Evaluation of the Effect of Seed Preparation Method on the Product Crystal Size Distribution for Batch Cooling Crystallization Processes

Abstract

This paper provides an experimental and simulation based analysis of the effect of seed quality on the shape of the product crystal size distribution of a seeded batch cooling crystallization process. Various seeds were prepared using different protocols, involving milling, washing, and sieving. The cooling batch crystallization processes of potassium dichromate in water with the different seeds were monitored using process analytical technologies (PAT), such as attenuated total reflectance (ATR) UV/vis spectroscopy, focused beam reflectance measurement (FBRM), and online laser diffraction for real-time crystal size distribution measurement. A population balance model with apparent size-dependent growth, which incorporates the effect of growth rate dispersion, is used to simulate the evolution of the crystal size distribution (CSD) using the different seed distributions as initial conditions. The simulation results were in good agreement with the experimental product CSD, when the good quality crystalline seed was used with no fines. However, the mean crystal size of the product was overpredicted by the growth-only model, when milled seeds were used with different fine contents. This was caused mainly by the excessive initial breeding, due to the different surface properties resulting from the preparation method, the Ostwald ripening promoted by the fines, and the pronounced agglomeration observed in these cases during the experiments. The simulation and experimental results provide evidence of the importance of consistent and well-defined seed quality and suitable preparation procedures for high quality crystalline products.