Kinetics and mechanisms for the formation of organic pollutants during pyrolysis and combustion

Results indicate the formation of higher molecular weight products has a maximum, as a function of temperature, in the 1200/sup 0/C to 1400/sup 0/C range for all aromatic systems studied thus far. This maximum is apparently nearly independent of pressure below about 10 torr. Initial results of the gas phase pyrolysis have supported the suggestion of two distinct routes for the formation of polycyclic aromatic hydrocarbons and soot. Below approximately 1450/sup 0/C direct condensation of aromatic precursor, leads to higher molecular weight compounds, and ultimately some soot formation. At higher temperatures initial pyrolysis reactions result in the formation of reactive lower molecular fragments (CH/sub 3/, C/sub 2/H/sub 2/, C/sub 3/H/sub 3/, C/sub 4/H/sub 2/, etc.), which are highly efficient in forming soot by heterogeneous processes but are less efficient in forming aromatic species (however, reaction does apparently speed greatly upon cooling). Our gas phase studies have also identified a number of highly reactive intermediate hydrocarbons for the formation of higher molecular weight compounds (e.g., C/sub 3/H/sub 3/, C/sub 4/H/sub 3/, C/sub 5/,H/sub 3/, and C/sub 7/H/sub 7/). Experiments are being planned to better define the heterogeneous chemistry of these high temperature aromatic systems, relate experimental results to actual combustion experiments and to explore equilibrium calculations for estimating the concentrations of important species at high temperatures.