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

ABSTRACT

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.

Key words:

Aqueous extracted fly ash; Brönsted sites; copper; de novo synthesis; Lewis sites; pH; polychlorinated dibenzofurans; polychlorinated dibenzo-p-dioxins