Industrial Chemistry, Organic

Industrial organic chemicals are those 100 or so organic compounds produced in the United States in quantities ranging from millions of pounds to billions of pounds per year. Most of them are derived from petroleum (oil) or natural gas. From organic compounds present in petroleum and natural gas are obtained an amazing variety of products that includes many kinds of plastics, synthetic fibers, elastomers, drugs, surface coatings, solvents, detergents, insecticides, herbicides, explosives, gasoline additives, and countless specialty chemicals.

Historically, most organic chemicals had been obtained as by-products from the coking of coal, e.g., from coal oil. During the twentieth century, however, oil and natural gas became the dominant sources of the world's industrial organic chemicals. By 1950 at least half of U.S. industrial "organics" were being made from oil and gas, and by 2000 more than 90 percent of the organic chemical industry was based on petroleum. In fact, the term "petrochemicals" has almost become synonymous with industrial organic chemistry. Yet, less than 10 percent of the oil and gas we consume each year goes into making organic chemicals and the many billions of pounds of products derived from them. Oil and gas are mainly burned as fuel.

Most industrial organic chemistry falls into one of the following categories:

C-1 chemistry, based on synthesis gas (syn gas)

C-2 chemistry, based on ethylene (ethene)

C-3 chemistry, based on propylene (propene)

C-4 chemistry, based on butanes and butenes

BTX chemistry, based on benzene, toluene, and xylenes

Synthesis gas or "syn gas" is a variable mixture of CO and H₂ produced by the high temperature reaction of water with coal, oil, or natural gas (mainly natural gas in the United States).

         (1)

Alkenes or olefins (ethylene, propylene, butenes, and butadiene) are mainly produced via thermal steam cracking. Here, a petroleum fraction is mixed with water and heated briefly (for about 1 second) at 800 to 900^°C (1,472–1,652^°F), which breaks C–C bonds to yield shorter chains and splits out adjacent hydrogen atoms to form double bonds. The distribution of products obtained is given in Table 1.

BTX (benzene, toluene, and xylenes), the simplest aromatics, are largely produced during catalytic reforming (platforming). In this process a naphtha rich in C₅ to C₉ alkanes is reacted at about 450^°C (842^°F) and 20 to 30 atm, over a Pt/SiO₂ catalyst, to yield reaction products that are about 60 percent aromatic hydrocarbons. Typically, the products might contain 3 percent benzene, 12 percent toluene, 18 percent xylenes, and 27 percent of C₉ alkylbenzenes (which have high octane numbers and are blended into gasoline). Because benzene is much more in demand for industrial purposes than toluene, the methyl group of toluene is ofte n removed by hydrogenation.

         (2)

Production of Some Important In dustrial Organic Chemicals

C-1 Chemistry (Syn Gas). Many important organic chemicals can be produced from the CO and H₂ mixture known as syn gas. They range from simple molecules, such as methanol, to high-grade synthetic crude oil.

The basic reaction for conversion of syn gas to mixtures of hydrocarbons is called the Fischer–Tropsch reaction, used in Germany during World War II to produce fuel mixtures for diesel and gasoline engines. Since the 1950s South Africa has also used this reaction, and currently there is much interest in using it to convert natural gas (methane) to more easily transported liquids.

Ammonia (NH₃), although it is not an organic compound, is often considered as part of C-1 chemistry, since it is produced via a reaction that uses hydrogen gas obtained from methane. It is made by the Haber process

         (3)

Ammonia and its derivatives, HNO₃, NH₄NO₃, and CO(NH₂)₂, are key fertilizers and ingredients for explosives, and their production consumes nearly 5 percent of the world's natural gas.

Methanol (methyl alcohol, CH₃OH), an important solvent and precursor for many organic chemicals, is made by a process developed in the 1920s

CO + 2 H₂ → CH₃OH          (4)

A major use of methanol is the production of acetic acid via carbonylation.

CH₃OH + CO → CH₃CO₂H          (5)

Acetic acid (ethanoic acid, CH₃CO₂H) was for many years made by the simple oxidation of ethanol, but the carbonylation of methanol has now largely displaced this process.

Butanal (butyraldehyde, CH₃CH₂CH₂CHO) is made via hydroformylation (the OXO reaction). Although this is a general reaction of syn gas with alkenes to produce aldehydes, the largest poundage reaction of this type (in industry, generating the greatest volume of product) is the reaction of propylene with syn gas to yield butanal.

         (6)

Phosgene (Cl₂CO) is made by reacting carbon monoxide from syn gas with chlorine (Cl₂) over activated charcoal at 250^°C (482^°F).

         (7)

Most phosgene is used in the manufacture of polyurethane plastics via diisocyanates.

         (8)

C-2 Chemistry (Ethylene or Ethene). With annual worldwide capacity running over 100 million tons, ethylene is the world's largest volume organic compound. Most of it (almost 60%) is used to make polyethylene, the world's highest poundage plastic.

Polyethylene comes in two basic types: high density and low density. The original polymer was a highly flexible branched product, first prepared in 1932 by a process that required high temperatures and ultrahigh pressures. It is now known as low-density polyethylene (LDPE), to differentiate

it from a linear polymer discovered later and known as high-density polyethylene (HDPE). For many applications the original branched LDPE has now been replaced by linear low-density polyethylene (LLDPE). HDPE is more rigid and less translucent than LDPE or LLDPE, and it has a higher softening point and tensile strength. HDPE is used to make bottles, toys, kitchenware, and so on, whereas LDPE and LLDPE are mainly used for film used in packaging (e.g., plastic bags).

Vinyl chloride (CH₂=CHCl) is the second-largest-volume chemical made from ethylene. It is made by adding chlorine to ethylene and then thermally cracking out HCl from the intermediate, ethylene dichloride. The vinyl chloride is polymerized to polyvinyl chloride (PVC), also called vinyl, which is used to make pipe, floor covering, wire coating, house siding, imitation leather, and many other products.

         (9)

         (10)

Styrene (phenylethylene or vinyl benzene, C₆H₅−CH=CH₂) is made from ethylene by reaction with benzene to form ethylbenzene, followed by dehydrogenation. Over 50 percent of manufactured styrene is polymerized to polystyrene for toys, cups, containers, and foamed materials used for insulation and packing. The rest is used to make styrene copolymers, such as styrene-butadiene rubber (SBR).

Ethylene oxide is made by air oxidation of ethylene. Most ethylene oxide (about 60%) is converted to ethylene glycol via acid catalyzed hydrolysis.

         (11)

Ethylene glycol (HOCH₂CH₂OH) is a toxic dialcohol. Approximately half of what is produced is used as automobile coolant (antifreeze); most of the rest is used to make polyesters for products such as fabrics, rigid films, and bottles.

C-3 Chemistry (Propylene or Propene). Polypropylene manufacture is by far the largest use of propylene. In the late 1950s Karl Ziegler and Giulio Natta developed some special coordination catalysts (aluminum alkyls and titanium salts) that yield very strong addition polymers from propylene. Almost 25 percent of polypropylene is used to make injection-molded articles, such as automotive battery cases, steering wheels, outdoor chairs, toys, and luggage. Another 25 percent is used to make fibers for upholstery, carpets, and special sports clothing. Oligomers (dimers, trimers, and tetramers) of propylene, which are made by acid-catalyzed polymerization, form mixtures known as polygas, used as high-octane motor fuel.

Acrylonitrile (CH₂=CH−CN) was made from acetylene and HCN until the 1960s. Today it is made by direct ammoxidation of propylene. Its major use is in making polyacrylonitrile, which is mainly converted to fibers (Orlon). It is also copolymerized with butadiene and styrene to produce high impact plastics.

         (12)

Propylene oxide is made via several methods. The classical one involves treating propylene with chlorine water to produce propylene chlorohydrin, and then using base to split out HCl. The primary use for propylene oxide is its oligomerization (to polypropylene glycols). These products combine with diisocyanates to produce high molecular weight polyurethane foams, which make very good padding for furniture and vehicle seats.

         (13)

Manufacture of propylene glycol (CH₃-CHOH-CH₂OH) consumes about 30 percent of the propylene oxide produced. Like ethylene oxide, propylene oxide undergoes hydrolysis to yield the corresponding glycol. Propylene glycol is mainly used to make polyester resins, but it is also used in foods, pharmaceuticals, and cosmetics.

         (14)

Cumene (isopropylbenzene) is made by Friedel–Crafts alkylation of benzene with propylene. Although cumene is a high-octane automotive fuel, almost all of the cumene produced is used to make phenol (C₆H₅OH) and acetone [(CH₃)₂CO]. Cumene is easily oxidized to the corresponding hydroperoxide, which is readily cleaved in dilute acid, to yield phenol and acetone.

         (15)

         (16)

Phenol and acetone each have a number of important commercial uses, but they also have an important use together. Phenol and acetone can be condensed to form bisphenol A, which is used in the production of poly-carbonate and epoxy resins.

         (17)

C-4 Chemistry (Butanes, Butylenes, Butadiene). Maleic anhydride is the main chemical made from n -butane. A complex catalyst is used for the oxidation reaction. The major uses for maleic anhydride are the making of unsaturated polyester resins (by reaction with glycol and phthalic anhydride) and tetrahydrofuran (by hydrogenation).

         (18)

         (19)

Methyl-tertiary-butyl ether (MTBE) is one of the leading chemicals currently being made from isobutylene (methyl propene) via the acid-catalyzed addition of methyl alcohol. MTBE has been added to gasoline as a required "oxygenate." However, it is under attack as a groundwater contaminant and is being phased out.

Polyisobutylenes are easily made via the acid-catalyzed polymerization of isobutylene. The low molecular weight polymers are used as additives for gasoline and lubricating oils, whereas higher molecular weight polymers are used as adhesives, sealants, caulks, and protective insulation.

Butyl rubber is made by polymerizing isobutylene with a small quantity of isoprene. Its main uses are in the making of truck tire inner tubes, inner coatings for tubeless tires, and automobile motor mounts.

Hexamethylenediamine [HMDA, H₂H-(CH₂)₆-NH₂] is the principal industrial chemical made from butadiene. HMDA is polymerized with adipic acid to make a kind of nylon.

Styrene-butadiene rubber (SBR) accounts for about 40 percent of the total consumption of butadiene. SBR is the material used to make most automobile tires. Other synthetic rubbers, such as polybutadiene and polychloroprene (neoprene), make up another 25 percent of the butadiene market.

ABS resin (acrylonitrile-butadiene-styrene) is a widely used terpolymer that accounts for about 8 percent of the butadiene market.

BTX Chemistry (Benzene, Toluene, Xylene). Styrene, discussed under C-2 chemistry, is one of the main industrial chemicals made from benzene. Most benzene is alkylated with ethylene to form ethylbenzene, which is dehydrogenated to styrene (see Equation 10).

Cumene, discussed under C-3 chemistry, is the second-largest-volume chemical product made from benzene. About 25 percent of manufactured benzene is alkylated with propylene to form cumene. Although its high octane number makes it desirable in gasoline, most cumene is oxidized to the

hydroperoxide, which is readily cleaved to phenol and acetone (see Equation 16).

Cyclohexane (C₆H₁₂) is made by hydrogenation of benzene (over Ni or Pt). Most of it is converted to adipic acid by oxidation, via the intermediaries cyclohexanol and cyclohexanone.

         (20)

Adipic acid [HO₂C(CH₂)₄CO₂H], the main product of cyclohexane, is reacted with hexamethylene diamine to produce nylon-6,6, a very strong synthetic fiber. Most carpets are made of nylon, as are many silklike garments, some kinds of rope, and many injection-molded articles.

Caprolactam (C₆H₁₁NO) is also used to make nylon. Nylon-6 is made by direct polymerization of caprolactam, often obtained by reaction of cyclohexanone with hydroxylamine, followed by rearrangement of the oxime. Although nylon-6,6 is the dominant nylon produced in the United States, nylon-6 is the leading nylon product in Europe.

Aniline (C₆H₅NH₂) is made by nitration of benzene to nitrobenzene, followed by hydrogenation over a Cu/SiO₂ catalyst. The major use of aniline is in making diisocyanates, which are used in producing polyurethane materials (e.g., for home insulation).

         (21)

Alkylbenzene sulfonates (R-C₆H₅-SO₃Na) are important surfactant compounds used in laundry detergents. Alkylbenzenes (made by the Friedel–Crafts alkylation of benzene using linear olefin molecules that have about twelve carbon atoms) are sulfonated, and the sulfonic acids are then neutralized with NaOH.

Benzene (C₆H₆), about 40 percent of it, is obtained from toluene by removal of the methyl group (hydrodealkylation, see Equation 2). Benzene production is the primary use of toluene (60%).

Toluene diisocyanate (TDI) is polymerized with diols to produce polyurethanes, which are used to make flexible foam for furniture cushions, mattresses, and carpet pads.

         (22)

Trinitrotoluene (TNT) is made via a stepwise nitration of toluene in the 2, 4, and 6 positions. TNT is a high explosive and missile propellant.

         (23)

Phthalic anhydride is made by air oxidation of ortho-xylene. About half of phthalic anhydride is used to make plasticizers, especially the compound dioctyl phthalate, for softening polyvinyl chloride plastic. Phthalic anhydride is also used to make unsaturated polyester resins and alkyd paints.

         (24)

A Look Toward the Future

Industrial organic chemistry was once based on coal oil. Today it is based mainly on petroleum and natural gas. However, both of these resources are limited in supply and may not last through the twenty-first century.

Because coal reserves are much greater than those of oil and natural gas, perhaps syn gas from coal will become a major source of organic chemicals. However, coal is also a finite raw material, and therefore there is much interest in developing methods for converting renewable resources, such as plants, into industrial organic chemicals. Recently a major chemical company announced its plan to build a small plant for the production of 1,3-propanediol from sugar. This same company has set a goal of producing 25 percent of its feedstocks from renewable resources by 2010. Although this might seem an unrealistic goal, it does indicate current thinking within the chemical industry.

see also Explosions; Fertilizer; Fossil Fuels; Organic Chemistry; Petroleum.

Kenneth E. Kolb

Kurt W. Field

Bibliography

Chenier, Philip J. (1992). Survey of Industrial Chemistry, 2nd revised edition. New York: Wiley-VCH Publishers.

Kroschwitz, Jacqueline I.; Howe-Grant, Mary; Kirk, Raymond E., and Othmer, Donald F.; eds. (1991). Encyclopedia of Chemical Technology, Fourth edition. New York: John Wiley.

Wittkoff, Harold A., and Reuben, Bryan A. (1996). Industrial Organic Chemicals. New York: Wiley-Interscience.