Mechanistic Aspects of Soot Formation from the Combustion of Pine Wood

Carbonaceous soot has been generated from pine in a range of appliances to simulate different combustion conditions. The fuel as well as biomass cell wall components have been studied by pyrolysis-GC−MS and pyrolysis-GC−TCD. In addition, the soots have been probed using both pyrolysis-GC−MS and direct inlet mass spectrometry (DI−MS). The material collected from the pine combustion is smoke, and the major component is a carbonaceous soot. The soots contain both organic carbon (adsorbed species) and black (solid) soot, and the organic carbon consists of primary pyrolysis products from the cell wall components, as well as decomposition products, PAH and oxidized PAH. The black carbon contains oxygen functionality (of the order of 5−10 wt % O), and there are indications that this is incorporated during soot growth, although surface oxidation on reactive sites could also be important. The decomposition products suggest an important additional PAH route is via cyclopentadiene, which is derived after cracking of lignin monomer fragments. Kinetic modeling also highlights the lignin monomers as important contributions to the soot production pathways. A model is proposed which, in addition to the hydrogen abstraction carbon addition (HACA) mechanism, incorporates the cyclopentadiene and the O-PAH addition routes to soot.