Ethylbenzene and styrene

Wilhelm Busch Diogenes, 1832-1908 (inventor of the cartoon strip) 

A small amount of EB is present in crude oil and also is formed in cat reforming. You might recall from Chapter 3 that there is only a 4°F difference between the boiling points of EB and para-xylene Consequently, a superdistillation column is needed for the separation-. In process engineers terms, it would have about 300 theoretical trays, be about 200 feet tall, and even then have a high reflux ratio to accomplish the separation. All this is necessary because the EB stream must be quite pure to be used for styrene manufacture. 

Alkylation of benzene is old technology. The French chemist, Charles Friedel, with his American partner, James Crafts, in 1877, stumbled (almost literally) across the technique for alkylating benzene with amyl chloride (C5H11CI). The use of a metallic catalyst, in this case aluminum, was the key. The Friedel-Crafts reaction is classical and remains a principal route for alkylating benzene with ethylene to make EB. 

Sometimes a catalyst promoter or accelerator, ethyl chloride, is added to the feed to speed up the reaction. The ethyl chloride actually works on the aluminum chloride catalyst, not the reactants. Its like offering a supervisor a bonus. He doesn t do any more work, but he gets more work done. 

The effluent stream leaving the reactor is cooled and then treated with caustic (sodium hydroxide) and water to remove the catalyst. The cleaned up stream then contains about 35% unreacted benzene, 50% EB,.15% polyethylbenzene (PEB), and a small amount of miscellaneous heavy materials. 

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Styrene is manufactured from ethylbenzene. Ethylbenzene [100-41-4] is produced by alkylation of benzene with ethylene, except for a very small fraction that is recovered from mixed Cg aromatics by superfractionation. Ethylbenzene and styrene units are almost always installed together with matching capacities because nearly all of the ethylbenzene produced commercially is converted to styrene. Alkylation is exothermic and dehydrogenation is endothermic. In a typical ethylbenzene—styrene complex, energy economy is realized by advantageously integrating the energy flows of the two units. A plant intended to produce ethylbenzene exclusively or mostly for the merchant market is also not considered viable because the merchant market is small and sporadic. 

Figure 5 illustrates a typical distillation train in a styrene plant. Benzene and toluene by-products are recovered in the overhead of the benzene—toluene column. The bottoms from the benzene—toluene column are distilled in the ethylbenzene recycle column, where the separation of ethylbenzene and styrene is effected. The ethylbenzene, containing up to 3% styrene, is taken overhead and recycled to the dehydrogenation section. The bottoms, which contain styrene, by-products heavier than styrene, polymers, inhibitor, and up to 1000 ppm ethylbenzene, are pumped to the styrene finishing column. The overhead product from this column is purified styrene. The bottoms are further processed in a residue-finishing system to recover additional styrene from the residue, which consists of heavy by-products, polymers, and inhibitor. The residue is used as fuel. The residue-finishing system can be a flash evaporator or a small distillation column. This distillation sequence is used in the Fina-Badger process and the Dow process. 

The initial composition is Imol each of ethylbenzene and styrene and 0.5 mol of hydrogen. 

This is a two-step reaction. The ethylbenzene is isolated in the first step and then contacted with a different catalyst at high temperature in the second step. Ethylbenzene and styrene plants are usually built together. 

Indeed our scale makes it possible to make a more subtle comparison of risk levels, which allows us to classify substances in ascending risk order and can be directly interpreted (an ii value of 4.62% for instance means that with a vapour equilibrium concentration at 21 C in air this concentration cannot exceed 4.62% of LEL value, which is equivalent to the reading of the dial of an explosimeter). Note in particular that it is clearly seen by examining the tables for these substances that the same code 11 set by the regulations or 3 by NFPA hide very different risk situations, which is well shown by II code. Vice versa, the threshold effects of these codes tend to overestimate insignificant risk differences (for instance between ethylbenzene and styrene). 

A column is to be designed to separate a mixture of ethylbenzene and styrene. The feed will contain 0.5 mol fraction styrene, and a styrene purity of 99.5 per cent is required, with a recovery of 85 per cent. Estimate the number of equilibrium stages required at a reflux ratio of 8. Maximum column bottom pressure 0.20 bar. 

Not unexpectedly, alkylation of the double carbonylated complex proceeds via a base-catalysed interfacial enolization step, but it is significant that the initial double carbonylation step also involves an interfacial reaction, as it has been shown that no pyruvic acid derivatives are obtained at low stirring rates. Further evidence comes from observations of the cobalt-catalysed carbonylation of secondary benzyl halides [8], where the overall reaction is more complex than that indicated by Scheme 8.3. In addition to the expected formation of the phenylacetic and phenylpyruvic acids, the reaction with 1-bromo-l-phenylethane also produces 3-phenylpropionic acid, 2,3-diphenylbutane, ethylbenzene and styrene (Scheme 8.4). The absence of secondary carbonylation of the phenylpropionylcobalt tetracarbonyl complex is consistent with the less favourable enolization of the phenylpropionyl group, compared with the phenylacetyl group. 

A high carbon monoxide pressure ( 5 atmos.) favours the formation of the butane. Possible mechanisms for its formation include homolytic cleavage of the benzyl-cobalt tetracarbonyl complex and recombination of the radicals to generate 2,3-diphenylbutane and dicobalt octacarbonyl, or a base-catalysed decomposition of the benzylcobalt tetracarbonyl complex (Scheme 8.4). The ethylbenzene and styrene could arise from the phenylethyl radical, or from the n-styrene hydridocobalt tricarbonyl complex. 

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. 

There are nine chemicals in the top 50 that are manufactured from benzene. These are listed in Table 11.1. Two of these, ethylbenzene and styrene, have already been discussed in Chapter 9, Sections 5 and 6, since they are also derivatives of ethylene. Three others—cumene, acetone, and bisphenol A— were covered in Chapter 10, Sections 3-5, when propylene derivatives were studied. Although the three carbons of acetone do not formally come from benzene, its primary manufacturing method is from cumene, which is made by reaction of benzene and propylene. These compounds need not be discussed further at this point. That leaves phenol, cyclohexane, adipic acid, and nitrobenzene. Figure 11.1 summarizes the synthesis of important chemicals made from benzene. Caprolactam is the monomer for nylon 6 and is included because of it importance. 

Benzene and toluene by-products are recovered in the overhead of the benzene-toluene distillation column. The bottoms from the benzene-toluene column are distilled in the ethylbenzene recycle column, where the separation of ethylbenzene and styrene is effected. The bottoms, are pumped to file styrene finishing column. The overhead product from this column is purified styrene. The bottoms are further processed in a residue-finishing system to recover additional styrene from the residue. 

Gramshaw, J.W., and Vandenburg, H.J., 1995. Compositional analysis of thermoset polyester and migration of ethylbenzene and styrene from thermosct polyester into pork during cooking. Food Add. and Contam. 12, 2, 223-234. 

Fig. 10.13. Integrated plant for manufacture of ethylbenzene and styrene. (Reproduced from Hydrocarbons Processing, Petrochemical Handbook, p. 169, 1985 November. Copyright Gulf Publishing Co. and used by permission of the copyright owner.)...

These values show that, with ambient cooling at 1 atm, hydrogen, methane, and ethylene are difficult to condense, but that steam, benzene, toluene, ethylbenzene, and styrene are easily condensed. Condensation will separate the latter five... 

The first operation is by far the most delicate given the small differential between the boiling points of ethylbenzene and styrene 9 at atmospheric pressure) and the pronounced tendency of styrene to polymerize easily, even under vacuum. Hence it requires special operating conditions including . ... 

Synthesis of styrene. The alkylation of toluene with methanol over a CsX-zeolite catalyst produces a mixture of ethylbenzene and styrene (Equation (9)). 

Benzene alkylation ZSM-5, REY Ethylbenzene and styrene production with low by-product yield... 

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