Dechlorination of PCBs with Supercritical Water Hydrolysis.

Abstract

Polychlorinated biphenyls (PCBs) were made harmless using supercritical water hydrolysis with an alkali catalyst such as sodium hydroxide. PCBs over a wide concentration range from 2 wt% in transformer oil to pure state were dechlorinated to biphenyl and, in some parts, decomposed to phenol, gases and other small molecules at 30 MPa, 653-723 K, and 20-100 min of reaction time. Furthermore no dioxins were detected in both gaseous and liquid products. Supercritical water hydrolysis has advantages as follows: (1) it dechlorinates pure PCBs rapidly and completely, (2) it realizes the selective dechlorination of dilute PCBs in transformer oil without thermal deterioration of the oil, and (3) it can reduce corrosion problems by neutralizing the product of hydrogen chloride.