Combined Ab Initio, Kinetic Modeling, and Shock Tube Study of the Thermal Decomposition of Ethyl Formate

The potential energy
surfaces (PESs) and reaction rate constants
of the unimolecular decomposition of ethyl formate (EF) were investigated
using high-precision theoretical methods at the CCSD­(T)/CBS­(T-Q)//M06-2X/6-311++G­(d,p)
level of theory. The calculated PESs of EF dissociation and molecular
decomposition reactions indicate that the intramolecular H-shift to
produce formic acid and ethylene is the dominant decomposition pathway.
A detailed chemical kinetic mechanism for EF pyrolysis was constructed
by incorporating the important reactions of EF and its radicals into
an existing mechanism previously developed for small methyl esters.
The updated mechanism was first used to reproduce CO, CO2, and H2O concentration time histories during EF pyrolysis
in the shock tube reported by Ren et al. [Ren, W.; Mitchell Spearrin, R.; Davidson, D. F.; Hanson, R. K. J. Phys.
Chem. A 2014, 118, 1785−1798]. The rate of production and
sensitivity analyses show that the competing dehydration and decarboxylation
channels of the intermediate formic acid control the final product
yields of EF pyrolysis. The EF mechanism was further validated against
the shock tube data of OH, CO, CO2, and H2O
time histories measured during EF oxidation (equivalence ratio Φ
= 1.0) at 1331–1615 K and 1.52–1.74 atm. This revised
EF mechanism captured all of the species’ time histories over
the entire temperature range. Such modeling capability was due to
the more accurate rate constants of EF reactions determined by high-precision
theoretical calculations and a high-fidelity C0–C2 basis mechanism.