Dehydration of Phenyl Ethanol to Styrene under Reactive Distillation Conditions: Understanding the Catalyst Deactivation

Styrene is commercially produced by the dehydration of phenyl ethanol generated during the coproduction of propene oxide. This reaction can be carried out at mild temperature under reactive distillation conditions using a medium-pore zeolite such as H-ZSM-5 (Lange, J.-P.; Otten, V. J. Catal. 2006, 238, 6). We investigate here the effect of process parameters on the formation of heavy byproducts and on the resulting catalyst deactivation. In particular, we looked at the effect of cofeeding bulky nitrogen-bases or radical scavenger, diluting the feed and improving the stripping of styrene. All these observations indicate that the heavy byproducts are formed inside the zeolite pores, prior to styrene desorption. Their formation seems to be enhanced by diffusion resistance in the catalyst. The deactivating role of heavy products was further confirmed by a significant recovery of activity and selectivity after calcination. A conceptual process design is proposed, based on a slurry reactor with continuous product removal and continuous catalyst regeneration. Such a regeneration loop is uncommon in the chemical industry.