Falling film melt crystallization (III): Model development, separation effect compared to static melt crystallization and process optimization

• Develops model to simulate the crystal layer growth and melt migration in SMC.
• Compares the separation effect of SMC and FFMC in details.
• Demonstrates the solidification of low solubility phosphate on the crystal interface, largely ignored up to now.
• Optimizes cooling and sweating profiles of melt crystallization.
• Proposes combined process to prepare the ultrapure chemicals with high efficiency.

This article describes the development of a model for the processes of crystal layer growth and sweating in static melt crystallization (SMC). Model foundations and fractal porous media theory were introduced from models of falling film melt crystallization (FFMC). Consistent simulation results were obtained for this model without using a fitting parameter. A systematic comparison of SMC and FFMC was conducted to reveal the advantages and disadvantages of separation in these two melt crystallization modes. The resulting models were used to optimize key operational profiles in FFMC and SMC. The average effective distribution coefficients Keff¯ of calcium and sodium ion impurities were determined to be 0.03 and 0.025, respectively, for a combined FFMC and SMC operation. The separation potential of melt crystallization is being explored using various models and simulations for application in the industrial preparation of ultrapure chemicals.

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