Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)

摘要: Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) constitute a group of persistent organic pollutants that form almost inexorably in all thermal combustion operations. This review focuses on mechanisms govern their formation, chlorination, dechlorination destruction. As consequence extreme toxicity propensity to bioaccumulate, PCDD/Fs have been subjected much scientific research, designed understand conditions emission rates congener distribution (fingerprints). Consensus opinions the literature points heterogeneous pathways contributing substantially more total yield systems than gas phase pathway. However, our view, great complexity both homogeneous routes uncertainties many thermochemical rate parameters enable no conclusive statement about contribution each route. Chlorination patterns precursors appear play major role final profiles PCDD/F emissions. According most recent theoretical studies, these seem consistent with thermodynamic stabilities dioxins furans produced processes, however, further investigations at accurate levels are needed clarify this matter further. Theoretical studies along experimental findings reveal PCDD/PCDF ratio remains very sensitive operating conditions, pyrolytic favouring formation PCDFs. A number reaction has proposed answer intriguing questions PCDD/Fs. These include models gaseous reactions, often inferred from quantum chemical calculations which incorporate steps responsible for destruction furans. The identifies gaps present understanding suggests progress field needs be facilitated by development reliable mechanistic (i) catalytic pathways, (ii) chlorination/dechlorination reactions including Deacon direct transfer chlorine solid surfaces into aromatic moieties, (iii) other chlorophenols, especially pesticides.