Heat Capacity of the H2O/KNaX Zeolite Adsorption System

Abstract

The heat capacity of the H2O/KNaX zeolite system has been measured at 34°C for various amounts of adsorption. The dependence of measured heat capacity of this system and calculated average molar heat capacity of adsorbate on the amount of adsorption passes through two distinct maxima. These maxima correspond to previously obtained waves in the plot of the heat of adsorption of water against the amount of adsorption for the same H2O/KNaX zeolite system. The maxima are due mainly to the contribution to the heat capacity of the heat of transfer of a part of the water molecules from the adsorption sites with higher heat of adsorption to those with lower heat of adsorption. The thermal stability of different water associates in zeolite pores has been investigated. The differential heat capacities of adsorbed water were calculated and the changes in the heat of adsorption of water when the temperature of the system was increased were determined. The results show that with increasing temperature there is a smoothing out of the waves produced in the plot of the differential heat of adsorption as the function of the amount of water adsorbed.