Ethylbenzene Dehydrogenation to Styrene Over Fresh and Used Commercial Catalysts

Dehydrogenation of ethylbenzene (EB) to produce styrene (ST) monomer is commercially performed over potassium-promoted iron oxide catalysts. Catalyst deactivation due to coke deposition and loss of potassium is a major operation and economic drawback in this process. To better evaluate the performance change of these catalysts over their life-cycle, dehydrogenation of EB to ST over the fresh and used commercial catalysts was experimentally investigated at temperatures from 590 to 639°C under atmospheric pressure. The fresh and the used catalysts were obtained from a styrene plant. The used catalyst had been continuously operated for two years under severe plant conditions. The catalyst activity tests were performed in a lab-scale continuous fixed bed reactor, maintained at constant temperature. For the fresh catalyst, the yield of styrene increased with a decrease in LHSV and reached its highest value of 79% at 0.48 h^-1 and T=627°C. At the same experimental conditions, it was found that the selectivity of styrene for the used catalyst was higher than that for the fresh catalyst. However, the reaction rates and conversion in the used catalyst were considerably lower than that in the fresh catalyst. Due to rapid coke deposition in the first 12 hour of the experiments, both the fresh and the used catalysts lost 22% of their initial activities before reaching pseudo steady state conditions.