MEK When manganese acetate is used as a catalyst more formic acid 25 is obtained at the expense of acetic acid Chapter 6 12201 1102 AM Page 175 Maleic Anhydride Catalytic oxidation of nbutane at 490 over a cerium chloride CoMo oxide catalyst produces maleic anyhydride 2 CH3CH2CH2CH3 7 O2 r Other catalyst systems such as iron V2O5P2O5 over silica alumina are used for the oxidation In the Monsanto process Figure 64 nbutane and air are fed to a multitube fixedbed reactor which is cooled with molten salt The catalyst used is a proprietary modified vanadium oxide The exit gas stream is cooled and crude maleic anhydride is absorbed then recovered from the solvent in the stripper Maleic anhydride is fur ther purified using a proprietary solvent purification system8 A new process for the partial oxidation of nbutane to maleic anhy dride was developed by DuPont The important feature of this process is the use of a circulating fluidized bedreactor Solids flux in the rizer 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 vanadium phosphorous oxides 176 Chemistry of Petrochemical Processes Figure 64 The Monsanto process for producing maleic anhydride from butane8 1 reactor 2 absorber 3 stripper 4 fractionator 5 solvent purification Chapter 6 12201 1102 AM Page 176 VO2P2O7 type which provides 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 occurs The reaction temperature is approximately 500C Subsequent hydrogenation of maleic anhydride produces tetrahydrofuran9 Figure 65 shows the DuPont butane to maleic anhydride process Oxidation of nbutane to maleic anhydride is becoming a major source for this important chemical Maleic anhydride could also be produced by the catalytic oxidation of nbutenes Chapter 9 and benzene Chapter 10 The principal use of maleic anhydride is in the synthesis of unsaturated polyester resins These resins are used to fabricate glassfiber reinforced materials Other uses include fumaric acid alkyd resins and pesticides Maleic acid esters are important plasticizers and lubricants Maleic anhy dride could also be a precursor for 14butanediol Chapter 9 Aromatics Production Liquefied petroleum gas LPG a mixture of propane and butanes is catalytically reacted to produce an aromaticrich product The first step is Ethane and Higher ParaffinsBased Chemicals 177 Figure 65 The DuPont butane to maleic anhydride process9 Chapter 6 12201 1102 AM Page 177 assumed to be the dehydrogenation of propane and butane to the corre sponding olefins followed by oligomerization to C6 C7 and C8 olefins These compounds then dehydrocyclize to BTX aromatics The follow ing reaction sequence illustrates the formation of benzene from 2 propane molecules 2CH3CH2CH3 r CH3CH2CH2CH2CHCH2 2H2 1Hexene 178 Chemistry of Petrochemical Processes Although olefins are intermediates in this reaction the final product con tains a very low olefin concentration The overall reaction is endothermic due to the predominance of dehydrogenation and cracking Methane and ethane are byproducts from the cracking reaction Table 61 shows the product yields obtained from the Cyclar process developed jointly by British Petroleum and UOP10 A simplified flow scheme for the Cyclar process is shown in Figure 66 The process consists of a reactor section continuous catalyst regen eration unit CCR and product recovery section Stacked radialflow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled The liquid product contains about 92 wt benzene toluene and xylenes BTX Figure 67 with a balance of C9 aromatics and a low nonaromatic content10 Therefore the product could be used directly for the recovery of benzene by fractional distillation without the extrac tion step needed in catalytic reforming Table 61 Product yield from saturated LPG feed to the cyclar process10 Yields wt of fresh feed Feedstock Aromatics Hydrogen Fuel gas Propane 100 631 59 310 Butanes 100 659 52 289 Basis Highyield mode Lower cost Cyclar units can be designed but for lower overall yields Chapter 6 12201 1102 AM Page 178 Ethane and Higher ParaffinsBased Chemicals 179 Figure 66 A flow diagram showing the Cyclar process for aromatization of LPG10 Figure 67 The liquid C6 product breakdown in weight units obtained from the Cyclar process10 Chapter 6 12201 1102 AM Page 179 Interest in the use of lowervalue light paraffins for the production of aromatics led to the introduction of two new processes similar to the Cyclar process the Zforming and the Aroformer processes which were developed in Japan and Australia respectively1213 Research is also being conducted in Japan to aromatize propane in presence of carbon dioxide using a Znloaded HZSM5 catalyst14 The effect of CO2 is thought to improve the equilibrium formation of aro matics by the consumption of product hydrogen from dehydrogenation of propane through the reverse water gas shift reaction CO2 H2 a CO H2O However it was found that the effect on the equilibrium formation of aromatics is not substantial due to thermodynamic considerations A more favorable effect was found for the reaction between ethylene formed via cracking during aromatization of propane and hydrogen The reverse shift reaction consumes hydrogen and decreases the chances for the reduction of ethylene to ethane byproduct CH2CH2 H2 r CH3CH3 ISOMERIZATION OF nBUTANE Isobutane Production Because of the increasing demand for isobutylene for the production of oxygenates as gasoline additives a substantial amount of nbutane is isomerized to isobutane which is further dehydrogenated to isobutene The Butamer process Figure 68 has a fixedbed reactor containing a highly selective catalyst that promotes the conversion of nbutane to isobutane equilibrium mixture15 Isobutane is then separated in a deisobutanizer tower The nbutane is recycled with makeup hydrogen The isomerization reaction occurs at a relatively low temperature CH3CH2CH2CH3 r CH3CHCH32 Isobutane ISOBUTANE CHEMICALS As has been mentioned in Chapter 3 isobutane is mainly used as an alkylating agent to produce different compounds alkylates with a high octane number to supplement the gasoline pool Isobutane is in high 180 Chemistry of Petrochemical Processes Chapter 6 12201 1102 AM Page 180 demand as an isobutene precursor for producing oxygenates such as methyl and ethyl tertiary butyl ethers MTBE and ETBE The produc tion and use of MTBE are discussed in Chapter 5 Accordingly greater amounts of isobutane are produced from nbutane through isomerization followed by dehydrogenation to isobutene The Catofin process is cur rently 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 a cracking furnace a vapor recovery section and a product fractionation section The Coastal isobu tane cracking process is reviewed by Soudek and Lacatena16 NAPHTHABASED CHEMICALS Light naphtha containing hydrocarbons in the C5C7 range is the pre ferred feedstock in Europe for producing acetic acid by oxidation Similar to the catalytic oxidation of nbutane the oxidation of light naph tha is performed at approximately the same temperature and pressure ranges 170200C and 50 atmospheres in the presence of manganese acetate catalyst The yield of acetic acid is approximately 40 wt Light naphtha O2 r CH3COOH byproducts H2O Ethane and Higher ParaffinsBased Chemicals 181 Figure 68 The UOP Butamer process for isomerization of nbutane to isobu tane15 12 deisobutanizer 3 reactor 4 separator for separation and recy cling H2 56 stabilizer Chapter 6 12201 1102 AM Page 181 The product mixture contains essentially oxygenated compounds acids alcohols esters aldehydes ketones etc As many as 13 distillation columns are used to separate the complex mixture The number of prod ucts could be reduced by recycling most of them to extinction Manganese naphthenate may be used as an oxidation catalyst Rouchaud and Lutete have made an indepth study of the liquid phase oxidation of nhexane using manganese naphthenate A yield of 83 of C1C5 acids relative to nhexane was reported The highest yield of these acids was for acetic acid followed by formic acid The lowest yield was observed for pentanoic acid17 In Europe naphtha is the preferred feedstock for the production of syn thesis gas which is used to synthesize methanol and ammonia Chapter 4 Another important role for naphtha is its use as a feedstock for steam cracking units for light olefins production Chapter 3 Heavy naphtha on the other hand is a major feedstock for catalytic reforming The prod uct reformate containing a high percentage of C6C8 aromatic hydrocar bons is used to make gasoline Reformates are also extracted to separate the aromatics as intermediates for petrochemicals CHEMICALS FROM HIGH MOLECULAR WEIGHT nPARAFFINS High molecular weight nparaffins are obtained from different petro leum fractions through physical separation processes Those in the range of C8C14 are usually recovered from kerosines having a high ratio of these compounds Vapor phase adsorption using molecular sieve 5A is used to achieve the separation The nparaffins are then desorbed by the action of ammonia Continuous operation is possible by using two adsorption sieve columns one bed on stream while the other bed is being desorbed n Paraffins 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 length18 Table 62 shows some physical properties of C5C16 nparaffins As with shorterchain nparaffins the longer chain compounds are not highly reactive However they may be oxidized chlorinated dehydrogenated sulfonated and fermented under special conditions The C9C17 paraffins are used to produce olefins or monochlorinated paraffins for the production of detergents The 1996 capacity for the US Europe and Japan was 30 billion pounds19 182 Chemistry of Petrochemical Processes Chapter 6 12201 1102 AM Page 182 OXIDATION OF PARAFFINS Fatty Acids and Fatty Alcohols The catalytic oxidation of longchain paraffins Cl8C30 over man ganese salts produces a mixture of fatty acids with different chain lengths Temperature and pressure ranges of 105120C and 1560 atmospheres are used About 60 wt yield of fatty acids in the range of Cl2Cl4 is obtained 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 Oxidation of paraffins to fatty acids may be illustrated as RCH2CH2nCH2CH2R 52O2 r RCH2nCOOH RCH2COOH H2O Oxidation of Cl2Cl4 nparaffins using boron trioxide catalysts was extensively studied for the production of fatty alcohols20 Typical reac tion conditions are 120130C at atmospheric pressure terButyl hydroperoxide 05 was used to initiate the reaction The yield of the alcohols was 762 wt at 305 conversion Fatty acids 89 wt were also obtained Product alcohols were essentially secondary with the same number of carbons and the same structure per molecule as the parent paraffin hydrocarbon This shows that no cracking has occurred under the conditions used The oxidation reaction could be represented as RCH2CH2 Rv l2O2 r RCH2CHOHRv Ethane and Higher ParaffinsBased Chemicals 183 Table 62 Selected properties of nparaffins from C5C16 Name Formula Density BPC MPC Pentane CH3CH23CH3 0626 360 1300 Hexane CH3CH24CH3 0695 690 950 Heptane CH3CH25CH3 0684 980 905 Octane CH3CH26CH3 0703 1260 570 Nonane CH3CH27CH3 0718 1510 540 Decane CH3CH28CH3 0730 1740 300 Undecane CH3CH29CH3 0740 1960 260 Dodecane CH3CH210CH3 0749 2160 100 Tridecane CH3CH211CH3 0757 2340 60 Tetradecane CH3CH2l2CH3 0764 2520 55 Pentadecane CH3CH213CH3 0769 2660 100 Hexadecane CH3CH214CH3 0775 2800 180 Chapter 6 12201 1102 AM Page 183 nParaffins can also be oxidized to alcohols by a dilute oxygen stream 34 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 commer cial importance for the production of nonionic detergents ethyoxylates 184 Chemistry of Petrochemical Processes Nonionic detergents are discussed in Chapter 7 Other uses of these alco hols are in the plasticizer field and in monoolefin production CHLORINATION OF nPARAFFINS Chloroparaffins Chlorination of nparaffins C10C14 in the liquid phase produces a mixture of chloroparaffins 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 The reaction may be represented as R CH2 CH2Rv Cl2 r R CHCl CH2Rv HCl Monochloroparaffins in this range may be dehydrochlorinated to the cor responding monoolefins and used as alkylating agents for the production of biodegradable detergents Alternatively the monochloroparaffins are used directly to alkylate benzene in presence of a Lewis acid catalyst to produce alkylates for the detergent production These reactions could be illustrated as follows Chapter 6 12201 1102 AM Page 184 Detergent production is further discussed in Chapter 10 Polychlorination on the other hand can be carried out on the whole range of nparaffins from C10C30 at a temperature range of 80120C using a high Cl2paraffin ratio The product has a chlorine content of approximately 70 Polychloroparaffins are used as cutting oil additives plasticizers and retardant chemicals SULFONATION OF nPARAFFINS Secondary Alkane Sulfonates SAS Linear secondary alkane sulfonates are produced by the reaction between sulfur dioxide and nparaffins in the range of C15C17 RH 2SO2 2O2 H2O r RSO3H H2SO4 The reaction is catalyzed by ultraviolet light with a wavelength between 33003600Å21 The sulfonates are nearly 100 biodegradable soft and stable in hard water and have good washing properties Sodium alkanesulfonates for detergent manufacture can also be pro duced from the freeradical addition of sodium bisulfite and alpha olefins RCHCH2 NaHSO3 r RCH2CH2SO3Na FERMENTATION USING nPARAFFINS Single Cell Protein SCP The term single cell protein is used to represent a group of microbial cells such as algae and yeast that have high protein content The pro duction of these cells is not generally considered a synthetic process but microbial farming via fermentation in which nparaffins serve as the substrate Substantial research efforts were invested in the past two decades to grow algae fungi and yeast on different substrates such as nparaffins methane methanol and even carbon dioxide The product SCP is constituted mainly of protein and variable amounts of lipids car bohydrates vitamins and minerals Some of the constituents of SCP limit its usefulness for use as food for human beings but can be used for animal feed A commercial process using methanol as the substrate was developed by ICI The product Pruteen is an energyrich material con taining over 70 protein22 One of the problems facing the use of nparaffins as a substrate for Candida yeast is the presence of residual hydrocarbons in the product23 Ethane and Higher ParaffinsBased Chemicals 185 Chapter 6 12201 1102 AM Page 185 The reliability and economics of producing highquality nparaffins is a critical factor in the use of nparaffins for the production of SCP REFERENCES 1 Petrochemical Handbook Hydrocarbon Processing Vol 52 No 11 1973 p92 2 CHEMTECH March 1998 p 3 3 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 185 4 Tucci E Dufallo J M and Feldman R J Commercial Performance of the Houdry CATOFIN Process for Isobutylene Production for MTBE Catalysts and Catalytic Processes Used in Saudi Arabia Workshop KFUPM Nov 6 1991 5 Hatch L F and Matar S Petrochemicals from nParaffins Hydrocarbon Processing Vol 56 No 11 1977 pp 349357 6 Iborra M Izquierdo J F Tejero J and Cunill F Getting the Lead Out of tButyl Ether CHEMTECH Feb 1988 pp 120122 7 Saunby J B and Kiff B W Hydrocarbon Processing Vol 55 No 11 1974 pp 247252 8 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 164 9 Haggin J Innovation in Catalysis Create Environmentally Friendly THF Process Chemical and Engineering News April 3 1995 pp 2023 10 Doolan P C and Pujado P R Make Aromatics from LPG Hydrocarbon Processing Vol 68 No 9 1989 pp 7276 11 Petrochemical Handbook Hydrocarbon Processing Vol 78 No 3 p 100 12 Kondoh T et al Zeoraito Vol 9 1992 p 20 13 Babier J C and Minkkinen A JPI Petroleum Refining Conference Tokyo 1990 14 Syoichi Y et al Aromatization of Propane in CO2 Atmosphere Second Joint Saudi Japanese Workshop on Recent Developments in Selected Petroleum Refining and Petrochemical Processes KFUPM Dhahran Saudi Arabia 1213 Dec 1992 15 Gas Processing Handbook Hydrocarbon Processing Vol 69 No 4 1990 pp 7376 16 Saudek M and Lacatena J J Crack Isobutane for Isobutylene Hydrocarbon Processing Vol 69 No 5 1990 pp 7376 186 Chemistry of Petrochemical Processes Chapter 6 12201 1102 AM Page 186 17 Rouchaud J and Lutete B Industrial and Engineering Chemistry Product Research Division Vol 7 No 4 1968 pp 266270 18 Speight J G The Chemistry and Technology of Petroleum 2nd Ed Marcel Dekker Inc New York 1991 p 344 19 Chemical Industries News Letter AprilJune 1998 p8 20 Marer A and Hussain M M Second Arab Conference on Petrochemicals United Arab Emirates paper No 6 p 3 March 1523 1976 21 Petrochemical Handbook Hydrocarbon Processing Vol 58 No 11 1979 p 186 22 Petrochemical Handbook Hydrocarbon Processing Vol 64 No 11 1985 p 167 23 Kent J A ed Riegels Handbook of Industrial Chemistry 8th Ed Van Nostrand Reinhold Co New York 1983 p 685 Ethane and Higher ParaffinsBased Chemicals 187 Chapter 6 12201 1102 AM Page 187 CHAPTER SEVEN Chemicals Based on Ethylene INTRODUCTION Ethylene is sometimes known as the king of petrochemicals because more commercial chemicals are produced from ethylene than from any other intermediate This unique position of ethylene among other hydro carbon intermediates is due to some favorable properties inherent in the ethylene molecule as well as to technical and economical factors These could be summarized in the following Simple structure with high reactivity Relatively inexpensive compound Easily produced from any hydrocarbon source through steam crack ing and in high yields Less byproducts generated from ethylene reactions with other com pounds than from other olefins Ethylene reacts by addition to many inexpensive reagents such as water chlorine hydrogen chloride and oxygen to produce valuable chemicals It can be initiated by free radicals or by coordination catalysts to produce polyethylene the largestvolume thermoplastic polymer It can also be copolymerized with other olefins producing polymers with improved properties For example when ethylene is polymerized with propylene a thermoplastic elastomer is obtained Figure 71 illustrates the most important chemicals based on ethylene Global demand for ethylene is expected to increase from 79 million tons in 1997 to 114 million tons in 20051 In 1998 the US consumption of ethylene was approximately 52 billion pounds Figure 72 shows the breakdown of the 1998 US ethylene consumption2 188 Chapter 7 12201 1104 AM Page 188 OXIDATION OF ETHYLENE Ethylene can be oxidized to a variety of useful chemicals The oxida tion products depend primarily on the catalyst used and the reaction con ditions Ethylene oxide is the most important oxidation product of ethylene Acetaldehyde and vinyl acetate are also oxidation products obtained from ethylene under special catalytic conditions Chemicals Based on Ethylene 189 Figure 71 Major chemicals based on ethylene Ethylene oxide EO is a colorless gas that liquefies when cooled below 12C It is highly soluble in water and in organic solvents Chapter 7 12201 1104 AM Page 189 Ethylene oxide is a precursor for many chemicals of great commercial importance including ethylene glycols ethanolamines and alcohol ethoxylates Ethylene glycol is one of the monomers for polyesters the most widelyused synthetic fiber polymers The current US production of EO is approximately 81 billion pounds Production The main route to ethylene oxide is oxygen or air oxidation of ethylene over a silver catalyst The reaction is exothermic heat control is important 190 Chemistry of Petrochemical Processes Figure 72 Breakdown of US 1998 ethylene consumption of 52 billion lb2 LLDPE 11 PVC 15 HDPE 24 LDPE 14 EG 13 6 7 7 Vinylacetate 3 Alpha olefins and linear alcohols Styrene Others EG Ethylene glycol HDPE Highdensity polyethylene LDPE Lowdensity polyethylene LLDPE Linear lowdensity polyethylene PVC Polyvinyl chloride Chapter 7 12201 1104 AM Page 190 A concomitant reaction is the complete oxidation of ethylene to carbon dioxide and water This reaction is highly exothermic the excessive temperature increase reduces ethylene oxide yield and causes catalyst deterioration Over 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 olefins Propylene and butylenes do not form epox ides through this route3 Using oxygen as the oxidant versus air is currently favored because it is more economical4 In the process Figure 73 compressed oxygen ethylene and recy cled gas are fed to a multitubular reactor5 The temperature of oxidation Chemicals Based on Ethylene 191 Figure 73 The Scientific Design Co Ethylene Oxide process5 1 reactor 2 scrubber 34 CO2 removal 5 stripper 67 fractionators Chapter 7 12201 1104 AM Page 191 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 200300C with a short residence time of one second A selectivity of 7075 can be reached for the oxygen based process Selectivity is the ratio of moles of ethylene oxide produced per mole of ethylene reacted Ethylene oxide selectivity can be improved when the reaction temperature is lowered and the con version of ethylene is decreased higher recycle of unreacted gases Derivatives of Ethylene Oxide Ethylene oxide is a highly active intermediate It reacts with all com pounds 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 polyethylene oxide derivatives with increased water solubility Many commercial products are derived from ethylene oxide by react ing with different reagents The following reviews the production and the utility of these chemicals Ethylene Glycol CH2OHCH2OH Ethylene glycol EG is colorless syrupy liquid and is very soluble in water The boiling and the freezing points of ethylene glycol are 1972 and 132C respectively Current world production of ethylene glycol is approximately 15 bil lion pounds Most of that is used for producing polyethylene terephtha late PET resins for fiber film bottles antifreeze and other products Approximately 50 of the world EG was consumed in the manufacture of polyester fibers and another 25 went into the antifreeze EG consumption in the US was nearly 13 of the worlds The use pat tern however is different about 50 of EG is consumed in antifreeze The US production of ethylene glycol was 555 billion pounds in 1994 the 30th largest volume chemical The main route for producing ethylene glycol is the hydration of eth ylene oxide in presence of dilute sulfuric acid Figure 746 192 Chemistry of Petrochemical Processes Chapter 7 12201 1104 AM Page 192 Chemicals Based on Ethylene 193 The hydrolysis reaction occurs at a temperature range of 50100C Contact time is approximately 30 minutes Di and triethylene glycols are coproducts with the monoglycol Increasing the waterethylene oxide ratio and decreasing the contact time decreases the formation of higher glycols A waterethylene oxide ratio of 10 is normally used to get approximately 90 yield of the monoglycol However the di and the triglycols are not an economic burden because of their commercial uses A new route to ethylene glycol from ethylene oxide via the intermedi ate formation of ethylene carbonate has recently been developed by Texaco Ethylene carbonate may be formed by the reaction of carbon monoxide ethylene oxide and oxygen Alternatively it could be obtained by the reaction of phosgene and methanol Ethylene carbonate is a reactive chemical It reacts smoothly with methanol and produces ethylene glycol in addition to dimethyl carbonate Figure 74 The Scientific Design Co process for producing ethylene glycols from ethylene oxide5 1 feed tank 2 reactor 345 multiple stage evaporators 4 operates at lower pressure than 3 while 5 operates under vacuum evaporated water is recycled to feed tank 6 light ends stripper 78 vacuum distilla tion columns Chapter 7 12201 1104 AM Page 193 The reaction occurs at approximately 80130C using the proper cat alyst Many catalysts 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 resins7 This route produces ethyl ene 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 sol vents It is used as a specialty solvent a methylating agent in organic synthesis and a monomer for polycarbonate resins It may also be con sidered as a gasoline additive due to its high oxygen content and its high octane rating Alternative Routes to Producing Ethylene Glycol Ethylene glycol could also be obtained directly from ethylene by two methods the Oxirane acetoxylation and the Teijin oxychlorination processes The production of ethylene glycol from formaldehyde and carbon monoxide is noted in Chapter 5 In the Oxirane process ethylene is reacted in the liquid phase with acetic acid in the presence of a TeO2 catalyst at approximately 160 and 28 atmospheres8 The product is a mixture of mono and diacetates of ethylene glycol The acetates are then hydrolyzed to ethylene glycol and acetic acid The hydrolysis reaction occurs at approximately 107130C and 12 atmos pheres Acetic acid is then recovered for further use 194 Chemistry of Petrochemical Processes Chapter 7 12201 1104 AM Page 194 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 obsolete chlorohydrin process for the production of ethyl ene oxide In this process ethylene chlorohydrin is obtained by the cat alytic reaction of ethylene with hydrochloric acid in presence of thalliumIII chloride catalyst CH2CH2 TlCl3 H2O r ClCH2CH2OH TlCl HCl Ethylene chlorohydrin is then hydrolyzed in situ to ethylene glycol Catalyst regeneration occurs by the reaction of thalliumI chloride with copperII chloride in the presence of oxygen or air The formed CuI chloride is reoxidized by the action of oxygen in the presence of HCI T1C1 2CuC12 r TICl3 Cu2Cl2 Cu2Cl2 2HCl 12O2 r 2CuCl2 H2O The overall reaction is represented as CH2CH2 H2O l2O2 r HOCH2CH2OH Ethoxylates The reaction between ethylene oxide and longchain fatty alcohols or fatty acids is called ethoxylation Ethoxylation of C10C14 linear alcohols and linear alkylphenols produces nonionic detergents The reaction with alcohols could be represented as Chemicals Based on Ethylene 195 Chapter 7 12201 1104 AM Page 195 The solubility of the product ethoxylates can be varied according to the number of ethylene oxide units in the molecule The solubility is also a function of the chainlength of the alkyl group in the alcohol or in the phenol Longerchain alkyl groups reduce water solubility In practice the number of ethylene oxide units and the chainlength of the alkyl group are varied to either produce watersoluble or oilsoluble surface active agents Surfactants properties and micelle formation in polar and nonpolar solvents have been reviewed by Rosen9 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 olefins Similarly esters of fatty acids and polyethylene glycols are produced by the reaction of longchain fatty acids and ethylene oxide The Cl2Cl8 fatty acids such as oleic palmitic and stearic are usually ethoxylated with EO for the production of nonionic detergents and emulsifiers Ethanolamines A mixture of mono di and triethanolamines is obtained by the reac tion between ethylene oxide EO and aqueous ammonia The reaction conditions are approximately 3040C and atmospheric pressure 196 Chemistry of Petrochemical Processes The relative ratios of the ethanolamines produced depend principally on the ethylene oxideammonia ratio A low EONH3 ratio increases monoethanolamine yield Increasing this ratio increases the yield of diand triethanolamines Table 71 shows the weight ratios of ethanola mines as a function of the mole ratios of the reactants10 Ethanolamines are important absorbents of acid gases in natural gas treatment processes Another major use of ethanolamines is the produc tion of surfactants The reaction between ethanolamines and fatty acids Chapter 7 12201 1104 AM Page 196 produces ethanolamides For example when lauric acid and mono ethanolamine are used N2hydroxyethyllauramide is obtained Chemicals Based on Ethylene 197 Table 71 Weight ratios of ethanolamines as a function of the mole ratios of the reactants10 Moles of ethylene oxidemoles of ammonia 01 05 10 Monoethanolamine 7561 2531 1215 Diethanolamine 2127 2832 2326 Triethanolamine 412 37 6559 Lauric acid is the main fatty acid used for producing ethanolamides Monoethanolamides are used primarily in heavyduty powder detergents as foam stabilizers and rinse improvers 13Propanediol 13Propanediol is a colorless liquid that boils at 210211C It is sol uble in water alcohol and ether It is an intermediate for polyester pro duction It could be produced via the hydroformylation of ethylene oxide which yields 3hydroxypropionaldehyde Hydrogenation of the product produces 13propanediol O CH2 CH2 CO H2 r HOC2H4CHO HOC2H4CHO H2 r CH2 CH2 CH2 OH OH The catalyst is a cobalt carbonyl that is prepared in situ from cobaltous hydroxide and nonylpyridine is the promotor Oxidation of the aldehyde produces 3hydroxypropionic acid 13Propanediol and 3hydroxypropi onic acid could also be produced from acrolein Chaper 811 Chapter 7 12201 1104 AM Page 197 ACETALDEHYDE CH3CHO Acetaldehyde is a colorless liquid with a pungent odor It is a reactive compound with no direct use except for the synthesis of other com pounds For example it is oxidized to acetic acid and acetic anhydride It is a reactant in the production of 2ethylhexanol for the synthesis of plas ticizers and also in the production of pentaerithritol a polyhydric com pound used in alkyd resins There are many ways to produce acetaldehyde Historically it was produced either by the silvercatalyzed oxidation or by the chromium activated coppercatalyzed dehydrogenation of ethanol Currently acetaldehyde is obtained from ethylene by using a homogeneous catalyst Wacker catalyst The catalyst allows the reaction to occur at much lower temperatures typically 130 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 198 Chemistry of Petrochemical Processes The Wacker process uses an aqueous solution of palladiumII chloride copperII chloride catalyst system In the course of the reaction the Pd2 ions are reduced to Pd metal and ethylene is oxidized to acetaldehyde CH2CH2 PdCl2 H2O r CH3CHO 2HCl Pd The formed Pd is then reoxidized by the action of CuII ions which are reduced to CuI ions Pd 2CuCl2 r PdCl22CuCl The reduced CuI ions are reoxidized to CuII ions by reaction with oxygen and HCl 2CuCl 12O2 2HCl r 2CuCl2H2O The oxidation reaction may be carried out in a singlestage or a two stage process In the singlestage ethylene oxygen and recycled gas are Chapter 7 12201 1104 AM Page 198 fed into a vertical reactor containing the catalyst solution Heat is con trolled by boiling off some of the water The reaction conditions are approximately 130C and 3 atmospheres In the twostage process the reaction occurs under relatively higher pressure approximately 8 atmos pheres to ensure higher ethylene conversion The reaction temperature is approximately 130C The catalyst solution is then withdrawn from the reactor to a tubeoxidizer to effect the oxidation of the catalyst at approx imately 10 atmospheres 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 olefins with ter minal double bonds With propene for example approximately 90 yield of acetone is obtained lButene gave approximately 80 yield of methyl ethyl ketone12 Acetaldehyde is an intermediate for many chemicals such as acetic acid nbutanol pentaerithritol and polyacetaldehyde Important Chemicals from Acetaldehyde Acetic Acid Acetic acid is obtained from different sources Carbonylation of methanol is currently the major route Oxidation of butanes and butenes is an important source of acetic acid especially in the US Chapter 6 It is also produced by the catalyzed oxidation of acetaldehyde Chemicals Based on Ethylene 199 The reaction occurs in the liquid phase at approximately 65C using man ganese acetate as a catalyst Uses of acetic acid have been noted in Chapter 5 nButanol nButanol is normally produced from propylene by the Oxo reaction Chapter 8 It may also be obtained from the aldol condensation of acetaldehyde in presence of a base Chapter 7 12201 1104 AM Page 199 The uses of nbutanol are noted in Chapter 8 200 Chemistry of Petrochemical Processes Vinyl acetate is a reactive colorless liquid that polymerizes easily if not stabilized It is an important monomer for the production of polyvinyl acetate polyvinyl alcohol and vinyl acetate copolymers The US production of vinyl acetate the 40th highestvolume chemical was approximately 3 billion pounds in 1994 Vinyl acetate was originally produced by the reaction of acetylene and acetic acid in the presence of mercuryII acetate Currently it is pro duced by the catalytic oxidation of ethylene with oxygen with acetic acid as a reactant and palladium as the catalyst The process is similar to the catalytic liquidphase oxidation of ethylene to acetaldehyde The difference between the two processes is the pres ence 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 corro sion 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 approximately 117C and 5 atmospheres The palla The formed 3hydroxybutanal eliminates one mole of water in the pres ence of an acid producing crotonaldehyde Hydrogenation of crotonalde hyde produces nbutanol Chapter 7 12201 1104 AM Page 200 dium 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 O2 Selectivities of 9194 based on ethylene are attainable OXIDATIVE CARBONYLATION OF ETHYLENE Chemicals Based on Ethylene 201 The liquid phase reaction of ethylene with carbon monoxide and oxy gen over a Pd2Cu2 catalyst system produces acrylic acid The yield based on ethylene is about 85 Reaction conditions are approximately 140C and 75 atmospheres The catalyst is similar to that of the Wacker reaction for ethylene oxida tion to acetaldehyde however this reaction occurs in presence of car bon monoxide Currently the main route to acrylic acid is the oxidation of propene Chapter 8 CHLORINATION OF ETHYLENE The direct addition of chlorine to ethylene produces ethylene dichlo ride 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 intermediate in the synthesis of many ethyl ene 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 Acrylic acid Chapter 7 12201 1104 AM Page 201 CH2CH2 HOCl r ClCH2CH2OH Ethylene chlorohydrin via this route was previously used for producing ethylene oxide through an epoxidation step Currently the catalytic oxy chlorination 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 ethylhydroxy group It is also used as a solvent for cellulose acetate Vinyl Chloride CH2CHCl Vinyl chloride is a reactive gas soluble in alcohol but slightly soluble in water It is the most important vinyl monomer in the polymer industry The US production of vinyl chloride the 16th highestvolume chemical was approximately 148 billion pounds in 1994 Vinyl chloride monomer VCM was originally produced by the reac tion of hydrochloric acid and acetylene in the presence of HgCl2 catalyst The reaction is straightforward and proceeds with high conversion 96 on acetylene HCCH HCl r CH2CHCl 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 chlorination of ethylene to produce ethylene dichloride Either a liquid or a vaporphase process is used CH2CH2 Cl2 r ClCH2CH2Cl The exothermic reaction occurs at approximately 4 atmospheres and 4050C in the presence of FeCl3 CuCl2 or SbCl3 catalysts Ethylene bromide may also be used as a catalyst The second step is the dehydrochlorination of ethylene dichloride EDC to vinyl chloride and HCl The pyrolysis reaction occurs at approximately 500C and 25 atmospheres in the presence of pumice on charcoal ClCH2CH2Cl r CH2CHCl HCl 202 Chemistry of Petrochemical Processes Chapter 7 12201 1104 AM Page 202 The third step the oxychlorination of ethylene uses byproduct HCl from the previous step to produce more ethylene dichloride CH2CH2 2HCl 12O2 r ClCH2CH2Cl H2O Ethylene dichloride from this step is combined with that produced from the chlorination of ethylene and introduced to the pyrolysis furnace The reaction conditions are approximately 225C and 24 atmospheres In practice the three steps chlorination oxychlorination and dehy drochlorination are integrated in one process so that no chlorine is lost Figure 75 illustrates the process14 PERCHLORO AND TRICHLOROETHYLENE Perchloro and trichloroethylenes could be produced from ethylene dichloride by an oxychlorinationoxyhydrochlorination process without byproduct hydrogen chloride A special catalyst is used Chemicals Based on Ethylene 203 Figure 75 The European Vinyls Corporation process for producing vinyl chlo ride14 1 chlorination section 2 oxychlorination reactor 3 steam stripping and caustic treatment of water effluent 4 EDC distillation 5 pyrolysis furnace 678 VCM and EDC separation 10 byproduct reactor Chapter 7 12201 1104 AM Page 203 2CICH2CH2CI 112Cl2 74O2 r ClCHCCl2 Cl2C CCl2 3l2H2O A fluidbed reactor is used at moderate pressures at approximately 450C The reactor effluent containing chlorinated organics water a small amount of HCl carbon dioxide and other impurities is condensed in a watercooled graphite exchanger cooled in a refrigerated condenser and then scrubbed Separation of perchlor from the trichlor occurs by successive distillation Figure 76 shows the PPG process15 Perchloro and trichloroethylene may also be produced from chlorina tion of propane Chapter 6 HYDRATION OF ETHYLENE Ethanol Production Ethyl alcohol CH3CH2OH production is considered by many to be the worlds oldest profession Fermenting carbohydrates is still the 204 Chemistry of Petrochemical Processes Figure 76 The PPG Industries Inc Chloroethylene process for producing per chloro and trichloroethylene15 1 reactor 2 graphite exchanger 3 refriger ated condenser 4 scrubber 5 phase separation of perchlor from trichlor 6 7 azeotropic distillation 8 distillation train 911 crude trichlor separationpurifi cation 1016 crude perchlor separationpurification Chapter 7 12201 1104 AM Page 204 Chemicals Based on Ethylene 205 main route to ethyl alcohol in many countries with abundant sugar and grain sources Synthetic ethyl alcohol known as ethanol to differentiate it from fer mentation alcohol was originally produced by the indirect hydration of ethylene in the presence of concentrated sulfuric acid The formed mono and diethyl sulfates are hydrolyzed with water to ethanol and sulfuric acid which is regenerated 3 CH2CH2 2H2SO4 r CH3CH2OSO3H CH3CH2O2SO2 CH3CH2OSO3H CH3CH2O2SO2 3H2O r 3CH3CH2OH 2H2SO4 The direct hydration of ethylene with water is the process currently used CH2CH2 H2O r CH3CH2OH H 40 KJmol The hydration reaction is carried out in a reactor at approximately 300C and 70 atmospheres The reaction is favored at relatively lower tempera tures 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 to 45 under these con ditions and unreacted ethylene is recycled A high selectivity to ethanol is obtained 9597 Uses of Ethanol Ethanols many uses can be conveniently divided into solvent and chemical uses As a solvent ethanol dissolves many organicbased mate rials such as fats oils and hydrocarbons 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 ethers ethylamines and many ethyl esters OLIGOMERIZATION OF ETHYLENE The addition of one olefin molecule to a second and to a third etc to form a dimer a trimer etc is termed oligomerization The reaction is normally acidcatalyzed When propene or butenes are used the formed Chapter 7 12201 1104 AM Page 205 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 olefins in the C12C16 range by an insertion mecha nism A similar reaction using triethylaluminum produces linear alcohols for the production of biodegradable detergents Dimerization of ethylene to butenel has been developed recently by using a selective titaniumbased catalyst Butenel is finding new mar kets as a comonomer with ethylene in the manufacture of linear low density polyethylene LLDPE ALPHA OLEFINS PRODUCTION The C12C16 alpha olefins are produced by dehydrogenation of n paraffins dehydrochlorination of monochloroparaffins or by oligomer ization of ethylene using trialkyl aluminum Ziegler catalyst Recently it was found that iridium complexes catalyze the dehydrogenation of nparaffins to αolefins The reaction uses a soluble iridium catalyst to transfer hydrogen to the olefinic acceptor16 The following shows the oligomerization of ethylene using triethylaluminum CH3CH23Al 112 n CH2CH2 r CH3CH2n13A1 CH3CH2n13Al 3CH3CH2CHCH2 r 3CH3CH2 n1CHCH2 CH3CH2CH2CH23A1 n 468 etc The triethylaluminum and lbutene are recovered by the reaction between tributylaluminum and ethylene CH3CH2CH2CH23Al 3CH2CH2 r CH3CH23Al 3CH3CH2CHCH2 Alpha olefins are important compounds for producing biodegradable detergents They are sulfonated and neutralized to alpha olefin sulfonates AOS RCHCH2 SO3 r RCHCHSO3H RCHCHSO3H NaOH r RCHCHSO3Na H2O 206 Chemistry of Petrochemical Processes Chapter 7 12201 1104 AM Page 206 Alkylation of benzene using alpha olefins produces linear alkylbenzenes which are further sulfonated and neutralized to linear alkylbenzene sulfonates LABS These compounds constitute with alcohol ethoxy sulfates and ethoxylates the basic active ingredients for household deter gents Production of LABS is discussed in Chapter 10 Alpha olefins could also be carbonylated in presence of an alcohol using a cobalt catalyst to produce esters RCHCH2 CO RvOH r RCH2CH2COORv Transesterification with penterithritol produces penterithritol esters and releases the alcohol17 LINEAR ALCOHOLS Linear alcohols Cl2C26 are important chemicals for producing vari ous compounds such as plasticizers detergents and solvents The pro duction of linear alcohols by the hydroformylation Oxo reaction of alpha olefins followed by hydrogenation is discussed in Chapter 5 They are also produced by the oligomerization of ethylene using aluminum alkyls Ziegler catalysts The Alfol process Figure 77 for producing linear primary alcohols is a fourstep process18 In the first step triethylaluminum is produced by the reaction of ethylene with hydrogen and aluminum metal 3 CH2CH2 112 H2 Al r CH3CH23Al In the next step ethylene is polymerized by the action of triethylalu minum at approximately 120C and 130 atmospheres to trialkylalu minum Typical reaction time is approximately 140 minutes for an average C12 alcohol production Chemicals Based on Ethylene 207 Chapter 7 12201 1104 AM Page 207 208 Chemistry of Petrochemical Processes Figure 77 The Alfol process for making evennumbered straightchain alpha alcohols18 Chapter 7 12201 1104 AM Page 208 The final step is the hydrolysis of the trialkoxides with water to the cor responding evennumbered primary alcohols Alumina is coproduced and is characterized by its high activity and purity19 Chemicals Based on Ethylene 209 Linear alcohols in the range of Cl0Cl2 are used to make plasticizers Those in the range of Cl2Cl6 are used for making biodegradable deter gents They are either sulfated to linear alkylsulfates ionic detergents or reacted with ethylene oxide to the ethoxylated linear alcohols non ionic detergents The Cl6Cl8 alcohols are modifiers for wash and wear polymers The higher alcohols C20C26 are synthetic lubricants and mold release agents BUTENEl A new process developed by Institut Francais du Petrole produces butenel lbutene by dimerizing ethylene20 A homogeneous catalyst system based on a titanium complex is used The reaction is a concerted coupling of two molecules on a titanium atom affording a titanium IV cyclic compound which then decomposes to butenel by an intramolec ular βhydrogen transfer reaction21 The oxidation of triethylaluminum is carried out between 2050C with bone dry air to aluminum trialkoxides Chapter 7 12201 1104 AM Page 209 The Alphabutol process Figure 78 operates at low temperatures 5055C and relatively low pressures 2227 atm The reaction occurs in the liquid phase without a solvent The process scheme includes four sections the reactor the cocatalyst injection catalyst removal and dis tillation The continuous cocatalyst injection of an organobasic com pound deactivates the catalyst downstream of the reactor withdrawal valve to limit isomerization of lbutene to 2butene Table 72 shows the feed and product quality from the dimerization process21 ALKYLATION USING ETHYLENE Ethylene is an active alkylating agent It can be used to alkylate aromatic compounds using FriedelCrafts type catalysts Commercially 210 Chemistry of Petrochemical Processes Figure 78 A flow diagram of the Institute Francais du Petrole process for pro ducing 1butene from ethylene21 Chapter 7 12201 1104 AM Page 210 ethylene is used to alkylate benzene for the production of ethyl benzene a precursor for styrene The subject is noted in Chapter 10 REFERENCES 1 Hydrocarbon Processing Vol 78 No 3 1999 p 29 2 Chemical and Engineering News July 5 1999 p 20 Chemicals Based on Ethylene 211 Table 72 Feed and product quality from dimerization of ethylene to 1butene21 Feed polymer grade ethylene Ethylene vol 9990 min Ethane methane vol 010 max Impurities max Methane ppmv 250 C3 and heavier ppmv 10 Acetylene H2 H2O methanol ppmv 5 each CO CO2 O2 ppmv 1 each Sulfur chlorine ppmw 1 each Product polymerization grade butenel Butenel wt 9950 min Other C4s wt 030 max Ethane wt 015 max Ethylene wt 005 max Impurities max C6 olefins ppmw 50 Ethers as DME ppmw 2 Sulfur chlorine ppmw 1 Dienes acetylenics ppmw 5 each CO CO2 O2 H2O methanol ppmw 5 each Byproduct C6 cut 3Methyl 1pentene wt 230 1Hexene wt 58 2Ethyl lbutene wt 577 Hexadienes wt 13 Other C6s wt 2 5 C8 wt 97 Properties Specific gravity gcm3 068 Octane number RON 95 MON 82 Distillation end point C less than 200 Chapter 7 12201 1104 AM Page 211 3 Matar S Mirbach M and Tayim H Catalysis in Petrochemical Processes Kluwer Academic Publishers Dordrecht 1989 p 85 4 DeMaglie B Hydrocarbon Processing Vol 55 No 3 1976 pp 7880 5 Petrochemical HandbookHydrocarbon Processing Vol 70 No 3 1991 p 156 6 Olefins Industrial Outlook II Chemical Industries Newsletter SRI International Menlo Park California JulyAugust 1989 p 5 7 Hajjin J Catalytic Cosynthesis Method Developed Chemical and Engineering News Vol 70 No 18 May 4 1992 pp 2425 8 Brownstein A M Trends in Petrochemical Technology Tulsa Petroleum Publishing Co 1976 pp 153154 9 Rosen M J Surfactants Designing Structure for Performance CHEMTECH May 1985 pp 292298 10 Petroleum Refiner Nov 1957 pp 36 231 11 Piccolinie R and Plotkin J Patent Watch CHEMTECH April 1999 p 19 12 Stern E W Catal Rev Vol 73 No 1 1967 13 Hatch L F and Matar S Chemicals from Ethylene Hydrocarbon Processing Vol 57 No 4 1978 pp 155166 14 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 192 15 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 150 16 Chemical and Engineering News July 5 1999 p 38 17 Herron S Chemical and Engineering News July 18 1994 p 156 18 Petrochemical Handbook Hydrocarbon Processing Vol 54 No 11 1975 p 110 19 Oil And Gas Journal May 26 1975 pp 103108 20 Commereuc D et al Dimerize Ethylene to Butenel Hydrocarbon Processing Vol 63 No 11 1984 p 118 21 Hennico A et al Butenel Is Made from Ethylene Hydrocarbon Processing Vol 69 No 3 1990 pp 7375 212 Chemistry of Petrochemical Processes Chapter 7 12201 1104 AM Page 212 CHAPTER EIGHT Chemicals Based on Propylene INTRODUCTION Propylene the crown prince of petrochemicals is second to ethyl ene as the largestvolume hydrocarbon intermediate for the production of chemicals As an olefin propylene is a reactive compound that can react with many common reagents used with ethylene such as water chlorine and oxygen However structural differences between these two olefins result in different reactivities toward these reagents For example direct oxida tion 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 cat alyzed chlorination of propylene produces allyl chloride through substi tution of allylic hydrogens by chlorine Substitution of vinyl hydrogens in ethylene by chlorine however does not occur under normal conditions The current chemical demand for propylene is a little over one half that for ethylene This is somewhat surprising because the added com plexity 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 comparison to ethylene Nevertheless many important chemicals are produced from propylene The 1997 US propylene demand ws 31 billion pounds and most of it was used to produce polypropylene polymers and copolymers about 46 Other large volume uses are acrylonitrile for synthetic fibers Ca 13 propylene oxide Ca 10 cumene Ca 8 and oxo alcohols Ca 71 213 Chapter 8 12201 1105 AM Page 213 Figure 81 shows the important chemicals based on propylene The fol lowing discusses the chemistry of the production of these chemicals OXIDATION OF PROPYLENE 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 214 Chemistry of Petrochemical Processes Figure 81 Important chemicals based on propylene Chapter 8 12201 1105 AM Page 214 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 acry lonitrile respectively The use of peroxides for the oxidation of propylene produces propy lene oxide This compound is also obtained via a chlorohydrination of propylene followed by epoxidation ACROLEIN CH2CHCHO Acrolein 2propenal is an unsaturated aldehyde with a disagreeable odor When pure it is a colorless liquid that is highly reactive and poly merizes easily if not inhibited The main route to produce acrolein is through the catalyzed air or oxy gen oxidation of propylene CH3CHCH2 O2 r CH2CHCHO H2O H 3405 KJmol 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 propene to acrolein2 Examples of commercially used cata lysts are supported CuO used in the Shell process and Bi2O3MoO3 used in the Sohio process In both processes the reaction is carried out at temperature and pressure ranges of 300360C and 12 atmospheres 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 the acroleinacetalde hyde mixture enters as an overhead stream Acrolein is then separated from acetaldehyde in a solvent extraction tower Finally acrolein is dis tilled and the solvent recycled MECHANISM OF PROPENE OXIDATION Much work has been invested to reveal the mechanism by which propylene is catalytically oxidized to acrolein over the heterogeneous catalyst surface Isotope labeling experiments by Sachtler and DeBoer revealed the presence of an allylic intermediate in the oxidation of propy lene to acrolein over bismuth molybdate3 In these experiments propy lene was tagged once at Cl another time at C2 and the third time at C3 Chemicals Based on Propylene 215 Chapter 8 12201 1105 AM Page 215 The formed acrolein was photochemically degraded to ethylene and carbon monoxide It has been found that radioactivity was exclusively associated with ethylene when propylene tagged with 14C at C2 was used Also carbon monoxide was found to be free from radioactivity 216 Chemistry of Petrochemical Processes When propylene tagged with 14C at either Cl or C3 was oxidized to acrolein and then degraded both CH2CH2 and CO were radioactive and the ratio of radioactivity was 1 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 Chapter 8 12201 1105 AM Page 216 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 system4 Uses of Acrolein The main use of acrolein is to produce acrylic acid and its esters Acrolein is also an intermediate in the synthesis of pharmaceuticals and herbicides It may also be used to produce glycerol by reaction with iso propanol discussed later in this chapter 2Hexanedial which could be a precursor for adipic acid and hexamethylenediamine may be prepared from acrolein Tail to tail dimenization of acrolein using ruthenium cata lyst produces trans2hexanedial The trimer trans6hydroxy5formyl 27octadienal is coproduced5 Acrolein may also be a precursor for 13propanediol Hydrolysis of acrolein produces 3hydroxypropionalde hyde which could be hydrogenated to 13propanediol6 CH2CHCHO H2O r HOCH2CH2CHO H2r HOCH2CH2OH The diol could also be produced from ethylene oxide Chaper 7 Chemicals Based on Propylene 217 There are several ways to produce acrylic acid Currently the main process is the direct oxidation of acrolein over a combination molybde numvanadium 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 Acrylic acid is usually esterified to acrylic esters by adding an esterifi cation reactor The reaction occurs in the liquid phase over an ion exchange resin catalyst An alternative route to acrylic esters is via a βpropiolactone interme diate The lactone is obtained by the reaction of formaldehyde and ketene a dehydration product of acetic acid Chapter 8 12201 1105 AM Page 217 The acidcatalyzed ring opening of the fourmembered ring lactone in the presence of an alcohol produces acrylic esters 218 Chemistry of Petrochemical Processes The production of acrylic acid from the oxidative carbonylation of eth ylene is described in Chapter 7 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 AMMOXIDATION OF PROPYLENE Acrylonitrile CH2CHCN 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 oxidesbased catalyst A successful application of this reaction produces acrylonitrile from propylene CH2CHCH3 NH3 112O2 r CH2CHCN 3H2O H 518 KJmol 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 recov ered 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 streams7 Table 81 shows the specifications of acry lonitrile HCN and acetonitrile8 Both fixed and fluidbed reactors are used to produce acrylonitrile but most modern processes use fluidbed systems The MontedisonUOP process Figure 82 uses a highly active catalyst that gives 956 propylene conversion and a selectivity above 80 for acrylonitrile89 The catalysts used in ammoxidation are similar to those used in propy lene oxidation to acrolein Oxidation of propylene occurs readily at Chapter 8 12201 1105 AM Page 218 322C over BiMo catalysts However in the presence of ammonia the conversion of propylene to acrylonitrile does not occur until about 402C This may be due to the adsorption of ammonia on catalytic sites that block propylene chemisportion As with propylene oxidation the first step in the ammoxidation reaction is the abstraction of an alpha hydrogen from propylene and formation of 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 producing water The adsorbed NH species then reacts with a neighboring allylic intermediate to yield acrylonitrile Uses of Acrylonitrile Acrylonitrile is mainly used to produce acrylic fibers resins and elas tomers Copolymers of acrylonitrile with butadiene and styrene are the ABS resins and those with styrene are the styreneacrylonitrile resins SAN that are important plastics The 1998 US production of acrylonitrile was approxi mately 31 billion pounds10 Most of the production was used for ABS resins and acrylic and modacrylic fibers Acrylonitrile is also a precursor for acrylic acid by hydrolysis and for adiponitrile by an electrodimerization Chemicals Based on Propylene 219 Table 81 Typical analysis of acrylonitrile HCN and acetonitrile8 Acrylonitrile Purity dry basis wt 999 Hydrogen cyanide wtppm 5 Acetonitrile wtppm 100 Acetaldehyde wtppm 20 Acrolein wtppm 10 Acetone wtppm 40 Peroxides as H2O2 wtppm 02 Water wt 0205 Hydrogen Cyanide HCN Hydrogen cyanide wt 997 Acrylonitrile wt 01 Acetonitrile if recovered as purified product Acetonitrile wt 990 Water wt 01 Acrylonitrile wtppm 500 Acetone wtppm Absent HCN wtppm Absent Chapter 8 12201 1105 AM Page 219 220 Chemistry of Petrochemical Processes Figure 82 A flow diagram of the MontedisonUOP acrylonitrile process8 Chapter 8 12201 1105 AM Page 220 Adiponitrile NCCH24CN Adiponitrile is an important intermediate for producing nylon 66 There are other routes for its production which are discussed in Chapter 9 The way to produce adiponitrile via propylene is the electrodimeriza tion of acrylonitrile11 The following is a representation of the electro chemistry involved Chemicals Based on Propylene 221 Propylene oxide is similar in its structure to ethylene oxide but due to the presence of an additional methyl group it has different physical and chemical properties It is a liquid that boils at 339C 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 fol lowed by epoxidation This older method still holds a dominant role in propylene oxide production Chlorohydrination is the reaction between an olefin and hypochlorous acid When propylene is the reactant propy lene chlorohydrin is produced The reaction occurs at approximately 35C and normal pressure without any catalyst CH3CHCH2 HOCl r CH3CHOHCH2Cl 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 Chapter 8 12201 1105 AM Page 221 Propylene oxide is purified by steam stripping and then distillation Byproduct propylene dichloride 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 CaCl2 Figure 83 is a flow diagram of a typical chlorohydrin processl2 The second important process for propylene oxide is epoxidation with peroxides Many hydroperoxides have been used as oxygen carriers for this reaction Examples are tbutylhydroperoxide ethylbenzene hydro peroxide 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 and 35 atmospheres in presence of molybdenum cat alyst A conversion of 98 on the hydroperoxide has been reported13 222 Chemistry of Petrochemical Processes Figure 83 A flow diagram of a typical chlorohydrin process for producing propy lene oxide12 The coproduct αphenylethyl alcohol could be dehydrated to styrene Ethylbenzene hydroperoxide is produced by the uncatalyzed reaction of ethylbenzene with oxygen Chapter 8 12201 1105 AM Page 222 C6H5CH2CH3 O2 r C6H5CHCH3OOH Table 82 shows those peroxides normally used for epoxidation of propy lene and the coproducts with economic valuel2 Epoxidation with hydrogen peroxide has also been tried The epoxida tion reaction is catalyzed with compounds of As Mo and B which are claimed to produce propylene oxide in high yield Chemicals Based on Propylene 223 Table 82 Peroxides actually or potentially used to epoxidize propylene12 Peroxide feedstock Epoxidation coproduct Coproduct derivative Acetaldehyde Acetic acid Isobutane tertButyl alcohol Isobutylene Ethylbenzene αPhenylethyl alcohol Styrene Isopentane Isopentanol Isopentene and isoprene Isopropanol Acetone Isopropanol Deriatives and Uses of Propylene Oxide 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 The 1994 US production of propylene oxide the 35th highestvolume chemical was approximately 37 billion pounds Table 83 shows the 1992 US propylene oxide capacity of the three firms producing it and the processes usedl4 The following describes some of the important chemicals based on propylene oxide Propylene Glycol CH3CHOHCH2OH Propylene glycol 12propanediol is produced by the hydration of propylene oxide in a manner similar to that used for ethylene oxide Chapter 8 12201 1105 AM Page 223 Depending on the propylene oxidewater ratio di tri and polypropy lene glycols can be made the main products 224 Chemistry of Petrochemical Processes Table 83 1992 US propylene oxide capacity14 Annual capacity millions Basic Location of lb process Arco Chemical Bayport Tex 1213 Peroxidation isobutane Channelview Tex 1100 Peroxidation ethylbenzene Dow Chemical Freeport Tex 1100 Chlorohydrin Plaquemine La 450 Chlorohydrin Texaco Chemical Port Neches Tex 400 Peroxidation isobutane Of this capacity 500 million lb is slated to come on stream with a new unit in thirdquarter 1992 Slated to start up in firstquarter 1994 The reaction between propylene oxide and carbon dioxide produces propylene carbonate The reaction conditions are approximately 200C and 80 atmospheres A yield of 95 is anticipated Chapter 8 12201 1105 AM Page 224 Propylene carbonate is a liquid used as a specialty solvent and a plasticizer Allyl Alcohol CH2CHCH2OH 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 Chemicals Based on Propylene 225 Allyl alcohol is used in the plasticizer industry as a chemical intermedi ate and in the production of glycerol Glycerol via Allyl Alcohol Glycerol 123propanetriol is a trihy dric 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 obtaining glycerol It is a byproduct from the manufacture of soap from fats and oils a nonpetroleum source Glycerol is also pro duced from allyl alcohol by epoxidation using hydrogen peroxide or peracids similar to epoxidation of propylene The reaction of allyl alco hol with H2O2 produces glycidol as an intermediate which is further hydrolyzed to glycerol Other routes for obtaining glycerol are also based on propylene It can be produced from allyl chloride or from acrolein and isopropanol see following sections Chapter 8 12201 1105 AM Page 225 OXYACYLATION OF PROPYLENE 226 Chemistry of Petrochemical Processes Like vinyl acetate from ethylene allyl acetate is produced by the vaporphase oxyacylation of propylene The catalyzed reaction occurs at approximately 180C and 4 atmospheres over a PdKOAc catalyst 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 approximately 125C and 3000 pounds per square inch The typical mole H2CO ratio is 21 The reac tion is exothermic and the reactor temperature may reach 180C during the course of the reaction Selectivity to 4acetoxybutanal is approxi mately 65 at 100 allyl acetate conversionl5 CHLORINATION OF PROPYLENE Allyl Chloride CH2CHCH2Cl Allyl chloride 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 chloride is used to make allyl alcohol glycerol and epichlorohydrin The production of allyl chloride could be effected by direct chlorina tion of propylene at high temperatures approximately 500C and one atmosphere The reaction substitutes an allylic hydrogen with a chlorine atom Hydrogen chloride is a byproduct from this reaction CH2CHCH3 Cl2 r CH2CHCH2Cl HCl The major byproducts are cis and trans 13dichloropropene which are used as soil fumigants The most important use of allyl chloride is to produce glycerol via an epichlorohydrin intermediate The epichlorohydrin is hydrolyzed to glycerol Chapter 8 12201 1105 AM Page 226 Glycerol a trihydric alcohol is used to produce polyurethane foams and alkyd resins It is also used in the manufacture of plasticizers HYDRATION OF PROPYLENE Isopropanol CH3CHOHCH3 Isopropanol 2propanol 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 49th ranked 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 vaporphase process The slightly exothermic reaction evolves 515 KJmol CH3CHCH2 H2O r CH3CHOHCH3 In the liquidphase process high pressures in the range of 80100 atmos pheres are used A sulfonated polystyrene cation exchange resin is the catalyst commonly used at about 150C An isopropanol yield of 935 can be realized at 75 propylene conversion The only important by product is diisopropyl ether about 5 Figure 84 is a flow diagram of the propylene hydration process16 Gas phase hydration on the other hand is carried out at temperatures above 200C and approximately 25 atmospheres The ICI process employs WO3 on a silica carrier as catalyst Chemicals Based on Propylene 227 Chapter 8 12201 1105 AM Page 227 Older processes still use the sulfation route The process is similar to that used for ethylene in the presence of H2SO4 but the selectivity is a little lower than the modern vaporphase processes The reaction condi tions are milder than those used for ethylene This manifests the greater ease with which an isopropyl carbocation a secondary carbonium ion is formed than a primary ethyl carbonium ion CH3CHCH2 H r CH3C HCH3 CH2CH2 H r CH3C H2 Table 84 compares sulfuric acid concentrations and the temperatures used for the sulfation of different light olefins17 PROPERTIES AND USES OF ISOPROPANOL 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 problems18 228 Chemistry of Petrochemical Processes Figure 84 A flow diagram for the hydration of propylene to isopropanol16 1 propylene recovery column 2 reactor 3 residual gas separation column 4 aqueous isopropanol azeotropic distillation column 5 drying column 6 iso propyl ether separator 7 isopropyl ether extraction Chapter 8 12201 1105 AM Page 228 About 50 of isopropanol use is to produce acetone Other important synthetic uses are to produce esters of many acids such as acetic iso propyl acetate solvent for cellulose nitrate myristic and oleic acids used in lipsticks and lubricants Isopropylpalmitate is used as an emul sifier for cosmetic materials Isopropyl alcohol is a solvent for alkaloids essential oils and cellulose derivatives Acetone Production Acetone 2propanone is produced from isopropanol by a dehydro genation oxidation or a combined oxidation dehydrogenation route The dehydrogenation reaction is carried out using either copper or zinc oxide catalyst at approximately 450550C A 95 yield is obtained Chemicals Based on Propylene 229 Table 84 Acid concentration and temperatures used for the sulfation of various olefins17 Acid conc Temperature Olefins Formula range range C Ethylene CH2CH2 9098 6080 Propylene CH3CHCH2 7585 2540 Butylenes CH3CH2CHCH2 7585 1530 CH3CHCHCH3 7585 1530 CH3 Isobutylene CH3CCH2 5065 025 The direct oxidation of propylene with oxygen is a noncatalytic reac tion occurring at approximately 90140C and 1520 atmospheres In this reaction hydrogen peroxide is coproduced with acetone At 15 iso propanol conversion the approximate yield of acetone is 93 and that for H2O2 is 87 Chapter 8 12201 1105 AM Page 229 The oxidation process uses air as the oxidant over a silver or copper catalyst The conditions are similar to those used for the dehydrogena tion 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 and one atmosphere It appears that the hydrogen produced from the dehydrogenation of iso propanol and adsorbed on the catalyst surface selectively hydrogenates the carbonyl group of acrolein 230 Chemistry of Petrochemical Processes A direct route for acetone from propylene was developed using a homogeneous catalyst similar to Wacker system PdCl2CuCl2 The reaction conditions are similar to those used for ethylene oxidation to acetaldehyde19 Today most acetone is obtained via a cumene hydroperoxide process where it is coproduced with phenol This reaction is noted in Chapter 10 Propertles and Uses of Acetone Acetone is a volatile liquid with a distinct sweet odor It is miscible with water alcohols and many hydrocarbons For this reason it is a highly desirable solvent for paints lacquers and cellulose acetate Acetone was the 41st highest volume chemical The 1994 US produc tion was approximately 28 billion pounds As a symmetrical ketone acetone is a reactive compound with many synthetic uses Among the important chemicals based on acetone are methylisobutyl ketone methyl methacrylate ketene and diacetone alcohol Mesityl Oxide This is an alphabeta unsaturated ketone of high reac tivity It is used primarily as a solvent It is also used for producing methylisobutyl ketone Mesityl oxide is produced by the dehydration of acetone Hydrogenation of mesityl oxide produces methylisobutyl ketone a sol vent for paints and varnishes Chapter 8 12201 1105 AM Page 230 Methyl Methacrylate CH2CCOOCH3 This is produced by the hydrocyanation of acetone using HCN The resulting cyanohydrin is then reacted with sulfuric acid and methanol producing methyl methacrylate Chemicals Based on Propylene 231 One disadvantage of this process is the waste NH4HSO4 stream Methacrylic acid MAA is also produced by the air oxidation of isobutylene or the ammoxidation of isobutylene to methacrylonitrile fol lowed by hydrolysis These reactions are noted in Chapter 9 Methacrylic acid and its esters are useful vinyl monomers for produc ing 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 alcohols As a phenolic compound it reacts with strong alkaline solutions Bisphenol A is an important monomer for producing epoxy resins polycarbonates and polysulfones It is produced by the condensation reaction of acetone and phenol in the presence of HCI See Chapter 10 p 273 CH3 Chapter 8 12201 1105 AM Page 231 ADDITION OF ORGANIC ACIDS TO PROPENE 232 Chemistry of Petrochemical Processes Isopropyl acetate is produced by the catalytic vaporphase addition of acetic acid to propylene A high yield of the ester can be realized about 99 Isopropyl acetate is used as a solvent for coatings and printing inks It is generally interchangeable with methylethyl ketone and ethyl acetate Isopropyl acrylate is produced by an acid catalyzed addition reaction of acrylic acid to propylene The reaction occurs in the liquid phase at about 100C Due to unsaturation of the ester it can be polymerized and used as a plasticizer HYDROFORMYLATION OF PROPYLENE THE OXO REACTION Butyraldehydes The catalytic hydroformylation of olefins is discussed in Chapter 5 The reaction of propylene with CO and H2 produces nbutyraldehyde as the main product Isobutyraldehyde is a byproduct20 Chapter 8 12201 1105 AM Page 232 Figure 85 shows the homogeneous Hoechst and Rhone Poulenc pro cess using rhodium catalyst21 Butyraldehydes are usually hydrogenated to the corresponding alco hols They are also intermediates for other chemicals The following reviews some of the important chemicals based on butyraldehydes nBUTANOLCH3CH2CH2CH2OH nButanol is produced by the catalytic hydrogenation of nbutyraldehyde The reaction is carried out at relatively high pressures The yield is high CH3CH2CH2CHO H2 r CH3CH2CH2CH2OH 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 2ETHYLHEXANOLCH3CH23CHC2H5CH2OH 2Ethylhexanol is a colorless liquid soluble in many organic solvents It is one of the chemicals used for producing PVC plasticizers by react Chemicals Based on Propylene 233 Figure 85 The Hoechst AG and Rhone Poulenc process for producing butyraldehydes from propene21 1 reactor 2 catalyst separation 3 stripper using fresh syngas to strip unreacted propylene to recycle 4 distillation Chapter 8 12201 1105 AM Page 233 ing with phthalic acid the product is di2ethylhexyl phthalate The 1998 US production of 2ethylhexanol reached 800 million pounds 2Ethylhexanol is produced by the aldol condensation of butyralde hyde The reaction occurs in presence of aqueous caustic soda and pro duces 2ethyl3hydroxyhexanal The aldehyde is then dehydrated and hydrogenated to 2ethylhexanol 234 Chemistry of Petrochemical Processes Figure 86 shows the Hoechst process22 DISPROPORTIONATION OF PROPYLENE Metathesis Olefins could be catalytically converted into shorter and longerchain olefins through a catalytic disproportionation reaction For example propylene could be disproportionated over different catalysts yielding ethylene and butylenes Approximate reaction conditions are 400C and 8 atmospheres 2CH3CHCH2 r CH2CH2 CH3CHCHCH3 Table 85 indicates the wide variety of catalysts that can effect this type of disproportionation reaction and Figure 87 is a flow diagram for the Phillips Co triolefin process for the metathesis of propylene to pro duce 2butene and ethylene23 Anderson and Brown have discussed in depth this type of reaction and its general utilization24 The utility with respect to propylene is to convert excess propylene to olefins of greater economic value More discussion regarding olefin metathesis is noted in Chapter 9 Chapter 8 12201 1105 AM Page 234 ALKYLATION USING PROPYLENE 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 The reaction is discussed in Chapter 10 Chemicals Based on Propylene 235 Figure 86 The Hoechst AG process for producing 2ethylhexanol from n butyraldehyde22 1 Aldol condensation reactor 2 separation organic phase from liquid phase 3 hydrogenation reactor 4 distillation column Table 85 Representative disproportionation catalysts Transition metal compound Heterogeneous Support M CO6 Al2O3 MoO3 Al2O3 CoOMoO3 Al2O3 Re2O7 Al2O3 WO3 SiO2 Homogeneous Cocatalyst WCl6 EtOH EtALCl2 MX2 NO2L2 R3Al2Cl3 R4N M CO5X RAlX2 ReCl5O2 RAlCl2 M Mo or W X halengen Cl Br l L Lewis base eg triphenylphosphine pyridien etc R Allyl groups butyl Chapter 8 12201 1105 AM Page 235 REFERENCES 1 Chemical and Engineering News March 23 1998 p 22 2 Gates B C Katzer J R and Schuit G C Chemistry of Catalytic Processes McGrawHill Book Company 1979 p 349 3 Sachtler W M and DeBoer N H Proceeding 3rd Int Cong Catal Amsterdam 1965 4 Matar S Mirbach M and Tayim H Catalysis in Petrochemical Processes Kluwer Academic Publishers Dordrecht The Netherlands 1989 pp 9394 5 Chemical and Engineering News Oct 31 1994 p 15 6 CHEMTECH April 1999 p 19 7 Borman S Chemical and Engineering News Vol 68 No 12 1990 p 15 8 Pujada P R Vora B V and Krueding A P Newest Acrylonitrile Process Hydrocarbon Processing Vol 56 No 5 1977 pp 169172 9 Oil and Gas Journal June 6 1977 pp 171172 10 Chemical and Engineering News June 28 1999 p 35 11 Davis J C Chemical Engineering Vol 82 No 14 1975 pp 4448 12 Stobaugh R B et al Hydrocarbon Processing Vol 52 No 1 1973 pp 99108 236 Chemistry of Petrochemical Processes Figure 87 The Phillips Petroleum Co process for producing 2butene and eth ylene from propylene23 1 metathesis reactor 2 fractionator to separate propy lene recycle from propane 3 4 fractionator for separating ethylene butylenes and C5 Chapter 8 12201 1105 AM Page 236 13 Landau R et al Proceedings of the 7th World Petroleum Congress Vol 5 Petrochemicals 1967 pp 6772 14 Ainsworth S J Chemical and Engineering News Vol 70 No 9 1992 pp 911 15 Brownstein A M and List H Hydrocarbon Processing Vol 56 No 9 1977 pp 159162 16 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 185 17 Hatch L F The Chemistry of Petrochemical Reactions Gulf Publishing Co Houston 1955 p 76 18 Matar S Synfuels Hydrocarbons of the Future PennWell Publishing Co Tulsa OK 1982 p 20 19 Petrochemical Handbook Hydrocarbon Processing Vol 58 No 11 1979 p 122 20 Cornils B Hydroformylation Oxo Synthesis Roelen Reaction New Synthesis with Carbon Monoxide Springer Verlag Berlin New York 1980 pp 1224 21 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 149 22 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 158 23 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 144 24 Anderson K L and Brown T D Hydrocarbon Processing Vol 55 No 8 1976 pp 119122 Chemicals Based on Propylene 237 Chapter 8 12201 1105 AM Page 237 CHAPTER NINE C4 Oleffins and Diolefins Based Chemicals INTRODUCTION The C4 olefins produce fewer chemicals than either ethylene or propy lene However C4 olefins and diolefins are precursors for some signifi cant bigvolume chemicals and polymers such as methylterbutyl ether adiponitrile 14butanediol and polybutadiene Butadiene is not only the most important monomer for synthetic rub ber production but also a chemical intermediate with a high potential for producing useful compounds such as sulfolane by reaction with SO2 14 hutanediol by acetoxylationhydrogenation and chloroprene by chlori nationdehydrochlorination CHEMICALS FROM nBUTENES The three isomers constituting nbutenes are lbutene cis2butene and trans2butene This gas mixture is usually obtained from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene Chapter 2 The mixture of isomers may be used directly for reactions that are common for the three isomers and produce the same inter mediates and hence the same products Alternatively the mixture may be separated into two streams one constituted of lbutene and the other of cis and trans2butene mixture Each stream produces specific chemicals Approximately 70 of lbutene is used as a comonomer with ethylene to produce linear lowdensity polyethylene LLDPE Another use of lbutene is for the synthesis of butylene oxide The rest is used with the 2butenes to produce other chemicals nButene could also be isomerized to isobutene1 238 Chapter 9 12201 1107 AM Page 238 This section reviews important reactions leading to various chemicals from nbutenes OXIDATION OF BUTENES The mixture of nbutenes 1 and 2butenes could be oxidized to dif ferent 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 lbutene oxidation of this isomer via a chlorohydrination route is similar to that used for propylene C4 Olefins and DiolefinsBased Chemicals 239 Currently the major route for obtaining acetic acid ethanoic acid is the carbonylation of methanol Chapter 5 It may also be produced by the catalyzed oxidation of nbutane Chapter 6 The production of acetic acid from nbutene mixture is a vaporphase catalytic process The oxidation reaction occurs at approximately 270C over a titanium vanadate catalyst A 70 acetic acid yield has been reported2 The major byproducts are carbon oxides 25 and maleic anhydride 3 Acetic acid may also be produced by reacting a mixture of nbutenes with acetic acid over an ion exchange resin The formed secbutyl acetate is then oxidized to yield three moles of acetic acid Chapter 9 12201 1107 AM Page 239 The reaction conditions are approximately 100120C and 1525 atmos pheres The oxidation step is noncatalytic and occurs at approximately 200C and 60 atmospheres An acetic acid yield of 58 could be obtained3 Byproducts are formic acid 6 higher boiling compounds 3 and carbon oxides 28 Figure 91 shows the Bayer AG twostep process for producing acetic acid from nbutenes3 Acetic acid is a versatile reagent It is an important esterifying agent for the manufacture of cellulose 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 240 Chemistry of Petrochemical Processes Acetic anhydride acetyl oxide 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 where one mole of acetic acid loses one mole of water Ketene further reacts with one mole acetic acid yielding acetic anhydride Acetic anhydride is mainly used to make acetic esters and acetyl sali cylic acid aspirin Methyl ethyl ketone MEK 2butanone is a colorless liquid similar to acetone but its boiling point is higher 795C The production of MEK from nbutenes is a liquidphase oxidation process similar to that used to Chapter 9 12201 1107 AM Page 240 C4 Olefins and DiolefinsBased Chemicals 241 Figure 91 The Bayer AG twostep process for producing acetic acid from nbutenes3 Chapter 9 12201 1107 AM Page 241 produce acetaldehyde from ethylene using a Wackertype catalyst PdCl2CuCl2 The reaction conditions are similar to those for ethylene The yield of MEK is approximately 88 242 Chemistry of Petrochemical Processes Methyl ethyl ketone may also be produced by the catalyzed dehydro genation of secbutanol over zinc oxide or brass at about 500C The yield from this process is approximately 95 MEK 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 MEK is also used to synthesize various compounds such as methyl ethyl ketone peroxide a polymeriza tion catalyst used to form acrylic and polyester polymers and methyl pentynol by reacting with acetylene Methyl pentynol is a solvent for polyamides a corrosion inhibitor and an ingredient in the synthesis of hypnotics Maleic anhydride a solid compound that melts at 53Cis 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 400440C and 24 atmospheres A special catalyst constituted of an oxide mixture of molybdenum vana dium and phosphorous may be used Approximately 45 yield of maleic anhydride could be obtained from this route Chapter 9 12201 1107 AM Page 242 Other routes to maleic anhydride are the oxidation of nbutane a major source for this compound Chapter 6 and the oxidation of benzene Chapter 10 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 important insecticide and maleic hydrazide a plant growth regulator C4 Olefins and DiolefinsBased Chemicals 243 Maleic anhydride is also a precursor for 14butanediol through an ester ification route followed by hydrogenation4 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 The ethanolwater mixture is distilled to recover ethanol which is recycled Hydrogenation of diethylmaleate in the vapor phase over a nonprecious metal catalyst produces diethyl succinate Successive hydrogenation produces γbutyrolactone butanediol and tetrahydrofuran Chapter 9 12201 1107 AM Page 243 244 Chemistry of Petrochemical Processes Selectivity to the coproducts is high but the ratios of the coproducts may be controlled with appropriate reactor operating conditions Figure 92 is a block diagram for the butane diol process4 14Butanediol from buta diene is discussed later in this chapter Figure 92 A block diagram for producing 14butanediol from maleic anhydride4 Butylene oxide like propylene oxide is produced by the chlorohydri nation of lbutene with HOCl followed by epoxidation The reaction conditions are similar to those used for propylene CH3CH2CHCH2 HOCl r CH3CH2CHOHCH2Cl Butylene chlorohydrin Chapter 9 12201 1107 AM Page 244 C4 Olefins and DiolefinsBased Chemicals 245 Butylene oxide may be hydrolyzed to butylene glycol which is used to make plasticizers 12Butylene oxide is a stabilizer for chlorinated sol vents and also an intermediate in organic synthesis such as in surfactants and pharmaceuticals Hydration of nButenes secButanol CH3CHOHCH2CH3 secButanol 2butanol secbutyl alcohol a liquid has a strong charac teristic odor Its normal boiling point is 995C which is near waters The alcohol is soluble in water but less so than isopropyl and ethyl alcohols secButanol is produced by a reaction of sulfuric acid with a mixture of nbutenes followed by hydrolysis Both 1butene and cis and trans2 butenes yield the same carbocation intermediate which further reacts with the HSO4 1 or SO4 2 ions producing a sulfate mixture The sulfation reaction occurs in the liquid phase at approximately 35C An 85 wt 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 MEK by dehydrogenation as mentioned earlier 2Butanol is also used as a solvent a paint remover and an intermediate in organic synthesis Isomerization of nButenes nButene could be isomerized to isobutene using Shell FER catalyst which is active and selective nButene mixture from steam cracker or Chapter 9 12201 1107 AM Page 245 246 Chemistry of Petrochemical Processes FCC after removal of C5 olefins 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 isobutene1 CH2CHCH2CH3 CH3CHCHCH3 r CH3CHCH2CH3 H H CC H CH3 C H H H H H CC H CH3 C H H H r CH2CCH3 r Isobutene H H CH3 METATHESIS OF OLEFINS Metathesis is a catalyzed reaction that converts two olefin molecules into two different olefins It is an important reaction for which many mechanistic approaches have been proposed by scientists working in the fields of homogenous catalysis and polymerization5 6 One approach is the formation of a fluxional fivemembered metallocycle The interme diate can give back the starting material or the metathetic products via a concerted mechanism Another approach is a stepwise mechanism that involves the initial for mation of a metal carbene followed by the formation of a fourmembered metallocycle species7 Chapter 9 12201 1107 AM Page 246 Olefin metatheses are equilibrium reactions among the tworeactant and twoproduct olefin molecules If chemists design the reaction so that one product is ethylene for example they can shift the equilibrium by removing it from the reaction medium8 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 2butene at 350C the maximum conversion to propylene is 63 Higher conversions require recycling unreacted butenes after fractionation9 This reaction was first used to produce 2butene and eth ylene from propylene Chapter 8 The reverse reaction is used to prepare polymergrade propylene form 2butene and ethylene10 CH3CHCHCH3 CH2CH2 S 2CH3CHCH2 The metathetic reaction occurs in the gas phase at relatively high tem peratures 150350C with molybdenum or tungsten supported cata lysts or at low temperature 50C with rheniumbased catalyst in either liquid or gasphase The liquidphase process gives a better conversion Equilibrium conversion in the range of 5565 could be realized depending on the reaction temperature8 In this process which has been jointly developed by Institute Francais du Petrole and Chinese Petroleum Corp the C4 feed is mainly composed of 2butene 1butene does not favor this reaction but reacts differently with olefins producing metathetic byproducts The reaction between 1 butene and 2butene for example produces 2pentene and propylene The amount of 2pentene depends on the ratio of 1butene in the feed stock 3Hexene is also a byproduct from the reaction of two butene molecules ethylene is also formed during this reaction The properties of the feed to metathesis are shown in Table 9111 Table 92 illustrates the results from the metatheses reaction at two different conversions The main byproduct was 2pentene Olefins in the range of C6C8 and higher were present but to a much lower extent than C5 Figure 93 shows a simplified flow diagram for the olefin metathesis11 C4 Olefins and DiolefinsBased Chemicals 247 Table 91 Properties of feed to the metathesis process11 Composition Wt nButane 28 Butene 1 72 Butene2 900 Chapter 9 12201 1107 AM Page 247 Table 92 Results of metathesis of 2butene at two conversion levels11 Item Case 1 Case 2 Ethylene feed kgh 81 81 Total C4 feed kgh 143 134 C4 recycle kgh 44 96 Butene2 conversion per pass 623 596 overall 878 946 Propylene product selectivity 938 966 yield from butene2 824 913 248 Chemistry of Petrochemical Processes Figure 93 A flow diagram showing the metathesis process for producing poly mer grade propylene from ethylene and 2butene11 OLIGOMERIZATION OF BUTENES 2Butenes after separation of lbutene can be oligomerized in the liquid phase on a heterogeneous catalyst system to yield mainly C8 and Cl2 olefins12 The reaction is exothermic and requires a multitubular car bon steel reactor The exothermic heat is absorbed by water circulating around the reactor shell Either a single 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 plas ticizers alkyl phenols for surfactants and tridecyl alcohols for detergent Chapter 9 12201 1107 AM Page 248 intermediates Branched oligomers are valuable gasoline components Figure 94 shows the Octol oligomerization process13 A typical analysis of Atype oligomers branched is shown in Table 9312 CHEMICALS FROM ISOBUTYLENE Isobutylene CH2CCH32 is a reactive C4 olefin Until recently almost all isobutylene was obtained as a byproduct with other C4 hydro carbons 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 isobuty lene This serves the dual purpose of using excess nbutane that must be removed from gasolines due to new rules governing gasoline vapor pres sure and producing the desired isobutylene Currently the major use of iosbutylene is to produce methylterbutyl ether The following section reviews the chemistry of isobutylene and its important chemicals C4 Olefins and DiolefinsBased Chemicals 249 Figure 94 The Octol Oligomerization process for producing C8s and C12s and C16s olefins from nbutenes13 1 multitubular reactor 2 debutanizer column 3 fractionation tower Chapter 9 12201 1107 AM Page 249 OXIDATION OF ISOBUTYLENE Methacrolein and Methacrylic Acid Much like the oxidation of propylene which produces acrolein and acrylic acid the direct oxidation of isobutylene produces methacrolein and methacrylic acid The catalyzed oxidation reaction 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 methacrolein over a molybdenum oxidebased catalyst in a temperature range of 350400C Pressures are a little above atmospheric 250 Chemistry of Petrochemical Processes Table 93 Typical analysis of branched oligomers Type A12 Densily 20C kgl 0755 Flash point C 4 Ignition temperature C 240 Pour point C below 40 Hydrocarbon no distribution by mass C6 07 C7 10 C8 662 C9 20 C10 30 C11 12 C12 166 C13 to C15 05 C16 78 C16 10 RON MON Gasoline hase stock unleaded low in olefins 970 857 5 oligomers 970 853 10 oligomers 968 850 In the second step methacrolein is oxidized to methacrylic acid at a relatively lower temperature range of 250350C A molybdenum supported compound with specific promoters catalyzes the oxidation Chapter 9 12201 1107 AM Page 250 Methacrylic acid is esterified with methanol to produce methyl methacrylate monomer Methacrylic acid and methacrylates are also produced by the hydrocya nation of acetone followed by hydrolysis and esterification Chapter 8 Ammoxidation of isobutylene to produce methacrylonitrile is a simi lar reaction to ammoxidation of propylene to acrylonitrile However the yield is low EPOXIDATION OF ISOBUTYLENE Isobutylene Oxide Production Isobutylene oxide is produced in a way similar to propylene oxide and butylene oxide by a chlorohydrination 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 82 could be obtained14 Direct noncatalytic liquidphase oxidation of isobutylene to isobuty lene oxide gave low yield 287 plus a variety of oxidation products such as acetone terbutyl alcohol and isobutylene glycol C4 Olefins and DiolefinsBased Chemicals 251 Hydrolysis of isobutylene oxide in the presence of an acid produces isobutylene glycol Isobutylene glycol may also be produced by a direct catalyzed liquid phase oxidation of isobutylene with oxygen in presence of water The catalyst is similar to the Wackercatalyst system used for the oxidation Chapter 9 12201 1107 AM Page 251 of ethylene to acetaldehyde Instead of PdCl2CuCl2 used with ethylene a TlCl3CuCl2 catalyst is employed15 252 Chemistry of Petrochemical Processes Liquidphase oxidation of isobutylene glycol produces othydroxyisobu tyric acid The reaction conditions are 7080C at pH 27 in presence of a catalyst 5 ptC16 Dehydration of the acid produces 95 yield of methacrylic acid ADDITION OF ALCOHOLS TO ISOBUTYLENE Methyl and EthylTerButyl Ether The reaction between isobutylene and methyl and ethyl alcohols is an addition reaction catalyzed by a heterogeneous sulfonated polystyrene resin When methanol is used a 98 yield of methylterbutyl ether MTBE is obtained The reaction conditions have been noted in Chapter 5 Ethylterbutyl ether ETBE is also produced by the reaction of ethanol and isobutylene under similar conditions with a heteroge neous acidic ionexchange resin catalyst similar to that with MTBE Chapter 9 12201 1107 AM Page 252 MTBE and ETBE constitute a group of oxygenates that are currently in high demand for gasoline octanenumber boosters Both MTBE and ETBE have a similar research octane number of 118 but the latter ether has a motor octane number of 102 versus 100 for MTBE17 However the oxygen content of MTBE is 182 compared to 157 for ETBE The lower oxygen content of ETBE is related to the airfuel ratio which may not require a change in the automobile carburetors A comparison between the two ethers regarding phase separation antiknock behavior and fuel economy has been reviewed by Iborra et al18 HYDRATION OF ISOBUTYLENE TerButyl Alcohol CH33COH The acidcatalyzed hydration of isobutylene produces terbutyl alco hol The reaction occurs in the liquid phase in the presence of 5065 H2SO4 at mild temperatures 1030C The yield is approximately 95 C4 Olefins and DiolefinsBased Chemicals 253 terButyl alcohol 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 gaso line additive The alcohol is a major byproduct from the synthesis of propylene oxide using tertiary butyl hydroperoxide Surplus terbutyl alcohol could be used to synthesize highly pure isobutylene for MTBE production by a dehydration step The reaction conditions the catalyst used in a pilotscale unit and the yield are reviewed by Abraham and Prescott19 It was concluded that MTBE conversion increases from 8 wt to 88 wt as the temperature increases from 400F to 600F at about 40 LHSV liquid hourly space velocity At a lower space velocity 20 LHSV conversion increased from 12 wt to 99 wt for the same temperature range Figure 95 shows the effect of temperature and LHSV on the conversion19 Chapter 9 12201 1107 AM Page 253 254 Chemistry of Petrochemical Processes Figure 95 Effect of temperature and liquid hourly space velocity on conversion19 Figure 96 A simplified flow diagram of a tertiary butyl alcohol pilot plant19 Chapter 9 12201 1107 AM Page 254 Figure 96 is a simplified flow diagram of a TBA dehydration pilot unit19 C4 Olefins and DiolefinsBased Chemicals 255 The addition of carbon monoxide to isobutylene under high pressures and in the presence of an acid produces a carbon monoxideolefin com plex an acyl carbocation Hydrolysis of the complex at lower pressures yields neopentanoic acid Neopentanoic acid trimethylacetic acid is an intermediate and an ester ifying agent used when a stable neo structure is needed DIMERIZATION OF ISOBUTYLENE 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 olefins is noted in Chapter 3 CHEMICALS FROM BUTADIENE Butadiene is a diolefinic hydrocarbon with high potential in the chem ical industry In 1955 it was noticed that the assured future of butadi ene CH2CHCHCH2 lies with synthetic rubber the potential of butadiene is in its chemical versatility its low cost ready availabil ity and great activity tempt researchers20 Butadiene is a colorless gas insoluble in water but soluble in alcohol It can be liquefied easily under pressure This reactive compound poly merizes readily in the presence of free radical initiators Chapter 9 12201 1107 AM Page 255 Butadiene is mainly obtained as a byproduct from the steam cracking of hydrocarbons and from catalytic cracking These two sources account for over 90 of butadiene demand The remainder comes from dehydro genation of nbutane or nbutene streams Chapter 3 The 1998 US pro duction of butadiene was approximately 4 billion pounds and it was the 36th highestvolume chemical Worldwide butadiene capacity was nearly 20 billion pounds 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 com mercial value ADIPONITRILE NCCH24CN 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 radical chlorination which produces a mixture of 14dichloro2butene and 34 dichlorolbutene 2CH2CHCHCH22Cl2 r ClCH2CHCHCH2Cl CH2CHCHClCH2Cl The vaporphase chlorination reaction occurs at approximately 200300C The dichlorobutene mixture is then treated with NaCN or HCN in presence of copper cyanide The product 14dicyano2butene is obtained in high yield because allylic rearrangement to the more thermo dynamically stable isomer occurs during the cyanation reaction ClCH2CHCHCH2ClCH2CHCHClCH2Cl 4NaCN r 2NCCH2CHCHCH2CN4NaCl The dicyano compound is then hydrogenated over a platinum catalyst to adiponitrile NCCH2CHCHCH2CN H2 r NCCH24CN Adiponitrile Adiponitrile may also be produced by the electrodimerization of acry lonitrile Chapter 8 or by the reaction of ammonia with adipic acid fol lowed by twostep dehydration reactions 256 Chemistry of Petrochemical Processes Chapter 9 12201 1107 AM Page 256 HEXAMETHYLENEDIAMINE H2NCH26NH2 Hexamethylenediamine 16hexanediamine is a colorless solid sol uble 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 NCCH24CN 4H2 r H2NCH26NH2 The reaction conditions are approximately 200C and 30 atmospheres over a cobaltbased catalyst ADIPIC ACID HOOCCH24COOH Adipic acid may be produced by a liquidphase catalytic carbonylation of butadiene21 A catalyst of RhCl2 and CH3I is used at approximately 220C and 75 atmospheres Adipic acid yield is about 49 Both αgul taric acid 25 and valeric acid 26 are coproduced CH2CHCHCH2 2CO 2H2O r HOOCCH24COOH BASF is operating a semicommercial plant for the production of adipic acid via this route22 A new route to adipic acid occurs via a sequential carbonylation isomerization hydroformylation reactions23 The follow ing illustrates these steps O CH2CHCH CH2 CO CH3OH r CH3CHCHCH2COCH3 O O O CH3CHCHCH2COCH3 2CO 3H2 r CH3CCH24COCH3 H2O C4 Olefins and DiolefinsBased Chemicals 257 Chapter 9 12201 1107 AM Page 257 O O O O CH3CCH24COCH3 O2 r HOCCH24COCH3 r Hydr Adipic acid The main process for obtaining adipic acid is the catalyzed oxidation of cyclohexane Chapter 10 BUTANEDIOL HOCH24OH The production of 14butanediol 14BDO from propylene via the carbonylation of allyl acetate is noted in Chapter 8 14Butanediol from maleic anhydride is discussed later in this chapter An alternative route for the diol is through the acetoxylation of butadiene with acetic acid fol lowed by hydrogenation and hydrolysis The first step is the liquid phase addition of acetic acid to butadiene The acetoxylation reaction occurs at approximately 80C and 27 atmos pheres over a PdTe catalyst system The reaction favors the 14addition product 14diacetoxy2butene Hydrogenation of diacetoxybutene at 80C and 60 atmospheres over a NiZn catalyst yields 14diacetoxybu tane The latter compound is hydrolyzed to 14butanediol and acetic acid 258 Chemistry of Petrochemical Processes Acetic acid is then recovered and recycled Butanediol is mainly used for the production of thermoplastic polyesters Chloroprene 2chloro 13butadiene a conjugated nonhydrocarbon diolefin is a liquid that boils at 592C and while only slightly soluble in water it is soluble in alcohol The main use of chloroprene is to poly merize it to neoprene rubber Chapter 9 12201 1107 AM Page 258 Butadiene produces chloroprene through a high temperature chlorina tion to a mixture of dichlorobutenes which is isomerized to 34dichloro lbutene This compound is then dehydrochlorinated to chloroprene C4 Olefins and DiolefinsBased Chemicals 259 Sulfolane tetramethylene sulfone is produced by the reaction of butadiene and sulfur dioxide followed by hydrogenation Optimum temperature for highest sulfolene yield is approximately 75C At approximately 125C sulfolene decomposes to butadiene and SO2 This simple method could be used to separate butadiene from a mixture of C4 olefins because the olefins do not react with SO2 Sulfolane is a watersoluble biodegradable and highly polar com pound valued for its solvent properties Approximately 20 million pounds of sulfolane are consumed annually in applications that include delignification of wood polymerization and fiber spinning and electro plating bathes25 It is a solvent for selectively extracting aromatics from reformates and coke oven products CYCLIC OLIGOMERS OF BUTADIENE Butadiene could be oligomerized to cyclic dienes and trienes using certain transition metal complexes Commercially a mixture of TiCl4 and Al2Cl3C2H53 is used that gives predominantly cis trans trans 159cyclododecatriene along with approximately 5 of the dimer 15cyclooctadiene24 Chapter 9 12201 1107 AM Page 259 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 nylon 12 REFERENCES 1 Chemical and Engineering News Oct 25 1993 p 30 2 Brockhaus R German Patent 1279 011 1968 3 Petrochemical Handbook Hydrocarbon Processing Vol 58 No 11 1979 p 120 4 Harris N and Tuck M W Butanediol via Maleic Anhydride Hydrocarbon Processing Vol 69 No 5 1990 pp 7982 5 Grubbs R H et al J Am Chem Soc Vol 98 1976 p 3478 6 Katz T J Adv Organomet Chem Vol 16 1977 p 283 7 Herisson J L and Chaurin Y Makromol Chem 141 1970 p 161 Tsonis C P Journal of Applied Polymer Science Vol 26 1981 pp 35253536 8 Stinson S New Rhenium Catalyst for Olefin Chemistry Chemical and Engineering News Vol 70 No 6 1992 p 29 9 Cosyns J et al Hydrocarbon Processing Vol 77 No 3 1998 p 61 10 Patton P A and McCarthy T J Running the Impossible Reaction Metathesis of Cyclohexene CHEMTECH July 1987 pp 442446 11 Amigues P et al Propylene From Ethylene and Butene2 Hydrocarbon Processing Vol 69 No 10 1990 pp 7980 12 Nierlich F Oligomerize for Better Gasoline Hydrocarbon Processing Vol 71 No 2 1992 pp 4546 13 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 166 14 Hucknall D J Selective Oxidation of Hydrocarbons Academic Press Inc New York 1974 pp 5569 15 British Patent 1 182 273 to Tejin 16 West German Offen 2 354 331 to Atlantic Richfield 17 Unzelman G H US Clean Air Act Expands Role for Oxygenates Oil and Gas Journal April 15 1991 18 Iborra M Izquierdo J F Tejero J and Cunil F CHEMTECH Vol 18 No 2 1988 pp 120122 260 Chemistry of Petrochemical Processes Chapter 9 12201 1107 AM Page 260 19 Abraham O C and Prescott G F Make Isobutene from TBA Hydrocarbon Processing Vol 71 No 2 1992 p 51 20 Hatch L F The Chemistry of Petrochemical Reactions Houston Gulf Publishing Co 1955 p 149 21 Belgian Patent 770 615 to BASF 1971 22 CHEMTECH April 1999 p 19 23 Heaton C A ed An Introduction to Industrial Chemistry 2nd ed Blacki and Son Ltd London 1991 p 395 24 Parshall G W and Nuget W A Functional Chemicals via Homogeneous Catalysis CHEMTECH May 1988 pp 314320 25 Chemical and Engineering News Sept 5 1994 p 26 C4 Olefins and DiolefinsBased Chemicals 261 Chapter 9 12201 1107 AM Page 261 CHAPTER TEN Chemicals Based on Benzene Toluene and Xylenes INTRODUCTION The primary sources of benzene toluene and xylenes BTX are refin ery streams especially from catalytic reforming and cracking and pyrol ysis gasoline from steam cracking and from coal liquids BTX and 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 Chapter 2 The reactivity of C6 C7 C8 aromatics 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 precur sors 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 com mercial 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 avail able for chemical attack The methyl group could be easily oxidized or chlorinated as a result of the presence of the phenyl substituent REACTIONS AND CHEMICALS OF BENZENE Benzene C6H6 is the most important aromatic hydrocarbon It is the precursor for many chemicals that may be used as end products or inter 262 Chapter 10 12201 1108 AM Page 262 mediates Almost all compounds derived directly from benzene are con verted to other chemicals and polymers For example hydrogenation of benzene produces cyclohexane Oxidation of cyclohexane produces cyclohexanone which is used to make caprolactam for nylon manufac ture Due to the resonance stabilization of the benzene ring it is not eas ily polymerized However products derived from benzene such as styrene phenol and maleic anhydride can polymerize to important com mercial products due to the presence of reactive functional groups Benzene could be alkylated by different alkylating agents hydrogenated to cyclohexane nitrated or chlorinated The current world benzene capacity is approximately 35 million tons The 1994 US production of benzene was about 147 million pounds1 The chemistry for producing the various chemicals from benzene is discussed in this section Figure 101 shows the important chemicals derived from benzene ALKYLATION OF BENZENE Benzene can be alkylated in the presence of a Lewis or a Bronsted acid catalyst Olefins such as ethylene propylene and Cl2Cl4 alpha olefins are used to produce benzene alkylates which have great commercial value Alkyl halides such as monochloroparaffins in the Cl2Cl4 range also serve this purpose The first step in alkylation is the generation of a carbocation carbo nium ion When an olefin is the alkylating agent a carbocation interme diate forms Chemicals Based on Benzene Toluene and Xylenes 263 Carboncations also form from an alkyl halide when a Lewis acid cat alyst is used Aluminum chloride is the commonly used FriedelCrafts alkylation catalyst FriedelCrafts alkylation reactions have been reviewed by Roberts and Khalaf2 RCI AlCl3 r R AlCl4 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 ben zene alkylate Chapter 10 12201 1108 AM Page 263 264 Chemistry of Petrochemical Processes Figure 101 Important chemicals based on benzene Chapter 10 12201 1108 AM Page 264 Ethylbenzene EB is a colorless aromatic liquid with a boiling point of 1362C very close to that of pxylene This complicates separating it from the C8 aromatic equilibrium mixture obtained from catalytic reform ing processes See Chapter 2 for separation of C8 aromatics Ethylben zene obtained from this source however is small compared to the syn thetic route The main process for producing EB is the catalyzed alkylation of ben zene with ethylene Chemicals Based on Benzene Toluene and Xylenes 265 Many different catalysts are available for this reaction AlCl3HCl is commonly used Ethyl chloride may be substituted for HCI in a mole formole basis Typical reaction conditions for the liquidphase AlCl3 catalyzed process are 40100C and 28 atmospheres Diethylbenzene and higher alkylated benzenes also form They are recycled and dealky lated to EB The vaporphase Badger process Figure 102 which has been com mercialized since 1980 can accept dilute ethylene streams such as those produced from FCC off gas3 A zeolite type heterogeneous catalyst is used in a fixed bed process The reaction conditions are 420C and 200300 psi Over 98 yield is obtained at 90 conversion45 Poly ethylbenzene polyalkylated and unreacted benzene are recycled and join the fresh feed to the reactor The reactor effluent is fed to the ben zene fractionation system to recover unreacted benzene The bottoms Chapter 10 12201 1108 AM Page 265 containing ethylbenzene and heavier polyalkylates are fractionated in two columns The first column separates the ethylbenzene product and the other separates polyethylbenzene for recycling An optimization study of EB plants by constraint control was conducted by Hummel et al They concluded that optimum operation could be maintained through a control system when conditions such as catalyst activity and heat trans fer coefficients vary during operation6 Ethylbenzene is mainly used to produce styrene Over 90 of the 127 billion pounds of EB produced in the US during 1998 was dehydro genated to styrene 266 Chemistry of Petrochemical Processes Figure 102 The Badger process for producing ethylbenzene3 1 reactor 2 fractionator for recovery of unreacted benzene 3 EB fractionator 4 poly ethylbenzene recovery column Styrene vinylbenzene is a liquid bp 1452C that polymerizes easily when initiated by a free radical or when exposed to light The 1998 US production of styrene was approximately 11 billion pounds 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 Chapter 10 12201 1108 AM Page 266 conditions for the vaporphase process are 600700C at or below atmospheric pressure Approximately 90 styrene yield is obtained at 3040 conversion Chemicals Based on Benzene Toluene and Xylenes 267 In the MonsantoLummus Crest process Figure 103 fresh ethylben zene with recycled unconverted ethylbenzene are mixed with superheated steam The steam acts as a heating medium and as a diluent The endother mic reaction is carried out in multiple radial bed reactors filled with pro prietary catalysts Radial beds minimize pressure drops across the reactor A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al7 Yields could be pre dicted and with the help of an optimizer the best operating conditions can be found Figure 104 shows the effect of steamtoEB ratio temper ature and pressure on the equilibrium conversion of ethylbenzene7 Alternative routes for producing styrene have been sought One approach is to dimerize butadiene to 4vinyl1cyclohexene followed by catalytic dehydrogenation to styrene8 Figure 103 Schematic diagram of the MonsantoLummus Crest styrene plant7 Chapter 10 12201 1108 AM Page 267 The process which was developed by DOW involves cyclodimerization of butadiene over a proprietary copperloaded zeolite catalyst at moder ate temperature and pressure 100C and 250 psig To increase the yield the cyclodimerization step takes place in a liquid phase process over the catalyst Selectivity for vinylcyclohexene VCH was over 99 In the second step VCH is oxidized with oxygen over a proprietary oxide cata lyst in presence of steam Conversion over 90 and selectivity to styrene of 92 could be achieved9 Another approach is the oxidative coupling of toluene to stilbene fol lowed by disproportionation to styrene and benzene 268 Chemistry of Petrochemical Processes Figure 104 Effect of steamEB temperature and pressure on the conversion of ethylbenzene7 Chapter 10 12201 1108 AM Page 268 High temperatures are needed for this reaction and the yields are low Chemicals Based on Benzene Toluene and Xylenes 269 Cumene isopropylbenzene a liquid is soluble in many organic sol vents but not in water It is present in low concentrations in light refin ery streams such as reformates and coal liquids It may be obtained by distilling cumenes BP is 1527C these fractions The main process for producing cumene is a synthetic route where benzene is alkylated with propylene to isopropylbenzene Either a liquid or a gasphase process is used for the alkylation reac tion In the liquidphase process low temperatures and pressures approximately 50C and 5 atmospheres are used with sulfuric acid as a catalyst Small amounts of ethylene can be tolerated since ethylene is quite unre active under these conditions Butylenes 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 and 40 atmospheres Phosphoric acid on Kieselguhr is a commonly used catalyst To limit polyalkylation 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 polyalky lation A selectivity of about 97 based on benzene can be obtained In the UOP process Figure 105 fresh propylene feed is combined with fresh and recycled benzene then passed through heat exchangers and a steam preheater before being charged to the reactor10 The effluent is separated and excess benzene recycled Cumene is finally clay treated and fractionated The bottom product is mainly diisopropyl benzene which is reacted with benzene in a transalkylation section Chapter 10 12201 1108 AM Page 269 To reduce pollution Dow developed a new catalyst system from the mor denitezeolite group to replace phosophoric acid or aluminum chloride catalysts The new catalysts eliminates the disposal of acid wastes and handling corrosive materials11 The 1998 US cumene production was approximately 67 billion pounds and was mainly used to produce phenol and acetone A small amount of cumene is used to make αmethylstyrene by dehydrogenation 270 Chemistry of Petrochemical Processes Figure 105 A flow diagram of the UOP cumene process10 1 reactor 23 two stage flash system 4 depropanizer 5 benzene column 6 clay treatment 7 fractionator 8 transalkylation section αMethylstyrene is used as a monomer for polymer manufacture and as a solvent Chapter 10 12201 1108 AM Page 270 Phenol and Acetone from Cumene Phenol C6H5OH hydroxybenzene is produced from cumene by a twostep process In the first step cumene is oxidized with air to cumene hydroperoxide The reaction conditions are approximately 100130C and 23 atmospheres in the presence of a metal salt catalyst Chemicals Based on Benzene Toluene and Xylenes 271 In the second step the hydroperoxide is decomposed in the presence of an acid to phenol and acetone The reaction conditions are approximately 80C and slightly below atmospheric In this process Figure 106 cumene is oxidized in the liquid phase12 The oxidation product is concentrated to 80 cumene hydroperoxide by Figure 106 The Mitsui Petrochemical Industries process for producing phenol and acetone from cumene12 1 autooxidation reactor 2 vacuum tower 3 cleavage reactor 4 neutralizer 511 purification train Chapter 10 12201 1108 AM Page 271 vacuum distillation To avoid decomposition of the hydroperoxide it is transferred immediately to the cleavage reactor in the presence of a small amount of H2SO4 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 fin ishing column distills product acetone from an acetonewateroil 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 Figure 107 is a simplified flow diagram of an acetone finishing column and Table 101 shows the feed composition to the ace tone finishing column13 Cumene processes are currently the major source for phenol and coproduct acetone Chapter 8 notes other routes for producing acetone Previously phenol was produced from benzene by sulfonation fol lowed by caustic fusion to sodium phenate Phenol is released from the sodium salt of phenol by the action of carbon dioxide or sulfur dioxide 272 Chemistry of Petrochemical Processes Figure 107 A simplified process flow chart of an acetone finishing column13 Chapter 10 12201 1108 AM Page 272 Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium platinum palladium or irridium The oxidizing agent is nitrous oxide which is unavoidable a byproduct from the oxidation of KA oil see KA oil this chapter to adipic acid using nitric acid as the oxidant14 Phenol is also produced from chlorobenzene and from toluene via a benzoic acid intermediate see Reactions and Chemicals from Toluene Properties and Uses of Phenol Phenol a white crystalline mass with a distinctive odor becomes red dish when subjected to light It is highly soluble in water and the solu tion is weakly acidic Phenol was the 33rd highestvolume chemical The 1994 US production of phenol was approximately 4 billion pounds The current world capacity is approximately 15 billion pounds Many chemicals and polymers derive from phenol Approximately 50 of production goes to phenolic resins Phenol and acetone produce bisphenol A an important monomer for epoxy resins and polycarbonates It is produced by condensing acetone and phenol in the presence of HCI or by using a cation exchange resin Figure 108 shows the Chiyoda Corp bisphenol A process15 Chemicals Based on Benzene Toluene and Xylenes 273 Table 101 Feed composition of acetone finishing column13 Component wt Acetone 48 Water 22 Cumene 24 Alphamethylstyrene and other heavy hydrocarbons 4 Neutralized organics sodium acetate sodium phenate etc 1 Free caustic 1 Chapter 10 12201 1108 AM Page 273 Important chemicals derived from phenol are salicylic acid acetylsali cyclic acid aspirin 24dichlorophenoxy acetic acid 24D and 245 triphenoxy acetic acid 245T which are selective herbicides and pentachlorophenol a wood preservative 274 Chemistry of Petrochemical Processes Figure 108 The CTBISA Chiyoda Corp process for producing bisphenol A from acetone and phenol15 1 reactor 24 distillation columns 5 phenol dis tillation column 6 crystallizer 7 solidliquid separator 8 prilling tower Other halophenols are miticides bactericides and leather preservatives Halophenols account for about 5 of phenol uses About 12 of phenol demand is used to produce caprolactam a monomer for nylon 6 The main source for caprolactam however is toluene Phenol can be alkylated to alkylphenols These compounds are widely used as nonionic surfactants antioxidants and monomers in resin poly mer applications Chapter 10 12201 1108 AM Page 274 Phenol is also a precursor for aniline The major process for aniline C6H5NH2 is the hydrogenation of nitrobenzene see Nitration of Benzene Linear Alkylbenzene Linear alkylbenzene LAB is an alkylation product of benzene used to produce biodegradable anionic detergents The alkylating agents are either linear C12C14 monoolefins or monochloroalkanes The linear olefins alpha olefins are produced by polymerizing ethylene using Ziegler catalysts Chapter 7 or by dehydrogenating nparaffins extracted from kerosines Monochloroalkanes on the other hand are manufactured by chlorinating the corresponding nparaffins Dehydrogenation of n paraffins to monoolefins using a newly developed dehydrogenation cat alyst by UOP has been reviewed by Vora et al16 The new catalyst is highly active and allows a higher perpass conversion to monoolefins Because the dehydrogenation product contains a higher concentration of olefins for a given alkylate production rate the total hydrocarbon feed to the HF alkylation unit is substantially reduced16 Alkylation of benzene with linear monoolefins is industrially pre ferred The Detal process Figure 109 combines the dehydrogenation of nparaffins and the alkylation of benzene17 Monoolefins from the dehy drogenation section are introduced to a fixedbed alkylation reactor over a heterogeneous solid catalyst Older processes use HF catalysts in a liq uid phase process at a temperature range of 4070C The general alky lation reaction of benzene using alpha olefins could be represented as Chemicals Based on Benzene Toluene and Xylenes 275 Chapter 10 12201 1108 AM Page 275 Typical properties of detergent alkylate are shown in Table 10216 Detergent manufacturers buy linear alkylbenzene sulfonate it with SO3 and then neutralize it with NaOH to produce linear alkylbenzene sul fonate LABS the active ingredient in detergents 276 Chemistry of Petrochemical Processes Figure 109 The UOP Detal process for producing linear alkylbenzene17 1 pacol dehydrogenation reactor 2 gasliquid separation 3 reactor for converting diolefins to monoolefins 4 stripper 5 alkylation reactor 678 fractionators CHLORINATION OF BENZENE Chlorination of benzene is an electrophilic substitution reaction in which Cl serves as the electrophile The reaction occurs in the presence of a Lewis acid catalyst such as FeCl3 The products are a mixture of mono and dichlorobenzenes The ortho and the paradichlorobenzenes are more common than metadichlorobenzene The ratio of the mono chloro to dichloro products essentially depends on the benzenechlorine ratio and the residence time The ratio of the dichloroisomers o to p to mdichlorobenzenes mainly depends on the reaction temperature and residence time Chapter 10 12201 1108 AM Page 276 Typical liquidphase reaction conditions for the chlorination of benzene using FeCl3 catalyst are 80100C and atmospheric pressure When a high benzeneCl2 ratio is used the product mixture is approximately 80 monochlorobenzene 15 pdichlorobenzene and 5 odichlorobenzene Chemicals Based on Benzene Toluene and Xylenes 277 Table 102 Typical properties of detergent alkylate16 Linear detergent alkylate Bromine number 002 Saybolt color 30 Alkylbenzene content wt 974 Doctor test NEGATIVE Unsulfonatable content wt 10 Water wt 01 Specific gravity at 60F 08612 Refractive index n20 D 14837 Flash point ASTM D93 F 280 Average molecular weight 240 Distillation ASTM D86 F IBP 538 10 vol 547 30 vol 550 50 vol 554 70 vol 559 90 vol 569 95 vol 576 EP 589 Saybolt color of a 5 sodium alkylbenzene sulfonate solution 26 Normal alkylbenzene wt 93 2Phenyl isomer wt 200 Paraffin wt 01 Biodegradability ASTM D2667 950 Chapter 10 12201 1108 AM Page 277 Continuous chlorination processes permit the removal of mono chlorobenzene as it is formed resulting in lower yields of higher chlori nated benzene Monochlorobenzene is also produced in a vaporphase process at approximately 300C The byproduct HCl goes into a regenerative oxychlorination reactor The catalyst is a promoted copper oxide on a sil ica carrier 278 Chemistry of Petrochemical Processes Higher conversions have been reported when temperatures of 234315C and pressures of 4080 psi are used18 Monochlorobenzene is the starting material for many compounds including phenol and aniline Others such as DDT chloronitrobenzenes polychlorobenzenes and biphenyl do not have as high a demand for monochlorobenzene as aniline and phenol NITRATION OF BENZENE Nitrobenzene C6H5NO2 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 ion NO 2 The liquidphase reaction occurs in presence of both concentrated nitric and sulfuric acids at approximately 50C Concentrated sulfuric acid has two functions it reacts with nitric acid to form the nitronium ion and it absorbs the water formed during the reac tion which shifts the equilibrium to the formation of nitrobenzene Chapter 10 12201 1108 AM Page 278 Most of the nitrobenzene 97 produced is used to make aniline Other uses include synthesis of quinoline benzidine and as a solvent for cellu lose ethers Aniline C6H5NH2 Aniline aminobenzene 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 Chemicals Based on Benzene Toluene and Xylenes 279 The hydrogenation reaction occurs at approximately 270C and slightly above atmospheric over a CuSilica catalyst About a 95 yield is obtained An alternative way to produce aniline is through ammonolysis of either chlorobenzene or phenol The reaction of chlorobenzene with aqueous ammonia occurs over a copper salt catalyst at approximately 210C and 65 atmospheres The yield of aniline from this route is also about 96 Ammonolysis of phenol occurs in the vapor phase In the Scientific Design Co process Figure 1010 a mixed feed of ammonia and phenol is heated and passed over a heterogeneous catalyst in a fixedbed sys tem19 The reactor effluent is cooled the condensed material distilled and the unreacted ammonia recycled Aniline produced this way should be very pure Chapter 10 12201 1108 AM Page 279 OXIDATION OF BENZENE Benzene oxidation is the oldest method to produce maleic anhydride The reaction occurs at approximately 380C and atmospheric pressure A mixture of V2O5MO3 is the usual catalyst Benzene conversion reaches 90 but selectivity to maleic anhydride is only 5060 the other 4050 is completely oxidized to CO220 280 Chemistry of Petrochemical Processes Figure 1010 The Scientific Co process for producing aniline from phenol19 1 fixedbed reactor 2 liquidgas separator 3 ammonia compression and recy cling 4 drier 5 fractionator Currently the major route to maleic anhydride especially for the newly erected processes is the oxidation of butane Chapter 6 Maleic anhy dride also comes from oxidation of nbutenes Properties and chemicals derived from maleic anhydride are noted in Chapter 9 Chapter 10 12201 1108 AM Page 280 HYDROGENATION OF BENZENE Chemicals Based on Benzene Toluene and Xylenes 281 The hydrogenation of benzene produces cyclohexane Many catalyst systems such as Nialumina and NiPd are used for the reaction General reaction conditions are 160220C and 2530 atmospheres Higher tem peratures and pressures may also be used with sulfided catalysts Older methods use a liquid phase process Figure 101110 New gas phase processes operate at higher temperatures with noble metal cata lysts Using high temperatures accelerates the reaction faster rate21 The hydrogenation of benzene to cyclohexane is characterized by a highly exothermic reaction and a significant decrease in the product volume Figure 1011 The Institut Francais du Petrole process for the hydrogenation of benzene to cyclohexane10 1 liquidphase reactor 2 heat exchanger 3 cat alytic pot acts as a finishing reactor when conversion of the main reactor drops below the required level 4 highpressure separator 5 stabilizer Chapter 10 12201 1108 AM Page 281 from 4 to 1 Equilibrium conditions are therefore strongly affected by temperature and pressure Figure 1012 shows the effect of H2benzene mole ratio on the benzene content in the products21 It is clear that benzene content in the product decreases with an increase of the reactor inlet pressure Another nonsynthetic source for cyclohexane is natural gasoline and petroleum naphtha However only a small amount is obtained from this source The 1994 US production of cyclohexane was approximately 21 billion pounds the 45th highest chemical volume Properties and Uses of Cyclohexane 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 282 Chemistry of Petrochemical Processes Figure 1012 Effect of hydrogen purity and pressure on benzene conversion to cyclohexane21 Chapter 10 12201 1108 AM Page 282 and its derivatives present in naphthas to aromatic hydrocarbons is an important reaction in the catalytic reforming process Essentialy all cyclohexane is oxidized either to a cyclohexanone cyclohexanol mixture used for making caprolactam or to adipic acid These are monomers for making nylon 6 and nylon 66 Oxidation of Cyclohexane CyclohexanoneCyclohexanol and Adipic Acid Cyclohexane is oxidized in a liquidphase process to a mixture of cyclohexanone and cyclohexanol KA oil The reaction conditions are 95120C at approximately 10 atmospheres in the presence of a cobalt acetate and orthoboric acid catalyst system About 95 yield can be obtained Chemicals Based on Benzene Toluene and Xylenes 283 KA oil is used to produce caprolactam the monomer for nylon 6 Caprolactam is also produced from toluene through the intermediate for mation 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 Chapter 9 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 HOOCCH24COOH 4H2 r HOCH26OH 2H2O HOCH26OH 2NH3 r H2NCH26NH2 2H2O Hexamethylenediamine is the second monomer for nylon 66 Chapter 10 12201 1108 AM Page 283 REACTIONS AND CHEMICALS OF TOLUENE Toluene methylbenzene is similar to benzene as a mononuclear aro matic 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 petro chemicals 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 mono nitrotoluene and dinitrotoluenes These compounds are important syn thetic intermediates The 1994 US toluene production of all grades was approximately 68 billion pounds Hydrodealkylating toluene to benzene was the largest end use in United States and West Europe followed by solvent applications DEALKYLATION OF TOLUENE Toluene is dealkylated to benzene over a hydrogenationdehydrogena tion catalyst such as nickel The hydrodealkylation is essentially a hydro cracking reaction favored at higher temperatures and pressures The reaction occurs at approximately 700C and 40 atmospheres A high ben zene yield of about 96 or more can be achieved 284 Chemistry of Petrochemical Processes Hydrodealkylation of toluene and xylenes with hydrogen is noted in Chapter 3 Dealkylation also can be effected by steam The reaction occurs at 600800C over Y La Ce Pr Nd Sm or Th compounds NiCr2O3 cat alysts and NiAl2O3 catalysts at temperatures between 320630C22 Yields of about 90 are obtained This process has the advantage of pro ducing rather than using hydrogen Chapter 10 12201 1108 AM Page 284 DISPROPORTIONATION OF TOLUENE The catalytic disproportionation of toluene Figure 101323 in the presence of hydrogen produces benzene and a xylene mixture Dispro portionation is an equilibrium reaction with a 58 conversion per pass theoretically possible The reverse reaction is the transalkylation of xylenes with benzene Chemicals Based on Benzene Toluene and Xylenes 285 Figure 1013 The Mobil Oil Corp IFP process for the disproportionation of toluene to mixed xylenes23 Typical conditions for the disproportionation reaction are 450530C and 20 atmospheres A mixture of CoOMoO3 on aluminosilicatesalumina catalysts can be used Conversions of approximately 40 are normally used to avoid more side reactions and faster catalyst deactivation24 The equilibrium constants for this reaction are not significantly changed by shifting from liquid to vapor phase or by large temperature changes25 Currently zeolites especially those of ZSM5 type are preferred for their higher activities and selectivities They are also more stable thermally Modifying ZSM5 zeolites with phosphorous boron or Chapter 10 12201 1108 AM Page 285 magnesium compounds produces xylene mixtures rich in the pisomer 7090 It has been proposed that the oxides of these elements pres ent in zeolites reduce the dimensions of the pore openings and channels and so favor formation and outward diffusion of pxylene the isomer with the smallest minimum dimension2627 OXIDATION OF TOLUENE 286 Chemistry of Petrochemical Processes Oxidizing toluene in the liquid phase over a cobalt acetate catalyst produces benzoic acid The reaction occurs at about 165C and 10 atmos pheres The yield is over 90 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 tereph thalic acid Caprolactam Production Caprolactam a white solid that melts at 69C can be obtained either in a fused or flaked form It is soluble in water ligroin and chlorinated hydrocarbons Caprolactams main use is to produce nylon 6 Other minor uses are as a crosslinking agent for polyurethanes in the plasti cizer industry and in the synthesis of lysine The first step in producing caprolactam from benzoic acid is its hydro genation to cyclohexane carboxylic acid at approximately 170C and 16 atmospheres over a palladium catalyst28 Chapter 10 12201 1108 AM Page 286 The resulting acid is then converted to caprolactam through a reaction with nitrosylsulfuric acid Chemicals Based on Benzene Toluene and Xylenes 287 Figure 1014 shows an integrated caprolactam production process28 Toluene the feed 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 Figure 1014 The SNIA BPD process for producing caprolactam28 1 toluene oxidation reactor 2 fractionator 3 hydrogenation reactor stirred autoclave 4 multistage reactor conversion to caprolactam 5 water dilution 6 crystallizer 7 solvent extraction 8 fractionator Chapter 10 12201 1108 AM Page 287 a byproduct of commercial value Recovered caprolactam is purified through solvent extraction and fractionation Phenol from Benzoic Acid The action of a copper salt converts benzoic acid to phenol The cop per reoxidized by air functions as a real catalyst The Lummus process operates in the vapor phase at approximately 250C Phenol yield of 90 is possible 288 Chemistry of Petrochemical Processes The overall reaction is In the Lummus process Figure 1015 the reaction occurs in the liquid phase at approximately 220240C over Mg2 Cu2 benzoate29 Magnesium benzoate is an initiator with the Cu2 reduced to Cu1 The copper 1 ions are reoxidized to copper II ions Chapter 10 12201 1108 AM Page 288 Chemicals Based on Benzene Toluene and Xylenes 289 Figure 1015 The Lummus benzoicacidtophenol process29 Chapter 10 12201 1108 AM Page 289 Phenol can also be produced from chlorobenzene and from cumene the major route for this commodity Terephthalic Acid from Benzoic Acid Terephthalic acid is an important monomer for producing polyesters The main route for obtaining the acid is the catalyzed oxidation of paraxylene It can also be produced from benzoic acid by a dispropor tionation reaction of potassium benzoate in the presence of carbon diox ide Benzene is the coproduct 290 Chemistry of Petrochemical Processes The reaction occurs in a liquidphase process at approximately 400C using ZnO or CdO catalysts Terephthalic acid is obtained from an acid treatment the potassium salt is recycled3031 Oxidizing toluene to benzaldehyde is a catalyzed reaction in which a selective catalyst limits further oxidation to benzoic acid In the first step benzyl alcohol is formed and then oxidized to benzaldehyde Further oxi dation produces benzoic acid Chapter 10 12201 1108 AM Page 290 The problem with this reaction is that each successive oxidation occurs more readily than the preceding one more acidic hydrogens after intro ducing the oxygen hetero atom which facilitates the oxidation 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 In another process the reaction goes forward in the presence of methanol over an FeBr2CoBr2 catalyst mixture at approximately 100140C 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 CHLORINATION OF TOLUENE The chlorination of toluene by substituting the methyl hydrogens is a free radical reaction A mixture of three chlorides benzyl chloride ben zal chloride and benzotrichloride results Chemicals Based on Benzene Toluene and Xylenes 291 Cl2 Chapter 10 12201 1108 AM Page 291 The ratio of the chloride mixture mainly derives from the toluenechlo rine ratio and the contact time Benzyl chloride is produced by passing dry chlorine into boiling toluene 110C until reaching a density of 1283 At this density the concentration of benzyl chloride reaches the maximum Light can initiate the reaction Benzyl chloride can produce benzyl alcohol by hydrolysis 292 Chemistry of Petrochemical Processes Benzyl alcohol is a precursor for butylbenzyl phthalate a vinyl chloride plasticizer Benzyl chloride is also a precursor for pheny lacetic 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 Chlorinated toluenes are not largevolume chemicals but they are pre cursors for many synthetic chemicals and pharmaceuticals NITRATION OF TOLUENE Nitration of toluene is the only important reaction that involves the aro matic ring rather than the aliphatic methyl group The nitration reaction occurs with an electrophilic substitution by the nitronium ion The reac tion conditions are milder than those for benzene due to the activation of the ring by the methyl substituent A mixture of nitrotoluenes results The two important monosubstituted nitrotoluenes are o and pnitrotoluenes Chapter 10 12201 1108 AM Page 292 Mononitrotoluenes are usually reduced to corresponding toluidines which make dyes and rubber chemicals Chemicals Based on Benzene Toluene and Xylenes 293 Dinitrotoluenes are produced by nitration of toluene with a mixture of concentrated nitric and sulfuric acid at approximately 80C The main products are 24 and 26dinitrotoluenes The dinitrotoluenes are important precursors for toluene diisocyanates TDI monomers used to produce polyurethanes The TDI mixture is synthesized from dinitrotoluenes by a firststep hydrogenation to the corresponding diamines The diamines are then treated with phosgene to form TDI The yield from toluene is approximately 85 oToluidine pToluidine Chapter 10 12201 1108 AM Page 293 An alternative route for TDI is through a liquidphase carbonylation of dinitrotoluene in presence of PdCl2 catalyst at approximately 250C and 200 atmospheres 294 Chemistry of Petrochemical Processes Trinitrotoluene TNT is a wellknown explosive obtained by further nitration of the dinitrotoluenes CARBONYLATION OF TOLUENE 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 could be further oxidized to terephthalic acid an important monomer for polyesters pTolualdehyde is also an intermediate in the synthesis of perfumes dyes and pharmaceuticals CHEMICALS FROM XYLENES Xylenes dimethylbenzenes 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 aromat ics Separating the aromatic mixture from the reformate is done by extractiondistillation and isomerization processes Chapter 2 Chapter 10 12201 1108 AM Page 294 paraXylene is the most important of the three isomers for producing terephthalic acid to manufacture 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 Table 103 shows the thermodynamic composition of C8 aromatics at three temperatures32 mXylene is usually isomerized 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 gasolines The 1998 US production of mixed xylenes for chemical use was approximately 95 million pounds pXylene alone was about 77 million pounds that year TEREPHTHALIC ACID HOOCC6H4COOH The catalyzed oxidation of pxylene produces terephthalic acid TPA Cobalt acetate promoted with either NaBr or HBr is used as a catalyst in an acetic acid medium Reaction conditions are approximately 200C and 15 atmospheres The yield is about 95 Chemicals Based on Benzene Toluene and Xylenes 295 Table 103 Thermodynamic equilibrium composition of C8 aromatics at three temperatures32 Composition Aromatics wt 200C 300C 500C pXylene 218 211 189 oXylene 206 216 230 mXylene 535 511 471 Ethylbenzene 41 62 110 Chapter 10 12201 1108 AM Page 295 Special precautions must be taken so that the reaction does not stop at the ptoluic acid stage One approach is to esterify toluic acid as it is formed with methanol This facilitates the oxidation of the second methyl group The resulting dimethyl terephthalate DMT may be hydrolyzed to terephthalic acid Another approach is to use an easily oxidized substance such as acetaldehyde or methylethyl ketone which under the reaction condi tions forms a hydroperoxide These will accelerate the oxidation of the second methyl group The DMT process encompasses four major pro cessing steps oxidation esterification distillation and crystallization Figure 1016 shows a typical pxylene oxidation process to produce terephthalic acid or dimethyl terephthalate33 The main use of TPA and DMT is to produce polyesters for synthetic fiber and film 296 Chemistry of Petrochemical Processes 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 375435C and 07 atmosphere The yield of phthalic anhydride is about 85 Figure 1016 A typical pxylene to dimethyl terephthalate process33 Chapter 10 12201 1108 AM Page 296 Chemicals Based on Benzene Toluene and Xylenes 297 Liquidphase oxidation of oxylene also works at approximately 150C 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 methylmaleic anhydride Maleic anhy dride could be recovered economically34 Phthalic anhydrides main use is for producing plasticizers by reac tions with C4C10 alcohols The most important polyvinyl chloride plas ticizer 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 phthalonitrile by an ammoxidation route used to produce phthalamide and phathilimide The reaction scheme for producing phthalonitrile phthalamide and phathilimide is shown in Figure 101734 The oxidation of mxylene produces isophthalic acid The reaction occurs in the liquidphase in presence of ammonium sulfite Chapter 10 12201 1108 AM Page 297 Isophthalic acids main use is for producing polyesters that are character ized 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 isophthalonitrile The reaction resembles the one used for ammoxidation of phthalic anhydride 298 Chemistry of Petrochemical Processes Figure 1017 The reaction scheme for oxylene to phthalonitrile34 Chapter 10 12201 1108 AM Page 298 Isophthalonitrile serves as a precursor for agricultural chemicals It is readily hydrogenated to the corresponding diamine which can form polyamides or be converted to isocyanates for polyurethanes REFERENCES 1 Chemical and Engineering News April 10 1995 p 17 2 Roberts R and Khalaf A FriedelCrafts Alkylation Chemistry Marcel Dekker Inc New York 1984 Chapter 2 3 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 154 4 Lewis P J and Dwyer F G Oil and Gas Journal Sept 26 1977 pp 5558 5 Dwyer F G Lewis P J and Schneider F H Chemical Engineering Jan 5 1976 pp 9091 6 Hummel H K DeWit G B and Maarleveld A The Optimization of EB Plant by Constraint Control Hydrocarbon Processing Vol 70 No 3 1991 pp 6771 7 Sundaram K M et al Styrene Plant Simulation and Optimization Hydrocarbon Processing Vol 70 No 1 1991 pp 9397 8 CHEMTECH Vol 7 No 6 1977 pp 334451 9 Chemical and Engineering News June 20 1994 p 31 10 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 152 11 Illman D Environmentally Benign Chemistry Aims for Processes That Dont Pollute Chemical and Engineering News Sept 5 1994 p 26 12 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 168 13 Fulmer J W and Graf K C Distill Acetone in Tower Packing Hydrocarbon Processing Vol 70 No 10 1991 pp 8791 14 Platkin J and Fitzgerald M Patent Watch CHEMTECH June 1999 p 39 US patent 5874646 Feb 23 1999 15 Petrochemical Handbook Hydrocarbon Processing Vol 78 No 3 1999 p 98 16 Vora B V et al Latest LAB Developments Hydrocarbon Processing Vol 63 No11 1984 pp 8690 17 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 130 Chemicals Based on Benzene Toluene and Xylenes 299 Chapter 10 12201 1108 AM Page 299 18 Frontier Chemical Co US Patent 3 148 222 1964 19 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 136 20 Matar S Mirbach M and Tayim H Catalysis in Petrochemical Processes Kluwer Academic Publishers The Netherlands 1989 pp 84108 21 Abraham O C and Chapman G L Hydrogenate benzene Hydro carbon Processing Vol 70 No 10 1991 pp 9597 22 Ohsumi Y and Komatsuzaki Y US Patent 3 903 186 Sept 2 1975 to Mitsubishi Chemical Industries Ltd and Asis Oil Co Ltd Japan 23 Petrochemical Handbook Hydrocarbon Processing Vol 78 No 3 1999 p 122 24 Vora B V Jensen R H and Rockett K W Paper No 20 PI Second Arab Conference on Petrochemicals Abu Dhabi March 1522 1976 25 Hasting S H and Nicholson D E J Chem Eng Data Vol 6 1961 p l 26 Kaeding W Chu C Young L and Butter S Selective Dispropor tionation of Toluene to Produce Benzene and pXylene Journal of Catalysis Vol 69 No 2 1981 pp 392398 27 Meisel S L Catalysis Research Bears Fruit CHEMTECH January 1988 pp 3237 28 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 150 29 Gelbein A D and Nislick A S Hydrocarbon Processing Vol 57 No 11 1978 pp 125128 30 Cines M R US Patent 3 746 754 July 17 1973 to Phillips Petroleum Co US Patent 2 905 709 and 2 794 830 31 Sittig M Aromatic Hydrocarbons Manufacture and Technology Park Ridge NJ Noyes Data Corp 1976 pp 303306 32 Masseling J H CHEMTECH Vol 6 No 11 1976 p 714 33 Braggiato C and Gualy R Improve DMT Production Hydrocar bon Processing Vol 77 No 6 1998 pp 6165 34 Sze M C and Gelbein A P Hydrocarbon Processing Vol 55 No 2 1976 pp 103106 300 Chemistry of Petrochemical Processes Chapter 10 12201 1108 AM Page 300 CHAPTER ELEVEN Polymerization INTRODUCTION 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 One natural polymer is cellulose the most abundant organic compound on earth a molecule made of many simple glucose units monomers joined together through a glycoside linkage1 Proteins the material of life are polypeptides made of αamino acids attached by an amide 301 linkage The polymer industry dates back to the 19th century when natural polymers such as cotton were modified by chemical treatment to pro duce artificial silk rayon Work on synthetic polymers did not start until the beginning of the 20th century In 1909 L H Baekeland prepared the first synthetic polymeric material using a condensation reaction between formaldehyde and phenol Currently these polymers serve as important thermosetting plastics phenol formaldehyde resins Since Baekelands discovery many polymers have been synthesized and marketed Many modern commercial products plastics fibers rubber derive from poly mers The huge polymer market directly results from extensive work in synthetic organic compounds and catalysts Zieglers discovery of a coordination catalyst in the titanium family paved the road for synthe sizing many stereoregular polymers with improved properties This chapter reviews the chemistry involved in the synthesis of polymers Chapter 11 12201 1110 AM Page 301 MONOMERS POLYMERS AND COPOLYMERS A monomer is a reactive molecule that has at least one functional group eg OH COOH NH2 CC Monomers may add to them selves as in the case of ethylene or may react with other monomers hav ing different functionalities A monomer initiated or catalyzed with a specific catalyst polymerizes and forms a macromoleculea polymer For example ethylene polymerized in presence of a coordination catalyst produces a linear homopolymer linear polyethylene n CH2CH2 r CH2CH2n Linear polyethylene A copolymer on the other hand results from two different monomers by addition polymerization For example a thermoplastic polymer with better properties than an ethylene homopolymer comes from copolymer izing ethylene and propylene 302 Chemistry of Petrochemical Processes Block copolymers are formed by reacting two different prepolymers which are obtained by polymerizing the molecules of each monomer separately A block copolymer made of styrene and butadiene is an important synthetic rubber Alternating copolymers have the monomers of one type alternating in a regular manner with the monomers of the other regardless of the com position of the reactants For example an alternate copolymer of vinyl acetate and vinyl chloride could be represented as Chapter 11 12201 1110 AM Page 302 Random copolymers have the different monomer molecules distrib uted randomly along the polymer chain A polymer molecule may have just a linear chain or one or more branches protruding from the polymer backbone Branching results mainly from chain transfer reactions see Chain Transfer Reactions later in this chapter and affects the polymers physical and mechanical properties Branched polyethylene usually has a few long branches and many more short branches Polymerization 303 Intentional branching may improve the properties of the product poly mer through grafting A graft copolymer can be obtained by creating active sites on the polymer backbone The addition of a different monomer then reacts at the active site and forms a branch For example polyethylene irradiated with gamma rays and then exposed to a reactive monomer such as acrylonitrile produces a polyethylenepolymer with acrylonitrile branches23 Crosslinked polymers have two or more polymer chains linked together at one or more points other than their ends The network formed improves the mechanical and physical properties of the polymer Crosslinking may occur during the polymerization reaction when multi functional groups are present as in phenolformaldehyde resins or through outside linking agents as in the vulcanization of rubber with sulfur POLYMERIZATION REACTIONS Two general reactions form synthetic polymers chain addition and condensation Chapter 11 12201 1110 AM Page 303 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 molecularweight olefinic compounds eg ethylene or styrene or con jugated diolefins eg butadiene or isoprene Condensation polymerization can occur by reacting 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 see Condensation Polymeri zation later in this chapter ADDITION POLYMERIZATION Addition polymerization is employed primarily with substituted or unsubstituted olefins and conjugated diolefins 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 IZ to the monomer For example in eth ylene polymerization with a special catalyst the chain grows by attach ing the ethylene units one after another until the polymer terminates This type of addition produces a linear polymer IZ CH2CH2 r ICH2CH2z Branching occurs especially when free radical initiators are used due to chain transfer reactions see following section Free Radical Polymerizations For a substituted olefin such as vinyl chloride the addition primarily produces the most stable intermediate I Inter mediate II does not form to any appreciable extent 304 Chemistry of Petrochemical Processes Iz a free radical I cation I or an anion I R alkyl phenyl Cl etc Propagation then occurs by successive monomer molecules additions to the intermediates Three addition modes are possible a Head to tail b Head to head and c tail to tail Chapter 11 12201 1110 AM Page 304 The headtotail addition mode produces the most stable intermediate For example styrene polymerization mainly produces the headto tail intermediate Polymerization 305 Headtohead or tailtotail modes of addition are less likely because the intermediates are generally unstable Chain growth continues until the propagating polymer chain terminates Free Radical Polymerization Free radical initiators can polymerize olefinic compounds These chem ical compounds have a weak covalent bond that breaks easily into two free radicals when subjected to heat Peroxides hydroperoxides 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 short lived and therefore not selective Chain transfer reactions often occur and result in a highly branched prod uct 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 propagat ing polymer intermediate which creates a new active center The new center can add more ethylene molecules forming a long branch Head totail mode Chapter 11 12201 1110 AM Page 305 Intermolecular chain transfer reactions may occur between two propa gating polymer chains and result in the termination of one of the chains Alternatively these reactions take place by an intramolecular reaction by the coiling of a long chain Intramolecular chain transfer normally results in short branches4 306 Chemistry of Petrochemical Processes Free radical polymers may terminate when two propagating chains com bine In this case the tailtotail addition mode is most likely Polymer propagation stops with the addition of a chain transfer agent For example carbon tetrachloride can serve as a chain transfer agent CH2CH2 CCl4 r CH2CH2Cl CCl3 The CCl3 free radical formed can initiate a new polymerization reaction Cationic Polymerization Strong protonic acids can affect the polymerization of olefins Chapter 3 Lewis acids such as AlCl3 or 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 polymeriza tion 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 Chapter 11 12201 1110 AM Page 306 The next step is the insertion of the monomer molecules between the ion pair CH32C HBF3OH n CH2CHCH3 f CH3 CH3 CH32CHCH2CHn1CH2CHBF3OH In ionic polymerizations 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 carbocation and usually copoly merizes with a small amount of isoprene using cationic initiators The product polymer is a synthetic rubber widely used for tire inner tubes Polymerization 307 Cationic initiators can also polymerize aldehydes For example BF3 helps produce commercial polymers of formaldehyde The resulting polymer a polyacetal is an important thermoplastic Chapter 12 CH2O In general the activation energies for both cationic and anionic poly merization are small For this reason lowtemperature conditions are normally used to reduce side reactions5 Low temperatures also minimize chain transfer reactions These reactions produce lowmolecular weight polymers by disproportionation of the propagating polymer X represents the counter ion Cationic polymerization can terminate by adding a hydroxy compound such as water Chapter 11 12201 1110 AM Page 307 Anionic Polymerization Anionic polymerization is better for vinyl monomers with electron withdrawing groups that stabilize the intermediates Typical monomers best polymerized by anionic initiators include acrylonitrile 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 polymerization Many initiators such as alkyl and aryllithium and sodium and lithium suspensions in liquid ammonia effect the polymerization For example acrylonitrile combined with nbutyllithium forms a carbanion intermediate 308 Chemistry of Petrochemical Processes 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 composition and orientation of the products For example the polymer ization of butadiene with lithium in tetrahydrofuran a polar solvent gives a high 12 addition polymer6 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 tem perature7 a higher cisoid conformation is anticipated for isoprene Chapter 11 12201 1110 AM Page 308 Coordination Polymerization Polymerizations catalyzed with coordination compounds are becom ing more important for obtaining polymers with special properties linear and stereospecific The first linear polyethylene polymer was prepared from a mixture of triethylaluminum and titanium tetrachloride Ziegler catalyst in the early 1950s Later Natta synthesized a stereoregular polypropylene with a Zieglertype catalyst These catalyst combinations are now called ZieglarNatta catalysts 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 Different theories about the formation of coordination complexes have been reviewed by Huheey8 In recent years much interest has been cen tered on using late transition metals such as iron and cobalt for polymer ization Due to their lower electrophilicity they have greater tolerence for polar functionality It was found that the catalyst activity and the polymer branches could be modified by altering the bulk of the ligand that sur rounds the central metal Such a protection reduces chaintransfer reactions and results in a high molecularweight polymer An example of these cata lysts are pyridine bisimine ligands complexed with iron and cobalt salts9 ZieglerNatta catalysts currently produce linear polyethylene non branched stereoregular polypropylene cispolybutadiene and other stereoregular polymers In polymerizing these compounds a reaction between αTiCl3 and tri ethylaluminum produces a five coordinate titanium III complex arranged octahedrally The catalyst surface has four Cl anions an ethyl group and a vacant catalytic site with the TiIII ion in the center of the octahedron A polymerized ligand such as ethylene occupies the vacant site Polymerization 309 The next step is the cis insertion of the ethyl group leaving a vacant site In another step ethylene occupies the vacant site This process continues until the propagating chain terminates Chapter 11 12201 1110 AM Page 309 When propylene is polymerized with free radicals or some ionic initiators a mixture of three stereoforms results Figure 11110 These forms are Atacticthe methyl groups are randomly distributed Isotacticall methyl groups appear on one side of the polymer chain Syndiotacticthe methyl groups alternate regularly from one side to the other The isotactic form of propylene 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 cen 310 Chemistry of Petrochemical Processes Figure 111 Propylene can undergo polymerization in three different ways to form atactic a isotactic b or syndiotactic polypropylene c10 Chapter 11 12201 1110 AM Page 310 ters of the polymer are the same is a crystalline thermoplastic By con trast atactic polypropylene in which the stereo centers are arranged ran domly is an amorphous gum elastomer Polypropylene consisting of blocks of atactic and isotactic stereo sequences is rubbery11 Polymeriz ing propylene with ZieglerNatta catalyst produces mainly isotactic polypropylene The CosseArlman model explains the formation of the stereoregular type by describing the crystalline structure of αTiCl3 as a hexagonal close packing with anion vacancies12 This structure allows for cis insertion However due to the difference in the steric require ments one of the vacant sites available for the ligand to link with the tita nium catalyst which has a greater affinity for the propagating polymer than the other site Accordingly the growing polymer returns rapidly back to that site as shown here Polymerization 311 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 lig and occupation of any available vacant site This course however results in a syndiotactic polypropylene when propylene is the ligand Chapter 11 12201 1110 AM Page 311 Adding hydrogen terminates the propagating polymer The reaction between the polymer complex and the excess triethylaluminum also termi nates the polymer Treatment with alcohol or water releases the polymer 312 Chemistry of Petrochemical Processes A chain transfer reaction between the monomer and the growing polymer produces 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 metallocenes The chiral form of metallocene produces isotactic polypropylene whereas the achi ral form produces atactic polypropylene As the ligands rotate the cata lyst produces alternating blocks of isotactic and atactic polymer much like a miniature sewing machine which switches back and forth between two different kinds of stitches11 CONDENSATION POLYMERIZATION StepReaction Polymerization Though less prevalent than addition polymerization condensation polymerization produces important polymers such as polyesters polyamides nylons polycarbonates polyurethanes and phenol formaldehyde resins Chapter 12 In general condensation polymerization refers to 1 A reaction between two different monomers Each monomer pos sesses 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 Chapter 11 12201 1110 AM Page 312 1 A similar reaction between a diamine and a diacid can also produce polyamides 2 Reactions between one monomer species with two different func tional groups One functional group of one molecule reacts with the other functional group of the second molecule For example polymerization of an amino acid starts with condensation of two monomer molecules Polymerization 313 In these two examples a small molecule water results from the con densation reaction Ring opening polymerization of lactams can also be considered a con densation 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 polymer ization 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 condensa tion 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 endings 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 Chapter 11 12201 1110 AM Page 313 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 crosslinking occurs and a thermoset ting polymer results Example of this type are polyurethanes and urea formaldehyde resins Chapter 12 Acid catalysts such as metal oxides and sulfonic acids generally cat alyze condensation polymerizations However some condensation poly mers form under alkaline conditions For example the reaction of formaldehyde with phenol under alkaline conditions produces methy lolphenols which further condense to a thermosetting polymer RING OPENING POLYMERIZATION Ring opening polymerization produces a small number of synthetic commercial polymers Probably the most important ring opening reaction is that of caprolactam for the production of nylon 6 314 Chemistry of Petrochemical Processes Although no small molecule gets eliminated the reaction can be consid ered a condensation polymerization Monomers suitable for polymeriza tion by ring opening condensation normally possess two different functional groups within the ring Examples of suitable monomers are lactams such as caprolactam which produce polyamides and lactons which produce polyesters Ring opening polymerization may also occur by an addition chain reaction For example a ring opening reaction polymerizes trioxane to a polyacetal in the presence of an acid catalyst Formaldehyde also pro duces the same polymer Chapter 11 12201 1110 AM Page 314 Monomers used for ring opening polymerization by addition are cyclic compounds that open easily with the action of a catalyst during the reac tion Small strained rings are suitable for this type of reaction For exam ple the action of a strong acid or a strong base could polymerize ethylene oxide to a high molecularweight polymer Polymerization 315 These water soluble polymers are commercially known as carbowax The ring opening of cycloolefins is also possible with certain coordi nation catalysts This simplified example shows cyclopentene under going a firststep formation of the dimer cyclodecadiene and then incorporating additional cyclopentene monomer units to produce the solid rubbery polypentamer13 Another example is the metathesis of cyclooctene which produces poly octenylene an elastomor known as transpolyoctenamer14 Chemische Werke Huls produces the polymer for use in blends with some conventional rubbersl5 This metathetic reaction has become an important synthetic tool in the polymer field1316 Catalyzed polymeriza tion of cycloolefins has been reviewed by Tsonis17 POLYMERIZATION TECHNIQUES Polymerization reactions can occur in bulk without solvent in solution in emulsion in suspension or in a gasphase process Interfacial poly merization is also used with reactive monomers such as acid chlorides Cyclodecadiene Polypentamer Chapter 11 12201 1110 AM Page 315 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 reac tion to low conversions and strong agitation Outside cooling can also control the exothermic heat In solution polymerization an organic solvent dissolves the monomer Solvents should have low chain transfer activity to minimize chain trans fer reactions that produce lowmolecularweight polymers The presence of a solvent makes heat and viscosity control easier than in bulk poly merization Removal of the solvent may not be necessary in certain appli cations 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 also used to polymerize many water insoluble 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 alkylbenzene 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 SO4 Xray and light scattering techniques show that the micelles start to increase in size by absorbing the macromolecules For example in the free radical polymerization of styrene the micelles increased to 250 times their original size In suspension polymerization the monomer gets dispersed in a liquid such as water Mechanical agitation keeps the monomer dispersed Initiators should be soluble in the monomer Stabilizers such as talc or polyvinyl alcohol prevent polymer chains from adhering to each other and keep the monomer dispersed in the liquid medium The final poly mer appears in a granular form Suspension polymerization produces polymers more pure than those from solution polymerization due to the absence of chain transfer reac tions As in a solution polymerization the dispersing liquid helps control the reactions heat Interfacial polymerization is mainly used in polycondensation reac tions with very reactive monomers One of the reactants usually an acid 316 Chemistry of Petrochemical Processes Chapter 11 12201 1110 AM Page 316 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 produces polycarbonates polyesters and polyamides The reaction occurs at the interface between the two immiscible liquids and the polymer is continuously removed from the interface PHYSICAL PROPERTIES OF POLYMERS The properties of polymers determine whether they can be used as a plastic a fiber an elastomer an adhesive or a paint Important physical properties include the density melt flow index crystallinity and average molecular weight Mechanical properties of a polymer such as modulus the ratio of stress to strain elasticity and breaking strength essentially follow from the physical properties The following sections describe some important properties of polymers CRYSTALLINITY A polymers tendency to have order and form crystallites derives from the regularity of the chains presence or absence and arrangement of bulky groups and the presence of secondary forces such as hydrogen bonding For example isotactic polystyrene with phenyl groups arranged on one side of the polymer backbone is highly crystalline while the atac tic form with a random arrangement of phenyl groups is highly amor phous Polyamides are also highly crystalline due to strong hydrogen bonding Highdensity polyethylene exhibits no hydrogen bonding but its linear structure makes it highly crystalline Lowdensity polyethylene on the other hand has branches and a lower crystallinity It does not pack as easily as the highdensity polymer The mechanical and thermal behaviors depend partly on the degree of crystallinity For example highly disordered dominantly amorphous polymers make good elastomeric materials while highly crystalline polymers such as polyamides have the rigidity needed for fibers Crystallinity of polymers correlates with their melting points MELTING POINT The freezing point of a pure liquid is the temperature at which the liquids molecules lose transitional freedom and the solids molecules Polymerization 317 Chapter 11 12201 1110 AM Page 317 become more ordered within a definite crystalline structure Polymers however are nonhomogeneous and do not have a definite crystalliza tion temperature When a melted polymer cools some polymer molecules line up and form crystalline regions within the melt The rest of the polymer remains amorphous The temperature at which these crystallites disappear when the crystalline polymer is gradually heated is called the crystalline melting temperature Tm Further cooling of the polymer below Tm changes the amorphous regions into a glasslike material The tempera ture at which this change occurs is termed the glass transition tempera ture Tg Elastomeric materials usually have a low Tg low crystallinity while highly crystalline polymers such as polyamides have a relatively high Tg VISCOSITY The viscosity of a substance measures its resistance to flow The melt viscosity of a polymer increases as the molecular weight of the polymer rises Polymers with high melt viscosities require higher temperatures for processing The melt flow index describes the viscosity of a solid plastic It is the weight in grams of a polymer extruded through a defined orifice at a specified time The melt viscosity and the melt flow index can measure the extent of polymerization A polymer with a high melt flow index has a low melt viscosity a lower molecular weight and usually a lower impact tensile strength MOLECULAR WEIGHT Polymerization usually produces macromolecules with varying chain lengths As a result polymers are described as polydisperse systems Commercial polymers have molecular weights greater than 5000 and contain macromolecules with variable molecular weights The methods for determining the average molecular weights of polymers include measuring some colligative property such as viscosity or sedimentation Different methods do not correlate well and determining the average molecular weight requires more than one method Two methods normally determine the number average and the weight average molecular weights of the polymer 318 Chemistry of Petrochemical Processes Chapter 11 12201 1110 AM Page 318 Number Average Molecular Weight The number average molecular weight Mn is related to the number of particles present in a sample It is calculated by dividing the sum of the weights of all the species present monomers dimers trimers and so on by the number of species present Polymerization 319 M W N N M N n i i i i i degree of polymerization dimer trimers etc Ni number of each polymeric species Mi molecular weight of each polymer species W total weight of all polymer species Mn depends not on the molecular sizes of the particles but on the number of particles Measuring colligative properties such as boiling point ele vation freezing point depression and vapor pressure lowering can deter mine the number of particles in a sample Weight Average Molecular Weight The weight average molecular weight Mw is the sum of the products of the weight of each species present and its molecular weight divided by the sum of all the species weights M W M W W M N M w i i i i i i Wi weight of each polymeric species Mi molecular weight of each polymeric species Substituting NiMi Wi the weight average molecular weight can be defined as M N M N M w i i i i 2 Larger heavier molecules contribute more to Mw than to Mn Light scat tering techniques and ultracentrifugation can determine Mw The following simple example illustrates the difference between Mn and Mw Suppose a sample has six macromolecules Three of them have Chapter 11 12201 1110 AM Page 319 a molecular weight 10 104 two have a molecular weight 20 104 and one has a molecular weight 30 104 320 Chemistry of Petrochemical Processes M M n w 3 0 4 0 3 0 10 6 1 7 10 3 1 0 10 2 2 0 10 1 3 0 10 3 1 0 10 2 2 0 10 1 3 0 10 2 0 10 4 4 4 2 4 2 4 2 4 4 4 4 In monodispersed systems Mn Mw The difference in the value between Mn and Mw indicates the poly dispersity of the polymer system The closer Mn is to Mw the narrower the molecular weight spread Molecular weight distribution curves for polydispersed systems can be obtained by plotting the degree of poly merization i versus either the number fraction Ni or the weight frac tion Wi CLASSIFICATION OF POLYMERS Synthetic polymers may be classified into addition or condensation polymers according to the type of reaction A second classification depends on the monomer type and the linkage present in the repeating unit into polyolefins polyesters polyamides etc Other classifications depend on the polymerization technique bulk emulsion suspension etc or on the polymers end use The latter classifies polymers into three broad categories plastics elastomers and synthetic fibers Plastics 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 resoftened by heat and thermosets which cannot be resoftened by heat Thermoplastics have moderate crystallinity They can undergo large elongation but this elongation is not as reversible as it is for elastomers Examples of thermoplastics are polyethylene and polypropylene Thermosetting plastics are usually rigid due to high crosslink ing between the polymer chains Examples of this type are phenol fomaldehyde and polyurethanes Crosslinking may also be promoted by using chemical agents such as sulfur or by heat treatment or irradiation with gamma rays ultraviolet light or energetic electrons Recently high Chapter 11 12201 1110 AM Page 320 energy ion beams were found to increase the hardness of the treated poly mer drastically18 Synthetic Rubber Synthetic rubber elastomers are high molecular weight polymers with long flexible chains and weak intermolecular forces They have low crystallinity highly amorphous in the unstressed state segmental mobility and high reversible elasticity Elastomers are usually cross linked to impart strength Synthetic Fibers Synthetic fibers are longchain polymers characterized by highly crys talline regions resulting mainly from secondary forces eg hydrogen bonding They have a much lower elasticity than plastics and elas tomers They also have high tensile strength a light weight and low moisture absorption REFERENCES 1 Fessenden R and Fessenden J Organic Chemistry 4th Ed BrooksCole Publishing Co 1991 p 926 2 Hoffman A S and Bacskai R Chapter 6 in Copolymerization G E Ham ed WileyInterscience New York 1964 3 Rodriguez F Principles of Polymer Systems 3rd Ed Hemisphere Publishing Corp New York 1989 p 108 4 Wiseman P Petrochemicals Ellis Horwood Ltd England 1986 p 45 5 Seymor R and Corraher C E Jr Polymer Chemistry 2nd Ed Dekker New York 1988 p 284 6 Kutz I and Berber A J Polymer Science Vol 42 1960 p 299 7 Stevens M P Polymer Chemistry Addison Wesley Publishing Co London 1975 p 156 8 Huheey J E Chapter 11 in Inorganic Chemistry 3rd Ed Harper and Row Publishers Inc New York 1983 9 Allison M and Bennet A Novel Highly Active Iron and Cobalt Catalysts for Olefin Polymerization CHEMTECH July 1999 pp 2428 Polymerization 321 Chapter 11 12201 1110 AM Page 321 10 Watt G W Hatch L F and Lagowski J J Chemistry New York W W Norton Co 1964 p 449 11 Baum R Elastomeric Polypropylene Oscillating Catalyst Controls Microstructure Chemical and Engineering News Jan 16 1995 pp 67 12 Arlman E and Cossee P J Catal Vol 3 1964 p 99 13 Wagner P H Olefin Metathesis Applications for the Nineties Chemistry and Industry 4 May 1992 pp 330333 14 Parshall G W and Nugent W A Functional Chemicals via Homogeneous Catalysis CHEMTECH Vol 18 No 5 May 1988 pp 314320 15 Banks R L in Applied Industrial Catalysis Leach B E ed Academic New York 1984 pp 234235 16 Platzer N CHEMTECH Vol 9 No 1 1979 pp 1620 17 Tsonis C P Catalyzed Polymerization of Cycloolefins Journal of Applied Polymer Science Vol 26 1981 pp 35253536 18 Dagani R SuperhardSurfaced Polymers Made by HighEnergy Ion Irradiation Chemical and Engineering News Jan 9 1995 pp 2426 322 Chemistry of Petrochemical Processes Chapter 11 12201 1110 AM Page 322 CHAPTER TWELVE Synthetic PetroleumBased Polymers INTRODUCTION 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 applica tions Polymerization could now be tailored to synthesize materials stronger than steell For example polyethylene fibers with a molecular weight of one million can be treated to be 10 times stronger than steel However its melting point is 148C A recently announced thermotropic liquid crystal polymer based on phydroxybenzoic acid terephthalic acid and p pvbiphenol has a high melting point of 420C and does not decompose up to 560C This polymer has an initial stress of 34 106 kgmm2 even after 6000 hours of testing2 The polymer field is versatile and fast growing and many new poly mers 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 improve ments have a great impact on the economy In the elastomer field for example improvements influenced the automobile industry and also related fields such as mechanical goods and wire and cable insulation 323 Chapter 12 12201 1111 AM Page 323 This chapter discusses synthetic polymers based primarily on monomers produced from petroleum chemicals The first section covers the synthe sis of thermoplastics and engineering resins The second part reviews thermosetting plastics and their uses The third part discusses the chem istry of synthetic rubbers including a brief review on thermoplastic elas tomers which are generally not used for tire production but to make other rubber products The last section addresses synthetic fibers THERMOPLASTICS AND ENGINEERING RESINS Thermoplastics are important polymeric materials that have replaced or substituted many naturallyderived products such as paper wood and steel Plastics possess certain favorable properties 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 construction electrical and mechanical goods and insulation One growing market that evolved fairly recently is engineer ing 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 Another important and growing market for plastics is the automotive field Many automobile parts are now made of plastics Among the most used polymers are polystyrene polymers and copolymers polypropylene polycarbonates and polyvinyl chloride These materials reduce the cost and the weight of the cars As a result gasoline consumption is also reduced Most bigvolume thermoplastics are produced by addition polymer ization Other thermoplastics are synthesized by condensation Table 121 shows the major thermoplastics3 POLYETHYLENE Polyethylene is the most extensively used thermoplastic The ever increasing demand for polyethylene is partly due to the availability of the monomer from abundant raw materials associated gas LPG naphtha Other factors are its relatively low cost ease of processing the polymer resistance to chemicals and its flexibility World production of all poly ethylene grades approximately 100 billion pounds in 1997 is predicted 324 Chemistry of Petrochemical Processes Chapter 12 12201 1111 AM Page 324 to reach 300 billion pounds in 2015 the largest increase for linear low density polyethylene4 Highpressure polymerization of ethylene was introduced in the 1930s The discovery of a new titanium catalyst by Karl Ziegler in 1953 revolu tionized the production of linear unbranched polyethylene at lower pres sures The two most widely used grades of polyethylene are lowdensity polyethylene LDPE and highdensity polyethylene HDPE Currently Synthetic PetroleumBased Polymers 325 Table 121 Major thermoplastic polymers Chapter 12 12201 1111 AM Page 325 a new LDPE grade has been introduced It is a linear lowdensity grade LLDPE produced like the highdensity polymer at low pressures Polymerizing ethylene is a highly exothermic reaction For each gram of ethylene consumed approximately 35 KJ 850 cal are released5 nCH2 CH2 r CH2CH2n H 92KJmol When ethylene is polymerized the reactor temperature should be well controlled to avoid the endothermic decomposition of ethylene to carbon methane and hydrogen CH2CH2 r 2C 2H2 CH2CH2 r C CH4 LowDensity Polyethylene Lowdensity polyethylene LDPE 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 HDPE due to its lower capability of packing Polymerizing ethylene can occur either in a tubular or in a stirred auto clave reactor In the stirred autoclave the heat of the reaction is absorbed by the cold ethylene feed Stirring keeps a uniform temperature through out the reaction vessel and prevents agglomeration of the 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 100200C and 100135 atmospheres Ethylene conversion is kept to a low level 1025 to control the heat and the viscosity However over all conversion with recycle is over 95 The polymerization rate can be accelerated by increasing the tempera ture the initiator concentration and the pressure Degree of branching and molecular weight distribution depend on temperature and pressure A higher density 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 comonomers such as vinyl acetate or ethyl acrylate The copolymers have lower crystallinity but bet ter flexibility and the resulting polymer has higher impact strength6 326 Chemistry of Petrochemical Processes Chapter 12 12201 1111 AM Page 326 HighDensity Polyethylene Highdensity polyethylene HDPE is produced by a lowpressure process in a fluidbed reactor Catalysts used for HDPE are either of the Zieglartype a complex of AlC2H53 and αTiCl4 or silica alumina impregnated with a metal oxide such as chromium oxide or molybdenum oxide Reaction conditions are generally mild but they differ from one process to another In the newer Unipol process Figure 121 used to produce both HDPE and LLDPE the reaction occurs in the gas phase7 Ethylene and the comonomers propene 1butene etc are fed to the reactor containing a fluidized bed of growing polymer particles Operation temperature and pressure are approximately 100C and 20 atmospheres 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 reactor is mixed with additives and then pelletized New modifications for gasphase processes have been reviewed by Sinclair8 The polymerization of ethylene can also occur in a liquidphase sys tem where a hydrocarbon diluent is added This requires a hydrocarbon recovery system Highdensity polyethylene is characterized by a higher crystallinity and higher melting temperature than LDPE due to the absence of branching Synthetic PetroleumBased Polymers 327 Figure 121 The Union Carbide Unipol process for producing HDPE7 1 reactor 2 singlestage centrifugal compressor 3 heat exchanger 4 discharge tank Chapter 12 12201 1111 AM Page 327 Some branching could be incorporated in the backbone of the polymer by adding variable amounts of comonomers such as hexene These comono mers modify the properties of HDPE for specific applications Linear LowDensity Polyethylene Linear lowdensity polyethylene LLDPE is produced in the gas phase under low pressure Catalysts used are either Ziegler type or new generation metallocenes The Union Carbide process used to produce HDPE could be used to produce the two polymer grades Terminal olefins C4C6 are the usual comonomers to effect branching Developments in the gasfluidizedbed polymerization reduced invest ments for high pressure processes used for LDPE The new technology lowers capital and operating costs and reduces reactor purgewaste streams Specific designed nozzles are located within the fluidized bed to disperse the hydrocarbons within the bed The liquid injected through the nozzles quickly evaporates hence removing the heat of polymerization These processes can produce a wide range of polymers with different melt flow indices MFI of 001 to 100 and densities of 890970 Kgm3 Types of reactors and catalysts used for HDPE and LLDPE have been reviewed by Chinh and Power9 LLDPE has properties between HDPE and LDPE It has fewer branches higher density and higher crystallinity than LDPE Properties and Uses of Polyethylenes Polyethylene is an inexpensive thermoplastic that can be molded into almost any shape extruded into fiber or filament and blown or precipi tated into film or foil Polyethylene products include packaging largest market bottles irrigation pipes film sheets and insulation materials Currently high density polyethylene is the largestvolume thermo plastic The 1997 US production of HDPE was 125 billion pounds LDPE was 77 billion pounds and LLDPE was 69 billion pounds10 Because LDPE is flexible and transparent it is mainly used to produce film and sheets Films are usually produced by extrusion Calendering is mainly used for sheeting and to a lesser extent for film production HDPE is important for producing bottles and hollow objects by blow molding Approximately 64 of all plastic bottles are made from HDPEl1 Injection molding is used to produce solid objects Another important market for HDPE is irrigation pipes Pipes made from HDPE 328 Chemistry of Petrochemical Processes Chapter 12 12201 1111 AM Page 328 are flexible tough and corrosion resistant They could be used to carry abrasive materials such as gypsum Table 122 shows the important prop erties of polyethylenes POLYPROPYLENE Polypropylene PP is a major thermoplastic polymer Although polypropylene did not take its position among the large volume polymers until fairly recently it is currently the third largest thermoplastic after PVC 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 crys tallinity it is not suitable for thermoplastic or fiber use The turning point in polypropylene production was the development of a Zieglertype cat alyst by Natta to produce the stereoregular form isotactic Catalysts developed in the titaniumaluminum alkyl family are highly reactive and stereoselective Very small amounts of the catalyst are needed to achieve polymerization one gram catalyst300000 grams polymer Consequently the catalyst entrained in the polymer is very small and the catalyst removal step is eliminated in many new processes12 Amoco has introduced a new gasphase process called absolute gas phase in which polymerization of olefins 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 application13 Synthetic PetroleumBased Polymers 329 Table 122 Important properties of polyethylenes Degree of Melting crystal Stiffness point Density linity modules Polymer range C gcm3 psi 103 Branched Low density 107121 092 6065 2530 Medium density 0935 75 6065 Linear High density Ziegler type 125132 095 85 90110 Phillips type 096 91 130150 Chapter 12 12201 1111 AM Page 329 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 gas phase process8 In the Union CarbideShell gas phase process Figure 122 a wide range of polypropylenes are made in a fluidized bed gas phase reactorl4 Melt index atactic level and molec ular 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 dis cussed before but a second reactor is added Homopolymers and ran dom copolymers are produced in the first reactor which operates at approximately 70C and 35 atmospheres Impact copolymers are pro duced in the second reactor impact reactor after transferring the polypropylene resin from the first reactor Gaseous propylene and ethyl ene 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 sec ond operates at lower pressure approximately 17 atmospheres The granular product is finally pelletized Random copolymers made by copolymerizing equal amounts of ethylene and propylene are highly amorphous and they have rubbery properties An example of the liquidphase polymerization is the Spheripol process Figure 123 which uses a tubular reactor7 Copolymerization 330 Chemistry of Petrochemical Processes Figure 122 The Union Carbide gasphase process for producing polypropy lene14 1 reactor 2 centrifugal compressor 3 heat exchanger 4 product dis charge tank unreacted gas separated from product 5 impact reactor 6 compressor 7 heat exchanger 8 discharge tank copolymer separated from reacted gas Chapter 12 12201 1111 AM Page 330 occurs in a second gas phase reactor Unreacted monomer is flashed in a twostage pressure system and is recycled back to the reactor Polymer yields of 30000 or more KgKg of supported catalyst are attainable and catalyst residue removal from the polymer is not required The product polymer has an isotactic index of 9099 New generation metallocene catalysts can polymerize propylene in two different ways Rigid chiral metallocene produce isotactic poly propylene whereas the achiral forms of the catalysts produce atactic polypropylene The polymer microstructure is a function of the reaction conditions and the catalyst design15 Recent work has shown that the rate of ligand rotation in some unbridged metallocenes can be controlled so that the metallocene oscillates between two stereochemical states One isomer produces isotactic polypropylene and the other produces the atac tic polymer As a result alternating blocks of rigid isotactic and flexible atactic polypropylene grow within the same polymer chain16 Properties and Uses of Polypropylene The properties of commercial polypropylene vary widely according to the percentage of crystalline isotactic polymer and the degree of polymer ization Polypropylenes with a 99 isotactic index are currently produced Synthetic PetroleumBased Polymers 331 Figure 123 The Himont Inc Spheripol process for producing polypropylene in a liquidphase7 1 tubular reactor 24 twostage flash pressure system to sepa rate unreacted monomer for recycle 3 heterophasic copolymerization gas phase reactor 5 stripper Chapter 12 12201 1111 AM Page 331 Articles made from polypropylene have good electrical and chemical resistance and low water absorption Its other useful characteristics are its light weight lowest thermoplastic polymer density high abrasion resistance dimensional stability high impact strength and no toxicity Table 123 shows the properties of polypropylene 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 filament processes have made polypropylene accessible for fiber production Lowcost fibers made from polypropylene are replacing those made from sisal and jute World demand for polypropylene is expected to be 30 billion pounds by 2002 This is the strongest growth forecast for any of the major ther moplastics 59 Many of the resins new applications particularly in packaging come at the expense of PS and PVC the two resins that have been the subject of regulatory restrictions related to solid waste issues and potential toxicity17 332 Chemistry of Petrochemical Processes Table 123 Properties of Polypropylene Density gcm3 090091 Fill temperature max C 130 Tensile strength psi 32005000 Water absorption 24 hr 001 Elongation 3700 Melting point Tm C 176 Thermal expansion 105 inin C 5810 Specific volume cm3lb 304308 Polyvinyl chloride PVC is one of the most widely used thermoplas tics 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 PVC can be prepolymerized in bulk to approximately 78 conver sion It is then transferred to an autoclave where the particles are poly merized to a solid powder Most vinyl chloride however is polymerized Chapter 12 12201 1111 AM Page 332 in suspension reactors made of stainless steel or glasslined The perox ide used to initiate the reaction is dispersed in about twice its weight of water containing 0011 of a stabilizer such as polyvinyl alcoholl8 In the European Vinyls Corp process Figure 124 vinyl chloride monomer VCM is dispersed in water and then charged with the addi tives to the reactor19 It is a stirred jacketed type ranging in size between 20105m3 The temperature is maintained between 5370C to obtain a polymer of a particular molecular weight The heat of the reaction is con trolled by cooling water in the jacket and by additional reflux condensers for large reactors Conversion could be controlled between 8595 as required by the polymer grade At the end of the reaction the PVC and water slurry are channelled to a blowdown vessel from which part of unreacted monomer is recovered The rest of the VCM 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 copoly mer with ethylene or propylene Tg 80C which is rigid is used for Synthetic PetroleumBased Polymers 333 Figure 124 The European Vinyls Corp process for producing polyvinyl chloride using suspension polymerization19 1 reactor 2 blowdown vessels to sepa rate unreacted monomer 3 stripping column 4 reacted monomer recovery 5 slurry centrifuge 6 slurry drier Chapter 12 12201 1111 AM Page 333 blow molding objects Copolymers with 620 vinyl acetate Tg 5080C are used for coatings Properties and Uses of Polyvinyl Chloride Two types of the homopolymer are available the flexible and the rigid Both types have excellent 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 PVC is that it is selfextinguishing due to presence of the chlorine atom Flexible PVC grades account for approximately 50 of PVC produc tion They go into such items as tablecloths shower curtains furniture automobile upholstery and wire and cable insulation Many additives are used with PVC polymers such as plasticizers antioxidants and impact modifiers Heat stabilizers which are particu larly important with PVC resins extend the useful life of the finished product Plastic additives have been reviewed by Ainsworth20 Rigid PVC is used in many items such as pipes fittings roofing auto mobile parts siding and bottles The 1997 US production of PVC and its copolymers was approxi mately 14 billion pounds 334 Chemistry of Petrochemical Processes Polystyrene PS is the fourth bigvolume thermoplastic Styrene can be polymerized alone or copolymerized with other monomers It can be polymerized by free radical initiators or using coordination catalysts Recent work using group 4 metallocene combined with methylalumi noxane produce stereoregular polymer When homogeneous titanium catalyst is used the polymer was predominantly syndiotactic The het erogeneous titanium catalyst gave predominantly the isotactic21 Copolymers with butadiene in a ratio of approximately 13 produces SBR the most important synthetic rubber Copolymers of styreneacrylonitrile SAN have higher tensile strength than styrene homopolymers A copolymer of acrylonitrile buta Chapter 12 12201 1111 AM Page 334 diene 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 cata lysts Bulk suspension and emulsion techniques are used with free rad ical initiators and the polymer is atactic In a typical batch suspension process Figure 125 styrene is sus pended in water by agitation and use of a stabilizer14 The polymer forms beads The beadwater slurry is separated by centrifugation dried and blended with additives Properties and Uses of Styrene Polymers 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 poly styrene is used in items such as automobile interior parts furniture and home appliances Packaging uses plus specialized food uses such as con tainers for carryout food are growth areas Expanded polystyrene foams which are produced by polymerizing styrene with a volatile solvent such as pentane have low densities They are used extensively in insulation and flotation life jackets Synthetic PetroleumBased Polymers 335 Figure 125 The Lummus Crest Inc process for producing polystyrene14 1 reactor 2 holding tank Polystyrene beads and water 3 centrifuge 4 pneu matic drier 5 conditioning tank 6 screening of beads 78 lubrication and blending 9 shipping product Chapter 12 12201 1111 AM Page 335 SAN Tg 105C is stiffer and has better chemical and heat resist ance than the homopolymer However it is not as clear as polystyrene and it is used in articles that do not require optical clarity such as appli ances and houseware materials ABS has a specific gravity of 103 to 106 and a tensile strength in the range of 6 to 75 103 psi These polymers are tough plastics with out standing mechanical properties A wide variety of ABS modifications are available with heat resistance comparable to or better than polysulfones and polycarbonates noted later in this section Another outstanding property of ABS is its ability to be alloyed with other thermoplastics for improved properties For example ABS is alloyed with rigid PVC for a product with better flame resistance Among the major applications of ABS are extruded pipes and pipe fit tings appliances such as refrigerator door liners and in molded automo bile bodies World polystyrene production in 1997 was approximately 10 million tons The demand is forecasted to reach 13 million tons by 200222 The 1997 US production of polystyrene polymers and copolymers was approximately 66 billion pounds ABS SAN and other styrene copoly mers were approximately 3 billion pounds for the same year NYLON RESINS Nylon resins are important engineering thermoplastics Nylons are produced by a condensation reaction of amino acids a diacid and a diammine or by ring opening lactams such as caprolactam The poly mers however are more important for producing synthetic fibers dis cussed later in this chapter 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 expansion 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 THERMOPLASTIC POLYESTERS Thermoplastic polyesters are among the largevolume engineering thermoplastics produced by condensation polymerization of terephthalic 336 Chemistry of Petrochemical Processes Chapter 12 12201 1111 AM Page 336 acid with ethylene glycol or 14butanediol These materials are used to produce film for magnetic tapes due to their abrasion and chemical resis tance low water absorption and low gas permeability Polyethylene terephthalate PET is also used to make plastic bottles approximately 25 of plastic bottles are made from PET Similar to nylons the most important use of PET is for producing synthetic fibers discussed later Polybutylene terephthalate PBT is another thermoplastic polyester pro duced by the condensation reaction of terephthalic acid and 14butanediol Synthetic PetroleumBased Polymers 337 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 7323 The 1997 US production of thermoplastic polyesters was approxi mately 43 billion pounds POLYCARBONATES Polycarbonates PC are another group of condensation thermoplastics used mainly for special engineering purposes These polymers are con sidered polyesters of carbonic acid They are produced by the condensa tion of the sodium salt of bisphenol A with phosgene in the presence of an organic solvent Sodium chloride is precipitated and the solvent is removed by distillation Chapter 12 12201 1111 AM Page 337 Another method for producing polycarbonates is by an exchange reaction between bisphenol A or a similar bisphenol with diphenyl carbonate 338 Chemistry of Petrochemical Processes Diphenol carbonate is produced by the reaction of phosgene and phe nol A new approach to diphenol carbonate and nonphosgene route is by the reaction of CO and methyl nitrite using Pdalumina Dimethyl car bonate is formed which is further reacted with phenol in presence of tetraphenox titanium catalyst Decarbonylation in the liquid phase yields diphenyl carbonate However the reaction is equilibrium constained and requires a compli cated processing scheme24 Properties and Uses of Polycarbonates 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 applications demanding strength and temperature resistance offer advantages of light weight low cost and ease of fabrication25 Materials made from polycarbonates are transparent strong and heat and breakresistant However these materials are subject to stress crack O O CO 2 CH3ONO r CH3OCCOCH3 2NO O O O OCCO OCO CO Decarbon O O O O CH3OCCOCH3 2 r OCCO 2 CH3OH Chapter 12 12201 1111 AM Page 338 ing and can be attacked by weak alkalies and acids Table 124 compares the properties of polycarbonates with other thermoplastic resins25 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 POLYETHER SULFONES Polyether sulfones PES are another class of engineering thermoplas tics generally used for objects that require continuous use of tempera tures around 200C They can also be used at low temperatures with no change in their physical properties Synthetic PetroleumBased Polymers 339 Table 124 Properties of polycarbonates compared with some thermoplastics25 Melting or glass Izod transition tensile compressive flexural impact temperature strength strength strength 18 in Resin C MPa MPa MPa Jm PPO impact 100110 117127 124162 179200 4353 modified PC 149 65 86 93 850 PC 30 glass 149 131 124 158 106 PCABS 149 4850 76 8994 560 Nylon 66 impact 240260 4855 160210 modified Nylon 66 33 265 151193 202 282 117138 glass PBT 232267 56 59100 82115 4353 PBT 30 glass 232267 117131 124162 179200 6985 Acetal 181 124 96 69122 homopolymer ABS impact 100110 3343 3155 5576 347400 modified PPO impact 135 4855 69 5676 320370 modified PPO 30 100110 117127 123 138158 90112 reinforced Chapter 12 12201 1111 AM Page 339 Polyether sulfones can be prepared by the reaction of the sodium or potassium salt of bisphenol A and 44 vdichlorodiphenyl sulfone Bisphenol A acts as a nucleophile in the presence of the deactivated aro matic ring of the dichlorophenylsulfone The reaction may also be cat alyzed with FriedelCrafts catalysts the dichlorophenyl sulfone acts as an electrophile 340 Chemistry of Petrochemical Processes Polyether sulfones could also be prepared using one monomer Properties and Uses of Aromatic Polyether Sulfones In general properties of polyether sulfones are similar to those of polycarbonates but they can be used at higher temperatures Figure 126 shows the maximum use temperature for several thermoplastics26 Aromatic polyether sulfones can be extruded into thin films and foil and injection molded into various objects that need hightemperature stability POLYPHENYLENE OXIDE Polyphenylene oxide PPO is produced by the condensation of 26 dimethylphenol The reaction occurs by passing oxygen in the phenol solution in presence of Cu2Cl2 and pyridine Chapter 12 12201 1111 AM Page 340 PPO is an engineering thermoplastic with excellent properties To improve its mechanical properties and dimensional stability PPO can be blended with polystyrene and glass fiber Articles made from PPO could be used up to 330C it is mainly used in items that require higher tem peratures such as laboratory equipment valves and fittings POLYACETALS Polyacetals are among the aliphatic polyether family and are produced by the polymerization of formaldehyde They are termed polyacetals to distinguish them from polyethers produced by polymerizing ethylene oxide which has two CH2 groups between the ether group The poly merization reaction occurs in the presence of a Lewis acid and a small amount of water at room temperature It could also be catalyzed with amines Synthetic PetroleumBased Polymers 341 Figure 126 Maximum continuous use temperature of some engineering thermo plastics26 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 Chapter 12 12201 1111 AM Page 341 Articles made from polyacetals vary from door handles to gears and bushings carburetor parts to aerosol containers The major use of poly acetals is for molded grades THERMOSETTING PLASTICS This group includes many plastics produced by condensation polymer ization Among the important thermosets are the polyurethanes epoxy resins phenolic resins and urea and melamine formaldehyde resins POLYURETHANES Polyurethanes are produced by the condensation reaction of a polyol and a diisocyanate 342 Chemistry of Petrochemical Processes No byproduct is formed from this reaction Toluene diisocyanate Chapter 10 is a widely used monomer Diols and triols produced from the reaction of glycerol and ethylene oxide or propylene oxide are suit able for producing polyurethanes Polyurethane polymers are either rigid or flexible depending on the type of the polyol used For example triols derived from glycerol and propylene oxide are used for producing 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 group27 Chapter 12 12201 1111 AM Page 342 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 Diisocyanates generally employed with polyols to produce polyure thanes are 24and 26toluene diisocyanates prepared from dinitro toluenes Chapter 10 Synthetic PetroleumBased Polymers 343 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 MDI 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 15080028 Improved polyurethane can be produced by copolymerization Block copolymers of polyurethanes connected with segments of isobutylenes exhibit hightemperature properties hydrolytic stability and barrier char acteristics The hard segments of polyurethane block polymers consist of RNHCOOn where R usually contains an aromatic moiety29 Properties and Uses of Polyurethanes 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 16 lbft3 for the flexible types and 150 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 Flame retardency of polyurethanes could be improved by using special additives spraying a coating material such as magnesium oxychloride or by grafting a halo gen phosphorous moiety to the polyol Trichlorobutylene oxide is Chapter 12 12201 1111 AM Page 343 sometimes copolymerized with ethylene and propylene oxides to pro duce 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 Figure 127 compares the degree of insulation of some insulating materials28 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 abra sion They are produced using shortchain polyols such as polytetram ethylene 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 high temperature properties hydrolyic stability and barrier characteristics29 EPOXY RESINS Epoxy resins are produced by reacting epichlorohydrin and a diphe nol Bisphenol A is the diphenol generally used The reaction a ring 344 Chemistry of Petrochemical Processes Figure 127 The comparative thickness for the same degree of insulation dry conditions28 Chapter 12 12201 1111 AM Page 344 opening polymerization of the epoxide ring is catalyzed with strong bases such as sodium hydroxide A nucleophilic attack of the phenoxy ion displaces a chloride ion and opens the ring Synthetic PetroleumBased Polymers 345 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 Properties and Uses of Epoxy Resins Epoxy resins have a wide range of molecular weights 100010000 Those with higher molecular weights termed phenoxy are hydrolyzed to transparent resins that do not have the epoxide groups These could be used in molding purposes or crosslinked by diisocyanates or by cyclic anhydrides 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 temperatures up to 500C Epoxy resins with improved stress cracking properties can be made by using toughening agents such as carboxylterminated butadieneacry lonitrile 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 forming ether linkages This material is tougher than epoxy resins and suitable for encapsulating electrical units Chapter 12 12201 1111 AM Page 345 Major 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 manifests its chemical resistance In 1997 approximately 681 million pounds of unmodified epoxy resins were produced in the US UNSATURATED POLYESTERS Unsaturated polyesters are a group of polymers and resins used in coatings or for castings with styrene 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 346 Chemistry of Petrochemical Processes 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 possible for preparing these resins The 1998 US production of polyesters was approximately 17 billion pounds PHENOLFORMALDEHYDE RESINS Phenolformaldehyde resins are the oldest thermosetting polymers They are produced by a condensation 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 exhaus tive work by Baekeland was published in 1909 In this paper he deseribes the product as far superior to amber for pipe stem and similar articles less flexible but more durable than celluloid odorless and fireresistant30 The reaction between phenol and formaldehyde is either base or acid catalyzed and the polymers are termed resols for the base catalyzed and novalacs for the acid catalyzed Chapter 12 12201 1111 AM Page 346 The first step in the basecatalyzed reaction is an attack by the phe noxide ion on the carbonyl carbon of formaldehyde giving a mixture of ortho and parasubstituted monomethylolphenol plus di and trisubsti tuted methylol phenols Synthetic PetroleumBased Polymers 347 The second step is the condensation reaction between the methylolphe nols 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 aromatic ring which forms methylene bridges The formed polymer is a threedimensional network thermoset 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 formation of meth ylene 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 formalde hyde and a small amount of hexamethylene tetramine hexamine Chapter 12 12201 1111 AM Page 347 CH26N4 Hexamine decomposes in the presence of traces of moisture to formaldehyde and ammonia This results in crosslinking and formation of a thermoset resin 348 Chemistry of Petrochemical Processes Properties and Uses of Phenolic Resins 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 psi31 Molding applications dominate the market of phenolic resins Articles produced by injection molding 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 Phenolics are also used in a variety of other applications such as adhe sives paints laminates for building automobile parts and ion exchange resins Global production of phenolformaldehyde resins exceeded 5 bil lion pounds in 1997 AMINO RESINS Aminoplasts Amino resins are condensation thermosetting polymers of formalde hyde with either urea or melamine Melamine is a condensation product of three urea molecules It is also prepared from cyanamide at high pres sures and temperatures Chapter 12 12201 1111 AM Page 348 UreaFormaldehyde and UreaMelamine Resins 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 Synthetic PetroleumBased Polymers 349 A similar reaction occurs between melamine and formaldehyde and pro duces methylolmelamines A variety of methylols are possible due to the availability of six hydro gens in melamine As with urea formaldehyde resins polymerization occurs by a condensation reaction and the release of water Properties and Uses of Aminoplasts Amino resins are characterized by being more clear and harder ten sile strength than phenolics However their impact strength breakabil ity and heat resistance are lower Melamine resins have better heat and moisture resistance and better hardness than their urea analogs 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 pro duce 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 dinnerware and laminates used to cover furniture Almost all molded objects use fillers such as cellulose asbestos glass wood flour glass fiber and paper The 1997 US production of amino resins was 26 billion pounds Chapter 12 12201 1111 AM Page 349 Polycyanurates A new polymer type which emerged as important materials for circuit boards are polycyanurates The simplest monomer is the dicyanate ester of bisphenol A When polymerized it forms threedimensional densly cross linked structures through threeway cyanuric acid 246triazinetriol 350 Chemistry of Petrochemical Processes The cyanurate ring is formed by the trimerization of the cyanate ester Other monomers such as hexaflurobisphenol A and tetramethyl bisphe nol F are also used These polymers are characterized by high glass tran sition temperatures ranging between 192 to 350C The largest application of polycyanurates is in circuit boards Their transparency to microwave and radar energy makes them useful for man ufacturing the housing of radar antennas of military and reconnaissance planes Their impact resistance makes them ideal for aircraft structures and engine pistons32 SYNTHETIC RUBBER Synthetic rubbers elastomers are longchain polymers 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 Chapter 12 12201 1111 AM Page 350 original polymer through crosslinking agents and additives Selected properties of some elastomers are shown in Table 12533 An important property of elastomeric materials is their ability to be stretched at least twice their original length and to return back to nearly their original length when released 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 brasilien sis a tree that grows in Malaysia Indonesia and Brazil Charles Goodyear 1839 was the first to discover that the latex could be vulcan ized crosslinked by heating with sulfur or other agents Vulcanization of rubber is a chemical reaction by which elastomer chains are linked together The long chain molecules impart elasticity and the crosslinks give load supporting strength34 Vulcanization of rubber has been reviewed by Hertz Jr35 Synthetic rubbers include elastomers that could be crosslinked such as polybutadiene polyisoprene and ethylenepropylenediene tere polymer 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 traditional rubber since they do not have the wide temperature performance range of thermoset rubber36 The major use of rubber is for tire production Nontire consumption includes hoses footwear molded and extruded materials and plasticizers Synthetic PetroleumBased Polymers 351 Table 125 Selected properties of some elastomers33 Tensile Temp Durometer strength Elongation range of Weather hardness at room at room service resis range temp psi temp C tance Natural rubber 20100 10004000 100700 55800 Fair Styrenebutadiene rubber SBR 40100 10003500 100700 55110 Fair Polybutadiene 30100 10003000 100700 60100 Fair Polyisoprene 20100 10004000 100750 55800 Fair Polychloroprene 2090 10004000 100700 55100 Very good Polyurethane 6295 A 10008000 100700 70120 Excellent 4080 D Polyisobutylene 30100 10003000 100700 55100 Very good Chapter 12 12201 1111 AM Page 351 Worldwide use of synthetic rubber not including thermoplastic elas tomers in 1997 was approximately 105 million metric tons Natural rubber use is currently about 6 million tonsyear and is expected to grow at annual rate of 33 Thermoplastic elastomer consumption approximately 08 million tons is forecasted to reach over one million tons by the year 2000 BUTADIENE POLYMERS AND COPOLYMERS 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 hydroperoxide a random polymer is obtained with three isomeric configurations the 14addition configuration dominating 352 Chemistry of Petrochemical Processes Polymerization of butadiene using anionic initiators alkyllithium in a nonpolar solvent produces a polymer with a high cis configuration37 A high cispolybutadiene is also obtained when coordination catalysts are used3839 Properties and Uses of Polybutadiene cis14Polybutadiene is characterized by high elasticity low heat buildup high abrasion resistance and resistance to oxidation However it has a relatively low mechanical strength This is improved by incorpo rating a cis trans block copolymer or 12vinyl block copolymer in the Chapter 12 12201 1111 AM Page 352 polybutadiene matrix40 Also a small amount of natural rubber may be mixed with polybutadiene to improve its properties trans 14Polybuta diene is characterized by a higher glass transition temperature Tg 14C than the cis form Tg 108C The polymer has the toughness resilience and abrasion resistance of natural rubber Tg 14C StyreneButadiene Rubber SBR Styrenebutadiene rubber SBR is the most widely used synthetic rub ber It can be produced by the copolymerization of butadiene 75 and styrene 25 using free radical initiators A random copolymer is obtained The micro structure of the polymer is 6068 trans 1419 cis and 1721 12 Wet methods are normally used to characterize polybutadiene polymers and copolymers Solid state NMR provides a more convenient way to determine the polymer micro structure41 Currently more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts The formed copolymer has better mechanical properties and a narrower molecular weight distri bution A random copolymer with ordered sequence can also be made in solution using butyllithium provided that the two monomers are charged slowly42 Block copolymers 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 SBR pro duced by coordinaton catalysts has better tensile strength than that pro duced by free radical initiators The main use of SBR is for tire production Other uses include footwear coatings carpet backing and adhesives The l997 US production of SBR was approximately 940 mil lion pounds NITRILE RUBBER NBR Nitrile rubber 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 rad icals are used a random copolymer is obtained Alternating copolymers are produced when a ZieglarNatta catalyst is employed Molecular weight can be controlled by adding modifiers and inhibitors When the polymerization reaches approximately 65 the reaction mixture is vac uum distilled in presence of steam to recover the monomer Synthetic PetroleumBased Polymers 353 Chapter 12 12201 1111 AM Page 353 The ratio of acrylonitrilebutadiene could be adjusted to obtain a poly mer with specific properties Increasing the acrylonitrile ratio increases oil resistance of the rubber but decreases its plasticizer compatibility NBR 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 Orings 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 hydrocar bons and oils and are used in fuel tanks and hoses hydraulic equipment and gaskets In 1997 the US produced 86 million pounds of solid nitrile rubber POLYISOPRENE Natural rubber is a stereoregular polymer composed of isoprene units attached in a cis configuration 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 354 Chemistry of Petrochemical Processes Stereoregular polyisoprene is obtained when ZieglarNatta catalysts or anionic initiators are used The most important coordination catalyst is α TiCl3 cocatalyzed with aluminum alkyls The polymerization rate and cis Chapter 12 12201 1111 AM Page 354 Synthetic PetroleumBased Polymers 355 Figure 128 A process for producing 14polyisoprene 99 by a continuous solution polymerization43 Chapter 12 12201 1111 AM Page 355 content depends upon AlTi ratio which should be greater than one Lower ratios predominantly produce the trans structure Figure 128 shows a process for producing cispolyisoprene by a solution polymerization43 Properties and Uses of Polyisoprene 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 insensi tivity to temperature changes but it has low abrasion resistance It is attacked by oxygen and hydrocarbons transPolyisoprene is similar to Gutta percha which is produced from the leaves and bark of the sapotacea 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 spe cialized mechanical products conveyor belts footwear and insulation POLYCHLOROPRENE Neoprene Rubber Polychloroprene is the oldest synthetic rubber It is produced by the polymerization of 2chloro13butadiene in a water emulsion with potassium sulfate as a catalyst 356 Chemistry of Petrochemical Processes The product is a random polymer that is vulcanized with sulfur or with metal oxides zinc oxide magnesium oxide etc Vulcanization with sul fur 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 BUTYL RUBBER Butyl rubber is a copolymer of isobutylene 975 and isoprene 25 The polymerization is carried out at low temperature below Chapter 12 12201 1111 AM Page 356 95C using AlCl3 cocatalyzed with a small amount of water The cocatalyst furnishes the protons needed for the cationic polymerization AlCl3 H2O r H AlCl3OH The product is a linear random copolymer that can be cured to a ther mosetting 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 ETHYLENEPROPYLENE RUBBER Ethylenepropylene rubber EPR is a stereoregular copolymer of eth ylene and propylene Elastomers of this type do not possess the double bonds necessary for crosslinking A third monomer usually a monocon jugated diene is used to provide the residual double bonds needed for cross linking 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 EPT can be crosslinked using sulfur Crosslinking EPR is also possible without using a third compo nent a diene This can be done with peroxides Important properties of vulcanized EPR and EPT include resistance to abrasion oxidation and heat and ozone but they are susceptible to hydrocarbons 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 TRANSPOLYPENTAMER Transpolypentamer TPR is produced by the ring cleavage of cyclopentene3344 Cyclopentene is obtained from cracked naphtha or gas oil which contain small amounts of cyclopentene cyclopentadiene and Synthetic PetroleumBased Polymers 357 Chapter 12 12201 1111 AM Page 357 dicyclopentadiene Polymerization using organometallic catalysts pro duce a stereoregular product trans 15polypentamer 358 Chemistry of Petrochemical Processes Due to the presence of residual double bonds the polymer could be crosslinked with regular agents TPR is a linear polymer with a high trans configuration It is highly amorphous at normal temperatures and has a Tg of about 90C and a density of 085 THERMOPLASTIC ELASTOMERS Thermoplastic elastomers TPES as the name indicates are plastic polymers with the physical properties of rubbers They are soft flexible and possess the resilience needed of rubbers However they are processed like thermoplastics by extrusion and injection molding TPEs 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 chemi cally bonded by block or graft copolymerization At least one of the phases consists of a material that is hard at room temperature45 Currently important TPEs include blends of semicrystalline thermo plastic polyolefins such as propylene copolymers with ethylenepropy lene terepolymer elastomer Block copolymers of styrene with other monomers such as butadiene isoprene and ethylene or ethylenepropy lene are the most widely used TPEs Styrenebutadienestyrene SBS accounted for 70 of global styrene block copolymers SBC Currently global capacity of SBC is approximately 11 million tons Polyurethane thermoplastic elastomers are relatively more expensive then other TPEs However they are noted for their flexibility strength toughness and abrasion and chemical resistance46 Blends of polyvinyl chloride with elastomers such as butyl are widely used in Japan36 Random block copolymers of polyesters hard segments and amor phous glycol soft segments alloys of ethylene interpolymers and chlori nated polyolefins are among the evolving thermoplastic elastomers Chapter 12 12201 1111 AM Page 358 Important properties of TPEs are their flexibility softness and resilience However compared to vulcanizable rubbers they are inferior in resistance to deformation and solvents Important markets for TPEs include shoe soles pressure sensitive adhesives insulation and recyclable bumpers SYNTHETIC FIBERS Fibers are solid materials characterized by a high ratio of length to diameter They can be manufactured from a natural 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 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 polyacrylics and polyolefins Polyesters and polyamides are produced by step polymerization reactions while polyacrylics and poly olefins are synthesized by chainaddition polymerization 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 1930 was the first to try to synthesize a polyester fiber by reacting an aliphatic diacid with a diol The polymers were not suit able because of their low melting points However he was successful in preparing the first synthetic fiber nylon 66 In 1946 Whinfield and Dickson prepared the first polyester polymer by using terephthalic acid an aromatic diacid and ethylene glycol Synthetic PetroleumBased Polymers 359 Chapter 12 12201 1111 AM Page 359 Polyesters can be produced by an esterification of a dicarboxylic acid and a diol a transesterification of an ester of a dicarboxylic acid and a diol or by the reaction between an acid dichloride and a diol The polymerization reaction could be generally represented by the esterification of a dicarboxylic acid and a diol as 360 Chemistry of Petrochemical Processes Less important methods are the self condensation of whydroxy acid and the ring opening of lactones and cyclic esters In self condensation of w hydroxy acids cyclization might compete seriously with linear polymer ization especially when the hydroxyl group is in a position to give five or six membered lactones Polyethylene Terephthalate Production Polyethylene terephthalate PET is produced by esterifying tereph thalic acid TPA and ethylene glycol or more commonly by the trans esterification of dimethyl terephthalate and ethylene glycol This route is favored because the free acid is not soluble in many organic solvents The reaction occurs in two stages Figure 12947 Methanol is released in the first stage at approximately 200C with the formation of bis2hydrox yethyl terephthalate In the second stage polycondensation occurs and excess ethylene glycol is driven away at approximately 280C and at lower pressures 001 atm Chapter 12 12201 1111 AM Page 360 Using excess ethylene glycol is the usual practice because it drives the equilibrium to near completion and terminates the acid end groups This results in a polymer with terminal OH When the free acid is used ester ification the reaction is self catalyzed 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 addi tives are used such as color improvers and dulling agents For example PET is delustred by the addition of titanium dioxide 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 to chips which are stored Batch polymerization is still used However most new processes use continuous polymerization and direct spinning An alternative route to PET is by the direct reaction of terephthalic acid and ethylene oxide The product bis2hydroxyethylterephthalate reacts in a second step with TPA to form a dimer and ethylene glycol which is released under reduced pressure at approximately 300C Synthetic PetroleumBased Polymers 361 Figure 129 The Inventa AG Process for producing polyethyleneterephthalate47 Chapter 12 12201 1111 AM Page 361 This process differs from the direct esterification and the transesterifi cation routes in that only ethylene glycol is released In the former two routes water or methanol are coproduced and the excess glycol released Properties and Uses of Polyesters As mentioned earlier polyethylene terephthalate is an important ther moplastic However most PET 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 determining the tensile strength of the fiber between 1822 denier and its shrinkage The degree of crystallinity and molecular orientation can be determined by Xray diffraction techniques48 Important properties of polyesters are the relatively high melting tem peratures 265C high resistance to weather conditions and sunlight and moderate tensile strength Table 12649 Melt spinning polyesters is preferred to solution spinning because of its lower cost Due to the hydrophobic nature of the fiber sulfonated terephthalic acid may be used as a comonomer to provide anionic sites for cationic dyes Small amounts of aliphatic diacids such as adipic acid may also be used to increase the dyeability of the fibers by disturbing the fibers crystallinity 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 poly esters 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 POLYAMIDES Nylon Fibers Polyamides are the second largest group of synthetic fibers after poly esters However they were the first synthetic fibers that appeared in the market in 1940 This was the result of the work of W H Carothers in USA who developed nylon 66 At about the same time nylon 6 was also developed in Germany by I G Farben Both of these nylons still domi nate the market for polyamides However due to patent restrictions and raw materials considerations nylon 66 is most extensively produced in USA and nylon 6 is most extensively produced in Europe 362 Chemistry of Petrochemical Processes Chapter 12 12201 1111 AM Page 362 Synthetic PetroleumBased Polymers 363 Table 126 Important properties of polyesters49 Mechanical properties at 21C 65 relative humidity using 60 minute strain rate Polyethyleneterephthalate PET Poly cyclo Filament yarns Staple and tow hexanedi methylene Regular High Regular High terephtha tensile tensile tensile tensile late staple Property strength strength strength strength and tow Breaking strength 2856 6095 2260 5860 2530 gdenier Breaking elongation 1934 1034 2565 2540 2434 Initial modulus 75100 115120 2540 4555 2435 gdenier Elastic recovery 8893 90 7585 8595 r at 5 at 5 at 5 at 2 elongation elongation elongation elongation Moisture regain 04 04 04 04 034 Specific gravity 138 138 138 138 122 Melting temper 265 265 265 265 290 ature C Grams per deniergrams of frorce per denier Denier is linear density the mass for 9000 meters of fiber The amout of moisture in the fiber at 21C 65 relative humidity Chapter 12 12201 1111 AM Page 363 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 monomer 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 num ber 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 produc tion of some important nylons is discussed in the following sections Nylon 66 Polyhexamethyleneadipate Nylon 66 is produced by the reaction of hexamethylenediamine and adipic acid see Chapters 9 and 10 for the production of the two monomers This produces hexamethylenediammonium adipate salt The product is a dilute salt solution concentrated to approximately 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 364 Chemistry of Petrochemical Processes The temperature is then increased to 270300C and the pressure to approximately 16 atmospheres which favors the formation of the poly mer The pressure is finally reduced to atmospheric to permit further water removal After a total of three hours nylon 66 is extruded under nitrogen pressure Nylon 6 Polycaproamide Nylon 6 is produced by the polymerization of caprolactam The monomer is first mixed with water which opens the lactam ring and gives wamino acid Chapter 12 12201 1111 AM Page 364 Caprolactam wAmino acid The formed amino acid reacts with itself or with caprolactam at approx imately 250280C to form the polymer Synthetic PetroleumBased Polymers 365 Temperature control is important especially for depolymerization which is directly proportional to reaction temperature and water content Figure 1210 shows the InventaFisher process50 Nylon 12 Polylaurylamide Nylon 12 is produced in a similar way to nylon 6 by the ring opening polymerization of laurolactam The polymer has a lower water capacity than nylon 6 due to its higher hydrophobic properties The polymeriza Figure 1210 The InventaFisher process for producing nylon 6 from caprolac tam50 1 Melting station 23 polymerization reactors 4 extruder 5 interme diate vessel 6 extraction column 78 extraction columns 9 cooling silo Chapter 12 12201 1112 AM Page 365 tion reaction is slower than for caprolactam Higher temperatures are used to increase the rate of the reaction 366 Chemistry of Petrochemical Processes The monomer laurolactam could be produced from 159cyclododeca triene a trimer of butadiene Chapter 9 The trimer is epoxidized with peracetic acid or acetaldehyde peracetate and then hydrogenated The saturated epoxide is rearranged to the ketone with MgI2 at 100C51 This is then changed to the oxime and rearranged to laurolactam Nylon 4 Polybutyramide Nylon 4 is produced by ring opening 2pyrrolidone Anionic polymer ization 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 Nylon 11 Polyundecanylamide Nylon 11 is produced by the condensation reaction of 11 aminounde canoic acid This is an example of the self condensation 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 poly mer is finally withdrawn for storage Chapter 12 12201 1112 AM Page 366 Other Nylon Polymers Many other nylons could be produced such as nylon nylon 5 nylon 7 nylon 610 and nylon 612 These have properties generally similar to those nylons described Table 127 shows the monomers used to produce important nylons and their melting points52 Synthetic PetroleumBased Polymers 367 Table 127 Melting points of various nylons and the monomer formula52 Chapter 12 12201 1112 AM Page 367 Properties and Uses of Nylons Nylons 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 factors 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 etfect on the physical properties of the polymer such as the crystallinity melting point and water absorption For example nylon 6 with six car bons has a melting point of 223C while it is only 190C 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 4 Nylons however 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 alkalies 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 eco nomic 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 The 1997 US production of nylon fibers was approximately 29 bil lion pounds 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 3585 acrylonitrile Acrylic fibers contain at least 85 acry lonitrile Orlon is an acrylic fiber developed by DuPont in 1949 Dynel is a modacrylic fiber developed by Union Carbide in 1951 368 Chemistry of Petrochemical Processes Chapter 12 12201 1112 AM Page 368 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 precipitates Precipitation polymerization whether self nucleation or aggregate nucleation has been reviewed by Juba53 The following equation is for an acrylonitrile polymer initiated by a free radical Synthetic PetroleumBased Polymers 369 Copolymers of acrylonitrile are sensitive to heat and melt spinning is not used Solution spinning wet or dry is the preferred process where a polar solvent such as dimethyl formamide is used In dry spinning the solvent is evaporated and recovered Dynel a modacrylic fiber is produced by copolymerizing vinyl chlo ride 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 Properties and Uses of Polyacrylics 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 resistance 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 CARBON FIBERS Graphite Fibers Carbon fibers are special reinforcement types having a carbon content of 9299 wt They are prepared by controlled pyrolysis of organic materials in fibrous forms at temperatures ranging from 10003000C Chapter 12 12201 1112 AM Page 369 The commercial fibers are produced from rayon polyacrylonitrile and petroleum pitch When acrylonitrile is heated in air at moderate temper atures 220C HCN is lost and a ladder polymer is thought to be the intermediate 370 Chemistry of Petrochemical Processes Further heating above 1700C in the presence of nitrogen for a period of 24 hours 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 met als and alloys54 These fibers have longitudinal tensile strengths and moduli ranging from 2570 GPa and 230590 GPa respectively A bending beam force detector was developed to measure longitudinal compressive strengths of polyacrylonitrilebased carbon fibers55 Most carbon fiber composites are based mainly on thermosetting epoxy matrices Current US production of carbon fibers is approximately ten million poundsyear POLYPROPYLENE FIBERS Polypropylene fibers represent a small percent of the total polypropy lene production Most polypropylene is used as a thermoplastic The fibers are usually manufactured from isotactic polypropylene Important characteristics of polypropylene are high abrasion resist ance strength low static buildup and resistance to chemicals Crystallinity of fibergrade polypropylene is moderate and when heated it starts to soften at approximately 145C and then melts at 170C The physical properties of fibergrade polypropylene are given in Table 128 Melt spinning is normally used to produce the fibers56 The high MP of polypropylene is attributed to low entropy of fusion arising from stiffen ing of the chain Polypropylene fibers are used for face pile of needle felt tufted car pets upholstery fabrics etc The total 1997 US production of polyolefin fibers including polypropylene fibers was approximately 25 billion pounds Chapter 12 12201 1112 AM Page 370 REFERENCES 1 Wittcoff H A Polymers in Pursuit of Strength CHEMTECH Vol 17 No 3 1987 pp 156166 2 Chemical Week No 14 1984 p 13 3 Hatch L F and Matar S From Hydrocarbons to Petrochemicals Gulf Publishing Co Houston 1981 p 171 4 Bennet A CHEMTECH Vol 29 No 7 1999 pp 2428 5 ElKhadi M and David O F Second Arab Conference on Petro chemicals United Arab Emirates Abu Dhabi March 1522 1976 6 Sittig M Polyolefin Production Processes Chemical Technology Review No 79 New Jersey Noyes Data Corp 1976 p 9 7 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 199l p 173 8 Sinclair K B For Polyolefins Estimate Gas Phase Production Costs Hydrocarbon Processing Vol 64 No 7 1985 pp 8183 9 Newton D Chinh J C and Power M Optimize Gasphase Polyethylene Hydrocarbon Processing Vol 77 1998 pp 8591 10 Chemical and Engineering News June 29 1998 p 44 l1 Sacks W Packaging Containers CHEMTECH Vol 18 No 8 August 1988 pp 480483 12 Modern Plastics Vol 52 No 6 1975 p 6 13 Chemical and Engineering News March 30 1992 p 17 14 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 176 Synthetic PetroleumBased Polymers 371 Table 128 Physical properties of fibergrade polypropylene56 Fibergrade Fibergrade Property homopolymer copolymer Specific gravity at 23C 09050910 08950905 Flow rate at 230C 2160 g load g10 min 6 3 Tensile yield at 2 inmin psi 5000 4000 Stiffness in flexure 103 psi 190 150 Unnotched izod impact at 0Fftlbin 10 20 Melting point dilatometer C 172 170 Water adsorption 24 hr 001 001 Environmental stress cracking failure none none Chapter 12 12201 1112 AM Page 371 15 Chemical and Engineering News Jan 16 1995 pp 67 16 Golab J T Making Industrial Decisions with Combutational Chemistry CHEMTECH Vol 28 No 4 1998 pp 1721 17 Hydrocarbon Processing Vol 77 No 11 1998 p 25 18 Rodriguez F Principles of Polymer Systems 3rd Ed Hemisphere Publishing Corp New York 1989 p 466 19 Petrochemical Handbook Hydrocarbon Processing Vol 70 No 3 1991 p 180 20 Ainsworth S J Plastics Additives Chemical and Engineering News August 31 1992 pp 3439 21 Kix M et al Polymer Bulletin Vol 41 1998 pp 349354 22 Hydrocarbon Processing Vol 77 No 9 1998 p 11 23 Hydrocarbon Processing Vol 70 No 12 1991 p 29 24 Piccolini R and Plotkin J Patent Watch CHEMTECH Vol 29 No 3 1999 p 31 25 Sikdar S K The World of Polycarbonates CHEMTECH Vol 17 No 2 1987 pp 112117 26 Leslie V J Rose J Rudkin G O and Fitzin J CHEMTECH Vol 5 No 5 1975 pp 426432 27 Guide to Plastics New York McGraw Hill Inc 1976 28 Modern Plastics International Vol 9 No 4 1979 p 810 29 Kennedy J P Polyurethanes Based on Polyisobutylenes CHEMTECH Vol 16 No11 1986 pp 694697 30 Baekeland L H The Journal of Industrial and Engineering Chemistry March 1909 CHEMTECH Vol 6 No 11 1979 pp 4053 31 Chemical Engineering Sept 15 1975 p 106 32 Stinson S Polycyanurates Find Applications Their Chemistry Remains Puzzling Chemical and Engineering News Sept 12 1994 pp 3031 33 Hall D and Allen E Chemistry Vol 45 No 6 1972 pp 612 34 Coran A Y CHEMTECH Vol 13 No 2 1983 p 106 35 Hertz D L Jr Curing Rubber CHEMTECH Vol 16 No 7 1986 pp 444447 36 Reisch M S Thermoplastic Elastomers Bring New Vigor to Rubber Industry Chemical and Engineering News May 4 1992 pp 2941 37 Stevens M P Polymer Chemistry Addison Wesley Publishing Co London 1975 p 156 38 Natta G J J Polymer Science Vol 48 1960 p 219 372 Chemistry of Petrochemical Processes Chapter 12 12201 1112 AM Page 372 39 British Patent 848065 to Phillips Petroleum Co April 16 1956 40 Platzer N CHEMTECH Vol 9 No1 1979 pp 1620 41 Jelinski L W NMR of Plastics CHEMTECH Vol 16 No 5 1986 pp 312317 42 Platzer N CHEMTECH Vol 7 No 8 1977 p 637 43 Petrochemical Handbook Hydrocarbon Processing Vol 54 No 11 1975 p 194 44 DallAsta G Rubber Chemical Technology Vol 47 1974 p 511 45 Holden G Condensed Encyclopedia of Polymer Science and Engineering John Wiley and Sons 1990 pp 296297 46 Chemical Industries Newsletter JanMar 1999 p 12 47 Petrochemical Handbook Hydrocarbon Processing Vol 56 No 11 1977 p 203 48 Farrow G and Bagley I Texas Research Journal Vol 32 1962 p 587 49 Brown A E and Reinhart K A Science Vol 173 No 3994 1971 p 290 50 Petrochemical Handbook Hydrocarbon Processing Vol 78 No 3 1999 p 128 51 Studiengesellschaft Kohle German Patent 1075610 52 Hatch L F Studies on Petrochemicals New York United Nations 1966 pp 511522 53 Juba M R A Review of Mechanistic Considerations and Process Design Parameters for Precipitation Polymerization in Polymeriza tion Reactions and Processes ACS Symposium Series No 104 Washington DC 1979 pp 267279 54 Riggs P R Condensed Encyclopedia of Polymer Science and Engineering John Wiley and Sons 1990 pp 105108 55 Oya N and Johnson J Direct Measurement of Longitudinal Compressive Strength in Carbon Fibers Carbon Vol 37 No 10 1999 pp 15391544 56 Brownstein E E International Seminar on Petrochemicals October 2530 1975 Baghdad Iraq Synthetic PetroleumBased Polymers 373 Chapter 12 12201 1112 AM Page 373 APPENDIX ONE Conversion Factors To convert from To Multiply by atmospheres mm of mercury 760 atmospheres poundssq inch psi 14696 barrels oil gallons US 42 bars atmospheres 098692 mm of mercury 0C 750062 pascal l 105 Btu calorie 25215105 joules 1055 103 calories gram meangram Btu mean pound 18 calories Btu 39658 103 joules 41840 centimeters angstrom 1 108 feet 00328 inches 03937 meters 001 microns 1 104 cubic feet ft3 gallons British 62288 gallons US 748052 liters 28317 cubic meters barrels US liquid 83865 cubic feet ft3 35314445 gallons US 264173 liters 999973 feet centimeters 3048 gallons US cubic feet ft3 01336805 liters 378543 grams ounces avdp 00352939 ounces troy 00321507 gramssq centimeter poundssq foot 204817 inches centimeters 2540005 kilograms pounds avdp 220462234 pounds troy 26792285 liters gallons British 0219976 gallons US 02641776 meters angstroms 1 1010 374 APP1 12201 1113 AM Page 374 To convert from To Multiply by inches 3937 poundssq inch pressure kilopascal kPa 68948 pounds avdp grams 45359 ounces avdp 16 pounds avdp ounces troy 145833 pounds troy ounces troy 12 poundssq inch gramssq centimeter 70307 tons metric kilograms 1000 pounds avdp 220462 tons short pounds 2000 watts abs Btu meanhour 341304 avdp avoirdupois Temperature Conversion degree Celsius C F 32 59 degree Fahrenheit F C 95 32 degree Kelvin K C 273 degree Rankine R F 460 Conversion Factors 375 APP1 12201 1113 AM Page 375 APPENDIX TWO Selected Properties of Hydrogen Important C1C10 Paraffins Methylcyclopentane and Cyclohexane Properties Hydrocarbon SpGr Boiling Freezing Heat of 204C Point C Point C Combustion K Calmol Hydrogen 008988 gl 2528 2593 68315 00694 Methane 0466164 164 182 21279 Ethane 05721004 886 1833 37281 1049 Propane 05853454 421 1897 53057 1562 2Methylpropane 05631 111 1598 6834 isobutane nButane 05788 05 1384 22Dimethylpropane 0591 95 165 neopenane 2Methylbutane 06201 278 8435 isopentane nPentane 06262 361 130 84516 22Dimethylbutane 06485 497 999 neohexane 23Dimethylbutane 06616 58 1285 2Methylpentane 06532 603 1537 3Methylpentane 06645 633 nHexane 06603 69 95 nHeptane 06837 984 906 11499 liquid nOctane 07026 1257 568 13027 liquid nNonane 07176 1508 51 nDecane 07300 1741 297 16102 liquid 376 APP2 12201 1114 AM Page 376 Properties Methylcyclopentane 07486 718 1424 9379 liquid Cyclohexane 07785 807 65 93687 liquid Handbook of Chemistry and Physics 70th Ed CRC Press Boca Raton Florida 1989 Heat of combustion is the heat liberated or absorbed when one gram mole of the substance is completely oxidized to liquid water and CO2 gas at one atmosphere and 20C or 25C C1C5 hydrocarbons and cyclohexane at 25C others at 20C The gross heating value in Btuft3 could be calculated as follows Using ethane as an example CH3CH3g 7202g 2CO2g 3H2O l H 37281 Kcalmol Volume of one mole gas at 25C one atm 2445 l Ideal gas at STP 224 l Density of gas Spgr to air 1 Condensed Chemical Dictionary 10th Ed revised by Gessner G Hawley Van Norstrand Reinhold Co New York 1981 Gross Kcal mol on ft t heating value e mol gas l 39658 btu Kcal l Btu f 372 81 24 45 28 317 1722 3 3 Selected Properties of Hydrogen 377 APP2 12201 1114 AM Page 377 378 Index ABS See Acrylonitrilebutadienestyrene copolymers Absorption chemical 4 physical 3 Selexolprocess XX Acetaldehyde acetic acid from 199 chemicals 199201 Aldol condensation of 199 production 198199 Acetic acid from acetaldehyde 199 from nbutane 175 from nbutenes 239240 from methanol 154155 Monsanto process for 156 uses 240 Acetic anhydride from acetic acid 240 ketene from 240 Acetone bisphenol A from 231 from acrolein and isopropanol 230 from cumene 271272 from isopropanol 229230 isoprene from 105 mesityl oxide from 230 properties and uses 230 purification 272 Acetylene butadiene from 104 14butanediol from 104 methyl pentynol from 242 vinyl acetate from 200 Acetylsalicylic acid 274 Acid gas treatment 35 Acrolein 215217 from propylene 215 oxidation 217 Acrylic acid from acrolein 217 from ethylene 201 from propiolactone 217 uses 218 Acrylic fibers 368369 Acrylonitnle 218260 adiponitrile from 221 copolymers with butadiene 353 process 220 specifications 219 uses 219 Acrylonitrilebutadienestyrene copolymers 334 Addition polymerization 304308 anionic 308 cationic 306 free radical 305 Adhesives amino resins for 348349 phenolformaldehyde for 346 Adipic acid from butadiene 257 from cyclohexane 283 hexamethyienediamine from 283 for nylon 66 364 Adiponitrile from acrylonitrile 221 from butadiene 256 hexamethylenediamine from 257 Adsorption processes 5253 Aldol condensation of acetaldehyde 199 of nbutyraldehyde 233 Alfol process for linear alcohols 208 Alkanes See Paraffinic hydrocarbons Alkylates for detergents 182 Alkylation of benzene 263276 using ethylene 265 3318 index 12201 1115 AM Page 378 Index 379 using monoolefins 275 using propylene 269 of olefins 8588 process conditions 88 Alkylbenzene sulfonate See also Linear alkylbenzene 207 Allyl acetate 14butanediol from 226 Allyl alcohol from acrolein and isopropanol 230 glycerol from 225 from propylene oxide 225 Allyl chloride 226 Alphabutol process for lbutene 210 Alpha olefins 206207 wAmino acids for nylons 364 Amino resins 348349 properties and uses 349 urea formaldehyde 349 urea melamine 349 Aminoundecanoic acid 367 Ammonia Haber process 144 hexamethylenetetramine from 154 hydrazine from 148 ICI process 143 nitric acid from 147 from synthesis gas 144145 uses 145 Ammonolysis of chlorobenzene 279 Ammoxidation of propylene 218 terAmyl methyl ether production 159 properties 160 Andrussaw process 137 Aniline from chlorobenzene 279 from nitrobenzene 279 from phenol and ammonia 279 Scientific Design Co process 280 Aromatic hydrocarbons 37 boiling and freezing points of 39 extraction 38 53 Union carbide process 38 from naphtha reforming 61 from LPG 177179 Cyclar process 179 octane rating 44 separation of C8 isomers 3940 Aspirin See Acetylsalicylic acid Associated gas 12 analysis 2 natural gas liquids from 8 Atmospheric distillation 5051 Bayer Process for acetic acid 241 Benzal chloride 291 benzaldehyde from 292 Benzaldehyde 290291 from toluene 291 Benzene alkylation of 263276 chemicals 262283 chlorination of 276278 cumene from 269 cyclohexane from 281 ethylbenzene from 265 linear alkylbenzene from 207 275 maleic anhydride from 280 nitration of 278 oxidation of 280 from toluene dealkylation 284 from toluene disproportionation 285286 Benzoic acid 286 caprolactam from 286287 phenol from 288 terephthalic acid from 290 from toluene 286 Benzotrichloride 291 benzoic acid from 292 Benzyl alcohol 292 Benzyl chloride 291 benzaldehyde from 292 Beta scission 73 Biodegradable detergents 185 206 Bisphenol A 231 273 Chiyoda process for 274 from acetone and phenol 273 for epoxy resins 345 for polycarbonates 337 for polyether sulfones 338 Bitumen from tar sand analysis 26 Bituminous coal 23 Bronsted acidity 70 BTX See also Benzene toluene and xylenes 3740 extraction of 38 Butadiene adiponitrile from 256 14 butanediol from 358 chemicals 255260 chloroprene from 258 3318 index 12201 1115 AM Page 379 380 Chemistry of Petrochemical Processes cyclododecatriene from 260 cyclooctadiene from 259 from dehydrogenation of C4 103104 polymerization with Li compounds 308 polymers and copolymers 352 production 103104 properties 37 14Butanediol 244 258 dehydration 104 from butadiene 258 from maleic anhydride 243 process for 244 in thermoplastic polyesters 337 Butamer isomerization process 181 Butanes acetic acid from 175 isomerization of nbutene to isobutane 180 UOP Butamer process 181 maleic anhydride from 176 oxidation of 175 properties 3132 nButanol from acetaldehyde 199 from butyraldehyde 233 sec Butanol 245 1Butene from ethylene 209 Alphabutol process 210 nButenes acetic acid from 239 boiling points of isomers 35 chemicals from 238249 maleic anhydride from 242 methyl ethyl ketone from 240 hydration of 245 oligomerization of 248 from propylene disproportionation 234 nButyl alcohol See nButanol terButyl alcohol 253 uses 253 Butylbenzyl phthalate 292 Butylene chlorohydrin 244 Butylene oxide 244 Butylenes See nButenes and isobutylene Butyl rubber 356 Butyraldehyde nbutanol from 233 2ethylhexanol from 233234 from propene 232 γButyrolactone 244 Caprolactam from benzoic acid 286287 from KA oil 283 nylon 6 from 364 process 287 Carbon black 118121 channel process 119 furnace process 119120 production 118119 properties 120 Carbon disulfide production 136 uses 136137 Carbon fibers 369370 Carbon monoxide in synthesis gas 122 disproportionation of 124 Carbon tetrachloride 140 Carbonylation of dinitrotoluene to TDI 293 isobutylene 255 methanol 154 Carbowax 315 Catalytic conversion processes 6093 Catalytic cracking 6977 catalysts 7072 deep catalytic cracking DCC 7778 feed and product analysis 77 fluidbed FCC 76 process conditions 75 reactor flow diagram 76 movingbed 76 products 76 reactions 7275 residuum fluid cracking RFCC 70 Catalytic reforming 6069 aromatization reactions 6365 catalysts 62 feeds 61 feeds and products analysis 67 isomenzation reactions 65 process 6869 Chevron Rheiniforming flow diagram 69 reforming reactions 6265 Catofin dehydrogenation process 173 Cellulose 301 Chain addition polymerization 304308 Charactenzation factor 22 Chemisorption 4 Chlorofluorocarbons 140 Chloroform 139 3318 index 12201 1115 AM Page 380 Index 381 Chloromethanes production 138 uses 139 Chloroprene from butadiene 258 polymerization 356 Claus process 116117 flow diagram 117 reactions 116 Coal analysis 23 classification 23 Condensation polymerization 312314 Conversion processes 5490 Coordination polymerization 309312 Cracking reactions 7275 Cresols for epoxy resins 345 properties 132 Cresylic acid 131133 extraction 131 uses 133 Crosslinking See Vulcanization Crotonaldehyde 200 nbutanol from 200 Crude oil 1122 API gravity 20 approximate ASTM boiling ranges for crude oil fractions 51 ash content 21 characterization factor 22 classification 2122 composition 1219 cycloparaffins in 13 density 19 fractionation distillation 5051 metallic compounds in 19 nitrogen compounds in 1617 oxygen compounds in 1718 porphyrins in 17 pour point of 21 processing 4990 propenies 1820 salt content 20 sulfur compounds in 1516 sulfur content 20 vacuum distillation 5152 Cumene 269272 acetone from 271 αmethylstyrene from 270 phenol from 271 production 269272 UOP process 270 Cyclododecane 260 Cyclododecantriene 259 Cyclohexane cyclohexanone from 283 from benzene 281 IFP process 281 from natural gasoline 282 operation effects on purity 282 properties and uses 282283 Cyclar process process 177179 flow diagram 179 product breakdown 179 product yield from LPG feed 178 Cyclohexane carboxylic acid 287 Cyclohexanol from cyclohexane 283 Cyclohexanone 283 Cyclooctadiene 259 Cyclooctene transpolyoctenamer from 315 Cycloparaffins dehydrogenation of 63 in crude oils 13 DDT 278 DEA See Diethanolamine Decyl alcohol 164 Deep catalytic cracking 7778 analysis of products 78 Dehydrate process 7 Dehydration of butanediol to butadiene 104 Dehydrogenation of teramylenes 105 butanes and butenes 103 cycloparaffins 63 propane 172 Dehydrocyclization of paraffins 63 Delayed coking 5758 feeds and products analysis 57 operating conditions 57 process flow diagram 58 types of petroleum cokes 59 Degussa process for HCN 137 Detergents 200 270 Diaminotoluenes 293 Dichlorobenzenes 277 Dichlorodiphenyl sulfone 340 Dichlorodifluoromethane Freon12 140 Dichloromethane 138 Dichlorophenoxy acetic acid 274 Dienes diolefins production 101107 3318 index 12201 1115 AM Page 381 382 Chemistry of Petrochemical Processes properties 36 Diethanolamine in acid gas absorption 4 production 196 Diethylene glycol hydrate removal 6 production 193 Diglycolamine for acid gas removal 4 Diisobutylene 255 Diisopropyl benzene 269 Diisopropyl ether 227 Dimerization butadiene 267 ethylene to lbutene 210 olefins 8890 Dimethylamine 161 Dimethyl carbonate 194 Dimethyldioxane pyrolysis to isoprene 106 Dimethylterephthalate 295296 process flow diagram 296 Dimethylphenol 340 Dinitrotoluene 293 toluene diisocyanates from 293 Diphenyl carbonate 338 Disproponionation of carbon monoxide 124 propylene 234 toluene 285 DMT See Dimethylterephthalate Dodecanedioic acid 260 Dyne fibers 369 Econamine process for acid gas removal 5 Elastomers See also Synthetic rubber properties 351 thermoplastic 358 Emulsion polymerization 316 Engineering thermoplastics nylon resins 336 polyacetals 341 polycarbonates 337 polyether sulfones 339 polyphenyleneoxide 340 thermoplastic polyesters 336 Epichlorohydrin 344 Epoxidation lbutene 244 ethylene 191 isobutylene 251 propylene 222 Epoxy resins 344346 production 344 properties and uses 345 EPR See Ethylene propylene rubber EPT See Ethylene propylene terepolymer Ethane chemicals from 169 cracking 96 ethyl chloride from 169 heating value 30 properties 3031 vinyl chloride from 171 Transcat process 170 Ethanol from hydration of ethylene 204205 uses 205 Ethanolamides 197 Ethanolamines 196197 Ethoxylates 195 Ethyl alcohol See Ethanol Ethylbenzene extraction 39 production 265 Badger process 266 styrene from 266 Ethyl chloride 169 Ethylene acetaldehyde from 198 acrylic acid from 201 1butene from 209 chemicals from 188211 chlorination 201 consumption 190 ethanol from 204 ethylbenzene from 265 ethylene dichloride from 202 ethylene glycol from 194 ethylene oxide from 190 from ethane cracking 96 hydration 204205 from LPG cracking 98 from naphtha and gas oil cracking 98101 oxidation 189192 oxidative carbonylation 201 perchloroethylene from 203 polymerization 324328 properties 3233 from propane cracking 97 from propylene disproportionation 234 vinyl acetate from 200 vinyl chloride from 202 world production 33 Ethylene carbonate 193 3318 index 12201 1115 AM Page 382 Index 383 Ethylene chloride 201 Ethylene dichloride 203 Ethylene glycol from ethylene acetoxylation 192 from ethylene carbonate 193 from ethylene oxide 192 Scientific Design process 193 from ethylene oxychlorination 195 in polyesters production 360 from synthesis gas 166 in unsaturated polyesters 346 Ethylene oxide ethanolamines from 196 ethoxylates from 195 ethylene glycol from 192 from ethylene epoxidation 189192 Scientific Design process 191 in polyurethane production 342 Ethylenepropylene rubber XXX Ethylenepropylene terepolymer 357 2Ethylhexanol from butyraldehyde 233234 Hoechst process 233 uses 233 297 Fatty acids 183 Fatty alcohols 183 FCC See Fluid catalytic cracking Fibers manmade 359 natural 359 synthetic 359371 Fischer Tropsch synthesis 123127 143 catalysts 124 mechanism 126129 process flow chart 125 product analysis 126 reactions 124 yield of various products 127 Fluid catalytic cracking See also Catalytic cracking 6977 Fluid coking 5859 Exxon flexicoking process 60 Formaldehyde in isoprene synthesis 106107 pentaerithritol from 154 phenolformaldehyde resins from 346 production 152153 Haldor Topsoe process 153 polyacetals from 341 propiolactone from 218 Free radicals initiators for polymerization 305306 in steam cracking reactions 91 in thermal cracking reactions 56 Freon 140 FTS See Fischer Tropsch synthesis Fuel oil 47 Gas medium Btu 23 natural 111 synthesis 121129 Gas hydrates 25 Gas oil analysis 46 steam cracking 9899 yields versus severity 98 Gasoline from methanol 161163 analysis of gasoline 162 octane rating 44 45 Glycerin See Glycerol Glycerol from allyl alcohol 225 from allyl chloride 227 in polyurethane production 342 αGlutaric acid 257 Glycidol 225 Glycolaldehyde 166 Haber process for ammonia 144 HCFCs 140 HDPE See Highdensity polyethylene Heating value of hydrocarbons 11 14Hexadiene for ethylenepropylene rubber 357 Hexamethylenediamine for nylon 364 from adipie acid 283 from adiponitrile 257 Hexamethylenetetramine hexamine 154 crosslinking agent for phenolformaldehyde resins 348 nHexane reforming overPt catalyst 64 16Hexanediol 283 Hexanes isomer equilibrium 89 Highdensity polyethylene See Polyethylenes Hydrates in natural gas 6 Hydration of 3318 index 12201 1115 AM Page 383 384 Chemistry of Petrochemical Processes butylene to 2butanol 245 ethylene to ethanol 204 isobutylene to terbutyl alcohol 253 propylene to isopropanol 227 Hydrazine production and uses 148149 Hydrocarbon compounds 2947 aromatics 3741 boiling points and octane ratings 45 from methanol 161163 olefins and diolefins 3237 paraffins 2932 Hydrocracking process 7881 catalysts and reactions 7980 feed and product analysis 79 process 7879 Chevron hydrocracking unit 82 Hydrodealkylation process 8183 Hydrofluoric acid for olefin alkylation 86 Hydroformylation See also Oxo reaction 162166 conditions 165 mechanism 165166 of olefins 163164 of propylene 232233 Rhone Poulenc process 233 Hydrogen 111114 from steam reforming hydrocarbons 112 from methanol and water 112 membrane separation of 114 115 recovery 113 uses 113 Hydrogenation of benzene to cyclohexane 281 nbutyraldehyde to nbutanol 233 nitrobenzene to aniline 279 Hydrogen cyanide 137138 from methane and ammonia 137 from methanol and ammonia 137 Hydrogen peroxide byproduct from propane oxidation 171 from isopropanol oxidation 229 Hydrogen sulfide byproduct from CS2 synthesis 136 feed to Claus process 116 from acid gas treatment 35 Hydrotreatment processes 8385 catalysts and reactions 8485 Exxon hydrotreating unit 84 αHydroxyisobutyric acid 252 HZSM5 catalyst in LPG aromatization 180 ICI process for synthesis gas 143 IFP deasphalting process 54 IFP process for hydrogenating benzene 281 IFP process for isoprene 106 Injection molding 348 Isoamylenes isoprene from 105 TAME from 159 Isobutane chemicals 180 for olefin alkylation 86 from nbutane 180 isobutene from 249 Isobutene See Isobutylene Isobutylene chemicals 249250 ethyl terbutyl ether from 160 isoprene from 106 isooctane from 87 methacrolein and methacrylic acid from 250 Isobutylene glycol 251 Isobutylene oxide 251 Isodecyl alcohol 164 Isomerization nbutane to isobutane 180 lbutene to 2butene 34 nbutenes to isobutene 245 equilibrium for hexane isomers 89 mxylene to pxylene 3940 Isooctane for octane ratings 44 from isobutylene 87 Isophthalic acid from mxylene 297 Isophthalonitrile 298 Isoprene from acetylene and acetone 105 from dehydrogenating teramylenes 105 from isobutylene and formaldehyde 106 from isobutylene and methylal 106 from propylene 107 polymers and copolymers 354 Isopropanol 2propanol 227229 acetone from 229 from propylene 227228 process 228 isopropyl acetate from 232 isopropyl acrylate from 232 Isopropylbenzene See Cumene IsoSiv process for nparaffins 53 Jet fuels from kerosine 46 3318 index 12201 1115 AM Page 384 Index 385 KA oil 283 Kerosine nparaffins from 182 properties 4546 Ketene for acrylic acid synthesis 218 from acetic acid 240 LAB See Linear alkylbenzene Laurolactam 365 Laurylamide 365 LDPE See Lowdensity polyethylene LeChateliers principle 144 173 Lewis acids 70 LHSV See Liquid hourly space velocity Linear alcohols from ethylene oligomerization 207 from hydroformylation of olefins 163 Linear alkylbenzene 207 275276 production 273276 UOP process 276 properties of detergent alkylates 277 Linear lowdensity polyethylene 328 Liquefied natural gas 910 Expander cycle process 9 MCR process 10 properties 10 Liquefied petroleum gas 8 54 Liquid hourly space velocity 68 LLDPE See Linear lowdensity polyethylene LNG See Liquefied natural gas Low density polyethylene 326 production 326 properties and uses 328 LPG See Liquefied petroleum gas Lummus process for benzoic acid to phenol 289 Lummus process for C4 dehydrogenation 103 Malathion 243 Maleic anhydride 14butanediol from 242243 from benzene 280 from butane 176 from nbutenes 242 in unsaturated polyester synthesis 346 Maleic hydrazine 243 MCR liquefaction process 10 MDI See Methylenediisocyanate MEA See Monoethanolamine Mechanical refrigeration See MCR process MEK See Methylethyl ketone Merox process 6 Melt flow index and melt viscosity 318 Melting point of polymers 317318 Melt spinning 362 Mesityl oxide 230 Metal passivation of residual fuels 47 Metallocenes 326 Metathesis ethylene and butene 247 flow chart for 248 propylene 234235 Phillips Co Triolefin Process 236 Methacrolein 250 Methacrylic acid 231 250 Methane carbon disulfide from 136 chemicals 136 chloromethanes from 138 heating value 11 hydrogen cyanide from 137 methyl chloride from 138 properties 30 synthesis gas from 140143 Methanol acetic acid from 154155 carbonylation of 155 chemicals 151163 formaldehyde from 152153 gasoline additive 152 hydrocarbons from 161163 methylamines from 160161 methyl terbutyl ether from 157159 olefins from 162 production 150151 ICI process 152 uses 151 Methyl alcohol See Methanol Methylamines 160161 production 160 uses 161 Methylbenzenes See also Toluene and xylenes 42 2Methyl13butadiene See Isoprene Methyl terbutyl ether 157159 252 production 157 BP Etherol process 157 properties 160 Methyl chloride from methane 138 from methanol 154 3318 index 12201 1115 AM Page 385 386 Chemistry of Petrochemical Processes Methylene chloride 139 Methylenediisocyanate 343 Methyl ethyl ketone from nbutenes 240 from 2butanol 242 Methylmethacrylates from acetone 231 Plexiglas from 231 Methylpentynol 242 Mitsui process for phenol and acetone 271 Monochloromethane See Methyl chloride Monoethanolamine absorption of acid gases 4 from ammonia 196 Monomers for polymer synthesis 302 Monsanto process for acetic acid 156 MontedisonUOP acrylonitrile process 220 Movingbed catalytic cracking See Catalytic cracking MTBE See Methyl terbutyl ether MTG process 161162 gasoline from analysis 162 Naphtha acetic acid from 181 analysis 44 chemicals from 181182 feed to catalytic reforming 61 steam cracking of 98 101 steam reforming of 122 uses 43 Naphthenes 13 63 Naphthenic acids 130131 extraction of 130 properties 130 uses 130 Natural gas analysis 2 heating value 11 liquefaction 910 Expander cycle process 9 MCR process 10 liquefied natural gas analysis 10 nonassociated 12 Natural gas liquids 89 Needle coke from petroleum coke 58 Neopentanoic acid 255 Neoprene rubber See Polychloroprene NGL See Natural gas liquids Nitration of benzene 278 propane 173 toluene 292 Nitric acid production 147 uses 148 Nitrile rubber 353 Nitroalcohols 174 Nitrobenzene 278 aniline from 279 Nitromethane 173 Nitropropanes 173 Nitrosyl sulfuric acid 287 Nitrotoluenes 293 Nonyl alcohols 248 Novalacs 346 Number average molecular weight Mn 319 Nylon fibers monomers for 367 production 364367 nylon 4 366 nylon 6 364365 Inventa AG process for 365 nylon 11 366 nylon 66 364 nylon 12 365 nylon 610 367 properties and uses 367368 Nylon resins 336 Octane ratings 44 Oil shale analysis 2425 Olefinic hydrocarbons from cracking ethane 97 from cracking gas oil or naphtha 98 from cracking various feedstocks 97 production 91101 properties of C2C4 olefins 3235 steam cracking process 91101 diagram for cracking liquid feeds 100 process variables 9596 Oligomerization of butadiene 259 butenes 248 Octol process for 248 ethylene 205206 propylene 88 analysis of products 90 Oligomers butadiene 259260 2butene 249 Orlon fibers 369 3318 index 12201 1115 AM Page 386 Index 387 Oxidation benzene to maleic anhydride 280 butanes to acetic acid 175 butanes to maleic anhydride 176 butenes to acetic acid 239 cyclohexane to KA oil 283 ethylene to acetaldehyde 198 ethylene to ethylene oxide 189 naphtha to acetic acid 181 propylene to propylene oxide 221 toluene to benzoic acid 286 pxylene to terephthalic acid 295 Oxidative carbonylation of ethylene 201 Oxirane ethylene acetyoxylation process 194 Oxo alcohols and aldehydes 163165 Oxo reaction 163165 232 nbutyraldehyde from 164 232 catalysts for 165 mechanism 165 Oxyacylation of propylene 226 Paraffinic hydrocarbons 2932 constituents of crude oils 12 dehydrocyclization of 64 octane rating 45 physical properties C1C4 30 nParaffins chlorination 184 fermentation 185 from kerosine 52 oxidation 183 physical properties C5C16 178 sultonation 185 PBT SeePolybutyleneterephthalate PC See Polycarbonates Pentaerythritol 153 Perchloroethylene perchlor 203 from ethylene 203 PPG process 204 PES See Polyether sulfones PET See Polyethylene terephthalate Petroleum coke 5959 from delayed coking 58 types and uses 59 Petroleum residues cracking 70 metal passivation 47 Phenol alkylphenols from 275 aniline from 279 Bisphenol A from 273 from benzoic acid 286 from chlorobenzene 273 from cumene 271 phenol formaldehyde resins from 346 properties and uses 273 salicylic acid from 274 Phenol formaldehyde resins crosslinking of 347 production 346348 properties 348 Phenylacetic acid 292 αPhenylethyl alcohol 223 Phosgene in polycarbonate synthesis 337 Phthalamide 297 298 Phthalic anhydride 296297 production and uses 297 Phthalonitrile reaction scheme 297 Lummus dehydrogenation process for butadiene 103 Physical absorption 3 Physical adsorption 3 52 Plastics thermoplastics 320 324337 thermosetting plastics 342350 Polyacetals 341 Polyacrylics Dynel fibers 369 Orlon fibers 368 properties 369 Polyamides See Nylon fibers Polybutadiene 352353 glass transition temperature 353 production 353 properties and uses 353 Polybutylene terephthalate 337 Polycaproamide See Nylon 6 Polycarbonates production 337338 properties 339 uses 338 Polychloroprene production 356 vulcanization 356 Polycyanurates 350 Polyester fibers See also Polyethylene terephthalate production 360363 Inventa process 361 properties and uses 362 Polyether sulfones maximum use temperature 341 3318 index 12201 1115 AM Page 387 388 Chemistry of Petrochemical Processes production 339340 properties and uses 340 Polyethylbenzenes 266 Polyethylenes highdensity 327 production 326328 linear lowdensity 328 lowdensity 326 polymerization with ZieglarNatta catalyst 309 312 Unipol process for HDPE 327 properties and uses 328 329 Polyethylene terephthalate from ethylene glycol and terephthalic acid 360362 process 361 properties 362 Polyhexamethylene adipate See Nylon 66 Polyisoprene production 354 process 355 tactic forms 354 Polymerization chain addition 304308 condensation 312314 coordination 309312 ring opening 314315 Polymerization techniques 315317 Polymers classification 320 crystallinity 317 melt flow index 318 melting point Tg and Tm 317318 molecular weight 318 viscosity 318 Polypropylene isotactic 310 from propylene using ZieglerNatta catalysts 310 production 330331 Spherical liquidphase process 331 Union Carbide gasphase process 330 properties and uses 331332 tactic forms 310 Polyphenylene oxide 340 Polypropylene fibers 370 properties 371 Polystyrene production 334335 batch suspension process 335 copolymers 334336 properties and uses 335 Polyurethanes Insulation degree compared 344 production 342344 properties and uses 343 Polyvinyl chloride production 332 European Vinyls Corp process 333 properties and uses 334 Porphyrins in crude oils 17 PPO See Polyphenyleneoxide Propane aromatics from 177179 chemicals 171 chlorination 172173 cracking 97 dehydrogenation 172 LummusCrest process 173 temperature effect on 172 heating value 30 nitration 173 oxidation 171 properties and uses 31 13Propanediol 197 from ethylene oxide 197 2Propanol See Isopropanol Propene See Propylene Propiolactone acrylic acid from 218 Propylene acetone from 229 allyl acetate from 226 chemicals 213 disproportionation 234 235 from propane 172 hydration 227 conditions using H2SO4 229 hydroformylation 163 catalysts and conditions 165 in benzene alkylation 269 isopropyl acetate from 232 isopropylacrylate from 232 oxidation mechanism 215217 oxyacylation of 226 polymerization 329 properties 3334 Propylene dichloride 221 Propylene glycol 223 Propylene oxide allyl alcohol from 225 coproduct with MTBE 158 from propylene chlorohydrin 221222 from propylene epoxidation 222 in polyurethane synthesis 342 3318 index 12201 1115 AM Page 388 Index 389 propylene carbonate from 224 propylene glycol from 223 uses 223 Pruteen from methanol 185 PVC See Polyvinyl chloride Pyrrolysis of ethane 91 97 Pyrrolidone 367 Refinery processes 5090 Reformats 38 55 68 aromatics from 39 from catalytic reforming 68 Reforming catalytic See Catalytic reforming Reid vapor pressure 31 Residual fuel oil 47 Residue desulfurization RDS 70 product analysis 71 Residuum fluid cracking 70 Resols 346 Ringopening polymerization 314315 cyclooctene to polyoctenylene 315 cyclopentadiene to polypentamer 315 trioxane to polyacetals 314 Rubber butyl 356 ethylenepropylene 357 natural 351 nitrile 353 polybutadiene 352353 polyisoprene 354 properties 351 styrenebutadiene SBR 353 synthetic 350358 transpolypentamer 357 Salicylic acid 274 SAN See Styrene acrylonitrile copolymers SBR See Styrenebutadiene rubber SCP See Single cell protein Selexol process 4 Shot coke 58 Single cell protein 185 Snamprogetti process for isoprene 105 SNIA Viscosa process for caprolactam 287 Sodium alkanesulfonates 185 Solution polymerization 316 Solution spinning 369 Solvent extraction aromatics 53 Sorbitol 343 Spandex 338 Sponge coke 58 Steam cracking 91101 ethane 91 block diagram for 94 gas feeds 9698 gas oil 99101 liquid feeds 98101 flow diagram for ethylene plant 100 naphtha 9899 process 9396 variables 95 propane 9798 raffinates 99 yields from various feeds 97 Steam reforming 121 140143 exit gas analysis 141 methanation 142143 shift conversion 142 naphtha 122 natural gas 140 ICI process for synthesis gas and ammonia 143 step reaction polymerization 312314 stilbene 268 Styrene copolymers with acrylonitrile and butadiene 334335 from butadiene 267 from ethylbenzene 266267 MonsantoLummusCrest process 267 operating parameters effect on conversion 267 268 from toluene 268 Styreneacrylonitrile copolymers 334 Styreneacrylonitrilebutadiene copolymers 334 Styrenebutadiene rubber 353 Sulfolane aromatic extraction 38 53 from butadiene 259 uses 259 Sulfur from hydrogen sulfide 116 process for 116 Super Claus process 117 sulfuric acid from 117118 uses 116118 Sulfuric acid as alkylation catalyst 86 from sulfur 117118 uses 118 3318 index 12201 1115 AM Page 389 390 Chemistry of Petrochemical Processes Surfactants 195196 Suspension polymerization 316 Synthesis gas ammonia from 144145 chemicals from 143149 combined reforming 150 ethylene glycol from 166167 from naphtha 122 from natural gas 122 140143 hydrocarbons from 123124 Synthol fluidbed reactor 125 methyl alcohol from 149 sources 122 uses 123 Synthetic fibers 321 359371 carbon 369370 polyacrylics 368 polyamides 362 polyesters 359 polypropylene 370371 Synthetic rubber 321 350359 butyl 356 ethylene propylene 357 nitrile 353 polyisoprene 354 properties 351 styrenebutadiene 353 transpolypentamer 357 Synthol process 125 TAME See terAmyl methyl ether Tar sand analysis of bitumen 26 TBA See terButyl alcohol TDI See Toluene diisocyanate Teflon 139 Terephthalic acid 295 from benzoic acid 290 from pxylene 295 process 296 Tetrachloro methane See Carbon tetrachlo ride Tetrahydrofuran 243 Tetramethylene sulfone See Sulfolane Thermal conversion processes delayed coking 5758 fluid coking 5859 viscosity breaking 5960 Thermoplastic elastomers 358 Thermoplastic polyesters 336 Thermoplastics polyacetals 341 polyamides nylon resins 336 polycarbonates 337339 polyesters 336337 polyether sulfones 339340 polyethylenes 324329 poly phenylene oxide 340 polypropylene 329331 polystyrenes 334336 polyvinyl chloride 332334 properties 325 Thermosetting plastics epoxy resins 344346 phenol formaldehyde resins 34648 polyurethanes 342344 unsaturated polyesters 346 ureaformaldehyde resins 349 ureamelamine resins 348349 pTolualdehyde 294 Toluene benzene from 284 benzoic acid from 286 carbonylation 294 chemicals 284294 hydrodealkylation 284 MobilIFP disproportionation process 285 nitration 292 Toluene diisocyanate 293 Toluic acid 295 Toluidine o and p 293 TPEs See Thermoplastic elastomers Transpolypentamer 357 Tributylaluminum 206 Trichloroethylene trichlor 203 Trichlorofluoromethane 140 Trichloromethane See Chloroform Tridecyl alcohol 164 Triethanolamine from ethylene oxide and ammonia 196 in polyurethane synthesis 343 Triethylaluminum 206 209 Triethylene glycol 6 193 Trimethylamine 161 224Trimethylpentane See Isooctane Trinitrotoluene TNT 294 UOP process for isobutane 181 Union Carbide Unipol process for HDPE 327 Unsaturated polyesters 346 Urea production 145147 3318 index 12201 1115 AM Page 390 Index 391 Snamprogetti process 147 uses 146 Urea formaldehyde resins 348349 properties and uses 349 Urea melamine resins 348349 Vacuum distillation 5152 flow diagram 51 Valerolactam for nylon 367 VCM See Vinyl chloride Vinyl acetate from acetylene 200 from ethylene 200 Vinyl chloride copolymers 333 from acetylene 202 from ethane 169 from ethylene 202 polymerization 332 Viscosity breaking analysis of feed and products 61 process 5960 Vulcanization of rubber 120 351 Wacker catalyst butene oxidation to MEK 240 ethylene oxidation to acetaldehyde 198 ethylene oxidation to vinyl acetate 200 propylene oxidation to acetone 230 Water removal from natural gas 6 Dehydrate process 7 Watson characterization factor 22 Weight average molecular weight Mw 318319 Xylenes boiling points 39 chemicals from 294299 from disproportionation of toluene 285 separation of isomers 3840 thermodynamic equilibrium composition of 295 mXylene isophthalic acid from 297 oXylene phthalic anhydride from 296 pXylene from isomerization of mxylene 3940 Mobil xylene isomerization process 40 terephthalic acid from 295 Zeolites acidity of 7071 alkylating catalysts for ethylbenzene synthesis 265 cracking catalysts 7172 ZSM5 zeolitecatalysts in conversion of methanol to gasoline 163 in disproportionation of toluene 285 in isomerization of mxylenes 40 in LPG conversion to aromatics 177 Ziegler catalyst for αolefins and linear alcohols from ethylene 206208 ZieglerNatta catalysts in ethylene and propylene polymerization 309 in production of nitrile rubber 353 in stereoregular polymerization of butadiene and isoprene 354 3318 index 12201 1115 AM Page 391 About the Authors Sami Matar PhD is a retired professor of chemistry at King Fahd University of Petroleum and Minerals Dharan Saudi Arabia He received a BSc from the University of Cairo and a PhD in chemistry from the University of Texas Austin Dr Matar has served as associate member of the board of the Egyptian Petroleum Institute and general manager of the chemical and research laboratories of Suez Oil Processing Co The author and contributor to many articles and books Dr Matar is also a member of the American Chemical Society and Society of Petroleum Engineers The late Lewis F Hatch PhD was well known and widely respected for his contributions to the fields of chemistry and petrochemical pro cessing He received his PhD in chemistry from Purdue University and was the author of numerous books and technical publications 392 3318 index 12201 1115 AM Page 392