DIFFERENTIAL ENTHALPY AND ENTROPY CHANGES OF HYDROGEN SULFIDE ADSORPTION IN ZEOLITE CaA (M-34)

The article presents the experimentally obtained values of the differential enthalpy of adsorption of hydrogen sulfide at a temperature of 303oC in CaA (M-34) zeolite of LTA type. Enthalpy values were measured using a Tiana-Calve DAC-1-1A microcalorimeter connected to a universal high-vacuum device. The change of the differential enthalpy value of hydrogen sulfide in CaA (M-34) zeolite is legally related to the amount of adsorption. Under experimental conditions, it was found that the adsorption capacity of hydrogen sulfide for 1 gram of CaA (M-34) zeolite is equal to 6.6 mmol/g. The differential enthalpy values showed a regular step change corresponding to the amount of Na+ and Ca2+ cations in the zeolite. The differential values of the free energy - Gibbs energy - were calculated from the equilibrium values of the pressure. Based on the values of differential heat and Gibbs energy measured in direct experiment, the adsorption entropy change and its average value were theoretically calculated using the Gibbs-Helmholtz formula. The values of the entropy change of adsorption of hydrogen sulfide molecules are lower than the entropy value in the liquid state at the experimental temperature, and its average value is -20 J/mol×K, which indicates that the mobility of hydrogen sulfide molecules in the zeolite matrix is close to the mobility of hydrogen sulfide in the liquid state.