The impact of the adsorbent energy heterogeneities by multidimensional-multicomponent PC-SAFT-DFT

Over the past few decades, the classical density functional theory (cDFT) models have gained importance in modeling inhomogeneous fluids. Notably, adsorption databases produced by non-local DFT (NLDFT), quenched solid DFT (QSDFT) and 2D-NLDFT approaches are used in different characterization methodologies to recover the pore size distribution (PSD) for a various nanoporous materials. This family of models has a much lower computational cost when compared to molecular simulation. However, it lacks formulations that use DFT for multidimensional-multicomponent systems with heterogeneous solids. In addition to the complexity of representing the interactions between confined molecules and their confined mixtures, it is challenging to represent surface heterogeneities. Here we study materials with equivalent external potential but presenting energy heterogeneities varying throughout the material using a multidimensional classical DFT approach consistent with the SAFT equation of state. For this purpose, we applied three external potentials to model three types of slit-like cavities. Among them, a classical slit-like pore was generated, in which the energy sites did not vary along with the material. In the other two cavities, the energy sites could vary along the cavity, simulating a cavity in which the external potential varies bidimensionally. Finally, we evaluate the effect of the energy heterogeneity of these cavities on the adsorption of Ar and Kr and their mixing. The results show that local heterogeneities can alter the shape of isotherm curves and adsorption selectivities. Solids with heterogeneity showed higher selectivity but lower capacity.