Study On The Crystallization Process And The Polymorphism Of Glycine

Glycine is the simplest amino acid and can be applied in many fields. Based on the quality problems of the glycine product made in China, such as poor crystal morphology, mixed polymorph and asymmetry CSD, the crystallization process and the polymorphism were investigated and analyzed systematically.The solubility of glycine in pure water and water-ethanol of different ratio was measured by dynamic method, which was shown that the solubility in water was fitted byλh equation preferably, while the solubility in water-ethanol was fitted by linear; The metastable zone was measured by laser method and the effects of cooling rate and agitation speed were investigated experimentally. The induction period of the crystallization process of glycine was also studied, by which the surface tension between crystal and solution was calculated.The cooling crystallization kinetics of glycine in water and water-ethanol were measured experimentally by batch dynamic method. The ASL and MJ2 size-dependent model were chosen to deal with the experimental data. By means of the moment transform method, the equations of the nucleation and crystal growth rates in the crystallization process of glycine in water and water-ethanol were obtained through the least square multivariate linear regression. The polymorphism of glycine was then investigated. The cultivating experiment of single crystal shown that theα-single crystal can be obtained by slow evaporation of the water solution of glycine, whileγ- single crystal can be obtained by adding NaCl or NaNO3. The crystal structures and parameters of the two polymorphs were gained through single crystal X-ray diffraction, power X-ray diffraction and IR. The polymorphic transformation was tested by DSC experiment. The results show thatαandγ-phase are belong to enantiotropy and the transformation between them is irreversible and endothermic. The morphologies of glycine under vacuum condition and in water solution were simulated by Cerius2 software with BFDH and AE models. After comparing with the experimental results, it is found that the morphologies ofα-phase simulated by AE model quite resemble those obtained in the experiments. Aimed at the quality demand of the glycine crystal product, the effects of operational parameters such as crystallization method, cooling rate, agitation intensity, seed and adding rate of ethanol etc. on the CSD, yield and morphology were investigated systematically by experiment and the experimental optimum operational conditions for the crystallization of glycine were finally obtained.