DETERMINATION OF INTRAPARTICLE DIFFUSIVITIES USING A SINGLE PELLET STRING FIXED-BED AND A SHALLOW-BED DIFFUSION CELL

Two experimental techniques and the corresponding theoretical models w ere used for determining gas adsorption equilibria and intraparticle m ass transport parameters. These methods include a diffusion cell adapt ed to be used with small particles (shallow-bed diffusion cell) and th e chromatographic method using a single pellet string fixed bed. The e xperimental systems used were oxygen, nitrogen, and argon in helium ov er the Rhone Poulene 4A and 5A zeolite and LaRoche alumina at various temperatures. The conditions where other mass transport resistances ca n be neglected (film diffusion in the chromatographic method) or indep endently obtained (bulk diffusion in the cell and axial dispersion in the fixed bed) are discussed. Also, a sensitivity analysis is used whi ch shows that it is not possible to estimate the microparticle diffusi vities in 5A zeolite and LaRoche alumina and also the macropore diffus itivites in 4A zeolite. In the last case we assume that the macropore diffusivities are the same as in 5A because both zeolites come from th e same manufacturer and so possibly only differ in the type and number of cations. The temperature dependency of the microparticle diffusivi ties follows an Arrhenius-like equation. The consistency of the result s obtained by both methods confirms that the experimental techniques a nd the corresponding models are reliable. Also, the shallow-bed diffus ion cell presents some advantages over the chromatographic method, suc h as simplicity, easy temperature control, no need for evaluation of f low patterns, and smaller amounts of materials.