A Study On Dilution Crystallization Process For Refining Of 5'-Uridylic Acid Disodium

Uridine is a kind of nucleotide compound, its disodiun 5'-monophosphate salt is of special value for food enrichment. Industrial crystallization is the most important process of producing disodium uridine-5'-monophosphate (5'-UMP Na2). The advanced technology for producing 5'-UMP Na2 is monopolized by Japan and South Korea in the world. Up to now, there are some differences between the home-made and the overseas 5'-UMP Na2 products in terms of the purity, the crystal size distribution and habit, etc. Therefore, the domestic products are incapable in competing with the overseas products in the international market. In allusion to this situatuin, the dilution crystallization process of 5'-UMP Na2 was systematically investigated. The sduty of the crystal structure is very important for exploring the crystal growing mechanism. The diffraction pattern and the single crystal CIF data for 5'-UMP Na2 were collected by powder and single crystal X-ray diffraction technique. The molecular structure and the crystal cell parameters were calculated by the Cerius2 software, and then the crystal habit of 5'-UMP Na2 were predicted by using the BFDH and AE models. The solubilities, the metastable zone width and the nucleation induction period of 5'-UMP Na2 in the mixure solvents with different volume ratio at different temperature were measured by the laser method. The melting point and the phase enthalpy of 5'-UMP Na2 were also measured by Differential Scanning Calorimetry(DSC). The crystallization kineties of 5'-UMP Na2 were studied by the batch dynamic method in this paper. The models for the nucleation rate and the crystal growth rate of 5'-UMP Na₂ were obtained by regressing the kinetic experimental data after translating them in moment forms. The effects of the operational parameters such as the supersaturation and the stir speed on the nucleation rate and the crystal growth rate were analyzed by these models. Based on the studies of the crystallization thermodynamics and kinetics, the crystallization technology of 5'-UMP Na2 was systematically investigated. The experimental results show that in order to get high quality crystal products from the feed liquor containing many impurities, the 5'-UMP Na2 material with high purity should be firstly obtained through a preparatory crystallization process and then be refined through a recrystallization process. The optimal operational condition for the preparatory crystallization process is as follow: a temperature at 10℃ , a stir speed at 400rpm and a ratio of ethanol to the feed liquor at 0.65. Under this condition, a 5'-UMP Na2 material with a purity of higher than 90% can be obtained with a yield of higher than 85%. The optimal operational condition for the recrystallization process is as follow: a temperature at 10℃ , a stir speed at 500rpm, an addition rate of diluent at 0.4ml/min and a seed quantity at 3%. Finally, a 5'-UMP Na2 product with a high purity, an identical CSD and an improved crystal habit was obtained.