Decomposition Process for Polychlorobiphenyls by Means of Basic Molten Salts

Abstract

The decomposition of polychlorobiphenyls (PCBs) by means of basic molten salts was investigated in order to construct a safe, simple and highly efficient waste treatment system for PCBs. PCBs (mono, di, tri, tetra, penta, hexa, hepta-chlorobiphenyls) solution was injected into basic molten salts (KOH–K₂CO₃ or NaOH–Na₂CO₃) at 773–973 K with oxygen or imitation air. The mass of residual PCBs in the exhaust after the decomposition and the mass of PCBs condensed inside the reaction vessel were measured by using gas chromatograph mass spectrometry, and the decomposition efficiency of PCBs was determined. The decomposition efficiency was also determined from the residual concentration of PCBs in the exhaust in some experiments. The decomposition efficiency was high regardless of the number of chlorine contained in PCBs and reached to very high of 99.999% in an optimum condition. Chlorine of PCBs was captured in basic molten salts, and organic compounds containing chlorine was not emitted from the molten salts. Some by-products comprising benzene rings were found at 773–873 K, but the by-products disappeared at 973 K.