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 α-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 H ₂, 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/N₂ = 3.7, H₂/CH₄ = 2.8, and H₂/SF₆ = 8.5).