Mechanism Of Ethylene Oxidation Research Articles

Numerical simulation of stable and unstable ram-mode operation of an axisymmetric ethylene-fueled inlet-isolator-combustor configuration

Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois's ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism including nitrous oxide formation reactions is used in the calculations (HyChem FFCM 2.0). Conjugate heat-transfer models based on an assumed penetration depth of the applied heating load are used to account for localized wall heating during the short durations (∼0.2 to 0.3 s) of the parts of the experiments simulated in this work. The results show a marked sensitivity to trace levels of atomic oxygen (∼1% by mass) in the free stream, a consequence of the arc-heating process. Atomic oxygen significantly reduces ignition delay at the relatively low pressures present within the configuration. With 1% atomic oxygen in the free stream, a jet-wake stabilized, partially-premixed flame structure emerges during thermal-throat ramjet operation at an equivalence ratio of 1.24, in accord with available experimental pressure and imaging measurements. Considering the free stream as pure air results in a cavity-wake stabilized, rich premixed flame. Simulations of unstable ram-mode operation leading to inlet unstart at an equivalence ratio of 1.97 also indicate a sensitivity to the free-stream composition. A reduction in atomic oxygen concentration to 0.8% by mass yields good agreement with the experimentally-observed isolator shock-train propagation speed. Both the computational and experimental results indicate that the shock train accelerates before being disgorged from the inlet. This acceleration stems from a rapid increase in the sizes of regions of low speed, sometimes separated flow behind Mach disks that form as the shock train proceeds upstream.

Chemical kinetic model reduction through species-targeted global sensitivity analysis (STGSA)

The uncertainty of the rate coefficients of elementary reactions in detailed chemical kinetic mechanisms can affect the predicted species concentrations and global properties. The size of reduced mechanisms generated by reduction methods, such as directed relation graph (DRG), can also be greatly affected by the uncertainties in the rate coefficients, because these methods eliminate species by comparing contributions of the production rates of important species from other species. In order to obtain the optimum reduced mechanism in the uncertainty domain of reaction rate parameters, the species-targeted global sensitivity analysis (STGSA) method is proposed to measure the importance of species in kinetic mechanisms and to simplify them by considering the input uncertainties. The demonstrations are performed for the ethylene oxidation mechanism using the USC-Mech II with 111 species and the n-heptane oxidation mechanism using the JetSurf (version 1.0) with 194 species. It is found that STGSA can accurately identify the redundant global species and generate more compact reduced mechanisms compared with the DRG-based methods, resulting in a 33-species reduced mechanism for ethylene oxidation and a 37-species reduced mechanism for n-heptane oxidation. These reduced mechanisms show accurate predictions for the ignition delay times and laminar flame speeds over a wide range of operating conditions.

Theoretical mechanistic study of the ethylene oxidation over permanganate: effect of BF3 Lewis acid

The mechanism of ethylene oxidation to ethylene glycol on the permanganate material has been investigated by density functional theory with the M06-L functionals. Effect of the BF3 coordination to the MnO4 − on the mechanism has been examined in details. The initial step is the activation of ethylene C=C bond via the [3+2] electrocyclic addition. The calculated reaction barrier of this step on MnO4 − material (53.67 kJ mol−1) is decreased significantly with the presence of BF3 (32.37 kJ mol−1). In the next step of cyclic intermediate hydration to ethylene glycol, the activation energies for the first and second hydrations are 136.14 and 93.03 kJ mol−1 on BF3–MnO4 −, and 147.08 and 134.87 kJ mol−1 on MnO4 −. These results demonstrate that the BF3 coordinated to the MnO4 − material can enhance the overall conversion of ethylene to ethylene glycol. Molecular orbital analysis provides more understanding regarding the role of BF3 in this reaction.

Large-eddy/Reynolds-averaged Navier–Stokes simulation of cavity-stabilized ethylene combustion

In this study, a hybrid large-eddy/Reynolds-averaged Navier–Stokes (LES/RANS) method is used to simulate ethylene combustion inside a cavity flameholder. The cavity flameholder considered is Configuration E of University of Virginia’s Scramjet Combustion Facility, which consists of a Mach 2 inlet nozzle, a constant-area isolator, a combustor, and an extender, through which the exhaust gases are vented to the atmosphere. To increase the fuel-residence time, a cavity is fitted along the upper wall inside the combustor section of the flameholder. The configuration has the capability of injecting ethylene through a series of ports located upstream of and inside the cavity along the upper wall the combustor. In the simulations, ethylene combustion is modeled using a 22-species ethylene oxidation mechanism. Also, a synthetic eddy method is used to introduce turbulence at the inflow plane of the flameholder. For an equivalence ratio of 0.15, a cavity stabilized flame is predicted. Predictions are compared with line-of-sight temperature, water column-density, water mole-fraction, CO column-density, and CO2 column-density measurements at three stations within and downstream of the cavity. Agreement with experiment is generally good within the cavity. Downstream of the cavity, the simulations predict higher temperatures near the wall. Analysis of the flame structure predicted by the LES/RANS method indicates that the flame propagates into a stoichiometric to fuel-rich mixture near the cavity. Flame angles captured in the simulation are in close agreement with those predicted through classical premixed turbulent flame-speed estimates. Further downstream, the flame structure is non-premixed in character, and near complete conversion of CO to CO2 is observed by the time the flame reaches the combustor exit.

Kinetic model of coherent synchronized ethylene monooxidation by hydrogen peroxide on a biomimetic catalyst, per-FTPhPFe3+OH/Al2O3

A kinetic model that fits the experimental data is studied on the basis of the most probable mechanism of ethylene oxidation by hydrogen peroxide over a biomimetic catalyst, perfluorinated iron (III) tetraphenylporphyrin, deposited on aluminum oxide (per-FTPhPFe3+OH/Al2O3). Effective rate constants for the catalase and oxygenase reactions and their effective activation energies are found.

An interpretation of the kinetics of ethylene oxidation over silver based on separate studies of kinetics of the reaction steps

The kinetics of the separate reaction steps, corresponding to the stepwise redox mechanism of ethylene oxidation over silver, was studied. The results are used for the interpretation of the kinetics of overall catalytic reactions by taking into account an influence of the adsorption of oxygen on the surface properties of silver.

COMPREHENSIVE DESCRIPTION OF CHEMISTRY IN COMBUSTION MODELING

ABSTRACT Recognizing the highly nonlinear and coupled nature of chemical reaction mechanisms of relevance to combustion, and that realistic combustion situations frequently involve extensive variations in the system pressure as well as the local temperature and composition, it is advocated that development of detailed and simplified reaction mechanisms should strive for comprehensiveness in their coverage in terms of thermodynamic parameters, combustion phenomena, and fuel hierarchy. The possibility of mechanism simplification without sacrificing comprehensiveness is demonstrated for a detailed ethylene oxidation mechanism that consists of 70 species and 463 elementary reactions. It is shown that this detailed mechanism can be first simplified, through application of the directed relation graph, to a skeletal mechanism that consists of only 33 species and 205 elementary reactions. This skeletal mechanism is then further simplified to a reduced mechanism that consists of only 21 species and 16 lumped reactions, obtained by assuming quasi-steadiness for species identified through computational singular perturbation. It is further demonstrated that these two mechanisms mimic closely and comprehensively the detailed mechanism for the homogeneous phenomena of perfectly stirred reactor and auto-ignition, and diffusive phenomena of the laminar flame speeds and counterflow ignition, over extensive variations in terms of the system pressure, temperature, and composition.

A directed relation graph method for mechanism reduction

A systematic approach for mechanism reduction was developed and demonstrated. The approach consists of the generation of skeletal mechanisms from detailed mechanism using directed relation graph with specified accuracy requirement, and the subsequent generation of reduced mechanisms from the skeletal mechanisms using computational singular perturbation based on the assumption of quasi-steady-state species. Both stages of generation are guided by the performance of PSR for high-temperature chemistry and auto-ignition delay for low- to moderately high-temperature chemistry. The demonstration was performed for a detailed ethylene oxidation mechanism consisting of 70 species and 463 elementary reactions, resulting in a specific skeletal mechanism consisting of 33 species and 205 elementary reactions, and a specific reduced mechanism consisting of 20 species and 16 global reactions. Calculations for laminar flame speeds and nonpremixed counterflow ignition using either the skeletal mechanism or the reduced mechanism show very close agreement with those obtained by using the detailed mechanism over wide parametric ranges of pressure, temperature, and equivalence ratio.

Ethylene oxidation in a well‐stirred reactor

AbstractThe detailed ethylene oxidation data set of Thornton [1], obtained for a well‐stirred reactor operated fuel‐lean at atmospheric pressure and for temperatures of 1003 K to 1253 K, is used as a basis for the comparison of chemical kinetic mechanisms reported in the literature and for the development of a new ethylene oxidation mechanism. The mechanisms examined are those of Westbrook and Pitz [2] and Dagaut et al. [3]. These mechanisms indicated that unusually large rates for the vinyl decomposition reaction are required to obtain agreement with the Thornton data set.A new ethylene oxidation mechanism is developed in order to overcome some of the drawbacks of the previous mechanisms. The new mechanism closely simulates the overall rate of loss of ethylene, and the concentration of CO, CO2, H2, CH2O, C2H2, CH3OH, CH4, and C2H6 measured for the stirred reactor. Predictions by this mechanism are dependent on a new high temperature vinyl oxidation route, with akC2H3+O2CH2CHO+C/kC2H3+O2CH2O+HCO branching ratio of 1.4 at 1053 K to 2.05 at 1253 K. The branching ratio values were dependent upon the extent of fall‐off for the C2H3 + O2 = CH2O + HCO reaction. © 1995 John Wiley & Sons, Inc.

Nitro and nitrato palladium complexes in oxidation processes: The mechanism of the formation of 1,1- and 1,2-addition products during ethylene oxidation in chloroform—acetic acid solution

The stoichiometric oxidation of ethylene by Pd(NO n ) m Cl 2- m L 2 complexes (where n=2, 3; m = 0, 1, 2; LCD 3CN) in chloroform—acetic acid solution was studied with 1H NMR. This reaction becomes catalytic in the presence of oxygen. The product distribution depends on the nature of the ligands and on the solvent composition. The reaction leads mostly to acetaldehyde, nitroethylene, ethylene glycol monoacetate, yand 1,1-disubstituted ethanes. Kinetics and spectral data indicate the formation of a number of intermediates. The mechanism of ethylene oxidation to 1,1- and 1,2-addition products is discussed.

CNDO-S 2: a new semiempirical SCF MO method for transition metal organometallics

A new semiempirical SCF MO procedure suitable for calculation of the energy and geometry of transition metal organometallic compounds is presented. The parametrization including H, C, N, O, Cl, Fe, Ni and Pd atoms has been developed and calculations of the energy and geometry for a number of organic compounds and some nickel, iron and palladium complexes have been performed. The relative stability of the palladium superoxo complexes formed by π- and σ-type coordinations of superoxoion to palladium atom in monomeric and trimeric palladium compounds has been investigated with the aid of CNDO-S 2. A detailed mechanism of ethylene oxidation by the palladium nitrite complex Pd(NO 2)Cl(CH 3CN) 2 has been studied with the help of CNDO-S 2.

Study of the mechanism of ethylene oxidation by palladium(II) complexes containing nitro and/or nitrato ligands in chloroform

Complexes of Pd(NO n ) 2− m Cl m L 2 (where n = 2, 3; m = 0,1, 2; L= CH 3CN, CD 3CN) were synthesized and their reactivities towards ethylene and propylene oxidation in a chloroform medium were investigated. The detailed mechanism of ethylene oxidation by dinitro- and mono-nitrato complexes of palladium in chloroform solutions was studied by IR and 1H NMR spectroscopy. The structures and routes of decomposition of the intermediates to reaction end products are proposed.

Study on the mechanism of ethylene oxidation by a nitrite complex of palladium in chloroform medium

A detailed mechanism of ethylene oxidation by a palladium nitrite complex Pd(NO 2)Cl(CH 3CN) 2 in chloroform solution is studied using IR and 1H NMR spectroscopy. Kinetic and spectral data obtained indicate the formation of a number of intermediates. The structure and routes of decomposition of the intermediates to end products are suggested.

The relationship of adsorbed species observed by infrared spectroscopy to the mechanism of ethylene oxidation over silver

A combined infrared and kinetic investigation was performed on the oxidation of ethylene over a silver catalyst. Based upon the surface structures deduced from the spectra and additional information taken from the literature, a mechanism was developed to interpret both the epoxidation and combustion processes. The proposed mechanism explains qualitatively the kinetics observed in the present investigation and the variations in selectivity as a function of reactant and product concentrations reported in the literature by previous investigators.

Kinetics and mechanism of ethylene oxidation. Reactions of ethylene and ethylene oxide on a silver catalyst

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics and mechanism of ethylene oxidation. Reactions of ethylene and ethylene oxide on a silver catalystRobert E. Kenson and M. LapkinCite this: J. Phys. Chem. 1970, 74, 7, 1493–1502Publication Date (Print):April 1, 1970Publication History Published online1 May 2002Published inissue 1 April 1970https://doi.org/10.1021/j100702a017RIGHTS & PERMISSIONSArticle Views8761Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Behaviour of surface oxide in ethylene oxidation at platinum in the oxide region

The development of surface oxide species at platinum anodes in the course of electro-oxidation of ethylene at intermediate potentials (0·7–1·2 V(nhe)) has been investigated in relation to the kinetics and mechanism of ethylene oxidation in this potential range. Effects of electrode rotation on the oxidation rate, and on the steady- and non-steady-state surface-oxide coverages are reported, and enable the true activation-controlled, inhibited current/potential curve to be delineated. It is shown that in the potential region where surface oxide coverage becomes appreciable, negative reaction orders can arise for a reaction step involving oxidative removal of chemisorbed “ethylene” species, and the results allow an examination of the extent to which a pathway involving blocked surface oxidation of the metal can be rate-determining over the range of intermediate potentials studied in the present work.