FORMATION OF DIOXINS - COMPETING RATES BETWEEN CHEMICALLY SIMILAR PRECURSORS AND DE-NOVO REACTIONS

The formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) on fly ash was investigated using polychlorinated phenols (principally 2,3,4,6-tetrachlorophenol) in competition with the de novo synthesis reaction (e.g., synthesis from native, nonextractable carbon in the fly ash). At the relatively high gas-phase concentrations employed, 38-370 ng ml-1, the chlorophenol pathway was up to 100 times faster than the de novo pathway. For short reaction times (t less-than-or-equal-to 5 min) chlorophenols do not yield PCDF, suggesting that the formation of PCDF in incinerators is not controlled by this reaction over short time scales.