Thermodynamic modeling of adsorption at the liquid-solid interface

Adsorption-based separation techniques are significantly energy efficient in comparison to the conventional thermal separation techniques such as distillation. Despite the extensive research and development activities undertaken for mixed gas adsorption, the use of adsorption techniques for the separation of multicomponent liquid mixtures is still limited. This is due to the lack of accurate adsorption thermodynamic models, which form the scientific foundation of process simulation of such systems, making the translation to the industrial scale challenging. In this work, we have rigorously computed the surface excess of adsorption for six binary liquid mixtures on silica gel at 303 K using the frameworks of the adsorbed solution theory and the generalized Langmuir isotherm model. The six binary liquid mixtures studied in this work were formed by the pair-wise combinations of four components: benzene, 1,2-dichloroethane, cyclohexane, and n-heptane. We have based our calculations by considering simultaneous equilibria of three phases: saturated binary vapor phase, binary liquid phase, and the adsorbed phase. The composition of the corresponding saturated vapor phase was determined by correlating the experimental vapor-liquid equilibria data using the Non-Random Two-Liquid activity coefficient model. The activity coefficients of the adsorbed phase were calculated using the adsorption Non-Random Two-Liquid activity coefficient model. Devoid of simplifying assumptions, our methodology for computing the surface excess of binary liquid adsorption should be applicable for the adsorption from a wide variety of liquid mixtures.