氯酸钠真空结晶工艺粒度控制

氯酸钠晶体粒度是用户最为关注的一项质量指标。介绍了氯酸钠真空结晶的工艺过程;着重研究氯酸钠真空结晶工艺结晶机理及生产过程中影响晶体成核速率和晶体生长速率的各项因素。详细叙述了结晶区间、外循环速率、晶种、小循环方式对晶体成核速率的影响,以及结晶器内液位高度、液体密度、温度对晶体生长速率与生长时间的影响。得到了真空结晶工艺生产粒度较大且均匀的氯酸钠晶体的具体操作方案。     

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。     

内循环外冷却封闭塔盘式碳化塔碳酸氢钠结晶动力学研究

本文对内循环外冷却封闭塔板式新型碳化塔结晶动力学问题进行研究。在内径为７０有机玻璃模拟塔内，以空气—ＮａＨＣＯ３饱和溶液为介质，探讨不同气、液流量对晶体生长速率Ｇ、成核速率Ｂ０、晶浆悬浮密度ＭＴ等动力学参数的影响。并给出了不同气、液流量下的结晶动力学关联式。     

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。     

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     

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。     

冷却速率对β成核剂改性PP结晶行为的影响

利用差示扫描量热仪研究了冷却速率对β成核剂改性聚丙烯(PP)结晶行为的影响。冷却速率越慢,高温停留时间越长,则PP中β晶型含量越高,PP的冲击强度越高。冷却速率为5℃/min时,PP中β晶型质量分数达86.12%;冷却速率为20℃/min时,β晶型质量分数为72.04%;而当试样以极快速冷却时,β晶型含量为0。β晶型PP的结晶速率慢于α晶型PP,只有在较高的温度范围内等温结晶时,β晶型PP的结晶速率才快于α晶型PP。因此,一般加工工艺条件下β晶型含量较少。     

α成核剂和β成核剂对高流动性聚丙烯结晶行为的影响

研究了α成核剂和β成核剂对高流动性聚丙烯(PP)结晶行为的影响,采用偏光显微镜、差示扫描量热法和广角X衍射对其微观结构和结晶形态进行了表征。结果表明:α成核剂的加入细化球晶而不改变结晶形态;β成核剂的加入改变球晶的形态,使部分α晶型向β晶型转变;两种成核剂的加入使高流动性PP的结晶速率加快结、晶过程的成核方式和生长机理发生改变,结晶活化能降低。     

非牛顿熔渣冷却析晶行为研究进展

气化技术是煤化工的龙头技术，气流床气化炉具有燃料适用广、转化率高等优势，是大型煤气化的发展方向。由于原料组分或操作条件变化，反应后的灰熔渣在流动过程中会因晶体析出呈现非牛顿流体特性，造成排渣不畅，因此掌握炉内熔渣析晶行为对控制熔渣的流变特性及设备稳定运行有重要指导意义。论述了非牛顿熔渣析晶行为研究，分析了灰渣中结晶行为的影响因素。不同过冷度带来的晶体生长驱动力不同，从而影响晶体生长速率。增大冷却速率会导致晶体孕育时间不足，晶体生长较小。冷却速率超过熔渣的临界冷却速率时，熔渣呈现玻璃体状态。熔渣中主要成分变化导致熔渣的扩散特性及晶体类型改变，熔体碱性组分增加会促进熔渣结晶。此外，不同晶体种类，晶体大小和形状、固液界面析晶反应、晶体生长速率等均发生变化，从而引起流变特性变化。因此，总结了熔渣中几种常见晶体(钙长石、黄长石和尖晶石)的生长特性，以及晶体对熔渣流变特性的影响。对于非牛顿气化渣，晶体析出种类及对应的晶体生长特性仍不明确，有待进一步研究。通过晶体生长预测和控制来调节熔渣流变行为，将实现炉内液态渣层沿程流动的黏度变化预测，对于优化工程中液态排渣炉内熔渣流动有重要指导意义。     

卡马西平多晶型结晶工艺研究

通过生物显微镜、X射线粉末衍射(XRD)、马尔文粒度分析仪,差热分析(DSC)及在线聚焦反射测量仪(FBRM)和粒子成像测量仪(PVM)研究了在卡马西平结晶过程中各种操作参数对产品质量特别是晶型的影响,具体考察了溶剂、晶种、结晶方式、干燥、温度、搅拌速率及冷却速率对晶体产品质量的影响。结果表明,不同溶剂中缓慢结晶,高介电常数溶剂(如醇类)中得到卡马西平晶型Ⅲ,乙醇-水混合物中当乙醇摩尔分数低于40%时结晶产物为二水物,四氢呋喃中结晶得到晶型Ⅱ,其他溶剂得到产品为混合晶型;对于醇类溶剂,蒸发结晶一般得到卡马西平晶型Ⅱ,而缓慢冷却得晶型Ⅲ;以正丙醇为溶剂,加大量颗粒较小的晶种可以得到粒度较均一的产品;晶型Ⅱ产品由于特殊的结构,易于有结晶用溶剂包藏在晶体中,加热到约140℃溶剂逸出;温度是影响晶型的重要因素,在较高温度区间(90~76℃)结晶得晶型Ⅱ,而在低温度区间(52~20℃)得晶型Ⅲ;搅拌速率在较低的温度下对晶型没有影响,搅拌速率大可以避免晶体的聚集,形成较均匀的颗粒;3种降温速率结果显示,产品均为卡马西平晶型Ⅲ,但先慢后快的降温速率可以得到更均匀的颗粒晶体。     

惰性粒子对气液固三相流化结晶粒度分布的影响

引　言换热壁面垢层的形成增加了热阻和流动阻力 ,降低了换热效率 ,严重时可产生局部过热损坏整个换热设备 ,使得设备的维护、检修费用增加 .李修伦、张利斌等[1,2 ] 80年代以来开发出的三相流化床蒸发沸腾换热技术较好地解决了这一问题 ,然而将该技术应用于带有结晶过程的体系 (如卤水蒸发器 )时 ,由于引入的惰性粒子对结晶过程来说为一外来杂质 ,会对晶体的生长产生影响[3] ,而早期的试验也出现过晶粒变小的问题[4 ] .因此有必要对此进行研究 ,为进一步完善和改进三相流化床技术的工业应用提供必要的基础 .1　实验研究1.1　实验装置及流程…     

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。     

CARBON COMBUSTION RATES AND TEMPERATURES IN SHALLOW FLUIDIZED BEDS

The mechanism of combustion of carbon in shallow fluidized beds at temperatures 750-1000°C is studied by measuring burning rates and temperatures of spherical carbon particles ranging from 2 mm to 12 mm diameter directly in an experimental fluidized bed. Among variables investigated were inert particle size, superficial fluidizing velocity, temperature, the influence of neighbouring active particles and oxygen concentration in the fluidizing gas.

Under the experimental conditions explored, combustion was mainly kinetically controlled, so that with carbon particles larger than about 4 mm, burning rates are significantly higher than those predicted by combustion models which assume combustion to be controlled by the rate at which oxygen diffuses through a stagnant particulate phase surrounding the burning particle. The higher burning rate seems to arise because the greater mobility of particles in the bed causes the restriction to oxygen flow to the carbon surface offered by the particulate phase to be reduced and has important consequences for combustor design.

Measured carbon particle temperatures were influenced considerably by bed operating conditions ranging from 15 to 215°C higher than bed temperature.

Measured burning rates of carbon particles were found to be reduced significantly when other active particles were present in the bed. This sensitivity of burning rate to changes in active particle concentration in the bed was shown to be increasingly important once the concentration of carbon in the bed exceeded about 1%

Increasing the bed inert particle size, superficial fluidizing velocity, oxygen concentration in the fluidizing gas and bed temperature resulted in higher burning rates. The implication of these findings on combustor design are discussed.     

Mass transfer in fluidized beds of inert particles Part II: Effect of particle size and density

The mass transfer rate in fluidized beds of inert particles (FIB) is shown to be dependent on the electrolyte flow velocity and the intensity of particle collisions with the electrode. The influence of particle size and density on the ratio of the magnitude of these two influences on the mass transfer rate in a FIB was studied. Use of particle materials of varying density in an FIB permits variation of the two effects. The influence of collision currents prevails in FIBs of low density materials, and the influence of interstitial velocity is dominant in beds of high density material. The ratio of these factors also depends on the size of particles of the same density. With smaller particle size the influence of collision currents is greater. Smoothing of mass transfer maxima in beds of particles both of small and high density is explained. The results establish a basis for the selection of FIB materials for electrochemical processes.     

脱硅中液固循环流化床清洁传热

考察了铝土矿熟料溶出粗液脱硅加热过程中的结垢行为,采用有机-无机复合材质的惰性固体颗粒研究了循环流化床对脱硅加热过程中硅渣结垢的清除及防止性能.结果表明：硅渣结垢曲线为具有诱导期的渐近式曲线,硅渣结垢机理为结晶结垢和微颗粒沉积结垢混合机理;循环流化床不仅能有效防止硅渣结垢的形成,而且能完全清除已有的硅渣垢层,硅渣结垢的清除速率随操作流速及固体颗粒浓度的增大而增大;惰性固体颗粒的引入不影响硅渣结垢的机理.根据液固流化床的防垢机理建立了结垢模型,其预报值与实验值吻合较好.     

CARBON COMBUSTION RATES AND TEMPERATURES IN SHALLOW FLUIDIZED BEDS

Abstract

The mechanism of combustion of carbon in shallow fluidized beds at temperatures 750-1000°C is studied by measuring burning rates and temperatures of spherical carbon particles ranging from 2 mm to 12 mm diameter directly in an experimental fluidized bed. Among variables investigated were inert particle size, superficial fluidizing velocity, temperature, the influence of neighbouring active particles and oxygen concentration in the fluidizing gas.

Under the experimental conditions explored, combustion was mainly kinetically controlled, so that with carbon particles larger than about 4 mm, burning rates are significantly higher than those predicted by combustion models which assume combustion to be controlled by the rate at which oxygen diffuses through a stagnant particulate phase surrounding the burning particle. The higher burning rate seems to arise because the greater mobility of particles in the bed causes the restriction to oxygen flow to the carbon surface offered by the particulate phase to be reduced and has important consequences for combustor design.

Measured carbon particle temperatures were influenced considerably by bed operating conditions ranging from 15 to 215°C higher than bed temperature.

Measured burning rates of carbon particles were found to be reduced significantly when other active particles were present in the bed. This sensitivity of burning rate to changes in active particle concentration in the bed was shown to be increasingly important once the concentration of carbon in the bed exceeded about 1%

Increasing the bed inert particle size, superficial fluidizing velocity, oxygen concentration in the fluidizing gas and bed temperature resulted in higher burning rates. The implication of these findings on combustor design are discussed.     

RESS法制备超细萘粒子

采用常规、简便的喷射装置，建立了一套超临界溶液快速膨胀（Rapid Expansion of Supercritical Solutions,RESS)实验装置。该装置能有效地防止堵塞。以CO2为溶剂，萘为溶质，考察了喷嘴直径及收集距离对沉积微粒粒径的影响，研究了在不同的收集距离时粒径随浓液浓度的变化规律。结果表明喷嘴直径增大将使产物粒子粒径增大；在50mm的范围内，产物粒径随着收集距离的增回而明显增加，结果也显示出RESS产物是通过更小粒子之间的碰撞凝结而生长。当收集距离较大时，晶体的生长过程相比于晶核的形成过程对沉积微粒的粒径影响更大，故粒子粒径随溶液浓度增加而增大；当收集距离较小时，晶核的形成过程占主导地位，因此产物粒径随溶液浓度的增加而减小，符合经典成核理论。     

Investigation of nonisothermal crystallization of hydroxyapatite/ethylene‐vinyl acetate (HA/EVA) composite

Hydroxyapatite/ethylene‐vinyl acetate (HA/EVA) composites were prepared by injection molding and characterized by X‐ray diffraction (XRD) and attenuated total multiple reflection infrared (ATR‐IR) spectroscopy. The nonisothermal crystallization behavior of HA/EVA composites at different cooling rates and with different HA content were examined by differential scanning calorimetry (DSC). The results exhibit the occurrence of interaction between HA and EVA, and the HA particles in EVA matrix act as effective nucleation agent. The addition of HA influences the mechanism of nucleation and growth of EVA crystallites. HA particles, as nucleus, are efficient to promote EVA crystallization at early stage but prevent EVA crystal growth in the late stage. The EVA crystallization in the composite is mainly through heterogeneous nucleation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mixing and Crystallization Kinetics in Gas‐liquid Reactive Crystallization

A study of gas‐liquid reactive crystallization for CO₂‐BaCl₂‐H₂O system was performed in a continuous flow crystallizer. The influences of mixing on the crystallization kinetics of barium carbonate crystals were investigated. The mixing parameters are stirrer speed, feed concentration, gas‐flow rate, pH of solution, addition rate of NaOH solution, and mean residence time. Under pH‐stat operation, the crystallization mechanism can be assessed by the addition rate of NaOH solution, which acts as an indicator for the absorption rate of carbon dioxide. Assuming a size‐independent agglomeration mechanism, the nucleation rate, growth rate and agglomeration kernel can be obtained, simultaneously, at steady state, by the method of moments. Evidence shows that feed concentration, feed rate, gas‐flow rate, and stirrer speed have a significant influence on the nucleation rates and mean particle sizes. This shows the effect of micromixing. The crystallization mechanism tends to be reaction limited when the feed concentration of barium chloride solution is higher than 5 mM, while at lower stirrer speeds and feed concentrations, the mechanism tends to be both mixing and reaction controlled. The growth rate depends on the mean supersaturation value and the pH of the solution and the mass‐transfer resistance cannot be completely eliminated in this work. For a monodispersal collision model, in the viscous sub‐range of turbulence, the agglomeration kernel can be expressed as β ∝ d^{3 –1/4}, showing a low efficiency of collision. The result is also demonstrated by the agglomeration kernel expression. Comparison with a liquid‐liquid‐mixing reactive crystallization system is also discussed.