十水硫酸钠冷冻结晶器的设计与优化

通过对十水硫酸钠结晶过程影响因素的分析,讨论了冷却结晶过程设计的关键点。分析了过饱和度对结晶过程初级成核的影响,研究了通过控制物料母液循环量从而控制过饱和度以避免初级成核的方法;探讨了通过改进设备内部结构,使晶核处于悬浮状态,与过饱和液体充分混合,达到促进晶体生长的目的;新的设备结构设计,还充分考虑减少晶体二次成核几率;同时在结晶器中增加细晶排出装置,降低晶核数量,提高晶体生长速率,达到改善结晶质量的目的。     

循环流化结晶过程传质与晶体生长速率模型

依据Whiteman传质膜理论 ,针对循环流化床结晶过程 ,建立了传质和晶体生长速率理论模型 .实验研究表明 ,在较宽的流速范围内 ,晶体生长速率仅与结晶物系的物性、晶种粒度和过饱和度有关 ,其基本规律为 :晶体的平均线生长速率与扩散系数、晶种特征长度、晶体与溶液相对密度差、过饱和度成正比 ;与溶液的黏度、晶体的密度成反比 .仅需结晶物系的物性、过饱和度等数据 ,利用所建模型可方便地预测循环流化床结晶过程的晶体生长速率     

SAPO-34分子筛晶化机理及晶化动力学研究

对SAPO-34分子筛晶化过程中预相形成、诱导期内晶核生成、晶体生长和晶化过程的研究进行综述。SAPO-34分子筛晶化过程首先形成不稳定的层状预相结构,进而发展为具有有序排列晶格骨架的晶核。结晶热力学控制晶相结构,晶化动力学控制晶体成核和生长速率。影响晶化动力学的关键因素是温度和浓度,成核速率和晶体生长速率互相竞争控制晶粒大小。晶化过程的Si取代机理和Si分布影响分子筛酸性。晶化动力学研究结果表明,温度升高,结晶速率增加,成核时间缩短。     

流动溶液中维生素C单晶生长动力学

引　言随着精细化工、生化、医药和染料工业的发展 ,结晶过程越来越受到重视[1] .人们充分认识到晶体生长速率在结晶器设计或评价中的作用 ,必须获取温度、过饱和度和流速等因素影响的准确信息 .结晶动力学是决定晶体产品粒度分布的重要因素 ,是进行结晶器分析、设计、操作和模     

溶剂超声波协同法用于有机物系结晶快速成核

<正> 引言 有机物系结晶大多属于溶液群体结晶范畴,是工业结晶的重要组成部分.晶核是过饱和溶液中新生成的微小晶体粒子,是晶体生长过程必不可少的核心. A.VanHook在论述晶核的生成时指出,声波辐照由于具有强烈的定向效应,有补充和加强形成临界晶核所需的波动作用,故能加速起晶过程.高大维提出了蔗糖溶液的溶剂超声波协同成核法,该法已被利用来进行味精、含水α-葡萄糖、木糖醇等的成核研究并获得成功,所需的成核溶剂、超声波强度及刺激时间因不同物质而异.与传统的晶种制备方法(如粉碎机破碎法、球磨法、晶浆中留一部分晶体作为晶种等)相比,该法具有简单、快速、晶核数目容易控制的优点.同时还具有晶核形状好、投种量小并减少结晶生长过程中用于整晶的能耗、成品质量高等优点.溶剂超声波协同成核法的原理是溶析效应与超声波的机械(分散)效应、空化效应的结合.从溶液成核速率公式可看出表面张力σ、粘度η和过饱和度S对成核速率J的关系     

木糖醇发酵模型液的结晶动力学研究

本研究基于发酵法生产木糖醇的特点配制木糖醇发酵模型液,研究了杂质、温度、过饱和度、晶种投入量及晶种规格等因素对木糖醇结晶过程中晶体生长速率的影响。实验表明,木糖醇晶体生长速率与温度及过饱和度成正比关系。山梨醇、阿东糖醇等共存杂质都会阻碍木糖醇的结晶。而晶种投入量及晶种规格对木糖醇晶体生长速率的影响很小,可忽略不计。根据公式及Arrhenius方程,建立木糖醇晶体生长动力学方程,计算晶体生长活化能的大小,并对木糖醇晶体生长限速机制进行了分析。在木糖醇晶体生长的不同阶段,速率控制机制与表面融合机制都起到了控制结晶的作用。     

旋流流化床中五水硫酸铜结晶生长动力学研究

基于微观平板对流传质理论,建立了五水硫酸铜晶体生长动力学模型。在循环旋流流化结晶实验装置中,分别考察了母液过饱和度、循环流速、晶种粒度、结晶温度对晶体生长速率的影响。结果表明:增大旋流流化床中的母液过饱和度、结晶温度、循环流速,或减小晶种粒径均能提高五水硫酸铜晶体的线性生长速率,其中母液过饱和度与结晶温度对晶体线性生长速率影响显著;在较宽的操作条件范围内,模型计算结果与实验值吻合较好,相对偏差在±10%以内,该模型可用于预测旋流流化床中五水硫酸铜晶体的生长速率,可为装置的工业放大设计提供理论指导。     

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。     

种子诱导结晶釉中硅酸锌晶化动力学(英文)

以ZnO为晶种,研究了SiO2-Al2O3-ZnO-CaO-MgO-K2O-Na2O系统结晶釉中硅酸锌的可控析晶过程。结果表明:起装饰作用的盘状硅酸锌晶体由冰针形状硅酸锌晶粒组成,受釉层厚度的限制,晶体生长沿0001方向。采用John William Mullin以及Johnson-Mehl-Avrami动力学模型模拟灼烧过程中晶体生长,低温下晶体生长主要受前驱体在玻璃相中扩散控制,在高温下,则主要受前驱体和晶核界面反应控制。     

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。     

水溶液中硫酸钾晶体生长动力学

The single crystal growth rates of potassium sulfate in pure aqueous solution under different conditions were determined by photomicrography in a flow system for crystal growth. The effects of themain controlling factors, such as supersaturation, crystal size, solution velocity and crystal growth temperature, on crystal growth rates of potassium sulfate were discussed in detail by using non-linear regression from the experimental data, and several empirical relationships were given. The results showed that the growth rates of crystals increased with supersaturation, crystal size, solution velocity and temperature. Moreover supersaturation was the most important controlling factor influencing growth rates of crystals, crystal size and solution velocity were the secondary and temperature was the least.Furthermore, It was found that the growth rate of crystals along the [100] crystallographic axis was higher than that along the [001] in the same condition. The effect of every factor on crystal growth rates along the [100] crystallographic axis was stronger than that along the [001].     

Unusual Crystal Growth Kinetics of (RS)‐Ibuprofen from Ethanolic Solutions

The solubility, secondary nucleation threshold, and growth kinetics of (RS)‐ibuprofen have been studied in an aqueous ethanol solvent. The metastable zone for secondary nucleation is very narrow at lower temperatures in this range, but greatly enlarged at higher temperatures. The crystal growth kinetics not only display significant dispersion of growth rates, but also a dead zone that is dependent on the growth rates of the crystals. Faster growing crystals display almost no dead zone, whereas the smallest crystals have a large dead zone. The size of the dead zone is largely responsible for the dispersion of crystal growth rates, perhaps due to differences in the thermodynamic stability of the different crystals. The mechanism of growth rate dispersion relates to that of the dead zone.     

GROWTH AND NUCLEATION KINETICS IN BATCH CRYSTALLIZATION OF TRICLOSAN

Batch crystallization of triclosan, a broad spectrum antibacterial agent, was carried out under isothermal conditions (at 10°C) with n-hexane as the solvent. Supersaturation was generated by cooling a seeded solution. Samples were collected at periodic intervals. Triclosan concentration in solution was determined by UV-spectrophotometry and particle size distribution by optical microscopy. Growth and nucleation kinetic parameters were obtained. The data indicated size independent growth. Growth kinetic parameters based on triclosan concentration in solution were in reasonable agreement with growth kinetic parameters obtained from cumulative size distribution data. Growth and nucleation kinetic orders were comparable to those reported in the literature.     

GROWTH AND NUCLEATION KINETICS IN BATCH CRYSTALLIZATION OF TRICLOSAN

Batch crystallization of triclosan, a broad spectrum antibacterial agent, was carried out under isothermal conditions (at 10°C) with n-hexane as the solvent. Supersaturation was generated by cooling a seeded solution. Samples were collected at periodic intervals. Triclosan concentration in solution was determined by UV-spectrophotometry and particle size distribution by optical microscopy. Growth and nucleation kinetic parameters were obtained. The data indicated size independent growth. Growth kinetic parameters based on triclosan concentration in solution were in reasonable agreement with growth kinetic parameters obtained from cumulative size distribution data. Growth and nucleation kinetic orders were comparable to those reported in the literature.     

Studies on the Removal of Bromocresol Green from Water by Solvent Sublation

Abstract

Bromocresol green (BG) was removed from an aqueous solution by solvent sublation of bromocresol green–hexadecyl‐pyridiumchlorid (HPC) complex (sublate) into 2‐octanol. The effects of many parameters, such as the amount of surfactant, airflow rates, pH, NaCl, and ethanol on the solvent sublation were studied. Different temperatures of the solvent sublation were also investigated. A ratio of surfactant to dye (1.25:1) was the most effective for the removal, with over 99% BG removed from the aqueous solution within 5 min. The removal rate was somewhat enhanced by higher airflow rates and almost independent of the volume of the organic solvent floating on the top of the aqueous column. The effects of electrolytes (e.g. NaCl) and non‐hydrophobic organics (e.g. ethanol) reduce the removal efficiency of solvent sublation. This process followed first order kinetics. A characteristic parameter, apparent activation energy of attachment of the sublate to bubbles, was estimated at a value of 1.3 kJ/mol. Furthermore, the simulation of the mathematical and experimental data was made with good results.     

Separation of fatty acids by crystallization using two liquid phases

First, the phase diagrams for the water+ethanol+fatty acids system were described, and the separation method was considered. Second, the separation of lauric acid+myristic acid mixture in the ethanol aqueous solution including ethanol by liquid-liquid extraction and crystallization has been examined. The extraction of fatty acids from the organic phase to the aqueous solution has been done. Fatty acids in the aqueous solution were crystallized using the aqueous SLE surface. The solvent-free mole fraction of lauric acid in the aqueous solution was a little higher than that in the organic phase. Fine crystals made in the aqueous solution had better purity for lauric acid than the solvent-free mole fraction of lauric acid in the aqueous solution. The effects of the mole fraction of ethanol in the aqueous solution, the mole fraction of lauric acid in the organic solution, extraction temperature and crystallization temperature on the purity of the crystals were reported.     

氢氧化钠的乙醇溶液对聚酯纤维的碱处理

用乙醇为溶剂的氢氧化钠溶液对聚酯纤维进行碱处理,所获得的减量率比在相同浓度、时间和温度条件下用氢氧化钠水溶液处理的要高。处理后纤维的性能不依赖于处理液中溶剂的成分,因此,采用乙醇作溶剂可大大缩短处理时间,得到与水相碱处理同样的效果。     

Isoconversional Kinetic Analysis of Isothermal Selective Ethanol Adsorption on Zeolite Type NaZSM‐5

The kinetic parameters of the selective isothermal adsorption of ethanol from an aqueous solution onto a hydrophobic zeolite type NaZSM‐5 were determined using a series of the so‐called standard methods (the initial rate, the saturation rate and the maximum rate methods). The kinetic model of ethanol adsorption was determined by the “model fitting” method. The dependence of the kinetic parameters on the degree of adsorption and the presence of a compensation effect were determined by the isoconversional method. The complex changes of the activation energy and pre‐exponential factor with the degree of adsorption were explained by the model of the activation energy distribution of elemental adsorption processes.     

Crystal nucleation and growth rates in single-component and binary melts under conditions of growth in a polycrystalline layer and in the case of single crystals

Crystal nucleation and growth rates in single-component and binary melts are found using the proposed versatile procedure for determining kinetic parameters in processes involving phase transformations. These kinetic dependences on supercooling at the interface for the same single-component and binary melts are experimentally derived under comparable conditions in the formation and growth of single crystals and in a polycrystalline layer. A discrepancy between growth rates in a polycrystalline layer (constrained conditions) and for single crystals under the same supercooling is found. The rate of nucleation under constrained conditions is also lower. In practice, when calculating the process of crystallization, it is necessary to use kinetic parameters obtained for constrained conditions of the process. In studying the mechanism of crystal nucleation and growth, kinetic parameters derived for single crystals should be used.     

An experimental study of the kinetics of the spherical crystallization of aylline sodium theophylline monohydrate

Direct agglomeration of sodium theophylline monohydrate crystals produced by salting out in a liquid was carried out in a stirred vessel. Addition of aqueous ethylenediamine solution of theophylline and sodium chloride solution to a mixture of chloroform and ethanol (mixing ratio of chloroform:ethanol = 0.1 to 0.505:1) with agitation yielded spherically agglomerated crystals of sodium theophylline monohydrate. The diameter of the spherical agglomerate decreased with increase in agitation speed of the chloroform fraction in the mixture. The spherical crystallization process was described by first-order kinetics. The rate constant was a function of the agitation speed of the system and the difference between the residual concentration of theophylline in the solvent in the initial and the equilibrium state.