Diffusion of n-hexane in large crystals of the ZSM-5 and KVS-5 (V-Sil-1) zeolites (MFI structure) was discussed. The theoretical description took into account the morphology of the microporous crystals. Two diffusion models were used to compare theoretical uptake curves with the experimental data and to determine the diffusion coefficient values. The results were related to the classic diffusion model assuming the spherical crystal shape. The model comprising the actual crystal morphology was more realistic and reflects the course of uptake curves clearly better than the classic spherical model does. It yields diffusion coefficient values of about 4 x 10-11m2/s, which were more than twice higher than the classic ones and, at the same time, somewhat lower than those from the measurements based on the equilibrium-state methods, including the crystal morphology that could bring closer together the results of non-equilibrium and equilibrium methods. This approach may have a more common applicability for the description of diffusion in crystalline microporous solids.

Is Diffusion Controlled by Crystal Morphology? Inclusion of Morphology to Modelling the n-Hexane Diffusion in MFI-type Zeolites. J.Wloch, J.Kornatowski: Microporous and Mesoporous Materials, 2008, 108[1-3], 303-10