Study On The Crystallization Process Of L-tryptophan

L-tryptophan is one of the essential amino acids for human and animals. It has been widely used in the fields of medicine, food and feed additives. At present, there are some problems in the manufacturing process of L-tryptophan, such as low purity, bad fluidity, defective morphology and so on. In order to improve the quality of L-tryptophan, the crystallization process of L-tryptophan was studied systematically in this article. The detailed contents of research are as follows:The crystal structure of L-tryptophan was investigated by solving the X-ray diffraction spectrum in the software of Materials Studio. Then, the crystal cell parameters, crystal system and space group of L-tryptophan were determined. Based on the data of crystal structure, the crystal habit was predicted by BEDH and AE models. By comparing with the experimental products, the relationship between crystal structure and crystal-growth rate was analyzed. The effects of solvents, coolling rate and ending temperature on crystal morphology were also studied.The solubilities of L-tryptophan in pure water, water with different pH, methanol-water, ethanol-water and 1-propanol-water were measured by synthetic method. Then, the experimental data was well correlated by different models. The relationship between the solvent properties and solubility abilities was analyzed as well. Meantime, the metatable zone of L-tryptophan in different solvents was measured to provide thermodynamic data for the nucleation control.Fluorescence technique was employed to probe the interactions of L-tryptophan molecules during nucleation. The basic fluorescence properties of L-tryptophan in solution were studied first, including the maximum excitation and emission wavelengths of fluorescence, the composition of fluorescence lifetime, and the effects of solvents, temperature, pH and concentration on the fluorescence. Crystallization is usually operated in concentrated solutions. However, the fluorescence of L-tryptophan will be quenched at high concentrations. In this case, the nature of concentration quenching was explored. Then, the change of fluorescence intensity, lifetime, anisotropy and light scattering of L-tryptophan during nucleation process were measured. Finally, the interaction of L-tryptophan molecules was deduced on the basis of quenching mechanism. The consistency of experimental results with the classical nucleation theory was analyzed. In addition, cefoperazone sodium was used as an example to check the reliability of the fluorescence method in this work. The induction time of L-tryptophan in the solvents mentioned above was measured by laser method. Then the mechanism of nucleation and growth of L-tryptophan in these solvents was determined. The secondary processes of crystallization such as agglomeration, breakage, Ostwald ripening and so on were investigated in detail by means of focused beam reflectance measurement (FBRM), particles visual measurement (PVM), malvern mastersizer and scanning electron microscope (SEM).Based on the investigation of crystal morphology, crystallization thermodynamics and nucleation and growth mechanism, best solvent and crystallization method were chosen. Then the optimum operation schedule was established after studying the effects of various operation parameters on the crystallization process of L-tryptophan. Compared with the products of factory, the products manufactured by the optimum operation schedule have low level of agglomeration and better fluidity. The purity was higher than 98%. The crystal mode size was 3 times as large as the products of factory. In addition, the crystal has perfect morphology.No similar report to above study results has been published in literature up to date.