D-核糖结晶工艺探讨

结晶过程的原则是争取最大的结晶速度，尽可能提高成品收率，保证晶粒的均匀整齐。而影响结晶的因素有：溶液浓度、晶种质量、晶体生长速率、过饱和度的大小、结晶温度、溶液pH值、溶液杂质等。本文探讨了D-核糖结晶过程中溶液浓度、溶媒（乙醇）含量和降温方式等工艺的优化。     

结晶控制技术对晶体形貌的影响

以晶体生长理论为依据,探讨了溶剂、温度、过饱和度、搅拌强度、加晶种的时机以及溶液pH值等对晶体生长习性的影响,寻求晶形貌与结晶工艺的关系,从而达到控制晶体外形的目的。     

苊冷却结晶动力学的间歇动态法研究

通过添加晶种的间歇冷却结晶实验研究了苊在乙醇中的结晶动力学。由苊晶体的粒数密度数据,通过矩量变换法按粒度无关生长模型求解粒数衡算方程,采用多元线性最小二乘法回归动力学数据,得到苊在乙醇中晶体生长及成核速率方程。对动力学方程的理论分析表明:搅拌速率对二次成核影响显著,随搅拌速率增加,晶体的成核速率明显增加。同时适宜的过饱和度及较低的悬浮密度,有利于苊晶体生长。该研究为苊冷却结晶特性的辨识、粒度分布的控制及工业放大提供了重要的理论指导。     

旋流流化床中五水硫酸铜结晶生长动力学研究

基于微观平板对流传质理论,建立了五水硫酸铜晶体生长动力学模型。在循环旋流流化结晶实验装置中,分别考察了母液过饱和度、循环流速、晶种粒度、结晶温度对晶体生长速率的影响。结果表明:增大旋流流化床中的母液过饱和度、结晶温度、循环流速,或减小晶种粒径均能提高五水硫酸铜晶体的线性生长速率,其中母液过饱和度与结晶温度对晶体线性生长速率影响显著;在较宽的操作条件范围内,模型计算结果与实验值吻合较好,相对偏差在±10%以内,该模型可用于预测旋流流化床中五水硫酸铜晶体的生长速率,可为装置的工业放大设计提供理论指导。     

循环流化结晶过程传质与晶体生长速率模型

依据Whiteman传质膜理论 ,针对循环流化床结晶过程 ,建立了传质和晶体生长速率理论模型 .实验研究表明 ,在较宽的流速范围内 ,晶体生长速率仅与结晶物系的物性、晶种粒度和过饱和度有关 ,其基本规律为 :晶体的平均线生长速率与扩散系数、晶种特征长度、晶体与溶液相对密度差、过饱和度成正比 ;与溶液的黏度、晶体的密度成反比 .仅需结晶物系的物性、过饱和度等数据 ,利用所建模型可方便地预测循环流化床结晶过程的晶体生长速率     

谷氨酸结晶中的细晶回用工艺

谷氨酸工业结晶过程中会产生大量难以分离回收的细晶,影响收率和产品质量。文中提出了结晶-粒径切割沉降-细晶回用的工艺设想,将不同粒径的晶体分步分离,细晶浓缩后作为晶种回用至结晶过程。使用扫描电镜和粉末X-衍射(PXRD)研究细晶的晶习及其作为晶种回用的可行性,进行不同条件下的分批等电结晶,参考结晶速率、聚结度、CSD等参数确定细晶回用量、适用过饱和度范围等回用条件。结果表明:液体细晶表观为非典型四方六面体,但在谷氨酸结晶中晶面具有自我修复能力;过饱和度和细晶回用量均影响结晶过程,液体细晶的最适过饱和度范围为1-3;在过饱和度S=2时液体细晶的最适回用量(质量分数)为1%,在S=3时最适回用量为3%。最终证明通过控制合适的晶体生长环境,细晶回用的谷氨酸结晶工艺是可行的。     

对二甲苯降膜结晶动力学

降膜结晶是工业生产对二甲苯的重要方法。以多孔介质分形理论为基础开展对二甲苯降膜结晶动力学的研究。通过动力学模型优化实验条件,结晶条件为进料速度为60 ml·min^-1、结晶温度-15℃、原料预冷温度25℃,发汗条件为升温速率1℃·min^-1、发汗终温5℃。在此条件下测定降膜结晶过程中对二甲苯结晶量以及液相夹带量,建立了晶体生长速率方程和液相夹带速率方程,相关系数分别为0.967和0.977,模型可靠。结果表明随着过饱和度的增加,液相夹带速率增长更快,晶层中夹带液相体积分数越大,晶层孔隙率越大。晶体生长速率方程和液相夹带速率方程的建立对工业降膜结晶生产对二甲苯过程中,通过调节液膜过饱和度控制晶层生长具有重要参考意义。     

十水硫酸钠冷冻结晶器的设计与优化

通过对十水硫酸钠结晶过程影响因素的分析,讨论了冷却结晶过程设计的关键点。分析了过饱和度对结晶过程初级成核的影响,研究了通过控制物料母液循环量从而控制过饱和度以避免初级成核的方法;探讨了通过改进设备内部结构,使晶核处于悬浮状态,与过饱和液体充分混合,达到促进晶体生长的目的;新的设备结构设计,还充分考虑减少晶体二次成核几率;同时在结晶器中增加细晶排出装置,降低晶核数量,提高晶体生长速率,达到改善结晶质量的目的。     

对二甲苯悬浮熔融结晶动力学

结晶法是工业上生产对二甲苯的主要方法之一。现有对二甲苯结晶动力学参数均单纯由结晶母液的温度和浓度变化通过非线性优化法而获得,未检测对二甲苯的晶体粒度数据,因而其准确性难以得到保证。本文利用超声在线粒度仪(OPUS)检测对二甲苯晶体的粒度分布,通过添加晶种的间歇悬浮熔融结晶实验,应用矩量变换法测定82%（质量）对二甲苯-间二甲苯体系中的对二甲苯结晶动力学。利用最小二乘法对动力学实验数据进行多元线性回归后得到了对二甲苯结晶动力学方程,研究结果表明,在对二甲苯悬浮熔融结晶过程中,溶液相对过饱和度对对二甲苯晶体成核速率的影响大于对晶体生长速率的影响,搅拌速率对成核过程影响明显,而晶浆悬浮密度对成核速率的影响不大。     

对二甲苯降膜结晶动力学

降膜结晶是工业生产对二甲苯的重要方法。以多孔介质分形理论为基础开展对二甲苯降膜结晶动力学的研究。通过动力学模型优化实验条件,结晶条件为进料速度为60 ml·min-1、结晶温度-15℃、原料预冷温度25℃,发汗条件为升温速率1℃·min-1、发汗终温5℃。在此条件下测定降膜结晶过程中对二甲苯结晶量以及液相夹带量,建立了晶体生长速率方程和液相夹带速率方程,相关系数分别为0.967和0.977,模型可靠。结果表明随着过饱和度的增加,液相夹带速率增长更快,晶层中夹带液相体积分数越大,晶层孔隙率越大。晶体生长速率方程和液相夹带速率方程的建立对工业降膜结晶生产对二甲苯过程中,通过调节液膜过饱和度控制晶层生长具有重要参考意义。     

Strategies for Xylitol Purification and Crystallization: A Review

This paper reviews the literature on the main aspects of purification and crystallization of xylitol produced either by chemical or biotechnological routes. Different strategies have been used to clarify media containing xylitol: activated charcoal, pH adjustment, ion-exchange resins, membrane separation, chromatographic methods, liquid-liquid extraction, and precipitation, or a combination of these techniques. This study explores the most recent results of research work carried out in this field as well as the main approaches to recover and crystallize xylitol in a pure form. The effects of impurities, temperature, supersaturation, crystal seed amount, and size on xylitol crystal growth are also discussed.     

氯化铵结晶过程实验研究

在混合悬浮结晶器中研究了氯化铵结晶热力学和动力学特性。以硝酸锰为添加剂,配制了质量分数为0.23%的硝酸锰水溶液,测定了氯化铵在该溶液中的溶解度及超溶解度。研究了硝酸锰对氯化铵晶体粒度分布的影响,得到了晶体变异系数。考察了过饱和度对氯化铵结晶线性生长速率和成核速率的影响,得到了成核-生长动力学方程。结果表明：介稳区宽度随温度升高而减小;添加晶种,介稳区宽度变窄。随硝酸锰溶液浓度增大,晶体变异系数逐渐降低并趋于平缓。当硝酸锰的质量分数逐渐增大到0.307%时,晶体变异系数几乎不再降低。线性生长速率和成核速率随溶液过饱和度的增大而增加,得到的动力学方程与实验数据吻合较好,有一定的工业参考价值。     

氯化钾间歇冷却结晶生长规律及粒度控制实验研究

采用聚焦光束反射测量技术（FBRM）考察了氯化钾（KCl）间歇冷却结晶过程中晶体成核和生长规律,重点研究了降温速率对KCl水溶液冷却时产生过饱和度的影响,以及添加晶种的相关条件（如晶种粒径和添加量等因素）与KCl晶体产品粒度的关系。同时,采用直接冷却刺激起晶产生“晶种”,并控制其生长达到控制晶体产品粒度的目的。结果表明,在添加晶种条件下,程序降温过程产生的低过饱和度不易引起爆发成核,且晶种的添加量决定着晶体产品的平均粒度与理想生长模型的偏差。另外,降温速率是冷却刺激起晶产生“晶种”粒径的关键因素。     

水溶液中硫酸钾晶体生长动力学

The single crystal growth rates of potassium sulfate in pure aqueous solution under different conditions were determined by photomicrography in a flow system for crystal growth. The effects of themain controlling factors, such as supersaturation, crystal size, solution velocity and crystal growth temperature, on crystal growth rates of potassium sulfate were discussed in detail by using non-linear regression from the experimental data, and several empirical relationships were given. The results showed that the growth rates of crystals increased with supersaturation, crystal size, solution velocity and temperature. Moreover supersaturation was the most important controlling factor influencing growth rates of crystals, crystal size and solution velocity were the secondary and temperature was the least.Furthermore, It was found that the growth rate of crystals along the [100] crystallographic axis was higher than that along the [001] in the same condition. The effect of every factor on crystal growth rates along the [100] crystallographic axis was stronger than that along the [001].     

源于发酵液的木糖醇的结晶热力学研究

研究了木糖醇的溶解特性,考察了温度、溶剂组成、杂质等对木糖醇溶解度的影响.结果表明,木糖醇属于溶解度温度系数较大的一类物质;乙醇的加入可降低木糖醇的溶解度;而阿东糖醇、山梨醇等杂质会适当增大木糖醇的溶解度.通过测定木糖醇发酵处理液的介稳区宽度,确定极限过饱和度σ值为0.22,为发酵液制备木糖醇结晶体时的过饱和度确定提供了依据.     

Industrial batch crystallization of a plate-like organic product. In situ monitoring and 2D-CSD modelling. Part 2: Kinetic modelling and identification

The batch seeded cooling solution crystallization of a fine organic material, exhibiting a platelet-like habit, was investigated and a model of the time variations of the crystal size distribution (CSD) was designed using two-dimensional population balance equations. Activated surface secondary nucleation and attrition secondary nucleation mechanisms were considered, coupled with growth mechanisms of two main dimensions of the crystal, resulting in a set of eight kinetic parameters. The model relates the effects of the main batch operating conditions: seeding temperature, cooling rate and total area of the seed particles, on both the supersaturation profile and bi-dimensional CSD. Surface secondary nucleation occurs first since it is promoted by the introduction of seeds and remains active as long as the relative supersaturation exceeds a threshold value of about 16%. It vanishes below which could be expected as we deal with an activated mechanism. Contact secondary nucleation occurs later when the concentration of solid is sufficient. It is spread over time until supersaturation disappears at the end of the batch process. This contact secondary mechanism is assumed to be the dominant nucleation mechanism as it generates about two-thirds of the final crystal number. Sharp desupersaturation profile following the introduction of seeds, which was observed experimentally, is shown to be quantitatively described through the growth of seed particles. The termination of the batch process is more difficult to represent. Due to crystal attrition, distinct growth rates between initial and secondary crystals or growth rate dispersion might explain such difficulty.     

基于PBM的L-谷氨酸粒度分布控制优化

针对β型L-谷氨酸冷却结晶过程,为获取期望粒度分布,采用特征曲线法（MOCH）来建立关于粒度相关生长率的种群平衡方程（PBE）,然后通过对种群平衡模型（PBM）参数辨识后确定最优过饱和度及控温曲线。由于辨识模型参数的目标函数具有非线性和非凸型性,因而采用少量经济性的批量冷却结晶实验,结合图像分析晶种和产品粒度分布得到的统计数据,拟合模型参数。根据实际要求的结晶过程时间,为达到目标粒度分布,通过优化结晶过程的过饱和度获得最优调温曲线,实现基于恒定过饱和度的晶体生长过程优化控制。实验结果表明通过优化的控温曲线,实现了基于最优过饱和度控制的期望目标粒度分布。     

A model for supersaturation and aspect ratio for growth dominated crystallization from solution

A model for predicting supersaturation, crystal growth rate, crystal size distribution, and aspect ratio is presented. The model applies to isothermal anti‐solvent crystallization where crystal growth is the dominant phenomena and for systems where crystal habit can be characterized by two‐dimensional variables. A parameter estimation algorithm was derived to extract solute integration coefficients in the two growth directions from experimental data about temporal evolution of concentration during crystallization, the final aspect ratio, and the aspect ratio at the end of the seed age period. Model's predictions for supersaturation and aspect ratio were in good agreement with experimental data obtained on an investigational drug that crystallizes in the parallelepipedic shape. Finally, model simulations predict that for a given initial seed size, the seed loading is the main factor impacting the final aspect ratio and thus identified the range of seed loading that would result in undesired powder flow. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4456–4469, 2015     

连续结晶器中十水草酸铈反应结晶动力学研究

采用连续稳态法,对十水草酸铈在混合悬浮、混合产品排出(MSMPR)结晶器中的连续反应结晶动力学进行了研究。实验测定了十水草酸铈晶体的粒数密度分布数据,并以此为基础,基于粒度无关生长速率模型,对不同实验条件下晶体的粒数密度分布数据进行拟合,确定了十水草酸铈的成核动力学方程和生长动力学方程,并计算得到十水草酸铈晶体的成核、生长速率相对于过饱和度的指数分别为4.211和0.752。同时,对方程的理论分析表明,低过饱和度有利于得到平均粒径更大的十水草酸铈晶体。十水草酸铈结晶动力学的研究,为其大规模工业生产提供了重要的动力学数据。