Consideration of adsorbate vibrations and their phase states in porous systems

Abstract

The phase state of adsorbate in porous systems is considered, in which the walls are characterized by interaction potential with adsorbate: from strong attraction to absence of attraction. The equations are based on discrete distribution functions (the lattice gas model) taking into account the contribution of the vibration motions of adsorbate. The vibration motion of molecules is taken into account in the modified quasi-dimer Mie model. Molecular distributions are calculated in the quasi-chemical approximation reflecting the effects of direct correlations of interacting particles using the Lennard-Jones potential. Conditions of express estimates of vibration frequencies are discussed in which vibration frequencies weakly affect molecular distributions in the case of strong adsorption. It is found that consideration of vibrations results in a shift in adsorption isotherms in the coordinates of chemical potential-density to higher values of vapor pressure in the range of high fillings. This is related to the necessity of additional vapor “compression” for its transition into the adsorbed state characterized by higher kinetic energy.