MODEL OF COMPETITIVE ADSORPTION OF ALKYLPYRIDINES ON SILICA AT SATURATION CONDITIONS

Adsorption selectivities, at saturation conditions, have been measured for 25 binary mixtures of alkylpyridines adsorbed on silica. Strong variations of the selectivity with the mixture composition have been observed. We propose a model that quantitatively represents and predicts such variations. The form of the model is a linear relationship, which is thermodynamically derived from the hypothesis of a strictly regular adsorbed solution using Hildebrand's activity coefficients. The coefficients of the model are expressed in terms of physicochemical parameters of the two constituents of the mixture: the pKa, the S° ortho steric parameter, and the area of adsorbent surface occupied by one adsorbed molecule. This model allows the a priori prediction of the selectivity values with an average error of 8%. On other hand, this model indicates that steric repulsions take place between the adsorbates and favor the adsorption of the smallest molecules. © 1990, American Chemical Society. All rights reserved.