Grand canonical molecular dynamics simulations of transport diffusion in geometrically heterogeneous pores

Abstract

Most transport diffusion simulation studies are carried out in single pores with simple geometries such as slit-like pores or straight cylindrical pores. Such models are gross simplifications of the structure of real, geometrically heterogeneous adsorbents. We carried out grand canonical molecular dynamics simulations of binary, counter diffusing CH₄/CF₄ mixtures in different cylindrical model pores with pore radii ranging from 11 to 23 Å. Each of these pore models represents a feature that can be found in real adsorbents such as pores with amorphous surfaces, pores with a change in the cross-sectional area, pores with kinks and simple pore networks. The results were compared to simulation results in straight pores with homogeneous surfaces to investigate the extent to which transport diffusion can be represented by these simplified model pores. Our results show that transport diffusion is hardly influenced by the different pore structures studied in this work. The simulation results can be reproduced by straight pores if the correct average radius, flow length and enclosing gradient are chosen.