Heat capacity of the H2O/KNaX zeolite adsorption system

Abstract

The heat capacity of the H20/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 H20/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.

Calorimetric Investigations of Molecular Interactions in the Adsorbate/Microporous Activated Carbon System. Towards the Mechanism of Adsorption in Micropores

“…As shown hy Berezin, Kiselev and co-workers (Chuikina et al 1974;Berezin et al 1973) and by Pace and co-workers (Pace et al. 1953), the heat capacity of adsorbed molecules as calculated by equation (5) is close to that determined from direct measurement.…”

Significant Temperature Dependence of the Isosteric Heats of Adsorption of Gases in Zeolites Demonstrated by Experiments and Molecular Simulations

“…In determining the isosteric heat of adsorption from experimental data, eq is typically applied to several isotherms measured at different temperatures. − In certain cases, calculations from a single experimental isotherm is possible, if an accurate model is available to predict isotherms at other temperatures . Calorimetry is used for direct measurements. ,− When a molecular model is available for an adsorbent, the isosteric heat of adsorption can be computed directly from molecular simulations. − The isosteric heat of adsorption is important in detailed design of adsorption beds, as variations in bed temperature lead to changes in adsorption equilibrium. − The isosteric heat of adsorption is also a useful proxy for adsorption selectivity in considering a range of materials for a separation of interest. ,, …”

“…There is a difference in the isosteric heats of adsorption of ∼7 kJ/mol between their experiments at 200 and 300 K. Simulations at the same temperatures also present a 7 kJ/mol difference in the isosteric heats of CO adsorption. The temperature dependence of the isosteric heat of adsorption characterizes the difference in the heat capacities between the adsorbed and bulk phases. ,, …”

Investigation of the adsorption in zeolites at zero filling

“…Finally, restructuring of the array when the central parts of zeolite cavities begin to fill again causes growth of and drop of cm down to a value rather close to that of the heat capacity of liquid water. Variations in the infrared spectrum, contrary to that found in zeolite NaX, show that the growth of n5 does bring about alternate 10 15…”

“…2) Not only isotherms but also calorimetric heats of adsorption are measured over a wide range of temperatures [4,5]. 3) An assumption about the similarity of adsorbate properties in zeolite to those of a liquid is being replaced by a comprehensive analysis of the adsorbate state and its effect on the cation distribution using various methods of optical and NMR spectroscopy [1, 2,[6][7][8][9] and direct calorimetric measurements of heat capacity in adsorbate-zeolite systems [10]. 4) The method of statistical thermodynamics is being more often used to describe the results of measuring thermodynamic properties of adsorbate-zeolite systems [1, 2,11,12].…”