Role of Copper Compounds in the De Novo Synthesis of Polychlorinated Dibenzo- p -dioxins/Dibenzofurans

When aqueous extracted fly ash is heated only small amounts of PCDD/F are formed. Addition of CuCl or CuCl2 enhances formation rates drastically. With CuCl, the reaction is first-order in [Cu+]. With CuCl2, the formation is first-order in [Cu2+] when [Cu2+] < 160 μmol/g; at higher concentrations, the apparent dependence suggests either another first-order reaction (but with a different slope) or an exponential increase. Both compounds favor formation of hepta and octa homologs at higher concentrations. Rates of formation are comparable for CuCl and CuCl2. The decline of PCDD/F formation with time for CuCl2 and the inactivity of unchlorinated copper compounds in this reaction suggests that CuCl and CuCl2 are more important as a chlorine source than as a true catalyst. The low concentration of copper in the original ash means that copper is not important in this particular ash in PCDD/F formation. Several other parameters that appear to play a role in PCDD/F formation in municipal solid waste incineration and waste wood boiler fly ashes are addressed.