Zeolite Membranes for Hydrogen and Water Separation under Harsh Conditions

To increase the efficiency of power plants, coal can be processed by integrated gasification combined cycle (IGCC) to H-2 and CO2. To minimize efficiency losses during gas separation, nanoporous membranes can be used advantageously for the separation of H-2 and CO2. This process has to be carried out under hydrothermal process conditions (40 to 400 degrees C, 1 to 40 bar and 0.4 to 35 % water). The same membranes can be used for water separation applications like in the Fischer-Tropsch synthesis (FTS). Sodalite (SOD) exhibits pore sizes in the range of the kinetic diameter of H-2 (0.29 nm), but is normally not hydrothermal stable. To increase the hydrothermal stability, the sodalite (H-SOD) was doped with sulphur (S-SOD). S-SOD is stable at 800 degrees C in dry atmosphere and 270 degrees C in 30 % water and approximately 40 bar. S-SOD membranes were synthesized on tubular alumina supports via a seeding procedure and subsequent hydrothermal synthesis. Crack free intergrown SOD-layers were found for membranes prepared with low concentrated seeding solutions. These membranes show a thickness of about 2 mu m. Single gas permeation measurements gave a H-2/CO2-permselectivity of 12 at room temperature for the best membranes. Variations of the seeding process lead to stable membranes up to at least 300 degrees C. These membranes showed an increasing selectivity with increasing temperature.