Harikrishnan Ramanan and Scott M. Auerbach,
``Modeling Jump Diffusion in Zeolites: I. Principles and Methods,'' in
NATO-ASI Series C: Fluid Transport in Nanopores, edited by
J. Fraissard and W.C. Conner, Kluwer Academic Publishers, Dordrecht, The
Netherlands, in press (2004).
Abstract
We review the macroscopic variables relevant to single-component
mass transfer through fixed zeolite particles or membranes. Through
the Fick and Maxwell-Stefan formulations of diffusion, we relate
these variables to transport coefficients calculable with molecular
simulations. Using the Fick formulation, we discuss the
diffusion-controlled and desorption-controlled limits of mass transfer.
Through the well-known relation between the Fickian and Maxwell-Stefan
diffusivities, we discuss expected temperature and loading
dependencies in the limits of fluid-like and jump-like intrazeolite
diffusion. We then review the statistical mechanical foundations
of self-diffusion and Fickian- or transport-diffusion in terms of
mean-square displacements. We outline how self-diffusion is
influenced by kinetic correlations, geometrical correlations,
vacancy correlations, single-file motion and disorder. For host-guest
systems where guest motion is dominated by rare site-to-site jumps,
we outline the use of transition state theory and kinetic Monte Carlo
for constructing diffusion coefficients. We emphasize the particular
difficulty in treating the competition between host-guest and
guest-guest interactions when modeling rare event dynamics in zeolites.
Prof SM Auerbach
11 Feb 2004