Detailed Kinetic Mechanism for the Oxidation of Vegetable Oil Methyl

Energy Fuels 2009, 23, 4254–4268 Published on Web 07/24/2009

: DOI:10.1021/ef900184y

Detailed Kinetic Mechanism for the Oxidation of Vegetable Oil Methyl Esters: New Evidence from Methyl Heptanoate Guillaume Dayma,*,† Casimir Togbe,‡ and Philippe Dagaut‡ †

Universit e Pierre et Marie Curie (Paris 6), Institut Jean Le Rond d’Alembert 2, Place de la Gare de Ceinture, 78210 Saint Cyr l’Ecole, France, and ‡CNRS-INSTII, 1c Ave de la Recherche Scientifique, 45071 Orl eans Cedex 2, France Received March 4, 2009. Revised Manuscript Received June 24, 2009

The oxidation of methyl heptanoate was studied experimentally in a jet-stirred reactor at 10 atm and a constant residence time of 0.7 s, over the temperature range 550-1150 K, and for fuel-lean to fuel-rich conditions. Concentration profiles of reactants, stable intermediates, and final products were obtained by sonic probe sampling followed by online GC and FTIR and off-line GC analyses. As previously shown for methyl hexanoate (Dayma, G.; Gail, S.; Dagaut, P. Energy Fuels 2008, 22, 1469-1479), the oxidation of methyl heptanoate under these conditions showed the well-known three regimes of oxidation observed for large hydrocarbons, namely, cool flame, negative temperature coefficient, and high temperature oxidation. The detailed chemical kinetic reaction mechanism built to model the oxidation of methyl heptanoate is an extended and revisited version of that previously developed for methyl hexanoate. This mechanism now involves 1087 species and 4592 reversible reactions. It was validated by comparing the present experimental results to the simulations. The main reaction pathways involved in methyl heptanoate oxidation were delineated computing the rates of formation and consumption of every species. Kinetic rate constants are proposed to model the oxidation of methyl esters.

1. Introduction With the increasing demand on oil products for transportation,2 it is becoming of paramount importance to find renewable resources to complement conventional fuels or even replace current petroleum-derived liquid fuels. In this context, the interest for biodiesel, monoalkyl esters of long carbon chain fatty acids obtained from the transesterification of renewable lipid feedstock with mostly methanol, but also ethanol, is increasing worldwide.3 Biodiesel is considered a valuable alternative to conventional fuels in diesel engines and gas turbines to solve the problem of limited resources of petroleum. Tests in conventional diesel engines as well as in current direct-injection engines showed very good results.3-7 However, several questions are arising regarding the reactivity of these compounds and their ability to produce new pollutants (e.g., aldehydes, unsaturated esters).8,9 To accurately predict combustion performance and emission characteristics, the kinetics of combustion of these fuels

Figure 1. Methyl heptanoate (C8H16O2) with carbon labeled for nomenclature.

must be known. Previous studies have demonstrated the similarities and differences between the kinetics of oxidation of n-alkanes and long-chain methyl esters.9-11 However, the proposed kinetic models needed to be better validated against experimental data obtained in well-characterized conditions. Several studies in the literature concern the kinetics of oxidation of simple methyl esters (methyl formate,12,13 methyl acetate,12,14,15 methyl butanoate,16-19 and methyl propenoate18). Unfortunately, the carbon chains of these species are too small to allow easy H-atom transfer onto the peroxy (10) Morin, C.; Chauveau, C.; Dagaut, P.; Gokalp, I.; Cathonnet, M. Combust. Sci. Technol. 2004, 176, 499–529. (11) Dagaut, P.; Gail, S.; Sahasrabudhe, M. Proc. Combust. Inst. 2007, 31, 2955–2961. (12) Wallington, T. J.; Dagaut, P.; Liu, R. H.; Kurylo, M. J. Int. J. Chem. Kinetics 1988, 20, 177–186. (13) Le Calve, S.; Lebras, G.; Mellouki, A. J. Phys. Chem. A 1997, 101, 9137–9141. (14) Dagaut, P.; Smoucovit, N.; Cathonnet, M. Combust. Sci. Technol. 1997, 127, 275–291. (15) Osswald, P.; Struckmeier, U.; Kasper, T.; Kohse-Hoinghaus, K.; Wang, J.; Cool, T. A.; Hansen, N.; Westmoreland, P. R. J. Phys. Chem. A 2007, 111, 4093–4101. (16) Fisher, E. M.; Pitz, W. J.; Curran, H. J.; Westbrook, C. K. Proc. Combust. Inst. 2000, 28, 1579–1586. (17) Gail, S.; Thomson, M. J.; Sarathy, S. M.; Syed, S. A.; Dagaut, P.; Dievart, P.; Marchese, A. J.; Dryer, F. L. Proc. Combust. Inst. 2007, 31, 305–311. (18) Sarathy, S. M.; Gail, S.; Syed, S. A.; Thomson, M. J.; Dagaut, P. Proc. Combust. Inst. 2007, 31, 1015–1022. (19) Metcalfe, W. K.; Dooley, S.; Curran, H. J.; Simmie, J. M.; El-Nahas, A. M.; Navarro, M. V. J. Phys. Chem. A 2007, 111, 4001–4014.

*To whom correspondence should be addressed. E-mail: guillaume. [email protected]. (1) Dayma, G.; Ga ¨ıl, S.; Dagaut, P. Energy Fuels 2008, 22, 1469–1479. (2) International Energy Agency, World Energy Outlook 2004. OECD/IEA: Paris (France), 2004. (3) Montagne, , X. SAE Technical Paper 962065; Society of Automotive Engineers: 1996; 247256 (4) Schroder, O.; Krahl, J.; Munack, A.; Bunger, J., SAE Technical Paper 1999-01-3561; Society of Automotive Engineers: 1999. (5) Krahl, J.; Munack, A.; Bahadir, M.; Schumacher, L.; Elser, N., SAE Technical Paper 962096; Society of Automotive Engineers: 1996; pp 319-338. (6) Graboski, M. S.; McCormick, R. L. Prog. Energ. Combust. Sci. 1998, 24, 125–164. (7) Ramadhas, A. S.; Jayaraj, S.; Muraleedharan, C. Renewable Energy 2004, 29, 727–742. (8) Pedersen, J. R.; Ingemarsson, A.; Olsson, J. O. Chemosphere 1999, 38, 2467–2474. (9) Dagaut, P.; Gail, S. J. Phys. Chem. A 2007, 111, 3992–4000. r 2009 American Chemical Society

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: DOI:10.1021/ef900184y

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Figure 2. Methyl heptanoate oxidation in a JSR at 10 atm, τ=0.7 s, and j=0.6. The initial mole fractions were: methyl heptanoate, 0.1%; O2, 1.83%; N2, 98.07%. Experimental data (symbols) for methyl heptanoate (mhp, *), ethylene (Δ), H2 (b), O2 (b), CO (Δ), CO2 (9), H2O ()), formaldehyde ()), methane (b), propene (Δ), methanol (b), but-1-ene (2), pent-1-ene ()), and ethane (0) are compared to calculations (lines with small symbols).

function via low-strain cyclic intermediate formation. Consequently, it does not exhibit strong cool flame behavior as biodiesel does. Hence, they do not represent suitable biodiesel fuel surrogates. Therefore, as part of a continuing laboratory effort to better understand and model the oxidation of conventional and reformulated liquid fuels, we performed a new experimental and modeling study of the kinetics of oxidation of methylheptanoate, C8H16O2 (CAS 106-73-0), a colorless liquid with a boiling temperature of 445 K and a density of 0.880 g mL-1 at 293 K. This methyl ester represents a reasonable candidate for surrogate biodiesel fuel studies because: (i) it shows cool flame and negative temperature coefficient oxidation behavior like biodiesel does; and (ii) its oxidation chemistry remains relatively simple due to its chemical structure. The present study aims at (i) providing an experimental database for the kinetics of oxidation of methylheptanoate and (ii) proposing a validated detailed chemical kinetic scheme for simulating its oxidation and that of other methyl esters.

admission in the reactor. All gases were preheated before injection in order to minimize temperature gradients inside the JSR. The reactants were diluted by a second flow of nitrogen and mixed at the entrance of the injectors. The pressure in the vessel was barometrically measured. High-purity reactants were used in these experiments: nitrogen (N2; C5, with ethylene being the most abundant 1-olefin. This ranking is consistent with n-alkanes oxidation results.22 Finally, at low temperature, we observed the expected increased reactivity of the fuel by increasing the initial oxygen concentration. This new set of experimental data, presented in Figures 2-4, was used to validate a detailed chemical kinetic reaction mechanism for the oxidation of methyl heptanoate. This scheme derives from that proposed earlier for the oxidation of methyl hexanoate in similar conditions.

MS detector operating in electron impact ionization mode (70 eV, GC/MS Varian 1200). Helium was used as a carrier gas except for measuring oxygen and hydrogen by TCD (nitrogen was used). For online FTIR analysis, a temperature-controlled (413 K) gas cell (10 m optical path length) was filled with the reacting gases. The sample pressure in the cell was 200 mbar. All the products were analyzed by chromatographic peak or infrared spectrum identification. This experimental setup allowed measuring mole fractions of oxygen, hydrogen, water, carbon monoxide, carbon dioxide, formaldehyde, methanol, methane, ethane, ethylene, propene, 1-butene, 1-pentene, and methyl heptanoate. All these species with their peak concentration measured at each equivalence ratio are provided as Supporting Information. A good repeatability of the results was observed. The accuracy of the mole fractions was typically (10% and better than 15%, whereas the uncertainty on the experimental temperature was ca. (5 K. The detection limits are 20 ppm for H2 and O2; 5 ppm for CO, CO2, and CH2O; and 1 ppm for hydrocarbons and oxygenates. A good repeatability of the measurements and a reasonably good carbon balance (100 ( 10%) were obtained in this series of experiments.

4. Kinetic Modeling The kinetic modeling was performed using the CHEMKIN23 computer package. We used the PSR code that computes species concentrations from the balance between the net rate of production of each species by chemical reactions and the difference between the input and output species flow rates. These rates are computed from the kinetic reaction mechanism and the rate constants of the reactions calculated at the experimental temperature, using the modified Arrhenius

3. Experimental Results For the first time, the kinetics of oxidation of methyl heptanoate was studied in a JSR at 10 atm, over the temperature range 5501150 K, and at a mean residence time of 0.7 s. The experiments were performed at three equivalence ratios: j=0.6, 1, and 2. The initial fuel mole fraction was 0.1%. In these conditions, three reaction regimes appear clearly in the lean and stoichiometric mixtures: • The cool flame zone (560-660 K), characterized by fuel consumption at low temperature. • The negative temperature coefficient zone (660-760 K), where the fuel reactivity decreases with rising temperature. • The high temperature zone (>760 K), while total consumption of the fuel could be observed.

(22) Ranzi, E.; Gaffuri, P.; Faravelli, T.; Dagaut, P. Combust. Flame 1995, 103, 91–106. (23) Kee, R. J.; Miller, J. A.; Jefferson, T. H. SAND80-8003, Sandia National Laboratories: Livermore, CA, 1980. (24) Glarborg, P.; Kee, R. J.; Grcar, J. F.; Miller, J. A. PSR: A FORTRAN Program for Modeling Well-stirred Reactors; SAND868209; Sandia National Laboratories: Livermore, CA, 1986.

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Figure 4. Methyl heptanoate oxidation in a JSR at 10 atm, τ=0.7 s, and j=2. The initial mole fractions were: methyl heptanoate, 0.1%; O2, 0.55%; N2, 99.35%. Experimental data (symbols) for methyl heptanoate (mhp, *), ethylene (Δ), H2 (b), O2 (b), CO (Δ), CO2 (9), H2O ()), formaldehyde ()), methane (b), propene (Δ), but-1-ene (2), pent-1-ene ()), and ethane (0) are compared to calculations (lines with small symbols). Table 1. Chemical Structure, Nomenclature, and Enthalpy of Formation (in kcal mol-1) at 298 K of Selected Species Used in This Model

Figure 5. Simplified flow rate analysis for the oxidation of methyl heptanoate at T=610 K, j=1, τ=0.7 s, and 10 atm. The thickness of the arrows is proportional to the importance of the reaction path (percentage is reported to the fuel).

belonging to the methyl heptanoate oxidation submechanism, thermochemical data were estimated using the software THERGAS,25 which is based on the group additivity methods proposed by Benson.26 The enthalpies of formation of some important species are given in Table 2.

equation, k=ATn exp(-E/RT). The reaction mechanism used here consisted of 1087 species and 4592 reactions, most of them reversible. The entire mechanism, including references and thermochemical data, is available from the authors ([email protected]). The rate constants for reverse reactions are computed from the corresponding forward rate constants and the appropriate equilibrium constants, Kc = kforward/kreverse, calculated from thermochemistry. For species

(25) Muller, C.; Michel, V.; Scacchi, G.; C^ ome, G.M. J. Chim. Phys. Phys.-Chim. Biol. 1995, 92, 1154–1178. (26) Benson, S. W., Thermochemical Kinetics, Second ed.; Wiley: Interscience: New York, 1976.

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Table 2. Methyl Heptanoate Oxidation Submechanism (k units: cm3, mol, s-1, cal)a No. 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970

reaction

A

mhp a mhp7j þ H mhp a mhp6j þ H mhp a mhp5j þ H mhp a mhp4j þ H mhp a mhp3j þ H mhp2j þ H a mhp mhp a mhpmj þ H mhp a mhx6j þ CH3 mhp a mpe5j þ C2H5 mhp a mb4j þ nC3H7 mhp a mp3j þ pC4H9 mhp a me2j þ C5H11-1 mhp a CH3OCO þ C6H13-1 C6H13CO þ CH3O a mhp mhp a hpaoj þ CH3 mhp þ O2 a mhp7j þ HO2 mhp þ O2 a mhp6j þ HO2 mhp þ O2 a mhp5j þ HO2 mhp þ O2 a mhp4j þ HO2 mhp þ O2 a mhp3j þ HO2 mhp þ O2 a mhp2j þ HO2 mhp þ O2 a mhpmj þ HO2 mhp þ H a mhp7j þ H2 mhp þ H a mhp6j þ H2 mhp þ H a mhp5j þ H2 mhp þ H a mhp4j þ H2 mhp þ H a mhp3j þ H2 mhp þ H a mhp2j þ H2 mhp þ H a mhpmj þ H2 mhp þ O a mhp7j þ OH mhp þ O a mhp6j þ OH mhp þ O a mhp5j þ OH mhp þ O a mhp4j þ OH mhp þ O a mhp3j þ OH mhp þ O a mhp2j þ OH mhp þ O a mhpmj þ OH mhp þ OH a mhp7j þ H2O mhp þ OH a mhp6j þ H2O mhp þ OH a mhp5j þ H2O mhp þ OH a mhp4j þ H2O mhp þ OH a mhp3j þ H2O mhp þ OH a mhp2j þ H2O mhp þ OH a mhpmj þ H2O mhp þ HO2 a mhp7j þ H2O2 mhp þ HO2 a mhp6j þ H2O2 mhp þ HO2 a mhp5j þ H2O2 mhp þ HO2 a mhp4j þ H2O2 mhp þ HO2 a mhp3j þ H2O2 mhp þ HO2 a mhp2j þ H2O2 mhp þ HO2 a mhpmj þ H2O2 mhp þ HCO a mhp7j þ CH2O mhp þ HCO a mhp6j þ CH2O mhp þ HCO a mhp5j þ CH2O mhp þ HCO a mhp4j þ CH2O mhp þ HCO a mhp3j þ CH2O mhp þ HCO a mhp2j þ CH2O mhp þ HCO a mhpmj þ CH2O mhp þ CH3 a mhp7j þ CH4 mhp þ CH3 a mhp6j þ CH4 mhp þ CH3 a mhp5j þ CH4 mhp þ CH3 a mhp4j þ CH4 mhp þ CH3 a mhp3j þ CH4 mhp þ CH3 a mhp2j þ CH4 mhp þ CH3 a mhpmj þ CH4 mhp þ CH3O a mhp7j þ CH3OH mhp þ CH3O a mhp6j þ CH3OH mhp þ CH3O a mhp5j þ CH3OH mhp þ CH3O a mhp4j þ CH3OH mhp þ CH3O a mhp3j þ CH3OH mhp þ CH3O a mhp2j þ CH3OH mhp þ CH3O a mhpmj þ CH3OH mhp þ CH2OH a mhp7j þ CH3OH mhp þ CH2OH a mhp6j þ CH3OH mhp þ CH2OH a mhp5j þ CH3OH

7.90 10 5.00 1015 5.00 1015 5.00 1015 5.00 1015 1.00 1014 7.90 1015 5.00 1016 7.94 1016 7.94 1016 7.94 1016 7.94 1016 1.13 1016 1.50 1013 3.16 1016 2.00 1013 4.00 1013 4.00 1013 4.00 1013 4.00 1013 4.00 1013 2.05 1013 9.40 1004 1.30 1006 1.30 1006 1.30 1006 1.30 1006 5.40 1004 1.44 1013 9.65 1004 4.77 1004 4.77 1004 4.77 1004 4.77 1004 8.80 1010 9.65 1004 5.25 1009 4.68 1007 4.68 1007 4.68 1007 4.68 1007 3.00 1006 7.10 1006 8.40 1012 5.60 1012 5.60 1012 5.60 1012 5.60 1012 6.40 1003 4.82 1010 1.02 1005 1.08 1007 1.08 1007 1.08 1007 1.08 1007 1.14 1009 1.02 1005 4.52 10-01 2.70 1004 2.70 1004 2.70 1004 2.70 1004 1.00 1011 4.52 10-01 1.58 1011 1.10 1011 1.10 1011 1.10 1011 1.10 1011 1.78 1012 1.58 1011 1.58 1011 1.10 1011 1.10 1011 15

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E

ref

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2.8 2.4 2.4 2.4 2.4 2.5 0 2.7 2.7 2.7 2.7 2.7 0.7 2.7 1 1.6 1.6 1.6 1.6 2 1.8 0 0 0 0 0 2.6 0 2.5 1.9 1.9 1.9 1.9 1.3 2.5 3.6 2.3 2.3 2.3 2.3 0 3.6 0 0 0 0 0 0 0 0 0 0

97 970 94 990 94 990 94 990 94 990 0 93 970 84 660 80 280 80 280 80 280 80 280 77 700 0 83 070 50 870 47 690 47 690 47 690 47 690 38 000 44 910 6280 4471 4471 4471 4471 -1900 6095 3716 2106 2106 2106 2106 3250 3716 1590 -35 -35 -35 -35 -1520 -596 20 440 17 690 17 690 17 690 17 690 12 400 12 580 18 500 17 000 17 000 17 000 17 000 15 500 18 500 7154 7287 7287 7287 7287 7300 7154 7000 5000 5000 5000 5000 1200 7000 7000 5000 5000

30 30 30 30 30 16 see text 30 30 30 30 30 see text 32 33 34 34 34 34 34 see text 21 16 16 16 16 16 46 21 16 16 16 16 16 46 21 16 16 16 16 16 35 21 16 16 16 16 16 46 21 16 16 16 16 16 38 38 16 16 16 16 16 46 16 16 16 16 16 16 38 16 16 16 16

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Table 2. Continued No. 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100

reaction mhp þ CH2OH a mhp4j þ CH3OH mhp þ CH2OH a mhp3j þ CH3OH mhp þ CH2OH a mhp2j þ CH3OH mhp þ CH2OH a mhpmj þ CH3OH mhp þ CH3O2 a mhp7j þ CH3O2H mhp þ CH3O2 a mhp6j þ CH3O2H mhp þ CH3O2 a mhp5j þ CH3O2H mhp þ CH3O2 a mhp4j þ CH3O2H mhp þ CH3O2 a mhp3j þ CH3O2H mhp þ CH3O2 a mhp2j þ CH3O2H mhp þ CH3O2 a mhpmj þ CH3O2H mhp þ C2H3 a mhp7j þ C2H4 mhp þ C2H3 a mhp6j þ C2H4 mhp þ C2H3 a mhp5j þ C2H4 mhp þ C2H3 a mhp4j þ C2H4 mhp þ C2H3 a mhp3j þ C2H4 mhp þ C2H3 a mhp2j þ C2H4 mhp þ C2H3 a mhpmj þ C2H4 mhp þ C2H5 a mhp7j þ C2H6 mhp þ C2H5 a mhp6j þ C2H6 mhp þ C2H5 a mhp5j þ C2H6 mhp þ C2H5 a mhp4j þ C2H6 mhp þ C2H5 a mhp3j þ C2H6 mhp þ C2H5 a mhp2j þ C2H6 mhp þ C2H5 a mhpmj þ C2H6 mhp þ a-C3H5 a mhp7j þ C3H6 mhp þ a-C3H5 a mhp6j þ C3H6 mhp þ a-C3H5 a mhp5j þ C3H6 mhp þ a-C3H5 a mhp4j þ C3H6 mhp þ a-C3H5 a mhp3j þ C3H6 mhp þ a-C3H5 a mhp2j þ C3H6 mhp þ a-C3H5 a mhpmj þ C3H6 mhp7j þ O2 a mhp7oo mhp6j þ O2 a mhp6oo mhp5j þ O2 a mhp5oo mhp4j þ O2 a mhp4oo mhp3j þ O2 a mhp3oo mhp2j þ O2 a mhp2oo mhpmj þ O2 a mhpmoo mhp7ooh6j þ O2 a mhp7ooh6oo mhp7ooh5j þ O2 a mhp7ooh5oo mhp7ooh4j þ O2 a mhp7ooh4oo mhp7ooh3j þ O2 a mhp7ooh3oo mhp6ooh7j þ O2 a mhp6ooh7oo mhp6ooh5j þ O2 a mhp6ooh5oo mhp6ooh4j þ O2 a mhp6ooh4oo mhp6ooh3j þ O2 a mhp6ooh3oo mhp6ooh2j þ O2 a mhp6ooh2oo mhp5ooh7j þ O2 a mhp5ooh7oo mhp5ooh6j þ O2 a mhp5ooh6oo mhp5ooh4j þ O2 a mhp5ooh4oo mhp5ooh3j þ O2 a mhp5ooh3oo mhp5ooh2j þ O2 a mhp5ooh2oo mhp4ooh7j þ O2 a mhp4ooh7oo mhp4ooh6j þ O2 a mhp4ooh6oo mhp4ooh5j þ O2 a mhp4ooh5oo mhp4ooh3j þ O2 a mhp4ooh3oo mhp4ooh2j þ O2 a mhp4ooh2oo mhp3ooh7j þ O2 a mhp3ooh7oo mhp3ooh6j þ O2 a mhp3ooh6oo mhp3ooh5j þ O2 a mhp3ooh5oo mhp3ooh4j þ O2 a mhp3ooh4oo mhp3ooh2j þ O2 a mhp3ooh2oo mhp2ooh6j þ O2 a mhp2ooh6oo mhp2ooh5j þ O2 a mhp2ooh5oo mhp2ooh4j þ O2 a mhp2ooh4oo mhp2ooh3j þ O2 a mhp2ooh3oo mhp2oohmj þ O2 a mhp2oohmoo mhpmooh2j þ O2 a mhpmooh2oo mhp7j a mhp4j mhp7j a mhp3j mhp6j f mhp3j mhp3j f mhp6j mhp3j a mhpmj mhp2j a mhp7j

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A

n

E

ref

1.10 1011 1.10 1011 3.60 1001 1.58 1011 8.40 1012 5.60 1012 5.60 1012 5.60 1012 5.60 1012 6.40 1003 8.40 1012 5.01 1011 4.00 1011 4.00 1011 4.00 1011 4.00 1011 4.00 1011 5.01 1011 5.01 1010 5.00 1010 5.00 1010 5.00 1010 5.00 1010 2.20 1000 5.01 1010 1.20 1002 8.00 1001 8.00 1001 8.00 1001 8.00 1001 8.00 1001 1.20 1002 9.00 1018 1.70 1019 1.80 1019 1.80 1019 1.05 1019 1.20 1010 3.50 1011 1.80 1019 1.80 1019 1.80 1019 1.05 1019 1.50 1018 1.05 1019 1.80 1019 1.05 1019 1.20 1010 9.00 1018 9.50 1018 1.05 1019 1.05 1019 1.20 1010 9.00 1018 1.70 1019 1.05 1019 3.00 1018 1.20 1010 9.00 1018 1.70 1019 1.80 1019 1.05 1019 1.20 1010 1.70 1019 1.80 1019 1.80 1019 1.00 1019 4.50 1012 1.20 1010 9.90 1007 1.70 1007 9.90 1007 9.90 1007 2.50 1007 4.40 1006

0 0 3 0 0 0 0 0 0 2.6 0 0 0 0 0 0 0 0 0 0 0 0 0 3.5 0 3.3 3.3 3.3 3.3 3.3 3.3 3.3 -2.5 -2.5 -2.5 -2.5 -2.5 0 0 -2.5 -2.5 -2.5 -2.5 -2.5 -2.5 -2.5 -2.5 0 -2.5 -2.5 -2.5 -2.5 0 -2.5 -2.5 -2.5 -2.5 0 -2.5 -2.5 -2.5 -2.5 0 -2.5 -2.5 -2.5 -2.5 0 0 1 1 1 1 1 1

5000 5000 10 000 7000 20 440 17 690 17 690 17 690 17 690 12 400 20 440 18 000 16 800 16 800 16 800 16 800 14 300 18 000 13 400 10 400 10 400 10 400 10 400 4140 13 400 19 840 18 170 18 170 18 170 18 170 17 170 19 840 0 0 0 0 0 -2300 -1700 0 0 0 0 0 0 0 0 -2300 0 0 0 0 -2300 0 0 0 0 -2300 0 0 0 0 -2300 0 0 0 0 0 -2300 17 300 12 000 17 300 17 300 14 500 19 900

16 16 38 16 16 16 16 16 16 as HO2 16 16 16 16 16 16 16 16 16 16 16 16 16 38 16 16 16 16 16 16 38 16 37 37 37 37 37 38 36 37 37 37 37 37 37 37 37 38 37 37 37 37 38 37 37 37 37 38 37 37 37 37 38 37 37 37 37 36 38 see text see text see text see text see text see text

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: DOI:10.1021/ef900184y

Dayma et al.


reaction mhp2j a mhp6j mhp2j a mhp5j mhp2j a mhpmj mhpmj a mhp4j mhp7oo a mhp7ooh6j mhp7oo a mhp7ooh5j mhp7oo a mhp7ooh4j mhp7oo a mhp7ooh3j mhp6oo a mhp6ooh7j mhp6oo a mhp6ooh5j mhp6oo a mhp6ooh4j mhp6oo a mhp6ooh3j mhp6oo a mhp6ooh2j mhp5oo a mhp5ooh7j mhp5oo a mhp5ooh6j mhp5oo a mhp5ooh4j mhp5oo a mhp5ooh3j mhp5oo a mhp5ooh2j mhp4oo a mhp4ooh7j mhp4oo a mhp4ooh6j mhp4oo a mhp4ooh5j mhp4oo a mhp4ooh3j mhp4oo a mhp4ooh2j mhp3oo a mhp3ooh7j mhp3oo a mhp3ooh6j mhp3oo a mhp3ooh5j mhp3oo a mhp3ooh4j mhp3oo a mhp3ooh2j mhp2oo a mhp2ooh6j mhp2oo a mhp2ooh5j mhp2oo a mhp2ooh4j mhp2oo a mhp2ooh3j mhp2oo a mhp2oohmj mhpmoo a mhpmooh2j mhp7j a C2H4 þ mpe5j mhp6j a C3H6 þ mb4j mhp5j a C4H8-1 þ mp3j mhp5j a CH3 þ mhx5d mhp4j a C5H10-1 þ me2j mhp4j a C2H5 þ mpe4d mhp3j a C6H12-1 þ CH3OCO mhp3j a nC3H7 þ mb3d mhp2j a pC4H9 þ mp2d C6H12CO þ CH3O a mhp2j mhpmj a CH2O þ C6H13CO CO2 þ C6H13-1 a hpaoj mhp7j a h þ mhp6d mhp6j a h þ mhp6d mhp6j a h þ mhp5d mhp5j a h þ mhp5d mhp5j a h þ mhp4d mhp4j a h þ mhp4d mhp4j a h þ mhp3d mhp3j a h þ mhp3d mhp3j a h þ mhp2d mhp2j a h þ mhp2d mhp7j þ O2 a mhp6d þ HO2 mhp6j þ O2 a mhp6d þ HO2 mhp6j þ O2 a mhp5d þ HO2 mhp5j þ O2 a mhp5d þ HO2 mhp5j þ O2 a mhp4d þ HO2 mhp4j þ O2 a mhp4d þ HO2 mhp4j þ O2 a mhp3d þ HO2 mhp3j þ O2 a mhp3d þ HO2 mhp3j þ O2 a mhp2d þ HO2 mhp2j þ O2 a mhp2d þ HO2 mhp6d þ HO2 a mhp7ooh6j mhp6d þ HO2 a mhp6ooh7j mhp5d þ HO2 a mhp6ooh5j mhp5d þ HO2 a mhp5ooh6j mhp4d þ HO2 a mhp5ooh4j mhp4d þ HO2 a mhp4ooh5j mhp3d þ HO2 a mhp4ooh3j mhp3d þ HO2 a mhp3ooh4j mhp2d þ HO2 a mhp3ooh2j

4260

A

n

E

ref

1.70 1007 9.90 1007 1.50 1008 2.90 1006 3.30 1009 5.70 1008 1.00 1008 1.72 1007 4.95 1009 3.30 1009 5.70 1008 1.00 1008 1.70 1007 8.55 1008 3.30 1009 3.30 1009 5.70 1008 1.00 1008 1.50 1008 5.70 1008 3.30 1009 3.30 1009 5.70 1008 2.50 1007 1.00 1008 5.70 1008 3.30 1009 3.30 1009 1.72 1007 1.00 1008 5.70 1008 3.30 1009 1.50 1008 1.00 1008 2.00 1013 2.00 1013 2.00 1013 1.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 5.00 1011 1.64 1022 1.00 1011 3.00 1013 3.00 1013 3.00 1013 3.00 1013 3.00 1013 3.00 1013 3.00 1013 3.00 1013 3.20 1013 3.00 1013 1.95 1012 8.07 1011 1.95 1012 1.95 1012 1.95 1012 1.95 1012 1.95 1012 1.95 1012 2.60 1011 1.58 1012 1.50 1011 1.50 1011 1.50 1011 1.50 1011 1.50 1011 1.50 1011 1.50 1011 1.50 1011 1.50 1011

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 -2.3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

12 000 17 300 22 800 17 400 32 500 25 000 22 000 21 000 35 500 32 500 25 000 22 000 16 000 28 000 32 500 32 500 25 000 17 000 25 000 25 000 32 500 32 500 18 000 24 000 22 000 25 000 32 500 27 500 21 000 22 000 25 000 32 500 28 500 21 700 28 700 28 700 28 700 31 000 24 700 28 700 30 500 28 700 28 700 -1000 31 950 39 360 38 000 39 000 38 000 38 000 38 000 38 000 38 000 38 000 34 800 50 000 5000 5000 5000 5000 5000 5000 5000 5000 2500 15 200 7800 7800 7800 7800 7800 7800 7800 7800 7800

see text see text see text see text 37 37 37 37 37 37 37 37 see text 37 37 37 37 see text 37 37 37 37 see text 37 37 37 37 see text 37 37 37 37 42 42 35 35 35 37 see text 35 see text 35 35 16 47 16 35 46 35 35 35 35 35 35 38 35 36 36 36 36 36 36 36 36 48 48 29 29 29 29 29 29 29 29 29

Energy Fuels 2009, 23, 4254–4268

: DOI:10.1021/ef900184y

Dayma et al.


reaction mhp2d þ HO2 a mhp2ooh3j mhp7ooh5j f mhx5d þ CH2O þ OH mhp7ooh4j f mpe4d þ C2H4O2H mhp7ooh3j f mb3d þ prooh1-3 mhp6ooh4j a mpe4d þ CH3CHO þ OH mhp6ooh3j a mb3d þ prooh2-1 mhp6ooh2j a mp2d þ C2H4 þ OH þ CH3CHO mhp5ooh7j a C2H4 þ mpe5*o þ OH mhp5ooh3j a mb3d þ C2H5CHO þ OH mhp5ooh2j a mp2d þ C4H8-1 þ HO2 mhp4ooh7j a mpe4d þ C2H4 þ HO2 mhp4ooh6j a mb4*o þ C3H6 þ OH mhp4ooh2j a mp2d þ nC3H7CHO þ OH mhp3ooh7j a mp3*o þ OH þ C2H4 þ C2H4 mhp3ooh6j a mb3ooh4j þ C3H6 mhp3ooh5j a mp3*o þ C4H8-1 þ OH mhp2ooh6j a mb2ooh4j þ C3H6 mhp2ooh5j a mp2d þ C4H8-1 þ HO2 mhp2ooh4j a me2*o þ C5H10-1 þ OH mhp7ooh5j f mhpcy7o5 þ OH mhp7ooh4j f mhpcy7o4 þ OH mhp7ooh3j f mhpcy7o3 þ OH mhp6ooh4j f mhpcy6o4 þ OH mhp6ooh3j f mhpcy6o3 þ OH mhp6ooh2j f mhpcy6o2 þ OH mhp5ooh7j f mhpcy7o5 þ OH mhp5ooh3j f mhpcy5o3 þ OH mhp5ooh2j f mhpcy5o2 þ OH mhp4ooh7j f mhpcy7o4 þ OH mhp4ooh6j f mhpcy6o4 þ OH mhp4ooh2j f mhpcy4o2 þ OH mhp3ooh7j f mhpcy7o3 þ OH mhp3ooh6j f mhpcy6o3 þ OH mhp3ooh5j f mhpcy5o3 þ OH mhp2ooh6j f mhpcy6o2 þ OH mhp2ooh5j f mhpcy5o2 þ OH mhp2ooh4j f mhpcy4o2 þ OH mhp2oohmj f mhpcy2om þ OH mhpmooh2j f mhpcy2om þ OH mhpcy7o5 þ H f mpe5j*o þ C2H4 þ H2 mhpcy7o5 þ H f mhx5d þ HCO þ H2 mhpcy7o4 þ H f mpe5j4*o þ C2H4 þ H2 mhpcy7o4 þ H f mpe4d þ CH2CHO þ H2 mhpcy7o3 þ H f mpe5j3*o þ C2H4 þ H2 mhpcy7o3 þ H f mb3d þ C2H4CHO þ H2 mhpcy6o4 þ H f mb4j*o þ C3H6 þ H2 mhpcy6o4 þ H f mpe4d þ CH3CO þ H2 mhpcy6o3 þ H f mb4j3*o þ C3H6 þ H2 mhpcy6o3 þ H f mb3d þ CH3COCH2 þ H2 mhpcy6o2 þ H f mp2d þ acetoch2 þ H2 mhpcy5o3 þ H f mp3j*o þ C4H8-1 þ H2 mhpcy5o3 þ H f mb3d þ C2H5CO þ H2 mhpcy5o2 þ H f mp2d þ C2H5COCH2 þ H2 mhpcy4o2 þ H f mp2d þ nC3H7CO þ H2 mhpcy2om þ H f C6H12CO þ OCHO þ H2 mhpcy7o5 þ OH f mpe5j*o þ C2H4 þ H2O mhpcy7o5 þ OH f mhx5d þ HCO þ H2O mhpcy7o4 þ OH f mpe5j4*o þ C2H4 þ H2O mhpcy7o4 þ OH f mpe4d þ CH2CHO þ H2O mhpcy7o3 þ OH f mpe5j3*o þ C2H4 þ H2O mhpcy7o3 þ OH f mb3d þ C2H4CHO þ H2O mhpcy6o4 þ OH f mb4j*o þ C3H6 þ H2O mhpcy6o4 þ OH f mpe4d þ CH3CO þ H2O mhpcy6o3 þ OH f mb4j3*o þ C3H6 þ H2O mhpcy6o3 þ OH f mb3d þ CH3COCH2 þ H2O mhpcy6o2 þ OH f mp2d þ acetoch2 þ H2O mhpcy5o3 þ OH f mp3j*o þ C4H8-1 þ H2O mhpcy5o3 þ OH f mb3d þ C2H5co þ H2O mhpcy5o2 þ OH f mp2d þ C2H5COCH2 þ H2O mhpcy4o2 þ OH f mp2d þ nC3H7CO þ H2O mhpcy2om þ OH f C6H12CO þ OCHO þ H2O mhpcy7o5 þ HO2 f mpe5j*o þ C2H4 þ H2O2 mhpcy7o5 þ HO2 f mhx5d þ HCO þ H2O2 mhpcy7o4 þ HO2 f mpe5j4*o þ C2H4 þ H2O2 mhpcy7o4 þ HO2 f mpe4d þ CH2CHO þ H2O2

4261

A

n

E

ref

1.50 1011 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 2.00 1013 9.10 1010 3.60 1009 1.70 1008 9.10 1010 3.60 1009 1.70 1008 9.10 1010 9.10 1010 3.60 1009 3.60 1009 9.10 1010 9.10 1010 1.70 1008 3.60 1009 9.10 1010 1.70 1008 3.60 1009 9.10 1010 3.60 1009 3.60 1009 2.40 1008 4.80 1008 2.40 1008 4.80 1008 2.40 1008 4.80 1008 2.40 1008 2.40 1008 2.40 1008 2.40 1008 9.60 1008 2.40 1008 2.40 1008 9.60 1008 9.60 1008 1.92 1009 1.20 1008 2.40 1008 1.20 1008 2.40 1008 1.20 1008 2.40 1008 1.20 1006 1.20 1006 1.20 1006 1.20 1006 4.80 1006 1.20 1006 1.20 1006 4.80 1006 4.80 1006 9.60 1006 2.00 1012 4.00 1012 2.00 1012 4.00 1012

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 0 0 0 0

7800 31 000 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 28 700 16 600 7000 1950 16 600 7000 1950 16 600 16 600 7000 7000 16 600 16 600 1950 7000 16 600 1950 7000 16 600 7000 7000 2005 2785 2005 2785 2005 2785 2005 2005 2005 2005 2005 2005 2005 2005 2005 2785 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 -1192 13 260 14 400 13 260 14 400

29 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 37 37 48 37 37 48 37 37 37 37 37 37 48 37 37 48 37 37 37 37 16 16 16 16 16 16 16 16 16 16 see text 16 16 see text see text see text 16 16 16 16 16 16 16 16 16 see text 16 16 16 see text see text see text 16 16 16 16

Energy Fuels 2009, 23, 4254–4268

: DOI:10.1021/ef900184y

Dayma et al.

Table 2. Continued No.

reaction

A

n

E

ref

1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461

mhpcy7o3 þ HO2 f mpe5j3*o þ C2H4 þ H2O2 mhpcy7o3 þ HO2 f mb3d þ C2H4CHO þ H2O2 mhpcy6o4 þ HO2 f mb4j*o þ C3H6 þ H2O2 mhpcy6o4 þ HO2 f mpe4d þ CH3CO þ H2O2 mhpcy6o3 þ HO2 f mb4j3*o þ C3H6 þ H2O2 mhpcy6o3 þ HO2 f mb3d þ CH3COCH2 þ H2O2 mhpcy6o2 þ HO2 f mp2d þ acetoch2 þ H2O2 mhpcy5o3 þ HO2 f mp3j*o þ C4H8-1 þ H2O2 mhpcy5o3 þ HO2 f mb3d þ C2H5CO þ H2O2 mhpcy5o2 þ HO2 f mp2d þ C2H5COCH2 þ H2O2 mhpcy4o2 þ HO2 f mp2d þ nC3H7CO þ H2O2 mhpcy2om þ HO2 f C6H12CO þ OCHO þ H2O2 mhpcy7o5 þ CH3O f mpe5j*o þ C2H4 þ CH3OH mhpcy7o5 þ CH3O f mhx5d þ HCO þ CH3OH mhpcy7o4 þ CH3O f mpe5j4*o þ C2H4 þ CH3OH mhpcy7o4 þ CH3O f mpe4d þ CH2CHO þ CH3OH mhpcy7o3 þ CH3O f mpe5j3*o þ C2H4 þ CH3OH mhpcy7o3 þ CH3O f mb3d þ C2H4CHO þ CH3OH mhpcy6o4 þ CH3O f mb4j*o þ C3H6 þ CH3OH mhpcy6o4 þ CH3O f mpe4d þ CH3CO þ CH3OH mhpcy6o3 þ CH3O f mb4j3*o þ C3H6 þ CH3OH mhpcy6o3 þ CH3O f mb3d þ CH3COCH2 þ CH3OH mhpcy6o2 þ CH3O f mp2d þ acetoch2 þ CH3OH mhpcy5o3 þ CH3O f mp3j*o þ C4H8-1 þ CH3OH mhpcy5o3 þ CH3O f mb3d þ C2H5CO þ CH3OH mhpcy5o2 þ CH3O f mp2d þ C2H5COCH2 þ CH3OH mhpcy4o2 þ CH3O f mp2d þ nC3H7CO þ CH3OH mhpcy2om þ CH3O f C6H12CO þ OCHO þ CH3OH mhpcy7o5 þ CH3O2 f mpe5j*o þ C2H4 þ CH3O2H mhpcy7o5 þ CH3O2 f mhx5d þ HCO þ CH3O2H mhpcy7o4 þ CH3O2 f mpe5j4*o þ C2H4 þ CH3O2H mhpcy7o4 þ CH3O2 f mpe4d þ CH2CHO þ CH3O2H mhpcy7o3 þ CH3O2 f mpe5j3*o þ C2H4 þ CH3O2H mhpcy7o3 þ CH3O2 f mb3d þ C2H4CHO þ CH3O2H mhpcy6o4 þ CH3O2 f mb4j*o þ C3H6 þ CH3O2H mhpcy6o4 þ CH3O2 f mpe4d þ CH3CO þ CH3O2H mhpcy6o3 þ CH3O2 f mb4j3*o þ C3H6 þ CH3O2H mhpcy6o3 þ CH3O2 f mb3d þ CH3COCH2 þ CH3O2H mhpcy6o2 þ CH3O2 f mp2d þ acetoch2 þ CH3O2H mhpcy5o3 þ CH3O2 f mp3j*o þ C4H8-1 þ CH3O2H mhpcy5o3 þ CH3O2 f mb3d þ C2H5CO þ CH3O2H mhpcy5o2 þ CH3O2 f mp2d þ C2H5COCH2 þ CH3O2H mhpcy4o2 þ CH3O2 f mp2d þ nC3H7CO þ CH3O2H mhpcy2om þ CH3O2 f C6H12CO þ OCHO þ CH3O2H mhp7ooh6oo f mhp6ooh7*o þ OH mhp7ooh5oo f mhp5ooh7*o þ OH mhp7ooh4oo f mhp4ooh7*o þ OH mhp7ooh3oo f mhp3ooh7*o þ OH mhp6ooh7oo f mhp7ooh6*o þ OH mhp6ooh5oo f mhp5ooh6*o þ OH mhp6ooh4oo f mhp4ooh6*o þ OH mhp6ooh3oo f mhp3ooh6*o þ OH mhp6ooh2oo f mhp2ooh6*o þ OH mhp5ooh7oo f mhp7ooh5*o þ OH mhp5ooh6oo f mhp5ooh6*o þ OH mhp5ooh4oo f mhp4ooh5*o þ OH mhp5ooh3oo f mhp3ooh5*o þ OH mhp5ooh2oo f mhp2ooh5*o þ OH mhp4ooh7oo f mhp7ooh4*o þ OH mhp4ooh6oo f mhp6ooh4*o þ OH mhp4ooh5oo f mhp5ooh4*o þ OH mhp4ooh3oo f mhp3ooh4*o þ OH mhp4ooh2oo f mhp2ooh4*o þ OH mhp3ooh7oo f mhp7ooh3*o þ OH mhp3ooh6oo f mhp6ooh3*o þ OH mhp3ooh5oo f mhp5ooh3*o þ OH mhp3ooh4oo f mhp4ooh3*o þ OH mhp3ooh2oo f mhp2ooh3*o þ OH mhp2ooh6oo f mhp6ooh2*o þ OH mhp2ooh5oo f mhp5ooh2*o þ OH mhp2ooh4oo f mhp4ooh2*o þ OH mhp2ooh3oo f mhp3ooh2*o þ OH mhp2oohmoo f mhpmooh2*o þ OH mhpmooh2oo f mhp2oohm*o þ OH mhp6ooh7*o f mhx6*o þ HCO þ OH

2.00 1012 4.00 1012 2.00 1012 2.00 1012 2.00 1012 2.00 1012 8.00 1012 2.00 1012 2.00 1012 8.00 1012 8.00 1012 1.60 1013 1.10 1011 2.19 1011 1.10 1011 2.19 1011 1.10 1011 2.19 1011 1.10 1011 1.10 1011 1.10 1011 1.10 1011 4.38 1011 1.10 1011 1.10 1011 4.38 1011 4.38 1011 8.76 1011 2.00 1012 4.00 1012 2.00 1012 4.00 1012 2.00 1012 4.00 1012 2.00 1012 2.00 1012 2.00 1012 2.00 1012 8.00 1012 2.00 1012 2.00 1012 8.00 1012 8.00 1012 1.60 1013 3.30 1009 5.70 1008 1.00 1008 1.70 1007 1.65 1009 1.65 1009 2.85 1008 5.00 1007 8.60 1006 2.85 1008 1.65 1009 1.65 1009 2.85 1008 5.00 1007 5.00 1007 2.85 1008 1.65 1009 1.65 1009 2.85 1008 8.60 1006 5.00 1007 2.85 1008 1.65 1009 1.65 1009 8.50 1006 5.00 1007 2.85 1007 1.65 1009 5.00 1007 1.00 1008 1.00 1016

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0

13 260 14 400 13 260 13 260 13 260 13 260 13 260 13 260 13 260 13 260 13 260 14 400 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 5000 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 17 700 35 500 28 000 25 000 24 000 32 500 32 500 25 000 22 000 21 000 25 000 32 500 32 500 25 000 22 000 22 000 25 000 32 500 32 500 25 000 21 000 22 000 25 000 32 500 32 500 16 000 17 000 20 000 27 500 21 700 28 500 43 000

16 16 16 16 16 16 see text 16 16 see text see text see text 16 16 16 16 16 16 16 16 16 16 see text 16 16 see text see text see text 16 16 16 16 16 16 16 16 16 16 see text 16 16 see text see text see text 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 see text see text see text see text 42 42 29

4262

Energy Fuels 2009, 23, 4254–4268

: DOI:10.1021/ef900184y

Dayma et al.

Table 2. Continued No. 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 a

reaction mhp5ooh7*o f mpe5*o þ CH2CHO þ OH mhp5ooh7*o f mb4j þ CHOCH2CHO þ OH mhp4ooh7*o f mb4*o þ C2H4CHO þ OH mhp4ooh7*o f mp3j þ CHOC2H4CHO þ OH mhp3ooh7*o f mp3*o þ C3H6CHO-1 þ OH mhp3ooh7*o f me2j þ CHOC3H6CHO þ OH mhp7ooh6*o f mhx6j*o þ CH2O þ OH mhp5ooh6*o f mpe5*o þ CH3CO þ OH mhp4ooh6*o f mb4*o þ CH3COCH2 þ OH mhp4ooh6*o f mp3j þ c4ald3oxo þ OH mhp3ooh6*o f mp3*o þ acetoch2 þ OH mhp3ooh6*o f me2j þ c5ald4oxo þ OH mhp2ooh6*o f CH3OCO þ c6ald5oxo þ OH mhp7ooh5*o f mhx6j5*o þ CH2O þ OH mhp6ooh5*o f mpe5j*o þ CH3CHO þ OH mhp4ooh5*o f mb4*o þ C2H5CO þ OH mhp3ooh5*o f mp3*o þ C2H5COCH2 þ OH mhp3ooh5*o f me2j þ c5ald3oxo þ OH mhp2ooh5*o f CH3OCO þ c6ald4oxo þ OH mhp7ooh4*o f mhx6j4*o þ CH2O þ OH mhp6ooh4*o f mpe5j4*o þ CH3CHO þ OH mhp5ooh4*o f mpe5*o4*o þ C2H5 þ OH mhp5ooh4*o f mb4j*o þ C2H5CHO þ OH mhp3ooh4*o f mp3*o þ nC3H7CO þ OH mhp2ooh4*o f CH3OCO þ c6ald3oxo þ OH mhp7ooh3*o f mhx6j3*o þ CH2O þ OH mhp6ooh3*o f mpe5j3*o þ CH3CHO þ OH mhp5ooh3*o f mb4j3*o þ C2H5CHO þ OH mhp4ooh3*o f mp3j*o þ nC3H7CHO þ OH mhp2ooh3*o f CH3OCO þ C4H9COCHO þ OH mhp6ooh2*o f mpe5j2*o þ CH3CHO þ OH mhp5ooh2*o f mb4j2*o þ C2H5CHO þ OH mhp4ooh2*o f mp3j2*o þ nC3H7CHO þ OH mhp3ooh2*o f me2j*o þ nC4H9CHO þ OH mhpmooh2*o f hpaoj2*o þ CH2O þ OH mhp2oohm*o f CHOOCO þ C5H11CHO þ OH

A

n

E

ref

1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016 1.00 1016

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000 43 000

29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29

Reactions not listed were taken from ref 16.

Preliminary tests have demonstrated that the set of rate constants used in our previous article1 was not able to accurately reproduce this new set of experiments. Therefore, the previously proposed scheme was revised in this study. The reaction mechanism developed earlier,1 built based on a comprehensive methyl butanoate oxidation mechanism16 for small esters, was added to a kinetic mechanism for E85 oxidation.27 For redundant reactions, those from Dagaut and Togbe27 were preferred. To this base scheme, we added a submechanism (676 reactions, see Table 2), written to model the oxidation of methyl heptanoate and related compounds from low to high temperatures. This subscheme was written using the same rules used to write the previously presented1 model for methyl hexanoate oxidation. It was built in a hierarchical and systematic way. Methyl heptanoate as well as methyl hexanoate and every radicals and stable intermediates were submitted to the different types of possible reactions. The new set of rate constants was applied to the methyl hexanoate sub mechanism. The different species were named using Fisher et al.16 nomenclature as shown in Figure 1. The reaction types are those considered for the oxidation of alkanes28,29 and by Fisher et al.16 for the oxidation of methyl butanoate. But, due to the higher carbon chain length of methyl heptanoate, some new reactions and rate constants were considered. In these cases, the rate constants used derived from literature data using

structure-reactivity relationships. In the following paragraphs, only these rate constants are discussed and presented. Initiation Reactions. In the case of unimolecular initiations by C-H bond breaking (reactions 897-903) and C-C bond breaking (reactions 904-911), we used the rate constants proposed by Dean30 for primary and secondary carbon atoms in n-butane. For C-H bond breaking on carbon “m” (Figure 1), we have decided to decrease the activation energy for regular alkane primary carbon by 4 kcal mol-1 (reaction 903), due to the proximity of the oxygen atom. For the two C-H bonds on carbon 2, we kept the rate constant proposed by Fisher et al.16 for the combination (reaction 902). For the C-C bond scission between the alkyl chain and the ester function (carbons 2 and 1), we used the rate constant given by Sato et al.31 for acetone initiation with an activation energy decreased by 4 kcal mol-1 (reaction 909) for the same reason as before. For the C-O single bond scission of the ester function (reaction 910), we used the rate constant proposed by Glaude et al.32 for the combination step of dimethyl carbonate. Finally, for the cleavage of the C-O bond leading to a methyl radical and a radical of heptanoic acid (reaction 911), we used the rate constant recommended by Batt et al.33 for dimethyl ether. The present computations are not sensitive to the kinetics of these unimolecular initiations. Hence more investigations (30) Dean, A. M. J. Phys. Chem. 1985, 89, 4600–4608. (31) Sato, K.; Hidaka, Y. Combust. Flame 2000, 122, 291–311. (32) Glaude, P. A.; Pitz, W. J.; Thomson, M. J. Proc. Combust. Inst. 2005, 30, 1111–1118. (33) Batt, L.; Alvarado-Salinas, G.; Reid, I. A. B.; Robinson, C.; Smith, D. B. Proc. Combust. Inst. 1982, 19, 81–87.

(27) Dagaut, P.; Togbe, C. Energy Fuels 2008, 22, 3499–3505. (28) Glaude, P. A.; Battin-Leclerc, F.; Fournet, R.; Warth, V.; C^ ome, G. M.; Scacchi, G. Combust. Flame 2000, 122, 451–462. (29) Curran, H. J.; Gaffuri, P.; Pitz, W. J.; Westbrook, C. K. Combust. Flame 1998, 114, 149–177.

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Table 3. Methyl Heptanoate Oxidation Sub-Mechanism: Rate Constants for H-Abstractions Leading to the Formation of mhp2j (k units: cm3, mol, s-1, cal) H O OH HO2 HCO CH3 CH3O CH2OH CH3O2 C2H3 C2H5 a-C3H5 RO2

Table 4. Methyl Heptanoate Oxidation Sub-Mechanism: Rate Constants for Additions of Primary Radicals with O2 (k=ATn exp (-E/ RT ) units: cm3, mol, s-1, cal)

A

n

E

ref

reaction

type

A

n

E

ref

5.4 104 8.8 1010 3.0 106 6.4 103 1.14 109 1.0 1011 1.78 1012 3.6 101 6.4 103 4.0 1011 2.2 8.0 101 1.0 1012

2.5 0.7 2 2.6 1.3 0 0 2.95 2.6 0 3.5 3.3 0

-1900 3250 -1520 12 400 15 500 7300 1200 10 000 12 400 14 300 4140 17 170 14 550

44 44 35 44 37 44 21 37 as HO2 16 37 37 37

mhp7j þ O2 a mhp7oo mhp6j þ O2 a mhp6oo mhp5j þ O2 a mhp5oo mhp4j þ O2 a mhp4oo mhp3j þ O2 a mhp3oo mhp2j þ O2 a mhp2oo mhpmj þ O2 a mhpmoo

ks kp þ ks 2ks 2ks ks þ kt allylic primary

9.0 1018 1.7 1019 1.8 1019 1.8 1019 1.05 1019 1.2 1010 3.5 1011

-2.5 -2.5 -2.5 -2.5 -2.5 0 0

0 0 0 0 0 -2300 -1700

37 37 37 37 37 38 36

we used the rate constant proposed by Touchard et al.38 for allylic radicals. This makes the addition much more difficult than previously:1 the rate constant is lowered by a factor of 14 at 600 K. Thus, isomerizations are favored, and the branching ratio between the different pathways is better balanced. This has also a strong impact on OH production at low and intermediate temperature, as demonstrated via the reaction rates analysis presented in the next section. The rate constants used for first additions to O2 are presented in Table 4. The rate constants for second additions of molecular oxygen were calculated following the same rules. Isomerizations of Alkyl and Alkylperoxy Radicals. As pointed out in the previous paragraph, the new rate constants used for esters radicals additions to O2 resulted in increased importance of isomerizations. Hence, the rate constants for the isomerizations of alkyl radicals used earlier were revisited. These reactions (1095-1104) are H-transfer through 5-, 6- and 7-membered ring transition states. The adopted rate constants were calculated following the method described in ref 38 for alkanes: the A-factor was calculated according to the formula developed by O’Neal,40 and the activation energy is the sum of the activation energy for H-abstraction and the ring-strain energy of the transition state. To be consistent with the rate constants determined by Tsang et al.41 for octyl radicals, the change in the number of internal rotations as reactant moves to the transition state (Δn‡i.rot) used in the formula " # ekB T 3:5 ðΔni:rot þ 1Þ rpd exp A¼ h R

are needed, particularly in shock tube, to determine these rate constants precisely. In the case of bimolecular initiations via H abstraction by O2 (reactions 912-918), the adopted rate constants were those proposed by Tsang34 for primary and secondary H atoms. For the two hydrogen atoms carried by carbon 2, the rate constants used by Fisher et al.16 were found to be underestimated due to their too high activation energy. As a result, the consumption of methyl heptanoate at high temperature started 50-70 K below that observed experimentally, since in our conditions reaction 917 proceeds in the reverse direction: mhp2j reacts with HO2 to form mhp and O2. This reaction inhibits the consumption of the fuel. Hence, we used a rate constant close to that proposed by Dayma et al.35 in the case of secondary allylic H atoms, with a pre-exponential factor of 4.0 10 þ 13 mol-1 s-2 and an activation energy of 38 000 cal mol-1. Actually, we did not consider the radical mhp2j as resonantly stabilized, but this radical is much more stable than the other primary radicals, and the set of rate constants preferred for allylic compounds fit our experimental results. Finally, when the abstracted hydrogen atom was linked to carbon m, the rate constant used for this initiation was that of methanol from Dayma et al.21 H Abstractions by Radicals. For this class of reactions, the rate constants proposed by Fisher et al.16 for H atoms carried by carbons 7-3 were used here. Moreover, to be consistent with the H abstraction by O2, the two H atoms carried by carbon 2 were considered as secondary and allylic. The rate constants used were taken from literature (Table 3). Finally, the reactivity of the three H atoms on the methoxy group (carbon m) was assumed to be identical to that in methanol.21 Additions of R• and •ROOH to O2. In the case of the first addition, when the radical site is on carbon m (reactions 1011), we used the rate constant proposed by Dagaut et al.36 for dimethyl ether. In the cases where the radical site is on carbons 7-3, we followed the recommendations of Buda et al.37 as we did earlier for methyl hexanoate.1 Finally, still considering a particular stability to the radical on carbon 2,

has to be modified compared to the recommendations given by Glaude et al.39 Moreover, the activation energy of the H-transfer between carbon m and carbon 2 has been increased by 3 kcal mol-1 because of the presence of the acyloxy group in the cycle of the transition state. The new rate constants are given in Table 5. In the case of peroxy radicals (reactions 1105-1134), the rate constants used here were calculated following the recent recommendations of Buda et al.37 When the hydrogen is abstracted from carbon 2, it was considered an alkane tertiary H atom and the activation energies were decreased by 2 kcal mol-1 compared to that given by Buda et al.37 When the acyloxy group was included in the cycle of the transition state (reactions 1133-1134), we used the rate constants recently calculated by Biet et al.42 A treatment similar to that done for alkyl radicals could have been

(34) Tsang, W. J. Phys. Chem. Ref. Data 1988, 17, 887–951. (35) Dayma, G.; Glaude, P. A.; Fournet, R.; Battin-Leclerc, F. Int. J. Chem. Kinetics 2003, 35, 273–285. (36) Dagaut, P.; Luche, J.; Cathonnet, M. Combust. Sci. Technol. 2001, 165, 61–84. (37) Buda, F.; Bounaceur, R.; Warth, V.; Glaude, P. A.; Fournet, R.; Battin-Leclerc, F. Combust. Flame 2005, 142, 170–186. (38) Touchard, S. Construction et Validation de Modeles Cinetiques Detailles Pour la Combustion de Melanges Modeles Des Essences. Ph.D. Thesis, Institut National Polytechnique de Lorraine, Nancy, 2005. (39) Glaude, P. A.; Conraud, V.; Fournet, R.; Battin-Leclerc, F.; C^ ome, G. M.; Scacchi, G.; Dagaut, P.; Cathonnet, M. Energy Fuels 2002, 16, 1186–1195.

(40) Brocard, J. C.; Baronnet, F.; O’Neal, H. E. Combust. Flame 1983, 52, 25–35. (41) Tsang, W.; McGivern, W. S.; Mannion, J. A. Proc. Combust. Inst. 2009, 32, 131–138. (42) Biet, J.; Warth, V.; Herbinet, O.; Glaude, P. A.; Battin-Leclerc, F., Proceedings of the 4th European Combustion Meeting, Vienna, Austria, April 14-17, 2009.

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Table 5. Methyl Heptanoate Oxidation Sub-Mechanism: Rate Constants for Isomerizations of Primary Radicals (k units: cm3, mol, s-1, cal) reaction mhp7j a mhp4j mhp7j a mhp3j mhp6j f mhp3j mhp3j f mhp6j mhp3j a mhpmj mhp2j a mhp7j mhp2j a mhp6j mhp2j a mhp5j mhp2j a mhpmj mhpmj a mhp4j

nature

A

5-membered ring 2Hs 6-membered ring 2Hs 5-membered ring 2Hs 5-membered ring 2Hs 6-membered ring 3Hp 7-membered ring 3Hp 6-membered ring 2Hs 5-membered ring 2Hs 5-membered ring 3Hp 7-membeed ring 2Hs

9.9 10 1.7 107 9.9 107 9.9 107 2.5 107 4.4 106 1.7 107 9.9 107 1.5 108 2.9 106 7

done for alkylperoxy radicals, but these isomerizations are balanced by the formation of cyclic ethers and experimental or theoretical data are clearly missing to help modifying the rate constants of such a large number of reactions (52 reactions). Also, the use of rate constants deriving from the theoretical works43,44 did not yield satisfactory simulations of our experimental results. β-Scissions. For β-scissions involving C-C bond breaking in alkyl radicals yielding a primary alkyl radical and an unsaturated compound (reactions 1145-1147, 1150, 1152, and 1153), the rate constants were taken from ref 35. For reaction 1149, where an alkyl radical yields 1-pentene and a radical from methyl ethanoate, it was considered that the bond between carbons 2 and 3 is weaker than a “regular” Csp3-Csp3 bond. This is consistent with earlier calculated by El-Nahas et al.45 for methyl butanoate. Hence, we used the rate constant proposed by Dayma et al.35 for the formation of an alkene with an activation energy lowered by 4 kcal mol-1 to fit the experimental profiles of 1-pentene during the oxidation of methyl heptanoate and that of 1-butene during that of methyl hexanoate. The rate constant for reaction 1148 forming CH3 was taken from Buda et al.37 For reaction 1151, yielding 1-hexene and methoxy formyl, we considered this last radical reacts as a tertiary vinylic radical and used the rate constant proposed by Touchard et al.46 with an activation energy decreased by 4 kcal mol-1 to take into account the presence of a methoxy group. For reaction 1155, yielding formaldehyde, we used the rate constant proposed by Dooley et al.47 for the similar reaction of mbmj. Finally, for β-scissions involving C-H bond breaking (reactions 1157-1166), the rate constants were taken from ref 46 for secondary hydrogen atoms, from ref 38 for primary H atoms, and from for secondary H atoms linked to carbon 2. Oxidation Reactions Yielding to Heptenoates. In our previous study,1 this class of reactions was not included. According to our new experimental data and the new set of rate constants used for the other reactions, these reactions needed to be considered at low temperature to simulate the experimental concentration profiles of unsaturated esters. Thus, we have included 10 reactions for methyl heptanoate (reactions 1167-1176) and 8 reactions for methyl hexanoate with rate constants taken from ref 37 and ref 48 for the formation of methyl 2-heptenoate and methyl 2-hexenoate.

n

E

ref

1 1 1 1 1 1 1 1 1 1

17 300 12 000 17 300 17 300 14 500 19 900 12 000 17 300 22 800 17 400

recalculated from ref 39 recalculated from ref 39 recalculated from ref 39 recalculated from ref 39 recalculated from ref 39 recalculated from ref 39 recalculated from ref 39 recalculated from ref 39 see text recalculated from ref 39

Table 6. Reactions and Rate Constants Modified from ref 27: Reactions Rates in Bold Were Use Here (k units: cm3, mol, s-1, cal) reaction

A

n

E

ref

CH2O þ HO2 a HCO þ H2O2

4.0 1012 4.11 104 5.42 103 4.5 1010 3.8 1010 1.95 1012

0 2.5 2.81 0 0 0

11 665 10 210 5862 5400 -2000 5000

27 49 27 38 27 37

C2H3 þ CH2O a C2H4 þ HCO C2H4 þ HCO a C2H3 þ CH2O pC4H9 þ O2 a 1-C4H8 þ O2

Reactions of •ROOH Radicals. The rate constants for the addition of HO2 on the double bond of heptenoates (reactions 1303-1312) were taken from ref 29. For the decomposition of •ROOH with the radical site located on carbons β, γ, or δ to the hydroperoxide group (reactions 1313-1330), we used the rate constant proposed by ref 35 for a C-C bond β-scission in an alkyl radical leading to the formation of a primary alkyl radical. Although we did not measure any cyclic ether, their formation was considered in our primary mechanism (reactions 1331-1350) with the rate constants proposed by ref 37 for 4- and 5-membered rings and from 48 for 6-membered ring. Decomposition of Cyclic Ethers and Reactions of Ketohydroperoxides (OQOOH). The decomposition of cyclic ethers (reactions 1351-1430) was globalized following ref 16. In addition, we have considered that when the cycle involves carbon 2, the hydrogen atom carried by this carbon could not be abstracted by small radicals (H, OH, HO2, CH3O, and CH3O2) due to steric effects. Moreover, the rate constants for the decomposition of these cyclic ethers on the other side of the oxygen atom were increased by a factor of 4 to reach a better agreement between methylpropenoate experimental and calculated profiles in the cool flame region during methyl hexanoate oxidation. Unfortunately, we did not measure small unsaturated esters, which are formed by the decomposition of cyclic ethers at low temperature, in methyl heptanoate experiments, and we assume these reactions could be reconsidered. For ketohydroperoxides formation (reactions 14311460), the rate constants were taken from ref 37 considering carbon 2 has the reactivity of a tertiary site again with an activation energy lowered by 2 kcal mol-1. Concerning the decomposition of these compounds (reactions 1461-1497), we used the rate constant given by ref 29. Modifications in the Mechanism Involving Small Species.16,27 Fisher’s mechanism16 for methyl butanoate oxidation was modified by removing redundant reactions with Dagaut’s mechanism27 for 1-hexene oxidation. In this last mechanism, some rate constants were modified and updated. These reactions with their previous and new rate constants are presented Table 6.

(43) Pfaendtner, J.; Yu, X.; Broadbelt, L. J. J. Phys. Chem. A 2006, 110, 10863–10871. (44) Wijaya, C. D.; Sumathi, R.; Green, W. H. J. Phys. Chem. A 2003, 107, 4908–4920. (45) El-Nahas, A. M.; Navarro, M. V.; Simmie, J. M.; Bozzelli, J. W.; Curran, H. J.; Dooley, S.; Metcalfe, W. J. Phys. Chem. A 2007, 111, 3727–3739. (46) Touchard, S.; Buda, F.; Dayma, G.; Glaude, P. A.; Fournet, R.; Battin-Leclerc, F. Int. J. Chem. Kinetics 2005, 37, 451–463. (47) Dooley, S.; Curran, H. J.; Simmie, J. M. Combust. Flame 2008, 153, 2–32. (48) Battin-Leclerc, F. Prog. Energy Combust. Sci. 2008, 34, 440–498.

(49) Dagaut, P.; Dayma, G. J. Phys. Chem. A 2006, 110, 6608–6616.

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the C-H bonds of carbon 2 are the weakest of the chain. This alkylhydroperoxide entirely decomposes into a cyclic ether (reaction 1336; 100%), which, in turn, yields methylpropenoate (reaction 1377; 94%). Mhp5oo isomerizes into mhp5ooh2j (reaction 1118; 99%), which yields mhpcy5o2, another cyclic ether (reaction 1339; 100%) leading to methylpropenoate. Mhp4oo isomerizes into mhp4ooh2j (reaction 1123; 92%) via 6-membered ring transition states. This alkylhydroperoxide then forms a cyclic ether (reaction 1342; 81%) or undergoes a second addition with O2 (reaction 1083; 19%). Mhp3oo isomerizes into mhp3ooh6j (reaction 1125; 51%), mhp3ooh5j (reaction 1126; 23%) or mhp3ooh2j (reaction 1128; 18%) via 7-, 6-, and 5-membered ring transition states, respectively. Mhp3ooh6j mostly yields mhpcy6o3 (reaction 1344; 86%); mhp3ooh5j undergoes another addition with O2 (reaction 1086; 93%) before decomposition into small species; mhp3ooh2j mostly gives methyl 2-heptenoate (reaction 1311; 92%). Finally, mhp2oo isomerizes into mhp2ooh5j (reaction 1130; 51%) through a 7-membered ring transition state, yielding the same cyclic ether as mhp5ooh2j (reaction 1339; 100%), or into mhp2ooh4j (reaction 1131; 24%) through a 6-membered ring. Mhp2ooh4j reacts via a second addition with O2 (reaction 1091; 96%) and formation and decomposition of a degenerated branching agent and gives propanal. Mhp2oo also isomerizes into mhp2ooh6j via an 8-membered ring transition state, which, in turn, gives a cyclic ether (mhpcy6o2), also responsible for the production of methyl propenoate (mp2d) like all the other cyclic ether involving carbon 2 in their cycle. Figure 6 presents the most sensitive reactions for methyl heptanoate oxidation under the same conditions. According to this modeling, the calculated mole fractions of methyl heptanoate are highly sensitive to the recombination of mhp2j and HO2 (reaction 917; S=0.095). Due to the relatively high stability of mhp2j, this reaction reduces the reactivity at low temperature. Among the other sensitive reactions, H-abstractions by OH giving mhp4j (reaction 936; S=-0.058), mhp3j (reaction 937; S=-0.066), mhp2j (reaction 938; S=-0.081), and mhpmj (reaction 939; S=-0.056) promote the conversion of the fuel. Increasing the rate constants of these reactions would accelerate methyl heptanoate consumption. This is especially true for reaction 938 since the following reactions are the most important OH producers. Methyl heptanoate is also sensitive to isomerization of peroxides (reactions 1126 and 1128). The signs of the sensitivity coefficients for these two reactions are opposed because reaction 1126 (S = -0.043) leads to a degenerated branching agent, producing OH radicals, and reaction 1128 (S=0.049) yields an unsaturated ester (methyl 2-heptenoate), a stable product. This explains why increasing the rate constant of reaction 1126 accelerates the consumption of methyl heptanoate, whereas increasing the rate constant of reaction 1128 inhibits the oxidation of the fuel. Among the reactions of simple intermediates, methyl heptanoate oxidation is sensitive to reactions yielding formaldehyde (reaction 3835) as formaldehyde acts as OH radical scavenger. The reaction pathways for the oxidation of methyl heptanoate at 950 K, 10 atm, a residence time of 0.7 s, and a stoichiometric mixture are presented in Figure 7. Under these conditions, the most important routes of consumption of methyl heptanoate are H-abstractions by H and OH to give mhp2j (reactions 924 and 938; 28%). This primary radical then undergoes a C-C bond breaking by β-scission and forms butyl radicals and methyl 2-propenoate (reaction 1153; 88%)

5. Discussion Figures 2-4 present a comparison between the present experimental and modeling results for the oxidation of methyl heptanoate at 10 atm, at a residence time of 0.7 s and an equivalence ratio of, respectively, 0.6, 1, and 2. As can be seen from these figures, the model gives an overall good representation of the data. For the three equivalence ratios, the reactivity of methyl heptanoate is well predicted over the cool flame region, the NTC region, and the high temperature region. For j = 2, the low temperature region was not investigated because we were not expecting any reactivity. Actually, our model predicts a small cool flame even under these conditions. The variation of the mole fraction of 1-olefins (from C2H4 to 1-C5H10) along temperature is well predicted. Ethylene is slightly overestimated between 800 and 900 K for the three equivalence ratios. Ethane, methane, methanol, and hydrogen concentration profiles are well predicted. This model slightly under-predicts the production of CH2O, CO, and H2O in the cool flame region whereas the fuel consumption is slightly overpredicted. At high temperature, the modeling is in rather good agreement with the experimental data for CO, CO2, and H2O. Sensitivity analyses and reactions path analyses based on computations of species reaction rate of production and rate of consumption were used to elaborate the presently proposed kinetic reaction mechanism and interpret the results. According to these computations under the present conditions, the kinetics of methyl heptanoate oxidation is mainly sensitive to a limited number of reactions pertaining to its oxidation submechanism and to reactions of simple intermediates. Figure 5 shows a schematic representation of the reaction rate analyses results for the oxidation of methyl heptanoate at 610 K, under stoichiometric conditions, at 10 atm, and for a residence time of 0.7 s. For sake of clarity, it has been decided not to show all the different species but to globalize them according to their chemical class. Furthermore, the percentage of each route refers to methyl heptanoate. Thanks to this scheme, it can be seen that, under these conditions, 11% of the fuel is consumed to form degenerated branching agents, while 67% yields cyclic ethers. In details, the main routes of consumption of methyl heptanoate are H-abstractions with OH leading to mhp2j (reaction 938; 28%). This results from the use of a high rate constant for this H-abstraction since stable radicals are formed. Other pathways with the same branching ratio yield mhp3j (reaction 937; 10%), mhp4j (reaction 936; 10%), mhp5j (reaction 935; 10%), and mhp6j (reaction 934; 10%). Another important radical for H-abstractions yielding mhp2j is methoxy (CH3O), responsible for about 15% in the consumption of methyl heptanoate. This implies relatively high yields of methanol measured either in the cool flame or in the high temperature region. All these major primary radicals then mostly react with O2 via addition, except a few percent (

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