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

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 CO₂ were investigated. The results demonstrated that the relative crystallinity of M-CP_S decreased 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 ΔGmθ values of exchange process of Li⁺, Cs⁺, Ca²⁺, or Sr² presented the increased trend with the enhanced exchange times, but they decreased as the temperature increased. The negative ΔGmθ values and the positive ΔHmθ and ΔSmθ values suggested that the exchanged procedure belonged to spontaneous, endothermic, and entropy-increasing behaviors; their kinetic performances followed a pseudo-second-order model. However, the calculated E values 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 CH₄ and 0.38 mmol/g of N₂ by (Na, K)-CP, and 2.32 mmol/g of CO₂ by Li-6-CP.