Experimental and modeling study of 1,2,4-trimethylbenzene pyrolysis at atmospheric pressure in a jet-stirred reactor

Abstract

The experimental and kinetic modeling results regarding the 1,2,4-trimethylbenzene (T124MBZ) pyrolysis in a jet-stirred reactor coupled with a synchrotron vacuum ultraviolet molecular beam mass spectrometer at the pressure of 1.0 atm and temperatures of 990–1170 K are reported. Seven monocyclic aromatic hydrocarbons, twelve polycyclic aromatic hydrocarbons (PAHs), and five light hydrocarbons were detected and quantified. A comprehensive kinetic model comprising 997 species and 6148 reactions was developed and extensively validated against the experimental data of pyrolysis, high-pressure oxidation, ignition delay times, and laminar burning velocities. The model demonstrates a reasonable ability to replicate these experimental results. ROP analysis indicates that the dominant consumption pathways for T124MBZ involve H-abstraction at methyl sites by H radicals. These H radicals are predominantly generated via H elimination from the methyl groups of o-dimethylbenzyl, yielding methylxylylene, highlighting the significance of isomerization reactions of dimethylbenzyl in T124MBZ pyrolysis. The most significant reactions promoting T124MBZ consumption are H-abstraction at the o-/m-/p-methyl sites of T124MBZ by H radicals and unimolecular decomposition at the C-H bonds of methyl sites of T124MBZ. Unimolecular decomposition of 1,2,3-trimethylbenzene producing 2,3-dimethylbenzyl is the most inhibiting reaction. Indene, indane, naphthalene, phenanthrene, methylphenanthrene, dimethylphenanthrene and pyrene are identified as the major PAHs produced, with o-/m-/p-methylstyrene, particularly o-methylstyrene, serving as key intermediates in PAHs formation.

Novelty and significance statement

The novelty of this research lies in its new experimental investigation of T124MBZ pyrolysis. Several intermediates and products formed during T124MBZ pyrolysis were detected and quantified using a synchrotron vacuum ultraviolet molecular beam mass spectrometer. Furthermore, a comprehensive kinetic model for T124MBZ was developed. The agreement observed between the experimental data and the model emphasizes the importance of dimethylbenzyl isomerization reactions in the pyrolysis of T124MBZ. This is significant as it demonstrates that the position of substituents plays a key role in the pyrolysis of aromatic compounds. The findings deepen our understanding of the pyrolysis of polysubstituted benzene derivatives, particularly for T124MBZ, providing valuable insights into the important reaction pathways involved in the pyrolysis of jet fuels, and thus designing more effective regenerative cooling and combustion systems.