Diffusion pathways of benzene, toluene and p-xylene in MFI

O. C. Gobin, S. J. Reitmeier, A. Jentys, J. A. Lercher

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40 Scopus citations

Abstract

The diffusion of alkyl-substituted aromatic molecules in H-ZSM-5 was investigated by means of the frequency response method decoupling particle size effects and intracrystalline diffusion. For zeolite crystals above 5 μm average diameter, the transport in the zeolite pores exerts a significant effect on the overall transport causing anisotropic diffusion as the aspect ratio of the aromatic molecules increases. Diffusion of benzene is nearly isotropic, while p-xylene shows marked differences between the diffusive processes in the straight and sinusoidal channel system of ZSM-5. The isotropic diffusion of benzene is rationalized on the basis of its ability to reorient between the two channel systems without major hindrances. For p-xylene, switching between the channels is only possible by energetically unfavorable rotational motions leading to a low probability for changing between both channel systems.

Original languageEnglish
Pages (from-to)3-10
Number of pages8
JournalMicroporous and Mesoporous Materials
Volume125
Issue number1-2
DOIs
StatePublished - 1 Oct 2009

Keywords

  • Aromatics
  • Frequency response
  • Intra-crystalline diffusion
  • MFI-type zeolites
  • Particle size distribution

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