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

Abstract

This paper summarises the results of four years' investigation of the thermodynamics of adsorption in activated carbon micropores. Five adsorbates, i.e. methane, methanol, ethanol, carbon dichloride and carbon tetrachloride were adsorbed at three temperatures (308, 328 and 348 K) on two polymeric microporous carbons. Adsorption isotherms, as well as differential heats of adsorption, were measured using adsorption calorimetry. From the experimental results, the entropy as well as the average heat capacity of the adsorbed molecules were calculated. The data obtained lead to the mechanism of adsorption in carbon micropores as well as to the influence of the oxidation of the carbon surface on this mechanism. By comparing the isosteric and differential heats of adsorption, it is shown that the isosteric enthalpy cannot be applied for a correct description of the adsorption energetics. Finally, some empirical relationships describing low-coverage adsorption are proposed and discussed.