A theoretical study on the isomerization and dissociation kinetics of methyl decanoate radicals

The isomerization and dissociation reactions of methyl decanoate (MD) radicals were theoretically investigated by using high-level theoretical calculations based on a two-layer ONIOM method, employing the QCISD(T)/CBS method for the high layer and the M06-2X/6-311++G(d,p) method for the low layer. Temperature- and pressure-dependent rate coefficients for involved reactions were computed by using transition state theory and Rice-Ramsperger-Kassel-Marcus/Master-Equation. Results show that the isomerization reactions are appreciably responsible for the population distribution of MD radicals at low and intermediate temperatures, while the ?-scission is dominant at higher temperatures. Although kinetic data of methyl butanoate specific to methyl esters are in excellent agreement with those of MD, methyl butanoate is unable to simulate most of dissociation reactions for real biodiesels due to its short aliphatic chain. Significant differences of rate constants for isomerization reactions were observed between the calculated results and the literature data estimated by analogy to alkane systems, but the rate constants of ?-scissions show generally good agreement between theory and experiment.