Chemistry of Polycyclic Aromatic Hydrocarbons Formation from Phenyl Radical Pyrolysis and Reaction of Phenyl and Acetylene

An experimental investigation of phenyl radical pyrolysis
and the
phenyl radical + acetylene reaction has been performed to clarify
the role of different reaction mechanisms involved in the formation
and growth of polycyclic aromatic hydrocarbons (PAHs) serving as precursors
for soot formation. Experiments were conducted using GC/GC-MS diagnostics
coupled to the high-pressure single-pulse shock tube present at the
University of Illinois at Chicago. For the first time, comprehensive
speciation of the major stable products, including small hydrocarbons
and large PAH intermediates, was obtained over a wide range of pressures
(25–60 atm) and temperatures (900–1800 K) which encompass
the typical conditions in modern combustion devices. The experimental
results were used to validate a comprehensive chemical kinetic model
which provides relevant information on the chemistry associated with
the formation of PAH compounds. In particular, the modeling results
indicate that the o-benzyne chemistry is a key factor
in the formation of multi-ring intermediates in phenyl radical pyrolysis.
On the other hand, the PAHs from the phenyl + acetylene reaction are
formed mainly through recombination between single-ring aromatics
and through the hydrogen abstraction/acetylene addition mechanism.
Polymerization is the common dominant process at high temperature
conditions.