Novel zero-length column analysis of desorption curves for single cylindrical pellets

A new analysis model has been developed for measuring intraparticle diffusivity within small cylindrical pellets, by the zero-length column (ZLC) chromatographic method. The model was applied to data obtained for aryl-DMF counter-diffusion in extrudates of zeolite Y and ZSM-5, using a conventional HPLC system, with comparisons drawn to a packed bed of spheres of the same material. It was observed that both single pellet and packed bed ZLC should be used in determining diffusion constants, with each method providing more information on macropore and micropore diffusion respectively. The diffusion constants for single cylindrical pellets resemble those found by PFG-NMR, with diffusion constants calculated within a factor of three, between 10−6–10−7 cm2 s−1. These ZLC results are self-consistent and trend well with PFG-NMR data, for which traditional ZLC measurements typically differ by two orders of magnitude. This study presents novel findings of diffusion data in single cylindrical pellets, and extrudates, often used in industry.