(695c) Surface Functionalized Composite Membranes for Solubility Based Separations

Surface-functionalized composite membranes were synthesized by modifying commercially available mesoporous and macroporous supports with selective materials. The membranes were evaluated for performance in separating light gases and vapors based on solubility differences. Three different types of membranes were studied.

Membralox gamma-alumina membranes with 5 nm nominal pore size were decorated with linear alkyl trichlorosilanes or hyper-branched triazine based dendrimers. These organic molecules were delivered in an organic solvent and anchored to porous inorganic surfaces as filling agents to give hybrid materials. Pure gas permeance of the alumina membranes decreased by two to three orders of magnitude after altering with organic groups. Our membranes showed a wide range of propane/nitrogen selectivity. The effect of residual solvent on composite membrane performance is also correlated with conditions employed in cleaning and drying the composite membranes.

Alumina-ordered mesoporous silica (OMS) hybrid membranes were fabricated using a variation of the evaporative-induced self-assembly process by coating of a Membralox 200 nm membrane with solution containing Brij surfactant and a silica source. The effective pore size of the membrane can be tuned based on the number of coating cycles used. Single gas permeation measurements were performed using hydrogen, helium, and nitrogen. The observed permselectivity of helium over nitrogen is slightly higher than that of commercial 5-nm Membralox membranes, which might be ascribed to the lack of pinhole defects. Also, from the permeation measurements and other materials characterization experiments we conclude that the final composite membrane has a pore size around 5 nm.

Finally, we are also exploring modification and functoinalization of nanoporous track-etched polycarbonate membranes for the separation of gases based on solubility.