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| - Diffusion of Binary Mixtures in Zeolites: Kinetic MonteCarlo versus Molecular Dynamics Simulations
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| - We report kinetic Monte Carlo (KMC) simulations of self-diffusion of a methane/perfluoromethane mixturein silicalite. The hopping rates and model setup were taken to match previously published MD simulationsand PFG-NMR data. In the case of the present KMC simulation the acceleration/deceleration of particleswith varying mixture composition can be attributed to correlation effects. The logarithmic interpolationrule for mixture self-diffusion coefficients reported by Snurr and Kärger (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 isnot able to cope with different saturation capacities of the two species; the influence of different saturationcapacities on mixture diffusion is accounted for by the Maxwell−Stefan theory. The Maxwell−Stefanformulation of diffusion in multicomponent mixtures is used to obtain explicit formulas for calculating thediffusivities of binary mixtures within a zeolite matrix. The theoretical development allows the estimationof the mixture diffusivities on the basis of the pure component diffusivities at zero loadings. We discussseveral mixture rules for the estimation of the exchange coefficient Đ12. Though none of them is fullysatisfying, we demonstrate the Đ12 value should have the same order of magnitude as the pure componentMaxwell−Stefan diffusivities in order to account properly for acceleration/deceleration behavior.
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