Styrene Production

Ethjlben ne Synthesis. The synthesis of ethylbenzene for styrene production is another process in which ZSM-5 catalysts are employed. Although some ethylbenzene is obtained direcdy from petroleum, about 90% is synthetic. In earlier processes, benzene was alkylated with high purity ethylene in liquid-phase slurry reactors with promoted AlCl catalysts or the vapor-phase reaction of benzene with a dilute ethylene-containing feedstock with a BF catalyst supported on alumina. Both of these catalysts are corrosive and their handling presents problems. 

Styrene undergoes many reactions of an unsaturated compound, such as addition, and of an aromatic compound, such as substitution (2,8). It reacts with various oxidising agents to form styrene oxide, ben2aldehyde, benzoic acid, and other oxygenated compounds. It reacts with benzene on an acidic catalyst to form diphenylethane. Further dehydrogenation of styrene to phenylacetylene is unfavorable even at the high temperature of 600°C, but a concentration of about 50 ppm of phenylacetylene is usually seen in the commercial styrene product. 

Styrene manufacture by dehydrogenation of ethylbenzene is simple ia concept and has the virtue of beiag a siagle-product technology, an important consideration for a product of such enormous volume. This route is used for nearly 90% of the worldwide styrene production. The rest is obtained from the coproduction of propylene oxide (PO) and styrene (SM). The PO—SM route is complex and capital-iatensive ia comparison to dehydrogenation of ethylbenzene, but it stiU can be very attractive. However, its use is limited by the mismatch between the demands for styrene and propylene oxides (qv). 

There are other conditions that result from the frozen-in stresses. In materials such as crystal polystyrene, which have low elongation to fracture and are in the glassy state at room temperature, a frequent result is crazing it is the appearance of many fine microcracks across the material in a direction perpendicular to the stress direction. This result may not appear immediately and may occur by exposure to either a mildly solvent liquid or vapor. Styrene products dipped in kerosene will craze quickly in stressed areas. 

J.N. Michaels, and C.G. Vayenas, Styrene Production from Ethylbenzene on Platinun in a zirconia Electrochemical Reactor, J. Electrochem. Soc. 131, 2544-2550 (1984). 

Styrene polymers brittle fracture of, 23 363 burning of, 23 403 extrusion of, 23 398 glass-reinforced, 23 311 tensile strengths of, 23 359 Styrene product, factors in the quality of, 23 338-339 Styrene vapors, 23 403 Styrenic block copolymers, 24 102, 703-704... 

The dominant share of styrene production comes from dehydrogenation of EB in plants like that shown in Figure 8-5. Some comes as a coproduct in propylene oxide/styrene plants. An even smaller amount is recovered from the gasoline fraction of olefins plants cracking heavy liquids. 

Ethylbenzene is a high volume petrochemical used as the feed stock for the production of styrene via dehydrogenation. Ethylbenzene is currently made by ethylene alkylation of benzene and can be purified to 99.9%. Ethylbenzene and styrene plants are usually built in a single location. There is very little merchant sale of ethylbenzene, and styrene production is about 30x10 t/year. For selective adsorption to be economically competitive on this scale, streams with sufficiently high concentration and volume of ethylbenzene would be required. Hence, although technology has been available for ethylbenzene extraction from mixed xylenes, potential commercial opportunities are limited to niche applications. 

Hodgson J, Jones R Mortality of styrene production, polymerization and processing workers of a site in northwest England. Scand J Work Environ Health 11 347-352, 1985... 

Because ethylbenzene is used almost exclusively to produce styrene, the product specification on ethylbenzene is set to provide a satisfactory feedstock for styrene production. Levels of cumene, -propylbenzene, ethyltoluenes and xylenes in ethylbenzene are controlled to meet the required styrene purity specification. A typical sales specification is as follows purity, 99.5 wt% min. benzene, 0.1-0.3 wt% toluene, 0.1-0.3wt% ort/io-xylene + cumene, 0.02 wt% max. meto-xylene + para-xylene, 0.2 wt% max. allylbenzene + a-propylbenzene + ethyltoluene, 0.2 wt% max. diethylbenzene, 20 mg/kg max. total chlorides (as chlorine), 1-3 mg/kg max. and total organic sulfur, 4 mg/kg max. (Coty et al., 1987). 

Ethylbenzene is almost exclusively (> 99%) used as an intermediate for the manufacture of styrene monomer. Styrene production, which uses ethylbenzene as a starting material, consumes approximately 50% of the world s benzene production. Less than 1% of the ethylbenzene produced is used as a paint solvent or as an intermediate for the production of diethylbenzene and acetophenone. The ethy lbenzene present in recovered mixed xylenes is largely converted to xylenes or benzene (Coty et al., 1987 Caimella, 1998). 

After styrene production, approximately 20% of benzene production is used to produce cumene (isopropylbenzene), which is converted to phenol and acetone. Benzene is also converted to cyclohexane, which is used to produce nylon and synthetic fibers. Nitrobenzene derived from benzene is used to produce aniline, which has widespread use in dye production. Besides the benzene derivatives mentioned in this section, countless other products are based on the benzene ring. Cosmetics, drugs, pesticides, and petroleum products are just a few... 

R.N. Haward and E. Joyce, Suspension polymerization process, US Patent 2 668 806, assigned to Styrene Products Ltd., February 09,1954. 

Base-catalyzed carbanionic alkylation, isomerization, polymerization reactions are of major significance. Base-catalyzed alkylation of alkylarenes, in contrast to acid-catalyzed ring alkylation, leads to alkylation of the side chain in the benzylic position [Eq. (1.28) see also Chapter 5] of particular interest is the alkylation of toluene to ethylbenzene (for styrene production). 

Styrene manufacture by dehydrogenation of ethylbenzene is used for nearly 90% of the worldwide styrene production. The rest is obtained from the coproduction of propylene oxide (PO) and styrene (SM). 

The qualities of the styrene product and toluene by-product depend primarily on three factors the impurities in the ethylbenzene feed-stock, the catalyst used, and the design and operation of the dehydrogenation and distillation units. Other than benzene and toluene, the presence of which is usually inconsequential, possible impurities in ethylbenzene are Cj-Cm nonaromatics and C Cm aromatics. The condensed reactor effluent is separated in the settling drum into vent gas (mostly hydrogen), process water, and organic phase. The organic phase with polymerization inhibitor added is pumped to file distillation train. 

Styrene is one of (he most important aromatic compounds Most styrene production comes from the dehydration of ethyl ben7ctic The mam commercial uses of styrene include poly styrene and various styrene copolymers such a> styrene-butadiene rubber Major styrene producers include Amoco. Dosv, Poster Grant, Monsanto, Shell, Sinclair-Koppers, and Union Carbide Styrene growth should continue to be good... 

Styrene, Product Bulletin of the Shell Chemical Company. 

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