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Publisher DOI: 10.1021/jp904267a
Title: On the effects of the external surface on the equilibrium transport in zeolite crystals
Language: English
Authors: Zimmermann, Nils E. R. 
Smit, Berend 
Keil, Frerich 
Keywords: molecular simulations;transport;hydrocarbons;zeolites;nanoporous materials;interface
Issue Date: 2010
Source: The Journal of Physical Chemistry C, 2010, 114 (1), pp 300–310
Journal or Series Name: The Journal of Physical Chemistry C 
Abstract (english): With the aid of molecular simulation techniques (molecular dynamics [MD], Grand-Canonical Monte Carlo [GCMC], and reactive flux correlation function [RFCF]), the influence of the external surface on the equilibrium permeation of methane and ethane into and out of an AFI-type zeolite crystal has been studied. In particular, “extended dynamically corrected transition state theory”, that has been proven to describe the transport of tracers in periodic crystals correctly, has been applied to surface problems. The results suggest that the molecules follow paths that are close to the pore wall in the interior, and also at the crystal surface. Moreover, the recrossing rate at the surface turns out to be non-negligible, yet, in contrast to the intracrystalline recrossing rate, remains almost constant over loading which gives indication to diffusive barrier crossing at the crystal surface. As a consequence of very different adsorption and desorption barriers, the corresponding permeabilities are shown to be not equal for one and the same condition (T , p). The critical crystal length, beyond which surface effects can be certainly neglected, is computed on basis of flux densities. Entrance/exit effects, in the present cases, are practically important solely for ethane at low pressures. The influence of the type of external surface on the surface flux is, hereby, rather small, because the transport at the surface is controlled by the slow supply from the gas phase. This has been evidenced by a simplified thermodynamic model that has been derived within this work and which is based on rapidly assessable simulation data. Finally, we propose a procedure for estimating the importance of different factors that have an impact on surface effects.
DOI: 10.15480/882.1531
ISSN: 1932-7455
Institute: Chemische Reaktionstechnik V-2 
Type: (wissenschaftlicher) Artikel
License: In Copyright In Copyright
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