Crystallite-pore network model of transport and reaction of multicomponent gas mixtures in polycrystalline microporous media Wenjin Ding a , Hui Li a , Peter Pfeifer a , Roland Dittmeyer a,b,⇑ a Institute for Micro Process Engineering, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen D-76344, Germany b Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen D-76344, Germany highlights  Crystallite-pore network model is proposed to represent polycrystalline media.  Maxwell–Stefan surface diffusion model is used to simulate transport in micropores.  Reaction represented by any type of kinetic expressions is allowed in this model.  Structural effects of polycrystalline media on transport and catalysis are studied. graphical abstract Crystallite-pore network model representing polycrystalline microporous media (left), in which the crystallite orientation is described by two angles W and v (right). article info Article history: Received 19 February 2014 Received in revised form 17 May 2014 Accepted 19 May 2014 Available online 5 June 2014 Keywords: Pore network model Surface diffusion ZSM-5 membrane Xylene isomerization abstract A three-dimensional pore network model has been developed to simulate anisotropic multicomponent diffusion and reaction in polycrystalline microporous media with coexisting intracrystalline micropores and intercrystalline mesopores (i.e., defects). Transport in these pores is modeled with the generalized Maxwell–Stefan surface diffusion model proposed by Krishna [11] and the Knudsen diffusion model, respectively. A new feature highlight of this model is the representation of polycrystalline media with a crystallite-pore network model. In contrast to previous pore network models, the crystallite-pore net- work model has the novel aspect of modeling the anisotropic transport inside the crystallites forming a polycrystalline layer by assigning to every crystallite two parameters to describe its orientation. The model was applied to simulate xylene isomerization in a polycrystalline ZSM-5 zeolite membrane, which had been experimentally investigated in a Wicke-Kallenbach cell by Haag et al. [13]. First, their experi- mental data were used to estimate adsorption and diffusion parameters of the xylene isomers in the ZSM-5 membrane via fitting single-gas permeance data of the xylene isomers. Second, adopting these parameters, the experimental data for xylene isomerization were used to determine kinetic parameters for xylene isomerization in the ZSM-5 membrane. Finally, effects of selected structural parameters – con- centration of defects, connectivity of defects, crystallite orientation, and crystallite size – were investi- gated using the obtained adsorption, diffusion, and reaction parameters. The simulation results show that high selectivity towards p-xylene requires a low concentration of defects in the polycrystalline layer and a low loading of xylene isomers in the membrane. The novel crystallite-pore network model is also applicable to many other reaction systems. Ó 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2014.05.081 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Institute for Micro Process Engineering, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen D-76344, Germany. Tel.: +49 721 608 23114; fax: +49 721 608 23186. E-mail address: roland.dittmeyer@kit.edu (R. Dittmeyer). Chemical Engineering Journal 254 (2014) 545–558 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej