Ethylene epoxidation in a catalytic packed-bed membrane reactor: effects of reactor configuration and 1,2-dichloroethane addition

The performance of different membrane reactors for the epoxidation of ethylene was compared with that of a conventional fixed-bed reactor (FBR), under identical overall reaction conditions, using a Cs-doped Ag catalyst supported on alpha-Al2O3. Two membrane reactor configurations were used, with either oxygen (PBMR-O) or ethylene (PBMR-E) as permeate, and the other reactant flowing over the catalyst bed. The addition of different levels (0-3.3 ppm) of 1,2-dichloroethane (DCE) in the feed, which promotes selective ethylene epoxidation, was studied. The experiments showed that high oxygen/ethylene ratio favors ethylene oxide selectivity. For all the conditions investigated. reactor configuration performance was in the order PBMR-E > FBR > PBMR-O, which could be enhanced further for the membrane reactors by increasing the residence time of reactants over the catalyst bed by partition of the nitrogen feed. Increasing the DCE concentration in the inlet stream entering the catalyst bed increased selectivity to values exceeding 80% for low ethylene conversions. The role of ethane was also studied and lies mainly in controlling the amount of chlorine adsorbed on the catalyst surface. High levels of DCE showed detectable catalyst deactivation after a few hours under reaction conditions, hence an optimum level exists (1-2 ppm) that maximizes ethylene oxide yield while maintaining a reasonably high stable catalyst activity. (C) 1999 Elsevier Science Ltd. All rights reserved.