High-Pressure Adsorption of Xe on NaX Zeolite by Microcalorimetry and Isosteric Analysis

A differential microcalorimetric technique for the investigation of high-pressure adsorption of fluids on microporous solids is developed. The thermodynamic analysis of the experimental scheme and the relationship between isosteric and calorimetric differential heats of adsorption are given. These values are obtained for the system Xe-zeolite Na X at pressures of 1 × 10 -5 -22 MPa and temperatures of 299-467 K. The strong dependence of differential calorimetric heats on adsorption on temperature observed at sufficiently high loadings is interpreted in terms of cooperative adsorbate-adsorbate interactions and adsorption deformation of the adsorbent. The notion of the area of thermodynamic inertness of the adsorbent is introduced and its frontiers are established for the system under question. In this region of comparatively low pressures and temperatures, the differential calorimetric heats and the isosteric heats of adsorption determined under the assumption of an inert adsorbent are in good agreement. Beyond this region, considerable differences between these values are shown to be due to adsorption deformation of adsorbent.