(539b) Comparison of Modeling and Experiments for Impregnation and Drying of Nickel-Alumina Catalysts

Supported catalysts are essential components in a variety of industrial processes, ranging from catalytic converters to production of new drugs. They are generally required because of their high surface area and high mechanical and thermal stabilities. The performance of a catalytic process is intimately related to the catalyst design - uniform, egg-yolk, egg-shell and egg-white metal profiles. Although catalyst preparation and catalytic processing have been investigated for many years, many aspects of catalyst manufacturing are still not fully understood and in industry the design of catalysts is usually based on trial and error.

It is generally believed that the metal profile is controlled by the conditions that are applied during impregnation where the metal contacts the solid support for the first time. However, experimental work has shown that drying may also significantly impact the metal distribution within the support. Therefore, to achieve a desired metal profile we need to understand both impregnation and drying. To the best of our knowledge, previous work has examined impregnation and drying separately. Therefore, the connection between impregnation and drying is not clear, and the impact of impregnation on drying has not been fully understood.

In this work we have developed theoretical models to simulate the impregnation and drying processes of Nickel/Alumina systems. The initial input of the drying model comes from the results from the impregnation simulations. Therefore, we can combine impregnation and drying together to analyze their effects on the preparation of supported catalysts. By computing regime maps, we find for weak or moderate adsorption, the final metal profiles are mainly determined by the drying conditions. For strong adsorption, the effect of impregnation on the final metal distribution becomes pronounced. This is determined by the ratio of the amount of the metal dissolved in the solvent to the amount deposited on the support during impregnation.

Of particular interest is to compare simulation results and experimental measurements to determine the key parameters used to predict the impregnation and drying processing. Experimental work has been carried out for impregnation and drying of Nickel/Alumina systems. To compare simulations and experiments, four parameters in theoretical models are required to be obtained from separate experiments: 1) the metal effective diffusion coefficient into the pores of the support, 2) the equilibrium adsorption constant and 3) the kinetic adsorption constant of the adsorption and desorption processing, and 4) the permeability of the support. We have established separate experiments to measure / calculate the above parameters. For low drying rate (uniform profiles), the simulations compare well with the experiments without considering the effect of film-breakage. For high drying rate, film-breakage becomes important to capture the egg-shell profiles.