Based on the importance of polymorphic regulation, the molecular mechanism of nucleation has been widely concerned. This review begins by introducing the development and limitations of nucleation theory for organic small molecule crystals, followed by a summary of the general research mentality adopted by current researchers. Moreover, the progress of the molecular mechanism of polymorphic nucleation and its application to the regulation of crystal forms are discussed. In addition, the development of scientific tools for the study of the molecular mechanism of polymorphic nucleation is also summarized, including experimental characterization and computational simulation, providing reference for relevant researchers. Finally, according to the main defects of current research and research ideas, research models and development directions of prospects and recommendations are put forward.

In this paper, the transient MRF approach coupled with the standard k-ε and SST k-ω turbulence models was employed to study the effect of bottom shape, impeller diameter (D _J) and bottom height (H ₂) on critical impeller off-bottom clearance (C). It was found the bottom shape and bottom height (H ₂) have obvious influence on the flow pattern transition from double-loop to single-loop of RT impeller. The flow pattern transition mechanism was inferred to relate to the relationship between the space required by the lower circulation zone and the actual space. The boundary conditions of critical C were further concluded to help distinguish the flow pattern and receive the expected one in the stirred vessel design.

Improving the separation efficiency of the layer melt crystallization process is a key but difficult task. Herein, a comprehensive model involving both crystallization and sweating was proposed and used to optimize the operating time of crystallization and sweating processes. The crystallization process was modeled based on the relationship between differential and integral distribution coefficients under a constant layer growth rate. For the sweating process, an empirical sweating equation was employed to govern the sweating model, the parameters of which were determined experimentally using P-xylene as the model substance. The separation efficiency was then optimized by minimizing the operating time at a given product purity and yield. A sensitivity analysis showed that the crystallization and sweating times nonlinearly increase with increasing yield. After the yield exceeds 0.65, an increasing crystallization time is the dominant factor in improving the separation efficiency, while the sweating time and ratio even slightly decrease. The total operating time at low yield is U-shaped with the layer growth rate. The optimal layer growth rate decreases with increasing yield. This model provides guidance for determining the optimal operating parameters of layer melt crystallization and sweating processes.