基于双尺度耦合模拟的甲烷化催化剂多级孔结构探究

以固定床甲烷化反应器中的催化剂颗粒为研究对象,建立了床层-颗粒双尺度耦合模型。针对甲烷化过程反应迅速、催化剂颗粒中内扩散影响显著的特点,探讨了颗粒大孔平均孔径、介孔平均孔径、大孔孔隙率和介孔孔隙率对甲烷化反应结果的影响,提出了多级孔结构催化剂的优化设计,以实现甲烷化过程的强化。模拟结果表明:双尺度耦合模型能较好地在床层尺度下探讨催化剂颗粒的微观孔隙结构对反应结果的影响规律;针对直径为5.4mm的球形颗粒,在模拟的生产条件下,反应结果对大孔孔隙率和平均介孔直径较为敏感;采用具有大孔和介孔的双模态催化剂颗粒可获得较高的甲烷产率。     

催化剂颗粒形状对甲烷水蒸气重整反应的影响及工业反应器模拟

甲烷水蒸气重整工艺是现阶段最主要的工业制氢技术,催化剂颗粒形状和反应器操作条件是影响重整反应器性能和产物组成的重要因素。首先从颗粒尺度研究催化剂形状对甲烷水蒸气重整反应的影响,在不同的反应温度和压力下,计算并比较了球形、柱形和环形催化剂的效率因子,其大小顺序为:柱形 < 球形 < 环形。其次,将反应器床层的质量、热量和动量传递与环形催化剂颗粒的扩散-反应方程相结合,建立了用于描述甲烷水蒸气重整工业反应器的一维轴向数学模型。计算并分析了反应器进口温度和压力对反应器床层的温度和压力分布、催化剂效率因子以及甲烷转化率和各组分浓度分布的影响,确定了适宜的工业反应器进口温度和压力,分别为773 K和3 MPa。     

耦合传质的羰基化固定床反应器传热模拟分析

固定床反应器中进行强放热反应时, 反应器的热点温度对操作参数变化敏感,容易引起飞温,导致转化率下降,影响催化剂寿命。为强化羰基化固定床反应器内热质传递与化学反应的协同性,建立考虑颗粒内扩散影响的羰基化固定床反应器拟均相一维传热模型,考察操作参数对床层热点温度、反应转化率、床层温升的影响。不仅体现传热传质和反应的协同作用,而且影响关系明晰、求解方便。为保证反应转化率,本实验条件下确定催化剂颗粒直径小于等于1.5 mm。反应器入口温度/冷却剂油温既要满足床层热稳定性需求,又要使反应转化率和床层温升都在合理范围内。模拟结果表明在床层入口温度升高的同时,可通过降低冷却剂油温获得良好的反应转化率和较小的床层温升。在此基础上,考察入口环氧乙烷浓度对反应转化率和床层温升的影响。本研究可为固定床反应器满足转化率要求、床层合理温升而选择催化剂颗粒直径、床层入口温度、冷却剂油温和床层入口浓度等操作参数提供计算依据。     

基于催化剂活性分布的甲醇重整制氢研究

为了探索填充床内催化活性分布对甲醇重整制氢的影响,文中采用铜基催化剂设计了3种不同活性布置的催化剂床层,并在管式反应器内开展了实验研究,考察了3种不同活性分布的床层上空速和温度对甲醇转化率及产氢速率的影响。通过甲醇蒸汽重整实验表明,3种床层上甲醇转化率及产氢速率随着反应温度和空速的变化规律相同。但床层Ⅰ的催化剂布置形式,改善了局部热效应,提高了催化剂的利用效率。结果显示:床层Ⅰ的催化剂布置形式优于其他2种催化剂布置形式;相同催化剂用量下,床层Ⅰ中的甲醇转化率比床层Ⅱ的甲醇转化率提高9.91%;最佳的活性布置方式是,催化剂用量由反应器入口到出口梯级增加。且在甲醇裂解实验中,床层Ⅰ中的H2体积分数高于床层Ⅱ中的。     

小型反应器内气相甲醇制二甲醚操作优化与分析

通过对小型反应器内气相甲醇催化制二甲醚反应进行高温热态实验,探究了反应温度与甲醇质量空速对催化剂床层轴向温度分布的变化规律,同时分析了不同的操作条件对甲醇转化率和二甲醚选择性的影响,从而优化小型反应器的操作参数。研究结果表明：当甲醇质量空速为1 h^-1时,在不同反应温度条件下,催化剂床层会出现约1.7～2.9℃的轴向绝热温升,且催化剂床层热点温度接近于催化剂床层轴向中部位置;当反应温度为250℃,甲醇质量空速为1 h^-1时,催化剂床层轴向温度分布曲线较为平缓,且甲醇转化率和二甲醚收率均较高,即反应温度为250℃及甲醇质量空速为1 h^-1可视为该小型反应较优的操作条件。     

蜂窝状催化剂中空结构对固定床反应器压降的影响

压降是衡量固定床反应器优劣的重要指标,直接影响了反应性能和综合能耗,催化剂颗粒的外形和尺寸是影响固定床反应器压降的关键因素。采用颗粒分辨计算流体力学模型,研究了工业上常用的蜂窝状催化剂颗粒上中空结构对固定床反应器压降的影响规律。首先,通过对比实验测量的催化剂床层空隙率和压降,验证了建立的颗粒分辨计算流体力学模型的合理性和准确性,其中模型计算获得的压降与实验值相差5%以内。接着,研究了蜂窝状催化剂颗粒开孔个数的影响,发现在催化剂颗粒体积和开孔体积相同的情况下,开孔个数不会显著影响催化剂床层的空隙率,但开孔个数增加会导致压降增大,这主要是由于孔径变小后增大了流体在孔内的动量损失。最后,考察了单孔柱催化剂颗粒尺寸的影响,发现可通过调变外圆柱半径、内孔半径和高度,进而大幅度改变催化剂床层空隙率和压降,当单孔柱壁面越薄时,空隙率越大,致使压降越低。研究结果可以为催化剂颗粒外形的优化设计提供强大的模型工具和一定的理论指导。     

固定床反应器床层压差激增原因分析研究

针对MTP固定床反应器床层压差激增的现象,分别以空隙率不同的新鲜MTP催化剂和破碎催化剂为实验对象,考察气体流速与床层压差的关系。结果表明,床层压差与气体流速的平方呈正比,且与催化剂的空隙率密切相关。反应器下线检修发现,装填催化剂的格栅脱落造成两级催化剂床层短接,反应物料流速急剧增高,且部分催化剂破碎严重。证实了反应器床层压差激增是气体流速变大和催化剂空隙率下降两方面共同作用的结果。     

甲醇水蒸气重整制氢固定床反应器的数学模拟

建立二维拟均相固定床反应器数学模型用于描述Cu₅₀Zn₃₀Ce₁₀Al₁₀催化剂颗粒的甲醇水蒸气重整制氢反应过程，该模型由流体相的质量、热量和动量传递方程组成，耦合催化剂颗粒内部的扩散-反应模型。通过将模型预测值与实验数据进行比较，验证反应器数学模型的准确性。在此基础上，分析关键组分CO₂和CO的效率因子随床层轴向的变化规律以及催化剂床层的轴径向温度分布。结果表明：催化剂床层的轴径向温差较大，导致CO₂效率因子变化较大，而CO由于浓度低，反应速率慢，其效率因子变化不明显。     

甲醇制氢反应器的一维模拟及工况分析

在温度220-280℃、液空速0．8-2．0h^-1、压力1．3-2．7MPa条件下，于无梯度反应器中测定了ALC-1A型双功能催化剂工业颗粒的宏观反应速率，得到了以速度表示的甲醇裂解重整多重反应的双速率宏观动力学方程。建立了甲醇裂解重整制氢工业管式反应器的一维拟均相数学模型，以工业反应器结构尺寸和操作数据为基准计算出计入壁效应及催化剂失活的活性校正因子。考察了不同的原料液配比、系统压力、液空速、壁温及进口温度下甲醇的转化率、氢气的时空产率和床层出口温度的变化。结果表明在一定范围内，降低甲醇在原料液中的含量，提高压力，选择适当的液空速和壁温，将有利于提高反应器的操作性能：单纯提高床层进口温度对反应几乎没有影响。     

甲醇制烯烃反应工艺、反应机理及其动力学研究进展

甲醇制烯烃工艺近年来已成为煤化工领域的研究热点。不同的甲醇制烯烃催化剂将导致不同的反应过程,以SAPO-34为催化剂时,甲醇主要遵循烃池机理,通过快速的平行反应直接生产乙烯和丙烯(MTO)等低碳烯烃;以ZSM-5为催化剂时,甲醇主要遵循双循环机理中的烯烃循环机理,通过甲基化-裂解等多步反应间接生产丙烯(MTP)。这种反应特征的不同也决定着反应器类型和工艺条件的不同:SAPO-34催化剂易失活的特性决定了工业MTO过程通常采用易再生的流化床反应器从甲醇一步生成乙烯和丙烯,而具有良好抗结焦能力的ZSM-5催化剂使得工业MTP过程通常选择易放大的固定床反应器,通过大量烯烃循环与分离逐步获得丙烯。针对SAPO-34催化剂上MTO过程以及ZSM-5催化剂上MTP过程的不同反应情况,综述了近年来甲醇制烯烃代表性的反应工艺、反应机理以及反应动力学等方面的研究进展,并根据其存在的问题提出了相应的发展方向。     

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.     

Sapindaceae,cyanolipids, and bugs

Scentless plant bugs (Heteroptera: Rhopalidae) are so named because adults of the Serinethinae have vestigial metathoracic scent glands. Serinethines are seed predators of Sapindales, especially Sapindaceae that produce toxic cyanolipids. In two serinethine species whose ranges extend into the southern United States,Jadera haematoloma andJ. sanguinolenta, sequestration of host cyanolipids as glucosides renders these gregarious, aposematic insects unpalatable to a variety of predators. The blood glucoside profile and cyanogenesis ofJadera varies depending on the cyanolipid chemistry of hosts, and adults and larvae fed golden rain tree seeds (Koelreuteria paniculata) excrete the volatile lactone, 4-methyl-2(5H)-furanone, to which they are attracted.Jadera fed balloon vine seeds (Cardiospermum spp.) do not excrete the attractive lactone. Loss of the usual heteropteran defensive glands in serinethines may have coevolved with host specificity on toxic plants, and the orientation ofJadera to a volatile excretory product could be an adaptive response to save time.Mention of a commercial product does not consititute an endorsement by the USDA.     

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.     

2008～2009年世界塑料工业进展

收集了2008年7月～2009年6月世界塑料工业的相关资料,介绍了2008～2009年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况。按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、环氧树脂、不饱和聚酯树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍。     

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。