Molecular dynamics simulation study of the concentration dependence of the self-diffusivity of methanol in NaX zeolite

Molecular dynamics simulations have been carried out to provide a microscopic description of the diffusion behavior of methanol in NaX zeolite. Previously calibrated existing force fields have been carefully examined and tested with respect to their ability to reproduce the experimentally observed adsorption behavior. The force field parameters, which were selected in this process, were used to examine temperature dependence of the self-diffusion coefficient of methanol over a wide range of methanol loadings. The simulation results were found to be in a qualitative agreement with the corresponding experimental data. The simulations provided new insights on the experimental concentration dependence of the self-diffusion coefficient. Collective effects of the mutual interactions of methanol molecules competing for the most preferable sites at the intercage window were found to be key factors responsible for the observed concentration dependence of the intercage self-diffusivity.