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

• The solvent system influences the activity and stability of catalysts in HDC reaction.
• The mechanism of this phenomenon is investigated by characterization analyses.
• A promising catalytic HDC solvent system of isopropanol–water (60/40, v/v) is developed.
• This solvent system is applicable to the complete HDC of high concentration PCBs with Pd/C catalyst.
• The Pd/C catalyst could be recovered and reused at least 10 times.

The influences of solvent system on the hydrodechlorination (HDC) of transformer oil-contained PCBs with H2 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.

The change of surface composition of 5% Pd/C(0) in isopropanol and isopropanol–water in the HDC of transformer oil-contained PCBs.Figure optionsDownload as PowerPoint slide