Identification of large polycyclic aromatic hydrocarbons in carbon particulates formed in a fuel-rich premixed ethylene flame

Large polycyclic aromatic hydrocarbons were identified in carbon particulate sampled in a fuel-rich premixed ethylene flame. The particulate was extracted with dichloromethane (DCM) in order to separate the soluble organic species (DCM-extract) from the solid carbon (soot). After DCM extraction soot was re-extracted with N-methyl pyrrolidone (NMP) obtaining the NMP-extract. Both the DCM-extract and NMP-extract were further fractionated by size exclusion chromatography in selected molecular weight (MW) ranges. Large polycyclic aromatic hydrocarbons obtained by regular incorporation of C2 and/or C2H2 unit (24/26 rule) occurring in both odd and even series of carbon atom number of polycyclic aromatic hydrocarbons, were identified by laser desorption ionization-mass spectrometry (LDI-MS) analysis of the lighter MW fractions of both the DCM-extract and NMP-extract (100-400 u MW of the DCM-extract and 200-600 u fractions of the NMP-extract). The LDI- MS spectra of the heaviest MW fractions of DCM-extract and NMP-extract (600-2000 u and 600-5000 u fraction) showed a continuous spectrum of masses typical of polymeric structures. The UV-visible absorption and emission spectral analysis corroborated the assignment of lighter and of heavier fractions of DCM-extract and NMP-extract to PAH and to polymeric aromatic structures, respectively.