Models based on classical density functional theory to obtain physical-chemical properties of adsorptive systems

Abstract

Here, it is presented methodologies to apply the Density Functional Theory (DFT) models to obtain the physical-chemical properties of confined fluids. For this purpose, algorithms were developed to obtain adsorption/desorption isotherms for simple species, chain-molecule species, and species with the effect of polarity in adsorbent cavities, considering pore walls with and without roughness. With these methodologies, the characterization process of adsorbents was studied, examining the pore size distribution (PSD) and obtaining absolute adsorption isotherms from excess isotherm experimental data. The study of rebuilding PSDs shows that applying statistical techniques is essential to obtain reliable PSD information. Also, the implementation of DFT models, consistent with PC-SAFT and PCP-SAFT, successfully described hydrocarbon and CO2 isotherms, even under supercritical conditions. In addition, it is presented a technique capable of optimizing the DFT routine to obtain the equilibrium isotherm for cases where there is sorption hysteresis. This methodology allows the direct calculation of the equilibrium isotherm and phase diagrams inside the pores.