Diffusion of Binary Mixtures in Zeolites: Kinetic Monte Carlo versus Molecular Dynamics Simulations

Abstract

We report kinetic Monte Carlo (KMC) simulations of self-diffusion of a methane/perfluoromethane mixture in silicalite. The hopping rates and model setup were taken to match previously published MD simulations and PFG-NMR data. In the case of the present KMC simulation the acceleration/deceleration of particles with varying mixture composition can be attributed to correlation effects. The logarithmic interpolation rule for mixture self-diffusion coefficients reported by Snurr and Karger (J. Phys. Chem. B 1997, 101, 6469) is validated for a broad range of loadings. However, a deficiency of the present KMC model is that it is not able to cope with different saturation capacities of the two species; the influence of different saturation capacities on mixture diffusion is accounted for by the Maxwell−Stefan theory. The Maxwell−Stefan formulation of diffusion in multicomponent mixtures is used to obtain explicit formulas for calculating the diffusivities of binary mixtures within a zeolite matrix. The theoretic...