Determination of Intraparticle Diffusivities Using a Single Pellet String Fixed Bed and a Shallow-Bed Diffusion Cell

Abstract

Two experimental techniques and the corresponding theoretical models were used for determining gas adsorption equilibria and intraparticle mass transport parameters. These methods include a diffusion cell adapted to be used with small particles (shallow-bed diffusion cell) and the chromatographic method using a single pellet string fixed bed. The experimental systems used were oxygen, nitrogen, and argon in helium over the Rhone Poulenc 4A and 5A zeolite and LaRoche alumina at various temperatures. The conditions where other mass transport resistances can be neglected (film diffusion in the chromatographic method) or independently obtained (bulk diffusion in the cell and axial dispersion in the fixed bed) are discussed. Also, a sensitivity analysis is used which shows that it is not possible to estimate the microparticle diffusivities in 5A zeolite and LaRoche alumina and also the macropore diffusivities in 4A zeolite. In the last case we assume that the macropore diffusivities are the same as in 5A because both zeolites come from the same manufacturer and so possibly only differ in the type and number of cations. The temperature dependency of the microparticle diffusivities follows an Arrhenius-like equation. The consistency of the results obtained by both methods confirms that the experimental techniques and the corresponding models are reliable. Also, the shallow-bed diffusion cell presents some advantages over the chromatographic method, such as simplicity, easy temperature control, no need for evaluation of flow patterns, and smaller amounts of materials