Heteropolyacid (HPA)-polymer composite films as heterogeneous catalysts and catalytic membranes

Abstract

Preparation, characterization, and catalytic application of membrane-like heteropolyacid (HPA)-polymer composite films as heterogeneous catalysts and catalytic membranes were reported in this work. HPA-polymer composite film catalysts were prepared by a membrane preparation technique by blending HPA with polymer using a common or a mixed solvent. HPA-polymer composite film catalysts were cut into small pieces, and they were applied as heterogeneous catalysts to the liquid-phase tert-butyl alcohol (TBA) synthesis, to the vapor-phase ethyl tert-butyl ether (ETBE) synthesis, and to the vapor-phase ethanol conversion. It was observed that HPA catalysts were finely dispersed throughout the polymer supports, and the blending patterns of the composite film catalysts were different depending on the identity of solvent and polymer material used. The HPA-polymer composite films showed enhanced catalytic activities in these reactions compared to the mother HPAs. Pore characteristics of the composite film catalysts could be controlled by a conventional membrane preparation technique, and they were related to the catalytic performance of the film catalysts. Shell- and tube-type membrane reactors comprising inert polymer membranes and HPAs were designed and applied to the vapor-phase methyl tert-butyl ether (MTBE) decomposition. Simulation and experimental results revealed that polyphenylene oxide (PPO)-based membrane reactor showed the best performance, among some polymer membranes examined. Selective removal of methanol through the polymer membrane inhibited the unfavorable reverse reaction (MTBE synthesis), and at the same time accelerated the MTBE decomposition. Shell- and tube-type catalytic membrane reactors (CMRs) utilizing HPA-polymer composite catalytic membranes were also designed for the vapor-phase MTBE decomposition. Experimental results showed that HPA-polymer composite catalytic membranes not only showed catalytic reactivity for the reaction, but also were perm-selective for methanol with respect to isobutene and MTBE. It has been demonstrated that HPA-polymer composite catalytic membranes have potential application in a membrane reactor for the MTBE decomposition.