Water-promoted catalytic hydrodechlorination of transformer oil-contained PCBs in liquid system under mild conditions

The influences of solvent system on the hydrodechlorination (HDC) of transformer oil-contained PCBs with H-2 over Pd/C catalyst were studied. The addition of water in solvent system significantly accelerated the HDC reaction, which suggested its critical role for enabling Pd/C catalyst to keep high activity and stability. The mechanism of this phenomenon was studied through catalyst characterization (TEM, XRD and XPS), and the change of surface composition of Pd/C catalyst in different solvent in the HDC reaction was raveled. Above results indicated that water in isopropanol-water prevented NaCl accumulating on the surface of catalyst, which avoided the decline in activity and stability of the catalyst. On the basis of these studies, isopropanol-water (60/40, v/v) solvent system was developed to dispose high concentration transformer oil-contained PCBs, where the chloride atom removal ratio of transformer oil-contained PCBs at 2% (w/w) and 5% (w/w) concentration could reach 95.2% and 88.0% for 10 h under mild conditions respectively, and the Pd/C could be recovered and reused at least 10 times without any loss of catalytic activity. (C) 2013 Elsevier B.V. All rights reserved.