Shell's styrene monomer and propylene oxide (SMPO) process: Lessons learnt from 28 years of highly selective catalytic propylene epoxidation

PETR 113

Jan Karel F. Buijink,, Jean-Paul Lange,, Rene A N R Bos, Andrew D Horton, and Frank G M Niele. Shell Global Solutions International B.V, P.O. Box 38000, 1030 BN Amsterdam, Netherlands
The SMPO process is an efficient Shell process for making two chemical commodities, PO and SM. The heart of the process is formed by the catalytic epoxidation of propylene over a heterogeneous titanium-on-silica catalyst. This catalyst is best thought of as a range of silica supported ultrafine titania particles containing catalytically active, coordinatively unsaturated titanate sites. Peroxolysis converts these titanate sites into electrophilically activated, η2-coordinated titanium peroxides, which we propose as the active intermediates in the propylene epoxidation step of SMPO. However, peroxolysis also opens up a path to catalyst deactivation by leaching of active species and consecutive growth of titania particles. Improved understanding of all aspects of the conversion steps in the SMPO process has been key in the design of process improvements that have lead to higher selectivity and hence better plant yields, reduced energy and capital consumption and a reduction of waste.