Fabrication and Evaluation of Trimethylmethoxysilane (TMMOS)-Derived Membranes for Gas Separation

Gas separation membranes were fabricated with varying trimethylmethoxysilane (TMMOS)/tetraethoxy orthosilicate (TEOS) ratios by a chemical vapor deposition (CVD) method at 650 degrees C and atmospheric pressure. The membrane had a high H-2 permeance of 8.3 x 10(-7) mol m(-2) s(-1) Pa-1 with H-2/CH4 selectivity of 140 and H-2/C2H6 selectivity of 180 at 300 degrees C. Fourier transform infrared (FTIR) measurements indicated existence of methyl groups at high preparation temperature (650 degrees C), which led to a higher hydrothermal stability of the TMMOS-derived membranes than of a pure TEOS-derived membrane. Temperature-dependence measurements of the permeance of various gas species were used to establish a permeation mechanism. It was found that smaller species (He, H-2, and Ne) followed a solid-state diffusion model while larger species (N-2, CO2, and CH4) followed a gas translational diffusion model.