DIFFUSION OF N-PARAFFINS IN OFFRETITE-ERIONITE TYPE ZEOLITES

Intracrystalline diffusivities are reported for a series of n-paraffins (C-6 to C-20) in four different offretite-erionite intergrowths with constraint indices (CI) varying from 2.1 to 115 (a low value of CI corresponds to nearly pure offretite, whereas a high value corresponds to erionite). The intracrystalline diffusivities for each sample show a monotonic decrease with carbon number, except for one of the intermediate samples (HZSM-34), which has the highest proportion of extraframework-AI. For the sorbates studied, the diffusivities decrease with the CI. Activation energies show different trends with carbon number, depending on the erionite/offretite character of the sample. The experimental evidence does not support the existence of a window effect, as suggested by Gorring (Gorring, R.L. J. Catal. 1973, 31, 13) on the basis of measurements with a zeolite of similar structure.