Microcalorimetric Study of the Change in Gibbs Free Energy and Differential Entropy of Adsorption of Water Molecules in Zeolite ۳A

The article presents the Gibbs free energy and differential molar entropy of water molecule adsorption in LTA-type KA zeolite. The Gibbs energy was calculated from the experimentally obtained equilibrium pressure values. The change in entropy was theoretically determined based on the Gibbs energy and differential enthalpy. A consistent relationship was identified between the amount of water adsorbed on the KA zeolite and the thermodynamic characteristics (ΔG, ΔS), as well as the adsorption mechanism up to the region where the heat of condensation of water decreases, and the regularity of water filling the volume of KA zeolite. Under experimental conditions, the adsorption capacity of KA zeolite toward water was shown to be approximately ۵.۵ mmol/g. It was established that the stepwise change in Gibbs free energy and differential molar entropy depends on the number of K⁺ cations in the KA zeolite. It was also proven that at a pressure of ۱۳ torr, water molecules form pentamer ۵H₂O:K⁺ ion-molecular complexes with potassium cations within the zeolite matrix. It was established that the average molar integral entropy of water adsorption in KA zeolite is -۱۳۴ J/mol·K, indicating that the mobility of water molecules in the zeolite is lower than in the liquid phase and approaches that of the solid phase, resulting in a strong hindrance to water mobility when adsorbed onto cations.

کلیدواژه ها:

Zeolite ، Adsorbate ، Gibbs energy ، Entropy ، Water ، Mechanism