Gas separation using sol-gel derived microporous zirconia membranes with high hydrothermal stability

A microporous zirconia membrane with hydrogen permeance about 5 × 10^{- 8} mol·m^{- 2}·s^{- 1}·Pa^{- 1}, H₂/CO₂ permselectivity of ca. 14, and excellent hydrothermal stability under steam pressure of 100 kPa was fabricated via polymeric sol-gel process. The effect of calcination temperature on single gas permeance of sol-gel derived zirconia membranes was investigated. Zirconia membranes calcined at 350 °C and 400 °C showed similar single gas permeance, with permselectivities of hydrogen towards other gases, such as oxygen, nitrogen, methane, and sulfur hexafluoride, around Knudsen values. A much lower CO₂ permeance (3.7 × 10^{- 9} mol·m^{- 2}·s^{- 1}·Pa^{- 1}) was observed due to the interaction between CO₂ molecules and pore wall of membrane. Higher calcination temperature, 500 °C, led to the formation of mesoporous structure and, hence, the membrane lost its molecular sieving property towards hydrogen and carbon dioxide. The stability of zirconia membrane in the presence of hot steam was also investigated. Exposed to 100 kPa steam for 400 h, the membrane performance kept unchanged in comparison with freshly prepared one, with hydrogen and carbon dioxide permeances of 4.7 × 10^{- 8} and ~ 3 × 10^{- 9} mol·m^{- 2}·s^{- 1}·Pa^{- 1}, respectively. Both H₂ and CO₂ permeances of the zirconia membrane decreased with exposure time to 100 kPa steam. With a total exposure time of 1250 h, the membrane presented hydrogen permeance of 2.4 × 10^{- 8} mol·m^{- 2}·s^{- 1}·Pa^{- 1} and H₂/CO₂ permselectivity of 28, indicating that the membrane retains its microporous structure.