A kinetic modeling study on the effect of alkylbenzenes structure on PAH formation at elevated pressures

Abstract

Alkylbenzene is one of the significant components of practical transport fuel, which is considered as the main reason leading to serious emissions of polycyclic aromatic hydrocarbon (PAH) from combustion processes. This work reports a kinetic modeling study on the impact of alkylbenzenes structure, i.e., the length and number of the alkyl side chain, on PAH formation at elevated pressures. A detailed kinetic model has been established and a large number of reactions concerning the PAH species formation have been updated according to the latest theoretical studies. The model is then verified by the previous experimental data containing the concentration profiles of PAH species. The fuel decomposition reactivity and the mole fraction curves of monocyclic aromatic hydrocarbon and polycyclic aromatic hydrocarbon can be well predicted by the present model. The kinetic analysis indicates that the dominant formation pathways of PAHs are barely influenced by the alkyl side chain length, especially at the high-temperature window. In the A1_C1-C4 linear alkylbenzenes pyrolysis system, the formation of benzene is mainly affected by the competition between the combination reaction of C5H3 with CH3 and the ipso-substitution reaction of A1CH3 by H. Unlike the A1_C1-C4 linear alkylbenzenes pyrolysis chemistry, fuel-related reactions associated with the formation of PAHs become more usual as the number of alkyl side chain increases, such as the formation pathway of C9 species in the pyrolysis chemistry of o-xylene and the formation pathway of phenanthrene in the oxidation chemistry of 1,3,5-trimethylbenzene.