THE RELATIONSHIP BETWEEN DE-NOVO SYNTHESIS OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS AND LOW-TEMPERATURE CARBON GASIFICATION IN FLY-ASH

Four fly ashes, three from municipal solid waste incinerators (MSWI) and one from a coal-fired power plant, were studied for their potential to promote carbon gasification and de novo synthesis of PCDD/F, chlorobenzenes, and chlorophenols from native carbon precursors in the temperature range 275-350-degrees-C. A fixed-bed tubular reactor employing mixtures of oxygen and nitrogen was used in this laboratory study. The incinerator fly ashes showed steadily increasing yields of chlorobenzenes with temperature and an optimum temperature window for PCDD/F formation in the range 300-325-degrees-C. The rate of PCDD/F formation for one of the fly ashes, found to be 2 x 10(-2) mug (PCDD/F) g-1 min-1, was constant for reaction times from 5 to 30 min. In addition, gasification rates of native carbon in the incinerator fly ashes were at least an order of magnitude greater than those of pure carbon, suggesting catalytic activity. Coal fly ash was inactive to both PCDD/F formation and carbon gasification. A possible correlation was noted between de novo synthesis of PCDD/F and carbon gasification rates.