Determination of operating conditions for controlled batch cooling crystallization

In batch cooling crystallization, the supersaturation courses, obtained at different operating conditions, directly influence the crystallization kinetics. Therefore, the product sizes obtained strongly depend on the operating conditions. In order to control the supersaturation level during batch processes, a cooling model was introduced which included the seeding conditions, cooling rate, batch time, and crystallization kinetics. The cooling profiles, which maintain the different constant levels of supersaturation, were, therefore, predicted by numerically solving the model equation. Furthermore, the mean product sizes, obtained with the different specified cooling profiles, were simulated using the mass balance and the moment transformation of the population balance. Based on the simulation results, the relationship between the operating conditions, the supersaturation level, and product size was established. Hence, a strategy to select the appropriate operating conditions, in order to meet the required mean product size, was demonstrated. The results highlight that, by using the developed strategy, the batch cooling crystallization can be operated at optimal conditions, e.g., short batch time, slow cooling rate, or low seed loading. A potassium dihydrogen phosphate (KDP) system was selected for the case study.