Sorption isotherms of methane, ethane, ethylene, and carbon dioxide on ALPO-5 and SAPO-5

The sorption of methane, ethane, ethylene, and carbon dioxide in ALPO-5 and SAPO-5 (temperature 305-353 K, and pressure 0-200 kPa) and the thermodynamics of sorption have been investigated under similar conditions using a gravimetric sorption apparatus. The Dubinin-Polanyi equation is found to fit the sorption of all the sorbates in both the sorbents except for carbon dioxide in ALPO-5. The Freundlich model fits the equilibrium data on the sorption of carbon dioxide in ALPO-5. The two sorbents differ widely in the isosteric heat of sorption and also in its variation with surface coverage of these sorbates. Entropy changes on the sorption have also been analyzed. The sorption of these gases in both the sorbents is found to be supermobile, the mobility being much higher in ALPO-5 than in SAPO-5.