Effectiveness factor for zeolite catalysed isomerization reactions

Baur, R. ; Krishna, R. (2004) Effectiveness factor for zeolite catalysed isomerization reactions Chemical Engineering Journal, 99 (2). pp. 105-116. ISSN 0300-9467

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Official URL: http://www.sciencedirect.com/science/article/pii/S...

Related URL: http://dx.doi.org/10.1016/j.cej.2003.09.007


We analyze the influence of diffusion on the reversible isomerization reaction A1↔A2, occurring within a zeolite catalyst, of spherical, cylindrical, and slab geometries. The intra-crystalline diffusion process is described by the Maxwell-Stefan (M-S) equations. Two different guest-host confinement scenarios are examined. For strongly confined guest molecules, the M-S diffusivities Ði decrease with loading inside the zeolite. For weakly confined guest molecules, the M-S diffusivities Ði are independent of the loading. The correlation effects, typical of zeolite diffusion, are described by introducing an exchange coefficient Ð12 in the M-S diffusion formulation. For facile exchange,Ð12→∞, correlation effects are washed out. For finite exchange, a logarithmic interpolation formula is used to calculate Ð12 from the two pure component M-S diffusivities Ði. Analytic expressions for the effectiveness factor are derived for a variety of confinement and exchange scenarios. In the development of the analytic solution we assume Langmuirian behavior of the pure components and that the mixture sorption loadings can be calculated from the multicomponent Langmuir isotherm. By means of a variety of numerical examples, we stress the various characteristic features of intra-crystalline diffusion influences in zeolite catalysis. The effectiveness factor is found to a strong function of (a) molecular loadings and mixture composition, (b) ratio of diffusivities of the participating species, and (c) the reaction equilibrium constant. Only for the case of low loadings of weakly confined guest molecules and vanishing correlation effects, is the classical formula for the effectiveness factor valid.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Maxwell-Stefan Theory; Zeolite Catalysis; Isomerization; Effectiveness Factor; Correlation Effects; Confinement Effects
ID Code:65386
Deposited On:17 Oct 2011 03:20
Last Modified:17 Oct 2011 03:20

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