Zeolite Membranes for Hydrogen and Water Separation under Harsh Conditions

Abstract

To increase the efficiency of power plants, coal can be processed by integrated gasification combined cycle (IGCC) to H₂ and CO₂. To minimize efficiency losses during gas separation, nanoporous membranes can be used advantageously for the separation of H₂ and CO₂. This process has to be carried out under hydrothermal process conditions (40 to 400 °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 H₂ (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 °C in dry atmosphere and 270 °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 µm. Single gas permeation measurements gave a H₂/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 °C. These membranes showed an increasing selectivity with increasing temperature.