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苯乙烯是重要的石油化工原料。本文介绍了国内外苯乙烯生产的发展概况,合成乙苯,苯乙烯所用的催化剂种类,并就苯乙烯生产及催化剂的发展趋势提出了自己的观点。 相似文献
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《国际聚合物材料杂志》2012,61(1-4):113-122
Abstract Kinetics and mechanisms of oxidation of 6 acetals by molecular oxygen and ozone in liquid phase have been studied. Reaction with molecular oxygen (70°C, 15–16 hr) leads to the formation monoethers of the corresponding glycols with 68–90% selectivity. Salts of metals and complexes with crown-ethers have increased the reaction rate significally. Ozone have reacted with acetals with formation similar products. The mechanisms of intermediate stages have been proposed. 相似文献
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The variation of the Au 4f binding energy of Au clusters with the cluster size has been established by measuring the binding energies of clusters whose size distributions were independently determined by HREM and STM. The binding energy increases significantly when the cluster size is less than 2 nm. Au-Cu bimetallic clusters of the composition Cu3Au have been deposited for the first time on carbon substrates. The shifts in the core level binding energies of the bimetallic clusters show the effect of alloying in the case of large clusters, but show effects of both alloying and cluster size in the case of the small clusters. The interaction of CO with Cu3Au clusters is stronger than with a bulk Cu metal. The interaction of CO with small Cu clusters also seems to be stronger than with bulk Cu or with large Cu clusters. 相似文献
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责任是人应主动承担的角色义务和对其因过失所造成后果应承担的责罚.有两层涵义:一是义务;二是后果.责任心是个体自觉做好分内事务和履行道德义务的心理倾向,是个性心理品质成分中自我特征维度上的重要内容.责任心具有两个方面的涵义:一是角色分内职责;二是角色道德义务.责任心是一种通过责任认知、责任个性和责任适应的动态形式表现出来的静态品质,责任心是责任心过程结构与责任心关系结构相互制约、相互影响的统一体. 相似文献
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对用甘油锌作光稳定剂的光稳定作用进行了测试,并与光稳定剂NBC,BZ进行了比较。研究了甘油锌,NBC和BZ与双酚A的复配效果。研究结果表明,甘油锌是一种性能优良的光稳定剂。 相似文献
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Antioxidative activity and phenolic composition of pilot-plant and commercial extracts of sage and rosemary 总被引:5,自引:0,他引:5
Marie-Elisabeth Cuvelier Hubert Richard Claudette Berset 《Journal of the American Oil Chemists' Society》1996,73(5):645-652
Eight sage (Salvia officinalis) and twenty-four rosemary (Rosmarinus officinalis) extracts, originating from pilot-plant or commercial sources, had different antioxidative activities as measured by accelerated
autoxidation of methyl linoleate. Twenty-seven compounds were characterized in the Labiatae family extracts by high-performance
liquid chromatography (HPLC) coupled with mass spectrometry, equipped with an atmospheric pressure chemical ionization interface,
and by HPLC coupled with a photodiode array spectrophotometer. Twenty-two compounds were identified, including phenolic acids,
carnosol derivatives, and flavonoids. The extracts showed great variation in their HPLC profiles, and no correlation was apparent
between their antioxidative efficiency and their composition, in twenty specific phenols. Data indicated that the most effective
compounds were carnosol, rosmarinic acid, and carnosic acid, followed by caffeic acid, rosmanol, rosmadial, genkwanin, and
cirsimaritin. 相似文献
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Synthesis and characterization of homopolymers and copolymers of various acrylates and acrylonitrile
Various homopolymers and copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, and acrylonitrile in different feed ratios were synthesized. These were characterized by IR, 13C-NMR, DSC, DTA, and TGA. Spectroscopic characterization helped in differentiating copolymers of different mol ratios. Thermal analysis revealed different degradation patterns for homopolymers and copolymers. The temperature and energy changes associated with various phase transitions were dependent on the chemical composition of homo- and copolymers, as expected. © 1993 John Wiley & Sons, Inc. 相似文献
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塑料挤出机螺杆,机筒耐磨损,耐腐蚀的强化与应用 总被引:4,自引:0,他引:4
对塑料挤出机,注塑机螺杆,机筒的磨损,腐蚀原因及提高螺杆,机筒耐磨损,耐腐蚀的方法、制造与应用作了较详尽的介绍。 相似文献
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Emmanuel Ginsburger Fernand Pla Christian Fonteix Silvère Massebeuf Philippe Swaels 《Chemical engineering science》2003,58(19):4493-4514
This work deals with modelling of emulsion polymerization processes using batch and semi-batch reactors. Specific attention is paid to copolymerization of the system styrene/butyl acrylate.The main key parameters of the model are identified on the basis of batch experimental data in order to describe the complete sketch of emulsion polymerization. The model is then used to simulate, under several operating conditions, the polymerization rate, the global monomers conversion, the number and weight average molecular weights as well as the particle size distribution and the glass transition temperature. Then, the model is generalized to the use of semi-batch processes and validated for this application. 相似文献
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David E. Hogan Fei Tian Scott W. Malm Laurel L. Kegel Lajos Z Szabó Anoop S. Hunjan Jeanne E. Pemberton Walter T. Klimecki Robin Polt Raina M. Maier 《Journal of surfactants and detergents》2020,23(4):715-724
In 2014, almost 16 million tons of surfactants were used globally for cleaning and industrial applications. As a result, massive quantities disperse into environmental compartments every day. There is great market interest in developing highly biodegradable, less-toxic, and renewable alternatives to currently used petroleum-based surfactants. Glycolipid surfactants, composed of a sugar headgroup and lipid tail, are effective surfactants and emulsifiers with a high tolerance to electrolytes and are easily tailored to address specific needs. The green synthesis and surfactant characteristics of a suite of cellobiosides and melibiosides were recently described. The biodegradability and toxicity of 1°-alkyl-O-cellobiosides, 2°-alkyl-O-cellobiosides, and 1°-alkyl-O-melibiosides with straight-chain alkyl tails of 8, 10, and 12 are reported in this study. Biodegradability was assessed by quantifying mineralization (CO2 evolution). All of the glycosides were inherently biodegradable and most were readily biodegradable according to OECD and US environmental protection agency (EPA) definitions. The Microtox acute toxicity assay showed both chain length and headgroup had significant effects on toxicity, but most of the molecules were practically nontoxic according to EPA definitions with EC50 values >100 mg L−1. Cytotoxicity to human lung (H1299) and keratinocyte cell lines (HaCaT) was measured by xCELLigence and MTS assays. Cytotoxicity values were comparable to similar glycosides previously reported. IC50 values were determined but in general, exceeded surfactant concentrations that are found in the environment. These data demonstrate the promising nature of these molecules as green alternatives to petrochemical surfactants. 相似文献
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This study aimed to investigate the structural features, antioxidant activity, tyrosinase inhibitory effect, and mechanism of proanthocyanidins from leaf and fruit of Leucaena leucocephala. MALDI-TOF-MS, thiolysis coupled with HPLC-ESI-MS, and 13C-NMR confirmed that these proanthocyanidins were complex mixtures of propelargonidins, procyanidins, and prodelphinidins. (Epi)catechin, (epi)gallocatechin, (epi)catechin gallate, and (epi)gallocatechin gallate were the main constitutive units. The findings obtained from enzyme analysis revealed that the proanthocyanidins had inhibitory effects on both monophenolase and diphenolase of tyrosinase. The IC50 values of leaf and fruit proanthocyanidins were 73.5?±?2.7 and 52.3?±?3.5 µg/mL for monophenolase activity, and 27.2?±?1.4 and 16.1?±?1.1 µg/mL for diphenolase activity, respectively. The inhibition of diphenolase by proanthocyanidins were proved to be reversible and mixed type. In addition, it was also found from various antioxidant methods that the proanthocyanidins in leaf and fruit possessed potent DPPH radical scavenging activity with IC50 values of 103.4?±?0.8 and 87.8?±?1.1 µg/mL, ABTS radical scavenging activity with IC50 values of 72.9?±?0.4 and 65.7?±?0.9 µg/mL, and ferric reducing antioxidant power with FRAP values of 3.74?±?0.03 and 4.02?±?0.15?mmol AAE/g, respectively. The results obtained suggested that the proanthocyanidins from leaf and fruit of L. leucocephala might have the potential to be exploited as natural tyrosinase inhibitors and antioxidants. 相似文献
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M.S. Baymak 《Electrochimica acta》2005,50(6):1347-1359
Electroreduction of terephthalaldehyde (benzene-1,4-dicarboxaldehyde) (I) in protic media is complicated by acid-base and hydration-dehydration equilibria. At pH 0-5.5 the diprotonated form of I is reduced in a reversible two-electron step to a diradical-quinonemethide. This species is at pH 1-3 converted into an aldol (4-HOCH2C6H4CHO), which is further reduced at a more negative potential. At pH 5.5-8.5 the monoprotonated form is reduced. The protonated formyl group is reduced first and then, at a more negative potential, the second formyl group in the aldol, formed in the first step, is further reduced. As terephthalaldehyde is in aqueous solutions present in about 15% as a monohydrate, the limiting currents in this pH range are controlled by the hydration-dehydration equilibrium, the establishment of which is acid and base-catalyzed. The reduction of the unprotonated form occurs at pH > 8.5. At pH > 10 addition of OH− ions takes place. The formation of a geminaldiol anion results in a decrease of reduction waves of the aldehyde, but an increase in the oxidation anodic wave of the diol. Dependence of anodic waves on activity of OH− ions indicates a consecutive addition of OH− ions to the two formyl groups. The understanding of the sequence of chemical (protonation, hydration) and electrochemical reaction steps enabled application of changes of polarographic i-E curves with time as an analytical method for following (in real time) concentration changes of the parent compound, its monohydrazones and monoximes as well as dihydrazones and dioximes. 相似文献
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介绍了全球和中国硫磺、硫酸生产、消费及需求情况。2012年全球硫磺需求量56500kt,供应总量53200kt;硫酸贸易量16500kt。2012年中国硫资源(以S计)表观消费量约30000kt,其中硫磺约14000kt;2012年中国硫酸表观消费量约85000kt,主要用于磷肥、钛白粉、氢氟酸、己内酰胺、粘胶纤维等生产。由于硫酸产能过剩、需求不旺引发的市场低迷仍将持续,预计未来2—3年中国硫磺和硫酸市场难有大的改观。 相似文献
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膜的污染和劣化及其防治对策 总被引:25,自引:0,他引:25
较为系统地介绍了膜污染和劣化的定义和特点,因膜污染和劣化而造成的膜性能变化,以及如何预防、减少或清除膜污染和劣化的一些通用方法。 相似文献