5 research outputs found
Importance of Fundamental sp, sp<sup>2</sup>, and sp<sup>3</sup> Hydrocarbon Radicals in the Growth of Polycyclic Aromatic Hydrocarbons
No full textThe most basic chemistry of products formation in hydrocarbons
pyrolysis has been explored via a comparative experimental study on
the roles of fundamental sp, sp<sup>2</sup>, and sp<sup>3</sup> hydrocarbon
radicals/intermediates such as ethyne/ethynyl (C<sub>2</sub>H<sub>2</sub>/C<sub>2</sub>H), ethene/ethenyl (C<sub>2</sub>H<sub>4</sub>/C<sub>2</sub>H<sub>3</sub>), and methane/methyl (CH<sub>4</sub>/CH<sub>3</sub>) in products formations. By using an in situ time-of-flight
mass spectrometry technique, gas-phase products of pyrolysis of acetylene
(ethyne, C<sub>2</sub>H<sub>2</sub>), ethylene (ethene, C<sub>2</sub>H<sub>4</sub>), and acetone (propanone, CH<sub>3</sub>COCH<sub>3</sub>) were detected and found to include small aliphatic products to
large polycyclic aromatic hydrocarbons (PAHs) of mass 324 amu. Observed
products mass spectra showed a remarkable sequence of mass peaks at
regular mass number intervals of 24, 26, or 14 indicating the role
of the particular corresponding radicals, ethynyl (C<sub>2</sub>H),
ethenyl (C<sub>2</sub>H<sub>3</sub>), or methyl (CH<sub>3</sub>),
in products formation. The analysis of results revealed the following:
(a) product formation in hydrocarbon pyrolysis is dominated by hydrogen
abstraction and a vinyl (ethenyl, C<sub>2</sub>H<sub>3</sub>) radical
addition (HAVA) mechanism, (b) contrary to the existing concept of
termination of products mass growth at cyclopenta fused species like
acenaphthylene, novel pathways forming large PAHs were found succeeding
beyond such cyclopenta fused species by the further addition of C<sub>2</sub>H<sub><i>x</i></sub> or CH<sub>3</sub> radicals,
(c) production of cyclopenta ring-fused PAHs (CP-PAHs) such as fluoranthene/corannulene
appeared as a preferred route over benzenoid species like pyrene/coronene,
(d) because of the high reactivity of the CH<sub>3</sub> radical,
it readily converts unbranched products into products with aliphatic
chains (branched product), and (e) some interesting novel products
such as dicarbon monoxide (C<sub>2</sub>O), tricarbon monoxide (C<sub>3</sub>O), and cyclic ketones were detected especially in acetone
pyrolysis. These results finally suggest that existing kinetic models
of product formation should be modified to include the reported novel
species and their formation pathways. It is expected that outcomes
of this study will be useful to understand the products formation
from reactors to interstellar atmospheres as well as the growth mechanism
of carbon nanomaterials
