A theoretical framework for the estimation of the isosteric heat of adsorption between an adsorbate (vapor) and an adsorbent (solid) is proposed based on the thermodynamic requirements of chemical equilibrium, Maxwell relations, and the entropy of the adsorbed phase. The derived equation for the isosteric heat of adsorption is verified against three sets of judiciously selected adsorbent+adsorbate data that are found in the literature and the predictions are found to agree within the experimental uncertainties of the reported data.
The construction of an apparatus for the rapid measurement of the adsorption equilibrium characteristics and evaluation of the isosteric heat of adsorption of activated carbons for gaseous adsorbates is described. The method is based on measuring the amount desorbed between two equilibrium adsorption states. The measurement system has been tested for methane adsorption over (5 to 75) °C and pressures from (2 to 24) bar on a Maxsorb-III specimen of activated carbon. The results are evaluated through regressions with various isotherm equations used in the literature for physisorption and are compared with results of other researchers for comparable adsorbentadsorbate combinations. A method of accounting for the adsorbed phase volume is proposed.
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