Porous ceramic membranes for catalytic reactors - overview and new ideas

The membrane reactor (MR) concept, combining in the same unit a conversion effect (catalyst) and a separation effect (membrane), already showed various potential benefits (increased reaction rate, selectivity and yield) for a range of reactions involving the membrane as extractor, distributor or contactor. Due to the generally severe conditions of heterogeneous catalysis, most MR applications use inorganic membranes, which can be dense or porous, inert or catalytically active. After a rapid overview of the working concepts of MRs, the main types of porous ceramic membranes, which have been developed for MR applications, are reported and discussed (characteristics and limitations). Starting from these general basis, our objective is to put recent developments into focus, with a special emphasis on porous composite infiltrated membranes and related synthesis methods. Some new ideas currently explored in our group, such as the 'chemical valve membrane' concept and the interest of nanophase materials for oxygen transport, will be also developed. An attempt in addressing the future developments of porous membranes for MRs will be finally proposed. (C) 2001 Elsevier Science B.V. All rights reserved.