Solubility-based gas separation with oligomer-modified inorganic membranes

The potential of hybrid organic-inorganic membranes for separating organic molecules from air, based on a solubility-selective mechanism, was evaluate d. Alumina membranes with average pore sizes near 5 and 12 nm were surface- derivatized with various alkyl trichlorosilanes, and their permeances to ni trogen, methane, and propane gases were evaluated at feed pressures up to 2 bar. The permeation rates in the modified membranes generally decreased by two to three orders of magnitude compared with the untreated membranes, wh ile the propane/nitrogen selectivity increased significantly. The membrane performance was correlated with the materials and synthesis conditions empl oyed in the modification, which indicated an ability to control the hydroph obic character and free volume of the hybrids. The maximum propane/nitrogen selectivity observed was 32, which compares very favorably to the best res ults reported for purely polymeric membranes. This study demonstrates that the synthesis of hybrid membranes with tunable free volume and surface chem istry is feasible, and that such membranes may achieve high performance in solubility-based separations. (C) 2001 Elsevier Science B.V. All rights res erved.