Influence of alkali cations on permeation properties of Y-type zeolite membranes

NaY-type zeolite membranes were synthesized on the outer surface of an α-alumina support tube by a hydrothermal process. The membranes were ion-exchanged with 0.01–0.50 mol/l aqueous solutions of KCl, RbCl or CsCl at 80 °C for 4 h. Gas permeation properties of the ion-exchanged membranes were determined at 35 °C for single component systems of CO2 and N2 and for an equimolar mixture, thereof. The CO2/N2 separation factor for permeation increased with increasing ion-exchange degree, which was dependent on the cation species. When the membrane was treated in a 0.50 mol/l solution of KCl, RbCl and CsCl, the ion-exchange degree reached 96, 78 and 62%, respectively. The CO2/N2 separation factors of the Y-type zeolite membranes ion-exchanged with K, Rb and Cs were 55, 47 and 46%, respectively, at a permeation temperature of 35 °C. The NaY-type zeolite membranes, which were impregnated with Cs ions, showed the highest CO2/N2 separation factor of 149 at 35 °C. These results suggest that the CO2/N2 separation factor was largely determined by the affinity between the membranes and the permeants.