Development of Molecular Sieving Inorganic Membranes and Separation System for High Temperature Gases

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Inorganic membranes can be used for gas separation at high temperature in an oxidative atmosphere where organic membranes are not resistant. In preparing molecular sieving inorganic membranes with high permeability, the pore structure should be strictly controlled. In this study, ceramic and palladium thin membranes were formed by novel preparation methods, and gas permeability and thermal and chemical stability of the membranes were examined.Palladium thin membrane was formed in macropores of an alpha-alumina support tube by cross-flow CVD method. Hydrogen permeance and selectivity to nitrogen were respectively higher than 10^<-6> mol・m^<-2>s^<-1>Pa^<-1> and 1000. The membrane was resistant against hydrogen embrittlement and sulfur poisoning. Silica membrane was also prepared by the same procedure using tetraethylorthosilicate. The membrane was stable in steam and showed a selectivity of hydrogen to nitrogen higher than 1000. Furthermore, Silica-based microporous membrane was prepared by controlled pyrolysis of polycarbosilane coated on a gamma-alumina-modified support tube. The membrane showed a permselectivity of hydrogen to nitrogen higher than the Knudsen value and was usable up to 400ﾟC.Perovskite oxide membrane was prepared by sol-gel methods and slicalite membrane formed by hydrothermal synthesis, respectively. Carbon dioxide was preferentially permeated through these membranes because of the surface diffusion, but the CO_2 permselectivity was insufficient. Further pore-size control is needed for the industrial uses.