Comparison of the Effects of Crystalline Particle Size Modified by Crystallization on the Mother Liquor Removal Profiles of Washing and Reslurry

In industrial crystallization, the mother liquor recovered with the crystalline product causes a significant decrease in product purity. Therefore, additional purification processes, such as washing or reslurry, are often necessary to remove mother liquor from the particles to produce high-purity crystalline products. Although it is important to understand the characteristics of the purification processes for effective removal, a direct comparison between these different purification processes has rarely been reported. Therefore, the characteristics of washing and reslurry were compared using particle properties determined by crystallization. Herein, the mother liquor removal profiles of washing and reslurry were investigated considering changes in the removal ratio. We compared the profiles by normalizing the operating loads in each purification process. The purification processes were characterized by analyzing the particle-size dependency on the removal profiles. The results suggested that the removal profiles of washing and reslurry depended on the particle sizes, and the removal ratio was higher for reslurry for all ranges of loading when the particle size was identical. According to the proposed classification of mother liquors, by introducing the consideration of removability, we found that a primary cause was the ratio of mother liquor segments, which can change between different states of the particles during washing or reslurry. The effect of decreasing particle size on improving mother liquor removal in reslurry was more significant compared with that of washing. Therefore, reslurry is more beneficial for mother liquor removal by particle size modification via crystallization, compared with washing. This study provides primary knowledge on the operation design of the crystallization process for purification

Effects of Properties of Crystalline Particles on Mother Liquor Holdup in Crystal Cake and Residue Behaviors of Impurities

In industrial crystallization, all impurity species need to be removed, regardless of the kind of impurity present in the raw materials. Removing the mother liquor is required because a crystal cake with mother liquor holdup is frequently formed by crystalline particles during solid-liquid separation in suspension-type melt crystallization. This study aims to make clear the relationship between the mother liquor holdup and the characteristics of the crystal cake, and the difference in residue behaviors of impurities based on the new concept for understanding the mother liquor holdup. As a result, the initial mother liquor holdup depended on the specific surface area of the crystal cake. Investigating the residue behavior of each impurity suggests that the impurity-based inclusion factors were different from the solvent-based inclusion factor depending on the kind of impurity. Furthermore, a certain impurity had a specific surface area dependence of the residual amount of impurity