Improvement in thermal stability of NaA zeolite composite membrane by control of intermediate layer structure

Abstract

Two NaA zeolite composite membranes of differing intermediate layer structure, one uniform and thin (less than 3 mu m), the other non-uniform and thick (6-26 mu m), were prepared by controlling the pore diameter of the applied support. The pevaporation performances of the membranes were evaluated in water/ethanol mixtures. The membranes having the thick intermediate layer were thermally more stable than those having the thin intermediate layer. The membranes were stable, even at about 130 degrees C, in the thermal shock pervaporation mode. The high thermal stability was due to the well-developed intermediate layer in which the NaA zeolite and support phases were three-dimensionally interconnected with each other. It is expected that in the novel intermediate layer, the contraction of the NaA zeolite phase is compensated and relaxed by the expansion of the support phase during heating. In the present study, it was experimentally proven that microstructural control of the intermediate layer is an effective tool for improving the thermal stability of zeolite membranes, especially those showing negative expansion during heating. (C) 2010 Elsevier B.V. All rights reserved.