First-principle kinetic studies of unimolecular pyrolysis of isopropyl esters as biodiesel surrogates

Unimolecular pyrolysis of isopropyl acetate (IPA) and isopropyl propanoate (IPP) esters as biodiesel surrogates has been carried out using density functional theory (DFT) at BMK/DZ, TZ level and CBS-QB3 ab initio calculations. Results were compared with isopropyl butanoate (IPB). The rate constants for unimolecular decomposition reactions are calculated based on transition state theory (TST) and compared with the available experimental data. Derived reaction rates have been calculated at a wide range of temperatures relevant to the interest of atmospheric and combustion communities. Among all dissociation channels of IPA, IPP and IPB, acid/propene formation is the most favorable reaction path from kinetic and thermodynamic points of view. On the other side, formation of lower esters is obstructed by high activation energy barriers and is improbable to occur except at high temperature for IPP and IPB. Reaction channels involving simple bond scission require less energy than new esters formation.