Mechanisms of dioxin formation from the high-temperature oxidation of 2-chlorophenol

The homogeneous, gas-phase oxidative thermal degradation of 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, reaction time of 2.0 s, over a temperature range of 300 to 1000 degrees C. Observed products in order of yield were as follows: 4,6-dichlorodibenzofuran (4,6-DCDF) > dibenzo-p-dioxin (DD) > 1-monochlorodibenzo-p-dioxin (1-MCDD), 4-chlorodibenzofuran (4-MCDF), dibenzofuran (DF), naphthalene, chloronaphthalene, 2,4-dichlorophenol, 2,6-dichlorophenol, phenol, chlorobenzene, and benzene. In contrast to pyrolysis, 4,6-DCDF is the major product rather than DD, and 1-MCDD and naphthalene are formed at temperatures as low as 400 degrees C. Under oxidative conditions, .OH and Cl. are the major carriers, which favors 4,6-DCDF formation over DD or 1-MCDD through abstraction of H. through diketo- and ether- intermediates. It is proposed that below 500 degrees C, unimolecular tautomerization/HCI elimination and CO elimination/isomerization reactions result in the formation of 1-MCDD and naphthalene, respectively.