PERMEATION AND SEPARATION STUDIES ON MICROPOROUS SOL-GEL MODIFIED CERAMIC MEMBRANES

Permeation and separation experiments with H-2, CO2, O-2, N-2, CH4 and isobutane with microporous sol-gel modified supported ceramic membranes were performed to determine the gas transport characteristics and the hydrogen separation performance of these membranes. It is found that the permeation is activated, and for defect-free membranes the apparent activation energies are in the ranges 13-15 and 5-6 kJ mol(-1) for H-2 and CO2, respectively. Correction for the pressure drop over the support results in apparent activation energies for the silica top-layer on the order of 17-22 and 10-15 kJ mol(-1) for H-2 and CO2 respectively. Due to the very thin top-layer, the permeation is relatively high, with representative values of 6 . 10(-7) and 20 . 10(-7) mol m(-2) s(-1) Pa-1 for H-2 at 25 and 200 degrees C, respectively. The H-2 permeation is almost pressure-independent up to pressures of at least 5 bar. Typical separation factors for H-2-CH4 and H-2-isobutane are approximately approximate to 40 and approximate to 200, respectively, at 200 degrees C for high-quality membranes. For moderate-quality membranes the H-2-CH4 separation factor is around 10, while the H-2-isobutane separation factor remains at a high value of around 100 at 200 degrees C and 120 at 300 degrees C.