On-stream modification of MFI zeolite membranes for enhancing hydrogen separation at high temperature

α-Alumina-supported MFI zeolite membranes were modified by on-stream catalytic thermal cracking of methyldiethoxysilane (MDES) molecules inside the zeolitic channels during the separation of H2/CO2 gas mixture at 450 °C and atmospheric pressure. The MDES vapor was carried by the H2/CO2 feed gas and the effect of modification was monitored continuously through online analysis of the permeate stream. The modified membrane exhibited a significant increase in H2 selectivity over CO2 with a moderate decrease in H2 permeance. At 450 °C, the modified MFI membrane obtained a H2/CO2 permselectivity of 17.5 with H2 single gas permeance of 1.86 × 10−7 mol m−2 s−1 Pa−1 as compared to a permselectivity of 2.78 and permeance of 2.75 × 10−7 mol m−2 s−1 Pa−1 for the membrane before modification. The modified membrane also showed good performance and stability in separation of H2/CO2 gas mixture containing up to 28.4% water vapor at 450 °C and atmospheric pressure.