Separation of CO2-CH4 and CO2-N2 systems using ion-exchanged FAU-type zeolite membranes with different Si/Al ratios

FAU-type zeolite membranes with different Si/Al ratios were hydrothermally synthesized on the outer surface of a porous alpha-Al2O, support tube. The permeances of the membranes to CO2, CH4 and N-2 were then measured at 308 K for single-component and equimolar binary systems. The separation properties were dependent on both the Si/Al ratio and the ion-exchange treatment. For single-component systems, a lower Si/Al ratio resulted in the incorporation of a larger number of Na+ ions. For a CO2-CH4 mixture, both CO2 permeances and CO2/CH4 selectivities were approximately half the values obtained for a binary CO2-N-2 mixture. The highest selectivities, obtained using the NaX(1) zeolite membrane, were 28 for CO2/CH4 and 78 for CO2/N-2. The RbY, RbX(1) and RbX(2) zeolite membranes showed larger CO2 permeances, compared with those of the original Na-type membranes. Ion-exchange with K+ ions was the most effective for the NaY zeolite membrane in that both the CO2 permeance and the CO2/CH4 selectivity were increased.