Intracrystalline diffusivities were reported for a series of n-paraffins (C6 to C20) in four different offretite-erionite intergrowths (table 18) with constraint indices varying from 2.1 to 115 (a low value of constraint index corresponded to nearly pure offretite, whereas a high value corresponded to erionite). The intracrystalline diffusivities for each sample revealed a monotonic decrease with carbon number, except for one of the intermediate samples (HZSM-34), which had the highest proportion of extra-framework Al. For the sorbates studied, the diffusivities decreased with the constraint index. Activation energies show different trends with carbon number, depending upon the erionite/offretite character of the sample. The experimental evidence did not support the existence of a window effect.

Diffusion of n-Paraffins in Offretite-Erionite Type Zeolites. C.L.Cavalcante, M.Eić, D.M.Ruthven, M.L.Occelli: Zeolites, 1995, 15[4], 293–307

Table 19

Permeability of Zeolite Membranes at 373K