Theoretical kinetic study for methyl levulinate: oxidation by OH and CH3 radicals and further unimolecular decomposition pathways.

Biofuels may represent a promising alternative in terms of energy sustainability and emission control. Until recently, simple compounds including only a single specific functional group was in the focus of the biofuel research while reported data on more complex structures are scarcer. Presence of multiple functional groups can make molecules more attractive for oxidative species providing attacking site for fast oxidation. Including both a carbonyl and an ester group, methyl levulinate (ML) can be such an excellent biofuel candidate due to its cellulosic origin, although its combustion kinetics is still unresolved. This work reports the first computational kinetic study on methyl levulinate oxidation relevant to combustion conditions. Absolute rate constants for H-abstraction reactions by OH and CH3 radicals were calculated using the G3//MP2/aug-cc-pVDZ level of theory coupled with Transition State Theory (TST). The fate of the forming ML radicals was also investigated by computing absolute rate constants for ß-scission as well as for H-transfer reactions. The outcomes of this work show that the sites between the two functional groups are the most favorable for H-abstraction reactions, and that methyl vinyl ketone (MVK) and methyl acrylate (MAC) are expected to be the main intermediate products of methyl levulinate oxidation. The present results will be useful for further detailed kinetic modeling.

Chemical kinetic study of the oxidation of a biodiesel-bioethanol surrogate fuel: methyl octanoate-ethanol mixtures.

There is a growing interest for using bioethanol-biodiesel fuel blends in diesel engines but no kinetic data and model for their combustion were available. Therefore, the kinetics of oxidation of a biodiesel-bioethanol surrogate fuel (methyl octanoate-ethanol) was studied experimentally in a jet-stirred reactor at 10 atm and constant residence time, over the temperature range 560-1160 K, and for several equivalence ratios (0.5-2). Concentration profiles of reactants, stable intermediates, and final products were obtained by probe sampling followed by online FTIR, and off-line gas chromatography analyses. The oxidation of this fuel in these conditions was modeled using a detailed chemical kinetic reaction mechanism consisting of 4592 reversible reactions and 1087 species. The proposed kinetic reaction mechanism yielded a good representation of the kinetics of oxidation of this biodiesel-bioethanol surrogate under the JSR conditions. The modeling was used to delineate the reactions triggering the low-temperature oxidation of ethanol important for diesel engine applications.