Crystal shape monitoring and supersaturation measurement in cooling crystallization with quartz crystal oscillator

A crystallization monitoring system using a quartz crystal oscillator was utilized to predict different shapes of crystal formation by measuring crystal growth rate and to measure supersaturation. Applying different rates of cooling, crystal formation of different shapes was induced, and the frequency variation of the oscillator and the crystal shape observed with an SEM were compared to determine how the frequency variation can be interpreted for the prediction of produced crystal shape. The experimental results obtained from the crystallization of potassium nitrate and cupric sulfate solutions showed that the proposed frequency measurement technique could be applied in the prediction of crystal shape of cooling crystallization processes. In addition, supersaturation was determined from the measurements of solution and coolant temperatures.     

晶型控制剂对沉淀碳酸钙晶型、形态的影响

碳酸钙是一种重要的无机化工产品，不同晶型、形态的碳酸钙有着不同的用途。晶型控制剂的加入在改变沉淀碳酸钙的晶型、形态方面都有着重要的作用。介绍了国内外在制备沉淀碳酸钙过程中，已经使用以及正在研究的各种晶型控制剂。总结了一些晶型控制剂的加入对沉淀碳酸钙晶型、形态所产生的影响，并且根据晶型控制剂类型的不同对其作用原理进行了解释。     

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。     

不同类型媒晶剂对硫酸铵晶体形态学指标的影响

选用硫酸铵这一物系,从实验和模拟两个角度研究了在媒晶剂作用下的结晶过程,探讨媒晶剂对晶体产品形态学指标的影响规律.利用粉末衍射仪(XRD)和扫描电镜(SEM)对晶体产品的晶体结构、形态学指标进行r了测定与分析.应用分子摸拟软件Materials Studio计算媒晶剂和硫酸铵各个晶面之间的单分子结合能数值,结合能数值与...     

Particle shape manipulation and optimization in cooling crystallization involving multiple crystal morphological forms

A population balance model for predicting the dynamic evolution of crystal shape distribution is further developed to simulate crystallization processes in which multiple crystal morphological forms co‐exist and transitions between them can take place. The new model is applied to derive the optimal temperature and supersaturation profiles leading to the desired crystal shape distribution in cooling crystallization. Since tracking an optimum temperature or supersaturation trajectory can be easily implemented by manipulating the coolant flowrate in the reactor jacket, the proposed methodology provides a feasible closed‐loop mechanism for crystal shape tailoring and control. The methodology is demonstrated by applying it to a case study of seeded cooling crystallization of potash alum. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

FOX-7晶体的制备和热性质

为了解FOX-7晶体形状和尺寸对其热性质的影响,通过冷却结晶和阻溶剂结晶的方法从DMF/H2O、NMP/H2O体系中获得FOX-7晶体.SEM结果表明,得到的晶体基本为延长的四面或六面棱柱和斜方菱晶两种类型,不同溶剂体系中得到晶体的尺寸不同和包含的颗粒数量也不同,超声处理得到的晶体具有单一形状,只是其表面较粗糙.DSC测试结果表明,不同结晶方式和不同溶剂体系中获得的FOX-7晶体的热性质有一定的差别.由此得出,不同的结晶方式和溶剂体系可以获得不同形状、尺寸和热性质的FOX-7晶体,而超声处理可以很好地控制晶体的形状.     

Isothermal crystallization of hydrogenated sunflower oil: II. growth and solid fat content

Isothermal crystallization of sunflower seed oil hydrogenated under two different conditions was studied by means of pulse nuclear magnetic resonance (pNMR) and optical microscopy. Solid fat content (SFC) curves showed two different shapes depending on supercooling. When supercooling was high, hyperbolic curves were found, whereas with low supercooling sigmoidal curves were obtained. Curves were interpreted with the modified Avrami equation. Photographs of the crystals were taken from the beginning of crystallization, every 15 s until 15 min and every 5 min until 60 min. Samples which exhibited hyperbolic curves showed a slight increase in crystal number, and crystals were needle-shaped in all cases. Samples which had sigmoidal crystallization curves showed a marked increase in crystal number with time, and crystals were spherical in shape. Crystallization behavior was also in agreement with the chemical composition of the samples. Samples which had the highest content of high-melting triacylglycerols (especially trielaidin) showed only hyperbolic curves. Supercooling is a very important parameter that defines the way nucleation occurs. Depending on the initial number of nuclei, two different growth mechanisms were found: a uniform linear growth of the nuclei for a small initial number (sigmoidal curves) and an aggregate of the nuclei for a high initial number (hyperbolic curves).     

A new strategy for protein crystallization : Effect of ionic liquids on lysozyme crystallization and morphology

Protein crystallization is a complex physical and chemical process. The high-quality protein crystal is still a persistent bottleneck to the application of X-ray crystallography in structural biology. The additives may promote formation of crystal nucleus and subsequent growth in protein crystallization. As a distinct material, ionic liquids (ILs) have aroused great attention and interest for protein crystallization due to their unique properties. We reviewed the progress of protein crystallization and reported research about protein crystal morphology control by ILs, as crystal growth template, in aqueous solutions. ILs encourage changes in some cases in terms of growth morphology and crystal size. The effect of ILs on lysozyme growth morphology can be attributed to changing interaction among lysozyme molecules in aqueous solutions. This work can provide some initial insight into the preparation of high quality crystal and the development of new crystal form.     

KNO3-H2O溶液间歇结晶动力学

基于ΔL定律推导了晶体线性生长速率的数学表达式,利用已建立的溶液间歇结晶动力学实验研究手段实现了溶液透光率和浓度的在线测量.利用经验模型关联线性生长速率和相对过饱和度求取了生长动力学参数,并与文献值进行了比较.结果发现：对于自发成核结晶过程,综合动态透光率、过饱和度和经验模型可对成核和生长阶段进行定性识别.     

KNO3-H2O溶液间歇结晶动力学

基于ΔL定律推导了晶体线性生长速率的数学表达式，利用已建立的溶液间歇结晶动力学实验研究手段实现了溶液透光率和浓度的在线测量.利用经验模型关联线性生长速率和相对过饱和度求取了生长动力学参数，并与文献值进行了比较.结果发现：对于自发成核结晶过程，综合动态透光率、过饱和度和经验模型可对成核和生长阶段进行定性识别.     

硫酸镍间歇结晶过程的工艺优化

文章采用聚焦光束反射测量仪(FBRM)研究了硫酸镍间歇结晶过程晶体的成核和生长规律,考察了搅拌桨形式、降温方式、搅拌速率、晶种添加量和晶种粒度对结晶过程中结晶动力学的影响。结晶工艺条件优化后,得到了粒径大、晶型好、分布均匀的晶体产品,为硫酸镍间歇结晶过程的工艺优化和工业放大提供了依据。     

Combining anti-solvent and cooling crystallization: Effect of solvent composition on yield and meta stable zone width

Combined cooling and anti-solvent crystallization (CCAC) of paracetamol was carried out from a water-isopropanol (IPA) mixture. Seeded and unseeded runs were performed in a 150 ml vessel with linear cooling rates varying from 0.028 to 2.0 K/min, and linear anti-solvent feed rates in the range from 0.88 to 5.0 g/min. The dynamic solvent composition is shown to have a substantial effect on the crystallization kinetics, and the meta stable zone width (MSZW). Existing models from the literature which predict the behavior of the MSZW have been applied to the CCAC process for the unseeded runs. The crystal growth rate was strongly influenced by the solvent composition. Hence, the performance of the crystallization process was increased substantially by first precipitating paracetamol by adding anti-solvent until a solvent composition was reached which caused a high growth rate. Subsequent cooling resulted in higher growth rates. This could be applied in industrial batch crystallization to decrease the required batch time, thus improving performance.     

Modeling the crystallization of proteins and small organic molecules in nanoliter drops

Drop‐based crystallization techniques are used to achieve a high degree of control over crystallization conditions in order to grow high‐quality protein crystals for X‐ray diffraction or to produce organic crystals with well‐controlled size distributions. Simultaneous crystal growth and stochastic nucleation makes it difficult to predict the number and size of crystals that will be produced in a drop‐based crystallization process. A mathematical model of crystallization in drops is developed using a Monte Carlo method. The model incorporates key phenomena in drop‐based crystallization, including stochastic primary nucleation and growth rate dispersion (GRD) and can predict distributions of the number of crystals per drop and full crystal size distributions (CSD). Key dimensionless parameters are identified to quickly screen for crystallization conditions that are expected to yield a high fraction of drops containing one crystal and a narrow CSD. Using literature correlations for the solubilities, growth, and nucleation rates of lactose and lysozyme, the model is able to predict the experimentally observed crystallization behavior over a wide range of conditions. Model‐based strategies for use in the design and optimization of a drop‐based crystallization process for producing crystals of well‐controlled CSD are identified. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Modeling and control of protein crystal shape and size in batch crystallization

In this work, the modeling and control of a batch crystallization process used to produce tetragonal hen egg white lysozyme crystals are studied. Two processes are considered, crystal nucleation and growth. Crystal nucleation rates are obtained from previous experiments. The growth of each crystal progresses via kinetic Monte Carlo simulations comprising of adsorption, desorption, and migration on the (110) and (101) faces. The expressions of the rate equations are similar to Durbin and Feher. To control the nucleation and growth of the protein crystals and produce a crystal population with desired shape and size, a model predictive control (MPC) strategy is implemented. Specifically, the steady‐state growth rates for the (110) and (101) faces are computed and their ratio is expressed in terms of the temperature and protein concentration via a nonlinear algebraic equation. The MPC method is shown to successfully regulate both the crystal size and shape distributions to different set‐point values. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2317–2327, 2013     

Static and dynamic light scattering studies of the crystallization of poly(ethylene oxide) from dilute solutions

We have monitored in situ the self-seeded crystallization of poly(ethylene oxide) from dilute toluene solutions by dynamic light scattering. In supercooled dilute solution, the radii (R) of the crystals grow linearly with time. the rate constant obtained from the slope of the plot R versus time depends on the temperature and the molecular weight of the polymer, both of which determine the degree of the supercooling. The maximum crystal size obtained from solutions of fixed concentration also depends on the temperature and the polymer molecular weight. It appears that crystal growth is limited because of molecular weight fractionation. Static light scattering from suspensions of stable crystals provides information on the crystal morphology. A comparison of experimental and theoretical particle scattering functions suggests that the crystals form short cylinders and that the crystal growth from the seeds is primarily two-dimensional. Some comparisons to melt crystallization are possible. The preparation and use of tiny seed crystals is critical to the success of these studies.     

On the use of process analytical technologies and population balance equations for the estimation of crystallization kinetics. A case study

The batch cooling solution crystallization of ammonium oxalate was performed in water at various constant cooling rates. Measurements of the solute concentration were obtained using in situ attenuated total reflectance fourier transform infrared (ATR‐FTIR) spectroscopy, and final estimates of the crystal size distribution (CSD) were computed; thanks to in situ image acquisition and off‐line image analysis. The crystallization process was then simulated using population balance equations (PBEs). Estimates of the nucleation and the growth parameters were computed through model/experiments fitting. According to the cooling rate, the PBE model allowed distinguishing between two distinct crystallization regimes, separated by an “intermediate regime.” The respective contributions and shortcomings of solute concentration measurements and granulometric data to the identification of nucleation and growth kinetic parameters are analyzed and discussed. It is shown in particular that no real separate estimation of nucleation and growth parameters can be obtained in the absence of CSD data. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Modeling layered crystal growth at increasing supersaturation by connecting growth regimes

Mechanistic modeling facilitates rational crystallization engineering and design space screening. For an accurate model, the dominant growth mechanism operating on each face must be determined, which is highly dependent on supersaturation. Considering the case of centrosymmetric growth units, we developed and connected existing mechanistic expressions for spiral and two‐dimensional‐nucleation growth regimes, through application of stationary nucleation rate theory. Our approach enables calculation of crossover supersaturations and forms a framework to model the specific mechanism operating on each face under given crystallization conditions. Increasing supersaturation can change the crystal morphology; as face families switch growth mechanisms, they may grow out of the steady‐state shape, or influence its aspect ratio. Application of the model to naphthalene, biphenyl, pentaerythritol and β‐HMX shows the ability to capture experimentally observed examples of such supersaturation‐dependent crystal habits. This methodology broadens the applicability of mechanistic crystal growth modeling to include higher‐supersaturation industrial processes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1338–1352, 2017     

Monitoring the particle size and shape in the crystallization of paracetamol from water

In this work, a technique capable of restoring bidimensional particle size distributions from images of the particles in suspension is applied to the seeded cooling crystallization of paracetamol from water. The effects of cooling rate and stirring rate on the final particle size and shape are studied and the average growth rates along different directions of particles are found to be strongly dependend on supersaturation. This observation is in line with previous studies, though in this work it has been established for the first time using populations of particles. The technique was capable of quantifying changes in particle size and shape, indicating particle sizes and shapes that correlated well with observations from electron microscopy images.     

粒数衡算与多相流耦合求解刮削制冰的晶粒特性

在考虑晶粒成核、生长、聚并和破碎的情况下,采用分组法求解粒数衡算方程,通过耦合粒数衡算与多相流方程,建立了多尺度的结晶模型,模拟了表面刮削式制冰装置内水的动态结晶过程,获得不同温度、刮削速度、制冰时间等外界条件下晶粒数密度分布、云图等信息,分析了外界宏观条件对水的动态结晶过程的影响。结果表明：由于碰撞引起的晶粒聚并和破碎使得晶粒的尺寸分布更为集中和均匀;在过冷温差（流体局部温度与水的相变温度差值）不大于20℃,刮削速度不大于10 r·s^-1范围内,降低壁面温度、增加刮削速度可以加速水的结晶与生长。