Separation of propylene/propane binary mixtures by bis(triethoxysilyl) methane (BTESM)-derived silica membranes fabricated at different calcination temperatures

Bis(triethoxysilyl) methane (BTESM), which consists of Si–C–Si bonds, was used as a membrane precursor in the control of amorphous silica network size for separation of C3H6 and C3H8 molecules. Single and binary-component gas permeation/separation characteristics were examined at temperatures ranging from 50 to 200 °C for BTESM-derived silica membranes fabricated at various temperatures. Normalized Knudsen-based Permeance (NKP) was applied to evaluate the effect of calcination temperatures on amorphous silica network size. Pore size distribution, as determined by single gas permeation as well as by NKP plotting, suggested that average pore size was successfully tuned by changing the calcination temperatures. BTESM-derived silica membranes showed C3H6 permeance (0.28–6.3×10−7 mol m−2 s−1 Pa−1) and a C3H6/C3H8 permeance ratio (6.9–33) at 50 °C. For binary-component gas separation at 50 °C, preferentially adsorbed C3H6 molecules could efficiently block the permeation of C3H8 molecules, resulting in C3H6/C3H8 permeance ratios that were higher than those obtained by single-gas permeation. The ratios of α (separation)/α (ideal) for BTESM-derived membranes fired at 200 °C were higher than those for membranes fired at 350 °C, due to the higher density of silanol groups, that can interact with the π-bond (C=C double bond) of C3H6 molecules.