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 °C and atmospheric pressure. The membrane had a high H₂ permeance of 8.3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with H₂/CH₄ selectivity of 140 and H₂/C₂H₆ selectivity of 180 at 300 °C. Fourier transform infrared (FTIR) measurements indicated existence of methyl groups at high preparation temperature (650 °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, H₂, and Ne) followed a solid-state diffusion model while larger species (N₂, CO₂, and CH₄) followed a gas translational diffusion model.