Mechanism and kinetics of low-temperature oxidation of a biodiesel surrogate−methyl acetate radicals with molecular oxygen

Abstract

Accurate description of reactions between methyl acetate (MA) radicals and molecular oxygen is an essential prerequisite for understanding as well as modeling low-temperature oxidation and/or ignition of MA, a small biodiesel surrogate, because their multiple reaction pathways either accelerate the oxidation process via chain branching or inhibit it by forming relatively stable products. The accurate composite CBS-QB3 level of theory was used to explore potential energy surfaces for MA radicals ? O 2 system. Using the electronic structure calculation results under the framework of canonical statistical mechanics and transition state theory, thermodynamic properties of all species as well as high-pressure rate constants of all reaction channels were derived with explicit corrections for tunneling and hindered internal rotations. Our calculated results are in good agreement with a limited number of scattered data in the literature. Furthermore, pressure-and temperature-dependent rate constants were then computed using the Quantum RiceRamsperger-Kassel and the modified strong collision theories. This procedure resulted in a thermodynamically consistent detailed kinetic mechanism for low-temperature oxidation of the title fuel. We also demonstrated that even the detailed mechanism consists of several reactions of different reaction types, only the addition of the reactants and the re-dissociation of the initially formed adducts are important for low-temperature combustion at engine-liked conditions.

Interplay of thermochemistry and Structural Chemistry, the journal (Volume 26, 2015, Issues 1–2) and the discipline

“…The results of a theoretical study of the kinetics of the reaction between methyl acetate radicals and O 2 were reported by Mai et al [111]. The calculated results were in accord with the literature data.…”

Ab Initio Kinetics of Initial Thermal Pyrolysis of Isopropyl Propionate: A Revisited Study

“…The geometry optimization and frequency calculations employ the hybrid density functional theory, namely, the B3LYP/CBSB7 − level of theory. Found to be suitable for investigating the detailed kinetics of the similar reactions of methyl propionate radicals /methyl acetate radicals with an O 2 molecule, the composite method CBS-QB3, based on the B3LYP/CBSB7 geometry, was used to obtain the energies of all species involved.…”

“…14 The geometry optimization and frequency calculations employ the hybrid density functional theory, namely, the B3LYP/CBSB7 15−17 level of theory. Found to be suitable for investigating the detailed kinetics of the similar reactions of methyl propionate radicals 18 /methyl acetate radicals 19 with an O 2 molecule, the composite method CBS-QB3, 20 based on the B3LYP/CBSB7 geometry, was used to obtain the energies of all species involved. The HIR corrections were thoroughly taken into account in thermodynamic/kinetic calculations, in which the hindrance potentials of the rotation along the C−C and C−O "single" bonds were calculated at the B3LYP/CBSB7 level via relaxed surface scans (cf.…”

Low Temperature Oxidation Kinetics of Biodiesel Molecules: Rate Rules for Concerted HO2 Elimination from Alkyl Ester Peroxy Radicals

“…Surrogates are typically used to emulate the physical and chemical properties of real conventional fuels that are too complicated for detailed investigation. Many investigations have been performed to study combustion-related processes of surrogate-biodiesel molecules, most of which are saturated methyl ester and ethyl esters. − Currently, there are some studies (e.g., Lai et al, , Wang et al, , Zhang et al, Das et al, Lin et al, and Kumar et al) in which theoretical mechanisms for biodiesel combustion have been developed. However, in those mechanisms, the rate constant assignment, which is based on limited sets of available rate constants, has certainly introduced considerable uncertainty to the rate constants.…”

“…Low-temperature combustion, which has potential to improve engine efficiency and reduce toxic emissions, has received much attention in developing oxidation of biodiesel surrogate systems. ,− All these studies pointed out that mechanisms and kinetics of low-temperature oxidation of biodiesel only involve a few crucial reaction channels such as the following: (i) alkyl methyl/ethyl ester peroxy (RO 2 • ) radicals, including dissociation (RO 2 • → R • + O 2 ), concerted elimination (RO 2 • → ester olefin + HO 2 ), and isomerization to form the hydroperoxy alkyl methyl/ethyl ester radical (RO 2 • → • ROOH); and (ii) hydroperoxy alkyl methyl/ethyl ester ( • ROOH) radicals, including β-scission to form olefin ester and HO 2 ( • ROOH → olefin ester + HO 2 ), ketone/aldehyde ester formation ( • ROOH → ketone/aldehyde ester + OH), and cyclic ether ester formation ( • ROOH → cyclic ether/ester + OH) , (cf. Figure for a summary of these important channels).…”