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Environmental Engineering Research 2006;11(4): 217-231. DOI: https://doi.org/10.4491/eer.2006.11.4.217
POLYCHLORINATED NAPHTHALENE (PCN) AND DIBENZOFURAN (PCDF) CONGENER PATTERNS FROM PHENOL PRECURSORS IN THERMAL PROCESS: [I] A PRIORI HYPOTHESIS OF PCN AND PCDF FORMATION PATHWAYS FROM MONOCHLOROPHENOLS
Jae-Yong Ryu1, Do Hyong Kim2, Kum-Chan Choi3, and Jeong-Min Sun4
1Environmental Research Team, Daegu-Gyeongbuk Development Institute, Daegu, Korea
2Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA
3Department of Environmental Engineering, Dong-A University, Pusan, Korea
4Department of Regional Environmental System Engineering, Pusan National University, Miyrang, Korea
Corresponding Author: Jae-Yong Ryu ,Tel: +82-53-770-5112, Fax: +82-53-770-5069, Email: jyryu@dgi.re.kr
Received: February 9, 2006;  Accepted: June 10, 2006.
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ABSTRACT
The gas-phase formation of polychlorinated naphthalenes (PCNs) and dibenzofurans (PCDFs) was experimentally investigated by slow combustion of the three chlorophenols (CPs): 2-chlorophenol (2-CP), 3-chlorophenol (3-CP) and 4-chlorophenol (4-CP), in a laminar flow reactor over the range of 550 to 750°C under oxidative condition. Contrary to the a priori hypothesis, different distributions of PCN isomers were produced from each CP. To explain the distributions of polychlorinated dibenzofuran (PCDF) and PCN congeners, a pathway is proposed that builds on published mechanisms of PCDF formation from chlorinated phenols and naphthalene formation from dihydrofulvalene. This pathway involves phenoxy radical coupling at unsubstituted ortho-carbon sites followed by CO elimination to produce dichloro-9, 10-dihydrofulvalene intermediates. Naphthalene products are formed by loss of H and/or CI atoms and rearrangement. The degree of chlorination of naphthalene and dibenzofuran products decreased as temperature increased, and, on average, the naphthalene congeners were less chlorinated than the dibenzofuran congeners. PCDF isomers were found to be weakly dependent to temperature, suggesting that phenoxy radical coupling is a low activation energy process. Different PCN isomers, on the other hand, are formed by alternative fusion routes from the same phenoxy radical coupling intermediate. PCN isomer distributions were found to be more temperature sensitive, with selectivity to particular isomers decreasing with increasing temperature.
Keywords: Municipal waste incinerator | Thermal process | Combustion | Polychlorinated Naphthalenes | Polychlorinated Dibenzofurans | Chlorophenol
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