25 June 2009 16:32 [Source: Chemical Report]
Styrene is produced predominately by ethylbenzene (EB)-based technology. EB is first made by the catalytic alkylation of benzene with ethylene, using either aluminium chloride or, more recently, zeolite catalysts. The reaction can be carried out in either vapour or liquid phases (see chemical intelligence report on ethylbenzene).
The EB is then dehydrogenated to styrene in the presence of steam over iron-chromium oxides or zinc oxide catalysts using either multiple bed adiabatic or tubular isothermal reactors. Generally, adiabatic dehydrogenation in multiple bed reactors is preferred but both methods are used. Shell has developed a direct heating method that is claimed to reduce investment and operating costs.
The coproduction of styrene with propylene oxide by the PO/SM process had been gaining popularity with this route employed by LyondellBasell, Shell/Seraya, Repsol and Ellba. In this process, EB is oxidised to its hydroperoxide, which is next reacted with propylene to produce propylene oxide and methyl benzyl alcohol. The latter product is then dehydrated to styrene.
The popularity of the PO/SM route with ?xml:namespace>
Dow Chemical and Snamprogetti are developing a process for making ethylbenzene/styrene from ethane and benzene. The process combines the dehydrogenation of ethane and ethylbenzene in one unit and integrates the processes for preparing ethylene, ethylbenzene and styrene. This process is claimed to have lower costs than the conventional route to styrene, largely stemming from the low cost of ethane in relation to ethylene. A pilot plant has been operating since 2002 and commercialisation could be possible by the end of the decade.
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