MECHANISM OF FORMATION OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS IN THE CATALYZED COMBUSTION OF CARBON

Combustion experiments of an activated carbon (Norit RX Extra), cataly zed by CuCl2, were conducted in triplicate in a flow of moist air cont aining 5 vol % HCI at 300-degrees-C to reveal the mechanism of formati on of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated di benzofurans (PCDFs). The catalyst concentration was varied from 0, 0.1 , 0.5, 1.0, to 5.0 wt %. After partial combustion (1 h), the samples w ere analyzed on the presence of PCDDs and PCDFs. The total yield of th ese compounds amounted to 19 (0.1 wt % CuCl2) and 2 (5.0 Wt % CuCl2) m ug/g of carbon. The PCDD/PCDF ratio showed a decrease from 33 to 0.2. At low copper concentrations, predominantly PCDDs are formed with an i somer pattern that can be explained completely as a product of chlorop henol condensation reactions. At high copper concentrations, the PCDD/ PCDF isomer distribution pattern shifts toward a characteristic waste incineration fly ash pattern. A proposal for the mechanism of formatio n of PCDDs and PCDFs in the catalyzed combustion of carbon will be pre sented. Condensation reactions of 2,4,6-trichlorophenol on carbon (0 w t % CuCl2) resulted in the formation of predominantly PCDDs with an id entical isomer distribution pattern as observed in the catalyzed combu stion of carbon. Active carbon was shown to catalyze the condensation reaction of 2,4,6-trichlorophenol into PCDDs.