Effects of acetylene addition on yields of the C1-C10 hydrocarbon products of catechol pyrolysis

To better understand the role Of C-2 species in the formation of polycyclic aromatic hydrocarbons (PAH) from complex solid fuels, we have performed pyrolysis experiments with the model fuel catechol (orthodihydroxybenzene)-a phenol-type compound representative of structural entities in coal, wood, and biomass-in an isothermal laminar-flow reactor, with acetylene added as a dopant. The catechol pyrolysis experiments are conducted at a residence time of 0.3 s, at temperatures of 500-1000 degrees C, and at a fixed catechol-to-acetylene molar feed ratio of 0.785. The pyrolysis products are analyzed by high-pressure liquid chromatography with ultraviolet-visible absorbance detection and by gas chromatography with flame-ionization and mass spectrometric detection. Product quantification reveals that acetylene addition to the catechol pyrolysis environment does not change catechol conversion or the yields of Most C-1-C-5 hydrocarbon products. Acetylene addition does, however, increase the yields of the C-3 products and facilitate consumption of the C-4 products. As for the one- and two-ring aromatics, acetylene addition brings about increases in the yields of benzene, toluene, phenylacetylene, and indene. Except for the highest temperature (1000 degrees C), however, the yields of naphthalene are unaffected by the addition of acetylene. The experimental results show consistency with acetylene addition to a benzyl radical being the dominant pathway for indene formation and with cyclopentadienyl radical self-addition being the dominant reaction pathway for naphthalene formation. Since the C-1-C-10 products are participants in reactions leading to PAH, the observed effects of acetylene addition are relevant to the mechanisms of PAH formation and growth.