Study On The Reactive Crystallization Of S-Benzyl-L-Cysteine

Reactive crystallization is a crystallization process by the chemical reaction oftwo or more components to produce supersaturation. It is one of the basic separationtechnology of chemical engineering. This technology was actively researched in 50'sand 60's of last century, but the research related to the reactive crystallization kept alag till the late 80's when this technology drew the attention of the researchers again.Nowadays the reactive crystallization technology is widely applied in fields of finechemical engineering, bio-chemical engineering and pharmacy. Specially the reactivecrystallization technology is very actively applied in the bio-chemical engineeringfield. In the present thesis, the reactive crystallization process of S-Benzyl-L-Cysteine(SBC) was investigated theoretically and experimentally. Solubilities of SBC inwater-ethanol system and water system were determinated and compared, therelationship between solubility and temperature was established. Solid-liquidinterfacial tension in process of SBC reactive crystallization was calculated withMullin equation, and with which, supersaturation was estimated, and metastabe zonewas predicted. In process of SBC reactive crystallization, the reaction temperature andpH of solution affected the solubility, supersaturation, and matastabe zone of thesolutes, and the effect of solution pH on SBC solubility was investigated, also theisoelectric point of SBC was confirmed as 5.50. Based on the results of investigation, the optimum conditions of SBC reactivecrystallization were obtained by orthogonal tests as follows: the feeding rate of themixture of Bzl-Cl/ethanol was 0.73mL/min, the molar ratio of Bzl-Cl and Cys was0.8:1.0, the reaction was conducted at 5℃, the revolving rate of stir was 250r/min.Under the optimum conditions, the yield of SBC was 90.18%, higher than that of theprevious reported. It was investigated with SEM that the better morphology ofcrystalline was obtained, under the optimum conditions, the temperature range of the ⅰABSTRACTmelting point was narrow, which closed to the reported. The test results by IR and MSmatched the standard spectrum reported, and the test result by HPLC demonstratedthe high purity of the products. Finally the main kinetic parameters of crystallization were measured off-line.Related to the population balance equation and mass balance equation, functionrelated to the nucleation and growth was established. With the help of the computersoftware, the coefficients of the nucleation and growth rate equations were obtained.Meanwhile, the relationship of induction time and supersaturation level was derived.When s<4.5, the SBC nucleation was mainly heterogeneous and the order was 4.49,while s>4.5, the SBC nucleation was mainly homogeneous, and the order was 1.48. In the present thesis, the reactive crystallization process of SBC was optimized,and the fundamental theoretical data and practical operation technique were provided,which lays the base for fulfilling the provincial key research program-the enzymaticsynthesis L-Gultathione and means great significance.