Mesoporous ceramic membranes for non-aqueous separations: Surface modification and solvent permeability

The permeability of water, ethanol, hexane, and liquid CO2 at 70 bar and 298 K through mesoporous native titania and alumina membranes was studied as well as those modified with C8 fluorocarbon and hydrocarbon silanes. Borrowing from silane grafting techniques developed for gas separation membranes, commercial 1 kDa titania and 5 nm alumina membranes were functionalized with octyltrichlorosilane and its fluorinated analog, trichloro(1H,1H,2H,2H-perfluorooctyl)-silane. Using this approach, the surface thickness of silane was similar (≈ 1.1 nm), while the "tail" chemical composition was different. Fluoroalkylsilane and alkylsilane modified membranes were referred to as C8F and C8H, respectively. In the C8H membranes, gas permeability measurements revealed pore opening with increasing pressure, consistent with tail mobility. Comparatively, gas permeability in the C8F analog was an order of magnitude lower due to the bulkier fluorinated tails. These results were consistent with recent gas separation studies. This is an abstract of a paper presented at the 2006 AIChE National Meeting (San Francisco, CA 11/12-17/2006).