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Oxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals, the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicals

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The rate constant for the reaction of CH3OCH2 radicals with O2 (reaction (1)) and the self reaction of CH3OCH2 radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k1 was studied at 296 K over the pressure range 0.025-1 bar and in the temperature range 296-473 K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH3OCH2 + O2 ↔ CH3OCH2O2# → CH2OCH2O2H# → 2HCHO + OH (kprod) CH3OCH2 + O2 ↔ CH3OCH2O2# + M → CH3OCH2O2 + M (kRO2) k1 = kRO2 + kprod, where kRO2 is the rate constant for peroxy radical production and kprod is the rate constant for formaldehyde production. The k1 values obtained at 296 K together with the available literature values for k1 determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: kRO2,0 = (9.4 ± 4.2) × 10-30 cm6 molecule-2 s-1, kRO2,∞ = (1.14 ± 0.04) × 10-11 cm3 molecule-1 s-1, and kprodi,0 = (6.0 ± 0.5) × 10-12 cm3 molecule-1 s-1 where kRO2,0 and kRO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH3OCH2O2 radicals and kprod,0 represents the bimolecular rate constant for the reaction of CH3OCH2 radicals with O2 to yield formaldehyde in the limit of low pressure. kRO2,∞ = (1.07 ± 0.08) × 10-11 exp(-(46 ± 27)/T) cm3 molecule-1 s-1 was determined at 18 bar total pressure over the temperature range 296-473 K. At 1 bar total pressure and 296 K, k3 = (4.1 ± 0.5) × 10-11 cm3 molecule-1 s-1 and at 18 bar total pressure over the temperature range 296-523 K, k5 = (4.7 ± 0.6) × 10-11 cm3 molecule-1 s-1. As a part of this study the decay rate of CH3OCH2 radicals was used to study the thermal decomposition of CH3OCH2 radicals in the temperature range 573-666 K at 18 bar total pressure. The observed decay rates of CH3OCH2 radicals were consistent with the literature value of k2 = 1.6 × 1013exp(-12800/T) s-1. The results are discussed in the context of dimethyl ether as an alternative diesel fuel.

OriginalsprogEngelsk
TidsskriftInternational Journal of Chemical Kinetics
Vol/bind29
Udgave nummer8
Sider (fra-til)627-636
Antal sider10
ISSN0538-8066
DOI
StatusUdgivet - 1 jan. 1997

ID: 227486805