Analysis of binary adsorption of polar and nonpolar molecules in narrow slit-pores by mean-field perturbation theory.

In the present research study, we present the development of a model for predicting the adsorption of binary mixtures of nonpolar molecules, as well as polar molecules, based on density functional theory with mean-field approximation in narrow slit-pores. The first system under consideration is comprised of a binary mixture of nonpolar molecules, modeled by considering intermolecular dispersion forces, whereas the second system comprised of a binary mixture of polar molecules is modeled by considering orientation averaged electrostatic interactions, namely dipole-dipole and dipole-induced dipole interactions as well as dispersion interactions. An explicit equation for the Helmholtz free energy of the pore phase binary fluid mixture is derived. The proposed model is used to simulate the selective sorption of ethane from an ethane-methane mixture and water from a methanol-water mixture in the slit-pore. The simulated results are interpreted by studying the relative contributions of fluid-wall and fluid-fluid interactions. Finally, simulation results obtained are compared with the results of existing models and molecular simulations in the literature.