[PCDD/Fs formation from pentachlorobenzene under the catalysis of CuO].

The formation processes of PCDD/Fs from pentachlorobenzene catalyzed by CuO under heating conditions were investigated. The results showed that, the amount of the formed PCDD/Fs increased with the temperature from 200 degrees C to 350 degrees C, and then decreased with futher increase of temperature from 350 degrees C to 450 degrees C. PCDD/Fs homologue pattern varied significantly according to the reaction temperature. At the lower temperature (200-250 degrees C), the major PCDD/Fs products were highly chlorinated ones; but at the higher temperature (400-450 degrees C), the low chlorinated PCDD/Fs predominated in the PCDD/Fs products. The change of temperature did not cause a systematical variation in the isomer distributions in each PCDD/Fs homologue. By comparing the formation of PCDD/Fs from pentachlorobenzene with the dechlorination of OCDD/F both under the catalysis of CuO at 400 degrees C, the precursor mechanism of PCDD/ Fs formation from pentachlorobenzene was speculated. Low chlorinated PCDDs mainly came from the dechlorination of highly chlorinated PCDDs which were formed from the pentachlorobenzene, whereas PCDFs could be mainly formed by the direct condensation of dechlorination products of pentachlorobenzene.