An Experimental and Kinetic Study of Ethene Oxidation at a High

Ind. Eng. Chem. Res. 2002, 41, 5659-5667

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An Experimental and Kinetic Study of Ethene Oxidation at a High Equivalence Ratio S. Jallais,* L. Bonneau, and M. Auzanneau Laboratoire de Combustion et De´ tonique, CNRS UPR 9028, Te´ le´ port 2, 1 avenue Cle´ ment Ader, ENSMA, BP 40109, 86961 Futuroscope Chasseneuil Cedex, France

V. Naudet and S. Bockel-Macal Air Liquide CRCD, BP 126, Les Loges en Josas, 78354 Jouy En Josas Cedex, France

Ethene oxidation has been investigated experimentally and theoretically. The reaction was studied in a perfectly jet-stirred reactor, at atmospheric pressure, at temperatures in the range of 773-900 K, and at high equivalence ratio (between 3 and 10). The product composition was analyzed on gas chromatographs. The data obtained have been compared with the predictions of two existing detailed kinetic models. Both failed to predict the experimental trends. One of the kinetic models tested has been updated with newer kinetic constant evaluations and then give better agreements for all of the investigated conditions. Finally, rates of production and consumption analysis are used to interpret the results and showed the importance of oxygenated intermediates. Introduction Ethene is an important intermediate species in the combustion of methane,1,2 larger aliphatic hydrocarbons,3,4 and aromatics.5 It is also widely used in the chemical industry particularly via oxirane production as polymers, solvents, and surfactant bases. Consequently, the knowledge of the ethene oxidation kinetics is of considerable interest to modeling of the combustion of hydrocarbons or to improving the safety in chemical plants.6 The chemistry of ethene oxidation and pyrolysis has been studied in a range of combustion devices such as laminar flow reactors,7,8 jet-stirred reactors,9,10 and shock tubes.11-13 Westbrook et al.10,14 and, subsequently, Marinov and Malte15 have developed a comprehensive ethene oxidation mechanism based on jet-stirred reactor data obtained at atmospheric pressure, low equivalence ratio, and temperatures ranging from 1003 to 1253 K. Dagaut et al.9 developed a kinetic model of ethene oxidation that they validated, with highly diluted jet-stirred experiments at pressures of 0.1-1 MPa, for different equivalence ratios ranging from 0.15 to 2, and for temperatures of 900-1200 K and also with ethene ignition delays reported in the literature.12 Recently, Hidaka et al.16 studied ethene pyrolysis and oxidation behind reflected shock waves from 1100 to 2100 K and between 0.15 and 0.45 MPa. They proposed a detailed kinetic model and outlined the uncertainties associated with the atomic oxygen attack on ethene and molecular oxygen attack on vinyl radicals. However, so far, no data have been obtained for intermediate temperature and fuel-rich conditions in a flow reactor. The purpose of this study was to experimentally investigate the kinetics of ethene oxidation in a jetstirred reactor for intermediate temperatures, from 750 * To whom correspondence should be addressed. E-mail: [email protected]. Tel: +33 5 49 49 83 15. Fax: +33 5 49 49 82 91.

to 900 K, at atmospheric pressure, and for high equivalence ratios varying from 3 to 10. The equivalence ratio is defined as the ratio between the stoichiometric oxygen concentration and the experimental one. These data will be used as a basis comparison between reported chemical kinetic mechanisms, such as those developed by Dagaut, Leconte, Chevailler, and Cathonnet17 (DLCC) and Barbe, Battin Leclerc, and Coˆme18 (BBLC), and then for the development of a new ethene oxidation mechanism. Experimental Setup Various laboratory setups have been developed for kinetic studies of combustion systems. The perfectly stirred reactor (PSR) is an interesting experimental configuration, conducting direct measurements of the formation or depletion rates of the involved chemical species. These data are not affected by fluid dynamics, provided that the characteristic mixing time is smaller than the chemical time.19 The experimental setup is shown in Figure 1. The atmospheric jet-stirred reactor used in this study has been designed and built following the criteria established by David and Matras.20 The three conditions such as the Reynolds number, the recirculation rate, and the maximum speed through the injectors required for good macromixing are verified. Homogeneity in temperature and concentration on the vertical axis of the reactor has been tested. It showed a good accordance with the results discussed by Dagaut et al.21 and David and Villermaux.22 Thus, the macromixing and micromixing can be considered as optimum for the operating conditions. The reactor, depicted in Figure 2, is a 60 mm diameter sphere made of silica to minimize wall catalytic reactions. Fast mixing is achieved by introducing the reactants through four 0.3 mm diameter nozzles of a cross-shaped injector. As shown in Figure 1, the reactor is located inside an oven, which maintains the reactor temperature at the desired value.

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with a mass spectrometer. This analytical combination is able to separate the main stable chemical molecular species involved in light hydrocarbon combustion, like O2, CO, CO2, CH4, C2H4, C2H6, C2H2, C2H4O epoxide, C3H6, and C3H8. For these measurements, a maximum error of about 5% has been estimated. The overall carbon atomic balance has been found to be accurate within 5%. The experiments were performed with mixtures all containing initially 5% of ethene, which permitted an important conversion for quite lower temperature than that used by Dagaut et al.9 Computational Models and Reaction Mechanisms

Figure 1. Experimental setup.

The present computations are carried out using the Sandia PSR code,23 which computes species concentrations from the balance between the net rate of production of each species by chemical reaction and the difference between the input and output flow rates of species. These rates are computed from the kinetic mechanism and the elementary reaction rate constants at the experimental measured temperature according to the modified Arrhenius expression

kj ) AjTβj exp

Figure 2. Description of the jet-stirred reactor.

The reactant gases are diluted in nitrogen and separately preheated. The fuel is introduced through a capillary tube. It reduces the residence time in the hot zone outside the reactor and so minimizes the fuel pyrolysis. The reactant gases are mixed at the entrance of the injectors so that the residence time inside the injectors, τinj, is negligible with respect to the residence time inside the reactor, τ (τinj/τ ) 10-2). Gases flow rates are measured and regulated through mass-flow controllers. The temperature of the reacting mixture is measured along the whole vertical axis (6 cm) with a mobile chromel-alumel thermocouple. A good thermal homogeneity is observed for each experiment (∆T e 10 K) in the reacting conditions. The last section of the apparatus is devoted to sampling and analysis of the products of the reaction. Small amounts of the products are sampled with a sonic quartz probe as shown in Figure 1. Sonic conditions at the orifice of the probe (about 50 µm) are maintained by a vacuum pump. The residual pressure in the probe is about 103 Pa, which is enough to freeze sampled gas compositions. The samples of reacting mixtures are stored in 1 L bulbs, compressed by a piston, and fed through two sampling valves in a gas chromatograph (TCD and FID) and in a gas chromatograph coupled

( ) -Ej RT

where kj ) reaction rate constant of the jth reaction, Aj, βj, and Ej ) kinetic parameters of the jth reaction, R ) ideal gas constant, and T ) temperature. The resulting set of nonlinear algebraic equations is solved using the Newton-Raphson method. The backward reaction rate constants are computed from the forward ones using the equilibrium constant values. Two different reaction schemes have been investigated: (1) the mechanism proposed by Dagaut, Leconte, Chevailler, and Cathonnet17 (the DLCC mechanism); (2) the mechanism proposed by Barbe, Battin Leclerc, and Coˆme18 (the BBLC mechanism). The DLCC mechanism has been originally validated by comparison with data obtained in a PSR at high dilution conditions and from 0.1 to 1 MPa, in lowpressure flames and in reflected shock tubes. These validation tests included the oxidation of hydrocarbons24-28 up to C3 and light oxygenated compounds (oxirane, methanal, and ethanal) in the intermediate and high temperature range. The thermodynamic data came from Burcat29 or from the CHEMKIN II library.30 The complete mechanism (DLCC) involves 606 reactions and 91 species. In this mechanism, many fittings of the rate constants have been done but always in agreement with the error limits recommended for each reaction. The BBLC mechanism has been built by using a reaction grid proposed by Tsang and Hampson.31 It then included all of the unimolecular or bimolecular reactions involving radicals or molecules containing less than three carbon atoms with the most recent kinetic parameters available in the literature. The thermodynamic data were obtained from the THERM software32 except for the biradicals CH2 (singlet), CH2 (triplet), O, and CO, for which the coefficients of the CHEMKIN II library30 are used. It has been validated on methane and ethane oxidation in various laboratory reactors18,33 (PSR, tubular flow reactor, and shock tube). The mechanism involved 439 reactions and 63 species. The

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preferred kinetic data were those proposed by Baulch et al.34 and Tsang.35 In this mechanism, fittings have been done only for the following reactions: for which the

CH3 + CH3 + (M) f C2H6 + (M) CH3 + CH3 f C2H5 + H CO + HO2 f CO2 + OH kinetic constants have been multiplied by 4 and by 5 and divided by 5, respectively, in order to reproduce the ethane and carbon monoxide profiles in methane oxidation. Results and Discussion Results of the Reported Mechanism. Concentration profiles for the measured stable species (C2H4, CO, CO2, CH4, C2H6, C2H2, and C2H4O oxirane) have been computed using the DLCC and BBLC mechanisms and compared with our experimental data. The data are reported in terms of the outlet concentrations for each chemical species as a function of the reactor temperature for three different equivalence ratios, φ (3, 5, and 10). The initial mole fractions were 0.05 for ethene and 0.05, 0.03, and 0.015 for oxygen for the three equivalence ratio values 3, 5, and 10, respectively. The residence time has been fixed to 1.3 s for all of the experiments. Because of the complexity of the combustion kinetics, a qualitative agreement between the experimental results and the model prediction is a good indication of the adequateness of the kinetic mechanism in the range of the operating conditions. Thus, we first compared the results from the detailed kinetic models with the experimental data in terms of qualitative trends. From this point of view, it can be seen that the DLCC mechanism shows good prediction of ethene conversion over a limited temperature range. As can be seen on Figure 3, for temperatures smaller than 880 K, the DLCC mechanism overpredicts the low-temperature reactivity of ethene and, consequently, it overpredicts the carbon monoxide and carbon dioxide profiles. In the temperature range of 880-910 K, ethene is well predicted but carbon monoxide is underpredicted and carbon dioxide is overpredicted. It shows a too high conversion of CO in CO2. The computed concentration profiles of methane and ethane are higher than those in the experimental data, but the ethyne formation is very well predicted by the model. The oxirane profile is strongly underpredicted. Similar trends are found for the three equivalence ratios investigated. The BBLC model reproduced rather well the experimental trends for C2H4, CO, CO2, and C2H4O. However, methane and ethane are strongly overpredicted and C2H2 is totally underpredicted. Similar observations have been done for the three equivalence ratios. A quantitative agreement between the models and experimental results concerning oxidation for an equivalence ratio of 3 is reported in Table 1. The percentage of error between experimental data and model predictions is used as a basis for the choice between the tested mechanisms. These data refer only to the nonzero concentrations for the six higher temperatures and for conversion higher than 15%. The analysis of the results reported in Table 1 leads to similar conclusions as those developed in the earlier qualitative comparison.

After the results were studied and considering the great interest of the ethene and oxirane predictions, the BBLC mechanism has been chosen as a basis for a new mechanism. Updating of the BBLC Detailed Kinetic Mechanism. This model was revised to obtain a more accurate reproduction of the experimental results. First, more recent rate constants have been included and a new reaction pathway has been added. Second, most of the rate constants have uncertainties near a factor of 2 or even more, and it has been necessary to adjust a few of them. The methyl and vinyl radicals are important products in fuel-rich conditions. However, there is still uncertainty regarding the product distribution of the C2H3 + O2 reactions. So, the Wang and Frenklach36 recommendation based on the QRRK theoretical study of Bozzeli and Dean37 has been used in the present mechanism instead of the Dagaut et al.38 estimation for the following reaction:

O2 + C2H3 f CH2O + HCO

(1)

Vinyl radicals are an important source of ethyne in our conditions in the reaction

C2H3 + O2 f C2H2 + HO2

(2)

The rate constant adopted comes from Cooke and Williams39 and is an estimation based on ethane ignition in a shock tube. Besides, the reaction

C2H3 + O2 f CH2CHO + O

(3)

was added to the mechanism following the Marinov and Malte recommendation.15 The rate constant used is a slightly modified version of the rate constant proposed by Bozzeli and Dean,37 i.e., divided by 1.7 according to the values used by Dagaut et al.38 in the DLCC mechanism. This expression is very close to the rate constants used by Wang and Frenklach36 and Marinov and Malte.15 The more recent Melius40 determination, based on the semiempirical BACMP4 methods, was preferred to the Colket et al.41 determination by experimental study of ethanal pyrolysis in a turbulent flow reactor for the reactions of the vinoxy radicals:

CH2CHO f CH3CO

(4)

CH2CHO f H + CH2CO

(5)

Ethanal is an important stable product of ethene oxidation in the low and intermediate temperature range. So, the more recent estimation of Marinov42 was preferred to the Cavanagh et al.43 determination for the reaction

CH3CHO + CH3 f CH3CO + CH4

(6)

For the reactions of OH radicals with ethene, two pathways were included in the original mechanism:

C2H4 + OH f CH2O + CH3

(7)

C2H4 + OH f C2H3 + H2O

(8)

Liu et al.44 reported that reaction (8) is dominant for

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Figure 3. Comparison between computed (full lines, BBLC; dashed lines, DLCC) and experimental (symbols) C2H4, CO, CO2, C2H4O, CH4, C2H6, and C2H2 profiles for the oxidation of ethene (φ ) 3 - τ ) 1.3 s).

temperatures above 720 K and that reaction (7) is dominant for temperatures below 560 K. For Atkinson,45 reaction (8) is the only pathway for temperatures above 700 K. Thus, reaction (7) proposed by Westbrook et al.10 on the basis of ethene oxidation experiments has been

removed from the mechanism. The consequence is a strong decrease of the ethene conversion, so we multiplied the rate constant (8) of the ethene H abstraction, which is the most important reaction of consumption of ethene, by a factor of 3 (recommended ∆log(k) ) 0.5).

Ind. Eng. Chem. Res., Vol. 41, No. 23, 2002 5663 Table 1. Percentage Errors between Experimental Data and Model Predictions species mechanism

Φ

DLCC BBLC DLCC BBLC DLCC BBLC

3 3 5 5 10 10

C2H4 CO CO2 CH4 C2H6 C2H2 C2H4O 16 11 10 8 4 4

41 29 31 30 20 11

258 42 248 45 205 26

182 301 175 272 122 449

116 183 93 125 28 133

16 86 28 90 44 91

95 8 93 9 94 30

This expression is very close to the one proposed by Ranzi et al.46 on the basis of reactivity-structure correlation. As shown in Figure 3, the methane is overpredicted by the BBLC and DLCC mechanisms. A rate of production analysis shows that the production of methane comes essentially from the following reaction:

C2H4+ CH3 f CH4 + C2H3

(9)

So, a good methane profile is obtained with a rate constant divided by a factor of 3 (recommended ∆log(k) ) 0.5). This expression is very close to that of Marinov.42 The rate constant of the reaction

C2H4 + HO2 f C2H4O + OH

(10)

has also been multiplied by 1.5 (recommended ∆log(k) ) 0.26) in order to improve the model agreement with experimental results for oxirane. This rate constant is an average value between the Baldwin et al.47 experimental determination and the Baulch et al.34 recommendation. The combination reaction of methyl radicals leading to ethane formation is very important in highly rich oxidation because of the high concentration of methyl radicals. To obtain a good agreement of the computed ethane profile, we reduced the fitting of Barbe et al.18 on the reaction

CH3 + CH3 + (M) f C2H6 + (M)

(11)

Originally, the rate constant has been multiplied by 5. Thus, the fitting has been reduced by a factor of 2, which is lower than the recommended Baulch et al. error limits.34 These adjustments must not be regarded as a determination of rate constants, but they could permit one to identify reactions whose uncertainties are large and need further investigation. Key reactions can be found in Table 2. This conducts to the elaboration of a new mechanism called the modified mechanism (NM), which is available directly from the authors (jallais@ lcd.ensma.fr).

Figure 4. Comparison between computed (lines) and experimental (symbols) C2H4, CO CO2, CH4, C2H6, C2H4O, and C2H2 profiles for the oxidation of ethene (φ ) 3 - τ ) 1.3 s).

Results of the NM. Experimental and computed concentration profiles for the three equivalence ratios investigated (3, 5, and 10) are reported (Figures 4-6) in terms of outlet mole fractions for each species of interest as a function of the measured reactor temperature. As can be seen in Table 3, the NM model reproduced satisfactorily the data (fuel conversion and product mole fractions). The errors were lower than those for for the BBLC and DLCC mechanisms. The influence of the equivalence ratio was well reproduced in terms of the loss of conversion, but for an equivalence ratio of 10, the predicted conversion started at a slightly lower temperature than that in the experimental results. This trend induced some discrepancies on the CO and CO2 computed profiles. Consequently, the average error reached 50% for the prediction at an equivalence ratio of 10. For all of the computations, the ethyne and oxirane predictions were slightly lower than those in the experimental measurements, but the percentage error was below 40% for the first one and below 25% for the second one. This new mechanism has been tested with three different experimental conditions. First, we compared

Table 2. Rate Coefficients for Key Reactions, k ) ATβ exp(-E/RT)a

a

reaction

A

O2 + C2H3 f CH2O + HCO O2 + C2H3 f CH2CHO + O O2 + C2H3 f C2H2 + HO2 CH2CHO f CH3CO CH2CHO f H + CH2CO CH3CHO + CH3 f CH3CO + CH4 C2H4 + OH f C2H3 + H2O C2H4 + CH3 f CH4 + C2H3 C2H4 + HO2 f C2H4O + OH CH3 + CH3 (+M) f C2H6 (+M)

1.64 × 15.8 × 1012 1.45 × 1015 1.0 × 1016 1.6 × 1016 3.9 × 107 6.0 × 1013 1.4 × 1012 3.3 × 1012 7.2 × 1013

Units are mol, cm, s, and cal.

1021

β

E

ref

-2.78 0 -0.78 0 0 5.8 0 0 0 0

2523 10000 3135 44 × 103 47 × 103 2200 5900 11.1 × 103 17.2 × 103 0

Wang and Frenklach36 Cooke and Williams39 Dagaut et al.38 Melius40 Melius 40 Marinov42 Baulch et al.34 × 3 Baulch et al.34/3 Baulch et al.34 × 1.5 Baulch et al.34 × 2

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Figure 7. Comparison between computed (lines with symbols) and experimental (symbols) C2H4, CO CO2, CH4, C2H6, and C2H2 profiles measured by Dagaut et al. for the oxidation of ethene (φ ) 0.15 - T ) 1023 K). Table 3. Percentage Errors between Experimental Data and Model Predictions (NM) species


the model predictions to the experimental points on methane and ethane oxidation for which the original BBLC was validated. These comparisons were not

Φ

C2H4

CO

CO2

CH4

C2H6

C2H2

C2H4O

3 5 10

5 4 3

6 14 19

7 14 8

23 37 131

20 20 33

42 30 32

10 14 32

reported here but showed reasonable agreement with the experimental results. The model improvement did not affect the modeling of the original validation case. Second, to test the mechanism in fuel-lean conditions, we compared the mechanism to the previously reported experiments of Dagaut et al.9 in an atmospheric jetstirred reactor for an equivalence ratio of 0.15 and at 1023 K. As shown in Figure 7, the present model reproduces well the major species concentration profiles (C2H4, CO, and CO2). For the minor species (CH4, C2H6, and C2H2), the agreement is less good, but the very small concentrations of these species make the comparison very difficult. Third, to test the modified mechanism at high temperature, we computed ignition delays in the conditions of the reflected shock wave study reported by Baker and Skinner.12 The ignition delays were modeled using the Senkin computer program,47 assuming constant density behind reflected shock waves. As shown on Figure 8, the modeling results are in relatively good agreement with the experimental data within the experimental errors. The model generally predicts shorter ignition delays that those observed especially at the higher temperature of the experiments at an equivalence of 1.

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the increase of the equivalence ratio, the relative importance of H abstraction [reaction (8)] decreases and the H addition [reaction (12)] increases. The reactions of ethene with peroxy radicals have the same importance on ethene conversion for the three equivalence ratios investigated. Vinyl radicals mostly re-form ethene by reaction with methanal and react with molecular oxygen to form vinoxy radicals and methanal:

Figure 8. Comparison between computed (lines with symbols) and experimental (symbols) ignition delays measured by Baker and Skinner for the oxidation of ethene ([ for a mixture of 1% C2H4-3% O2-96% Ar at φ ) 1 and ] for 1% C2H4-1.5% O2-97.5% Ar at φ ) 2).

C2H3 + CH2O f C2H4 + HCO ROC(C2H3) ) -0.618 (14) C2H3 + O2 f CH2CHO + O ROC(C2H3) ) -0.260 (3) C2H3 + O2 f CH2O + HCO ROC(C2H3) ) -0.115 (1) Vinoxy radicals isomerize to acetyl radicals, leading to methyl radical formation by molecular decomposition, or decompose to ketene by release of a hydrogen atom:

CH2CHO f CH3CO ROC(CH2CHO) ) -0.627 (4) CH2CHO f H + CH2CO ROC(CH2CHO) ) -0.169 (5)

Figure 9. Reaction pathway of ethene oxidation at 850 K (φ ) 3 - τ ) 1.3 s).

So, the improvements of the mechanism do not affect the accuracy of the model in the conditions of the earlier studies. Computations of normalized reaction rates of production (ROP) and normalized reaction rates of consumption (ROC) with the modified mechanism were used to interpret the results obtained in this study. Rate of Production and Consumption Analysis. A schematic description of the reaction pathway for ethene oxidation at 850 K for an equivalence ratio of 3 is shown in Figure 9. Ethene mostly reacts through metathesis, yielding vinyl radicals, and to a lower extent by H addition, yielding ethyl radicals, and with peroxy radicals producing oxirane and ethanal:

C2H4 + OH f C2H3 + H2O ROC(C2H4) ) -0.554 (8) C2H4 + H (+M) f C2H5 (+M) ROC(C2H4) ) -0.209 (12) C2H4 + HO2 f C2H4O + OH ROC(C2H4) ) -0.062 (10) C2H4 + HO2 f CH3CHO + OH ROC(C2H4) < -0.05 (13) In our experimental conditions, the atomic oxygen attack on ethene is very low [ROC(C2H4) < -0.03]. With

CH3CO f CH3 + CO ROC(CH3CO) ) -0.99 (15) Vinyl radicals constitute the main pathway for the formation of ethyne by the reaction with molecular oxygen:

C2H3 + O2 f C2H2 + HO2

ROP(C2H2) ) 0.99 (2)

Ethyne mainly reacts with molecular oxygen, yielding the ketenyl radical and OH. To a lower extent, ethyne reacts with atomic oxygen, peroxy radicals, and hydrogen atom for re-forming vinyl radicals:

O2 + C2H2 f HCCO + OH ROC(C2H2) ) -0.425 (16) O + C2H2 f CH2 + CO ROC(C2H2) ) -0.140 (17) O + C2H2 f HCCO + H ROC(C2H2) ) -0.061 (18) HO2 + C2H2 f CH2CO + OH ROC(C2H2) ) -0.136 (19) C2H2 + H (+M) f C2H3 (+M) ROC(C2H2) ) -0.191 (20) Methane is mainly produced by the methyl attack

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reaction on ethene and is essentially consumed by H abstraction:

C2H4 + CH3 f CH4 + C2H3 ROP(CH4) ) 0.672 (9) CH4 + OH f CH3 + H2O ROC(CH4) ) -0.986 (21) Ethane is principally formed by the recombination of the methyl radicals and is essentially consumed by H abstraction:

CH3 + CH3 (+M) f C2H6 (+M) ROP(C2H6) ) 0.733 (11) C2H6 + OH f C2H5 + H2O ROC(C2H6) ) -0.940 (22) Oxirane, mostly formed by reaction (10), is consumed in four different ways. It reacts with OH radicals, yielding vinoxy radicals, or isomerizes in ethanal and at a lesser extent decomposes in methyl and HCO radicals or reacts with peroxy radicals, yielding hydrogen peroxide and vinoxy radicals:

C2H4O + OH f CH2CHO + H2O ROC(C2H4O) ) -0.493 (23) C2H4O f CH3CHO ROC(C2H4O) ) -0.226 (24) C2H4O f CH3 + HCO ROC(C2H4O) ) -0.111 (25) C2H4O + HO2 f H2O2 + CH2CHO ROC(C2H4O) ) -0.084 (26) Ethanal is oxidized by H2O and OH radicals, yielding acetyl radicals:

HO2 + CH3CHO f CH3CO + H2O2 ROC(CH3CHO) ) -0.484 (27) CH3CHO + OH f CH3CO + H2O ROC(CH3CHO) ) -0.344 (28) This ROP and ROC analysis showed that oxygenated species are key intermediates in ethene oxidation. However, many uncertainties still remain on the rate constants of these reactions. This confirms the necessity of theoretical and experimental determinations of these reaction rates. Conclusions New experimental results have been obtained for ethene oxidation at high equivalence ratios (3-10) and temperature in the intermediate range (773-900 K) at a fixed residence time of 1.3 s. A jet-stirred reactor operating at atmospheric pressure has been used with sonic probe sampling and offline GC(TCD/FID) and GC/ MS to measure the reactant, stable intermediate, and final product concentrations. Two reported detailed kinetic mechanisms, the DLCC and BBLC mechanisms,

were examined by comparing predicted species concentrations versus temperature to our experimental measurements. This process served as a starting point for the development of a new ethene oxidation mechanism. A useful agreement has been obtained for the new mechanism between the computed concentration profiles and the experimental measurements. Rates of production (ROP) and consumption (ROC) were used to interpret the present results and confirm the importance of oxygenated species in the combustion process. Literature Cited (1) Dagaut, P.; Cathonnet, M. Kinetics of methane oxidation in a high-pressure jet stirred reactor: experimental results. J. Chim. Phys. 1990, 87, 221. (2) Warnatz, J. In Combustion Chemistry; Gardiner, W. C., Ed.; Springer-Verlag: New York, 1985. (3) Chakir, A.; Cathonnet, M.; Boettner, J. C.; Gaillard, F. Kinetic study of n-butane oxidation. Combust. Sci. Technol. 1991, 65, 207. (4) Pitz, W. J.; Westbrook, C. K.; Proscia, W. M.; Dryer F. L. A comprehensive chemical kinetic reaction mechanism for the oxidation of n-butane. Proceedings from the 20th Symposium (International) on Combustion; The Combustion Institute: Pittsburgh, PA, 1984; p 831. (5) Brezinsky, K. The high-temperature oxidation of aromatics hydrocarbons. Prog. Energy Combust. Sci. 1986, 12, 1. (6) Gustin, J. L. Safety of ethoxylation reactions. Inst. Chem. Eng. Symp. Ser. 2000, 251. (7) Cathonnet, M.; Gaillard, F.; Boettner; J. C.; Cambray; P.; Karmed, D.; Bellet, J. C. Experimental study and kinetic modelling of ethylene oxidation in tubular reactors. Proceedings from the 20th Symposium (International) on Combustion; The Combustion Institute: Pittsburgh, PA, 1984; p 819. (8) Carriere, T.; Westmoreland, P. R.; Kazakov, A.; Stein, Y. S.; Dryer, F. L. Modeling ethylene combustion from low to high pressure. Proceedings from the 2nd Joint Meeting of the Combustion Institute, Oakland, CA, 2001. (9) Dagaut, P.; Cathonnet, M.; Boettner, J. C.; Gaillard, F. Kinetic Modeling of Ethylene Oxidation. Combust. Flame 1988, 71, 295. (10) Westbrook, C. K.; Thornton, M. M.; Pitz, W. J.; Malte, P. C. A kinetic Study of Ethylene Oxidation in a Well-Stirred Reactor. Proceedings from the 22nd Symposium (International) on Combustion; The Combustion Institute: Pittsburgh, PA, 1988; p 863. (11) Jachimowski, C. J. An Experimental and Analytical Study of Acetylene and Ethylene Oxidation Behind Shock Waves. Combust. Flame 1977, 29, 55. (12) Baker, J. A.; Skinner, G. B. Shock Tube Studies on the Ignition of Ethylene-Oxygen-Argon Mixtures. Combust. Flame 1972, 19, 347. (13) Brown, C. J.; Thomas, G. O. Experimental Studies of the Shock Induced Ignition and Transition to Detonation in Ethylene and Propane Mixtures. Combust. Flame 1999, 117, 861. (14) Westbrook, C. K.; Dryer, F. L.; Schug, K. P. A Comprehensive Mechanism for the Pyrolysis and Oxidation of Ethylene. Proceedings from the 19th Symposium (International) on Combustion; The Combustion Institute: Pittsburgh, PA, 1982; p 153. (15) Marinov, N. M.; Malte, P. C. Ethylene Oxidation in a Well Stirred Reactor. Int. J. Chem. Kinet. 1995, 27, 957. (16) Hidaka, Y.; Nishimori, T.; Sato, K.; Henmi, Y.; Okuda, R.; Inami, K. Shock Tube and Modeling Study of Ethylene Pyrolysis and Oxidation. Combust. Flame 1999, 117, 755. (17) Dagaut, P.; Leconte, F.; Chevailler, S.; Cathonnet, M. The Reduction of NO by Ethylene in a Jet Stirred Reactor at 1 atm: Experimental and Kinetic modelling. Combust. Flame 1999, 119, 494. (18) Barbe, P.; Battin Leclerc, F.; Coˆme, G. M. Experimental and modelling study of methane and ethane oxidation between 773 and 1573 K. J. Chim. Phys. 1995, 92, 1666. (19) Miller, J. A.; Fisk, G. A. Combustion Chemistry. Chem. Eng. News 1987, 31, 22. (20) David, R.; Matras, D. Re`gles de construction et d’extrapolation des re´acteurs auto-agite´s par jets gazeux. Can. J. Chem. Eng. 1975, 53, 297.

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Received for review July 2, 2001 Revised manuscript received March 19, 2002 Accepted March 29, 2002 IE010568W

An Experimental and Kinetic Study of Ethene Oxidation at a High

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