添加晶种的KNO_3水溶液间歇结晶动力学模型

针对添加晶种的二次成核结晶过程的特点,并基于Beer Lambert定律、ΔL定律和粒数衡算理论,建立了包含透光率变量的间歇结晶动力学模型。运用该模型对KNO3水溶液冷却结晶实验的溶液质量分数、相对过饱和度以及透光率数据进行关联,一次性获得了结晶体系的二次成核和生长动力学参数,其值与文献值吻合较好。尝试以光学法关联动力学模型的研究,将有助于结晶机理的深入认识,为动力学模型的进一步发展提供思路。     

用动态间歇法研究硫酸钠结晶动力学参数

论述了用DTB型结晶器结晶硫酸钠结晶模型。应用拉氏变换方法将偏微分方程化为常微分方程求解，通过对实验数据的处理得到了硫酸钠的结晶动力学参数。     

添加晶种的间歇结晶器数学模型

动力学参数是设计结晶器和优化过程操作的主要依据。针对添加晶种的二次成核结晶过程，采用经验方程将反映结晶固相信息的透光率数据与CSD的二阶矩量进行关联，建立了包含透光率、液相浓度和相对过饱和度的动力学模型。并以KNO3-H2O为对象，运用该模型求取了结晶成核和生长动力学参数，结果与文献值相近。     

精对苯二甲酸连续多级蒸发结晶的模拟

利用研究得到的精对苯二甲酸结晶动力学,建立了精对苯二甲酸连续多级降压蒸发结晶过程的数学模型,并采用工业数据进行验证。结果表明研究得到的模型能够较好地用于模拟精对苯二甲酸连续多级降压蒸发结晶过程,并进一步研究了主要工艺变量对精对苯二甲酸结晶过程的影响。     

硝基胍结晶热力学

测定了在不同温度下,硝基胍在不同浓度硝酸中的溶解度。用不同的溶解度模型回归了溶解度数据,建立硝基胍在硝酸溶液中的溶解度方程和模型参数方程,并对硝基胍在不同浓度的硝酸溶液的溶解度进行预测。数据为结晶工艺的开发提供理论依据。     

Na_2CrO_4-NaOH-H_2O体系中Na_2CrO_4真空蒸发结晶动力学研究

在液相氧化法铬盐清洁生产工艺中,中间产品铬酸钠的结晶相分离为重要的组成部分,采用真空蒸发结晶的方法可从Na2CrO4-NaOH-H2O体系中分离得到铬酸钠晶体。文中研究了Na2CrO4在NaOH溶液中晶体成核与生长动力学规律。采用间歇动态法中的矩量变换法建立了结晶过程的动力学模型,用最小二乘法对动力学实验数据进行多元线性回归,得到了动力学参数,并验证了动力学模型的可靠性。结果表明:在粒度大于50μm的范围内,铬酸钠晶体的生长符合粒度无关生长模型;晶浆的悬浮密度、搅拌强度和过饱和度对成核速率均有显著影响;溶液过饱和度对成核速率的影响大于对生长速率的影响。结晶动力学的研究为液相氧化法铬盐清洁生产工艺中铬酸钠和氢氧化钠的分离工艺优化提供了理论基础。     

精对苯二甲酸(PTA)结晶动力学

建立了精对苯二甲酸连续多级降压蒸发结晶过程的数学模型,通过工业实验获得了各级结晶器不同操作条件下的产品粒度分布数据,并构造了模型计算值和工业实验值相拟合的优化目标函数,采用单纯形法优化回归得到了精对苯二甲酸结晶动力学参数。研究结果表明,优化回归得到的精对苯二甲酸结晶动力学方程能够较好地模拟PTA连续多级降压蒸发结晶过程。     

均四甲苯静态结晶动力学研究

均四甲苯与其同分异构体沸点相近、熔点相差较大,不适合采用精馏精制,而宜采用熔融结晶方法进行分离。在考虑固液相界面温度随冷剂温度变化的前提下,采用解析迭代法研究均四甲苯熔融结晶动力学并设计实验进行验证。利用非线性最小二乘法对等温实验数据进行拟合得到不同冷剂温度下的组合动力学参数,并通过多项式拟合得到了组合动力学参数随冷剂温度的变化关系。将其应用于模拟非等温结晶过程的晶体生长,计算结果与实验数据基本吻合,表明该模型能很好地预测晶层生长过程。     

环丙沙星冷却结晶动力学测定

依据粒数衡算方程,采用分离变量方法求解粒数密度函数表达式,依据该方法通过加晶种的间歇冷却结晶实验研究了环丙沙星在23％(体积)水/乙醇溶液中的结晶动力学数据,得到了结晶动力学方程,为工业结晶动力学的测定、结晶特性辨识、粒度分布预测和控制提供了新的方法.     

PBT非等温结晶动力学

用差示扫描量热法研究聚对苯二甲酸丁二酯（PBT）的非等温结晶动力学，并分别用Ozawa,Jeziorny和考虑综合因素法来处理PBT的非等温结晶数据。结果表明，PBT非等温结晶过程与Ozawa动力学方程相吻合，但不符合用Jeziorny方法处理的Avrami动力学方程；综合考虑温度和结晶程度对聚合物结晶速度的影响。PBT非等温结晶过程符合结晶动力学方程。     

crystSim: A software environment for modelling industrial batch cooling crystallization

Crystallization modelling is limited by the availability of methods to reliably predict mixing, temperature and concentration distributions, supersaturation, nucleation and growth kinetics for crystallization systems of industrial size. A new software environment for modelling batch cooling crystallization has been developed integrating crystallization and fluid dynamics. The mathematical model can reliably predict mixing in stirred vessels of a given geometry and its effect on the crystallization kinetics and crystal product properties thus reducing the cost and time required for the design and scale-up of industrial crystallizers. The paper describes the development and application of crystSim for modelling industrial crystallization in stirred tanks. The software is developed in Visual C# making full use of Object Oriented Programming (OOP) and multithreading.     

Kinetics of formation of carbon dioxide clathrate hydrates

The new experimental apparatus capable of observing the clathrate hydrate formation kinetics was developed in this study. Experimental data on the kinetics of carbon dioxide hydrate formation were carefully measured. The experiments were carried out in a semi-batch stirred tank reactor with stirring rate of 500 rpm at three different temperatures between 275.2 and 279.2 K and at pressures ranging from 2.0 to 3.5 MPa. The kinetic model was adopted to predict the growth of hydrates with only one adjustable parameter which represented the rate constant for the hydrate particle growth. The model was based on the crystallization theory coupled with the two-film theory for gas absorption into the liquid phase. The model predictions matched the experimental data very well with the largest deviation of 7.18%, which is within experimental error range. This study is the first for the kinetic data of carbon dioxide hydrate formation and important in developing carbon dioxide fixation process using clathrate hydrate phenomenon.     

Isothermal and nonisothermal crystallization of polyethylene

Differential scanning calorimetry is employed to study the crystallization kinetics of two commercial injection-molding high-density polyethylene resins. Also, polarized light microscopy has been used to elucidate the morphological structures formed at various crystallization conditions. Corrections and operating procedures are recommended in order to correct for temperature lag in scanning, transient response during isothermal crystallization and for thermal gradients within the polymer sample. As a result of these studies, a modified Avrami equation has been proposed in order to obtain a more extensive and reliable characterization of isothermal crystallization kinetics. Moreover, a procedure is recommended and employed to predict nonisothermal crystallization behavior on the basis of isothermal crystallization kinetics.     

Computer Modeling and Simulation for 3D Crystallization of Polymers. II. Non-Isothermal Case

A 3D computer modeling and simulation has been used to predict crystallization kinetics and crystal morphology in polymers under the non-isothermal condition. A parametric study is used to explore the influences of thermal conditions on the crystallization. The results indicate that cooling rate has a strong impact on the crystallization kinetics as well as the morphology. The initial temperature only affects the crystallization kinetics and has no impact on the final morphology. It is observed that the distribution of spherulite size in non-isothermal case is much broader than that in the isothermal case.     

Growth kinetics: a thermodynamic approach

The analysis and development of industrial crystallization processes requires knowledge of the kinetics of the crystal growth process. This has led to a large number of studies of crystallization kinetics in a variety of systems. A review of these studies reveals the general use of an empirical power-law model for crystal growth kinetics, along with a variety of different definitions of supersaturation. In this work, supersaturation, the driving force for crystallization has been examined from a thermodynamic perspective and combined with the Burton-Cabrera-Frank crystal growth model to obtain a simplified and consistent method to analyze crystal growth data and obtain kinetics with only a single constant. This method is applied to a number of systems employing kinetic data obtained from the literature and thermodynamic data measured in this laboratory. The results demonstrate the simplicity and utility of the method.     

Modification of the Avrami model for application to the kinetics of the melt crystallization of lipids

The Avrami model was developed to model the kinetics of crystallization and growth of a simple metal system. The original assumptions of the model do not apply for high-volume-fraction crystallizing lipids, although it is incorrectly and frequently applied. A modified form of the Avrami model, wellsuited to complex lipid crystallization kinetics, is developed. It produces excellent fits to experimental data and allows the prediction of physically meaningful parameters, such as changes in nucleation rate and type, growth rate, morphology, and dimensionality. Morphological changes highlighted by time-resolved temperature-controlled polarized light microscopy support its application to crystallizing lipids. The kinetics of crystallization for six separate lipid samples were monitored by pulsed NMR, and fits were performed using the classical and modified Avrami model. In all cases, the modified model provided superior fits to the data compared with that of the classical model. The modified model supports the theory that lipids crystallize and grow into networks via very specific growth modes. Furthermore, the case is made that it is useful for interpreting crystallization kinetics of other systems such as polymer melts, which have nonconstant growth rates, dimensionalities, and nucleation conditions, and whose growth become diffusion-limited within specific regimes.     

蒸氨废水化学沉淀除氟结晶动力学模型

以质量扩散-表面反应两步结晶理论为基础,推导出氟化钙沉淀结晶动力学模型,以蒸氨废水为研究对象,氯化钙为沉淀剂,采用间歇结晶和在线粒度监测技术测定了氟化钙结晶动力学数据,采用非线性优化技术获得了氟化钙结晶动力学模型参数,并对该模型进行了实验验证,结果表明模型及模型参数效果良好,模型值与实验值平均相对误差为3.37%。氟化钙沉淀结晶过程属于表面反应控制过程,氟化钙存在明显的聚结现象。模型模拟结果表明:钙离子浓度一定时,氟离子初始浓度越高则初始阶段氟离子浓度下降越快,初始氟离子浓度过高或过低,最终均不利获得较低的氟离子浓度;适当提高操作温度可以促进氟离子的净化,但温度过高则不利。     

间歇结晶器中地塞米松磷酸钠溶析结晶动力学的研究

在间歇结晶器中,利用矩量变换法对地塞米松磷酸钠溶析结晶过程动力学进行了理论研究。由实验得到的地塞米松磷酸钠晶体的粒数密度分布数据,采用非线性最小二乘法分别对与粒度相关和与粒度无关线性生长速率模型进行了参数估值,通过由各种模型得到的晶体生长速率的计算与实验值的比较,发现与粒度无关生长速率模型不仅计算过程简单且计算的精度也更好。最后,以与粒度无关生长速率模型为基础,由不同实验条件下晶体的粒数密度分布数据非线性回归出其成核速率方程和生长速率方程。对方程的理论分析表明,低过饱和度、低悬浮密度和较高的结晶温度有利于得到平均粒径更大的地塞米松磷酸钠晶体。     

Drying of semicrystalline polymers: mathematical modeling and experimental characterization of poly(vinyl alcohol) films

A mathematical model was developed to predict the drying mechanism of semicrystalline polymers involving multiple solvents. Since drying of semicrystalline polymers can be accompanied by changes in polymer degree of crystallinity, the model integrates crystallization kinetics and the Vrentas-Duda diffusion model to provide a better understanding of the mechanism. The model considers the effect of external conditions such as temperature, film shrinkage and diffusion and evaporation of multiple solvents during drying. Poly(vinyl alcohol) (PVA)/water/methanol was chosen as a test system. The drying kinetics of PVA films swollen in water and methanol were investigated using gravimetric techniques. The model predicts that higher temperatures, lower film thicknesses and lower methanol to water ratios increase the drying rate. The model predictions were compared with experimental data and showed good agreement.