BENCH-SCALE STUDIES ON THE SIMULTANEOUS FORMATION OF PCBs AND PCDDs/Fs FROM COMBUSTION SYSTEMS

摘要

The presence of endocrine disrupting chemicals (EDCs) in the environment has wide-ranging potential ecologicalrnand health impacts on animals and humans. A significant amount of experimental and theoretical work hasrnbeen performed the examining formation and control of polychlorinated dibenzo-p-dioxins and polychlorinatedrndibenzofurans (PCDDs/Fs), which account for only part of the EDCs being emitted from combustion devices.rnGenerally accepted mechanistic theories for PCDD/F formation propose heterogeneous reactions in the coolerrnregions of the combustor involving gas-phase organic precursors (such as chlorobenzenes or chlorophenols), arnchlorine donor [such as hydrogen chloride (HCl)], and a flyash-bound metallic catalyst (such as copper chloride).rnThere is evidence that some other proposed EDCs, including polychlorinated biphenyls (PCBs), are formedrnthrough a similar mechanistic pathway as PCDDs/Fs. In addition, there is evidence that certain important steps inrnthe catalytic reaction between the copper catalyst and the organic precursors may suggest a common rate limitingrnstep for the heterogeneous formation of the previously mentioned EDCs.rnThis paper reports on a bench-scale experimental study to characterize a newly built reactor system that wasrnbuilt to: produce levels and distributions of PCDD/F production similar to those achieved by previous researchers;rnverify similar responses to changes in independent variables; examine the hypothesis that PCB formation ratesrnexhibit trends similar to PCDD/F formation rates as reactor variables are changed; and begin to explore the dependencernof PCB formation on temperature and precursor type. The reactor system has been built, and initial reactorrncharacterization studies have been performed. Initial experiments yielded results that support the hypothesis of arnsimilar formation mechanism of PCBs and PCDDs/Fs in combustors. Initial experiments uncovered potential deficienciesrnwith the reactor system and the experimental procedures and have suggested corrective action to improvernthe experimental system.