C3H6-permselective silica hybrid membranes were prepared by using a counter-diffusion chemical vapor deposition (CVD) method. Propyltrimethoxysilane and hexyltrimethoxysilane (HTMOS) were used as silica precursors and O3 and O2 were used as oxidants. HTMOS was a suitable silica precursor for high-temperature CVD because of its high thermal stability. The N2/SF6 permeance ratio decreased from 64 to 12 as the deposition time increased from 5 to 90 min. The maximum N 2/SF6 permeance ratio was 2.2 × 105 through the membrane deposited at 450 °C for 5 min. The C3H 6/C3H8 permeance ratio was 414 (C 3H6 permeance 1.0 × 10-8 mol m -2 s-1 Pa-1) through this membrane.
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