Preparation of inorganic gas separation membranes with controlled microstructures

Abstract

Microporous inorganic membranes with molecular-sieving permeation properties were synthesized for gas separation. To create tailor-made micropores by the sol-gel technique, alkylalkoxysilanes which served as templates were added to the ethanol solution of tetraethylorthosilicate (TEOS). The micropore volume was increased, and the pore size distribution was narrowed by the presence of the templates. Silica membranes, prepared from the sol contained either methacryloxypropyl trimethoxysilane (MPTMS) or isooctyltrimethoxysilane (ITMS) and calcined at 600℃, showed high permeances and selectivities, while the TEOS-MTESU (O-(methacryloxyethyl)-N-(triethoxysilylpropyl) urethane) membrane showed low selectivities. When the calcination temperature was increased beyond 600℃, the permeances to small sized gases decreased. The binary selectivity increased with increasing the temperature in the permeate, for the mixtures of $H_2/CO_2$, $H_2/CH_4$ and $H_2/SF_6$. Surfactant-templated mesoporous silica thin film (~1 μm) with narrow pore size distribution was formed on a porous α -alumina support. Alkyltrimethylammonium bromide (CnTAB) or cetylpyridinium chloride was used as surfactant template. The present study showed that continuous mesoporous silica thin film with large crack-free area could be successfully formed on a porous support by prefilling the support pores and smoothening the support surface with the water soluble polyvinyl alcohol (PVA) or paraffin which was insoluble in water. Thermoplastic polymers were also introduced by in-situ polymerization. Pore filling substances could be removed by proper solvents or thermal decomposition and, if necessary, prefilled surface was planerized by mechanical polishing. Surfactant-templated silica was successfully formed on the pretreated support for most of the attempted pore filling substances. Considering the roughness of porous support, coated crack-free silica film (~1 μm) exhibited very thin thickness. The alignment of...