(380ag) Effect of Viscosity on Liquid Penetration in the Catalyst Impregnation Process: Experiments and Simulations

Dry catalyst impregnation of active metals onto a porous catalyst support is an important step in the preparation of heterogeneous catalyst. In a typical dry impregnation process, metal solutions are sprayed over a particulate bed in a mixing vessel until the pore volume is reached. The inter-particle variability of the impregnated liquids inside the particles and metal content may significantly affect the activity and selectivity of the resulting catalyst. In this process, metal salts or complexes are dissolved in a typically aqueous solution and added to porous catalyst support particles. The viscosity of the metal solution can affect the penetration and diffusion of the liquid into the pores. The aim of this work is to understand how viscosity of the metal solution affects the impregnation process and how the viscosity affects the uniformity of the liquid content in the particle bed.

We studied impregnation of alumina particles with viscous solutions consisting of different level of viscosities and concentrations of Nickel Nitrate and Polyethylene Glycol (PEG, molecular weight of 400 g/mol). Polyethylene Glycol was considered as the viscous agent in our experiments. The viscosities of the PEG solution with different concentrations were measured by a Brookfield DV3T viscometer. Impregnation of viscous solutions on alumina particles were performed and compared with one to one DEM simulations.

We developed a new viscous liquid transfer algorithm that is based on a Langmuir isotherm. We performed a series of adsorption experiments with the goal of determining the adsorption parameters used in the Langmuir isotherm with two adsorption parameters: K_L is the equilibrium constant and q_max is the maximum adsorption capacity.

We developed a predictive model for the impregnation and transfer of a viscous solution in a rotating vessel. We performed experiments to obtain the Langmuir parameters (K_L and q_max) for different values of viscosities, and we observed that for low values of the viscosities qmax does not show a lot of variation until 2cp, but for viscosities > 2cp, it decreases with increase in viscosity. In general, experimental results show that the viscosity delays the impregnation process. The higher the viscosity the longer it takes to reach the equilibration phase. Metal absorbed in the pores depends strongly on the viscosity of the solution. In general, higher the viscosity, smaller the amount of metal absorbed. We also found the viscosity of the solution affects the Langmuir equilibrium parameters K_L and q_max, which decrease with increasing viscosity. DEM simulations incorporating these parameters for a viscous solution were considered to reveal the amount of metal absorbed and the uniformity of the particle bed. Using the Langmuir model coupled with the mass balance, the total amount of metal absorbed on solid and the amount metal in the liquid phase can be calculated. Our simulation results show good agreement with the experiments. Both DEM simulations and experiments confirm that metal absorbed in the pores depends strongly on the viscosity of the solution.

In addition, we studied the penetration time of viscous PEG solution droplet into alumina particles. The drop penetration time is defined as the time taken for the drop to penetrate completely into the porous particle with no liquid remaining on the surface. Results show that that the penetration time increases with solution viscosity.