Gas permeation properties of silica membranes with uniform pore sizes derived from polyhedral oligomeric silsesquioxane

Abstract

The sol-gel method was applied in the fabrication of homogenous polyhedral oligomeric silsesquioxane (HOMO-POSS)-derived silica membranes. Single gas permeation characteristics in a temperature range of 100–500^°C were examined to discuss the effect of silica precursor on amorphous silica networks. HOMO-POSS-derived membranes showed a CO₂ permeance of 1.1 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with a CO₂/CH₄ permeance ratio of 131 at 100^°C, which is a superior CO₂/CH₄ separation performance by comparison with tetraethoxysilane (TEOS)-derived silica membranes. Normalized Knudsen-based permeance (NKP) was applied for quantitative evaluation of pore size. HOMO-POSS-derived membranes had loose amorphous silica structures compared to TEOS-derived membranes and pore size was successfully tuned by changing the calcination temperatures. The activation energy for a HOMO-POSS-derived membrane fired at 550^°C with a uniform pore size of ∼ 0.42 nm increased linearly with the ratio of the kinetic diameter of the gas molecule to the pore diameter, λ (=d_k/d_p), and showed a trend similar to that of DDR-type zeolite membranes. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1733–1743, 2012