Molecular Dynamics Simulation of Methane Hydrate Decomposition in the Presence of Alcohol Additives

The decomposition process of methane hydrate in pure water and methanol aqueous solution was studied by molecular dynamics simulation. The effects of temperature and pressure on hydrate structure and decomposition rate are discussed. The results show that decreasing pressure and increasing temperature can significantly enhance the decomposition rate of hydrate. After adding a small amount of methanol molecules, bubbles with a diameter of about 2 nm are formed, and the methanol molecules are mainly distributed at the gas-liquid interface, which greatly accelerates the decomposition rate and gas-liquid separation efficiency. The radial distribution function and sequence parameter analysis show that the water molecules of the undecomposed hydrate with ordered ice-like configuration at a temperature of 275 K evolve gradually into a long-range disordered liquid structure in the dynamic relaxation process. It was found that at temperatures above 280 K and pressures between 10 atm and 100 atm, the pressure has no significant effect on hydrate decomposition rate, but when the pressure is reduced to 1 atm, the decomposition rate increases sharply. These findings provided a theoretical insight for the industrial exploitation of hydrates.     

过氧化氢水溶液作用下甲烷水合物分解特性的分子动力学模拟研究

采用分子动力学模拟方法研究过氧化氢水(HP)溶液作用下结构I型(SI)甲烷水合物晶体分解特性. 系统分析甲烷水合物在过氧化氢水溶液作用下由晶态向液态转变过程的机理, 对比相同摩尔浓度乙二醇(EG)溶液作用下甲烷水合物分解变化规律, 得出HP与水合物热力学抑制剂EG一样对甲烷水合物分解具有促进作用, 为HP溶液促进甲烷水合物分解实验研究提供参考.     

Palladium-Catalyzed Hydroesterification of Alkenes in the Presence of Molecular Hydrogen

The effects of molecular hydrogen on the palladium-catalyzed alkene-alcohol-carbon monoxide and alkene-formate reactions have been studied. Yields of esters were generally increased, especially in the alkene-formate reaction, in which an improvement up to 46% yield has been observed. A possible explanation is proposed in which the molecular hydrogen promotes the oxidative addition of formate to palladium. Decarbonylation of formate ester is unlikely to be the initial step.     

氢还原重量法测定三氯化钌产品中钌的含量

建立了氢还原重量法测定三氯化钌产品大样中钌含量的新方法,研究并优化了测定条件,结合原子吸收光谱法(AAS)、电感耦合等离子体原子发射光谱法(ICP-AES)和氯化铵纯度考察了杂质元素对了分析结果的误差影响。结果表明,钌含量为0.3~0.6g的三氯化钌与5~7g氯化铵能完全形成(NH4)2RuCl6配合物,于约100℃烘干水分、350℃分解铵盐、750℃氢还原为海绵钌和105℃干燥水气的条件下,测定3.94%,5.88%,7.32%,9.47%,10.84%和12.93%含量的钌,极差、标准偏差(S)、相对标准偏差(RSD,n=22)和重复性限(r)分别为±0.01%,0.0030%~0.0050%,0.0369%~0.0761%和0.008%~0.014%。样品加标回收率99.96%~99.98%。方法的结果准确,精密度好,且与YS/T562—2009标准分析方法的吻合。     

Decomposition of ammonia on rhenium I. Hydrogen adsorption on rhenium

Field emission microscopy and thermal desorption studies of hydrogen adosrption on a monocrystal tip and a polycrystalline rhenium wire indicate dissociative adsorption which proceeds with an initial sticking coefficient of S_o0.2 and an isosteric adsorption heat of about 138 kJ/mol.

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. , , S_o0.2 138 /.

     

Kinetics of the Decomposition of Hydrogen Peroxide in the Presence of Aqua-Pentacyanoferrate (II)

The decomposition of hydrogen peroxide has been studied in the presence of a large number of metal ions and their complexes^1,2). Interest in radiation chemistry of aqueous solutions where hydrogen peroxide is one of the products and the use of acidic ferrous sulphate solutions as dosimeter in these studies has particularly stimulated the investigation on the kinetics of decomposition of hydrogen peroxide in the presence of Fe⁺², Fe⁺³ and their complexes^1,2). Ferrous sulphate solution can be used as a dosimeter under acidic conditions only, as at higher pH the hydrolysis of Fe⁺² and Fe⁺³ interferes. Recent studies^3-6) have shown the possibility of using the aqueous solutions of ferro- and ferri-cyanides over a range of pH as dosimeter. In the studies of ferrocyanide and ferricyanide catalysed decomposition of hydrogen peroxide^7-11), it is suggested that the catalytic properties of hexacyano ferrates are through their hydrated products. The present study aims at studying the interaction of aquapentacyanoferrate¹¹) with hydrogen peroxide over a range of pH, concentration and temperature.     

Predicting the Limit of Intramolecular Hydrogen Bonding with Classical Molecular Dynamics

The energetics of intramolecular recognition processes are governed by the balance of pre‐organization and flexibility, which is often difficult to measure and hard to predict. Using classical MD simulations, we predict and quantify the effective strength of intramolecular hydrogen bonds between donor and acceptor sites separated by a variable alkyl linker in several solvents and crowded solutions. The balance of entropic and enthalpic contributions poses a solvent‐dependent limit to the occurrence of intramolecular H‐bonding. Still, free energies show a constant offset among different solvents with, for example, a 13 kJ mol^?1 difference between water and chloroform. Molecular crowding shows little effect on the thermodynamic equilibrium, but induces variations on the H‐bond kinetics. The results are in quantitative agreement with experiments in chloroform and showcase a general strategy to investigate molecular interactions in different environments, extending the limits of current experiments towards the prospective prediction of H‐bond interactions in a variety of contexts.     

Assessment of Additives for Nitrogen, Carbon, Hydrogen and Sulfur Determination by Organic Elemental Analysis

 A survey is reported on the use of additives in organic elemental analysis of compounds containing functional groups that may compromise the combustion process. 28 substances containing the following functional groups were selected: organic fluorine, hexafluorophosphate, tetrafluoroborate, tetraphenylborate, sulfonate, phosphine, nitrile, carbide, organometallic. Six additives (powdered silver, silver tungstate with magnesium oxide, silica oxide, tungsten (VI) oxide with magnesium oxide, powdered tin, cerium (IV) oxide) in various sample:additive ratios were assayed. Silver tungstate with magnesium oxide (mixture 1:1, w/w) turned out to be most efficient for the analysis of nitrogen, carbon, hydrogen and sulfur for almost all the compounds assayed. Author for correspondence. Received August 2, 2002; accepted December 12, 2002 Published online May 19, 2003     

Hydrogen Production by Decomposition of Light Paraffins over Ni/Ca/Carbon Catalysts in the Absence or Presence of Impurities

The decomposition of light paraffins was investigated using a Ni/Ca/carbon-based catalyst and an Ag-Pd membrane-type reactor (PMR). The use of this combined system resulted in the formation of smaller amounts of methane (<10% yield) than in fixed-bed reactor systems (10–50% yield). The initial activity of CH₄ decomposition seems to be little affected by these impurities such as NO, SO₂, CO₂, and H₂O. The activity in the presence of SO₂, however, was found to be completely lost after 250 min. This revised version was published online in June 2006 with corrections to the Cover Date.     

Analysis of Decomposition for Structure I Methane Hydrate by Molecular Dynamics Simulation

Under multi-nodes of temperatures and pressures, microscopic decomposition mechanisms of structure I methane hydrate in contact with bulk water molecules have been studied through LAMMPS software by molecular dynamics simulation. Simulation system consists of 482 methane molecules in hydrate and 3027 randomly distributed bulk water molecules. Through analyses of simulation results, decomposition number of hydrate cages, density of methane molecules, radial distribution function for oxygen atoms, mean square displacement and coefficient of diffusion of methane molecules have been studied. A significant result shows that structure I methane hydrate decomposes from hydrate-bulk water interface to hydrate interior. As temperature rises and pressure drops, the stabilization of hydrate will weaken, decomposition extent will go deep, and mean square displacement and coefficient of diffusion of methane molecules will increase. The studies can provide important meanings for the microscopic decomposition mechanisms analyses of methane hydrate.     

Hydrogen Promoted Decomposition of Ammonium Dinitramide: an ab initio Molecular Dynamics Study

Thermal decomposition of a famous high oxidizer ammonium dinitramide (ADN) under high temperatures (2000 and 3000 K) was studied by using the ab initio molecular dynamics method.Two different temperature-dependent initial decomposition mechanisms were observed in the unimolecular decomposition of ADN, which were the intramolecular hydrogen transfer and N-NO₂ cleavage in N (NO₂)^-.They were competitive at 2000 K, whereas the former one was predominant at 3000 K.As for the multimolecular decomposition of ADN, four different initial decomposition reactions that were also temperature-dependent were observed.Apart from the aforementioned mechanisms, another two new reactions were the intermolecular hydrogen transfer and direct N-H cleavage in NH₄⁺.At the temperature of 2000 K, the N-NO₂ cleavage competed with the rest three hydrogen-related decomposition reactions, while the direct N-H cleavage in NH₄⁺ was predominant at 3000 K.After the initial decomposition, it was found that the temperature increase could facilitate the decomposition of ADN, and would not change the key decomposition events.ADN decomposed into small molecules by hydrogen-promoted simple, fast and direct chemical bonds cleavage without forming any large intermediates that may impede the decomposition.The main decomposition products at 2000 and 3000 K were the same, which were NH₃, NO₂, NO, N₂O, N₂, H₂O, and HNO₂.     

Irradiation of Polyethylene in Presence of Several Additives as Studied by Chemiluminescence

Abstract

The protecting effect against radiation induced oxidation of poly-ethylene provided by several additives, namely pyrene, Irganox 1222 and Irganox 1010 has been investigated by mean of FTIR spectroscopy and chemiluminescence (CL) technique. Pyrene appears to be more effective and more stable to irradiation than phenolic antioxidants. Thus, about half of initial pyrene seems to remain unchanged after an exposure of the material to γ⁶⁰Co rays at 240 kGy (dose rate 1 kGy/h) in presence of air. Under the same conditions, about 90% of initial Irganox 1010 seems to be consumed as indicate a comparison of induction oxidation times of initial and irradiated material. The stabilizing effect of the residues resulted by pyrolysis at 850°C in inert atmosphere of several polymers, such as polyacrylonitrile, polyvinylchloride and methyl cellulose is discussed as well.     

A Study of the Reaction of Phosphorus Trichloride with Paraformaldehyde in the Presence of Carboxylic Acids

Abstract

We investigated the mechanism of the reaction of paraformaldehyde with phosphorus trichloride in the presence of carboxylic acids (acetic, propanoic, and formic). Our results revealed that bisphosphonic acids were obtained without the use of water. The structures of the reaction products were studied by 1D and 2D homonuclear and heteronuclear ¹H-, ¹³C-, ³¹P- NMR spectroscopy.

[Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional tables.]     

Decomposition of Benzoyl Peroxide in the Presence of Ferrocene

Russian Journal of General Chemistry - Decomposition of benzoyl peroxide in the presence of ferrocene has been shown to proceed simultaneously via several pathways—thermal decomposition, the...     

Oxidative Cracking of Propane in the Presence of Hydrogen

Russian Journal of Applied Chemistry - An effect of hydrogen additions to the initial mixture on the parameters of the oxidative cracking of propane at atmospheric pressure, temperatures of...     

聚乙烯唑啉作用下甲烷水合物分解的分子动力学模拟

利用分子动力学模拟系统研究了不同质量浓度下(1.25%、2.50%、6.06%)聚乙烯唑啉(PEtO)对甲烷水合物的分解作用. 模拟体系为甲烷水合物2′2′2的超胞和聚合物对接体系. 模拟发现水分子间氢键构架的水合物笼型结构在PEtO的作用下出现扭曲, 最终导致水合物笼型结构完全坍塌. 通过氧原子径向分布函数、均方位移以及扩散系数比较不同浓度PEtO的作用, 证实在一定浓度范围内, PEtO的浓度越高, 其水合物分解作用越强. 此外, PEtO 具有一定的可生物降解性. PEtO 对水合物的作用为: PEtO 吸附在水合物表面, 其中的酰胺基(N―C＝O)与成笼的水分子形成氢键, 破坏邻近的笼形结构, 令水合物分解; PEtO不断分解表面的水合物, 直到水合物笼完全分解.     

Dialkyl Peroxides Decomposition in the Presence of Quaternary Ammonium Halides

Decomposition of dicumyl peroxide and cumyl tert-butyl peroxide was studied in the presence of tetraethylammonium halides in acetonitrile, dimethylformamide, 2-propanol, and acetic acid. The tetraethylammonium halides accelerate the decomposition of dialkyl peroxides in 2-propanol and acetic acid, but do not affect the reaction velocity in dimethylformamide and acetonitrile. The decomposition products character depends on the solvent nature.     

Assay of Peracid in the Presence of Excess Hydrogen Peroxide

ABSTRACT

A simple and rapid colorimetric method for the determination of peracids in the presence of excess hydrogen peroxide is described. The method is based on the selective destruction of hydrogen peroxide by the enzyme catalase, a procedure which leaves the peracid unaffected. The residual solution, then containing only peracid, can be assayed using the stoichiometric oxidation of 2, 2′-azino-bis-(3-ethyl-benzthiazoline-6-sulfonate) diammonium salt (ABTS) in the presence of peroxidase, a reaction that can be quantified photometrically at 405 run. The double-enzyme method was extended to microtiter plate-based systems, thus providing an easy way of analyzing multiple samples for their peracid content.     

Anti-inhibition and Promotion of Radiolytic Hydrogen Formation in Water by Hydroxonium Ions

The ability of hydroxonium ions to enhance the yield of radiolytic hydrogen in aqueous potassium nitrate and potassium chloride solutions is shown. The proposed explanation of the effect is based on the concept of a presolvated electron as a hydrogen precursor. The interception of electrons by H⁺ _aq ions yielding the weakly bound transient species (H⁺ _aq...e^–) retards the hydration of electrons, thus providing a possibility of their longer involvement in hydrogen formation reactions and, hence, enhancement of the yield of hydrogen. The revealed effect is similar to the phenomenon known in positronium chemistry as hydrogen anti-inhibition occurring in a nonpolar liquid containing an electron scavenger, when a second solute that, unlike the first solute, weakly binds electrons is added.