Preferential Adsorption in Ethane/Carbon Dioxide Fluid Mixtures Confined within Silica Nanopores

Abstract

Molecular Dynamics simulations have been performed to investigate the structural and dynamical properties of fluid ethane confined within cylindrical silica nanopores of 3.8~nm and 1~nm diameters. Pure ethane and equimolar mixtures of ethane and CO2 were considered for the analysis. Computer simulations were carried out along the supercritical isotherm T=320 K, exploring densities within the range $\\rho/\\rho_c$ = 0.05-2.28. Density profiles along the axial and radial directions of the pore, orientational distribution functions, analysis of interfacial dynamic properties and estimations of diffusion coefficients are presented. In agreement with experimental data, the results show the formation of a dense adsorption layer, with densities that may be up to 10 times larger than those of the bulk phase, in particular at low densities and under sub-nanometer confinement. The incorporation of CO2 changes the scenario, leading to preferential adsorption of CO2 over ethane species. The dynamics of ethane also chan...