Hydrocarbon permeation properties through microporous fluorine-doped organosilica membranes with controlled pore sizes

Abstract

F-BTESM membranes were fabricated by doping a fluorine source into bis(triethoxysilyl)methane (BTESM), which is an organosilica precursor composed of Si–CH2–Si bonds. Pore size controllability and C3–C4 hydrocarbon permeation properties for F-BTESM membranes with different concentrations of fluorine were evaluated using single-gas permeation and N2/C3–C4 hydrocarbon binary separation. The pore size of an organosilica membrane can be precisely controlled via doping with the correct concentration of fluorine. The molecular sieving properties for C3/C4 hydrocarbon separation such as that for C3H6/iso-C4H8 was dramatically enhanced with the addition of a fluorine concentration of F/Si = 0.05, and this membrane showed a C3H6/iso-C4H8 permeance ratio of 388 at 50 °C. The permeance of hydrocarbon gases was increased with an expansion of the pore size, and F-BTESM (F/Si = 0.15) showed a high level of C3H6 permeance (>5.0 × 10−7 mol m−2 s−1 Pa−1). The results of hydrocarbon adsorption and single permeation properties showed that the carbon number of the hydrocarbons and the presence of unsaturated bonds enhanced the adsorption affinity to silica-derived materials. In the binary separation of N2/C3–C4 hydrocarbons, N2 permeance was remarkably decreased by comparison with single-gas permeation, which was due to a blocking effect by the hydrocarbons adsorbed inside the pores. Hydrocarbon gases with a stronger affinity tended to inhibit the permeation of N2.