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Predicting Benzene Fluxes in NaX Membranes from Atomistic Simulations of Cooperative Diffusivities

Summary: Predicting Benzene Fluxes in NaX Membranes from Atomistic Simulations of Cooperative
Harikrishnan Ramanan,, Scott M. Auerbach,*,, and Michael Tsapatsis*,,
Departments of Chemical Engineering and of Chemistry, UniVersity of Massachusetts,
Amherst, Massachusetts 01003, and Department of Chemical Engineering and Materials Science,
UniVersity of Minnesota, Minnesota 55455
ReceiVed: June 2, 2004; In Final Form: August 11, 2004
In the preceding companion article, we reported high-temperature molecular dynamics (MD) simulations to
trace single-molecule as well as collective mean square displacements over a range of temperatures (600-
1500 K) and loadings (infinite dilution to four benzenes per supercage) to evaluate respectively the self-
diffusivities and cooperative (alternatively Maxwell-Stefan) diffusivities of benzene in NaX (Si:Al ) 1.2).
In this follow-up article, we use the loading- and temperature-dependent Maxwell-Stefan diffusivities to
predict single-component fluxes for benzene in NaX membranes at steady state as a function of typical
experimental parameters such as temperature, benzene feed side and permeate side partial pressures. We
explore whether support resistances need to be included in our transport model. We compare our model
predictions with experimental permeation data and find that our MD-simulated diffusivities overestimate
experimental fluxes by about 2 orders of magnitude when support resistance is ignored. On the other hand,
when support resistances are included, our predictions come within 1 order of magnitude of experimental
data. The remaining discrepancy, which is analogous to those between microscopic and macroscopic probes
of diffusion in zeolites, may arise from defects within zeolite membranes.


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


Collections: Chemistry