Study On Crystallization Process Of 24-Epibrassinolide

24-epibrassinolide is a plant growth regulator with strong physiological activity.It can show various activities at low concentration,and can greatly promote plant growth,so it has a good application prospect.Currently,research on the 24-epibrassinolide crystallization process is few,with the majority of studies focusing on the substance’s production route and effects on plant development.Moreover,there are certain issues with the 24-epibrassinolide production process,including high production costs,low yields,a wide grain size distribution,and small crystal size that make filtration challenging.Based on this background,the crystallization process of 24-epibrassinolide was systematically studied in this paper,and a new crystallization process of dilution and cooling coupling was developed.The solubility of 24-epibrassinolide in binary mixed solvents（ethanol+water,isopropanol+water,acetone+water,acetonitrile+water）at different temperatures and mole ratios was determined by laser dynamic method,and the solubility patterns of24-epibrassinolide with temperature and solvent composition were obtained.The solubility data were correlated using Apelblat model,Van’t Hoff model,NRTL model,Wilson model and Three-Suffix Margules model,and the models were evaluated based on ARD and RMSD values.The solubility of 24-epibrassinolide in mixed solvents was analyzed by preferential solvation method.Based on experimental data and Wilson model parameter values,thermodynamic mixing properties(Δ_mixG、Δ_mix、Δ_mixH)of24-epibrassinolide in different solvent systems were calculated.The thermodynamic data provide the data basis for the subsequent development of the crystallization process.Based on the experimental data of the induction period and the classical homogeneous nucleation theory,the nucleation parameters,such as solution interfacial tension,surface entropy factor,critical nucleation radius,and nucleation free energy,were determined.The batch dynamic method was used to study the kinetics of the crystallization process of 24-epbrassinolactone in ethanol+water system.The growth rate model and nucleation rate model of the crystallization process of 24-epbrassinolactone in ethanol+water system were calculated based on the population balance and the moment transformation method.The results provided theoretical support for the experimental design of process optimization.Under the guidance of the analysis of crystallization thermodynamics and crystallization dynamics,a 24-epibrassinolide diluting-cooling coupling crystallization process was developed,and the single factor experiment was used to investigate the effects of different crystallization process conditions（stirring rate,diluent drop addition amount,diluent drop acceleration rate,crystallization time,crystallization end point temperature and seed addition amount）on the particle size and distribution of crystalline products.The optimal process parameters were determined.The crystal products with large average particle size,concentrated particle size distribution and good fluidity were prepared by the optimized process.