WorkPackage 3

Thermochemical properties and kinetics

  • Theoretical calculations will be particularly useful for a better determination of the thermochemical properties of species involved in the oxidation of 2G-biofuels, reaction pathways, and kinetic parameters of the elementary steps involved in the kinetic mechanisms. Ab initio methods have been shown to be reliable tools for estimating the thermochemistry of many compounds. However, the most accurate of these methods, namely the G3 or G2 methods, are computationally too expensive for large molecules. Density functional methods, (B3LYP/6-311G(d,p) for instance) using conventional atomization approach, have been shown to provide a reasonable way to treat large molecules. For very complex molecules, a protocol with a smaller basis set is required. Consequently, a B3LYP/6-31G(d,p) method using atomization approach was derived previously. A comparative study of several existing approaches indicated that the B3LYP/6-31G(d,p) protocol appears to be a good compromise between numerical accuracy and expense. Four atomic corrections were derived: one for H-atoms, one for C-atoms, one for O-atoms, and one for C-radicals. The method employed earlier was based on ca. 300 compounds having well-calibrated enthalpies of formation with uncertainty less than 1 kcal/mol. Currently the estimation of kinetic parameters in models is mainly obtained through structure/reactivity correlations and by analogy with similar reactions leading to a lack of accuracy in the used data. Kinetic parameters will be obtained based on ab-initio and RRKM computations. It is expected to provide tabulated rate expression for modelling the oxidation of new fuels with same chemical structures.