The oxidation of large alkylbenzenes: An experimental and modeling study

This paper describes the first development of detailed kinetic models for the alkylbenzenes actually present in diesel fuels. Thanks to a new version of the software EXGAS dedicated to alkylbenzenes, the first detailed models for the oxidation of alkylbenzenes with an alkyl chain containing more than 2 atoms of carbon have been automatically generated. These models are based on an aromatic reaction base consisting of a recent ethylbenzene detailed kinetic model. They involve a new type of generic primary reaction for EXGAS mechanisms, ipso-addition, and new generic rules for the estimation of kinetic parameters involved in primary and secondary mechanisms. The existing experimental data on the oxidation of n-propylbenzene and n-butylbenzene, as well as new results on the oxidation of n-hexylbenzene obtained in a jet-stirred reactor from 500 to 1100 K under 1 atm, have been successfully modeled. Simulations well reproduce the more important low-temperature reactivity which is observed for n-hexylbenzene compared to n-butylbenzene. This new tool has also been used to numerically investigate the behavior of alkylbenzenes from n-propylbenzene up to n-decylbenzene. Simulations using this model show an important enhancement of low-temperature reactivity when the alkyl chain in the compounds increases. Flow rate analyses show that this significant increase is due to a decreasing influence of resonance stabilized benzylic radicals obtained from the reactant by H-abstractions on the carbon atom neighboring the ring.