EFFECT OF CATIONS ON METHANE ADSORPTION BY NAY, MGY, CAY, SRY, AND BAY ZEOLITES

Methane isotherms on NaY, MgY, CaY, SrY, and BaY zeolites are measured between 25 and 70-degrees-C and upto 6760 kPa. All isotherms are of t ype I. The initial heat of adsorption for divalent cationic forms decr eased with decreasing charge density (CaY > MgY > SrY > BaY) except fo r MgY. Similar anamoly was observed for methane adsorption on MgX (Zha ng, S. Y.; Talu, O.; Hayhurst, D. T. J. Phys. Chem. 1991, 95, 1722) an d it is attributed to incomplete dehydration (activation) at normal ac tivation temperatures. The cation type significantly affected adsorpti on properties even at loadings as high as 7.5 molecules/cavity. CaY ha s the largest capacity per weight, but the methane pore density decrea sed in order of decreasing cationic size (BaY > SrY > CaY > MgY > NaY) at 25-degrees-C and 5200 kPa fugacity. This unexpected result is attr ibuted to possible differences in molecular packing around the cations at high loadings. The data were satisfactorily correlated by the viri al isotherm model.