Bench-scale studies on the simultaneous formation of PCBs and PCDD/Fs fromcombustion systems

The presence of endocrine disrupting chemicals (EDCs) in the environment ha s wide-ranging potential ecological and health impacts on animals and human s. A significant amount of experimental and theoretical work has been perfo rmed the examining formation and control of polychlorinated dibenzo-p-dioxi ns and polychlorinated dibenzofurans (PCDD/Fs), which account for only part of the EDCs being emitted from combustion devices. Generally accepted mech anistic theories for PCDD/F formation propose heterogeneous reactions in th e cooler regions of the combustor involving gas-phase organic precursors (s uch as chlorobenzenes or chlorophenols), a chlorine donor [such as hydrogen chloride (HCl)], and a flyash-bound metallic catalyst (such as copper chlo ride). There is evidence that some other proposed EDCs, including polychlor inated biphenyls (PCBs), are formed through a similar mechanistic pathway a s PCDD/Fs. In addition, there is evidence that certain important steps in t he catalytic reaction between the copper catalyst and the organic precursor s may suggest a common rate limiting step for the heterogeneous formation o f the previously mentioned EDCs. This paper reports on a bench-scale experi mental study to characterize a newly built reactor system that was built to : produce levels and distributions of PCDD/F production similar to those ac hieved by previous researchers; verify similar responses to changes in inde pendent variables; examine the hypothesis that PCB formation rates exhibit trends similar to PCDD/F formation rates as reactor variables are changed; and begin to explore the dependence of PCB formation on temperature and pre cursor type. The reactor system has been built, and initial reactor charact erization studies have been performed. Initial experiments yielded results that support the hypothesis of a similar formation mechanism of PCBs and PC DD/Fs in combustors. Initial experiments uncovered potential deficiencies w ith the reactor system and the experimental procedures and have suggested c orrective action to improve the experimental system. Published by Elsevier Science Ltd.