Preparation of silica-based microporous inorganic gas separation membranes

Fully inorganic silica-based membranes have been prepared using sol-gel procedures starting from sodium silicate solutions. An asymmetric membrane structure is obtained by multiple deposition of colloidal silica sols onto commercial ceramic supports. The microporous structure of the silica which forms the active top layer remains stable up to 873 K and is characterised by a mean pore diameter of 1.6 nm, a narrow pore size distribution and a porosity of 35%. The continuous silica top layer of the membrane was analysed by SEM and checked by gas permeation measurements. The permeabilities of CH4, N2 and CO2 were measured for membranes deposited onto zirconia supports as a function of temperature. The preliminary experimental results indicate reproducible and relatively high fluxes as well as a transport mechanism which basically follows Knudsen flow with contributions from surface and microporous diffusion.