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

Abstract

This work reports a detailed mechanism of the initial thermal pyrolysis of isopropyl propionate, (C2H5C(=O)OCH(CH3)2), an important biodiesel additive/surrogate, for a wide range of T = 500–2000 K and P = 7.6–76 000 Torr. The detailed kinetic behaviors of the title reaction on the potential energy surface constructed at the CBS-QB3 level were investigated using the RRKM-based master equation (RRKM-ME) rate model, including hindered internal rotation (HIR) and tunneling corrections. It is revealed that the C3H6 elimination occurring via a six-centered retro-ene transition state is dominant at low temperatures, while the homolytic fission of the C–C bonds becomes more competitive at higher temperatures. The tunneling treatment is found to slightly increase the rate constant at low temperatures (e.g., ∼1.59 times at 563 K), while the HIR treatment, being important at high temperatures, decreases the rate (e.g., by 5.9 times at 2000 K). Showing a good agreement with experiments in low-temperature kinetics, the kinetic model reveals that the pressure effect should be taken into account at high temperatures. Finally, the temperature- and pressure-dependent kinetic mechanism, consisting of the calculated thermodynamic and kinetic data, is provided for further modeling and simulation of any related systems.