In this study the influence of pH and ionic strength on the final metal distribution is investigated. After impregnation, catalysts are usually dried at temperatures between 50°C and 200°C. During this process, a redistribution of the metal occurs, which is a complex function of the drying conditions, the properties of the impregnating solution and the support material. In our model, transport in the gas and liquid phase is described by the dusty gas model, and the Nernst-Plank equation, respectively. The metal adsorption on the porous support is described by the Revised Physical Adsorption model developed by Agashe and Regalbuto (J. Colloid Interface Sci. 185 (1997) 174). In their model, the adsorption constant is a function of the pH and the ionic strength of the liquid solution. The results show that for a positively charged metal complex, the impact of drying is strong when the initial pH of the liquid solution is below the point of zero charge (PZC). In such a case, the metal accumulates at the particle surface when the convective flow is strong (high temperature), and at the particle center when the solute-metal diffusivity is high. A comparison of our model with a drying model that assumes a constant adsorption equilibrium constant shows that the variations of pH and ionic strength cannot be ignored when the initial adsorption constant is low and the pH below the PZC. In such cases, the adsorption constant increases over several orders of magnitude when pH and ionic strength effects are accounted for.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering
- Drying model
- Ionic strength
- Metal profile
- Supported catalysts