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。     

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。     

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。     

硝酸钾结晶生长特性的研究

利用5LMSMPR结晶器,通过改变停留时间、过饱和度和搅拌速度等因素,对硝酸钾结晶的粒度分布、平均粒径、主粒径、成核及生长速率等动力学特性进行了研究,并在结晶温度25℃、过饱和度2℃、搅拌速度400r/min和停留时间10～50min条件下,建立了硝酸钾晶体生长动力学模型:B°=6.19×1022G2.02。研究结果表明:当停留时间大于30min、搅拌速度为400r/min时,晶体的平均粒径和主粒径较大;过饱和度的减小也会使晶体粒径增大,但其影响较小。     

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。     

阿莫西林成核与生长动力学

阿莫西林现有结晶工艺获得的晶体粒度过小,直接影响到后续的过滤、干燥以及包装运输,研究其结晶动力学参数以指导结晶工艺,控制结晶过程中晶体的成核速度与生长速度,对提高晶体粒度有着重要意义。文章分别采用激光法和显微摄像的方法对阿莫西林结晶过程中初级成核、二次成核和单晶体生长速度进行了测定,计算出动力学相关数据。通过实验确定阿莫西林初级成核中均相成核与非均相成核的分界过饱和度S=4.5以及各自对应的成核自由能与成核半径,确定了二次成核发生时间与过饱和度间的关系以及阿莫西林晶体的生长速率与过饱和度的关系,并由生长指数m=1.995 5推出阿莫西林的生长机制为螺旋错位生长。通过阿莫西林结晶动力学研究为改进和优化结晶过程提供了理论基础。     

五水柠檬酸钠连续结晶动力学研究

研究了五水柠檬酸钠的连续结晶过程。利用马尔文激光粒度分析仪对不同温度和停留时间下连续结晶过程产品的粒度分布进行分析。通过实验数据和粒度无关生长模型,分别计算了连续结晶过程中五水柠檬酸钠晶体生长与成核速率方程。研究表明,在33.3℃的连续结晶过程中,五水柠檬酸钠的成核速率较生长速率对溶液的过饱和度变化更敏感,增加溶液过饱和度更易形成较小粒度的晶体。     

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。     

搅拌反应器中氯化钠的结晶动力学研究

氯化钠广泛应用于多个领域,为更好地了解氯化钠的结晶原理,优化其结晶过程,对氯化钠在搅拌反应器中的结晶动力学进行了实验模拟,以研究氯化钠晶体在30℃条件下搅拌结晶过程中晶体的成核过程和生长过程,以及搅拌速度、过饱和度和悬浮密度对氯化钠晶体结晶过程的影响,并通过测得的多组数据采取多元非线性拟合的方法构建氯化钠晶体的成核和生长动力学模型。     

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.     

Nucleation Kinetics and Growth Model of Penicillin Sulfoxide in Butyl Acetate

Nucleation kinetics and a growth model of penicillin sulfoxide in butyl acetate were studied. Nucleation parameters such as energy per unit volume, radius of critical nucleus, critical free energy barrier, and nucleation rate were evaluated. A laser method was selected to detect the first crystal in induction period studies. By means of scanning electron microscopy and surface entropy factor, the growth model of penicillin sulfoxide developed from butyl acetate could be determined.     

Kinetics of Primary Nanoparticle Agglomeration in Precipitation of Silver

The precipitation kinetics of silver was studied using a lab‐scale batch crystallizer with special attention to characterization of agglomeration of primary nanoparticles. The vessel was operated at different feed concentrations, molar ratios, and stirrer speed. Nucleation, volume average crystal growth rates, and agglomeration kernels were determined. Empirical relations were obtained between the rates of the different crystallization steps with supersaturation, magma density, and energy dissipation rate. The results show that larger crystals will be obtained at high supersaturation due to dominance of agglomeration, because the rate of agglomeration also increases with supersaturation, thereby suppressing the primary nucleation rate and enhancing the observed average volume growth rate.     

Crystallization of high purity ammonium meta-tungstate for production of ultrapure tungsten metal

The growth mechanism of Ammonium Meta-Tungstate (AMT) crystal was interpreted as two-step model. Growth rates of AMT crystals were measured in a fluidized bed crystallizer. The effects of temperature, supersaturation and crystal size on the crystal growth were investigated. The contribution of the diffusion step increased with the increase of temperature, crystal size and supersaturation. The nucleation kinetics from measurements on the width of the metastable region of Ammonium Meta-Tungstate (AMT) was also evaluated. The crystal size distribution from a programmed cooling crystallization system was predicted by the numerical simulation of a mathematical model using the kinetics of nucleation and crystal growth. It was also observed that the shape of AMT crystals was changed during the growth period. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

Impeller geometry effect on crystallization kinetics of borax decahydrate in a batch cooling crystallizer

The effects of impeller type and diameter in a batch cooling crystallizer on the nucleation and crystal growth kinetics as well as on the shape and size distribution of borax decahydrate crystals were investigated. Two different types of impellers of various sizes were applied. Chosen impeller configurations generate completely different fluid flow patterns in the crystallizer what allows to investigate the influence of the axial and radial flow on the kinetic parameters as well. The nucleation in crystallizer was taking place by the heterogeneous nucleation mechanism at all mixing conditions. The number of crystals formed by this mechanism increases as ratio D/d_T decreases and it is higher when an axial flow pattern in crystallizer has been developed. The crystal growth rate increases with increasing the impeller size in observed supersaturation range. The radial impeller defined by ratio D₂/d_T = 0.58 could be considered as viable option for growth of borax crystal, since the further enlargement of this ratio does not increase growth rate and can only cause higher power consumption. The maxima in the coarser and finer fractions of CSD indicate a different influence of mixing conditions on the crystal grow and secondary nucleation. An axial flow pattern in crystallizer favors agglomeration of growing crystals increasing that way product mean crystal size, while radial flow results with more regular shape of borax crystals.     

Simulation of batch crystallization

The closed mathematical model of a well-mixed batch crystallizer has been presented. This model takes into consideration crystals growth rate fluctuations producing an increased spread of crystal sizes. The numerical methods for solving partial integro-differential system of this model equations are proposed for the cases of when growth rate is expressible as product of supersaturation and size functions.Simultaneous population and mass balance equations have been calculated together with power law kinetics of nucleation and growth to determine crystal-size distribution functions (CSD), variation coefficients (CV), produced crystal sizes and numbers. The case of size-dependent crystal growth determined by sequential processes of diffusion and surface reaction is also investigated.The computer results are presented in the dimensionless form as functions on both diffusion and fluctuation Peclet numbers and dimensionless cooling rate. In particular, it has been established that the CV of weight CSD increases approximately twice due to fluctuations and becomes close to 40%; the CV also increases owing to the decrease of cooling rate and approaches 28%. Some formulae are suggested for predicting the kinetics of crystallization (or precipitation) and determining the kinetic parameters of crystals growth and nucleation.     

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。     

A study on crystallization kinetics of pentaerythritol in a batch cooling crystallizer

The crystallization kinetics of pentaerythritol (PeE) in aqueous solution in the presence of impurity or not in a batch cooling crystallizer was explored. Also, the solubility and the nucleation and crystal growth kinetics of PeE in aqueous solution were investigated. A second-order dependence of PeE growth rate on supersaturation is observed in pure PeE-water system. The crystal growth rate of PeE-water system in the presence of impurity is proportional to the supersaturation to the 3.5 power. The nucleation and crystal growth behaviors for PeE-water system in a batch cooling crystallizer were grasped according to Mersmann's criteria. The nucleation in this crystallizer was found to act with heterogeneous nucleation. In this system, it suggests that the crystal growth is controlled by a complex mechanism behavior of surface integrated and diffusion limited. Simplified relation was derived for calculation of mean crystal size of product crystals from the batch cooling crystallizer. The obtained relation was verified by a set of experiments.     

基于分子运动学的水汽在细颗粒表面异质核化的数值模拟

为研究过饱和水汽在细颗粒表面异质核化特性,准确预测成核参数,基于分子运动学异质核化理论建立了过饱和水汽在燃煤细颗粒表面异质核化的运动学模型。数值分析了液滴晶核长大过程中水汽分子和水分子两种扩散凝结机制对晶核长大的促进作用及其相对重要性,数值预测了水汽过饱和度和宏观接触角对成核速率的影响;数值计算了不同温度和宏观接触角下细颗粒的临界过饱和度。结果表明：当液滴晶核尺寸小于临界晶核半径时,颗粒表面吸附水分子扩散凝结速率与水蒸气分子直接扩散凝结速率的比值大于100,颗粒表面吸附水分子的扩散凝结机制对晶核长大起主导作用。提高水汽过饱和度或减小宏观接触角均可显著提高液滴晶核的成核速率;成核速率随水汽过饱和度增大呈指数型增长。提高气相主体中水汽温度或减小细颗粒物的宏观接触角均可显著降低异质成核的临界过饱和度;对于粒径小于0.1 μm的细颗粒物,随着细颗粒粒径的增大,异质核化的临界过饱和度显著减小。     

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。