THE NARROWING OF CRYSTAL SIZE DISTRIBUTIONS IN A SONICATOR-MSMPR CRYSTALLIZER SYSTEM

Obtaining small crystals of a narrow crystal size distribution is an important problem in many pharmaceutical, biotechnological, and ceramic processing applications. This paper describes the use of a two-stage system to reproducibly produce pilot-scale quantities of a ceramic precursor powder.

The population balance is used to determine the crystal size distributions obtained from a staged crystallization system. The staged crystallization system consists of two units, a mininucleator (sonicator) and an MSMPR crystallizer. Experimental and theoretical studies of this system showed that the use of the mininucleator leads to narrowing of the crystal size distribution obtained from the MSMPR crystallizer. The resulting expression for the population density distribution allows direct fitting of experimental log population density data from the second stage to determine the growth and nucleation kinetics for both the mininucleator and the MSMPR crystallizer     

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。     

Kinetics of the cooling crystallization of sodium sesquisulfate from 4.5 mol/l sulfuric acid

Simulating effluent from chlorine dioxide generators, the crystallization kinetics of sodium sesquisulfate from 4.5 mol/L sulfuric acid were studied under cooling conditions. The crystal growth and nucleation rates were determined using the population balance concept and the crystal size distribution from a continuous mixed suspension mixed product removal (MSMPR) crystallizer. Crystallization temperatures studied were 45, 50, 55 and 60°C. The crystal growth and nucleation rate data were correlated to supersaturation and temperature. Nucleation rate was found to be a function of suspension density (secondary nucleation). The activation energies for nucleation and growth are reported.     

Effect of sinusoidal Taylor vortex flow on cooling crystallization of L-lysine

An elliptical Couette-Taylor (ECT) crystallizer with a unique sinusoidal Taylor vortex flow was developed to promote the recovery and size distribution of L-lysine crystals in cooling crystallization. When using the ECT crystallizer, the recovery was enhanced to a maximum of 100% with a mean residence time of only 15 min. When comparing the crystallization efficiency, the recovery and size distribution of the L-lysine crystals in the ECT crystallizer were over 33% and 50% higher, respectively, than those in the conventional MSMPR crystallizer and slightly higher than those in the circular Couette-Taylor (CT) crystallizer. This improved crystallization in the ECT crystallizer was explained in terms of the sinusoidal profile of the Taylor vortex intensity. Plus, since the nucleation and growth processes determine the recovery and crystal size distribution, the mean residence time, inner cylinder rotation speed, and feed concentration were all varied to investigate their influence on the crystallization efficiency.     

Mathematical modelling and experimental validation of a novel periodic flow crystallization using MSMPR crystallizers

The challenges of insufficient residence time for crystal growing and transfer line blockage in conventional continuous mixed‐suspension mixed‐product removal (MSMPR) operations are still not well addressed. Periodic flow crystallization is a novel method whereby controlled periodic disruptions are applied to the inlet and outlet flows of an MSMPR crystallizer to increase its residence time. A dynamic model of residence time distribution in an MSMPR crystallizer was first developed to demonstrate the periodic flow operation. Besides, process models of periodic flow crystallizations were developed with an aim to provide a better understanding and improve the performance of the periodic flow operation, wherein the crystallization mechanisms and kinetics of the glycine‐water system were estimated from batch cooling crystallization experiments. Experiments of periodic flow crystallizations were also conducted in single‐/three‐stage MSMPR crystallizers to validate the process models and demonstrate the advantages of using periodic flow operation in MSMPR stages. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1313–1327, 2017     

Neuro‐Fuzzy Control of a Continuous Cooled MSMPR Crystallizer

This work deals with the design and application of a neuro‐fuzzy controller of the magma density of the fine crystals for the stabilisation of the crystal size distribution (CSD) of the product from an MSMPR (Mixed Suspension, Mixed Product Removal) continuous crystallizer. The cooling crystallization of potassium sulphate from aqueous solutions in a pilot‐scale stirred vessel was investigated. A control strategy, based on the elimination of fines by using a combined sedimentation‐dissolution device, is presented. The control scheme was successfully applied to a pilot‐scale draft‐tube (DT) crystallizer and yielded promising results. The proposed process control system allowed the reduction of the fines fraction by more than 30 %, while maintaining operation stability and short transient responses.     

Reaction‐Crystallization of Struvite in a Continuous Liquid Jet‐Pump DTM MSMPR Crystallizer with Upward Circulation of Suspension in a Mixing Chamber – an SDG Kinetic Approach

The experimental results concerning kinetic aspects of struvite precipitation in a continuous DTM‐type crystallizer with internal circulation of suspension forced by a liquid jet‐pump are presented and discussed. Nucleation and crystal growth rates of struvite during reaction‐crystallization processes in diluted water solutions of magnesium, ammonium, and phosphate ions were identified. Kinetic parameters were calculated on the basis of population density distributions adopting a simplified model of the mass crystallization process in a MSMPR crystallizer taking under consideration size‐dependent growth (SDG) mechanism. The Rojkowski hyperbolic SDG model has proved to be the equation best statistically fitted to our own data set.     

Crystallization and agglomeration kinetics of nickel ammonium sulphate in an MSMPR crystallizer

Precipitation of nickel ammonium sulphate achieved by mixing solutions of nickel sulphate and ammonium sulphate in a 5 1 MSMPR crystallizer is used to investigate both crystallization and agglomeration kinetics from the steady-state crystal size distribution. An iterative non-linear parameter estimation procedure is used to deduce the kinetic rate parameters in the solution of the agglomeration model suggested by Liao and Hulburt from the data-set obtained by size analysis of the product crystals. The results obtained are correlated in terms of conventional power law kinetic expressions.     

阻垢分散剂对氟硅酸钾(钠)结晶过程的影响

在试验分析十余种阻垢分散剂及将有机膦酸和聚羧酸（盐）复配使用的防垢效果的基础上，选取效果较佳的3种在MSMRP结晶器中研究了对Na2SiF6,K2SiF6从湿法磷酸溶液中结晶的影响。结果表明，所选用的阻垢分散剂均可减小晶体生长速率及平均粒径，但可增大晶核数密度及成核速率，并使晶体形态发生严重畸变，NaSiF6由八面体变为粒状及其他不规则小晶体，K2SiF6则由立方体晶体聚在一起的取晶转为小的粒状，立方体及小聚晶等。     

Slurry filtrability of potash alum

Crystal slurries produced both by cooling and by precipitation with acetone from aqueous solution in a continuous MSMPR crystallizer reported earlier (Jones and Mydlarz, 1990) are analysed in terms of the effect of their crystal size distribution and shape on filtrability characteristics. Crystals produced by precipitation are much smaller but more highly agglomerated than those from cooling crystallization and give rise to lower filter bed permeabilities, a performance which is slightly improved by precipitant dilution. The overall particle size is, however, similar in both modes and is relatively insensitive to crystallizer operating conditions. The filtrability data for the precipitated crystals are compared with predictions of the Carman-Kozeny equation, assuming an idealized crystal shape. Relatively large scatter is observed, with the Kozeny coefficient, K, being in the range 2 to 8.     

头孢拉定连续结晶工艺研究

采用三级混合悬浮混合产品出料结晶器(MSMPR),搭建了头孢拉定连续结晶实验装置。通过单因素实验研究了养晶pH值、晶种添加量、原料液浓度、停留时间、结晶系统温度及搅拌速率等结晶工艺条件对头孢拉定连续结晶产品收率及粒度分布的影响,优化了头孢拉定连续结晶工艺参数。通过实验获得优化结晶工艺参数：结晶温度293.15 K,搅拌速率180 r·min^-1,养晶pH=2.85,晶种添加量为3%(质量分数),头孢拉定原料液浓度11%(质量分数),停留时间33.3 min,此条件下可以获得平均粒径为85.3μm,收率为76.53%的头孢拉定连续结晶产品。     

Barium Sulfate Crystallization Kinetics in the Used Quenching Salts Treatment Process

The research results and kinetic studies on the barium ions precipitation process by means of crystalline ammonium sulfate addition are presented. The influence of: barium, sodium, potassium and calcium chlorides concentration in the feeding solution and also the process temperature on barium sulfate mass crystallization kinetics are investigated. Experiments were carried out in the MSMPR crystallizer with internal circulation of suspension. The barium sulfate nucleation and crystal growth rates were estimated from crystal size distribution taking into account a size dependent growth (SDG). Research results may be utilized in the used quenching salts processing technology.     

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。     

木糖结晶动力学模型

<正>木糖(D-xylose)是一种新型的甜味剂.其生产原料为农业植物纤维废料,如玉米芯、甘蔗渣、棉子壳、甘蔗髓、稻壳等.中国是农业大国,木糖的原料极其丰富,生产木糖是一个具有较高附加值的二次资源利用项目.国内已有数家企业投入生产,但许多技术问题尚未解决,制约了经济效益,其中结晶工序也是瓶颈之一.本文作为木糖生产新工艺的重要环节,研究了木糖连续冷却结晶过程,并根据结晶动力学的粒数衡算理论(Population Balance)及其连续稳态的动力学测定方法,探索了木糖的结晶动力学模型.国内外迄今尚无这方面的报道.1 粒数衡算理论     

Crystallization kinetics from transients of an MSMPR crystallizer

Transient population density curves from a continuous MSMPR crystallizer obtained in response to an application of external non-homogeneous forcing functions (like changes in feed concentration or flowrate) were used to deduce simultaneously nucleation and growth kinetics. Several simplified parameter estimation procedures were examined using simulated experimental observations of population densities and gave consistent results. Results however obtained from an experiment performed in a small continuous MSMPR crystallizer for the precipitation of calcium oxalate showed apparent scatter in all the algorithms. Methods using transient population density information by themselves may be useful to determine and also to provide an independent check on the reliability of kinetic parameter estimates.     

丙烯酰胺的结晶动力学

采用MSMPR连续结晶器研究了丙烯酰胺的成核 -生长动力学。实验结果表明 ,丙烯酰胺的晶体生长基本符合生长速率与粒度无关的ΔL定律。在小于 1 0 0 μm的晶体粒度范围内 ,存在大量的细小晶粒 ,分析了产生这种现象的 4种可能原因。得到结晶温度分别为 1 0、1 5、2 0℃时 ,丙烯酰胺的成核 -生长动力学模型分别为 :n0 =1 2 6× 1 0 - 5G3 6 6 、n0 =3 92× 1 0 - 5G2 92 、n0 =7 65× 1 0 - 5G3 31 。在 1 0～ 2 0℃内 ,丙烯酰胺的成核 -生长动力学级数为 4 30。动力学级数对温度敏感性较小 ,不能通过调节晶浆密度来控制晶体产品的主粒度。进行了丙烯酰胺结晶的应用研究 ,完成了连续三步式结晶新工艺的概念设计。     

Characteristics of multistage column crystallizer for gas-liquid reactive crystallization of calcium carbonate

Crystallization of calcium carbonate using a gas (CO₂)-liquid (Ca(OH)₂) reaction was conducted using a three-stage column crystallizer. In this study, the staging effect of the multistage column crystallizer and the effect of the operating parameters on the particle size distribution were experimentally and theoretically investigated. From an economic viewpoint, the multistage column crystallizer has been developed to replace a cascade of MSMPR crystallizers, which requires a large installation area and high operating cost because some crystallizers are connected in a series. In the multistage column crystallizer, a narrower particle size distribution was obtained compared to that obtained in the standard column crystallizer. The theoretical approach to predict the particle size distribution is based on the population balance equation which takes account of the back flow into the crystallizer. The calculation results of particle size distribution fairly coincide with the experimental results, which indicates the particle size distribution in the multistage column crystallizer can be roughly predicted by this theoretical model.     

导流筒浆态连续结晶器内鸟粪石的反应结晶动力学——器内流体力学的影响

A laboratory-scale reaction-crystallization process of struvite synthesis from diluted water solution of Mg2+, and ions was studied. The research covered the tests of two original constructions of continuous jet-pump Draft Tube Magma (DTM)-type crystallizers with internal circulation of suspension (upward/downward). Interactions between constructional, hydrodynamic and kinetic factors were established and discussed. Nucleation and linear growth rates of struvite crystals were calculated on the basis of population density distribution. Kinetic model of idealized Mixed Suspension Mixed Product Removal (MSMPR) crystallizer considering the size-dependent growth mechanism was applied (Rojkowski hyperbolic equation). For comparison purposes the kinetic data corre-sponded to a simpler, continuous draft tube-type crystallizer equipped with propeller agitator were analyzed. It was concluded that crystal product of larger size was withdrawn from the jet-pump DTM crystallizer of the descending flow of suspension in a mixing chamber.     

二水硫酸钙结晶过程及活化疏松剂对其影响的研究

以碳酸钙、磷酸和硫酸为原料。在MSMPR结晶器中研究二水硫酸钙的结晶过程。分别讨论了结晶温度、平均停留时间、硫酸质量分数等因素对结晶成核速率、晶体成长速率以及晶体形状、大小的影响。另外还研究了添加不同类型的活化疏松剂对二水硫酸钙结晶过程的影响。