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Theory and simulation of cohesive diffusion in nanopores: Transport in subcritical and supercritical regimes
 

Summary: Theory and simulation of cohesive diffusion in nanopores: Transport
in subcritical and supercritical regimes
Chandra Saravanan
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003
Scott M. Auerbacha)
Departments of Chemistry and Chemical Engineering, University of Massachusetts, Amherst,
Massachusetts 01003
Received 19 January 1999; accepted 17 March 1999
We have studied a lattice model of self-diffusion in nanopores, to explore how loading, temperature,
and adsorbate coupling influence benzene self-diffusion in Na­X and Na­Y zeolites. We propose
a simple method for determining how adsorbate­adsorbate interactions modify activation energies
of site-to-site jumps. We apply a mean-field approximation that describes transport
semiquantitatively for a wide variety of system parameters, simplifying kinetic Monte Carlo
simulations. We also derive an analytical diffusion theory that provides semiquantitative apparent
activation energies, and qualitatively reasonable loading dependencies. We have found that
supercritical systems exhibit three characteristic loading dependencies of diffusion, depending upon
the degree of degeneracy of lattice sites. Subcritical diffusion systems are dominated by cluster
formation, exhibiting intriguing loading dependencies with broad regions of constant diffusivity.
Our model for benzene in Na­X is in excellent qualitative agreement with pulsed field gradient
nuclear magnetic resonance NMR diffusivities, and in qualitative disagreement with tracer

  

Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst

 

Collections: Chemistry