旋转填充床中沉淀过程的模型及实验验证(英文)

A mixing-precipitation model based on the modified coalescence-redispersion model was presented to describe the flow, mixing, nucleation and growth in a rotating packed bed (RPB). The model was coupled with population balance, mass balance and crystallization kinetics. It predicted well the influence of coalescence probability, which represents the mixing intensity among drop-lets, on the particle number density, supersaturation and mean particle size of the produced precipitates. The effects of the radial thickness of packing, liquid flow rate and rotating speed on the product particle size were also investigated. The results indicate that the needed radial length of packing is short for sparingly soluble substance precipitation (about 40-50 mm in this work), and the mean particle size of precipitates decreases with the increase of rotating speed and liquid flow rate, respectively. The validity of this model was verified by experiment on BaSO4 precipitation in RPB.     

间歇结晶器中维生素C的结晶热力学与动力学研究

The bench-scale cooling crystallization for ternary solution of L-ascorbic acid (Vitamin C) was studied.The solid-liquid phase diagram of Vitamin C-water-ethanol system was obtained on the basis of differential scanning calorimeter (DSC) curves. The heat of crystallization of Vitamin C was calculated with the aid of quantitative analysis. According to the population balance equation under unsteady state, the rates of nucleation and growth were determined. The parameters of crystallization kinetics equations were estimated by regression of experimental data. Crystal morphology and size were determined with x-ray diffraction and TA Ⅱ Coulter Counter.     

盐酸大观霉素溶析结晶过程模拟与分析

A mathematical model for dilution crystallization of spectinomycin dihydrochloride pentahydrate was established on the basis of the population and mass balance. Three operating modes, i.e., constant mass rate addition of diluent, constant mass fraction of diluent and constant size-independent growth rate, were investigated over a wide range of controlled parameters. The intrinsic characteristics of the crystallization process and the influence of operation parameters were analyzed in detail. Suitable strategy for better performance was suggested.     

添加剂EDTA对氢氧化镁反应结晶过程的影响(英文)

The effects of additive ethylenediaminetetraacetic acid (EDTA) on crystallization process were investigated by the induc-tion time of MgSO4-NaOH system. Nucleation and growth rates, growth mechanism and particle size distribution of magne-sium hydroxide precipitation were involved with. The induction time in unseeded and seeded precipitation of magnesium hydroxide with and without additive EDTA was measured. The conductivity method was used to determine the induction period. Theoretical relations of the induction time and supersaturation ratio for different growth mechanisms and a combined analysis on the induction time were applied to determine nucleation and growth rates. The growth mechanism of magnesium hydroxide precipitation was dis-closed by analyzing the experimental data with and without additive. The analysis on induction time indicated that additive EDTA had a significant influence on both nucleation and growth of magnesium hydroxide precipitation. The mechanism underlying the effect of EDTA on crystal growth was 2-dimension nucleation-mediated growth model.     

MSMPR反应结晶器中地塞米松磷酸钠晶体生长模型的研究

The reactive crystallization process of dexamethasone sodium phosphate was investigated in a continuous mixed-suspension, mixed-product-removal(MSMPR) crystallizer. Analyzing experimental data, it was found that the growth of product crystal was size-dependent. The Bransom, CR, ASL, M J2 and M J3 size-dependent growth models were discussed in details. Using experimental steady state population density data of dexamethasone sodium phosphate, parameters of five size-dependent growth models were determined by the method of non-linear least-squares. By comparison of experimental population density and linear growth rate data with those obtained from the five size-dependent growth models, it was found that the MJ3 model predicts the growth more accurately than do the other four models. Based on the theory of population balance, the crystal nucleation and growth rate equations of dexamethasone sodium phosphate were determined by non-linear regression method. The effects of different operation parameters such as supersaturation, magma density and temperature on the quality of product crystal were also discussed, and the optimal operation conditions were derived.     

应用CFD技术对工业结晶过程进行模拟和放大

Some empirical mixing models were used to describe the imperfect mixing in precipitation process.However, the models can not, in general, reflect the details of interactions between mixing and crystallization in a vessel. In this study, CFD (computational fluid dynamics) technique were developed by simulating the precipitation of barium sulphate in stirred tanks by integration of population balance equations with a CFD solver. Two typical impellers, Rushton and pitched blade turbines, were employed for agitation. The influence of feed concentration and position on crystal product properties was investigated by CFD simulation. The scale-up of these precipitators was systematically studied. Significant effect on the crystal properties was found for the scale-up under some conditions.Keywords simulation, scale up, precipitation, CFD(computational fluid dynamics)     

Modeling of segregation in magnetized fluidized bed with binary mixture of Geldart-B magnetizable and nonmagnetizable particles

For the magnetized fluidized bed(MFB)with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles,the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities(H),leading to the deterioration of the fluidization quality.The critical intensity(H_(ms))above which such segregation commences varies with the gas velocity(U_g).This work focuses on establishing a segregation model to theoretically derive the H_(ms)–U_g relationship.In a magnetic field,the magnetizable particles form agglomerates.The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles.Consequently,the segregation model was established in two steps:first,the size of agglomerates(d_A)was calculated by the force balance model;then,the H_(ms)–U_g relationship was obtained by substituting the expression of d_Ainto the basic size segregation model for binary mixtures.As per the force balance model,the cohesive and collision forces were 1_2 orders of magnitude greater than the other forces exerted on the agglomerates.Therefore,the balance between these two forces largely determined d_A.The calculated d_A increased with increasing H and decreasing U_g,agreeing qualitatively with the experimental observation.The calculated H_(ms)–U_ g relationship agreed reasonably with the experimental data,indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.     

油酸修饰纳米CaCO3对PP结晶行为和力学性能的影响

Oleic acid (OA)-modified CaCO3 nanoparticles were prepared using surface modification method. Infrared spectroscopy (IR) was used to investigate the structure of the modified CaCO3 nanoparticles, and the result showed that OA attached to the surface of CaCO3 nanoparticles with the ionic bond. Effect of OA concentration on the dispersion stability of CaCO3 in heptane was also studied, and the result indicated that modified CaCO3 nanoparticles dispersed in heptane more stably than unmodified ones. The optimal proportion of OA to CaCO3 was established. The effect of modified CaCO3 nanoparticles on crystallization behavior of polypropylene (PP) was studied by means of DSC. It was found that CaCO3 significantly increased the crystallization temperature, crystal-lization degree and crystallization rate of PP, and the addition of modified CaCO3 nanoparticles can lead to the for-mation of β-crystal PP. Effect of the modified CaCO3 content on mechanical properties of PP/CaCO3 nanocompo-sites was also studied. The results showed that the modified CaCO3 can effectively improve the mechanical proper-ties of PP. In comparison with PP, the impact strength of PP/CaCO3 nanocomposites increased by about 65% and the flexural strength increased by about 20%.     

Free radical reaction model for n-pentane pyrolysis

A mathematical mechanism of the n-pentane pyrolysis process based on free radical reaction model was presented.The kinetic parameters of n-pentane pyrolysis are obtained by quantum chemistry and the reaction network is established.The solution of the stiff ordinary differential equations in the n-pentane pyrolysis model is completed by semi implicit Eular algorithm.Then the pyrolysis mechanism based on free radical reaction model is built,and the computational efficiency increases 10 times by algorithm optimization.The validity of this model and its solution method is confirmed by the experimental results of n-pentane pyrolysis.     

A Population Balance Model for Disperse Systems： Particle Size Distribution in Suspension Polymerization

On the basis of population balance a mathematical model is developed to describe the formation of polymer partlcle in styrene suspension polymerization. The characteristics of coalescence and breakage of droplets and the gel effect are analyzed in particular. Parameters of the models are esthnztted by experimental. on reaction conversion and particle size distributlon. The results show that the model is suitable for predicting polymerization processes.     

工业结晶过程的多相流与粒数衡算的CFD耦合求解

考虑不同尺寸的晶体为不同的分散相,通过有限体积法差分不同尺寸组的晶体求解粒数衡算方程,建立了质量衡算与粒数衡算之间的联系,在考虑晶体成核和生长的条件下,建立了稳态结晶过程的粒数衡算方程与多相流方程的耦合求解方法,得到了工业结晶过程的计算流体力学模拟模型。使用商业软件ANSYS CFD,采用该模型对DTB 型工业结晶器中氯化钾-水体系的结晶过程进行了模拟,最终获得不同尺寸晶体的流场和固体含量的分布信息,从而实现结晶过程的仿真模拟。对部分模拟结果与实验值进行了比较,结果表明模拟结果与实验结果吻合较好。     

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。     

聚集结晶动力学研究方法的改进

在Hounslow工作的基础上,推导了新的聚集机理,改进了聚集模型。通过粒数衡算和质量衡算,结合改进的聚集模型建立了聚集结晶动力学辨识的新方法。文中以头孢哌酮钠结晶过程为例,应用新方法确定了该物系的晶体生长、聚集以及成核动力学。结果表明新方法研究聚集结晶动力学具有一定的可靠性。     

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。     

A MODEL FOR ALUMINIUM TRIHYDROXIDE CRYSTALLIZATION FROM PURE AND IMPURE SOLUTIONS

Mannitol has been used as a model hydroxy organic compound to simulate the influence or organic compounds on the growth, nucleation and agglomeration mechanisms of aluminium trihydroxide crystallization. As little as 151·6rngmannitol/m³ of seed was sufficient to completely suppress the crystallization. A population balance equation including terms for nucleation, growth and agglomeration, coupled with a mass balance equation forms the basis of a mechanistic model for batch crystallization of aluminium trihydroxide. The presence of mannitol at a level as low as 92·2 mg mannitol/m² of seed reduced the growth rate coefficient by an order of magnitude and the nucleation rate coefficient by two orders of magnitude. This low mannitol concentration also increased the agglomeration parameter. Four different kernels of shear flow, turbulent flow, size independent, and an empirical kernel were checked for best fit in the present study. Crystallization in the absence of mannitol was best fitted with no agglomeration term in the model.     

采用粒数衡算模型研究沉淀过程中粒子的聚结和破裂

通过采用MSMPR反应沉淀器,研究了普鲁卡因青霉素反应沉淀过程中粒子的聚结和破裂对过程的影响机理,并对用生死函数表征聚结和破裂的粒数衡算模型采用新的分析方法。结果表明,将二元破裂模型应用于该粒数衡算模型是可行的。     

普鲁卡因青霉素的结晶动力学

通过对用生死函数表征粒子聚结和破裂的粒数衡算模型,采用新的分析计算方法来研究普鲁卡因青霉素反应结晶过程中粒子的聚结和破裂对过程的影响机理;采用ＭＳＭＰＲ结晶实验获得了普鲁卡因青霉素反应结晶的结晶动力学。     

采用粒数衡算模型研究沉淀过程中粒子的聚结和破裂

通过采用MSMPR反应沉淀器,研究了普鲁卡因青霉素反应沉淀过程中粒子的聚结和破裂对过程的影响机理,并对用生死函数表征聚结和破裂的粒数衡算模型采用新的分析方法。结果表明,将二元破裂模型应用于该粒数衡算模型是可行的。     

间苯二甲酸连续多级结晶的数学模拟

以粒数衡算为基础,对间苯二甲酸精制的多级连续蒸发结晶流程建模。通过对模型预测和实测最终产品的比较,确定了间苯二甲酸在水中的结晶动力学参数,并利用所建模型和得到的结晶动力学方程分析了各种操作参数对结晶产品粒度分布的影响,提出了改善结晶产品的粒度分布的条件并实际应用于工业生产。