Decomposition of Perfluorinated Ionic Liquid Anions to Fluoride Ions in Subcritical and Supercritical Water with Iron-Based Reducing Agents

Decomposition of perfluorinated ionic liquid anions [(CF3SO2)(2)N](-) and [(C4F9SO2)(2)N](-) in subcritical and supercritical water was investigated with the aim of developing a technique to recover the fluorine component from ionic liquid wastes. Addition of zerovalent iron to the reaction system dramatically increased the yield of F-: when the reaction of [(CF3SO2)(2)N](-) was carried out at 344 degrees C for 6 h, the F- yield was 69.0%, which is 186 times the yield without iron. Increasing the temperature and reaction time in the presence of zerovalent iron further increased the yield: when [(CF3SO2)(2)N](-) and zerovalent iron were heated in supercritical water at 375 degrees C for 18 h, 76.8% of the fluorine content in the initial [(CF3SO2)(2)N](-) was transformed into F-. [(CF3SO2)(2)N](-) also decomposed in the presence of FeO, which underwent in situ disproportionation to form zerovalent iron, which acted as the reducing agent. Although the FeO-induced decomposition of [(CF3SO2)(2)N](-) was initially slower than the zerovalent iron-induced decomposition, after prolonged reaction (18 h) at 378 degrees C, the F- yield of the former reaction reached 85.7%, which was the highest yield obtained. This result suggests that the zerovalent iron that formed in situ reacted preferentially with the substrate, as opposed to water.