Fundamental study of perfluoro oil degradative treatment by subcritical water reaction and design of bench-scale equipment

Abstract

Various types of machine oil are used for analysis and utility equipment, and these organic liquid wastes are stored in nuclear facilities and laboratories due to a lack of appropriate treatment processes. Treatment of organic liquid waste is one of the principal tasks since radiolysis of organic material generates various hazardous products. Perfluoro oil, generally used in vacuum pumps, is difficult to decompose because of its chemical stability. Calcination of fluorine compounds is possible to generate toxic and corrosive gas products. In order to achieve complete mineralization of the organic liquid wastes, the application of a subcritical water reaction was examined. In this study, the effect of introducing a functional group into a perfluoro compound on its decomposition performance was experimentally evaluated. First, we carried out the transformation of perfluorohexane to perfluorohexyl iodide or perfluoroheptanoic acid based on reported procedures. Next, laboratory scale batch-wise decomposition tests with subcritical water on perfluorohexyl iodide and on perfluoro heptanoic acid were carried out. Analyses of degraded organic products remaining in the aqueous phase by atmospheric pressure ionization mass spectrometry and liquid chromatography-mass spectrometry were carried out. The decomposition products of each fluorine compound were identified, confirming that subcritical treatment is a promising treatment method.

Keywords

• subcritical water reaction
• radioactive
• perfluoro oil
• perfluorohexyl iodide
• perfluoroheptanoic acid