Formation of Two-Ring Aromatics in Hexylbenzene Pyrolysis

The formation of two-ring aromatics
in hexylbenzene pyrolysis is
used in this work as a model system toward understanding the underlying
chemistry of coke formation during crude oil upgrading processes.
In this work, batch reactor experiments were performed at 55 bar and
450 °C to study the pyrolysis of hexylbenzene utilizing two dimensional
gas chromatography mass spectrometry (GC×GC–qMS) as an
analysis tool. This work finds many different classes of aromatic
species with more than one ring, including bridged two-ring aromatics,
nonfully aromatized fused two-ring aromatics, fully aromatized fused
two-ring aromatics, and >2-ring species. A kinetic model detailed
with elementary chemical reactions is constructed using the reaction
mechanism generator, with thermodynamic and kinetic parameters calculated
by the CBS-QB3 quantum chemistry method. The results of the generated
model were compared to batch reactor experiments. For many compounds,
the predicted selectivities agree with the data within a factor of
2. The formation pathways of previously less-understood species were
clarified based on evidence of intermediates predicted by the model
and measured in this work’s experiments. Despite these advances,
there are larger model-versus-data discrepancies in the selectivities
of some species, and also, the overall conversion rate is underestimated,
indicating the need for future work to further improve thermochemical
and kinetics data of alkylaromatics.