Molecular Origin of Decreased Diffusivity with Loading for Benzene/HY

On the basis of our recently proposed "ideal" and "insertion" adsorption mechanisms of aromatics in HY zeolites, changes in energetic and dynamic properties with loading were investigated through Monte Carlo and molecular dynamic ( MD) calculations. Loading-dependent isosteric heat could be divided into three linear ranges. The two inflection points were attributed to adsorbate interactions and inherent adsorption mechanism changes. With regard to the loading dependence of diffusivity, diffusivity decreased faster at high loadings than at low and medium loadings, separated by an inflection point. This result confirmed a two-stage diffusion mechanism based on the distribution of adsorbate from MD simulations which was able to qualitatively predict the further restriction of the mobility. This study provided insights into the modeling of mobility at high loadings on the basis of site-hopping mechanism. (C) 2016 American Institute of Chemical Engineers