Preparation of Composite Microporous Silica Membranes Using TEOS and 1, 2-Bis(triethoxysilyl)ethane as Precursors for Gas Separation

This paper reports on a new microporous composite silica membrane prepared via acid-catalyzed polymeric route of sol-gel method with tetraethylorthosilicate (TEOS) and a bridged silsesquioxane [1, 2-bis(triethoxysilyl)ethane, BTESE] as precursors. A stable nano-sized composite silica sol with a mean volume size of ∼5 nm was synthesized. A 150 nm-thick defect-free composite silica membrane was deposited on disk support consisting of macroporous a-Al2O3 and mesoporous γ-Al2O3 intermediate layer by using dip-coating approach, followed by calcination under pure nitrogen atmosphere. The composite silica membranes exhibit molecular sieve properties for small gases like H2, CO2, O2, N2, CH4 and SF6 with hydrogen permeances in the range of (1-4)(10−7 mol·m−2·s−1·Pa−1 (measured at 200 (C, 3.0×105 Pa). With respect to the membrane calcined at 500 (C, it is found that the permselectivities of H2 (0.289 nm) with respect to N2 (0.365 nm), CH4 (0.384 nm) and SF6 (0.55 nm) are 22.9, 42 and <1000, respectively, which are all much higher than the corresponding Knudsen values (H2/N23.7, H2/CH42.8, and H2/SF68.5).