Preferential adsorption in ethane/CO2 fluid mixtures confined within silica nanopores

ELOLA, M. DOLORES; RODRIGUEZ J.

Buenos Aires

Workshop; Structure and Dynamics of Glassy, supercooled and nanoconfined fluids. 2019 Workshop; 2019

Molecular Dynamics simulations have been performed to investigate the structural and dynamical properties of fluid ethane confined within cylindrical silica nanopores of diameters 4 and 1 nm. The pure ethane phase and equimolar mixtures of ethane and CO, were considered for the analysis. Computer simulations were carried out along the isotherm T = 320 K, exploring densities in the range p/p, = 0.05 - 2.18. 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, particularly at low densities and under sub-nanometer confinement. Theincorporation of CO2 within the pores, in equimolar mixtures, modifies the structure of ethane species, leading to preferential adsorption of CO, over ethane species. This preference is reflected in adsorption layers having mole fractions of CO above 50%, that rise up to 80% at the highest bulk density studied. The dynamics of ethane is also modified in mixtures, as manifested by the oil increments measured in the diffusion coefficients of confined ethane in presence of CO2, in 4 accordance with experiments. In contrast with experimental data, our results for the diffusion coefficients of confined ethane showed a monotonic decreasing behavior with increasing bulk density. Possible reasons for this discrepancy between experiments and simulations are discussed.