Observation of Cyclopenta-Fused and Ethynyl-Substituted PAH during the Fuel-Rich Combustion of Primary Tar from a Bituminous Coal

High-performance liquid chromatography (HPLC) with ultraviolet−visible (UV) diode-array detection was used to analyze the condensed-phase products from the fuel-rich combustion, at 1000 °C, of bituminous coal primary tar. Experiments were performed using a quartz two-stage reactor consisting of a fluidized-bed reactor coupled to a tubular-flow reactor. Eight cyclopenta-fused polycyclic aromatic hydrocarbons (CP−PAH) were identified, four of which have never before been observed as products of a bituminous coal and have also never been observed from the fuel-rich combustion of any coal: cyclopent[ hi ]acephenanthrylene, cyclopenta[ cd ]fluoranthene, dicyclopenta[ cd, jk ]pyrene, cylopenta[ bc ]coronene. In addition to these CP−PAH, two ethynyl-substituted PAH, 2-ethynylnaphthalene and 1-ethynylacenaphthylene, were identified for the first time as bituminous coal products. Yields of individual CP−PAH spanned a range of 4 orders of magnitude. Out of the eight CP−PAH identified, acenaphthylene was found to be the most abundant under all conditions investigated. CP−PAH of higher ring number were present in successively lower amounts, consistent with CP−PAH formation via hydrocarbon growth reactions. CP−PAH yields decreased with increasing oxygen concentration, indicating that rates of CP−PAH oxidation exceeded those of CP−PAH formation under the conditions investigated. Possible mechanisms of CP−PAH formation are discussed, but the complexity of the starting fuel precludes definitive delineation of the reaction pathways leading to CP−PAH and ethynyl-substituted PAH during the fuel-rich combustion of tar.