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Page i

Chemical Processing HandbookEdited by

John J. McKetta

The University of Texas at AustinAustin,Texas

Page ii

Library of Congress Cataloging-in-Publication DataChemical processing handbook / edited by John J. McKetta.p. cm.Articles excerpted from: Encyclopedia of Chemical Processingand DesignIncludes bibliographical references and index.ISBN 0-8247-8701-31. Chemical engineering--Handbooks, manuals, etc. I. McKetta,John J. II. Encyclopedia of chemical processing anddesign.TP151.C573 1993 93-20256660-dc20 CIP

The contents of these volumes were originally published in Encyclopedia of ChemicalProcessing and Design, edited by J. J. McKetta and W. A. Cunningham. 1977, 1978,1979, 1982, 1983, 1985, 1986, 1987, 1988, 1990, 1992 by Marcel Dekker, Inc.

The publisher offers discounts on this book when ordered in bulk quantities. For moreinformation, write to Special Sales/Professional Marketing at the address below.

This book is printed on acid-free paper.

Copyright 1993 by Marcel Dekker, Inc. All Rights Reserved.

Neither this book nor any part may be reproduced or transmitted in any form or by anymeans, electronic or mechanical, including photocopying, microfilming, and recording, orby any information storage and retrieval system, without permission in writing from thepublisher.

Marcel Dekker, Inc.270 Madison Avenue, New York, New York 10016

Current printing (last digit):10 9 8 7 6 5 4 3 2 1

PRINTED IN THE UNITED STATES OF AMERICA

Page iii

PrefaceWe are pleased to present many chemical processes in an alphabetically organized, easy-to-read and understandable manner. This handbook covers up-to-date processingoperations in the chemical industry. Each section is written by a world expert in thatparticular area in such a manner that it is easily understood and applied. Eachprofessional practicing engineer or industrial chemist involved in chemical processingshould have a copy of this book on his or her working shelf.

Each of the processing articles contains information on plant design as well as significantchemical reactions. Wherever possible, shortcut methods of calculations are included,along with nomographic methods of solutions. In the front of the book are two convenientsections that will be very helpful to the reader: (1) conversion to and from SI units and(2) cost indexes that will enable the reader to update any cost information.

As editor, I am grateful for all the help I have received from the great number of authorswho have contributed to this book. I am also grateful to the huge number of readers whohave written to me with suggestions of topics to be included.

JOHN J. MCKETTA

Page v

Contents

Preface iii

Contributors vii

Conversion to SI Units xi

Bringing Costs up to Date xiii

Chemicals from Natural GasDuffer B. Crawford, Charles A. Durr, James A. Finneran, andWilliam Turner

2

Chemicals from PetroleumJ. L. James and D. Shore 20

Gas ProcessingEdited by John J. McKetta 59

AlkylationG. Stefanidakis and J. E. Gwyn 80

AminationLewis F. Hatch 139

Bromination and Bromine CompoundsDavid W. Bunch and Kestutis A. Keblys 148

Catalysis and CatalystsA. G. Oblad, S. K. Goyal, R. Ramakrishnan, and S. Sunder 167

Precious Metals CatalysisRobert J. Farrauto and Ronald M. Heck 238

Chlorination, Liquid Phase and Vapor PhaseRoberto Lee and Alice O. Lee 295

Chlorinated SolventsJ. I. Jordan, Jr. 353

ChloroethanesJ. I. Jordan, Jr. 356

ChlorohydrinsC. E. Rowe 382

ChloromethanesE. M. DeForest 427

Chlorobenzene and DichlorobenzeneB. E. Kurtz and E. W. Smalley 483

Chlorolysis, Carbon Tetrachloride from Hydrocarbon WasteD. Rebhan 501

Clathrates and Other Inclusion CompoundsEverett J. Fuller 509

Page vi

DehydrogenationHervey H. Voge 541

DeionizationW. F. McIlhenny 555

Electrochemical Engineering: TheoryFrancis M. Donahue 568

Electrochemical Process Design and OperationRonald L. Dotson 584

Enzyme ProcessingK. Venkatasubramanian and W. R. Vieth 607

EsterificationRobert M. Simons 637

Fisher-Tropsch SynthesisBernd Bssemeier, Carl Dieter Frohning and Boy Cornils 658

Hydrogenation CatalystsJ. P. Boitiaux, J. L. Cosyns, M. L. Derrien, and G. Leger 696

IsomerizationR. E. Conser, T. Wheeler, and F. G. McWilliams 723

Laser-Assisted Chemical ProcessingHenry A. McGee, Jr. 748

NitrationErnest O. Ohsol 762

Olefin ProcessesYee Chien Hu 768

Oxidation of AromaticsErnest O. Ohsol 819

Oxidation of HydrocarbonsCharles C. Hobbs and Michael B. Lakin 829

Petroleum ProcessingHarold L. Hoffman and John J. McKetta 851

PolymerizationLyle F. Albright 892

Polymerization, Emulsion

Louis R. Roberts 925Polysilicon Processes, EconomicsCarl L. Yaws and Jack R. Hopper 939

Index 953

Page vii

ContributorsLyle F. Albright, Ph.D. Professor, School of Chemical Engineering, Purdue University, WestLafayette, Indiana

J. P. Boitiaux, Ph.D. Deputy Manager, Kinetics and Catalysis Unit, Institut Franais duPtrole, Rueil-Malmaison, France

David W. Bunch Supervisor, Research and Development Department, Ethyl Corporation,Baton Rouge, Louisiana

Bernd Bssemeier, Ph.D. Head, Environmental Department, Hoechst AG WerkRuhrchemie, Oberhausen, Germany

R. E. Conser Assistant Director of Marketing Services, UOP, Inc., Des Plaines, Illinois

Boy Cornils, Ph.D. Head, Division A (Chemicals), Hoechst AG, Frankfurt am Main,Germany

J. L. Cosyns, Ph.D. Petrochemical Manager, Industrial Direction, Institut Franais duPtrole, Rueil-Malmaison, France

Duffer B. Crawford Consultant, The M. W. Kellogg Company, Houston, Texas

E. M. DeForest (deceased) Director of Technology, Chemicals and Metal Group, VulcanMaterials Company, Wichita, Kansas

M. L. Derrien Hydrogenation Technology Coordinator, Institut Franais du Ptrole, Rueil-Malmaison, France

Francis M. Donahue Professor, Department of Chemical Engineering, University ofMichigan, Ann Arbor, Michigan

Ronald L. Dotson, Ph.D. Senior Consulting Scientist, Process Technology, Olin Chemicals,Olin Corporation, Charleston, Tennessee

Charles A. Durr The M. W. Kellogg Company, Houston, Texas

Robert J. Farrauto, Ph.D. Research Fellow, Corporate Research, Engelhard Corporation,Iselin, New Jersey

James A. Finneran Vice President, Product and Systems Marketing (retired), The M. W.Kellogg Company, Houston, Texas

Carl Dieter Frohning, Ph.D. Group Leader, Research, Hoechst AG Werk Ruhrchemie,Oberhausen, Germany

Everett J. Fuller Corporate Research Laboratories, Exxon Research and Engineering

Company, Linden, New Jersey

Page viii

S. K. Goyal, Ph.D. Process Specialist, Amaco Oil Corporation, Napierville, Illinois

J. E. Gwyn, Ph.D., P.E. Consultant, Katy, Texas

Lewis F. Hatch (deceased) Professor of Chemistry, The University of Petroleum andMinerals, Dharan, Saudi Arabia

Ronald M. Heck, Ph.D. Research Group Leader, Environmental Catalyst Department,Engelhard Corporation, Iselin, New Jersey

Charles C. Hobbs, Ph.D. Consultant in Oxidation Chemistry, formerly Senior ResearchAssociate, Hoechst Celanese Corp., Technical Center, Corpus Christi, Texas

Harold L. Hoffman Editor, Hydrocarbon Processing, Houston, Texas

Jack R. Hopper, Ph.D. Professor and Chair, Chemical Engineering Department, LamarUniversity, Beaumont, Texas

Yee Chien Hu, Ph.D. Staff Engineer, Petrochemicals, Oxy Chem, Alvin, Texas

J. L. James The M. W. Kellogg Company, Wembley, Middlesex, England

J. I. Jordan, Jr. (deceased) Manager, Research and Development, Chemicals Division,Vulcan Materials Company, Wichita, Kansas

Kestutis A. Keblys Supervisor, Research and Development Department, Ethyl Corporation,Ferndale, Michigan

B. E. Kurtz Director, Engineering Research, Syracuse Technical Center, IndustrialChemicals Division, Allied Chemical Corporation, Solvay, New York

Michael B. Lakin, Ph.D. Senior Engineering Associate, Hoechst Celanese Corporation,Corpus Christi, Texas

Alice O. Lee Consultant, Chemical Businesses, St. Louis, Missouri

Roberto Lee, Ph.D. Group Consultant, Engineering, Monsanto Company, St. Louis,Missouri

G. Leger Research Engineer, Institut Franais du Ptrole, Solaize, France

Henry A. McGee, Jr., Ph.D. Director, Chemical and Thermal Systems Division, NationalScience Foundation, Washington, D.C.

W. F. Mcllhenny Associate Scientist, Dow Chemical U.S.A., Texas Division, Freeport,Texas

John J. McKetta, Ph.D., P.E. The Joe C. Walter Professor of Chemical Engineering, TheUniversity of Texas at Austin, Austin, Texas

F. G. McWilliams Consultant, UOP, Inc., Des Plaines, Illinois

Page ix

A. G. Oblad, Ph.D. Distinguished Professor, Chemical and Fuels Engineering Department,University of Utah, Salt Lake City, Utah

Ernest O. Ohsol, Sc.D. Consulting Chemical Engineer and Chairman, Unipure Corporation,Houston, Texas

R. Ramakrishnan, Ph.D. President, A&B Environmental Services, Houston, Texas

D. Rebhan Hoechst Aktiengesellschaft, Frankfurt, Germany

C. E. Rowe (deceased) Consultant (formerly Principal Engineer, Olin Corporation), St.Louis, Missouri

Louis R. Roberts L. R. Roberts Engineering, Inc., Austin, Texas

D. Shore Former Senior Consultant, The M. W. Kellogg Company, Wembley, Middlesex,England

Robert M. Simons, Ph.D. Senior Development Associate, Development and ControlDepartment, Acid Division, Tennessee Eastman Company, Kingsport, Tennessee

E. W. Smalley Senior Research Chemist, Syracuse Technical Center, Industrial ChemicalsDivision, Allied Chemical Corporation, Solvay, New York

G. Stefanidakis, Ph.D. Research Associate, Shell Development Company, Houston, Texas

S. Sunder, Ph.D. Lead Staff Engineer, Air Products, Allentown, Pennsylvania

William Turner The M. W. Kellogg Company, Wembley, Middlesex, England

K. Venkatasubramanian Visiting Professor, Department of Chemical and BiochemicalEngineering, Rutgers University, New Brunswick, New Jersey

W. R. Vieth, Sc.D. Distinguished Professor, Department of Chemical and BiochemicalEngineering, Rutgers University, New Brunswick, New Jersey

Hervey H. Voge (deceased) Sebastopol, California

T. Wheeler Marketing Representative, Catalyst and Sorbents, UOP, Inc., Des Plaines,Illinois

Carl L. Yaws, Ph.D. Professor, Chemical Engineering Department, Lamar University,Beaumont, Texas

Page xi

Conversion to SI Units

To convert from To Multiply by

acre square meter (m2) 4.046 103

angstrom meter (m) 1.0 10-10

are square meter (m2) 1.0 102

atmosphere newton/square meter(N/m2)1.013 105

bar newton/square meter(N/m2) 1.0 105

barrel (42 gallon) cubic meter (m3) 0.159

Btu (International Steam Table) joule (J) 1.055 103

Btu (mean) joule (J) 1.056 103

Btu (thermochemical) joule (J) 1.054 103

bushel cubic meter (m3) 3.52 10-2

calorie (International SteamTable) joule (J) 4.187

calorie (mean) joule (J) 4.190

calorie (thermochemical) joule (J) 4.184

centimeter of mercury newton/square meter(N/m2)1.333 103

centimeter of water newton/square meter(N/m2) 98.06

cubit meter (m) 0.457

degree (angle) radian (rad) 1.745 10-2denier (international) kilogram/meter (kg/m) 1.0 10-7

dram (avoirdupois) kilogram (kg) 1.772 10-3

dram (troy) kilogram (kg) 3.888 10-3

dram (U.S. fluid) cubic meter (m3) 3.697 10-6dyne newton (N) 1.0 10-5

electron volt joule (J) 1.60 10-19erg joule (J) 1.0 10-7

fluid ounce (U.S.) cubic meter (m3) 2.96 10-5

foot meter (m) 0.305

furlong meter (m) 2.01 102

gallon (U.S. dry) cubic meter (m3) 4.404 10-3

gallon (U.S. liquid) cubic meter (m3) 3.785 10-3

gill (U.S.) cubic meter (m3) 1.183 10-4grain kilogram (kg) 6.48 10-5

gram kilogram (kg) 1.0 10-3

horsepower watt (W) 7.457 102

horsepower (boiler) watt (W) 9.81 103

horsepower (electric) watt (W) 7.46 102

hundred weight (long) kilogram (kg) 50.80

hundred weight (short) kilogram (kg) 45.36

inch meter (m) 2.54 10-2

inch mercury newton/square meter(N/m2)3.386 103

inch water newton/square meter(N/m2) 2.49 102

kilogram force newton (N) 9.806

Page xii

To convert from To Multiply by

kip newton (N) 4.45 103

knot (international) meter/second (m/s) 0.5144

league (Britishnautical) meter (m)

5.559 103

league (statute) meter (m) 4.83 103

light year meter (m) 9.46 1015

liter cubic meter (m3) 0.001

micron meter (m) 1.0 10-6

mil meter (m) 2.54 10-6

mile (U.S. nautical) meter (m) 1.852 103

mile (U.S. statute) meter (m) 1.609 103

millibar newton/square meter (N/m2) 100.0

millimeter mercury newton/square meter (N/m2) 1.333 102

oersted ampere/meter (A/m) 79.58

ounce force(avoirdupois) newton (N) 0.278

ounce mass(avoirdupois) kilogram (kg)

2.835 10-2

ounce mass (troy) kilogram (kg) 3.11 10-2

ounce (U.S. fluid) cubic meter (m3) 2.96 10-5

pascal newton/square meter (N/m2) 1.0

peck (U.S.) cubic meter (m3) 8.81 10-3

pennyweight kilogram (kg) 1.555 10-3

pint (U.S. dry) cubic meter (m3) 5.506 10-4

pint (U.S. liquid) cubic meter (m3) 4.732 10-4

poise newton second/square meter (N .s/m2) 0.10

pound force(avoirdupois) newton (N) 4.448

pound mass(avoirdupois) kilogram (kg) 0.4536

pound mass (troy) kilogram (kg) 0.373

poundal newton (N) 0.138

quart (U.S. dry) cubic meter (m3) 1.10 10-3

quart (U.S. liquid) cubic meter (m3) 9.46 10-4

rod meter (m) 5.03

roentgen coulomb/kilogram (c/kg) 2.579 10-4second (angle) radian (rad) 4.85 10-6

section square meter (m2) 2.59 106

slug kilogram (kg) 14.59

span meter (m) 0.229

stoke square meter/second (m2/s) 1.0 10-4

ton (long) kilogram (kg) 1.016 103

ton (metric) kilogram (kg) 1.0 103

ton (short, 2000pounds) kilogram (kg)

9.072 102

torr newton/square meter (N/m2) 1.333 102

yard meter (m) 0.914

Page xiii

Bringing Costs up to DateJohn J. McKetta

Cost escalation via inflation bears critically on estimates of plant costs. Historical costs ofprocess plants are updated by means of an escalation factor. Several published costindexes are widely used in the chemical process industries:

Nelson-Farrar Cost Indexes (Oil and Gas J.), quarterly

Marshall and Swift (M&S) Equipment Cost Index, updated monthly

CE Plant Cost Index (Chemical Engineering), updated monthly

ENR Construction Cost Index (Engineering News-Record), updated weekly

All these indexes were developed with various elements, such as material availability andlabor productivity, taken into account. However, the proportion allotted to each elementdiffers with each index. The differences in overall results of each index are due to unevenprice changes for each element. In other words, the total escalation derived by eachindex will vary because different bases are used. The engineer should become familiarwith each index and its limitations before using it.

Table 1 compares the CE Plant Index with the M&S Equipment CostTABLE 1 Chemical Engineering and Marshall and Swift Plant and Equipment CostIndexes since 1950Year CE Index M&S Index Year CE Index M&S Index1950 73.9 167.9 1971 132.3 321.31951 80.4 180.3 1972 137.2 332.01952 81.3 180.5 1973 144.1 344.11953 84.7 182.5 1974 165.4 398.41954 86.1 184.6 1975 182.4 444.31955 88.3 190.6 1976 192.1 472.11956 93.9 208.8 1977 204.1 505.41957 98.5 225.1 1978 218.8 545.31958 99.7 229.2 1979 238.7 599.41959 101.8 234.5 1980 261.2 659.61960 102.0 237.7 1981 297.0 721.31961 101.5 237.2 1982 314.0 745.61962 102.0 238.5 1983 316.9 760.81963 102.4 239.2 1984 322.7 780.41964 103.3 241.8 1985 325.3 789.61965 104.2 244.9 1986 318.4 797.61966 107.2 252.5 1987 323.8 813.61967 109.7 262.9 1988 342.5 852.01968 113.6 273.1 1989 355.4 895.11969 119.0 285.0 1990 357.6 915.11970 125.7 303.3 1991 361.3 930.6

Page xiv

TABLE 2 Nelson-Farrar Inflation Refinery Construction Indexes since 1946(1946 = 100)

Date Materials Component LaborComponent Miscellaneous EquipmentNelson-Farrar Inflation

Index1946 100.0 100.0 100.0 100.01947 122.4 113.5 114.2 117.01948 139.5 128.0 122.1 132.51949 143.6 137.1 121.6 139.71950 149.5 144.0 126.2 146.21951 164.0 152.5 145.0 157.21952 164.3 163.1 153.1 163.61953 172.4 174.2 158.8 173.51954 174.6 183.3 160.7 179.81955 176.1 189.6 161.5 184.21956 190.4 198.2 180.5 195.31957 201.9 208.6 192.1 205.91958 204.1 220.4 192.4 213.91959 207.8 231.6 196.1 222.11960 207.6 241.9 200.0 228.11961 207.7 249.4 199.5 232.71962 205.9 258.8 198.8 237.61963 206.3 268.4 201.4 243.61964 209.6 280.5 206.8 252.11965 212.0 294.4 211.6 261.41966 216.2 310.9 220.9 273.01967 219.7 331.3 226.1 286.71968 224.1 357.4 228.8 304.11969 234.9 391.8 239.3 329.01970 250.5 441.1 254.3 364.91971 265.2 499.9 268.7 406.01972 277.8 545.6 278.0 438.51973 292.3 585.2 291.4 468.01974 373.3 623.6 361.8 522.71975 421.0 678.5 415.9 575.51976 445.2 729.4 423.8 615.71977 471.3 774.1 438.2 653.01978 516.7 824.1 474.1 701.11979 573.1 879.0 515.4 756.61980 629.2 951.9 578.1 822.81981 693.2 1044.2 647.9 903.81982 707.6 1154.2 622.8 976.91983 712.4 1234.8 656.8 1025.81984 735.3 1278.1 665.6 1061.01985 739.6 1297.6 673.4 1074.41986 730.0 1330.0 684.4 1089.91987 748.9 1370.0 703.1 1121.51988 802.8 1405.6 732.5 1164.51989 829.2 1440.4 769.9 1195.91990 832.8 1487.7 797.5 1225.71991 832.3 1533.3 827.5 1252.9

Page xv

Index. Table 2 shows the Nelson-Farrar Inflation Petroleum Refinery Construction Indexessince 1946. It is recommended that the CE Index be used for updating total plant costsand the M&S Index or Nelson-Farrar Index for updating equipment costs. The Nelson-Farrar Indexes are better suited for petroleum refinery materials, labor, equipment, andgeneral refinery inflation.

Since

Here, A = the size of units for which the cost is known, expressed in terms of capacity,throughput, or volume; B = the size of unit for which a cost is required, expressed in theunits of A; n = 0.6 (i.e., the six-tenths exponent); CA = actual cost of unit A; and CB = thecost of B being sought for the same time period as cost CA.

To approximate a current cost, multiply the old cost by the ratio of the current indexvalue to the index at the date of the old cost:

Here, CA = old cost; IB = current index value; and IA = index value at the date of oldcost.

Combining Eqs. (1) and (2),

For example, if the total investment cost of plant A was $25,000,000 for 200-million-lb/yrcapacity in 1974, find the cost of plant B at a throughput of 300 million lb/yr on the samebasis for 1986. Let the sizing exponent, n, be equal to 0.6.

From Table 1, the CE Index for 1986 was 318.4, and for 1974 it was 165.4. Via Eq. (3),

Chemicals from Natural GasDuffer B. Crawford,Charles A. Durr,James A. Finneran,and William Turner

Natural gas may be converted to a variety of industrial chemicals, petrochemicals, andfertilizers. These are indicated along with the processes used in their manufacture. Moredetailed information, such as yield data and scale of commercial production capacity, areidentified for ammonia and its fertilizer derivatives.

Introduction

Natural gas is an excellent feedstock in the chemical industry. Figure 1 indicates thecomponents that can be separated from natural gas in a typical processing plant. Thisarticle will review the first and second step chemical derivatives that are manufacturedfrom methane, ethane, propane (LPG), and butane. However, the primary emphasis is onthe chemical products that are

Fig. 1

manufactured from methane; i.e., the ''vertical integration" of chemicals and fertilizersthat are produced from methane is presented in more detail.

The use of natural gas as a feed to chemical plants is based primarily upon the chemicalproduction and consumption experienced in the United States. The statistics presented donot directly apply to the rest of the world; however, these statistics are useful becausethey demonstrate the utilization of natural gas in a country where, until recently, naturalgas was considered to be plentiful. Also, the utilization of natural gas as a chemical feedis more developed in the United States than in any other country in the world.

Natural Gas

Natural gas is a mixture of hydrocarbons ranging from methane to pentane or heavier.These hydrocarbons are mostly paraffins but do include a small amount of naphthenes.Natural gas is highly desirable because it is a relatively clean fuel as well as an excellentfeedstock for the chemical industry. Natural gas may be steam reformed for theproduction of ammonia which serves as a fertilizer or as the main building block in thesynthesis of other fertilizers and chemicals.

The natural gas components heavier than methane are usually separated via a cryogenicfractionating step prior to use as a petrochemical feedstock. The ethane may be"cracked" to form ethylene; likewise, the propane and butane may be cracked toethylene/propylene or can be used as a fuel. The heaviest components, known as naturalgasoline, may be used in gasoline blending, may be charged to a refinery assupplemental feed, or may be cracked to form ethylene/propylene and its by-products.

Natural Gas Usage

A recent study [1] estimates that 2.6% of the natural gas consumption in the UnitedStates is used by the petrochemical industry as a feedstock while another 4.6% is usedas a fuel. Thus the consumption of natural gas for petrochemicals is not large. However,for the petrochemical industry, natural gas is its major supplier of fuel and feedstock.Table 1 shows the results of a study for the Federal Energy Administration in the UnitedStates. This study was made to determine the consumption of fuels and petroleumproducts within the chemical industry. Thirty-seven chemicals were chosen to representthe broad range of chemicals that are actually manufactured; these represent 63% of thetotal process and feedstock energy consumption for all chemicals in the United States.

Table 1 indicates that natural gas supplies 49.9% of the total energy requirements forthe chemicals while LPG supplies another 23.7%. Thus it is obvious that, even though thenatural gas and LPG used for chemicals is only a small portion of the available supply inthe United States, they are vital as a source of fuel and feedstock energy to thepetrochemical industry.

TABLE 1 Consumption of Fuels and Feedstocks in the ChemicalIndustry of the United States, 1973 (based on 37 selected chemicals)[2]

Source of Energy Process Energy(%)Feedstock Energy

(%)Total

Energy(%)

Dry natural gas 34.2 15.7 49.9Coal 3.9 Minor 3.9Residual fuel oil 0.8 0.8Distillate oil 1.3 1.3Fuels 0.7 0.7Ethane/propane(LPG) 23.7 23.7Naphtha and other 14.7 14.7Benzene 5.0 5.0Total 40.9 59.1 100.0

Fig. 2

Natural Gas Processing Plants

Usually "wet" natural gas is processed to separate the heavy paraffins from the methane.This may be done via an absorption process, a refrigerated absorption process, or acryogenic process. In general, if a high recovery is desired only for the propane andheavier components, the absorption process is used; for an intermediate level of ethanerecovery, the refrigerated absorption process; and for high ethane recovery, a cryogenicprocess would be used.

During 1971, 80% of the available natural gas in the United States was processed innatural gas processing plants. During this processing, about 51 million t of natural gasliquids (NGL) were extracted. About 47% of this NGL was exported for use in refinerieswhile the remainder was for direct use as fuel, power, and feedstock. About 17.6 million twere used for a chemical feedstock, mostly to ethylene plants.

Components of Natural Gas As a Chemical Feed

Figure 2 shows the basic "chemical tree" of chemicals, building blocks, etc. that can beproduced from natural gas. The "chemical tree" will be developed to indicate the first andsecond stage chemical derivatives using methane, ethane, LPG, and C4 hydrocarbon asthe feedstock. However, more detail will be presented covering the primary, secondary,and in some cases the tertiary derivatives from methane.

Ethane and LPG

Almost all of the ethane and LPG that is used as a chemical feed is used in themanufacture of ethylene. Although ethylene has very few direct end uses, it is one of themost important chemical building blocks in producing such products as polyethylene,ethylene oxide, ethanol, and styrene. This importance derives from the reactivity of thedouble bond and due to its capability to copolymerize with itself and other monomers;these properties have resulted in the large volume production of a wide variety ofethylene derivatives. The consumption pattern of ethylene is shown in Table 2 fromwhich it is apparent that polyethylene is the major consumer of ethylene followed byethylene oxide and ethylene dichloride. High- and low-density polyethylene is used in themanufacture of films and in injection molding. Ethylene oxide is used in the production ofglycol ethers, ethylene glycols, and ethanolamines.

Table 3 lists the type, number, and capacity of ethylene or ethylene derivative plants thatare either under construction, planned, or proposed in the world as of February 1975.

TABLE 2 Consumption of Ethylene in the United States in 1974 [3]%

Polyethylene (low-density) 27.9Polyethylene (high-density) 12.7Ethylene oxide (and glycol) 19.5Ethylene dichloride 14.0Ethanol 5.5Styrene (via ethyl benzene) 8.5Others 11.9

Total 100.0

Today, most of the ethylene is made by the thermal cracking of any naphthenic orparaffinic hydrocarbon heavier than methane (see Table 4); the amount of ethylene andby-products formed will depend upon the molecular weight of the feed. As the molecularweight increases above that of ethane, the amount of by-products increases dramatically.Thus the simplest and least expensive plant will result when ethane is used as afeedstock. Heavier feeds, such as gas oil and naphtha, are also used in makingethylene/propylene and its by-products. In this case the market values of the by-productsare important in determining the plant's economic viability.

Ethane and LPG are preferred feeds for chemical companies that are not fully integratedto market the by-products produced with heavier feeds. The major trend in recent yearsin the United States has been toward the use of heavier feeds such as naphtha or gas oilbecause of the unavailability of ethane and LPG. This trend has increased the proportionof ethylene that has been manufactured by oil companies. This is mainly because the oilcompanies have better access to the available feed and because they are also in a betterposition to sell the various by-products.TABLE 3 Ethylene-Based Plants (under construction, planned, or proposed)in the World as of February 1975 [4]

Product Number of NewPlantsTotal New Capacity (thousand

tons/yr)Ethylene 76 19,284Polyethylene 77 5,970Ethylene oxide 18 1,240Ethylene glycol 13 731Styrene 16 2,223Polystyrene 16 676Ethylenedichloride 3 485

TABLE 4 Ethylene Production from Various Feedstocks in the UnitedStates, 1974 [5]Feedstock Thousand Tons/YearEthane 5,580LPG 3,040Naphtha 680Gas oil 953

Total 10,253

In Japan and Europe the lack of natural gas as a source of ethane/LPG forced olefinproducers to select naphtha as their main feedstock. However, this trend may bemodified in Europe if the North Sea gas contains significant amounts of ethane/LPGcomponents.

Propane and Butane Hydrocarbons

The chemical use of these hydrocarbons has been growing in recent years. Propane isobtained from the light end of crude oil or the heavy end (NGL) extracted from naturalgas along with ethane and butane. Approximately 30% of the propane produced in theUnited States is used as a chemical feed, primarily in producing ethylene/propylene. Theremaining 70% is used in the energy sector of the economy [6]; i.e., industrial fuel, utilitygas, and producing SNG.

About one-third of the butane produced today comes from natural gas liquids; theremainder comes from refineries. The chemical applications for butanes are only minorwhen compared to the amounts used for gasoline production. About 8% is used as achemical raw material. For example, n-butane may be dehydrogenated to producebutadiene (primary derivative) or n-butenes. Isobutane is also consumed as a chemicalfeed. However, only about 2% of it is used in this manner. The remainder is used inalkylation.

Synthesis Gas

Natural gas and other hydrocarbons are used to make synthesis gas; i.e., carbonmonoxide and hydrogen. This synthesis gas is used in the manufacture of ammonia,methanol, phosgene, and oxo alcohols, which in turn are used in

the manufacture of many other fertilizers and industrial chemicals. Depending upon whichproduct is desired, the composition of the synthesis gas is selected in order to have theproper ratio of hydrogen and carbon monoxide. For example, to produce methanol, theratio is 2H2:1CO (or 3H2:1CO2); for the oxo reaction, 1H2:1CO. For ammonia, the requiredratio of 3H2:1N2 is satisfied by obtaining the hydrogen from the hydrocarbon and thenitrogen from air that is introduced into the process. In making phosgene, formic acid,and oxalic acid, only the carbon monoxide is required; for producing peroxide and inhydrogenation processes, only the hydrogen is required. Synthesis gas can also beproduced from coke oven gas, coal gas, or the electrolysis of water. However,

Fig. 3

TABLE 5 Synthesis Gas-Based Plants (under construction, planned, orproposed) in the World as of February 1975 [4]

Product Number of New PlantsTotal NewCapacity

(thousand tons/yr)Ammonia 90 27,400Ammonium nitrate 17 4,247Urea 61 23,000Nitric acid 27 5,775Ammonium sulfate 2 333Acrylonitrile 16 1,089Methanol 20 2,772Formaldehyde 16 440Carbon monoxide Not available Not availablePhosgene 2 75Oxo alcohols 3 130

the main methods practiced today are the steam reforming or partial oxidation ofhydrocarbons. In particular, steam reforming is the primary method.

Figure 3 shows the chemical products and/or intermediates that can be manufacturedfrom synthesis gas. This section of this article will review these chemicals and theirderivatives as shown in the figure. Table 5 lists the type, number, and capacity ofsynthesis gas-based plants that are either under construction, planned, or proposed in theworld.

Ammonia

Ammonia is the second largest volume chemical produced in the United States; secondonly to sulfuric acid. Its great value stems from the fact that it is a raw material forfertilizers, explosives, synthetic fibers, and plastics. Table 6 shows the consumptionbreakdown for ammonia. This indicates that 76.3% of the ammonia consumed in theUnited States is used directly as a fertilizer or is converted into another fertilizer. In fact,almost all nitrogen fertilizers are manufactured from anhydrous ammonia. Notice that26.6% of the ammonia consumption is applied directly to the soil in the liquid form. Thisconsumption pattern is unique to the United States. Most other countries first convert allthe ammonia into a solid fertilizer before it is applied to the soil.

Most of the ammonia production in the world is based on steam-hydrocarbon reforming;this accounts for about 75 to 80% of world production with 60 to 65% of this usingnatural gas as the feed. It is expected that this percentage will hold for the near-termfuture. However, on a long-range basis it is expected that heavier feeds and coal willincrease their percentage as a feedstock, gradually displacing natural gas.

TABLE 6 Major Domestic Uses and Consumption Distribution of Ammonia in theUnited States in 1972 [7]

Consuming AreasAmmonia and Derivatives Fertilizers(%)

Other(%)

Total(%)

Ammonia, direct applicationa 26.6 26.6Ammonium nitrate (AN) 17.0 4.0 21.0Ammonium phosphate 11.2 11.2Urea 10.1 2.4 12.5Ammonium sulfate 5.9 5.9Nitric acid for non-AN uses 1.1 5.8 6.9Nitrogen solutions and mixed fertilizers 4.4 4.4Acrylonitrile 2.2 2.2Other 9.3 9.3

Total 76.3 23.7 100.0aAs anhydrous or aqua ammonia.

In order to produce the hydrogen for ammonia production, the raw synthesis gas fromsteam reforming, containing carbon monoxide, carbon dioxide, and hydrogen, must befurther processed. First, the carbon monoxide plus steam is shifted to produce morecarbon dioxide and hydrogen. Second, the carbon dioxide is removed from the gas by aliquid absorption system. Third, the remaining traces of CO are removed by converting itback to methane. Since nitrogen (in the form of air) was added to the raw synthesis gasduring its generation, the final output is the required synthesis gas containing the ratio3H2:1N2 necessary for ammonia production.

As indicated previously, most ammonia is converted into a solid fertilizer, such as urea orammonium nitrate, before it is applied to the soil. It is worthwhile to examine how andwhy these nitrogen conversion steps are employed. In particular, ammonium nitrate,ammonium phosphate, urea, and ammonium sulfate will be examined. In addition, theproduction of nitric acid and acrylonitrile from ammonia will be covered.

Table 7 gives production information about ammonia and its derivatives. The columnlabeled "Feed" lists the feedstocks necessary to manufacture the product. The nextcolumn indicates the amount of feed required to produce 1 ton of product. The fourthcolumn gives the amount of natural gas required to produce a ton of product. Forexample, 965.4 normal m3 of natural gas are required to produce 1 ton of ammonia. Inthe case of the ammonia derivative products, the natural gas consumption wasdetermined by multiplying the ammonia requirement per ton of product by 965.4 normalm3/ton of ammonia. Thus this indicates the amount of natural gas that must be fed to theammonia plant to produce the fertilizer. Of course, ammonia (and nitric acid) is an

intermediate product in this case. This column of the table is interesting because thesenumbers can be used as coefficients in an equation to determine the approximate netoutput for each product in a fertilizer complex:

where X= natural gas feed to ammonia plant (m3/d)

A= net production of ammonia (tons/d)

AN= net production of ammonium nitrate(tons/d)

AP= net production of ammonium phosphate(tons/d)

U= net production of urea (tons/d)

AS= net production of ammonium sulfate(tons/d)

NA= net production of nitric acid (tons/d)

This equation will determine the possible blend of product outputs in a nitrogen fertilizercomplex when the feedstock is limited to X m3/d of natural gas. The equation assumesthat natural gas is used to supply the process energy for the ammonia plant and thatsome other fuel is used in the ammonia derivative plants. Also, the above equationassumes that sufficient carbon dioxide is generated in the ammonia plant to supply therequirement for the urea plant. The last column in Table 7 gives the capacity ofcommercial producing plants for each of the products.TABLE 7 Production of Ammonia Derivative Fertilizers and Chemicals

TonFeed

Product Feed TonProductNormal Cubic Meter Gasa

per Ton ProductCommercial Production

Capacity (tons/d)Ammonia Natural gas 965.4 10001500Ammoniumnitrate Ammonia 0.215 207.6 1400

Nitric acid(100%) 0.795

217.2424.8

Ammoniumphosphate Ammonia 0.22 214.3 1500

Phosphoricacid (52%) 0.660

Urea Ammonia 0.580 559.9 1725Carbondioxide 0.770

Ammonium Ammonia 0.263 253.9 1000

sulfate Sulfuric acid(98%) 0.767

Nitric acid(100%) Ammonia 0.283 273.2 1100aBased on natural gas having a lower heating value of 37,266 kJ per normal m3. Thiscolumn gives the amount of natural gas that must be fed to a typical existingammonia plant in order to produce 1 t of product.

Ammonium Nitrate. Ammonium nitrate is the largest solid fertilizer use for ammonia.About 84% (1973) of this ammonium nitrate is used in the United States as a fertilizerwhile the remainder is used in ammonium nitrate-based explosives.

Ammonium nitrate is made by the neutralization of nitric acid with ammonia. Sinceammonia is also required to make nitric acid, the general arrangement is that anammonia, nitric acid, and ammonium nitrate plant will be located at the same site. Also,the integral production of urea, ammonia, ammonium nitrate, and nitric acid may beaccomplished in order to produce a urea-ammonium nitrate fertilizer solution for directapplication to the soil. The 83 to 85% ammonium nitrate solution from the plant may besold in the liquid form or may be converted into a solid by prlling or another suchtechnique.

Ammonium nitrate and urea can both be used to supply nitrogen as a nutrient to the soil.Several factors must be considered in choosing the best fertilizer for a specific situation.For example, ammonium nitrate has an advantage in that about one-half of its nitrogen isin the nitrate form; this nitrate is quick acting and is good when the crop needs a quicksupply of nutrient. This occurs because most plants assimilate the nitrogen in the nitrateform. However, urea has an advantage over ammonium nitrate because urea does notleach out of porous soils as easily as ammonium nitrate does. Thus more nitrogennutrient may be absorbed by the plants in the case of urea. The best fertilizer will thendepend upon the specific situation. However, the trend in the last decade has been thatthe ammonium nitrate growth pattern has slowed down considerably due to the fact thatthe less expensive nitrogen compounds such as urea or anhydrous ammonia have cut intothe demand for ammonium nitrate.

Urea. Urea is a large consumer of ammonia. Most of the urea consumed in the UnitedStates is used for fertilizer; the remainder is for livestock feed, resins, etc.

Urea is manufactured by the dehydration of ammonium carbamate which, in turn, ismade from ammonia and carbon dioxide. Since carbon dioxide is a waste stream from thesynthesis gas preparation step (steam-methane reforming) in an ammonia plant, almostall urea plants are located next to ammonia plants.

The type of desired product from the fertilizer complex decides the type of urea processthat is used. A "once thru" process is used when small amounts of urea are required forcomplexes producing an ammonium nitrate-urea solution fertilizer. In this case theammonia-rich off gas from the urea plant is used in nitric acid and ammonium nitrateproduction. A "total recycle" process is employed when solid urea is the main product. Inthis situation the off gases are completely recycled to produce the maximum amount ofurea from the ammonia feed. As indicated previously, urea is taking up some of theammonium nitrate market because it is cheaper to manufacture and because it does notleach out of sandy soils easily. Also, urea has the highest nitrogen content (46% N) ofany ammonium derivative fertilizer. Thus it is easier to transport and apply to the soil.

Urea did not become a major fertilizer for many years because of the corrosion problemsassociated with urea and ammonium

carbamate. However, engineering improvements have minimized these problems to suchan extent that urea is the fastest increasing fertilizer being produced today.

Ammonium Phosphate and Sulfate. Ammonium phosphate is manufactured from thereaction between ammonia and phosphoric acid. Almost 100% of the ammoniumphosphate produced in the United States is used in fertilizers. Most of the ammoniumphosphate produced is made in the binutrient form and is then mixed with potash tomake a complete mixed fertilizer. Diammonium phosphate (18-46-0) is the leading gradein the United States and accounts for about 80% (1973) of the total production ofammonium phosphates [8].

Ammonium sulfate is also used mostly as a fertilizer. It is important both for its sulfur andnitrogen content. Ammonium sulfate is made by neutralizing ammonia with sulfuric acidand then evaporating the water in a crystallization step. This fertilizer is also obtained asa by-product in many processes. For example, ammonium sulfate is formed during theammonia scrubbing with sulfuric acid during coke gas cleanup. Also, in the manufacture ofacrylates and caprolactam, ammonium sulfate is produced as a by-product.

Ammonium sulfate is low in nitrogen content (21%). However, its sulfur content (23%)makes it desirable for soil requiring sulfur fertilization. Also, it is helpful on alkaline soilsbecause of its acidity.

Nitric Acid. Nitric acid consumes about 28% of the ammonia produced in the UnitedStates. Of this nitric acid, about 75% is converted directly into ammonium nitrate. Theremaining 25% is used in making explosives, adipic acid, isocyanates, potassium nitrate,and various fertilizers.

Nitric acid is made by the oxidation of ammonia to nitrogen oxide, which in turn isoxidized to nitrogen dioxide; this nitrogen dioxide is then reacted with water to form nitricacid. Most nitric acid is produced in the concentration range of 54 to 60% which isacceptable for the production of ammonium nitrate. However, nitric acid of 93%concentration must be employed for producing explosives and isocyanates. In order toproduce the stronger acids, some method such as dehydrating with sulfuric acid must beused.

Acrylonitrile. Most acrylonitrile in the United States is produced by the reaction ofammonia with propylene via the Sohio process; this method has replaced the previousone of catalytically reacting acetylene with hydrogen cyanides. In 1973, most of theacrylonitrile production was consumed by acrylic fibers, ABS (acrylonitrile-butadiene-styrene), SAN (styrene-acrylonitrile) resin, nitrile elastomers, etc.

Methanol

Table 8 shows the consumption pattern of methanol in the United States in 1973. As canbe seen in the table, about 39% of the methanol produced is a captive intermediary for

formaldehyde production. In fact, almost all the major producers of formaldehyde alsoproduce methanol.

TABLE 8 Methanol Consumption in the United States (1973) [3]Formaldehyde 39Solvent useage 8Dimethyl terephthalate 6Methyl halides 6Exports 12Others 29

Total 100

Most methanol is produced using either a high-pressure process or a lowpressure process.Almost all the methanol produced in the United States is based on the steam-reforming ofnatural gas. Some may be produced by using off gases from acetylene manufacture.

In the high-pressure process (above 275 bars), synthesis gas is made by reformingnatural gas and forming carbon monoxide, carbon dioxide, and hydrogen. Since thereforming of methane produces an excess amount of hydrogen, it is advantageous tolocate the methanol plant near an ammonia plant in order to obtain carbon dioxide tobalance the excess hydrogen by the equation

This, in effect, produces more methanol. This integration is possible because carbondioxide is removed from the synthesis gas used to make ammonia.

In the low-pressure (50 to 100 bars) methanol process, the excess hydrogen is purgedfrom the synthesis loop and is not used to produce methanol. In this method, a largerreformer must be built in order to produce the equivalent amount of methanol.

Methanol plants are usually constructed in the size of 1000 tons/d. However, studies arebeing made for 5000 tons/d plants (with multiple reformers). Several plants would belocated in a giant complex and could supply methanol to a fleet of tankers that wouldtransport it from Algeria, Iran, etc. to the United States, Europe, etc. as a fuel source.This operation would be in competition with LNG transportation schemes.

Formaldehyde. Formaldehyde is consumed mostly in making urea-formaldehyde andphenol-formaldehyde resins: these resins are used in making adhesives for plywood andparticle board. Also, it is used in the manufacture of acetal resin, pentaerythritol, andmelamine-formaldehyde resins. Formaldehyde is made from methanol via an oxidation-dehydrogenation process in the vapor state and also by catalytic oxidation in the vaporstate.

Dimethyl Terephthalate and Methyl Halides. Many processes are used to

manufacture dimethyl terephthalate by the oxidation of p-xylene, in which methanol isused to esterfy the two acid radicals. Most of the dimethyl terephthalate is used in themaking of polyester fibers.

Methyl halides, that is, methyl chloride, methylene chloride, and methyl bromide, can beproduced from methanol. Of the above products, methyl chloride is produced in thelargest volume. Methyl chloride is made by the chlorination of methane or by thehydrochlorination of methanol; the amount being made from methanol is increasing sothat only a minor amount is made from methane today. Methyl chloride is used mostly inmaking silicon elastomers and tetramethyl lead.

Carbon Monoxide

Carbon monoxide is used in the manufacture of acetic acid, phosgene, formic acid, andoxalic acid.

Acetic Acid. Most of the acetic acid made in the United States is from the oxidation ofbutane and the secondary oxidation of acetaldehyde. However, some is manufactured byreacting carbon monoxide with methanol.

Phosgene. Amost all phosgene is manufactured by the reaction between carbonmonoxide and dry chlorine in the presence of activated carbon. Most phosgene is used inthe manufacture of toluene diisocyanate and polymethylene polyphenylisocyanate usedfor the production of polyurethane resins and foams.

Formic Acid and Oxalic Acid. Both formic and oxalic acids can be made from carbonmonoxide. Formic acid is made by absorbing carbon monoxide in caustic soda followed byneutralization. It is used instead of sulfuric acid in high temperature acid textile drying.Oxalic acid is made from carbon monoxide via the intermediate compound, sodiumformate. It is used mostly in the pharmaceutical industry.

Oxo Alcohols

Oxo alcohols are manufactured by reacting olefins with carbon monoxide and hydrogen.In order to produce the required ratio, 1H2:1CO, for the oxo chemicals, the raw synthesisgas from steam reforming must be altered. For example, a low-temperature separation ofthe raw synthesis gas into hydrogen and a 1H2:1CO mixture may be employed, or CO2and steam may be added to natural gas before reforming to obtain the correct H2/COratio in the synthesis gas.

The short-chain-length oxo alcohols are used mostly as solvents; the intermediate chainlength for plastizers for PVC, and the long-chain alcohols for detergents and lubricants.

Carbon Dioxide

Today most of the carbon dioxide used in the United States is obtained as a byproduct inthe manufacture of synthesis gas for the production of ammonia, methanol, and otherchemicals. The carbon dioxide is removed from the synthesis gas by an absorptionprocess. Carbon dioxide is consumed as refrigeration in the food industry, carbonation,inerting, and as a captive raw material in the production of urea, sodium carbonate (bythe Solvay process), and the manufacture of sodium bicarbonate from sodium carbonate.By far the greatest use of captive carbon dioxide is in the production of urea in whichammonia and carbon dioxide form ammonium carbamate which is dehydrated to formurea.

Methane

Figure 4 shows the products that can be made from methane as a feedstock; this, ofcourse, excludes the chemicals that are made from synthesis gas. In general, thesechemicals from methane have a much lower volume production in comparison to theproducts from synthesis gas. However, they are still important products.

Carbon Disulfide

Traditionally, cabon disulfide has been made by reacting charcoal with sulfur in a retort orfurnace. However, all the plants built in recent years are based on the Thacker processwhich uses methane as the feedstock. In 1971 the manufacture of rayon and cellophaneaccounted for most of the United States production of carbon disulfide. The remainder ofthe carbon disulfide production was consumed in the manufacture of carbon tetrachlorideand other chemicals.

Chlorinated Methane

Methane can be chlorinated to form methyl chloride, methylene chloride, chloroform, andcarbon tetrachloride. Depending upon the process design, one or more of thesechloromethane products (or coproducts) may be produced.

Methyl chloride is produced by the chlorination of methane or by the hydrochlorination ofmethanol. Today, only minor amounts of methyl chloride in the United States areproduced from methane. The remainder uses methanol as the feedstock.

Almost all of the methylene chloride produced in the United States is made by thechlorination of methane. Most of the methylene chloride production is used in themanufacture of paint removers, aerosol cans propellents, and solvent degreasing; i.e., itsmain use is as a service chemical and it has very little value as an intermediate product.

Fig. 4

Chloroform is produced by the chlorination of methane. It is used in the manufacture offluorocarbon refrigerants, propellents, and resins.

Carbon tetrachloride is manufactured by the chlorination of methane. However, asignificant amount is produced by the chlorination of carbon disulfide and as a coproductin the manufacture of perchlorethylene from a hydrocarbon feed. Carbon tetrachloride isused in the manufacture of fluorocarbon 11 and 12 refrigerants.

Hydrogen Cyanide

Hydrogen cyanide produced in the United States is manufactured from methane,ammonia, and oxygen via the Andrusson (called Goodrich process in the United States)process. The remainder comes from the by-product recovery of hydrogen cyanide fromacrylonitrile production. Hydrogen cyanide is used in the manufacture of acetonecyanohydrin, adiponitrile for nylon 66, and acrylonitrile. Today, very little hydrogencyanide is consumed in the production of acrylonitrile because this product is nowpredominantly made from propylene and ammonia rather than the old route ofacethylene and hydrogen cyanide. In fact, as indicated above, hydrogen cyanide is nowbeing recovered as a by-product in acrylonitrile production.

Carbon Black

Carbon black is made from natural gas or liquid hydrocarbons, mainly by the furnaceprocess. The natural gas or liquid hydrocarbon is partially combusted or thermallycracked. In 1955 about one-half of the carbon black manufactured in the United Statesused natural gas as the raw material. However, in 1973 only 7% of the total productioncame from natural gas with the remainder coming from liquid hydrocarbons. In 1973 therubber industry consumed most of the carbon black production in the United States; theremainder was used in making paint and printing ink.

Acetylene

Acetylene can be produced from calcium carbide or a hydrocarbon feed. The use ofacetylene as a chemical feed has decreased greatly in the last few years; the productionof acetylene decreased from 453,000 tons/yr in 1970 to 226,000 tons/yr in 1974. Thisoccurred mostly because of the switch from acetylene-based to ethylene-based processesin the production of vinyl chloride and vinyl acetate. In addition, butadiene is now beingused in making neoprene, and propylene is used in making acrylonitrile.

Presently, acetylene production is used in the manufacture of vinyl chloride, acrylates,and vinyl acetate and for industrial use for welding and metal cutting. It is not expectedthat any new plants will be built in the United States in the near future because of itscompetitive disadvantages with other raw materials.

Conclusion

Natural gas is a very valuable feedstock for the chemical and fertilizer industry in that itsupplies most of the feed. Also, most plants that can use natural gas or an alternate feedwill be cheaper if they were based on natural gas. Thus future

plans for the allocation of natural gas must take into account its great importance as afeedstock for the petrochemical industry.

This material was presented in part before the Institute of Chemical Engineers in Dublin,Ireland, April 7, 1976.

Bibliography

Hahn, A., The Petrochemical Industry, McGraw-Hill, New York, 1970.

References

1. Chemical and Engineering News, ''Decontrol of Natural Gas Prices Hoped for," August25, 1975, pp. 1214.

2. J. Garton, M. Kramer, D. Robertson, M. Fortune, and N, Leggett, Industrial EnergyStudy of the Industrial Chemicals Group, International Research and Technology Corp.,Washington, D. C., August 30, 1974.

3. United States Tariff Commission, Synthetic Organic Chemicals, U. S. Production andSales, Washington, D.C., 1974.

4. Hydrocarbon Processing, "World Wide HPI Construction Boxscore," February 1975.

5. T. Wett, "Ethylene to Stay Tight in U. S. Despite Big Expansion," Oil Gas J., 72, 9597(September 23, 1974).

6. R. Ericsson, "Steady Growth Forecast C3 C5 Hydrocarbon," Chem. Eng., 80(23), 3839(October 8, 1973).

7. J. Finneran and T. Czuppon, "Economics of Production and Consumption of Ammonia,"in Dinitrogen (N2) Fixation, Wiley, New York, 1975, Chap, 7.

8. U.S. Department of Commerce, Current Industrial Reports, Bureau of Census SeriesM28B, M28D, 1974.

Chemicals from PetroleumT. L. Tanesand D. Shore

Introduction and Overview

In Volume 1 of his outstanding History of Chemistry [1], Partington traced the origins ofchemicals by detailed analysis and convincing argument, back past the alchemists andthe Greek philosophers to the Phoenicians of 1200 B.C. and beyond. But it was not until theearly nineteenth century that the heavy chemicals industry proper really became firmlyestablished as a viable entity in the rapidly growing industrial countries of WesternEurope and America. As is still the case today, the large-scale production of chemicalsrequired markets, raw materials, process plant, manpower, finance, and efficienttransportation systems to succeed. These were all to be found in those nations whichwere already well advanced in general industrialization.

Throughout the nineteenth century the heavy chemicals industry was concerned primarilywith the production of alkalis for soap, paper and glass manufacture, bleaching agentsand dyes for textiles processing, and explosives for mining and military use [2].

This was also a period of concentrated research into all aspects of organic chemistry.Many new compounds were isolated for the first time and progress made on thetheoretical explanation of the structure of organic substances. Two events were ofparticular importance to the emerging heavy chemicals industry and were to have far-reaching effects on its course of development. These were the discovery by Liebig ofbenzene in coal tar in 1834 [3] and the successful researches by Perkin, Caro, Graebe,Liebermann, and others on synthetic dyestuffs.

The former discovery triggered off a series of intensive studies by many famous workersinto the chemical nature of the products of coal distillation. Important discoveriesfollowed rapidly, one upon the other, so that by the time the industry was ready forsynthetic dyestuffs, good supplies of relatively cheap raw materials, obtained as by-products from coal gas and coke manufacture, were already available to it. Thisconjunction enabled the synthetic dyestuffs section of the industry to make rapidadvances at the turn of the century and led to the emergence of the heavy organicchemical industry as a distinct entity based on coal as the primary raw material.

The importance of coal as the industry's preferred source of carbon was furtherstimulated by the discovery in 1892 of the process for the direct production of calciumcarbide from lime and coke. This gave rise to the widespread use of acetylene, first as anilluminant and later as a source of many organic chemicals by direct reaction and throughthe important intermediate, acetaldehyde [4].

And in 1913 the successful operation of the world's first large-scale ammonia plant usingthe Haber-Bosch synthesis route (with hydrogen produced by coke gasification) firmlyestablished coal as the then preeminent raw material for the heavy chemicals industry[5].

It was during the same period, in the second half of the nineteenth century, that thepetroleum industry also became firmly established. Dating for all practical purposes from1859the year of Drake's first well at Oil Creek in Pennsylvaniathe petroleum industrydeveloped for many years quite independently of the chemicals industry. The demand forthe principal products which could then be separated from petroleum, namely gasoline,kerosene, and gas oils, kept the growing industry fully occupied as suppliers of fuels.

Although the chemical nature of petroleum was already under investigation in the latterpart of the nineteenth century, it is at first sight surprising that no serious plans for its useas a raw material for the chemicals industry were made until the 1920s.

There are a number of reasons for this. In the first place the most easily separated lightfractions of petroleum were identified as consisting predominantly of paraffinichydrocarbons which were recognized as being of low reactivity and therefore unsuitablefor organic synthesis into the products then required.

In the second place the demands placed upon the petroleum refining section of theindustry in terms of the quantity and quality of products required, enabled it to functionfor many years by simply separating crude oil into its several characteristic fractions usingstandard distillation processes. This resulted in the suppression of the development ofalready discovered processes for the conversion of naturally occurring petroleumhydrocarbons into the more reactive species which would have been of particular interestto the chemicals industry.

And in the third place, as already noted, the major industrialized nations were alreadycommitting themselves to coal as a basic chemical feedstock. Industrial inertia,complacency, and perhaps the fear of technological innovation restrained companies frominvesting in a technology which was foreign to them.

In the United States, however, the situation changed drastically in the early 1900s. Theintroduction of relatively cheap, mass produced motor cars increased the demand forgasoline so much that it forced refiners to explore ways in which the yield of gasolinefrom a given quantity of crude oil could be increased. It became apparent that a balancein refinery products could not be maintained by crude distillation alone, and that the timehad come for the introduction of more sophisticated petroleum refining processes.

In 1912 William Burton successfully demonstrated the first commercial thermal crackingprocess which converted low valued fuel oil into higher valued gasoline. This was the firstindustrial application of hydrocarbon pyrolysis.

As well as solving the gasoline demand problem, the introduction of thermal crackinggave rise to a significant yield of low molecular weight olefinic gases. Initially these wereburned as fuel gas or sent to the flare in the refineries. In an attempt to upgrade thesepotentially valuable products, the Standard Oil Company of New Jersey, in collaborationwith others, developed processes for the manufacture of isopropanol, acetone, and other

derivatives from the propylene contained in thermal cracker off-gases.

So was born what today is known as the petrochemicals industrythe year was 1920.

At the same time the Union Carbide Corporation, under the leadership of G. O. Curne andJ. G. Davidson, was undertaking a detailed study of the possibilities of developing newprocess routes to heavy organic chemicals using as primary intermediates ethylene andpropylene produced by the selective pyrolysis of ethane and propane. Their proposalswere implemented, and by 1925 at Clendennin, near South Charleston, West Virginia,Union Carbide was producing ethylene, ethylene chlorhydrin, ethylene glycol, andethylene dichloride on a commercial scale. Two years later ethylene oxide and glycolethers were added to the product slate and by 1930 the world's first synthetic ethanolwas produced [6].

From this point onward the petroleum-based chemicals industry progressed steadily inthe United States, limited only by the development of process technology and the marketdemand for the products thereby made available.

The interaction between the two industries which necessarily occurred brought benefits toboth parties. Thus the chemicals industry, largely used to "pots and pans" type processdesign, became aware of the advantages of large capacity continuous processing, for longa feature of the petroleum industry. In a similar way, the petroleum industry learned thatempiricism was not essential to their operation, that a scientific approach to developmentand design could yield valuable results in their search for improved processes. The unitingfactor was undoubtedly the science of chemical engineering, then becoming accepted asa separate discipline in its own right.

But the flow of information, ideas, and techniques across this interface caused it tobecome increasingly blurred. Both petroleum refining companies and chemical companiesset up their separate petrochemicals organizations so that today, some 50 years later, itis difficult in many cases to define precisely where petroleum refining ceases andchemicals manufacture starts.

In Europe the development of the petrochemicals industry was not as fast as in NorthAmerica. The lack of indigenous sources of crude oil, coupled with the need for strategicsupplies of organic chemicals in the event of armed conflict, inhibited its growth until theearly 1950s. Then with a seemingly assured supply of cheap crude oil from the MiddleEast, with refineries being built in all major European countries, the political conditionswere judged favorable for a great surge forward into petrochemicals.

At this point it is most constructive to consider the rate of growth of the petrochemicalsindustry during its 50 years of existence so far. A word of caution is required, however,when petrochemicals statistics are presented for interpretation.

In the first place, unlike the petroleum industry, reliable data are hard to come by in thechemicals industry. Different researchers may have access to different sources ofinformation, and discrepancies in quoted figures are not only likely but common.

Then there is the problem of double counting which, in this context, is meant the addition

of demand or production statistics for two or more related intermediates, say for benzeneand cyclohexane. Such a figure, if combined in an assessment of "total petrochemicals,"would be misleading since a large proportion of benzene is in fact utilized in theproduction of cyclohexane. For

TABLE 1 Ethylene Demand, 19501980 (millions of metric tons per year)Year North America Western Europe World

1930 0.014 0.0141940 0.12 0.121950 0.64 0.03 0.671960 2.5 0.7 3.31970 7.9 5.9 18.71980 (predicted) 1821 1820 5464

this reason "total petrochemicals" statistics are not considered truly representative of theindustry.

A more acceptable procedure is to consider the demand figures for an important primaryintermediate, such as ethylene, which can be considered a general pointer to trends inthe industry. Table 1 shows the relevant statistics taken from the published work of Silsbyand Ockerbloom [7] and Stanley [8].

These figures indicate an average worldwide annual compound growth rate over the 30-year period 1940 to 1970 of 18% or, in other terms, the demand doubled every 5 yearsor soa truly remarkable sustained rate of growth. For Western Europe the growth rateover the last 20 years was even greater (approaching 30%/yr during peak periods) andmost predictions indicate that the Western European annual ethylene demand shouldexceed that for North America by the early 1980s.

Similar statistics have been quoted for finished petrochemicals products. Table 2 listspertinent data for three of the principal categories of end products of the petrochemicalsindustry derived from the published work of Balas and Jara [9].

Again, the growth rates for these products have been extraordinarily high, illustratingtheir general acceptance by the consumer and their production economics to be such thatthey can successfully compete with alternative materials.

In recent months, owing especially to the general worldwide downturn inTABLE 2 World Production of Finished Petrochemical Products (millions of metrictons per year)

Year Plastics SyntheticRubbersSynthetic

Fibers1950 1.5 0.81 0.071960 7.1 1.9 0.431970 17.9 4.6 4.9Equivalent average annual compound growthrate, % 16 9 24

economic activity, there has been a substantial fall in the demand for petrochemicalsproducts. This has influenced many informed commentators to express their opinions onthe possible future of the industry. As is to be expected, these opinions vary from thevery pessimistic, suggesting a continued decline leading to zero or negative growth ratesfor the foreseeable future, to the very optimistic, suggesting that the present fall indemand is just a temporary situationsuch as has been experienced many times in thechemicals and petroleum industriesand that in the long term the market will continue toexpand as before.

Most analysts would predict, however, that the future for petrochemicals lies, in allprobability, somewhere between these two extremes. Certainly, higher prices will tend tosuppress growth rates; at the same time, though, new uses for existing products willcontinue to be found and, hopefully, new products will also be introduced. As in the past,both of these effects will stimulate overall demand. The net effect is likely to be positivegrowth in the future but at rates somewhat lower than those experienced during theboom period of 19501970.

To those who question whether the world's unrenewable hydrocarbon resources shouldbe utilized to manufacture synthetic materials which could well be replaced byalternatives, attention is drawn to Table 3 which compares the total energy equivalents(including raw material and conversion energies) of a representative list of basicmaterials. These data were published in 1974 by ICI [10].

It is readily seen that with the exception of glass and paper, the synthetic materialsutilize significantly lower total energies per unit volume for their production than do theirnonpetrochemical alternatives. When expressed in terms of the total energy required forfinished fabricated products, the plastics rank even lower than glass and paper since, foran equivalent strength, far thinner sections are required in the case of the plastics.TABLE 3 Total Energy Inputs of Basic Materials (kcal/cm3)MetalsAluminum 158Steel billet 82Tin plate 102Copper billet 112PlasticsPolystyrene 36Polyvinyl chloride 28LD polyethylene 22HD polyethylene 24Polypropylene 24OthersGlass bottles 11Paper and board 12Cellulose film 70

TABLE 4 Utilization of Oil and Natural Gas in OECD Countries during 1972Millions of

Metric TonsOil Equivalent

Electricity generation 363.5 (13.6%)Energy sector and losses 128.4 (4.8%)Industry 607.7 (22.8%)Transportation 738.0 (27.7%)Residential/commercial 639.9 (24.0%)Nonenergy 186.5 (7.1%)

2664.0 100.0

Three other factors are also pertinent. First, the growth in many synthetics has not beento the detriment of nonpetrochemicals materials. This is particularly the case in fiberswhere the demand for cotton and wool still continues to grow (albeit slowly) and wherethe present demand for total fibers certainly could not now be met by existing orprojected supplies of naturally occurring materials.

The second point is that there are now many examples where the properties of thesynthetic petrochemically based products are so superior to the alternatives that they arevirtually irreplaceable. Cable insulation, injection-molded components, detergents, andnylon hosiery all come into this category.

And the third and final point is that despite its apparent size, the petrochemicals industrystill absorbs only a small fraction of the world's total hydrocarbons consumption. Table 4presents data published by the Organization for Economic Co-operation and Development(OECD) for 1972 [11].

Table 4 shows that the nonenergy utilization of hydrocarbons in OECD countries in 1972,which includes all the raw materials used in the petrochemicals industry, was no morethan 7.1% of the total. Put another way, of all the hydrocarbons consumed in 1972,92.9% was used in energy applications (and was therefore essentially degraded to heat,water, and carbon oxides), leaving just 7.1% to be upgraded to valuable chemicalproducts.

Perhaps the question one should really ask is: Can society afford to spend so high aproportion of its nonrenewable hydrocarbon resources on applications other thanpetrochemicals?

Description of Products

The question of what is or is not a petrochemical has concerned many writers on thesubject. In this presentation a petrochemical is considered to be any

chemical, final product, or intermediate which is derived commercially from petroleum-based raw materials; that is, from natural gas and/or crude oil.

In most cases the petroleum-based raw material is required for its carbon content, but inothers it is the actual and potential hydrogen content which appears in the final endproduct. Potential hydrogen is that extra hydrogen which can be derived from reactingthe carbon in the hydrocarbon molecule with water. All petroleum-based synthesis gasderivativesammonia includedare petrochemicals under this definition.

The products of the petrochemicals industry may be divided into seven main categoriesas follows:

Plastics

Synthetic fibers

Synthetic rubbers(elastomers)

Synthetic detergents

Paints and solvents

Fertilizers

Other products

The general properties of some of the main products of these subdivisions are brieflydescribed under separate headings below.

Some 80% of the petrochemicals industry's organic chemicals output is produced in theform of synthetic polymers which are most widely used for plastics, synthetic fibers,synthetic rubbers, and paints.

Polymers are high molecular weight materials consisting of long-chain molecules, whichare built up of smaller molecules linked together by strong, attractive forces. Somepolymers occur naturally, others are synthesized from component small moleculematerials or monomers.

Two distinctly separate types of polymers may be identified: thermoplastic polymerswhich can be repeatedly softened on heating and thermosetting polymers which cannot.Thermosetting polymers consist of rigid molecular structures which make them brittle andunsuitable for synthetic rubbers and fibers; they are, however, suitable for certain plasticsapplications. In contrast, thermoplastic polymers may be used for many purposesdepending upon the physical properties of the finished material.

Plastics

Three thermoplastics, polyethylene, polyvinyl chloride, and polystyrene, and one group ofthermosetting plastics, the formaldehyde resins, dominate the world plastics market.

Other plastics, including polyurethane, the acrylonitrile-butadiene-styrene copolymers(ABS resins), polypropylene, and polyester resins, are produced in intermediatequantities, while the remainder are made on a much smaller scale for very specializedmarkets.

Polyethylene is produced in two forms: low-density polyethylene (LDPE), which was firstdeveloped in the 1930s, and high-density polyethylene (HDPE), a slightly moreexpensive, more highly crystalline version developed later.

LDPE is produced by polymerizing ethylene at high pressure in the presence of traces ofoxygen. LDPE is partially crystalline and is almost transparent, which makes it suitable forits biggest outlet, transparent wrapping sheet. Significant quantities are also used forinjection moldings (bowls, buckets, etc.), pipes, and insulating coatings. HDPE isproduced at about atmospheric pressure by bubbling ethylene through a catalystsuspended in an organic liquid. In contrast to LDPE, HDPE is almost completely crystallineand opaque. It has a higher tensile strength, more rigidity, and a higher softeningtemperature than LDPE: it is also resistant to hot water and solvents. Its main use is forthin-walled containers, which can be made by blow molding.

Polypropylene (PP) is produced in a similar way to HDPE and it has a similar crystallinestructure. It is a better plastic than HDPE in a number of ways: lower density, highertensile strength, greater rigidity, and higher melting point. It is also resistant to chemicalattack and to abrasion. These superior properties make PP competitive with HDPE in anumber of film and molding services.

Polyvinyl chloride (PVC) is produced from the monomer, vinyl chloride, by a number ofalternative processes. It is a slightly crystalline polymer and is almost opaque. PVC canbe produced in many forms, ranging from rigid to pliable, by the addition of differentquantities of plasticizera material which when added to a polymer softens it. PVC hasbeen found to be more suitable than any other polymer for use with plasticizers, and soabout 90% of all plasticizers are used in PVC processing. Esters of phthalic acid are themost widely used of many different types of plasticizer. Plasticized PVC is used for sheet,fabric coating, floor coverings, cable insulation, hosepipes, shoes, and boots. Rigid PVC isused for piping, ductwork, gramophone records, bottles, and sheet.

Polystyrene, produced from the monomer styrene, has low crystallinity, is transparent,and is somewhat brittle. Its particular advantages are its ease of molding, dimensionalstability, and freedom from odor, taste, and toxicity. Its great disadvantage is that it isdegraded by ultraviolet light and so cannot be used for outdoor applications.

Polystyrene is suitable for producing transparent film or sheet, the brittleness beingreduced by stretching. Its main outlets are as moldings (vending cups, food containers,refrigerator internals, electrical insulation, flower pots, etc.) and as polystyrene foam(packaging, thermal insulation, etc.).

To increase its impact resistance, 3 to 10% of styrene-butadiene rubber (SBR) orpolybutadiene may be included in the polystyrene formulation. High impact polystyreneproduced in this way is rapidly superceding general purpose polystyrene, particularly inmolding applications.

The acrylonitrile-butadiene-styrene (ABS) copolymers are similar in many respects to highimpact polystyrene, both having discreet rubber particles dispersed in a thermoplasticpolymer phase. The recipe for ABS resins usually requires approximately 50% styrene,25% butadiene, and 25% acrylonitrile.

There are a number of different ways of producing ABS resins and many types of product.They are characterized by their high heat resistance, high tensile strength, and goodgeneral engineering properties.

ABS resins are used widely in the automotive industry and for high quality

precision moldings (such as telephones, calculator housings, etc.). It is also possible tochromium plate ABS, and in this form it is able to replace chromium-plated metal parts insome applications.

The most important group of thermosetting plastics are the formaldehyde resins. Thephenol formaldehyde (PF) resins were discovered in the nineteenth century anddeveloped in the 1920s under the trade name Bakelite. The onestage resins are made bypolymerizing phenol and formaldehyde in the presence of an alkaline catalyst directly tothe thermosetting plastic. They are used for high impact moldings and with cloth or paperto produce laminates.

The two-stage resins are first polymerized with an acid catalyst to give an intermediatethermoplastics polymer. This is used as a general-purpose molding material and may bemixed with up to 85% of an inert filler which can be sawdust, stone, asbestos, mica, etc.The second stage of the polymerization to the finished thermosetting plastic is carried outin the mold with the addition of formaldehyde and heat.

The great attraction of PF resins is that they are the cheapest of all molding materialssince the finished article can contain such a high proportion of inert filler. PF resins,however, cannot be colored and they possess poor mechanical properties. They are usedfor general purpose, low impact moldings, as bonding agents (grinding wheels and brakelinings), and as binders for chipboard and similar products. An important application forPF resins is in exterior or marine grade plywood where they provide the necessary waterresistance.

The world production of PF resins is still increasing slightly though at nothing like the rateof the three main thermoplastics.

The urea formaldehyde (UF) resins are about as important as the PF resins. They are notas resistant to water as the PF resins, but are almost colorless and stable to light.

UF resins are used for molding powders, as binders for chipboard and similar products,and for interior-grade plywood. They are also used to creaseproof cotton fabrics and toimpart wet strength to paper goods.

Melamine formaldehyde (MF) resins are produced on a smaller scale. They are colorless,stable to light, and resistant to water. They find wide application in high quality laminatesand for tableware.

Polyester resins are produced by the reaction of ethylene or propylene glycol with maleicanhydride or phthalic anhydride. They are viscous liquids which are cured by cross-linkingwith styrene in the presence of a catalyst. Polyester resins are mainly used with afiberglass filler in the construction of boat hulls, car bodies, etc. They have the advantageover the formaldehyde resins in that they can be cured without the application of heatand no water is driven off during the process. They are, however, very much more

expensive than the formaldehyde resins.

Polyurethanes are produced by reacting diisocyanates with suitable polyhydroxycompounds; tolylene diisocyanate and polypropylene glycol are the usual reactants.Polyurethanes are produced in four distinct forms; namely rigid foams (used inconstruction, roofs, walls, etc.), flexible foams (furniture, bedding, buoyancy aids, etc.),elastomers (industrial tires, foundation garments), and surface coatings.

Fibers

Fibers are materials which are much stronger along their length than across it. They arepolymers with long straight chain molecules lying side by side, held together byentanglement forces. Most fibers exhibit some degree of crystallinity which improves thesynthetic fibers' strength and is usually increased during processing by stretching attemperatures above the softening point of the noncrystalline material. Fibers must bethermoplastic polymers but the polymer molecules must not have long bulky branchchains, since these interfere with the drawing operation and prevent ordered alignment.

Fibers fall into four distinct categories: two occur naturally, a third is semisynthetic, andthe fourth is wholly synthetic.

The two naturally occurring groups are vegetable and animal fiber. Cotton, the principalvegetable fiber, still holds the number one position in the world market and is about thecheapest of the quality fibers. Wool, the main animal fiber, accounts for a much smallerpercentage of the world market and is at the top of the fiber price range.

Rayon, the most important, nonpetrochemical semisynthetic fiber, was introduced in the1920s and rapidly gained a large share of the world market as a substitute for cotton at acompetitive price. Rayon is produced by chemically dissolving naturally occurringcellulose, typically wood pulp, and regenerating the cellulose polymer as a continuousfilament. Rayon is a cheap, versatile fiber which is still produced in larger quantities thanany single synthetic fiber. It can compete in both the low cost and the higher qualitymarkets and is finding increasing application as a cotton substitute for blending withsynthetic fibers.

The fourth category of fibers are those that are truly synthetic and produced today frompetrochemicals intermediates. Nylon was first produced in the 1930s and polyester fiberin the 1940s but both had to await major advances in technology before their basic rawmaterial could be produced cheaply enough for their competitive introduction to themarket.

Currently, over 90% of the world fiber market is held by 6 fibers: cotton 47%, viscoserayon 14%, nylon 10%, polyester 9%, wool 7%, and acrylics 5%. Production of thenatural fibers, cotton and wool, is almost static, rayon output is still increasing but not asfast as the syntheticsnylon, polyester, and acrylics.

Nylon is a generic term which applies to a family of polymersthe polyamides. Twomembers of this family are produced on a large scale, and these are known respectivelyas nylon 66 and nylon 6.

Nylon 66 is the polymerized salt of adipic acid and hexamethylene diamine and is theearlier product, predominating in the United States and the United Kingdom.

Nylon 6 is polymerized caprolactam. It has similar properties to nylon 66 but posseses

better abrasion resistancehence its preferred use when this property is important, e.g.,automotive upholstery and seat belts.

Since the introduction of polyester fibers, nylon has been steadily replaced as a syntheticfiber for clothing; its use in hosiery, however, is still unsurpassed. The nylons are stillused widely for domestic and industrial fabrics, carpeting,

etc. In the United States they also find application for reinforcing in tires although rayonis far more commonly used for this purpose in other countries.

Polyester refers almost exclusively to polyethylene terephthalate. It is made by thecondensation of ethylene glycol with terephthalic acid. Polyester does not absorb waterand does not shrink. It has to be heated to about 150C during drawing to increasecrystallinity, consequently any creases put into fabrics at these temperatures will remainin place at ordinary temperatures and the garment will not become creased duringnormal washing. Polyester is usually blended with cotton, wool, or rayon to produce atough, crease-resistant, moisture-absorbent, soft-textured fabric. Polyester is largelyreplacing nylon as the preferred synthetic fiber for clothing.

Polyester is a very versatile fiber finding increasing applications in many fields includingfabrics, tires, carpets, and hosepipes. It is the fastest growing synthetic fiber at thepresent time.

Acrylic fibers are usually made from the polymer of acrylonitrile. Polymerization takesplace in water and the fibers are spun from solution, since polyacrylonitrile decomposesbefore melting. Acrylic fiber competes mainly with wool where its lower price hasprovided it with an expanding market in knitted goods. It is also utilized in carpeting.

Synthetic Rubbers

Rubbers or elastomers are materials which stretch easily and return to their originalshape when the stress is removed. Synthetic rubbers are produced from thermoplasticpolymers which in their initial state can easily be permanently deformed. The elastomeris produced by loosely fixing the molecular chains relative to each other by linking themwith sulfur atoms; this is the process of vulcanization. Synthetic rubbers are vulcanized bysimilar methods to natural rubbers, soft rubbers requiring about 4% sulfur. As more sulfuris added, the rigidity of the rubber increases until it becomes a hard cross-linkedthermoset plastic.

The essential component in natural rubber is polyisoprene, which is the liquid (latex)obtained from rubber trees. Although isoprene was first synthetically polymerized in thenineteenth century, the product was far inferior to natural rubber. Technological advancessince then, however, have been such that the structure of natural rubber can now be soclosely reproduced that synthetic polyisoprene can be used for almost all applicationswhich would otherwise require natural rubber. Polyisoprene has been shown to besuperior to alternative synthetic rubbers in certain special applications such as in heavyduty and aircraft tires.

Butadiene is by far the most important chemical in the synthetic rubber industry. About60% of the world market is held by styrene-butadiene rubber (SBR), which is based on acopolymer of about 75% butadiene and 25% styrene. Polybutadiene rubber (BR) itselfholds almost 20% of the market.

Butyl rubber, a copolymer of isobutylene and isoprene (3%), is the next most importantrubber. It is an extremely stable synthetic rubber used for conveyor belts and tire innertubes but it appears to be decreasing in importance as other, cheaper products areintroduced.

The nitrile rubbers are copolymers of butadiene and acrylonitrile. They have goodchemical and oil resistance and are used in applications where these properties areparticularly important such as fuel hoses and printing rolls.

Synthetic Detergents

A detergent is used with water to remove dirt from the surface of an article and to hold itin the water as an emulsion and so prevent redeposition on the surface.

Detergent molecules are long, though not as long as those of polymers. A necessaryfeature is that the two ends of the detergent molecule are chemically different; one endis a hydrocarbon and therefore hydrophobic (water repellant), while the other end is aninorganic salt of sodium or potassium, which is hydrophilic (water soluble).

When dirt molecules are loosened from the surface the detergent molecules surroundthem with the hydrophobic end toward the dirt and the hydrophilic ends facing outward tothe water. The dirt particles are thereby held as an emulsion in the water and cannotredeposit on the article.

Soaps are sodium salts of straight chain organic acids made from natural fats and oils.These are good detergents and are biodegradable, that is, they can be broken down bybacteria, but they form insoluble calcium and magnesium salts which reduce theirefficiency in hard waters. Their main disadvantage is the cost and limited supply of thenatural oils required to produce them. Synthetic detergents have therefore filled theincreasing market for cleansing materials.

The most important class of synthetic detergents are the sodium salts of sulfonic acids.The sulfonic acid is produced by reacting benzene with a high molecular weight olefin andsulfonating with sulfur trioxide. Originally, the olefins were produced by polymerizingpropylene; however, this produced branched chain molecules which were notbiodegradable. Detergents in liquid effluents accumulated in rivers and built up to toxiclevels; they also produced stable foams which floated on the rivers.

It was found that when straight chain olefins were reacted with benzene and sulfurtrioxide, biodegradable detergents could be produced. Most developed countries

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Chemical Processing Handbook