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

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 N-2/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 degrees 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 x 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 N-2/C3-C4 hydrocarbons, N-2 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 N-2.

Automated summary

F-BTESM membranes were fabricated by doping a fluorine source into BTESM, resulting in controllable pore size and enhanced hydrocarbon permeation properties. The addition of fluorine at the correct concentration improved molecular sieving for C3/C4 hydrocarbon separation, showing high C3H6 permeance with an expanded pore size. In binary N-2/C3-C4 hydrocarbon separation, the permeance of N-2 was decreased due to a blocking effect by hydrocarbons with stronger affinity inhibiting N-2 permeation.