An Experimental Investigation of the Role of Small Hydrocarbons and Combustion-Generated Nanoparticles on the Formation and Growth Reactions of Polycyclic Aromatic Hydrocarbons during the Pyrolysis of a Model-Fuel and Hydrocarbon Gases
Polycyclic aromatic hydrocarbons (PAH) are an important class of environmental pollutants formed during fuel combustion or pyrolysis. Therefore, an experimental study has been undertaken to better understand the formation and growth pathways of PAH. To investigate the efficacy of C3 species as PAH growth agents in the context of solid fuels, pyrolysis experiments have been performed in an isothermal quartz flow reactor in the temperature range of 700–1000 °C and a fixed residence time of 0.3 s. Experiments are performed with the C3 hydrocarbon, propyne; with catechol (ortho-dihydroxybenzene), a model-fuel representative of aromatic moieties in coal and biomass fuels; and with propyne and catechol together. Further, to better understand the role of fuel components and their decomposition products in PAH growth reactions, pyrolysis and co-pyrolysis experiments are performed using 1,3-butadiene (C4 hydrocarbon) and propyne as fuels at the above described experimental conditions. The results of the catechol/propyne as well as the 1,3-butadiene/propyne co-pyrolysis experiments reveal important synergistic effects that lead to enhanced production of PAH ≥ 3 rings. Product yields will be presented, as functions of temperature, and the reactions responsible for the enhanced yields of PAH will be discussed. The third set of experiments are performed to investigate the effects of inorganics on PAH and their precursor species. A product mixture generated from gas-phase pyrolysis of catechol at 825 °C and a residence time of 5 s is passed through a bed of NiO (the prevalent form of nickel in combustion-generated ash particles) before exiting the reactor. NiO causes the following dramatic effects – PAH yields are reduced by 86% as compared to the case when no inorganics are present, complete depletion of all the acetylenic species is observed, and no solid carbon is observed. The same experiment performed at 1000 °C exhibits similar effects of NiO. High-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection and mass spectrometric detection (HPLC/UV/MS), an isomer-specific technique for PAH analysis has been employed. HPLC analysis of the pyrolysis products of catechol, brown coal, propyne, catechol/propyne, and 1,3-butadiene/propyne reported in this study is one of the most extensive of its kind for these fuels.
PAH, Catechol, HPLC/UV/MS, Pyrolysis, Nickel oxide, Propyne, Butadiene
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