Study On The Polymorphism And Caking Mechanism Of Glycine

Glycine is the simplest amino acid and can be applied in many fields. So far there are three known polymorphs of glycine,namely,formα,βandγ. China is one of the main manufacture countries in the world. However, as the crystallization technology is undeveloped in China, the polymorph of glycine can't be controlled in the production process. Glycine made in China is all of theα-form which is metastable and can easily transform into theγ-form during storage. The polymorphic tranaformation can causes caking. The discommodiousness caused by caking in using process is unpleasant. In allusion to the problems mentioned above, the crystallization conditions ofα- andγ-form and the polymorphic transformation mechanism were investigated systematically.The single crystals ofα- andγ-glycine were crystallized in different solution environments. The crystal structures were tested through the single crystal X-ray diffraction (XRD) and powder X-ray diffraction. The packings of molecules in the single crystals ofα- andγ-glycine were analyzed. The analytical method of polymorphic mixture ofα- andγ-glycine was certained by the powder XRD pattern.The solubility ofα- andγ-glycine in pure water and the NaCl and NaOH aqueous solutions were measured experimentally by the laser dynamic method. The experimental data were correlated with Van't-Hoff equation and Grant equation. It was found that Van't-Hoff equation and Grant equation could correlate the solubility data very well. Polymorphic transformation of glycine was analyzed thermodynamically. The thermodynamic properities of polymorphic transformation and fusion process ofα- andγ-glycine was tested by Differential Scanning Calorimetry (DSC).The crystallization processes of different polymorphs of glycine were studied experimentally. Crystallization mechanisms of different forms of glycine were ananlyzed. The effects of several parameters on the polymorphic transformation were investigated experimentally and theoretically. Through systemic study of the polymorphic crystallization and transformation, the operational conditions of the crystallization of the appointed form and the effect factors of polymorphic transformation were obtained. It supplied the evidences to realize the control of the polymorph of glycine and avoid polymorphic transformation and caking during storage.