Properties and separation performance of Ge-ZSM-5 membranes

Germanium-substituted ZSM-5 zeolite membranes with various Si/Ge ratios were synthesized by in situ crystallization on porous tubular stainless steel and alpha-Al2O3 supports. For a Si/Ge ratio in the synthesis gel,of 25, the Si/Ge ratio in the membrane was 41-82, depending on the support. When the Si/Ge ratio was 5, extra framework compounds that contained Ge formed. The fraction of permeation through non-zeolite pores increased as the Si/Ge ratio decreased. The Ge-ZSM-5 membranes were effective for separating acetone from water by pervaporation. The highest acetone/ water selectivity of 330 (at 323 K) and the highest total flux of 0.95 kg/m(2) h (at 333 K) were obtained for a membrane with a Si/Ge ratio of 41. This membrane selectively removed alcohols, ketones, carboxylic acids, esters, and propionaldehyde from 5 wt.% aqueous solutions because the organics preferentially adsorbed. The C-3 organics showed higher organic/water selectivities than C-2 or C-4 organics with the same functional group. The organic/water separation selectivity increased as the liquid-phase fugacity of the organic in the feed increased. (C) 2002 Published by Elsevier Science Inc.