A Comparative Study of the Formation of Aromatics in Rich Methane Flames Doped by Unsaturated Compounds

TL;DR

This study compares how different unsaturated hydrocarbons influence aromatic formation in rich methane flames, using a unified model to analyze reaction pathways and sensitivities for benzene production.

Contribution

It introduces a comprehensive mechanism modeling benzene and toluene formation from various C4 and cyclopentene additives in methane flames.

Findings

Reaction pathways vary with different additives.

Allene and propyne promote benzene via propargyl radicals.

Cyclopentene leads to benzene through cyclopentadienylmethylene radicals.

Abstract

For a better modeling of the importance of the different channels leading to the first aromatic ring, we have compared the structures of laminar rich premixed methane flames doped with several unsaturated hydrocarbons: allene and propyne, because they are precursors of propargyl radicals which are well known as having an important role in forming benzene, 1,3-butadiene to put in evidence a possible production of benzene due to reactions of C4 compounds, and, finally, cyclopentene which is a source of cyclopentadienylmethylene radicals which in turn are expected to easily isomerizes to give benzene. These flames have been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as dilutant, for equivalence ratios (?) from 1.55 to 1.79. A unique mechanism, including the formation and decomposition of benzene and toluene, has been used to model the oxidation of allene, propyne, 1,3 butadiene and cyclopentene. The main reaction pathways of aromatics formation have been derived from reaction rate and sensitivity analyses and have been compared for the three types of additives. These combined analyses and comparisons can only been performed when a unique mechanism is available for all the studied additives.