LABORATORY SCALE PYROLYSIS EXPERIMENTS USING HALOGENATED BENZENES

1,3,5-Trichlorobenzene, 1,2,3,4-tetrachlorobenzene and hexachlorobenzene were pyrolyzed in a closed ampoule (volume 10 ml) either alone or in combination, at various temperatures ranging from 200 to 550°C in a tube furnace. Pyrolysis was carried out either in vessels closed at normal ambient atmosphere or under vacuum (to exclude oxygen). Product analysis by GC-FID, GC-ECD and GC/MS shows: (a) time-dependent degradation of starting materials; (b) formation of compounds containing a larger number of chlorine atoms than the starting materials (e.g. hexachlorobenzene and pentachlorobenzene from 1,2,3,4-tetrachlorobenzene); (c) fairly efficient formation of a rather small number of polychlorinated biphenyls (e.g. PCBs 174, 170, 194, 206 and 209 from the combination of 1,2,3,4-tetrachlorobenzene+hexachlorobenzene); (d) formation of minute amounts of octachlorodibenzofuran in some of the experiments. The effect of active surfaces (Al2O3; SiO2; AlCl3) on the pyrolysis products are discussed. Potential reaction mechanisms are also presented. © 1990.