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。     

Kinetics of butterfat crystallization

Fractionation of butterfat by melt crystallization is a commercial process in many countries for making butter fractions with varying melting, textural and flavor properties for use as food ingredients. However, the crystallization phenomena in this complex system are poorly understood and difficult to optimize and control. In this study, the crystallization kinetics of anhydrous butterfat were determined by cooling a melted sample to the final crystallization temperature in either a lab-scale (2 L) batch crystallizer or a pilot-scale (20 L) crystallization vessel. The butterfat was cooled sequentially from an initial temperature of 60°C to final temperatures of 30, 20 and 15°C at a constant cooling rate. Crystals formed at each temperature were separated by vacuum filtration, with the liquid cooled to the next crystallization temperature. Nucleation rates were determined by counting the number of crystals in a given volume of suspension during the course of crystallization. Crystal growth rates were obtained from image analysis of optical photomicrographs. Changes in viscosity, turbidity and mass of crystals also were determined. Effects of impeller velocity (75, 100 or 125 rpm) on the crystallization kinetics were determined. Nucleation and mass deposition rates increased while crystallization lag times decreased with increasing agitator velocities. Growth rates increased with agitator rpm at 20 and 15°C, but decreased with agitator rpm at 30°C, indicating different growth mechanisms. At 20 and 30°C, aggregation was the primary mechanism of crystal growth, whereas little aggregation was observed at 15°C. Crystallization at the larger scale, 20 L, showed only minor differences.     

基于PBM的L-谷氨酸粒度分布控制优化

针对β型L-谷氨酸冷却结晶过程,为获取期望粒度分布,采用特征曲线法（MOCH）来建立关于粒度相关生长率的种群平衡方程（PBE）,然后通过对种群平衡模型（PBM）参数辨识后确定最优过饱和度及控温曲线。由于辨识模型参数的目标函数具有非线性和非凸型性,因而采用少量经济性的批量冷却结晶实验,结合图像分析晶种和产品粒度分布得到的统计数据,拟合模型参数。根据实际要求的结晶过程时间,为达到目标粒度分布,通过优化结晶过程的过饱和度获得最优调温曲线,实现基于恒定过饱和度的晶体生长过程优化控制。实验结果表明通过优化的控温曲线,实现了基于最优过饱和度控制的期望目标粒度分布。     

不同相对黏度PA6的非等温结晶动力学研究

以相对黏度(ηr)为2.0,2.4,2.8,3.4,4.0的5种聚酰胺6(PA6)切片为研究对象,采用差示扫描量热法测试其在不同冷却速率(?)下的非等温结晶过程;基于Jeziorny法和Mo法对不同 ηr的PA6的非等温结晶动力学进行对比分析,并采用Kissinger法计算其结晶活化能(△E).结果表明:PA6的 ηr...     

Effect of HIPS on polymorphism,melting, and crystallization behavior of sPS crystallized dynamically from melting state

Syndiotactic polystyrene/highly‐impact polystyrene (sPS/HIPS) blends were prepared with a twin‐screw extruder. Differential scanning calorimetry and wide angle X‐ray diffractometry were used to investigate the effect of the maximal melting temperature, the content of HIPS and cooling rates on the melting and crystallization behavior and crystal forms of sPS. The experimental results indicated that the addition of low content of HIPS induced the formation of more α‐crystal, whereas the addition of high content of HIPS favored the formation of β‐crystal for sPS/HIPS blends crystallized dynamically from low melting temperature. Both sPS and its blends produced only β‐crystal as crystallized from high melting temperature. The crystallization temperatures of sPS and its blends decreased as the melting temperature increased, favoring the formation of β‐crystal. Higher temperature of sPS crystallization favored the formation of more content of α‐crystal while lower temperature of sPS crystallization produced more content of β‐crystal. Cooling rates showed no significant effect on the crystal form of sPS and its blends, but influenced the melting behavior of both sPS and its bends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3353–3361, 2007     

Flow‐induced morphology of cast polypropylene

The crystal structures of different grades of cast polypropylene (CPP) extrudates were characterized by Differential Scanning Calorimetry (DSC) and Wide Angle X‐ray Diffraction (WAXD). The effects of the crystallization temperature, draw ratio, and cooling rate on crystal structure are discussed in detail. The results demonstrate that stretching cannot induce the formation of the γ crystal, but the crystallization temperature and the cooling rate do affect the formation of the γ crystal. The slower the cooling rate, the more easily the γ crystal develops. It was found that at the optimum crystallization temperature (T_c) of about 110°C, the γ crystal developed distinctly, and a slower cooling rate made the formation of γ crystal easier. Also, the crystal structures of different resins at the same conditions were discriminative, suggesting that the formation of the γ crystal was due to interruptions of comonomer units in the isotactic propylene sequences, which prevented the PP chain segment from entering the crystal lattice of the α crystal in some degree. If the length of the comonomer sequences was shorter and the distribution of the comonomer units more symmetrical, the formation of the γ crystal would be more distinct. Polym. Eng. Sci. 44:1656–1661, 2004. © 2004 Society of Plastics Engineers.     

氯化钾间歇冷却结晶生长规律及粒度控制实验研究

采用聚焦光束反射测量技术（FBRM）考察了氯化钾（KCl）间歇冷却结晶过程中晶体成核和生长规律,重点研究了降温速率对KCl水溶液冷却时产生过饱和度的影响,以及添加晶种的相关条件（如晶种粒径和添加量等因素）与KCl晶体产品粒度的关系。同时,采用直接冷却刺激起晶产生“晶种”,并控制其生长达到控制晶体产品粒度的目的。结果表明,在添加晶种条件下,程序降温过程产生的低过饱和度不易引起爆发成核,且晶种的添加量决定着晶体产品的平均粒度与理想生长模型的偏差。另外,降温速率是冷却刺激起晶产生“晶种”粒径的关键因素。     

Modeling of crystal growth and nucleation rates for pentaerythritol batch crystallization

The kinetics of crystallization – nucleation and crystal growth – was determined for a seeded batch cooling process. Several experiments were done utilizing always the same condition: initial concentration, seed mass and size distribution, and cooling rate. From one experiment to other the agitation speed was varied. As the utilized reactor is able to measure torque of the impeller, the power dissipated in agitation was monitored during the crystallization, as well as reactor temperature and turbidity of the suspension. Turbidity monitoring and the measurement of particle size distribution from seeds and final product allowed obtaining the evolution of the second moment of the particles during the crystallization. The crystallization process was modeled utilizing the Method of Moments and the nucleation and crystal growth kinetics were obtained from least-square minimization of calculated second moments of the crystals. A crystal growth kinetic was determined and the secondary nucleation rate was described as a function of dissipated power and as functions of impeller tip speed. Additional experiments were done, in which cooling rate, seed mass and seed size were varied. The calculated kinetics could satisfactorily describe the results of the additional experiments, corroborating the quality of the modeling.     

Effect of processing conditions on crystallization kinetics of a milk fat model system

Crystallization behavior of three blends of 30, 40, and 50% of high-melting fraction (MDP=47.5°C) in low-melting fraction (MDP=16.5°C) of milk fat was studied under dynamic conditions in laboratory scale. The effect of cooling and agitation rates, crystallization temperature, and chemical composition of the blends on the morphology, crystal size distribution, crystal thermal behavior, polymorphism, and crystalline chemical composition was investigated by light microscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and gas chromatography (GC). Different nucleation and growth behavior were found for different cooling rates. At slow cooling rate, larger crystals were formed, whereas at fast cooling rate, smaller crystals appeared together. Slowly crystallized samples had a broader distribution of crystal size. Crystallization temperatures had a similar effect as cooling rate. At higher crystallization temperatures, larger crystals and a broader crystal size distribution were found. Agitation rate had a marked effect on crystal size. Higher agitation rates lead to smaller crystal size. Cooling rate was the most influential parameter in crystal thermal behavior and composition. Slowly crystallized samples showed a broader melting diagram and an enrichment of long-chain triacylglycerols. Crystallization behavior was more related to processing conditions than to chemical composition of blends.     

纳米SiO2改性PP的结晶结构与特性研究

采用偏光显微镜观察和研究了三种不同表面处理的纳米SiO2改性PP的结晶结构，并通过DSC分析方法，研究了它们的结晶特性。结果表明：纳米SiO2在PP中具有成核剂作用，PP以异相成核方式结晶，使PP的结晶温度提高，结晶速度增大，球晶颗粒变得细小而均匀，但基本不影响PP的结晶度和熔点。纳米SiO2在PP中的粒度越小，分散均均匀，或适当提高其含量，上述作用越明显。纳米SiO2的表面处理对PP／纳米SiO2材料的结晶结构和特性影响很大，其中经表面偶联剂加分散剂处理的纳米SiO2－AB对PP结晶的上述影响最为明显。     

Kinetics of Crystal Growth of Calcium Tungstate from Solutions in Sodium Tungstate Melts by Continuous Cooling

Crystallization kinetics of calcium tungstate from unstirred supersaturated solutions in sodium tungstate melts was studied by continuous cooling from initial crystallization temperature T _O=1000° to 800°C to room temperature at cooling rates R_T =0.67° to 3.3°C min⁻¹. Crystals were examined by optical microscopy and analyzed by various methods. The main crystal growth was diffusion-rate-controlled. The final crystal growth was rate-controlled by the development rate of excess solute concentration. Diffusion rate constant ( k_D ) values were estimated. These values increased with cooling rate and initial crystallization temperatures but they are very much smaller than the rate constants for diffusion-controlled growth of calcium tungstate from lithium chloride melts.     

几种无纺布聚丙烯专用料的性能研究

选取了国内无纺布企业主要用的几种聚丙烯专用料，测定了其力学性能、流动性能，并在此基础上考察了不同热处理温度下的熔融特性以及不同降温速率下的结晶特性。结果表明：PP S2040的熔体质量流动速率较高，易于加工成型，但对温度的依赖性较大。PP1700的拉伸强度、拉伸屈服强度和缺口冲击强度比PP S2040、Exxon3155高，而断裂伸长率却最低。这是由于PP1700的熔体流动速率小，相对摩尔质量大，强度相对提高。热处理后，由于聚丙烯的结晶程度更加完善，几种专用料的熔融起始温度Tm0、熔融峰温Tmp均有所上升。随着降温速率增加，低温进入晶区的部分增多，使结晶范围变宽，结晶温度Tc和结晶峰都向低温方向移动，结晶度有所增加。在相同的降温速率下，PP S2040的结晶时间ts略小，而结晶焓较高，说明在较短的时间内达到较高的结晶度，结晶速度较快。     

低温控温结晶法分离提纯1,8-桉叶油素的工艺

采用全结晶工艺对原料桉叶油[w(cineole)=63.24%]进行分离提纯,在无晶种添加下,降温速率4℃/h、结晶终温-30℃、发汗速率5℃/h、发汗终温-19℃时,可将原料油提纯至77.52%。添加晶种后,可有效提高操作温度,缩小结晶温度的操作范围,提高产品的纯度,在降温速率4℃/h、结晶终温-25℃、发汗速率4℃/h、发汗终温-6℃的操作条件下,将原料油提纯至89.63%。实验得到了低温控温添加晶种结晶法分离提纯1,8-桉叶油素的适宜工艺流程和操作参数,该方法相对其他分离方法具有较为明显的优势。     

静态熔融结晶法提纯均四甲苯（英文）

The purification and separation of durene from the mixture containing durene isomers were studied. Since the boiling points of tetramethyl benzene isomers are very close but their melting points are of great differences, stat-ic melt crystallization was applied to separate and purify durene from its isomers. Crystallization experiments were carried out under various operating conditions. The effects of cooling rate, crystallization temperature, sweating temperature and sweating time on the yield and purity of crystal were investigated. Orthogonal exper-imental design method was adopted to analyze the factors that may affect the yield of durene. Under the optimal crystal ization conditions, the purity of durene could reach as high as 99.06%with the yield of 75.3%through one crystal ization process. By fitting purification data based on sweating time in isothermal operations, the purifica-tion rate coefficient was obtained.     

Membrane assisted cooling crystallization: Process model,nucleation, metastable zone,and crystal size distribution

The membrane assisted cooling crystallization was proposed and investigated by the simulation and experiments. The developed process model concerned the supersaturation evolution on the membrane interface, the combined nucleation rate in the crystallizer. The impact of different membrane on reducing the nucleation barrier was investigated by introducing the metastable zone width theory. The influence of membrane distillation conditions on the crystal nucleation and growth kinetic was uncovered based on the simulation and experiments results. The experimental results indicated that membrane assisted cooling mode with optimized profiles did improve the crystal size distribution and crystal habit comparing with conventional cooling mode. Terminal coefficient of variation decreased from 55.4 to 33.9 under similar mean crystal growth rate, 2.27 × 10^?7 m s^?1 (conventional cooling) and 1.98 × 10^?7 m s^?1 (membrane assisted cooling). Finally, the brief summary on the advantages and key issues of this propose membrane assisted crystallization operation were concluded. © 2015 American Institute of Chemical Engineers AIChE J, 62: 829–841, 2016     

Effect of cooling rate on crystallization behavior of milk fat fraction/sunflower oil blends

The effect of cooling rate (slow: 0.1°C/min; fast: 5.5°C/min) on the crystallization kinetics of blends of a highmelting milk fat fraction and sunflower oil (SFO) was investigated by pulsed NMR and DSC. For slow cooling rate, the majority of crystallization had already occurred by the time the set crystallization temperature had been reached. For fast cooling rate, crystallization started after the samples reached the selected crystallization temperature, and the solid fat content curves were hyperbolic. DSC scans showed that at slow cooling rates, molecular organization took place as the sample was being cooled to crystallization temperature and there was fractionation of solid solutions. For fast cooling rates, more compound crystal formation occurred and no fractionation was observed in many cases. The Avrami kinetic model was used to obtain the parameters k _n and n for the samples that were rapidly cooled. The parameter k _n decreased as supercooling decreased (higher crystallization temperature) and decreased with increasing SFO content. The Avrami exponent n was less than 1 for high supercoolings and close to 2 for low supercoolings, but was not affected by SFO content.     

Isothermal and non‐isothermal crystallization of poly(L‐lactic acid)/poly(butylene terephthalate) blends

Isothermal and non‐isothermal crystallization kinetics of poly(l ‐lactic acid)/poly(butylene terephthalate) (PLLA/PBT) blends containing PLLA as major component is detailed in this contribution. PLLA and PBT are not miscible, but compatibility of the polymer pair is ensured by interactions between the functional groups of the two polyesters, established upon melt mixing. Crystal polymorphism of the two polyesters is not influenced by blending, as probed by wide‐angle X‐ray analysis. The addition of PLLA does not affect the temperature range of crystallization kinetics of PBT, nor the crystallinity level attained when the blends are cooled from the melt at constant rate. Conversely, PBT favors crystallization of the biodegradable polyester. The addition of PBT results in an anticipated onset of crystallization of PLLA during cooling at a fixed rate, with a sizeable enhancement of the crystal fraction. Isothermal crystallization analysis confirmed the faster crystallization rate of PLLA in the presence of PBT. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40372.     

硫酸镍间歇结晶过程的工艺优化

文章采用聚焦光束反射测量仪(FBRM)研究了硫酸镍间歇结晶过程晶体的成核和生长规律,考察了搅拌桨形式、降温方式、搅拌速率、晶种添加量和晶种粒度对结晶过程中结晶动力学的影响。结晶工艺条件优化后,得到了粒径大、晶型好、分布均匀的晶体产品,为硫酸镍间歇结晶过程的工艺优化和工业放大提供了依据。     

碳纤维增强聚酰胺6复合材料的结晶行为研究

通过偏光显微镜和差示扫描量热仪(DSC)研究了碳纤维(CF)和滑石粉对聚酰胺6(PA6)结晶行为的影响。结果表明,CF的加入在PA6和CF的界面诱发横晶,CF和滑石粉在PA6基体中起到了异相成核作用,改变PA6的成核机理和晶体生长方式,提高了起始结晶温度和结晶速率。结晶速率随普等温结晶温度的升高而下降。当冷却速率增大时,起始结晶温度下降,结晶度增大。     

Effect of crystallization temperature of palm oil on its crystallization. IV. The influence of tripalmitoylglycerol (PPP) on the crystallization of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-glycerol (POO)

Triacylglycerin in Palm Oil contains POP (1,3-dipalmitoyl-2-oleoyl-glycerol) at 30%, POO (1,2-dioleoyl-3-palmitoyl-glycerol) at 20% and PPP (tripalmitoylglycerol) at 5%. The crystallization temperature of PPP is high and the rates of crystal nuclear formation and growth are fast. It is thus considered that PPP may have some effect on the manner or mode of Palm Oil. Examination was thus made to clarify how PPP may affect the crystallization of POP and POO by differential scanning calorimetry (DSC) and X ray diffractometry (XRD) conducted on PPP/POP and PPP/POO mixtures. High and low temperature peaks were noted to appear on the DSC crystallization curve for either of these mixtures. The high temperature peak was considered possibly due to PPP, and the low temperature peak, to POP or POO. DSC isothermal analysis indicated the rate of crystal growth of either mixture to exceed that of pure of POP or POO. Crystal mixture structure was also seen to be complicated than either compound in pure form. The present findings thus clearly indicate that clarification should be made of the effects of high melting point triacylglycerin, such as PPP, on the crystallization of Palm Oil.