ENTHALPY AND ENTROPY CHANGE OF METHANETHIOL ADSORPTION IN ZEOLITE CaA (M-22)
Abstract
The article presents experimentally obtained values of the differential enthalpy of methanethiol adsorption on zeolite CaA (M-22) of the LTA type at 303 K. The enthalpy values were measured using a Tiana-Calve DAC-1-1A microcalorimeter connected to a universal high-vacuum device. Differential values of free energy (Gibbs energy) were calculated from the equilibrium values of pressure. Based on the experimentally measured values of differential heat and Gibbs energy, the change in adsorption entropy and its average value were theoretically calculated using the Gibbs-Helmholtz formula. A regular relationship is shown between the amount of methanethiol adsorption on zeolite CaA (M-22), the values of differential enthalpy and the changes in entropy. The mechanism of adsorption from the initial adsorption zone to the reduction zone by the heat of methanethiol condensation and the law of filling the zeolite volume with methanethiol molecules were also determined. Based on the regular change in the values of differential enthalpy depending on the amount of Na+ and Ca2+ cations in the zeolite, it was established that methanethiol molecules first form mono- and dimer complexes 2CH3SH:Na+ with sodium cations, then monomer 1CH3SH:Ca2+ ion-molecular complexes with calcium cations.
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