Predicting the Effect of Drying on Supported Coimpregnation Catalysts

Abstract

In this paper, a model was developed to describe the catalyst redistribution that occurs during drying of a coimpregnation catalyst. The model takes into account convective flow, catalyst and coimpregnant diffusion, adsorption on the support, and transport in the gas phase. For low catalyst adsorption capacity and low initial coimpregnant concentrations, the system behaves in a manner similar to systems without a coimpregnant. At higher coimpregnant concentration when the coimpregnant has the higher adsorption constant, the catalyst faces strong competition for adsorption sites at the external surface. It therefore migrates toward the center where free sites are available. If the catalyst has the higher adsorption constant, it adsorbs preferentially at the surface, and the coimpregnant hinders the back-diffusion of the catalyst. This can lead to rather sharp egg-shell profiles. Finally, we discuss how to develop a drying strategy that will lead to a desired catalyst profile.