An interesting letter has recently been published in this total micropore volume of the solid, the thermal expansion Journal by Lodewyckx and Vansant [1], introducing the coefficient of the adsorptive and its molar volume in the idea of an affinity coefficient for water with respect to liquid state. G(1 1 1/n) is the tabulated 'Gamma' function, benzene, the usual reference in Dubinin's theory. This which takes values between 0.89 and 0.92 when n varies concept is valid for carbons with relatively low oxygen from 1.5 to 5. This means that the enthalpy of immersion contents, where the water adsorption isotherm is of type V depends essentially on the characteristic energy E 5 bE . is only a fraction of the total enthalpy of immersion. with active carbons containing variable amounts of oxygen From Eqs. (2) and (3), it follows that the enthalpy of and basic groups. The starting point is the DA equation immersion of a given adsorptive can be calculated from the [3,6] parameters of the DA isotherm. A good agreement has n been found for a variety of liquids [2,3]. Table 1,
In the case of simple vapour mixtures adsorbed by active carbons, the activity coefficients seem to depend essentially on the composition of the adsorbed phase, rather than on the degree of micropore filling. Consequently, the liquid-solid adsorption equilibrium of benzene + 1,2-dichloroethane mixtures has been investigated at 293 K, using a typical active carbon and following earlier work for adsorption from the vapour phase. This system has the advantage that the mixture is ideal in the liquid state, which provides a convenient reference for the study of the adsorbed phase. The activity coefficients, as well as the excess enthalpy of immersion of the carbon into the liquid mixtures, provide information on the modifications in the adsorbed state with respect to the ideal mixture. It is also shown that the introduction of the activity coefficients derived from the solidliquid equilibrium increases considerably the accuracy of the MyersPrausnitz-Dubinin model for the adsorption of the vapour mixtures.
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