Styrene and Propylene Oxide SMPO Process

Ethylbenzene and propene. The former is produced from benzene and ethene. Product Use 

Styrene is the monomer for polystyrene and styrene-butadiene rubber. Propylene oxide is mainly used for the manufacture of propylene glycol and polyurethanes. 

About 10 million tons of styrene and 3.5 million tons of propylene oxide are produced annually, worldwide. Most of the styrene is still produced by dehydrogenation of ethylbenzene and it is estimated that ca. 800,000 tons of styrene and 400,000 tons of propylene oxide are produced by the SMPO process. 

Two variations of the process are used, the only essential difference being the catalyst employed in the epoxidation step. In the Arco (Atlantic Richfield) process a homogeneous molybdenum catalyst is used. The Shell process employs a heterogeneous titanium/silica catalyst. 

The stoichiometry of the reaction is such that ca. 2 tons of styrene are produced per ton of propene oxide. The SMPO route to styrene is cleaner and much less energy intensive than the conventional dehydrogenation route. The amount of styrene that can be produced is limited by the amount of propylene oxide that can be sold. The flow diagram for the process is shown in Fig. 2.15. 

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