Role of phenoxy radicals in PCDD/F formation

In this work, the role of phenoxy radicals in polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans (PCDD/F) formation was investigated by studying the slow oxidation of 2‐chlorophenol (2‐CP) and 2‐chloroanisole (2‐CA) at a gas‐phase concentration of 4 ppm (∼2.1 × 104 μg/m3) over a temperature range of 400–800°C. Residence times were maintained at 2.0 ± 0.10 s. PCDD/F reaction products were dibenzofuran, dibenzo‐p‐dioxin, 4‐chlorodibenzofuran, 1‐chlorodibenzo‐p‐dioxin, 4,6‐dichlorodibenzofuran, and 1,6‐dichlorodibenzo‐p‐dioxin (1,6‐DCDD). Major products observed in these experiments were 2,6‐dichlorophenol, 3‐phenyl‐2‐propenal, 1‐indanone, 1,3‐isobenzofurandione, and 3‐phenyl‐2‐propenoyl chloride. The 2‐CP and 2‐CA experiments, along with the variable concentration 2‐CA experiments, showed that the concentration of radicals present in the oxidation system has a significant effect on the PCDD/F product distribution and ultimately the PCDD/PCDF ratio. Also, the observation of dichlorinated phenoxy phenol and dichlorinated dihydroxybiphenyl, the proposed intermediate species in the radical–radical mechanism, suggests that radical–radical mechanism dominates gas‐phase PCDD/F formation. This information will be helpful in constructing a detailed kinetic mechanism of PCDD/F formation/destruction in combustor postcombustion zone.