Hybrid H₂-Selective Silica Membranes Prepared by Chemical Vapor Deposition

Abstract

Hybrid organic-inorganic H₂-selective membranes consisting of single-layer or dual-layers of silica incorporating aromatic groups are deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. The single-layer silica membranes, which are made by the simultaneous decomposition of phenyltriethoxysilane (PTES) and tetraethylorthosilicate (TEOS), have good hydrothermal stability at high temperature and a high permeance for hydrogen in the order of 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 873 K, while preventing the passage of other larger molecular gases such as CH₄ and CO₂. The dual-layer silica membranes, which are obtained from the sequential decomposition of PTES and TEOS, exhibit an extremely high permeance for hydrogen of 3.6 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 873 K with a permselectivity of hydrogen over methane of 30. A normalized Knudsen based permeance method is applied to measure the pore size of PTES-derived silica membrane on the dual-layer silica membrane before treatment with TEOS. The method indicates that the pore size of the silica network is approximately in the range of 0.50–0.85 nm, which is higher than the characteristic length of pure silica membranes of 0.3 nm, accounting for the high permeance of the hybrid membranes.

Keywords:

• CVD
• gas separation
• hybrid membrane
• hydrophobic membranes
• silica membrane

Notes

*CVD was carried out at 823 K.

*Data obtained from reference (8).

**Permeance measured at 823 K after 78 h of CVD.