【作者】 陈巧力；

【导师】 王静康；

【作者基本信息】 天津大学 ， 化学工程， 2012， 博士

【摘要】 L-色氨酸是人和动物维持生命活动所必需的氨基酸,广泛应用于医药、食品、饲料等领域。针对目前L-色氨酸产品存在纯度低、流动性差、晶习不完美等问题,本文对L-色氨酸的结晶分离纯化过程进行了系统工程的研究,具体内容如下:对L-色氨酸进行了晶体形态学研究。利用Materials studio软件对X-射线粉末衍射数据进行解析,确定了L-色氨酸的晶体结构,包括晶胞参数、所属晶系和空间群。采用BFDH、AE模型预测了L-色氨酸的晶习,通过与实验产品的对比,分析了晶体结构与晶面生长速率、晶习之间的关系。另外,考察了溶剂、冷却速率、结晶终温等因素对晶体形态的影响。采用动态法分别测定了L-色氨酸在纯水、不同pH值水溶液、甲醇-水、乙醇-水、正丙醇-水溶剂中的溶解度,建立了溶解度模型,并分析了溶剂的物化性质与溶解特性之间的关系。同时,测定了L-色氨酸在不同溶剂体系中的介稳区宽度,以便为结晶过程中成核的控制提供依据。运用荧光检测手段研究了L-色氨酸成核过程中分子间的相互作用。考察了L-色氨酸溶液的基本荧光性质,包括荧光最大激发波长和发射波长、荧光寿命的特征和成分以及溶剂、温度、pH和浓度对荧光强度和寿命的影响。针对高浓度情况下L-色氨酸荧光发生猝灭的特性,分析了其猝灭机理。测定了L-色氨酸成核过程中荧光强度、荧光寿命、光散射强度、荧光各向异性的变化,结合L-色氨酸的猝灭机制判断出成核过程中L-色氨酸分子之间的相互作用,并将实验结果与经典成核理论进行了比照。另外,以头孢哌酮钠为研究体系,对荧光法研究成核过程这一检测手段的可靠性进行了再次验证。采用激光法测定了L-色氨酸在上述不同溶剂中的结晶诱导期,揭示了L-色氨酸的成核和生长机理。利用聚焦光束反射测量仪(FBRM)、粒子成像仪(PVM)、马尔文粒度分析仪(Malvern Mastersizer)、扫描电子显微镜(SEM)等在线和离线分析手段对L-色氨酸结晶过程中的聚结、破碎、老化等二次过程进行了详细考察。在L-色氨酸晶体形态学、结晶热力学、成核和生长机理研究基础上,综合考虑各种实际因素,筛选出了最佳溶剂体系和结晶工艺。通过考察不同操作参数对结晶产品的影响,最终确定了L-色氨酸结晶的优化操作时间表。与厂家产品相比,优化操作条件下得到的L-色氨酸产品纯度达到98%以上;主粒度增大至原来的3倍,晶习完美;从而使得产品聚结程度下降、流动性改善。以上有关研究内容尚未见文献报道。更多还原

【Abstract】 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.更多还原