(298i) Impregnation of Catalysts with Viscous Metal Solutions Using Experiments and DEM 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 significantly affects 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 aim of this work is to understand how the viscosity of the metal solution affects the dry impregnation process.

We studied impregnation of Alumina particles with viscous solutions consisting of different concentrations of Nickel Nitrate and Polyvinyl alcohol (PVA, 80% hydrolyzed). PVA solution was used as viscous liquid in our experiments. The viscosities of the PVA solution with different concentrations were measured by a Brookfield DV3T viscometer. Results show that the viscosity of PVA solution is increasing with the increasing concentration.

Langmuir isotherm can be applied to illustrate the adsorption of metal in a viscous solution, where K_L is the equilibrium constant and q_max is the maximum adsorption capacity. The two parameters used in the Langmuir model (K_L and q_max) need to be determined for the adsorption of a viscous solution on alumina. A series of adsorption experiments were performed for different PVA concentrations. The metal concentration at equilibrium (C_e) was measured by UV-Vis Spectroscopy, and the amount of metal adsorbed (q_e) was calculated using a mass balance. Plot 1/C_e vs. 1/q_e, a straight fitting line was obtained and the two Langmuir equilibrium parameters were derived from the intercept and slope for different viscosities. Experimental results show that the viscosity slows down the impregnation process. The higher the viscosity the longer it takes to reach the equilibration state. The metal absorbed in the pores depends strongly on the viscosity of the solution. The higher the viscosity the smaller the amount of metal is absorbed. We also found the viscosity of the solution affects the Langmuir equilibrium parameters K_L and q_max, which decrease with increasing viscosity.

In addition 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.