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A simple method of distinguishing between one-dimensional and three-dimensional diffusion in zeolite crystals is suggested based on the difference in the expressions obtained for the zerolength column (ZLC) desorption curve for slab and spherical diffusion models. The application of this approach is illustrated by experimental data for diffusion in erionite (three-dimensional channel system)...
A wall-coated capillary column provides a relatively simple macroscopic method for measuring intracrystalline diffusion in small (micron-sized) zeolite crystals. We report here a procedure for the preparation of such columns.
The self-diffusivity of methanol in NaX zeolite has been measured, at 100°C, over a wide range of concentration, by the newly developed tracer ZLC (zero length column) technique. The diffusivity values agree well with the values measured by p.f.g. n.m.r., and the unusual maximum in the trend of self-diffusivity with loading, shown by the n.m.r. data, is confirmed.
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...
A novel method of measuring diffusion in small (micron-sized) zeolite crystals has been developed based on measurement of the chromatographic response for a capillary column, the internal surface of which is coated with an incomplete monolayer of the zeolite crystals. Special techniques are needed to prepare such a column; in the commercially available wall-coated zeolite columns the surface coverage...
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