膜辅助添加晶种的过硫酸铵冷却结晶在线监测与过程调控

冷却结晶是经典的溶液结晶过程,常用于分离溶解度随温度变化较大的物质,制备高品质晶体产品。直接进行降温会导致成核速率不可控,得到的晶体产品质量差。在工业中通常选择在溶液结晶介稳区内投放适量晶种来诱导成核,但晶种制备过程复杂,而且成功的添加晶种过程取决于晶种的粒度分布、数量、投放时机和操作人员的经验等因素,降低了产品质量的批次重复性。本文利用聚四氟乙烯（PTFE）中空纤维膜组件为结晶溶液和冷却液提供换热界面,结晶溶液温度降低,在膜界面处形成较均匀的过冷度梯度,进而在低过饱和度下发生异相成核,实现膜辅助添加晶种的过硫酸铵冷却结晶过程调控。膜组件中产生的晶种进入结晶釜中继续生长,将成核和生长过程进行解耦。在线结晶检测系统捕捉到的照片证实了通过控制膜组件使用温度和时长两个操作参数便可得到具有较好的形貌、较窄的粒度分布的晶种。相比直接冷却结晶,在相近的降温速率下,膜辅助添加晶种过程制备的晶体产品具有更大的平均粒径,且粒度分布更集中,表面更加光滑。因此,膜辅助冷却结晶呈现了良好的成核控制能力,有望实现晶种自动制备和添加功能,为高附加值晶体产品的冷却结晶过程开发提供了新方向。     

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。     

TNAZ溶析结晶动力学研究

基于分级法[1]求解1,3,3-三硝基氮杂环丁烷(TNAZ)问歇溶析结晶过程的粒数衡算方程,通过激光粒度分布测量仪测量了结晶过程中粒度分布随温度、搅拌强度、溶析剂滴加速率的变化规律.利用已建立的TNAZ间歇溶析结晶过程的粒数衡算方程求解模型得到生长动力学参数,最后用最小二乘法模拟出成核速率和生长速率方程[2].成核速率...     

杂质对溶液结晶过程影响的研究进展

综述了杂质对结晶过程及结晶产品性质的影响。在溶液结晶过程中,杂质对溶液状态以及晶体成核、生长及团聚等过程产生影响,进而影响到晶体习性、粒径和粒度分布。从微观水平分析了杂质对晶体表面台阶生长速率的影响。阐述了杂质对结晶过程影响研究的重要性、该领域存在的问题及今后的研究方向。     

溶剂结晶法精制萘的研究——甲醇作溶剂精制萘的考察

本文采用溶剂结晶法工艺,用甲醇作溶剂对本钢焦化厂工业萘的精制进行了系统的研究,考察了溶剂比、降温速度等因素对精萘产品质量的影响。实验结果表明,甲醇作溶剂对与萘形成共熔体及固体溶液的主要杂质硫茚一次结晶脱除率达50％,精萘产品的结晶点为79.5℃左右,符合二级精萘的部颁标准;二次结晶精萘产品的结晶点为79.72℃,完全符合一级精萘的部颁标准。研究表明,在一定的降温速度下,溶剂比小时,结晶过程由成核和生长两个因素控制;溶剂比大时,结晶过程主要由生长因素控制。在一定的溶剂比下,降温速度快,结晶过程主要由成核因素决定;降温速度慢,结晶过程主要由生长因素决定。     

溶液结晶中的介尺度成核过程研究进展

成核作为溶液结晶的第一步,是决定晶体产品质量的关键因素。目前,成核理论主要包括经典成核理论和非经典成核理论。相比于仅以原子、离子或分子等均匀稳定结构为单元的经典成核理论,非经典成核理论以纳米级前聚体为单元,这类单元涵盖了聚集体、纳米粒子等介尺度非均匀动态结构,导致形成的非经典成核过程更为复杂,需在传统的化学、化学工程和过程系统工程研究方法的基础上,充分利用介尺度科学研究方法完成其核心规律的探究。为此,总结了二步成核理论、预成核团簇理论、粒子附着晶化理论以及其他新提出的非经典成核理论,分析了其中的介尺度结构及其时空动态行为,并探讨了利用介尺度数学模型对现有成核数学模型的修正和优化的思路,最后对溶液结晶中晶体成核的介尺度研究范式及理论发展进行了展望。     

1,2,3-三硝基氮杂环丁烷溶析结晶动力学研究

基于分级法[1]求解了TNAZ间歇溶析结晶过程的粒数衡算方程,通过激光粒度分布测量仪测量了结晶过程中粒度分布随不同温度、搅拌强度、溶析剂滴加速率的变化规律。利用已建立的TNAZ间歇溶析结晶过程的粒数衡算方程求解模型得到了生长动力学参数,最后用最小二乘法模拟出了成核速率和生长速率方程[2]。成核速率和生长速率是结晶模拟过程中最核心的控制条件。     

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。     

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.     

溶液结晶中晶体形态与结构调控

综述了化学因素(溶剂和添加剂等)和工程因素(过饱和度,晶种和搅拌等)对溶液结晶中晶体形态与结构的影响,分析了这些因素会影响溶质分子在溶液主体中的聚集形式及其在晶体界面的扩散和吸附过程,进而影响晶体的成核和生长机理及速率,并由此改变最终产品的形貌和结构。调控结晶工艺参数和优化操作条件可得到目标结晶产物。     

The Nucleation and Growth of Succinic Acid in the Presence of Surfactants

Impurities may have a marked effect on crystal nucleation and growth. To further understand the role of impurities, the crystallization (solubility, nucleation, growth) of succinic acid in water in the presence of surfactants such as polyethylene glycol sorbitan monooleate (Tween 80), cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzenesulfonate (SDBS) was investigated experimentally. The presence of CTAB, SDBS or Tween 80 had little influence on succinic acid solubility but did slow crystallization kinetics. The surfactant monomer in solution, not micelles, proved to play the primary role affecting nucleation. The nucleation inhibition by surfactant was analyzed on the base of a two‐step nucleation process: (1) the inhibition on the formation and growth of succinic acid nanodroplets and (2) the influence on succinic acid single nucleus (SASN) in secondary nucleation. SASN may play important role in secondary nucleation, although further work is necessary to conform this. The length of the surfactant hydrocarbon chain was found to affect crystal habit development.     

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.     

DMT甲醇溶液结晶介稳区性质的研究

研究了对苯二甲酸二甲酯（ＤＭＴ）甲醇溶液的结晶特性。测定了ＤＭＴ在甲醇中的溶解度、ＤＭＴ甲醇溶液于不同降温速率、搅拌转速下的结晶介稳区宽度以及不同过饱和度下的结晶成核诱导期。结果表明：ＤＭＴ在甲醇溶液中的溶解度随温度升高而增加;溶液的结晶介稳区随降温速率的增加变宽,随搅拌转速的增加而变窄,且ＤＭＴ甲醇溶液的结晶诱导期随相对过饱和度的增加而缩短。     

大颗粒氯化钾聚结结晶及其粒径控制

利用聚焦反射光束测量技术（FBRM）测定了氯化钾在水中的溶解度,研究了在转速为250 r/min时,颗粒氯化钾晶体的制备及其粒径控制的规律,并考察了在此转速下溶液中氯化钾聚结过程中初级粒子、降温速率、过饱和度对聚结的影响。研究结果表明：氯化钾溶解度随温度升高而增大;降温速率越快,溶液瞬时过饱和度越大,越易爆发成核,产生的粒子数越多;初级粒子在每100 mL溶液的最佳添加量为0.05~0.1 g时,制备的晶体平均粒径可达1 900~2 000 μm,产品粒径较大,球形度也较好。     

季戊四醇水溶液结晶介稳区性质的研究

用激光自动检测法测定了季戊四醇水溶液在不同降温速率、搅拌转速下的结晶介稳宽度以及不同过饱和度下的结晶成核诱导期。实验还采用折射率法测定了季戊四醇在水中的溶解度     

A systematic approach for preferential crystallization of 4-hydroxy-2-pyrrolidone: Thermodynamics, kinetics, optimal operation and in-situ monitoring aspects

A systematic approach has been developed and applied to the preferential crystallization of 4-hydroxy-2-pyrrolidone in isopropanol. The concept of critical supersaturation control was introduced for preferential crystallization process. System thermodynamics, crystallization kinetics, optimal operation and in-situ monitoring were combined and integrated to establish the strategy for the critical supersaturation control. Subsequently, the solubility and metastable zone widths of 4-hydroxy-2-pyrrolidone with different compositions in isopropanol under different cooling rates were determined using an automatic lab reactor (Mettler Toledo LabMax) system equipped with Lasentec Focused Beam Reflectance (FBRM) probe. The crystal nucleation and growth kinetics were measured with s-plane analysis. A modified technique was proposed for size-dependent crystal growth. Based on the thermodynamics properties and crystallization kinetics, a simplified cooling profile was proposed and applied to the critical supersaturation control. The final product's high optical purity, good crystal size distribution, SEM imagines and the in-situ observations, all suggested that the critical supersaturation control was essential and the systematic approach was successful and applicable for preferential crystallization.     

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.     

Determination of metastable zone and induction time of analgin for cooling crystallization

The solubility, metastable zone width, and induction time of analgin for unseeded batch cooling crystallization in ethanol–aqueous system were experimentally determined. The solubility data could be well described by the van't Hoff equation model. The metastable zone width at various cooling rates was measured, and some parameters of nucleation kinetic were calculated using the Ny'vlt theory. Furthermore, the induction period of various temperatures and supersaturation ratios was also measured. According to classical nucleation theory, some nucleation parameters and interfacial energy was calculated through the induction time(t_(ind)) data. Homogeneous nucleation tended to occur when the supersaturation is high, whereas heterogeneous nucleation was more likely to occur when the supersaturation is low.     

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。     

苹果酸杂质存在条件下的乳酸锌结晶提纯

研究了苹果酸杂质存在条件下溶液结晶过程参数对乳酸锌晶体产品收率、纯度、晶体结构和形态的影响。结果表明,溶液结晶过程参数对乳酸锌晶体结构和形态没有明显影响,但与纯乳酸锌晶体相比,苹果酸的引入增加了乳酸锌晶体的长径比。晶体纯度的下降与产品收率的上升为近似线性关系,但如结晶过程中发生大量二次成核,晶体产品的纯度将显著下降。