Study On Crystallization Process Of L-Threonine

Threonine is one of the eight necessary amino acids to human beings. It has great importance in food, pharmatheutical and forage industry. There were some problems about local threonine product for medicine, such as small crystal size and bad morphology. Therefore study on crystallization of Threonine was carried out.The crystal of Threonine produced using the crystallization process designed by our laboratory was analyzed by X-ray diffraction and its structure was determined. Using the Cerius2 software, the threonine crystal morphology in the vacuum was calculated based on BFDH principle and AE principle. The factors that may affect the crystal habit, including impurity in mother liquid, organic solvent (such as ethanol, acetone and Isopropanol) were discussed.Crystallization threomdymics is the key factor in diciding the production yield and the selection of crystallization process. In this thesis, the solubility and metastable zone of threonine was determined using laser method. The effect of cooling rate, temperature and agitation rate on the width of metastable zone was studied. Through experiments it was found that the liquid-solid equilibria had little or no influence on the vapor-liquid equilibria. The vapor-liquid equilibria relation during evaporation crystallization process was studied on the basis of observation and theoretical analysis.Crystallization kinetics is the basis for understanding of the crystallization behavior and crystallizer scale-up design. According to the crystallization process, the unsteady state method was employed to measure the nucleation and growth kinetics and the equations of nucleation and growth rate of threonine in pure water were got. The effect of operation parameters on nucleation and growth rate was discussed.On the basis of thermodynamics and kinetics study, the coupling crystallization process of vacumm evaportion and cooling was optimized experimentally. The effect of parameters, such as seeds added, agitation speed, fine resolve water, evaporation rate, cooling rate, on the product quality was studied. The crystallization processes were optimized and the threonine crystal product has been produced with the size of 559.36um and the C.V. of 95.95%. The product purity was 99.5% and met all the requirements of Chinese Pharmacopoeia 2000 edition and the Pharmacopoeia of foreign advanced countries.