Transport properties of polyimide/silica composite membranes.

Abstract

Polyimide/silica composite membranes were prepared by the sol-gel reaction of tetraethoxysilane, methyltriethoxysilane or phenyltriethoxysilane in the solution of polyamic acid prepared by condensation of equimolar amount of pyromellitic dianhydride, 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride or 2, 2-bis(3, 4-dicarboxyphenyl)hexafluoropropane dianhydride with 4, 4′-oxydianiline in N-methyl pyrollidone. Silica-coated polyimide membranes were also prepared by the sol-gel method. Gas permeation for H2, CO2, CO, O2, N2 and CH4 and water vapor permeation were reported. A slight reduction in gas permeability was observed for the composite membrane. The permeability of water vapor increased in polyimide/silica composite membranes, while silica coating resulted in a reduction of the permeability. Transient sorption and desorption experiments were also investigated at water vapor activity of 0.5. An increase in permeability of water vapor can be attributable to an increase in solubility of water vapor due to the presence of hydroxy species of silica.