(784e) Simulation and Experimental Studies of Dry Catalyst Impregnation for Improved Content Uniformity and Scale up

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. Current scale-up practices lead to poor fluid distribution and inhomogeneity in metal content. The aim of this work is to understand the dynamic behavior of the particles under the spray nozzle, which is essential for desired content uniformity, and to develop a scale-up model for the dry impregnation process.

In this work, Discrete Element Method (DEM) simulations coupled with a novel algorithm allowing the transfer of metal solution to and between particles were used in combination with geometrically equivalent experiments to model dry catalyst impregnation. Metal adsorption is considered in the simulation for accurate metal/liquid transfer. Once a droplet of metal solution, containing the metal ions, comes in contact with a support particle, the droplet penetrates into the pores. The deposition of the metal ions takes place during the equilibration of the liquid phase inside the pores and solid surface of the pores. The adsorption mechanism can be modeled by Langmuir isotherm, which depicts a relationship between the extent of adsorption of the surface (or the fraction of the adsorption sites occupied) and the molar concentration of the solution. Solving Langmuir model coupled with the mass balance, the equilibrated absorbed metal and the concentration of metal in the liquid phase can be calculated. Simulation results are compared with experiments with identical setup, where nickel nitrate hexahydrate was dissolved in aqueous solution and used as the metal precursor. Experiments were conducted at a rotation speed of 9 rpm and a spray rate of 1.7 L/hr. Good agreement was observed in the metal content in particles along the axis of rotation.

Two dimensionless numbers are used to characterize the scale up of the system: Froude number (Fr) and Spray Flux number (Ψ). The Froude number is defined as the ratio of inertial force to gravitational force. The calculation of Fr gives the correlation between rotation speed (Ï?) and vessel size (R). Spray Flux number measures the density of spray droplet in the spray zone. The location and area of spray zone can significantly affect the overall content uniformity. Results in the cylindrical vessel show that a homogeneous liquid distribution with optimal particle mixing is obtained by minimizing the spray rate and Ψ for an optimal Fr number. It is found that keeping Fr number at the optimal value and lower spray rates increase the content uniformity of the resulting particles. The ability to control dry impregnations and establish effective models for large batches can significantly reduce the amount of time required per batch while simultaneously achieving a more homogeneous distribution of metal ions.