Separating organics from water by pervaporation with isomorphously-substituted MFI zeolite membranes

ZSM-5 zeolite membranes on porous, stainless steel supports were prepared by in situ crystallization with Al, Fe, B, and Ge isomorphously-substituted into their structures. Single-gas permeances at 473 K decreased as the kinetic diameter of the diffusing molecule increased, indicating these membranes were of high quality for gas separations. They were also effective for pervaporation of alcohol/water and ketone/water mixtures. All substituted membranes exhibited higher separation factors than a silicalite-1 membrane for methanol/water pervaporation, and a B -ZSM-5 membrane exhibited the highest separation factors (101 for a 5 wt.% methanol feed). The separation factors and fluxes for all the membranes except Ge-ZSM-5 were in the order: methanol > ethanol > 2-propanol. The Ge-ZSM-5 membrane was the most selective for ethanol and 2-propanol mixtures. For 5 wt.% ketone feeds to the B-ZSM-5 membrane, the separation factors for acetone/water and methyl ethyl ketone/water at 333 K were 440 and 380, respectively. Separation of alcohols and ketones is based on both selective adsorption of organics in the zeolite pores and diffusivity differences. (C) 2002 Elsevier Science B.V. All rights reserved.