Synthesis of defect-free FAU-type zeolite membranes and separation for dry and moist CO₂/N₂ mixtures

In this paper, the effects of synthesis conditions, including the seeding approach, gel composition, and hydrothermal treatment process, on the quality of porous α-alumina-supported Y-type FAU membranes were studied. Defect-free, pure NaY-type zeolite membranes have been synthesized and investigated for separation of equimolar CO₂/N₂ mixtures under dry and moist conditions at atmospheric pressure. At room temperature, the CO₂ selectivity was about 31.2 for the CO₂/ N₂ dry gas mixture with a CO₂ permeance of 2.1 × 10^-8 mol/m²·Pa·s. The addition of water vapor to the feed stream decreased the permeance for both CO₂ and N₂ in a temperature range of 23-200°C. The existence of water vapor significantly enhanced the CO₂ selectivity at 110-200°C but drastically lowered the CO₂ selectivity below 80°C. At 200°C, with increasing water partial pressure, the CO₂ selectivity increased and then decreased after reaching a maximum of 4.6 at a water partial pressure of 12.3 kPa.