(348a) Liquid Transfer between Particles in the Impregnation of Catalysts in a Rotating Drum: Axial Dispersion Studies and the Effect of Particle-Particle Contact

Impregnation of active metals onto a porous catalyst support is an important step in the preparation of heterogeneous catalysts. In a typical 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. The dispersion of material in the axial direction is the most critical factor determining the final uniformity of metal content in the particle bed. The aim of this work is to characterize water/metal transfer in an alumina particle system, which is essential for a desired content uniformity in the catalyst impregnation process.

A series of mixing experiments and matching simulations were designed to characterize the axial dispersion in a horizontally rotating cylinder. The experiments are initially set up with a 3-inch band of the impregnated particles located at the center of the cylinder. At each side of the center band, a band of dry particles is placed in a symmetric way. The cylinder is set to rotate for 16 minutes at a constant rotational speed, with samples being taken at 5 evenly spaced locations along the rotational axis, every 2 minutes. The concentration profiles of water or metal content start with a maximum value at the center, and then as time progresses the profiles approach a flat line. Based on a “wide band” model [Sherritt et al, 2003], axial dispersion coefficients are calculated for the cases of both metal transfer and water transfer in the rotating drum. Results are compared between the same experiment made with water or metal solution and show that in the rolling regime the dispersion coefficient increases with the rotational speed.

In addition, a particle-particle contact experiment was designed to further understand the impregnation of liquid with different concentrations and to determine simulation parameters to be incorporated in the liquid transfer algorithm. A fully impregnated particle (saturated with water or nickel nitrate solution of different concentrations) is placed next to a dry particle on the bottom of a small vial. Transfer of liquid is observed during different lengths of contacting time (range from 1min to 20min). Results show that the rate of transfer for a concentration of 3M is 2 times larger than that of 0.1M. Impregnation simulations incorporating different rates of transfer are considered and different metal concentrations are compared.