The geometrical evaluation of effective diffusion coefficient in the liquid phase for porous bodies consisting of spherical elementary particles

To evaluate the intraparticle diffusion coefficient, De, of a component in a liquid, it was assumed that the pore structure of a porous catalyst was a space between an assembly of fine particles. This structure has been found for the metal oxide catalysts. The diffusivity ratio, δ (= De/D), was geometrically estimated in the direction normal to the representative plane (100), (110) or (111) of cubic closed, body centered cubic, simple cubic, or diamond packing of spherical elementary particles. The value δ was found to approximate the porosity ϵ. Larger pore constrictions gave smaller δ/ϵ values. Reaction rates were measured for the hydrogenation of nitrobenzene in ethanol. The efficiency of this evaluation of De was supported by the agreement of the experimental effectiveness factor with the theoretical factor. Pour evaluer le coefficient de diffusion intraparticulaire, De, d'un compose dans un liquide, on a assimile la structure des pores d'un catalyseur poreux a l'espace entre les particules d'un ensemble de fines particules. On a trouve une telle structure pour les oxydes metalliques catalyseurs. Le rapport des diffusivites δ(= De/D), a ete estime geometriquement dans la direction normale aux plans (100), (110) et (111) d'empilements de particules elementaires spheriques de type cubique face centree, cubique centre, cubique simple et de type diamant. On a trouve que la valeur de δ est une approximation de la porosite ϵ. Des constrictions de pores plus gros donnent des valeurs de δ/ϵ plus petites. Les vitesses de reaction ont ete mesurees pour 1'hydrogenation du nitrobenzene en ethanol. La validite de l'evaluation de De est renforcee par la concordance entre le facteur d'efficacite experimental et sa valeur theorique.