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.