Dramatic innovation of propene epoxidation efficiency derived from a forced flow membrane reactor

Abstract

AbstractIt is possible to develop a selective epoxidation process for propene using heterogeneous catalysis in a forced‐flow membrane reactor. The most innovative processes required two catalysts, Cs–Ag and Re–Ag, which were immobilized in the membrane pores of a micro‐porous glassy (MPG) substance, and three different reactor systems for reaction gas flows in the membrane pores. The systems included a convection‐flow reactor (CFR), a diffusion‐flow reactor (DFR), and a packed‐bed‐flow reactor (PFR). The three types were examined over temperatures ranges from 420 to 525 K, while keeping the total conversion of propene to less than 10%. The membrane reactor systems followed two common Langmuir‐type equations of reaction rates for CO2 and propylene oxide (PO) formation under steady state operations at atmospheric pressure. The amount of the intermediate for CO2 formation, whose structure retained the CCC bond of a propene molecule, was sensitively controlled by the types of catalysts and reactor systems used. Comparing the three immobilized catalysts, Cs–Ag, Re–Ag, and Ag2O, the larger the amount of intermediate formed on the catalysts the higher was the propylene oxide (PO) selectivity and thus the PO selectivity followed the order of Re–Ag > Cs–Ag > Ag2O. The CFR with Re–Ag/MPG clearly demonstrated hysteresis kinetics depending on the increase (C‐up) or decrease (C‐down) in the propene concentration. The PO selectivity was separately evaluated as 73–35% for the C‐up and 35–21% for the C‐down. The convection flow rate of reactants in the pores effectively contributed to an enhancement of the PO production rate from 18 to 41% of PO selectivity, for the reactant flow rate of 70–130 cm3 min−1 at 483 K.© 2003 Society of Chemical Industry