Efficient FeO-induced decomposition of the fluorinated room-temperature ionic liquid [Me 3 PrN][(CF 3 SO 2 ) 2 N] to fluoride ions in subcritical and supercritical water

Abstract

Decomposition of [Me3PrN][(CF3SO2)2N], a typical room-temperature ionic liquid used for electrochemical devices, in subcritical and supercritical water was investigated with the aim of developing a technique to recover the fluorine component from ionic liquid wastes. When the reaction was carried out in pure subcritical water at 342 °C for 6 h, 99% of the anionic moiety, [(CF3SO2)2N]−, remained, and the F− yield was only 1%. In contrast, in the presence of zerovalent iron, the yield of F− increased to 52%. Although the reactivity of FeO toward the anionic moiety in subcritical water was lower than that of zerovalent iron, the reactivity of FeO increased dramatically when the water was heated to the supercritical state, under which conditions FeO underwent in situ disproportionation to form zerovalent iron and Fe3O4. Specifically, when the reaction was carried out at 376 °C for 18 h, the F− yield reached 90%, which was the highest yield obtained under the tested conditions. In addition, under these conditions, the formation of environmentally undesirable CF3H was suppressed.