Structural characterization of products from fuel-rich combustion: An approach based on size exclusion chromatography

High molecular weight carbonaceous materials formed in the combustion of ethylene were collected from a premixed laminar flame operating under fuel-rich combustion conditions. Particulates collected from the flame were extracted with dichloromethane (DCM) to separate condensed species, soluble in DCM, from solid carbonaceous material (soot), insoluble in DCM. These samples were examined by size exclusion chromatography (SEC) using NMP as eluent, with detection by UV absorbance and light scattering. SEC of soot and related materials has provided a path to a more thorough characterization of these materials than has been hitherto available. The data show that there are step changes in structures from the small near-planar polycyclic aromatic hydrocarbon molecules, to large components with elution times corresponding to polystyrenes of mass about one million and to the very large species that are caught by the 20-nm filter. While the suggested molecular masses are enormous, to date no evidence could be found to show that these materials consist of aggregated smaller molecular structures.