CONSEQUENCE OF DISTRIBUTED PROPERTIES ON EFFECTIVE DIFFUSIVITIES IN POROUS SOLIDS

Effective diffusivities in porous solids are global parameters which lump a complicated geometrical structure together with the diffusion process. Lumping is different depending on the measurement method and this may lead to strongly biased coefficients. Three geometrical effects are studied - Effect of pore size distribution on apparent diffusivities measured by Wicke-Kallenbach method, chromatographic method and diffusion limitation of a first order catalytic reaction - Influence of external porosity distribution in a packed bed - Effect of crystal size distribution in zeolite based catalysts. These three examples show that raw effective diffusivities have to, and can be corrected for geometrical effects. © 1990.