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One of the major issues in the thermo chemical conversion of biomass is the formation of soot. Soot formation is undesirable as it can lead to catalyst deactivation. Polycyclic aromatic hydrocarbons (PAH) formed during the pyrolysis and combustion of solid fuels like coal, wood, and biomass are widespread environmental pollutants and precursors to soot. Some PAH are also known to exhibit carcinogenic and mutagenic activity. Hence, understanding the chemical reactions responsible for PAH formation is of utmost importance.

To better understand the reactions leading to the formation of PAH from complex solid fuels, pyrolysis and oxidation experiments have been performed in an isothermal laminar-flow reactor, using the model fuel catechol (ortho-dihydroxybenzene), a phenol-type compound representative of structural entities in coal, wood, and biomass. Catechol pyrolysis experiments have also been performed in the presence of 1,3-butadiene, a major product of the pyrolysis of coal, wood, and biomass. Experiments have been conducted over a temperature range of 500-1000 oC and at a fixed residence time of 0.3 s.

The pyrolysis products are analyzed by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection and mass spectrometric detection, by gas chromatography with flame-ionization and mass spectrometric detection, and by nondispersive infrared analysis. Analysis of the catechol pyrolysis products has led to the identification of 13 C1-C6 non-aromatic species, 5 one-ring aromatics, 7 oxygen-containing organics, and 101 PAH. Of these, 50 (including 47 PAH) have never before been reported as products of catechol or any phenol-type fuel.

Product quantification reveals that catechol's relatively labile O-H bond and capacity for generating oxygen-containing radicals accelerate both fuel conversion and the pyrolysis reactions leading to 1- and 2-ring aromatics and PAH. Among the C1-C5 species, 1,3-butadiene appears to be the most important intermediate and source of growth species in PAH formation from catechol. The results are consistent with the C2 and C4 radicals being the dominant growth species. Reactions responsible for the formation of the C1-C10 products from catechol are discussed. A tentative PAH formation mechanism during catechol pyrolysis is presented.