气相流化床聚乙烯颗粒粒径分布的定制

基于气相法聚乙烯流化床反应器颗粒粒径分布的预测[1],提出了颗粒粒径分布定制模型.通过模型的优化计算,可得到催化剂粒径及其分布、操作气速、反应温度、乙烯浓度和丁烯浓度等生产操作参数,由此进行生产可获得具有良好流态化特性的聚乙烯颗粒粒径分布,能为生产具有特定粒径分布的聚乙烯颗粒提供理论指导.模型由工业装置的生产数据分析了计算结果的合理性.最后,以三种粒径分布的聚乙烯颗粒为例讨论了模型的可行性.同时,运用粒子群优化算法求解模型的非线性规划问题,算法具有调整参数少、收敛速度快和全局优化等优点.     

乙烯气相聚合流化床反应器内Geldart B类和Geldart D类颗粒流动特性的三维数值模拟

乙烯气相聚合流化床反应器的设计、操作和优化依赖于对聚合物颗粒粒径大小和分布、气泡运动特性及聚合反应状况的准确描述。采用Eulerian-Eulerian 双流体模型和群体平衡模型耦合方法对某乙烯气相聚合中试规模的工业流化床反应器分别处于常规聚合工艺(属Geldart B 类颗粒)和免造粒工艺(属Geldart D 类颗粒)时床体的气固流动特征以及不同颗粒类型对反应器操作状态和颗粒运动特性的影响进行了三维数值模拟研究。与传统聚乙烯生产工艺相比,免造粒工艺时的Geldart D 类聚合物颗粒更易聚集于气体入口处区域,而且会产生明显的旋涡并出现较大的气泡。研究结果可为免造粒聚乙烯生产工艺的工业推广应用提供参考。     

振荡操作制备双峰聚乙烯的模拟

以流化床乙烯气相聚合工艺为例,提出了通过控制聚合反应条件的振荡操作,在单一反应器内实现制备双峰分子量分布聚乙烯的新工艺.通过模拟计算,分别考察了氢气、乙烯、共聚单体进料速率和反应温度的振荡操作对聚乙烯分子量分布的影响.计算结果表明,采取振荡操作后,聚乙烯树脂的分子量分布呈明显的双峰分布,表明在一个反应器里通过控制反应条件的振荡来制备双峰聚乙烯是可行的,而控制氢气进料速率的振荡操作是制备双峰聚乙烯最为有效的方法.     

气相法聚乙烯工艺冷凝态操作模式的稳定性和动态行为

气相法聚乙烯工艺冷凝态操作模式由于显著提高了循环气移热能力和反应器时空产率,已成为流化床乙烯聚合工艺的主流操作模式。建立了气相法聚乙烯工艺冷凝态操作模式的数学模型,包括流化床反应器模型,多级换热器模型和反应温度、压力以及循环气组成的控制模型。基于此,采用流程模拟方法,计算了系统在反应器温度采用闭环控制时的稳态解;根据系统对小扰动的动态响应特点,定性判断了反应器温度采用开环控制和闭环控制时聚合反应系统的稳定性;考察了系统对1-己烯分压和催化剂进料速率的阶跃响应特性。结果表明,反应器温度采用闭环控制时,聚合反应系统在所考察操作条件下均是稳定的,而采用开环控制时,解曲线被分叉点分割为稳定区域和不稳定区域。反应器温度对1-己烯分压阶跃变化的动态响应表明聚合反应系统存在长、短周期两类振荡,表明冷凝态操作模式下乙烯聚合反应过程是一个多控制回路耦合的复杂过程。     

气相法聚乙烯工艺冷凝态操作模式的稳定性和动态行为

气相法聚乙烯工艺冷凝态操作模式由于显著提高了循环气移热能力和反应器时空产率,已成为流化床乙烯聚合工艺的主流操作模式。建立了气相法聚乙烯工艺冷凝态操作模式的数学模型,包括流化床反应器模型,多级换热器模型和反应温度、压力以及循环气组成的控制模型。基于此,采用流程模拟方法,计算了系统在反应器温度采用闭环控制时的稳态解;根据系统对小扰动的动态响应特点,定性判断了反应器温度采用开环控制和闭环控制时聚合反应系统的稳定性;考察了系统对1-己烯分压和催化剂进料速率的阶跃响应特性。结果表明,反应器温度采用闭环控制时,聚合反应系统在所考察操作条件下均是稳定的,而采用开环控制时,解曲线被分叉点分割为稳定区域和不稳定区域。反应器温度对1-己烯分压阶跃变化的动态响应表明聚合反应系统存在长、短周期两类振荡,表明冷凝态操作模式下乙烯聚合反应过程是一个多控制回路耦合的复杂过程。     

乙烯气相聚合工艺研究与技术进展

聚乙烯已成为全球产量最大、用途最广的合成材料。由于生产流程短和设备投资低的优势,流化床气相聚合工艺是聚乙烯的主要生产路线,得到了广泛而深入的研究和开发。本文综述了国内外乙烯气相聚合工艺技术的研发历程,特别是中国在气相法聚乙烯技术方面做出的重要贡献。总结了气相聚合工艺的七种操作模式,即干法气相聚合、超干法气相聚合、气相冷凝聚合、气相超冷凝聚合、气液固云雾聚合、露点聚合以及交替交变聚合。分析了各操作模式所涉及的关键科学问题和工程技术解决方案,例如反应器时空产率模型、冷凝态聚合操作点优化、溶剂的作用、黏性流化颗粒熔融温度预测、流化质量监控与声发射、多流型复合以及一器多用等,并重点介绍了气-液-固云雾聚合流化床反应器中颗粒团聚、气泡运动的新特征,云雾聚合流化床运行的新稳定机制,以及实现聚合物产品结构调控的新途径——乙烯的露点聚合和交替交变聚合技术。指出聚合反应工程学科正从聚焦传统的过程强化,发展到过程强化与产品多样化相互兼顾的变化趋势。     

环流流化床反应器中乙烯气相聚合反应研究

研究开发了１种新型的用于乙烯气相聚合反应的环流流化床反应器。通过对工业Ａ催化剂和实验室自制的ＱＣＰ－０１催化剂的乙烯气相聚合反应评价及聚合物产品的颗粒形态等方面的研究,认为环流流化床反应器具有聚合反应平稳、催化剂的聚合活性高、产品粒径分布均匀等特点,是１种具有良好应用前景的新型反应器。     

气相法聚乙烯BCG-Ⅱ型催化剂的开发和应用

对气相法聚乙烯BCG-Ⅱ型催化剂的组成、粒径分布及催化剂的淤浆聚合性能进行了研究。研究结果表明，BCG—Ⅱ型催化剂的活性较高，聚合物堆密度适中，应用在Unipol乙烯气相聚合工艺装置上操作良好，所生产的树脂颗粒均匀。干爽且流动性好，产品质量合格、稳定。     

平均粒径对气-固流态化特性的影响

运用一种新型的隔离稀相床层塌落技术,研究了3种不同平均粒径的FCC催化剂流化床层的塌落特性和高表观操作气速条件下床层的乳相结构。实验采用摄像技术,记录了细颗粒床层的塌落过程,获得了床层料面的塌落曲线。考察了颗粒流化床层的乳相和泡相特性,并进一步分析了平均粒径对颗粒床层塌落性质的影响。实验结果表明:在操作气速较高的条件下,在所选用的粒径范围内,平均粒径为30μm左右的FCC催化剂颗粒的塌落时间最长,乳相密度最小,泡相体积分率亦明显高于较粗颗粒的对应值。这些结果表明平均粒径为30μm左右的FCC催化剂颗粒具有比较独特的流化性能。     

抗冲共聚聚丙烯生产工艺主要操作控制参数分析

通过对环管反应器工艺参数控制分析、流化床气相聚合的特点以及影响因素进行分析,确定环管反应器内停留时间决定了反应时间也即主催化剂的产率,同时操作气速、流化质量、反应温度以及换热器的换热效果都是影响收率的主要因素,环管反应器操作的关键是努力提高浆料密度,这样可以有效降低反应丙烯进料量,减少回收丙烯量,从而降低生产能耗和操作费用。     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

ICP-MS法测定地球化学样品中As、Cr、Ge、V等18种微量痕量元素的研究

建立了测定地球化学样品中包括As、Cr、Ge、V等18种微量、痕量元素的ICP-MS方法。地化试样用HF-HNO3混酸分解后,以1 1 HNO3溶解干渣。由于制样不使用盐酸,避免了Cl对As、Cr、Ge、V的质谱干扰。用国家一级地球化学标准物质GBW 07309制备溶液优化仪器工作参数,并用于校准。方法测定限(6s)为:0.007~6.4μg/g,精密度(RSD%,n=12)为:29%~9.4%,经过国家一级地球化学标准物质的分析验证,结果与标准值吻合。方法已应用于国土资源调查的试样分析。