Preparation of highly selective silica membranes on defect-free γ-Al2O3 membranes using a low temperature CVI technique

A low temperature (250 °C) CVI technique was employed to lab made γ-Al2O3 membranes, in order to reduce the pore size and increase the gas separation performance. The membranes were characterized before and after modification in terms of permeance and permselectivity using He, H2, N2, CO2 and C3H8. The porous structure of the membranes was studied with the permporometry technique. The γ-Al2O3 membranes were defect-free, with a narrow pore size distribution but they had low permselectivities characteristic of a Knudsen diffusion mechanism. The pore size of the CVI silica membranes decreased to the microporous regime with a concomitant decrease of permeance and a significant improvement of permselectivities at 250 °C (H2/N2: 27.8, H2/CO2: 81, He/N2: 19.4, H2/C3H8: >150). The CVI technique on sol–gel γ-Al2O3 membranes provides an effective method for the production of H2 selective silica membranes, at low temperatures (250 °C) where available sealing technologies can be used.