TY - JOUR
T1 - Dimethyl ether oxidation
T2 - Kinetics and mechanism of the CH3OCH2 + O2 reaction at 296 K and 0.38-940 Torr total pressure
AU - Sehested, J.
AU - Møgelberg, T.
AU - Wallington, T. J.
AU - Kaiser, E. W.
AU - Nielsen, O. J.
PY - 1996/10/24
Y1 - 1996/10/24
N2 - The title reaction was studied at 296 K and 0.38-940 Torr total pressure using a FTIR smog chamber technique. The overall rate constant for reaction of CH3OCH2 radicals with O2 may be written, k1 = kRO2 + kprod, where kRO2 is the rate constant for peroxy radical production and kprod is the rate constant for the production of other species from reaction 1. k1 was measured relative to the pressure independent reaction of CH3OCH2 radicals with Cl2 (k4). There was no discernible effect of pressure on k1 in the range 200-940 Torr. Between 200 and 2 Torr total pressure k1 decreased by approximately a factor of 2. For pressures below 2 Torr k1 was again independent of pressure. The reaction proceeds via the formation of an activated complex, CH3OCH2O2#, that is either collisionally stabilized to form the peroxy radical, CH3OCH2O2, or undergoes intramolecular H-atom abstraction followed by decomposition to give two formaldehyde molecules and an OH radical: CH3-OCH2 + O2 ⇌ CH3OCH2O2#, CH3OCH2O2# + M → CH3OCH2O2 + M, CH3OCH2O2# → CH2OCH2O2H# → 2HCHO + OH. The products from this reaction were studied as a function of total pressure. The molar yield of formaldehyde increased from <2% at 700 Torr total pressure to ∼200% at 0.38 Torr total pressure, while the combined yield of methyl formate and methoxy methylhydroperoxide decreased from ∼100% to 4% over the same pressure range. Fitting the product yields and relative rate data using a modified Lindemann expression gave the following rate constants: kRO2.0/k4 = (1-97 ± 0.28) × 10-19 cm3 molecule-1, kRO2.∞/k4 = 0.108 ± 0.004, and kprod,0/k4 = (6.3 ± 0.5) × 10-2 where kRO2.0 and kRO2,∞ are the overall termolecular and bimolecular rate constants for formation of the CH3OCH2O2 radical 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. These data and absolute rate data from the literature were used to derive a rate constant for the reaction of CH3OCH2 radicals with Cl2 of (1.00 ± 0.16) × 10-10 cm3 molecule-1 s-1. The results are discussed in the context of the use of dimethyl ether as an alternative diesel fuel.
AB - The title reaction was studied at 296 K and 0.38-940 Torr total pressure using a FTIR smog chamber technique. The overall rate constant for reaction of CH3OCH2 radicals with O2 may be written, k1 = kRO2 + kprod, where kRO2 is the rate constant for peroxy radical production and kprod is the rate constant for the production of other species from reaction 1. k1 was measured relative to the pressure independent reaction of CH3OCH2 radicals with Cl2 (k4). There was no discernible effect of pressure on k1 in the range 200-940 Torr. Between 200 and 2 Torr total pressure k1 decreased by approximately a factor of 2. For pressures below 2 Torr k1 was again independent of pressure. The reaction proceeds via the formation of an activated complex, CH3OCH2O2#, that is either collisionally stabilized to form the peroxy radical, CH3OCH2O2, or undergoes intramolecular H-atom abstraction followed by decomposition to give two formaldehyde molecules and an OH radical: CH3-OCH2 + O2 ⇌ CH3OCH2O2#, CH3OCH2O2# + M → CH3OCH2O2 + M, CH3OCH2O2# → CH2OCH2O2H# → 2HCHO + OH. The products from this reaction were studied as a function of total pressure. The molar yield of formaldehyde increased from <2% at 700 Torr total pressure to ∼200% at 0.38 Torr total pressure, while the combined yield of methyl formate and methoxy methylhydroperoxide decreased from ∼100% to 4% over the same pressure range. Fitting the product yields and relative rate data using a modified Lindemann expression gave the following rate constants: kRO2.0/k4 = (1-97 ± 0.28) × 10-19 cm3 molecule-1, kRO2.∞/k4 = 0.108 ± 0.004, and kprod,0/k4 = (6.3 ± 0.5) × 10-2 where kRO2.0 and kRO2,∞ are the overall termolecular and bimolecular rate constants for formation of the CH3OCH2O2 radical 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. These data and absolute rate data from the literature were used to derive a rate constant for the reaction of CH3OCH2 radicals with Cl2 of (1.00 ± 0.16) × 10-10 cm3 molecule-1 s-1. The results are discussed in the context of the use of dimethyl ether as an alternative diesel fuel.
UR - http://www.scopus.com/inward/record.url?scp=24644511011&partnerID=8YFLogxK
M3 - Journal article
AN - SCOPUS:24644511011
SN - 0022-3654
VL - 100
SP - 17218
EP - 17225
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
IS - 43
ER -