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 language | English |
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Pages (from-to) | 3-10 |
Number of pages | 8 |
Journal | Microporous and Mesoporous Materials |
Volume | 125 |
Issue number | 1-2 |
DOIs | |
State | Published - 1 Oct 2009 |
Keywords
- Aromatics
- Frequency response
- Intra-crystalline diffusion
- MFI-type zeolites
- Particle size distribution