Polycyclic aromatic hydrocarbons from the co-pyrolysis of catechol and 1,3-butadiene

In order to better understand the reactions responsible for the formation and growth of polycyclic aromatic hydrocarbons (PAH) from solid fuels, we have performed pyrolysis experiments in an isothermal laminar-flow reactor (at temperatures of 600-1000 °C and a fixed residence time of 0.3 s) with catechol, a model fuel representative of the aromatic moieties in coal and biomass fuels; 1,3-butadiene, a major product of biomass pyrolysis; and with catechol and 1,3-butadiene together (in a catechol-to-1,3-butadiene molar ratio of 0.83). No PAH of ⩾3 rings are produced at temperatures <700 °C, but PAH production becomes significant at temperatures ⩾800 °C. Analysis of the higher-temperature reaction products by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection has led to the identification of over 100 PAH (ranging in size to 10 fused aromatic rings) - 47 of which have never before been reported as products of any phenol-type fuel. Quantification of the product yields shows that a much higher percentage of fed carbon is converted to PAH in the catechol-only pyrolysis experiments than in the 1,3-butadiene-only pyrolysis experiments - a result attributable to catechol's relatively labile O-H bond and capacity for generating oxygen-containing radicals, which accelerate both fuel conversion and the pyrolysis reactions leading to 1- and 2-ring aromatics and PAH. When the two fuels are co-pyrolyzed, the percentage of the total fed carbon converting to PAH is more than two times higher than the amount calculated for the hypothetical case of the two fuels together behaving as a linear combination of the two fuels individually. This elevated production of PAH from the co-pyrolysis experiments reflects not only the reaction-accelerating role of the oxygen-containing radicals but also the efficacy, as growth agents, of the C2 - and especially the C4 - species abundantly present in the catechol/1,3-butadiene co-pyrolysis environment.