Ultrathin hydrophobic MFI membranes

Abstract

Hydrophobic MFI membranes with a film thickness of less than 500nm and a very low amount of defects were grown on α-alumina supports in fluoride media at near neutral pH (denoted TPAF–MFI membrane). These membranes are at least 4 times thinner than previous membranes prepared in fluoride media at near neutral pH; moreover, corresponding separation performance is the first time reported in this paper. For comparison, MFI membranes with a film thickness of about 500nm were grown in hydroxide media at high pH (denoted TPAOH–MFI membrane). According to the permporometry results, the amount of defects in the TPAF–MFI membranes is about half of that in the TPAOH–MFI membranes, and most of the defects in both membranes are smaller than 1nm. The membranes were evaluated for separation of a feed of 5kPa n-butanol and 5kPa water, with 91kPa helium as balance gas and 101kPa helium as sweep gas. Both membranes displayed high permeance and the TPAF–MFI membrane was more selective to n-butanol than the TPAOH–MFI membrane. Interestingly, the total permeance and n-butanol/water separation factor increased to 11×10−7mol/(m2sPa) and 19, respectively, after activation of the TPAF–MFI membrane at 300°C in a helium flow saturated with n-butanol at 25°C. The TPAF–MFI membrane also displayed a CO2/H2 separation factor of 6 at 25°C and a CO2 permeance of 26×10−7mol/(m2sPa) for a feed of 450kPa CO2 and 450kPa H2 and 101kPa helium sweep gas.