Restricted diffusion through granular materials
Article first published online: 17 JUN 2004
Copyright © 1990 American Institute of Chemical Engineers
Volume 36, Issue 2, pages 242–248, February 1990
How to Cite
Limbach, K. W. and Wei, J. (1990), Restricted diffusion through granular materials. AIChE J., 36: 242–248. doi: 10.1002/aic.690360210
- Issue published online: 17 JUN 2004
- Article first published online: 17 JUN 2004
- Manuscript Revised: 27 NOV 1989
- Manuscript Received: 18 JUL 1989
The restricted diffusion of nickel etioporphyrin is experimentally measured in six granular catalyst support materials. These materials include five γ-aluminas and one small-pore silica-alumina. Pore size distribution is narrow for three of the supports and roughly bimodal for the remaining three. Diffusivities are determined by a transient uptake technique utilizing a Freundlich equilibria adsorption isotherm.
Experimentally determined diffusivities agree well with restricted diffusion theory based on a circular pore model when the appropriate characteristic length scales are used to describe the molecule and pore size. For the restricted diffusion of dilute solute molecules in neutral pores, the appropriate measure of granular pore size is the hydraulic pore radius. Molecule size, in this case, is best described by a mean projected molecule radius for partitioning and a Stokes-Einstein radius for hydrodynamic aspects of restricted diffusion.