Decomposition of Pentachlorobenzene and 1,2,3,4-tetrachlorodibenzo-p-dioxin by Electron Irradiation
Masao Takeuchi*, Takeshi Hatanaka*, Kentaro Tsuchiya*, Akio Kitajima*, Kazuhiko Harada** and Teruhisa Hirashima**Abstract
Decomposition characteristics of pentachlorobenzene(P5CBz)and 1,2,3,4-tetrachlorodibenzo-p-dioxin(1,2,3,4-T4CDD)with electron irradiation was studied. To confirm the possibility of irradiation as a flue gas treatment, P5CBz or 1,2,3,4-T4CDD made to be absorbed in magnesium silicate powder that was used as a model fly ash, and the electrons were irradiated on powder placed in glass laboratory dishes. The highest obtained destruction efficiency of P5CBz itself is 96% at a dose of 300kGy. However, that of total chlorobenzenes remained at 62% at the same dose, because the dechlorination reaction produced low-chlorinated benzenes. The results with 1,2,3,4-T4CDD indicates almost the same efficiency.
Results of the experiment and an ab initio molecular orbital calculation of P5CBz indicate that 2(3)position of 1,2,3,4-T4CDD is more easily dechlorinated than other positions. So, the isomers produced in the electron irradiation are expected to have a low toxic equivalency factor. Also, though the highly chlorinated benzenes and dioxins are dechlorinated, the considerable amount of low-chlorinated molecules might be decomposed by an open-ring reaction, because the detailed analysis indicated that only a few low-chlorinated benzenes and dioxins could be detected in the decomposition products.
Key words: dioxin, pentachlorobenzene, electron irradiation, dechlorination, ab initio moleculer orbital calculation