青霉素亚砜结晶生长与成核动力学

利用Mydlarz 和 Jones 模型（MJ2）,对乙酸丁酯中青霉素亚砜的成核与生长动力学进行研究。通过矩量法对MJ2模型进行处理后,利用晶体产品的粒度分布计算得到青霉素亚砜的生长速率与成核速率,然后利用最小二乘法拟合回归求解出成核与生长动力学方程参数。通过实验设计考察了过饱和度、温度与搅拌速度对青霉素亚砜晶体成核和生长过程的影响。研究表明青霉素亚砜晶体生长速率随过饱和度比的增加呈现指数型增长,确定青霉素亚砜晶体生长属于晶体表面生长控制过程。由于高速搅拌会增加青霉素亚砜晶体的破碎,促进了二次成核过程,随着搅拌速度的增加,晶体生长速率出现小幅下滑,而成核速率则明显升高。青霉素亚砜成核与生长动力学研究将有助于工业生产过程优化。     

氯氧化铋反应结晶动力学研究

在铋盐水解制备氯氧化铋的反应结晶过程中,控制氯氧化铋晶体成核和生长速率可影响氯氧化铋晶体的形貌、粒径和分散性。为此,选用间歇动态法研究了氯氧化铋晶体成核与生长动力学,采用矩量变换法建立了结晶过程动力学模型,并用最小二乘法对实验数据进行多元线性回归,获取了动力学模型参数。研究结果表明：当氯氧化铋晶体粒度≥3 μm时,其晶体生长速率符合粒度无关生长模型;晶浆悬浮密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较生长速率的影响更为显著。     

波面管式结晶器处理含盐废水的实验研究

研究设计一种新型波面管式结晶器,建立晶体生长的动力学模型,测试晶体成核和晶体生长的动力学参数,并拟合出盐水中晶体在结晶器内的成核速率方程和生长速率方程。实验结果表明,改变进料温度和进料流量,会改变晶体产率。     

蛋氨酸CO2酸化半间歇反应结晶动力学研究

针对海因法合成蛋氨酸工艺，利用间歇动态法、以蛋氨酸钾为原料研究了CO₂酸化条件下蛋氨酸的反应结晶过程，建立结晶动力学模型。通过矩量变化法求解粒数衡算方程，利用最小二乘法对数据多元线性回归得到结晶动力学参数。结果表明：晶体生长类型为粒度无关生长，晶体生长活化能为21.01 kJ·mol^-1,成核与生长速率方程中过饱和度的指数分别为0.62和1.52,晶体聚结对结晶过程的影响不可忽略。气体表观速率、搅拌速率对晶体成核与聚结均有明显影响。高过饱和度与高搅拌转速不利于晶体平均粒径的增加。     

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。     

湿法磷酸介质中氟硅酸钾（钠）结晶动力学研究

运用粒数平衡方程,在MSMPR结晶器中研究了氟硅酸钾（钠）在湿法磷酸中的结晶动力学,建立了成核速率－晶体生长速率及成核速率－晶体生长速率－悬浮密度的动力学模型。     

SAPO-34分子筛晶化机理及晶化动力学研究

对SAPO-34分子筛晶化过程中预相形成、诱导期内晶核生成、晶体生长和晶化过程的研究进行综述。SAPO-34分子筛晶化过程首先形成不稳定的层状预相结构,进而发展为具有有序排列晶格骨架的晶核。结晶热力学控制晶相结构,晶化动力学控制晶体成核和生长速率。影响晶化动力学的关键因素是温度和浓度,成核速率和晶体生长速率互相竞争控制晶粒大小。晶化过程的Si取代机理和Si分布影响分子筛酸性。晶化动力学研究结果表明,温度升高,结晶速率增加,成核时间缩短。     

氯酸钠真空结晶工艺粒度控制

氯酸钠晶体粒度是用户最为关注的一项质量指标。介绍了氯酸钠真空结晶的工艺过程;着重研究氯酸钠真空结晶工艺结晶机理及生产过程中影响晶体成核速率和晶体生长速率的各项因素。详细叙述了结晶区间、外循环速率、晶种、小循环方式对晶体成核速率的影响,以及结晶器内液位高度、液体密度、温度对晶体生长速率与生长时间的影响。得到了真空结晶工艺生产粒度较大且均匀的氯酸钠晶体的具体操作方案。     

二水硫酸钙的结晶动力学研究

用MSMPR结晶器对二水硫酸钙结晶的动力学进行了研究,在假设ΔL定律适应于MSMPR结晶过程的前提下,测量了晶体的粒数密度n和晶体平均粒度L,根据ln(n)-L直线在坐标轴上的截距及其斜率所计算出的晶核粒数密度n0和晶体生长速率G之间的关系推导出结晶过程的成核速率B0。最后从ln(n0)与ln(G)之间的直线关系再推导出二水硫酸钙在60℃情况下的成核速率B0与晶体生长速率G之间的动力学表达式:B0=k2Gi=1.142×103G0.54,同时还研究了添加不同类型的活化疏松剂对二水硫酸钙结晶的影响情况。     

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。     

CRYSTALLIZATION KINETICS OF 2-CHLORO-4,6-DINITRORESORCINOL BY BATCH COOLING CRYSTALLIZATION METHOD

Crystallization kinetics of 2-chloro-4,6-dinitroresorcinol in ethanol was studied by the method of intermittent dynamic analysis. The nucleation rate and crystal growth rate of 2-chloro-4,6-dinitroresorcinol under different crystallization temperatures and stirring rates were estimated. The results show that with an increase of crystallization temperature, both the nucleation rate and crystal growth rate increase. It is further found that when the stirring rate increases, the nucleation rate increases and the crystal growth rate decreases. The technological conditions of cooling crystallization of 2-chloro-4,6-dinitroresorcinol were studied. It is found that when the stirring rate is 180 rpm and the solution is cooled slowly to - 8°C, the particle size of the products is even and the highest yield of 2-chloro-4,6-dinitroresorcinol is 40.6%.     

CRYSTALLIZATION KINETICS OF 2-CHLORO-4,6-DINITRORESORCINOL BY BATCH COOLING CRYSTALLIZATION METHOD

Crystallization kinetics of 2-chloro-4,6-dinitroresorcinol in ethanol was studied by the method of intermittent dynamic analysis. The nucleation rate and crystal growth rate of 2-chloro-4,6-dinitroresorcinol under different crystallization temperatures and stirring rates were estimated. The results show that with an increase of crystallization temperature, both the nucleation rate and crystal growth rate increase. It is further found that when the stirring rate increases, the nucleation rate increases and the crystal growth rate decreases. The technological conditions of cooling crystallization of 2-chloro-4,6-dinitroresorcinol were studied. It is found that when the stirring rate is 180 rpm and the solution is cooled slowly to ? 8°C, the particle size of the products is even and the highest yield of 2-chloro-4,6-dinitroresorcinol is 40.6%.     

Computer simulation of crystallization kinetics in fiber-reinforced composites

A computer simulation model was developed to investigate spherulitic growth in polymers of infinite and plate-limited volume as well as in fibre-reinforced polymer composite systems. Parameters like thermal nucleation rate and athermal nucleation density, plate distance, and fibre content were varied. The simulation crystallization process was evaluated following Avrami's method in the case of infinite volume and by stepwise approximation by Avrami functions in the case of limited volume. In addition, the simulation method allows the visualization of the growing entities at any phase of crystallization. Therefore the geometry of growing entities can be easily compared with the corresponding crystallization exponent. A good agreement between the crystallization exponent and the growth geometry was found. Depending on nucleation mode, “infinite” systems yield Avrami exponents of 3 and 4. In plate-limited volume, a transcrystallization effect was observed in case of high athermal nucleation density on plate surface and large plate distances. This particular skin effect decreases the three-dimensional growth to a one-dimensional needle-shaped one. Small plate distance changes the spherical to a disk-like growth, resulting in crystallization exponents of 2 or 3, depending on nucleation mode. The crystallization behaviour of fibrereinforced composite systems is more complex. Low fibre content or large fibre distance and high athermal nucleation density on the fibre surface induce the formation of transcrystalline zones. The three-dimensional growth of the spheres at the beginning is restricted by their neighbours, so that their geometry changes to a pyramidical one. They grow with a front normal to the fibre surface and the crystallization exponent is shifted in between 2.0 and 2.6 depending on nucleation density. High fibre content leads to a growth along the triangular channels between three adjacent fibres; the corresponding exponent amounts to 1.6. © 1994 John Wiley & Sons, Inc.     

EFFECT OF TEMPERATURE ON SUSPENSION CRYSTALLIZATION PROCESSES

A mathematical analysis was carried out to examine the effect of temperature on the nucleation and growth rates in continuous suspension crystallization systems. The analysis included consideration of the population balance, mass balance, nucleation and growth kinetics, and the temperature dependence of the nucleation and growth rate constants. This study provides a reasonable basis to understand the relationships between nucleation and growth rates and such factors as supersaturation, “overall” activation energies, and the kinetic order, i Various temperature behaviors that had been observed for different solute systems were also discussed based on the analysis of this work.     

Investigation of the crystallization behavior of isotactic polypropylene polymerized with different Ziegler‐Natta catalysts

Detailed characterization of the crystallization behavior is important for obtaining better structure property correlations of the isotactic polypropylene (iPP), however, attributed to the complexity in ZN‐iPP polymerization, the relationship between crystallization behavior and the stereo‐defect distribution of iPP is still under debate. In this study, the crystallization kinetics of the primary nucleation, crystal growth and overall crystallization of two iPP samples (PP‐A and PP‐B) with nearly same average isotacticity but different stereo‐defect distribution (the stereo‐defect distribution of PP‐B is more uniform than PP‐A) were investigated. The results of isothermal crystallization kinetics showed that the overall crystallization rate of PP‐A was much higher than that of PP‐B; but the analysis of self‐nucleation isothermal crystallization kinetics and the polarized optical microscopy (POM) observation indicated that the high overall crystallization rate of PP‐A was attributed to the high primary nucleation rate of the resin. The stereo‐defect distribution plays an important role in determining both the nucleation kinetics and crystal grow kinetics, and thus influence the overall crystallization kinetics. A more uniform distribution of stereo‐defects restrains the crystallization rate of iPP, moreover, it has more influence on nucleation kinetics, comparing with the crystal growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

CRYSTALLIZATION KINETICS AND PRODUCT PURITY OF α-GLUTAMIC ACID CRYSTAL

A continuous mixed-suspension mixed-product removal lpar;CMSMPR) crystallizer was used to study the crystallization kinetics and product purity of glutamic acid crystal in pure solution and impure solution with L-phenylanaline as the impurity. Under the assumption that the crystal growth rate was a function of crystal size, the population balance equation was solved to give the crystal growth and nucleation rates by use of the steady-state population density data. The crystal growth and nucleation rates were suppressed by the presence of impurity. The impurity contents in the crystal products, which were analyzed by a HPLC pre-column method, were found to be related to crystal size, supersaturation, and impurity concentration of solution     

水热合成中负离子配位多面体生长基元模型与粉体的晶粒粒度

在负离子配位多面体生长基元模型的基础上深入研究了晶粒的结晶过程,认为成核过程主要包括生长基元的形成和生长基元之间的脱水反应过程,并从成核速度的角度分析了影响晶粒粒度的主要原因,揭示了影响晶粒粒度的主要原因为生长基元的生成能,晶体的晶格能,由此总结出不同结构类型的氧化物粉体晶粒粒度的相对大小,合理地解释了由水热法制得的氧化物粉体的晶粒粒度差别较大的原因以及反应介质,反应温度对晶粒粒度的影响。     

ISOTHERMAL CRYSTALLIZATION AND SUBSEQUENT MELTING BEHAVIOR OF POLY(ETHYLENE TEREPHTHALATE)/SILICA NANOCOMPOSITES

The crystallization process of nanocomposites was investigated by differential scanning calorimetry (DSC) and analyzed by the Avrami method. It was found that the crystallization of pure poly(ethylene terephthalate) (PET) is fitted for thermal nucleation and three-dimensional spherical growth in the whole process, while the crystallization of PET/silica nanocomposites exhibits two stages: the first stage corresponds to athermal nucleation and three-dimensional spherical growth, and the second one corresponds to recrystallization caused by the earlier spherulite impingement. The crystallization rate increases markedly and the activation energies decrease greatly with adding silica nanoparticles. The subsequent melting behavior of the crystallized samples shows that the melting point (T_m) of nanocomposites is higher than that of pure PET, which might result from two reasons: (1) some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; and (2) more perfect crystals being formed due to the higher crystallization temperature and lower activation energy of PET/silica nanocomposites.     

剪切流场中聚乙烯结晶过程的建模与模拟

基于Eder模型推导了剪切流场中球晶、串晶形态演化的数学模型,将第一法向应力差作为串晶成核的驱动,并引入两相悬浮模型描述体系,认为其由无定形相和半结晶相组成,分别用FENE-P模型和刚性哑铃模型描述。基于上述数学模型,分别构造了捕捉球晶、串晶生长的Monte Carlo法与体系控制方程求解的有限差分法,成功模拟了二维剪切流场中聚乙烯的结晶过程,给出了球晶、串晶的形态演化,分析了剪切时间、剪切速率对串晶成核密度、结晶速率、流体黏度等的影响。数值结果表明:所构造的Monte Carlo法合理有效,不仅成功捕捉了晶体的生长与碰撞,而且较为准确地预测了结晶速率。此外,提高剪切时间或剪切速率,将增加串晶成核密度、提高结晶速率、使流体黏度突增的时间点提前。