Is chlorination one of the major pathways in the formation of polychlorinated naphthalenes (PCNs) in municipal solid waste combustion?

The chlorination patterns of unsubstituted naphthalene were studied using a laminar flow reactor with a 1 cm particle bed of 0.5% (mass) copper(II) chloride (CuCl2) mixed with silicon dioxide (SiO2), operated over a temperature range of 100 to 400 °C and at gas velocities of 2.7 and 0.32 cm/s. The polychlorinated naphthalene (PCN) yield increased until a temperature reached at 250 °C, where a peak yield of 3.07% (percent of naphthalene input, carbon basis) was observed. All PCN homologue groups, mono- through octa-chlorinated naphthalenes, were observed. To test the hypothesis that PCNs in combustion processes are formed via chlorination pathways, the PCN homologue and isomer patterns from the experiments were compared with those observed in municipal solid waste combustion (MSW) incinerators. PCN congeners with 1,4-substituents dominated formation in the naphthalene chlorination experiments, whereas 2,3-substituents were major congeners in both MSW combustion flue gas and fly ash samples. These results suggest that contrary to the hypothesis, chlorination is not a primary PCN formation route in either the flue gas or fly ash from MSW combustion. Even so, naphthalene chlorination pathways presented in this paper provide an improved means for evaluating PCN formation mechanisms in combustion processes.