EFFECT OF PRESORBED WATER AND TEMPERATURE ON ADSORPTION OF NITROGEN AND OXYGEN IN NACAA AND NAMGA ZEOLITES

Adsorption of N2 and O2 has been studied on Ca2+ exchanged NaA zeolites (NaCaA) and on a NaMgA zeolite using elution gas chromatography. N2 specific retention volume and adsorption selectivity increase with increase in calcium content (0 to 97% exchange) of the zeolite. However, the increase in much higher at above 90% calcium exchange. Specific retention volumes and adsorption selectivity decrease with increase in temperature for both the adsorbates. N2 specific retention volume decreases with presorbed water in the zeolite. For zeolite samples NaA and NaCaA having > 90% calcium exchange even 0.9 mmol/g of presorbed water suppressed the N2 selectivity substantially. Zeolite NaMgA shows higher heats of adsorption and lower specific retention volume and selectivity compared to NaCaA with similar ion exchange for nitrogen. Pronounced decrease in N2 specific retention volume, selectivity and heat of adsorption is observed for NaMgA even with 0.9 mmol/g of presorbed water. These results have been explained in terms of interaction of adsorbate molecules with extra-framework cations and their distribution in zeolite A.