Styrene manufacture

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). 

A further 15% of the AICI3 is used in the production of ethyl benzene for styrene manufacture, and 13% in making EtCI or EtBr (for PbEt4) ... 

Benzene oxychlorination process, of phenol manufacture, 18 751 Benzeneperoxyseleninic acid, 13 466 Benzene rings, in liquid crystalline materials, 15 103-104 Benzene sulfonation process, of phenol manufacture, 18 751 Benzenesulfonic acid, 3 602 Benzene-toluene fraction, in styrene manufacture, 23 341-342 Benzene-toluene-xylene (BTX), 10 782 ... 

Hydrogen pinch, applications of, 20 764 Hydrogen polysulfides, 23 568, 639-640 Hydrogen processing, 12 404 15 217 Hydrogen-producing reactions, 13 766-767 Hydrogen product oxidation, in styrene manufacture, 23 343... 

Polymerization inhibitors miscellaneous, 23 383 in styrene manufacture, 23 338 Polymerization initiators alkyllithiums as, 74 251 cerium application, 5 687 peroxydicarbonates as, 74 290 Polymerization kinetics, in PVC polymerization, 25 666-667 Polymerization mechanism, for low density polyethylene, 20 218 Polymerization methods, choice of,... 

Styrene-divinylbenzene resins, 23 353 Styrene-DVB copolymers, 14 388 Styrene ionomers, 14 466, 481 properties of, 14 470-473 Styrene liquid, 23 347 Styrene-maleic anhydride (SMA) copolymers, 23 391 copolymer, 10 207 Styrene manufacture, 24 259 Styrene manufacturing, 23 326, 334-345 development of high selectivity catalyst for, 23 339... 

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. 

Table 9.4 shows the uses of styrene. These are dominated by polymer chemistry and involve polystyrene and its copolymers. We will study these in detail later, but the primaiy uses of polystyrene are in various molded articles such as toys, bottles, and jars, and foam for insulation and cushioning. Styrene manufacture is a large business. With a production of 11.4 billion lb and a price of 30C/lb styrene has a commercial value of approximately 3.4 billion. 

For more expensive enzymes the continuous use of enzymes made possible by their iimnobihsation can result in considerable savings. By comparison typical chemical catalysts represent a smaller proportion of the total manufacturing costs. Thus the catalysts used in ammonia, cyclohexane and styrene manufacture have been estimated to cost approximately only 0.7, 0.6 and 0.6% of the total production costs respectively. Thus biocatalysts are still in general comparatively expensive compared with chemical catalysts. 

Ethylbenzene has not been separated commercially from Cg aromatics because it cannot be obtained therefrom in high purity as readily as it can be synthesized from benzene and ethylene by alkylation to provide the necessary stock for styrene manufacture. The current shortage of benzene, however, re-establishes interest in separating ethylbenzene from hydroformed stocks. 

Alkylation. Friedel-Crafts alkylation (qv) of benzene with ethylene or propylene to produce ethylbenzene [100-41 -4], CgH10, or isopropylbenzene [98-82-8], C9H12 (cumene) is readily accomplished in the liquid or vapor phase with various catalysts such as BF3 (22), aluminum chloride, or supported polyphosphoric acid. The oldest method of alkylation employs the liquid-phase reaction of benzene with anhydrous aluminum chloride and ethylene (23). Ethylbenzene is produced commercially almost entirely for styrene manufacture. Cumene [98-82-8] is catalytically oxidized to cumene hydroperoxide, which is used to manufacture phenol and acetone. Benzene is also alkylated with C1Q—C20 linear alkenes to produce linear alkyl aromatics. Sulfonation of these compounds produces linear alkane sulfonates (LAS) which are used as biodegradable deteigents. 

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). 

Example 2 Synthesis of a styrene process. Styrene, the monomer of polystyrene, has enjoyed strong market growth over the past two decades. It is prepared starting with benzene and ethylene which react to form ethylbenzene the ethylbenzene is dehydrogenated to yield styrene. Further information about styrene manufacture, properties, and uses is available. 3 In this example, the steps involved in synthesizing a process to produce styrene from ethylbenzene will be illustrated. The procedure followed is analogous to that followed by the PIP program. 

Friedel-Crajts alkylations are widely used in both the bulk and fine chemical industries. For example, ethylbenzene (the raw material for styrene manufacture) is manufactured by alkylation of benzene with ethylene (Fig. 2.12). 

Fig. 6.10. Styrene manufacture by isothermal dehydrogenation of ethylbenzene. BASF process.

The dehydrogenation of ethylbenzene is an important process used for styrene manufacture, and uranium oxide catalysts have been inveshgated for this reaction. A catalyst of uranium dioxide supported on alumina showed high selectivity to styrene of 96% at high conversion [62, 63]. The catalyst was synthesized as a higher oxide of uranium and inihally it was not UO2. Consequently, over the initial onstream period only carbon dioxide and water were observed, as the catalyst produced total oxidahon products. However, as the reachon proceeded the uranium oxide was reduced in situ by the ethylbenzene and hydrogen to form the active UO2 phase. It was only when the uranium oxide was fully reduced to UO2 that styrene was produced with high selectivity. 

Polystyrene pyrolysis yielded an oil with a high content of styrene monomer (Fig.4). The reaction conditions were optimized to maximize the yield of styrene. A maximum of l6% (by weight) was obtained. The oil is suitable for reuse in the styrene manufacturing process. 

---