Chemical kinetic modeling and shock tube study of methyl propanoate decomposition

The unimolecular decomposition kinetics of methyl propanoate (MP), including the direct C−O/C−C bond fissions and molecular reaction channels, were studied by using high-level ab initio calculations and Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) theory. Four homolytic bond-fission and ten hydrogen transfer reactions of the MP unimolecular decomposition were identified. The phenomenological rate constants were determined using the RRKM/ME theory over a temperature range of 1000−2000 K and a pressure range of 0.01 atm to the high-pressure limit. At 1 atm, the branching ratios show that the dissociation reactions MP ↔
- CH2C(O)OCH3 + CH3, MP ↔ CH3OC
- (O) + C2H5 and MP ↔ CH3CH2C(O)O
-  + CH3 dominate MP pyrolysis over the temperature range of 1000−1500 K. Our calculated rate constants were adopted in a detailed kinetic model to reproduce the laser-absorption measured CO and CO2 concentration time-histories during the pyrolysis of 0.2% MP/Ar in a shock tube from 1292−1551 K and at 1.6 atm. The updated mechanism accurately predicted the early-time CO and CO2 formation over the entire temperature range. In particular, our mechanism well reproduced the CO2 time-histories from the early-time formation to the final plateau level.