Styrene Production and Manufacturing Process

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 PO producers, compared to the conventional chlorohydrin process, has been put down to better process economics and environmental perspectives. Around 20% of styrene production is based on PO/SM technology. However, new processes to make PO without the styrene coproduct are being developed and they are expected to find favour over the PO/SM route.

 

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.

 

Exelus, the Livingston, New Jersey, research organisation, has tested in the laboratory a styrene process based on the alkylation of toluene with methanol. It claims that the new process lowers greenhouse gas emissions while reducing feedstock costs. Long term testing and development of the catalyst is continuing. Research is funded jointly by the US Department of Energy and the New Jersey Commission on Science and Technology.





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