Effects of solution composition and operational conditions on the characteristics of particles via oiling-out

In crystallization processes where particles precipitate from a liquid phase, the occurrence of oiling-out often hinders precise control over crystallization and particle characteristics. However, when oiling-out occurs, it can form a solution composition with an exceptionally high concentration driving force. This study explored the utilization of oiling-out, which is typically considered undesirable, aiming at the production of crystalline particles with unconventional characteristics. Specifically, the effect of the unique solution composition formed by oiling-out and multiple operational conditions such as rotation speed and temperature when the oiling-out occurs on the characteristics of crystalline particles was investigated.

The experimental results show that the particle size and agglomeration behavior were strongly affected by the solution composition. Evaluation using local concentration driving force (ΔC_Local) revealed that the high ΔC_Local generated by oiling-out leads to the precipitation of fine primary particles. Furthermore, secondary particle size increased as ΔC_Local increased. Consequently, it was suggested that the agglomeration degree of crystalline particles can be controlled by the ΔC_Local.

Additionally, this study experimentally demonstrated that both particle sizes and agglomeration behavior could also be changed by operational conditions. In particular, it was found that the sizes of both primary and secondary particles could be varied by approximately two by adjusting the rotation speed and temperature under the solution composition formed by oiling-out. These findings provide fundamental insights into the utilization of oiling-out as a method for obtaining crystalline particles with unconventional characteristics.