Explorations on Thermodynamic and Kinetic Performances of Various Cationic Exchange Durations for Synthetic Clinoptilolite

Various cation–exchanged clinoptilolites (M–CPs, M = Li+, Cs+, Ca2+, Sr2+) were prepared, and their exchanged thermodynamic (and kinetic) properties and adsorption performances for CH4, N2, and CO2were investigated. The results demonstrated that the relative crystallinity of M–CPSdecreased with the increase of exchange times. Their chemisorbed water weight loss gradually increased with the increasing exchange times, except that of Cs–x–CP. The ΔrGmθvalues of exchange process of Li+, Cs+, Ca2+, or Sr2presented the increased trend with the enhanced exchange times, but they decreased as the temperature increased. The negative ΔrGmθvalues and the positive ΔrHmθand ΔrSmθvalues suggested that the exchanged procedure belonged to spontaneous, endothermic, and entropy-increasing behaviors; their kinetic performances followed a pseudo–second–order model. However, the calculatedEavalues of exchange process showed the increased tendencies with the enhanced exchange times, indicating that the exchange process became more difficult. Finally, the preliminary adsorption results indicated that the maximum adsorption amount at 273 K and 1 bar was 0.51 mmol/g of CH4and 0.38 mmol/g of N2by (Na, K)–CP, and 2.32 mmol/g of CO2by Li–6–CP.