Influence of iron and copper oxides on polychlorinated diphenyl ether formation in heterogeneous reactions

Polychlorinated diphenyl ether (PCDE) has attracted great attention recently as an important type of environmental pollutant. The influence of iron and copper oxides on formation of PCDEs was investigated using laboratory-scale flow reactors under air and under nitrogen at 350 °C, a temperature corresponding to the post-combustion zone of a municipal solid waste incinerator. The results show that the 2,2′,3,4,4′,5,5′,6-otachlorodiphenyl ether (OCDE) formed from the condensation of pentachlorophenol (PCP) and 1,2,4,5-tetrachlorobenzene (Cl 4 Bz) is the predominant congener formed on the SiO 2 /Fe 2 O 3 surface with and without oxygen. This indicated that HCl elimination between PCP and 1,2,4,5-Cl 4 Bz molecules formed 2,2′,3,4,4′,5,5′,6-OCDE in the presence of Fe 2 O 3. On the other hand, decachlorodiphenyl ether, nonachlorodiphenyl ether, and OCDE were the dominant products on the SiO 2 /CuO surface without oxygen, although the 2,2′,3,4,4′,5,5′,6-OCDE was the dominant product on the SiO 2 /CuO surface with oxygen. Therefore, the presence of Fe 2 O 3 and CuO influences the formation and homologue distribution of PCDEs, which shifted towards the lower chlorinated species. Fe 2 O 3 can promote both the condensation and dechlorination reaction without oxygen . On the contrary, with oxygen, Fe 2 O 3 suppresses the condensation of chlorobenzene and chlorophenol to form PCDEs and polychlorinated dibenzo- p -dioxins and polychlorinated dibenzofurans (PCDD/Fs). CuO can increase the formation of lower chlorinated PCDEs and PCDDs without oxygen. In conclusion, the different fly ash components have a major influence on PCDE emissions.