Study On The Crystallization Process Of L-proline

L-proline is one of the most important parts of biological organisms, which is a non-essential amino acid. L-proline is prepared usually by three methods: chemical synthesis, protein hydrolysis and biological fermentation. Ion-exchange is used to separate the mixture of L-proline and L-hydroxyproline during the protein hydrolysis of celluloid, There are 95%(mass fraction) L-proline and 5%(mass fraction) L-hydroxyproline in the waste water, No report to separate L-proline and L-hydroxyproline in the residual water has been published in literature up to date. This paper, dilution and cooling crystallization for separation of L-proline and L-hydroxyproline was presented based on a systematic study of crystallization thermodynamics, crystallization kinetic and crystallization process.The single crystal of monoclinic L-proline monohydrate cultivated by evaporation was analyzed by X-ray single crystal diffraction, And its structure was determined. The crystals of L-proline and monoclinic L-proline monohydrate were of the different structure and thermal properties were characterized by X-ray powder diffraction, Thermogravimetry(TG) and Differential Scanning Calorimetry(DSC).The solubility of L-proline and L- hydroxyproline in water, methanol, and the aqueous alcohols(methanol, ethanol and isopropyl alcohol) mixtures was measured by a dynamic method via a laser monitoring technique. The experimental solubility was fitted by modified Apelblat equation. Isopropyl alcohol was chosen to be the anti-solvents for drowning-out crystallization by experimented data. Based on the experimental data of L-proline, the dissolving enthalpy and entropy were calculated by Van’t Hoff equation. The metastable zone width was also measured by the laser method and the effects of cooling rate and stirring rate were investigated experimentally.The factors that influence L-proline crystallization of dilution and cooling in aqueous solution and methanol solution, respectively, such as cooling rate, agitation speed, breeding time and addition rate of diluent et al., were explored in detail. And the optimal operation parameters were determined.The crystallization processes of the waste water of protein hydrolysis were optimized and the L-proline crystal product has been produced by the dilution and cooling crystallization.