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O2 System (o2 + system)

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Chemistry	60%

Selected Abstracts

Measurement of mutual diffusion coefficients of gases by the Taylor method: Measurements on H2,Air,H2,N2, and H2,O2 systems

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2002
Naoki Matsunaga
Abstract Mutual diffusion coefficients of hydrogen gas (H2) into air and its component gases (N2 and O2) have been measured in the temperature range of 30 to 180°C and at atmospheric pressure via the Taylor dispersion method. For a H2,N2 system, the composition dependence of the mutual diffusion coefficient has been studied with both H2 and N2 as the carrier gas. The mutual diffusion coefficients for the H2,air and H2,N2 systems are almost the same and smaller than that for the H2,O2 system by about 5%. The present data for the H2,N2 system, corrected to an equimolar composition, agree well with the accurate data reported by the groups of P. J. Dunlop and of R. J. J. Van Heijningen. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 182,193, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10025 [source]

Kinetics of the simultaneous oxidation of nickel(II) and sulfur(IV) by oxygen in alkaline medium in Ni(II),sulfur(IV),O2 system

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2010
Anil Kumar Sharma
In the Ni(II),S(IV),O2 system in the region of pH > 8.4, both Ni(II) and S(IV) are simultaneously autoxidized, and when sulfur is consumed fully NiOOH precipitates. At pH > 8.4, ethanol has no effect on the rate, whereas ammonia strongly inhibits the reaction when pH > 7.0. The kinetics of the reaction, in both the presence and the absence of ethanol, is defined by the rate law where k is the rate constant, KO is the equilibrium constant for the adsorption of O2 on Ni(OH)2 particle surface. In ammonia buffer, the factor F is defined by where K, KOH, K1, K2, K3, and K4 are the stability constants of NiSO3, NiOH+, Ni(NH3)2+, Ni(NH3), Ni(NH3), and Ni(NH3), respectively. In unbuffered medium, the factor F reduces to The values of k and Ksp were found to be (1.3 ± 0.08) × 10,1 s,1 and (4.2 ± 3.5) × 10,16, respectively, at 30°C. A nonradical mechanism that assumes the adsorption of both SO32, and O2 on the Ni(OH)2 particle surface has been proposed. At pH , 8.2, Ni(II) displays no catalytic activity for sulfur(IV)-autoxidation and it is also not oxidized to NiOOH. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 464,478, 2010 [source]

A hybrid density functional theory study of the low-temperature dimethyl ether combustion pathways.

ISRAEL JOURNAL OF CHEMISTRY, Issue 2-3 2002
I: Chain-propagation
Dimethyl ether (DME) has been proposed to be a promising alternative to conventional diesel fuel because of its favorable compression ignition property (high cetane number) and its soot-free combustion. A radical chain mechanism for hydrocarbon autoignition has been proposed for DME at low temperatures. In this mechanism, the chain initiation step consists of DME undergoing hydrogen abstraction by a highly reactive species (typically ·OH). The CH3O·H2 created in the initiation step then combines with O2; the subsequent CH3OCH2OO· radical is involved in a Lindemann-type mechanism, which can lead to the production of formaldehyde (CH2 = O) and ·OH. This concludes the chain-propagating step: the one ·OH produced then sustains the chain-reaction by creating another CH3O·H2. A relatively stable intermediate (·CH2OCH2OOH), formed via isomerization of CH3OCH2OO· in the chain-propagation step, can combine with a second O2 to produce a radical (·OOCH2OCH2OOH) that can potentially decompose into two ·OH radical (and other products). This path leads to chain-branching and an exponential increase in the rate of DME oxidation. We have used spin-polarized density functional theory with the Becke-3-parameter Lee,Parr,Yang exchange-correlation functional to calculate the structures and energies of key reactants, intermediates, and products involved in (and competing with) the chain-propagating and chain-branching steps of low-temperature DME oxidation. In this article, Part I, we consider only the chain-propagation mechanism and its competing mechanisms for DME combustion. Here, we show that only certain conformers can undergo the isomerization to ·CH2OCH2OOH. A new transition state has been discovered for the disproportionation reaction ·CH2OCH2OOH , 2CH2O + ·OH in the chain-propagating step of DME autoignition that is much lower than previous barriers. The key to making this decomposition pathway facile is initial cleavage of the O,O rather than the C,O bond. This renders all transition states along the chain-propagation potential energy surface below the CH3O·H2 + O2 reactants. In contrast with the more well-studied CH3·H2 (ethyl radical) + O2 system, the H-transfer isomerization of CH3OCH2OO· to ·CH2OCH2OOH in low-temperature DME oxidation has a much lower activation energy. This is most likely due to the larger ring strain of the analogous transition state in ethane oxidation, which is a five-membered ring opposed to a six-membered ring in dimethyl ether oxidation. Thus low-temperature ethane oxidation is much less likely to form the ·ROOH (where R is a generic group) radicals necessary for chain-branching, which leads to autoignition. Three competing reactions are considered: CH3O·H2 , CH2O + ·CH3; ·CH2OCH2OOH , 1,3-dioxetane + ·OH; and ·CH2OCH2OOH , ethylene oxide + HOO·. The reaction barriers of all these competing paths are much higher in energy (7,10 kcal/mol) than the reactants CH3O·H2 + O2 and, therefore, are unlikely low-temperature paths. Interestingly, an analysis of the highest occupied molecular orbital along the CH3O·H2 decomposition path shows that electronically excited (1A2 or 3A2) CH2O can form; this can also be shown for ·CH2OCH2OOH, which forms two formaldehyde molecules. This may explain the luminosity of DME's low-temperature flames. [source]