升温速率和晶化模式对固相转化合成SAPO-5的影响

固相转化法有利于合成硅取代型磷酸铝分子筛(SAPO-5)。采用XRD、SEM、EDS表征方法研究了升温速率和晶化模式对SAPO-5分子筛结构的影响。结果表明,在高升温速率(140℃·h^-1)和低升温速率(5.8℃·h^-1)下能合成出纯SAPO-5分子筛,在中等升温速率(17.5～70℃·h^-1)下则有SAPO-34分子筛与SAPO-5伴生。此外,晶化模式对SAPO-5分子筛的形貌有显著影响。在中等升温速率下,动态晶化形成的SAPO-5分子筛为球形,静态晶化则为六边形片状,但Si的取代机制均可能为SM3取代。在高升温速率和低升温速率下,晶化模式不影响SAPO-5分子筛的形貌。而Si在动态晶化时为SM2取代,静态晶化时为SM3取代。     

Fe-AlPO4-5分子筛的水热晶化过程研究

采用X射线粉末衍射(XRD)研究了Fe—AlPO4—5分子筛在不同晶化温度下的水热结晶过程。以相对结晶度为指标测定了结晶动力学曲线,用Arrhenius方程计算了Fe—AlPO4-5分子筛的表观成核活化能和表观晶体生长活化能,分别为82．7kJ／mol和28．2kJ／mol。晶化过程中样品单位晶胞体积的测定结果表明大部分骨架位Fe^3 在晶体生长阶段的早期就已经进入了分子筛骨架结构中。晶化温度高于453K时,Fe—AlPO4-5分子筛在结晶度达到最大后还要进行结构调整直至形成热力学上相对稳定的结构。     

两步晶化法合成SAPO-34分子筛及其催化氯甲烷制低碳烯烃研究

以吗啡啉为模板剂,考察了晶化条件对SAPO-34分子筛粒径的影响,利用XRD、SEM、BET和NH3-TPD等方法对所合成的SAPO-34分子筛结构性质进行了一系列表征。结果表明,当晶化温度为200℃时,降低晶化时间可以将SAPO-34分子筛的粒径从10μm左右减小到约3μm;随SAPO-34分子筛粒径减小,其硅元素质量分数略有增加,比表面积及孔体积均有所增大;NH3-TPD结果表明,减少粒径使分子筛弱酸及强酸中心的数目增加。在420℃,空速为1.89 h-1的条件下,考察了SAPO-34的粒径对其催化氯甲烷的反应影响,结果表明,减小粒径可以延缓SAPO-34分子筛失活,同时增加积碳含量,然而并未对低碳烯烃的选择性产生明显影响。     

液相晶化法合成SAPO-34分子筛

分别以吗啉(Mor)和吗啉-四乙基氢氧化铵(Mor-TEAOH)为模板剂,采用液相晶化法合成SAPO-34分子筛,考察晶化温度、晶化时间和模板剂对合成SAPO-34分子筛的影响和SAP-34分子筛催化甲醇制低碳烯烃(MTO)的性能.结果表明,合成SAPO-34的适宜晶化温度和时间分别为140～180℃和96～120 h,采用吗啉-四乙基氢氧化铵(Mor-TEAOH)为模板剂合成的分子筛晶粒较小.MTO反应的较佳条件为甲醇与水的体积比为2,质量空速5 h-1,催化剂8 g,常压,380℃.该条件下,甲醇转化率达98%以上,C2H4与C3H6总的选择性达84.01%.     

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。     

晶核形成温度下的热处理对含TiO_2的MgO-Al_2O_3-SiO_2系统玻璃晶化的影响

本文采用XRD、DTA、SEM、SAXS等现代测试方法详细地探讨了晶核形成的热处理对MgO-Al_2O_3-siO_2-TiO_2系统玻璃晶化的影响。结果发现在晶核形成的温度下预热处理时,玻璃中析出的镁铝钛酸盐结晶核数越多,高温二次热处理后该结晶粒子的半径就小,对β石英固溶体等亚稳晶相的析出就越不利。虽然镁铝钛酸盐结晶粒子作为异相核能够促进玻璃整体的均匀晶化,但是在镁铝钛酸盐结晶粒子尚未成长到为其他晶相的成核提供有效异物界面的大小时,该结晶粒子的存在不仅不能促进其他晶相的析出,相反会阻碍其他晶相的成核。     

表征手段在SAPO-34分子筛合成过程及晶化机理研究中的应用概述

介绍了SAPO -34分子筛合成过程及晶化机理研究所应用的典型表征方法,XRD 、SEM 、NMR、XRF等离线或原位表征技术在SAPO-34分子筛合成过程、晶化机理研究的应用,为凝胶制备过程和晶化过程液、固相化学组成、配位环境变化规律研究提供了强大检测手段,为晶化机理的提出提供了数据支持,为实现分子筛的可控制备提供了可能.     

预晶化液法合成纳米级ZSM-5分子筛

本文采用水热法在添加预晶化液的条件下合成了纳米级ZSM-5分子筛。采用扫描电镜(SEM)、X射线衍射(XRD)、红外光谱(IR)等手段对产物进行表征,并讨论了预晶化液添加量对分子筛晶化速率、相对结晶度和粒径大小的影响。结果表明,添加预晶化液可以显著提高晶化速率,且当晶化温度为150℃,晶化时间为30h,预晶化液量为10%(占原料总量)时,产品相对结晶速率最大,粒径最小。     

SAPO-34分子筛粒径的控制方法

SAPO-34分子筛具有独特的骨架结构,应用于甲醇制低碳烯烃反应时速率较快且不易堵塞。小晶粒SAPO-34分子筛可有效缓解产物聚合结焦,提高催化剂寿命,但通过简单的合成方法得到粒径小于100 nm的SAPO-34纳米颗粒非常困难。综述影响SAPO-34分子筛粒径的因素,通过选择合适的材料,老化和结晶条件,达到有效控制SAPO-34分子筛粒径的目的。以拟薄水铝石为铝源,液态硅为硅源,采用在水热体系中溶解度较高的四乙基氢氧化铵为模板剂,通过适当延长陈化时间和缩短晶化时间,较容易得到粒径较小的SAPO-34分子筛。     

惰性粒子对流化结晶过程动力学特性的影响

通过惰性粒子对氯化钾流化结晶过程成核速率、晶体生长速率及晶型影响的实验研究，揭示了外加惰性粒子对流化床结晶动力学特性的影响机理和规律,并回归建立了相关数学模型。实验结果表明，惰性粒子主要通过与晶体的碰撞产生大量二次晶核，进而对晶体生长速率产生负面影响，并改变了晶型。其主要影响因素为惰性粒子的密度和尺寸。     

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.     

Effects of crystallization conditions on sedimentation in canola oil

The effects of various factors on sediment formation in canola oil were studied. The crystallization temperature of sediment varied with cooling rate, whereas the melting temperature depended on heating rate as well as the cooling rate during sediment formation. The final crystal size depended on cooling rate. The crystal habit of sediment was generally rod-like but could change to a round and leaf-like shape at low cooling rates (<0.5°C/min). Crystal nucleation occurred in the initial stage of crystallization, while crystal growth was observed during the whole crystallization process, decreasing as cooling proceeded. Crystal growth rate of the sediment was proportional to the crystal surface area Lecithin did not affect the phase transition temperatures of sediment, but retarded crystal growth.     

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。     

Isothermal crystallization kinetics and morphology development of isotactic polypropylene blends with atactic polypropylene

The crystallization kinetics and morphology development of pure isotactic polypropylene (iPP) homopolymer and iPP blended with atactic polypropylene (aPP) at different aPP contents and the isothermal crystallization temperatures were studied with differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy. The spherulitic morphologies of pure iPP and larger amounts of aPP for iPP blends showed the negative spherulite, whereas that of smaller amounts of aPP for the iPP blends showed a combination of positive and negative spherulites. This indicated that the morphology transition of the spherulite may have been due to changes the crystal forms of iPP in the iPP blends during crystallization. Therefore, with smaller amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends increased with increasing aPP and presented a lower degree of perfection of the γ form coexisting with the α form of iPP during crystallization. However, with larger amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends decreased and reduced the γ‐form crystals with increasing aPP. These results indicate that the aPP molecules hindered the nucleation rate and promoted the molecular motion and growth rate of iPP with smaller amounts of aPP and hindered both the nucleation rate and growth rate of iPP with larger amounts of aPP during isothermal crystallization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1093–1104, 2007     

Investigation of the crystallization behavior of isotactic polypropylene polymerized with different Ziegler‐Natta catalysts

Detailed characterization of the crystallization behavior is important for obtaining better structure property correlations of the isotactic polypropylene (iPP), however, attributed to the complexity in ZN‐iPP polymerization, the relationship between crystallization behavior and the stereo‐defect distribution of iPP is still under debate. In this study, the crystallization kinetics of the primary nucleation, crystal growth and overall crystallization of two iPP samples (PP‐A and PP‐B) with nearly same average isotacticity but different stereo‐defect distribution (the stereo‐defect distribution of PP‐B is more uniform than PP‐A) were investigated. The results of isothermal crystallization kinetics showed that the overall crystallization rate of PP‐A was much higher than that of PP‐B; but the analysis of self‐nucleation isothermal crystallization kinetics and the polarized optical microscopy (POM) observation indicated that the high overall crystallization rate of PP‐A was attributed to the high primary nucleation rate of the resin. The stereo‐defect distribution plays an important role in determining both the nucleation kinetics and crystal grow kinetics, and thus influence the overall crystallization kinetics. A more uniform distribution of stereo‐defects restrains the crystallization rate of iPP, moreover, it has more influence on nucleation kinetics, comparing with the crystal growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

聚合物辅料对阿司匹林结晶动力学影响机制的非平衡热力学建模及预测

探究聚合物辅料对难溶性药物结晶的影响机制,是指导无定形固体分散体制剂设计和制备中辅料筛选的关键。研究了不同因素（温度、搅拌速率、聚合物浓度、聚合物分子量和聚合物种类等）对阿司匹林晶体生长动力学的影响。首先,采用基于三种不同晶体生长机制的化学势梯度模型结合UNIQUAC活度系数模型,描述和预测了阿司匹林在不同条件下的结晶动力学。进一步分析了不同因素对晶体生长速率常数k_t和结晶热力学推动力?\mu的影响以及对阿司匹林结晶动力学的影响机制。结果表明,阿司匹林晶体生长速率随着结晶温度、聚合物浓度的增加而降低,随搅拌速率的增加而升高;聚乙烯吡咯烷酮（PVP K25）和羟丙基甲基纤维素（HPMC E3）显著抑制了阿司匹林的晶体生长,在PVP K25和HPMC E3水溶液体系下阿司匹林的晶体生长属于二维成核机制,在纯水和PEGs水溶液体系下晶体生长属于粗糙生长机制。所采用的化学势梯度模型能很好预测不同温度和搅拌速率下阿司匹林的结晶动力学,可有效减少实验所需的人力、物力和财力。研究可为固体分散体制剂制备中聚合物的筛选提供理论研究基础。     

Effect of rod-like imide unit on crystallization of copoly(ethylene terephthalate-imide)

The effect of the imide unit on the isothermal and non-isothermal crystallization, kinetics crystallization of a new family of copoly(ethylene terephthalate-imides) (called copolyesterimides or PETIs) was investigated using differential scanning calorimetry. With a combined Avrami and Ozawa equation, one can describe the non-isothermal crystallization process of copolyesterimides, and the results show the same tendency as that in the isothermal crystallization process. These studies show that the processes of crystal nucleation and growth result in mainly three-dimensional growth with a thermal nucleation. In both isothermal and non-isothermal crystallization processes, the crystallization rate of PETIs, with imide content below 0.5%, is higher than that of neat PET, while PETI-3 (0.3 mol% imide) has the highest crystallization rate. This rate is significantly enhanced over PET homopolymer. It is proposed that imide units precipitate from the melt and act as nucleating agents during the crystallization process of these novel copolyesterimides.     

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。     

Monitoring nonisothermal crystallization of thermoplastic polymers using a quartz crystal resonator

A new monitoring device for the nonisothermal crystallization of thermoplastic polymers, polyethylene, polypropylene, polystyrene, and polyamide, is developed utilizing a quartz crystal resonator, and its performance is evaluated by comparing the measurements with the results of DSC thermoanalysis and microscopic observation. The experimental results of four different polymers indicate that the variation of resonant freency of the quartz crystal resonator is a good means to monitor the crystallization process. Though the measurements of melting and crystallization are close to the DSC outcome, more deviation is observed with the new device. The change in crystalline morphology during the crystallization process is also detected from the slope changes of the frequency decrease. In comparison with the microscopic observation of polymer films, it is found that the processes of nucleation and crystal growth in nonisothermal crystallization can be explained with the variation of the resonant frequency of the quartz crystal resonator. In addition, crystallization kinetics is modeled with the Avrami equation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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。