(538c) Optimization of Catalyst Impregnation Process Using a Combination of Experimental and DEM Modeling Study

Catalyst impregnation is one of the most crucial steps for preparing industrial catalysts. In this process, metal salts or complexes are typically dissolved in an aqueous solution and contacted with a porous oxide catalyst support such as alumina (Al2O3) or silica (SiO2). During a contact time of typically 30-60 minutes the metal is adsorbed from the solution onto the high surface area support. The catalyst is dried and further pretreated to transform the metal from its precursor state into its active form. Generally, the process of impregnation is performed in rotating vessels with one or more nozzles that distribute the solution with the metal precursor into the catalyst support. This study aims to optimize the impregnation process by studying the fundamental process of water absorption to and transfer within particles using a combination of designed experiments and discrete element method (DEM) based mechanistic modeling. A Patterson-Kelly double cone blender with a retrofitted impregnator featuring a central spray nozzle was used for experimental study. The catalyst support in the form of spherical beads of &gamma-Alumina was impregnated using 1M Copper (II) Nitrate Trihydrate solution. Experiments were ten minutes in duration; each minute seven samples were removed from the catalyst bed using a disposable powder thief for a total weight of approximately two grams bed; samples were 3.5 cm apart. Samples were dried and weighed for water content. Subsequently, samples were soaked in 10 mL of 0.1 M HCl for 12 hours to remove the metal, the resulting solutions were then tested for copper concentration using an Ocean Optics (USA) UV-Spectrophotometer. Three flow rates (1.5, 2.5 and 5L/Hr) were used for impregnation. It was found that the water and metal distribution was more uniform at low spray rates. Density segregation was also observed with heavier particles (due to water impregnation) preferring the center region of the bed. The computational study using discrete element method was performed using EDEM? (DEMSolutions Inc.). The contact model was modified so that there were two groups of particles, the Alumina particles and the smaller water droplets which form a spray. The water droplets add their weight to the Alumina particles as soon as they hit them. Once supersaturated, the Alumina particles can transfer water to any unsaturated particle. The DEM simulations agree with the experimental findings and suggest that lower flow rates produce a more uniform moisture distribution in the bed.