Agglomeration behavior of anhydrous L-ornithine-L-aspatate crystals during semi-batch drowning-out crystallization

Crystallization of L-ornithine-L-aspartate (LOLA) by drowning out was carried out to produce the anhydrous form of agglomerates. The primary crystal size in the agglomerate remained unchanged after completion of the crystallization. The LOLA aqueous solution introduced into the system was immediately dispersed and cluster coagulated on the surface of the crystals. On the surface of the crystals, a cluster reached critical nuclei size, nucleated and intergrowth to form agglomerates. It was proposed that a spherical agglomeration occurred during secondary nucleation by coagulation model and intergrowth. The agglomerates size and size distribution were varied with the process parameters. The agglomerate sizes of LOLA crystals appeared to be ruled not only by secondary nucleation rate but also by the mass of suspended agglomerates. Moreover, the agglomeration rates of fine particles were higher than the agglomeration rates of large agglomerates. Using these properties, the uniform agglomerates size distribution could be obtained.     

CL‐20 Evaporative Crystallization under Reduced Pressure

The effect of parameters of the CL‐20 crystallization process carried out by solvent removal by evaporation in vacuo on shape, polymorph type, crystal size, and on their shock sensitivity was studied. The CL‐20 crystallization process by this technique was shown to allow a precise control of the crystallization process parameters and of the process run. The o‐xylene/ ethyl acetate system proved to be highly effective. Selecting suitable values of the parameters such as: pressure, process time, temperature, stirring rate, CL‐20 crystals were obtained in the ε form (even with no need for inoculation of the crystallization system with polymorph ε seeds) and of the shape close to a spherical one. The crystal growth modifiers added allowed to additionally control the shape and size of the CL‐20 crystals formed and to produce crystals of reduced impact and friction sensitivity.     

磷酸氢钙结晶聚结过程及主要影响杂质的探究

聚结现象常常伴随着反应结晶过程发生,是影响产品粒度、形貌等性状的主要因素之一。围绕磷酸氢钙的聚结现象分析了聚结发生的过程步骤,并探究了工业生产中阻碍聚结现象的主要杂质元素。结果表明,以纯净稀磷酸为原料,可制得粗大、均匀、稳定性好的大颗粒磷酸氢钙产品,这种大尺寸聚结体经历了单晶团聚、小尺寸簇状晶聚结、大尺寸簇状球形晶形形成等3个关键生长步骤。结晶母液中含氟元素胶体微粒隔断聚结第二步的发生,成为阻碍聚结现象的最关键因素。探索合理利用聚结现象的工艺方法,将为饲料级磷酸氢钙工业生产中解决过滤难、干燥成本高等问题开辟新思路。     

表面活性剂对丁二酸冷却结晶中聚结的抑制

借助聚焦光束反射测量仪(FBRM)和颗粒录影显微镜(PVM)对丁二酸冷却结晶过程中的聚结现象进行研究,通过加晶种实验和不加晶种实验初步推断大小颗粒的共存及颗粒间的相互结合力是形成聚结需要考虑的两个因素。在此基础上,将3种类型的表面活性剂十六烷基三甲基溴化铵(CTAB)、十二烷基苯磺酸钠(SDBS)和吐温80(Tween80)加入到丁二酸冷却结晶系统,考察了表面活性剂对结晶过程中颗粒聚结的抑制作用。晶体形貌变化表明,所选的表面活性剂均能吸附于晶体表面,且可大大降低聚结,可推测表面吸附产生的机械隔离能够降低晶体间的相互结合力,并促使结晶产品的粒度更为均匀。这一研究证明添加表面活性剂可降低结晶过程的聚结程度。     

间歇结晶过程中几种可能的粒度分布

对间歇溶液结晶过程,依据粒数衡算方程,在忽略二次过程如聚集、破碎和老化等且混合良好情况的假设下,采用分离变量方法对粒度相关生长或生长分散的粒度分布进行理论分析,推导出间歇结晶过程中的几个粒数密度与结晶时间和晶体粒度的关系式.这些关系式可以用于间歇结晶过程中,选择合适的晶体生长机理与测定线性晶体生长速率,预测粒度分布与优化结晶过程,以及回归粒度分布.结果表明,本方法在溶液结晶过程中具有良好的应用价值.     

Modeling the crystallization of proteins and small organic molecules in nanoliter drops

Drop‐based crystallization techniques are used to achieve a high degree of control over crystallization conditions in order to grow high‐quality protein crystals for X‐ray diffraction or to produce organic crystals with well‐controlled size distributions. Simultaneous crystal growth and stochastic nucleation makes it difficult to predict the number and size of crystals that will be produced in a drop‐based crystallization process. A mathematical model of crystallization in drops is developed using a Monte Carlo method. The model incorporates key phenomena in drop‐based crystallization, including stochastic primary nucleation and growth rate dispersion (GRD) and can predict distributions of the number of crystals per drop and full crystal size distributions (CSD). Key dimensionless parameters are identified to quickly screen for crystallization conditions that are expected to yield a high fraction of drops containing one crystal and a narrow CSD. Using literature correlations for the solubilities, growth, and nucleation rates of lactose and lysozyme, the model is able to predict the experimentally observed crystallization behavior over a wide range of conditions. Model‐based strategies for use in the design and optimization of a drop‐based crystallization process for producing crystals of well‐controlled CSD are identified. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

CSD-controlled reactive crystallization of SrSO4 in the presence of polyethylenimine

Reactive crystallization of SrSO₄ was performed in the presence of polyethylenimine (PEI) using a double-jet crystallizer. PEI dosage suggested important dependence on crystal size distributions (CSDs) leading to obtain micron-sized crystals with mono-dispersed distribution. A plausible role of PEI was considered to be a multiple inhibitor of growth, continuous nucleation and agglomeration. PEI might be an effective polyelectrolyte additive for the production of mono-dispersed fine crystals.     

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.     

The influence of organic additives on the crystallization and agglomeration of gibbsite

During the crystallization of gibbsite Al(OH)₃, which leads to the synthesis of alumina in the Bayer process, crystals go through a step of agglomeration. In this work, we present a study concerning the influence of different organic compounds, polycarboxylic acids and polyalcohols on the crystallization and agglomeration of gibbsite crystals. It has been determined that they act as crystal habit modifiers and inhibitors of the agglomeration occurring during the formation of alumina crystallites. Simply by following the kinetics of the reaction, it has been observed that polyalcohols are stronger inhibitors than polycarboxylic acids, which can be linked to the structure of gibbsite crystals. The influence of the characteristics of the additive, such as the number of carboxylic groups and the distance between them for polyacids, the stereochemistry and the length of the carbon chain in the case of polyalcohols, is demonstrated to have a significant effect.     

Is spherical crystallization without additives possible?

The quasi-emulsion solvent diffusion method of spherical crystallization consists in producing in one step crystallization and agglomeration of small crystals in droplets of an emulsion. Additives are generally used to stabilize the emulsion before crystallization. The aim of this study is to investigate the feasibility of spherical crystallization without surfactant. Experiments were performed in an automated batch laboratory scale crystallization process to study the influence of the process operating conditions on the structure of the particles obtained. The results clearly show that, for the experiments performed two types of particles are formed: primary spherical particles and secondary agglomerates. The pattern of the primary particles, observed under scanning electron microscopy, suggests that these particles results from a spherulitic crystal growth mechanism inside the droplet. The secondary agglomerates results of the agglomeration of the spherical particles. In addition, a set of experiments were performed with carefully selected solvents to study the influence of the crystallization solution/water interfacial tension, at constant hydrodynamic conditions and supersaturation level. The results of these experiments demonstrate that the interfacial tension is not a key parameter for designing such a process.     

饲料级磷酸氢钙结晶过程中团聚的研究

在反应结晶过程中,一般过饱和度很大,很容易形成大量细小颗粒,这些小颗粒相互作用形成团聚体,会影响最后产品的粒度分布、纯度、晶体形貌、堆密度等参数。饲料级磷酸氢钙生产过程中极易形成团聚体,通过探索团聚体形成的pH范围,对团聚体形成的原因做了分析,并研究了中和条件对团聚形成的影响。结果表明,形成团聚体的pH范围为2.82~3.60。此外,提高反应温度、增加搅拌速度均对团聚体有减缓效果。实验最后建立了磷酸氢钙团聚尺寸模型。     

碳酸锂气液固三相反应结晶过程研究

碳酸锂的气液固三相反应结晶过程包含碳酸锂碳化反应和碳酸氢锂溶液的热析分解两个过程。首先对于碳化过程,考察了碳酸锂碳化转化率和反应速率的影响因素;建立并求解构建碳化微观机理模型,进而确定了碳酸锂碳化过程为气体传质控制。对于热析分解过程,研究了碳酸锂晶体产品的粒度分布、晶体形貌和聚结程度等与反应物浓度、温度、搅拌、晶种以及外场等因素的关系,尤其是在超声结晶条件下能够获得形貌完整且不聚结的碳酸锂棒状晶体。最后,揭示了碳酸锂的结垢机理,并基于实验验证提出了光滑表面、介稳区控制和晶种添加等方案可有效抑制结垢。     

Modelling of multiple-mechanism agglomeration in a crystallization process

A three-level agglomeration model coupled with crystal growth is developed. It accounts for Brownian, laminar, and turbulent agglomeration. The desupersaturation profiles, the particle size distributions, the average sizes, and variances (or standard deviations), as well as the instantaneous agglomeration degrees for each mechanism, can be calculated as functions of time. The model is applied to the crystallization of an amorphous solid into a crystalline polymorph in a batch crystallizer. A runaway phenomenon is detected for agglomeration when crystals are switching over from the Brownian regime to the laminar one: this switchover significantly affects the desupersaturation curve and the crystal shapes.     

Si/F/K/Na杂质对硫酸钙结晶过程的影响

考察了湿法磷酸生产过程中Si, F, K和Na等杂质对CaSO4结晶过程的影响规律. 结果表明,两种碱金属对CaSO4结晶有不同作用,K有利于CaSO4晶体生长,而Na含量增加则会抑制CaSO4团聚;不同形式的K, Si和F对CaSO4结晶的作用不同,SiO2对CaSO4粒径影响不大,但会使其形貌不规则,H2SiF6会造成CaSO4晶体分散,而K2SiF6有利于CaSO4晶体生长.     

磁场影响溶液结晶过程研究进展

论述了磁场对溶液结晶过程影响的研究进展情况，指出磁场不仅可以化溶液结晶过程，刺激结晶成核，提高结晶生长速率，控制晶体粒径的分布，也可抑制溶液的结晶，降低结晶生长速率。针对不同的工程目的，选择合理的磁处理参数显得尤为重要。并提出磁场技术目前存在的问题和展望。     

Modeling batch crystallization processes: Assumption verification and improvement of the parameter estimation quality through empirical experiment design

In this work, experimental data of different batches was used for estimation of the kinetic parameters for the secondary nucleation framework of Gahn and Mersmann [Gahn, C. and Mersmann, A., 1999. Brittle fracture in crystallization processes. Chem. Eng. Sci. 54, 1273–1292].An empirical experiment design procedure was used to design an informative batch experiment through optimization of the seed quality, size and mass and process conditions at seeding. The parameters estimated using the data of the designed experiment showed smaller magnitudes of the confidence ellipsoids and standard deviations as compared to those obtained by using the data of conventional (un)seeded batch experiments. It was shown that the designed experiment allowed reducing uncertainty in the initial conditions, namely, the mass and crystal size distribution of the initial population of crystals and the initial supersaturation.It was also demonstrated that the main reason for the model/process mismatch was the origin of nuclei. Dynamic experimental data could be described better if the state of the crystals forming the crystallization system corresponded to the assumptions of the used kinetic model. Differences in the crystal surface properties, shape, and strain content could be responsible for a divergent nucleation and growth behavior in batches that were initiated either by primary nucleation, seeding with small ground seeds or seeding with coarse crystals from the product of the previous batch.     

均匀水凝胶片层高效调控一水合尿酸钠晶习

结晶机理和晶习调控是结晶工程研究和应用的关键。例如,尿酸盐结晶对高尿酸血症引起的痛风的研究有重要意义。使用制造的仿生水凝胶材料控制结晶是一种新颖的方法,本文以聚丙烯（PP）膜作为基膜,使用紫外光交联法制备了8种不同聚合结构的水凝胶复合膜,优选了界面诱导结晶性能优异的聚乙二醇二甲基丙烯酸酯-N-异丙基丙烯酰胺（PEGDA-NIPAM）水凝胶材料继续优化。综合分析NaCl液滴蒸发实验和水凝胶制备的可重复性,选用PEGDA-NIPAM（物质的量比2∶1）制备水凝胶切片（HGS）。该种HGS具有均匀表面、垂直结构,厚度、切片质量可通过面积进行直接量化制备。研究NaCl盐溶解吸附-结晶实验,表明制备的HGS拥有pH-温度混合的高效界面成核和浓度调控功能,可作为调控溶液结晶的功能微平台。将HGS引入二水合尿酸晶体与模拟体液的混合晶浆中,调控尿酸钠一水合物晶体（MSUM）的结晶过程和晶体形貌。结果表明,HGS的加入可以强化晶体转化过程,结晶时间由传统方法的72h缩短为水凝胶片层法的20h。同时,HGS还能促进晶体生长和晶体间团聚,能快速获得不同层级多尺度结构的晶体,形成与无HGS条件制备的晶体完全不同的全新晶习。本工作为揭示发展相关晶体的形貌控制方法提供了新的思路。     

Additives effects on crystallization and morphology in a novel caustic aluminate solution decomposition process

A novel process of caustic aluminate solution decomposition by alcohol medium was developed by the Institute of Process Engineering, Chinese Academy of Sciences in order to solve the problem of low decomposition ratio in the traditional Bayer seeded hydrolysis process. In this research, effects of additives on the crystallization ratio, secondary particle size and morphology of aluminum hydroxide in the new process were studied to obtain high-quality products. On the basis of primary selection of additives, an orthogonal design L9(3⁴) was used as a chemometric method to investigate the effects of additives. The studied parameters include the reaction style, quantity of additives, caustic soda concentration, as well as the combination manner. The crystallization ratios of sodium aluminate solution and crystal size of aluminum hydroxide, determined by ICP-OES, SEM and MLPSA (Malvern Laser Particle Size Analyzer), were used to evaluate the effects of the additives. The results showed that different combination manners could promote agglomeration or dispersion. An additive composed by Tween 80 and PEG 200 could promote agglomeration, while a spot of PEG species had a relatively strong dispersion effect. However, the additives had little effects on the crystallization ratios. According to the Raman spectra result, the added alcohol medium might serve as a kind of solvent.     

超声波对阿洛西林酸晶体形态的影响

针对阿洛西林酸（ALPC）生产中存在晶形差、产品聚结的问题,研究了超声波对ALPC晶体形态的影响。首先测定了纯水中的介稳区,分析了超声波影响产品晶习的机理,然后考察了超声波下初始浓度、流加速率和搅拌速率对阿洛西林酸反应结晶过程的影响,从而确定出了最适宜结晶工艺条件。结果表明：超声波可以改善阿洛西林酸产品的晶习、粒度分布并能降低产品聚结程度,实验所得符合厂家的要求。     

球形氯化钾结晶过程与聚结机理研究

针对球形氯化钾结晶过程与聚结机理不明的问题,以冷却结晶法通过过程取样制备与表征了两种不同形貌的氯化钾在不同结晶阶段的晶体形貌与粒度分布特征,从而对比分析了球形氯化钾的结晶过程。并从结晶热力学、经典浸润理论和Lifshitz-Van der Waals酸碱理论出发解释了球形氯化钾形成的主要机理是添加剂的添加减小了结晶体系的介稳区宽度及增大了晶体颗粒在结晶溶剂中的粘附自由能,导致结晶体系更容易以聚结的方式实现球形结晶。介稳区宽度减小和晶体颗粒在结晶溶剂中粘附自由能增大的同步调控有助于实现氯化钾的球形结晶。