DIFFERENTIAL ENTHALPY AND ENTROPY OF ETHANE ADSORPTION ON LTA- TYPE ZEOLITE

Abstract

In this study, the thermodynamic characteristics of ethane adsorption on LTA-type zeolite with the composition Ca5Na3[(AlO2)12(SiO2)12] were investigated using an adsorption– calorimetric method at 303 K. The measurements were carried out with a Tian–Calvet microcalorimeter (type DAK-1-1A), which provides high sensitivity and accuracy in recording thermal effects at low gas pressures. Based on the experimental data, the differential entropy was calculated as a function of the amount of adsorbed ethane. It was established that at the initial stage of adsorption (a<0.5 mmol/g), the differential enthalpy values reach 65-70 kJ/mol, which is associated with the strong interaction between ethane molecules and the Ca2+ and Na+ cationic centers. With further surface coverage, a gradual decrease in enthalpy to 25-30 kJ/mol is observed, indicating a transition to less energetically favorable micropores and predominantly physisorption interactions. The change in entropy increases with the degree of adsorption, reflecting a decrease in the structural order of the adsorbed layer. The results provide deeper insight into the energetic heterogeneity of the zeolite surface and the adsorption mechanism of hydrocarbons in microporous aluminosilicate frameworks.