Gibbsian Surface Excess for Gas AdsorptionRevisited

Abstract

The Gibbsian surface excess (GSE) represents the true experimental variable for measuring pure and multicomponent gas adsorption equilibria and kinetics by all conventional adsorption methods (volumetric, gravimetric, chromatographic, column dynamic, total desorption, isotope exchange, etc). The GSE can be used as primary variables to formulate the general thermodynamic and kinetic models for adsorption on energetically homogeneous and heterogeneous adsorbents. Thus, practical thermodynamic properties like surface potentials, isosteric heats of adsorption of components, and heat capacities of adsorption systems can be estimated using GSE. Several thermodynamic consistency tests (differential and integral) for binary adsorption systems can also be formulated using GSE. A mathematical framework describing the isothermal and nonisothermal column dynamics for adsorption of multicomponent gas mixtures can be developed using GSE. It can be used to simulate practical process design models (pressure and thermal swing adsorption) for gas mixture separation and purification. There is no need to estimate actual amounts adsorbed from the measured GSE variables by making ambiguous assumptions about the size of the adsorbed phase. The experimental GSE can be used to completely describe all practical thermodynamic, kinetic, column dynamic, and process design aspects of gas adsorption technology.