Sorption isotherms of methane, ethane, ethene and carbon dioxide on NaX, NaY and Na-mordenite zeolites

The sorption of methane, ethane, ethene and carbon dioxide in NaX, NaY and Na-mordenite zeolites (at 305–353 K and 0–200 kPa) and the thermodynamics of sorption have been investigated using a novel gravimetric sorption apparatus. The Dubinin–Polanyi equation fits the sorption of methane in all three zeolites, whereas the Langmuir model fits the sorption of carbon dioxide in all the zeolites. It was not possible to fit the sorption data for ethane and ethene in the different zeolites to a single isotherm equation. The isosteric heat of sorption and its variation with surface coverage of these gases are dependent on the sorbate and the zeolite sorbent. Except for ethene in NaM, the sorbed molecules are supermobile in the three zeolites, and their mobility is influenced by the surface coverage. Ethene sorbed in NaM exhibits an intermediate degree of freedom and the two-dimensional (2D) translational motion of the sorbed molecules parallel to the zeolite surface itself is restricted.