Kinetics of ε‑CL-20 during Reduced Pressure Evaporation Crystallization

In this work, the efficient crystallization of ε-CL-20 was achieved through precise reduced pressure evaporation, enabling the preferential separation of the good solvent. This novel method, compared with previous techniques, resulted in a more gradual change in CL-20 concentration, a more uniform particle size distribution, and excellent crystallization efficiency ensured by the high driving force. Additionally, the ASL model was employed to accurately describe the size-dependent growth behavior of the ε-CL-20 crystals. Nonlinear fitting methods were used to determine the nucleation and growth kinetic equations of the crystals under reduced pressure evaporation in three binary solvent systems (ethyl acetate + bromobenzene/dibromomethane/1,1,2,2-tetrachloroethane). Process experiments validated the kinetic equations: 1,1,2,2-tetrachloroethane system produced crystals with the highest growth rate and most uniform particle size distribution; the bromobenzene system exhibited the highest nucleation rate, yielding the smallest crystal size, while the dibromomethane system was the least sensitive to external influences and produced the largest crystal size. A moderate increase in the stirring rate was found to enhance mass transfer and crystal growth. These findings provide new insights into the production of ε-CL-20, offering theoretical guidance and data support for solvent system selection, experimental parameter optimization, and particle size distribution control.