A Study On The Crystallization Process Of L-Serine

L-serine has many important physiological functions and is widely used in many fields, such as medicine, food, cosmetics, et al. In view of the quality problems of the L-serine product made in China, such as the poor crystal morphology, the low purity, the mixed polymorph and asymmetry CSD. The crystallization process and the polymorphism of L-serine were investigated and analyzed systematically.The solubility and supersaturation of L-serine in water were measured by the laser method. The effects of the cooling rate and the agitation speed on the width of the metastable zone were investigated experimentally.L-serine has the pseudo-polymorphic characteristic. The polymorphic transition temperature is about 310.35K, which is obtained by fitting the solubility data. The monohydrate crystal would be grown from the aqueous solution under 310.35K, while the anhydrous crystals would be grown upon this transition temperature. Thus, in order to obtain large-sized anhydrous L-serine product, the final temperature of the cooling crystallization process should be higher than 310.35K.The structures of the monohydrate and anhydrous crystals were tested by the single crystal X-ray diffraction, and the structure parameters of these two crystals were obtained. The polymorphic transition phenomenon of L-serine in the cooling crystallization process was real time monitored by Particle Vision Measurement and Focused Beam Reflectance Measurement. When the slurry is cooled under the polymorphic transition temperature, the rod-like anhydrous crystals will translate to the hexagonal monohydrate form.The habits of the monohydrate and anhydrous L-serine crystals were simulated by Cerius2 software with BFDH and AE models. After comparing with the experimental results, it is found that the habits predicted by AE model quite resemble those obtained in the experiments.Based on the study of thermodynamics and pseudo-polymorphic phenomenon of L-serine, comparative analysis of the cooling, evaporation and dilution crystallization methods were performed. An optimum vacuum evaporation crystallization technology was finally developed. The effects of operational parameters, such as the final temperature, seeding, the agitation speed, the evaporation rate and drying, on the quality of the final product were investigated. The L-Serine crystal product obtained by the optimum technology is completely anhydrous with main size larger than 400 μm. The quality of the product measures up the international standards.