Formation of hydrogen permselective silica membrane for elevated temperature hydrogen recovery from a mixture containing steam

A silica membrane was formed by chemical vapor deposition using tetraethylorthosilicate in macropores of an α-alumina tube or a γ-alumina film coated on the α-alumina tube. The reactant was evacuated through the porous wall, and silica was deposited in the macropores at 600–700 °C. When the silica membrane was formed in a γ-alumina film coated on the α-alumina tube, hydrogen permeance at a permeation temperature of 600 °C was 3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹, which was one order of magnitude higher than that of a membrane formed directly on the α-alumina tube. H₂/N₂ selectivity determined from the permeance of each component was 100–1000. To separate hydrogen selectively from abundant steam, however, a higher permselectivity was required. The membrane formed in the γ-alumina film at 650 °C showed a hydrogen permeance of 3 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and an H₂/H₂O selectivity of 7.6 at 400 °C.