Catalytic hydrodechlorination of a PCB dielectric oil

Results of catalytic hydrodechlorination of PCBs in a commercial dielectric oil are reported. Experimental runs were carried out in a batch reactor (300 cm(3)) at PH2 = 50 bar and T = 280-300-320-350 degreesC. Dielectric oil (2 wt %) in admixture with hexadecane (98 wt %) was treated using a sulfided Ni-Mo catalyst. Dielectric oil composition is 58-60 wt % PCBs and 40-42 wt % chlorobenzenes. PCBs in the oil are mainly from penta- to nonachlorobiphenyls. Total chlorine content is 58 wt %. Liquid-phase samples were withdrawn during the reaction run and analyzed by GC-ECD and GC-FID. Destruction and removal efficiency has been evaluated in function of the operating conditions. The results show that PCBs are transformed into biphenyl and hydrochloric acid, and quite complete hydrodechlorination was accomplished in about 200 min at T = 350 degreesC. At lower temperatures longer reaction times are needed. The reaction organic chlorine --> inorganic chlorine has been modeled, and Arrhenius parameters have been evaluated. In the absence of specific data, these Values can be used to size HDCl reactors for the treatment of PCB oils.