Complete Mineralization of Fluorinated Ionic Liquids in Subcritical Water in the Presence of Potassium Permanganate

Abstract

Reactions of [Me3PrN][(CF3SO2)2N] and [C3mpip][(CF3SO2)2N] (C3mpip = 1-methyl-1-propylpiperidium) in subcritical water were investigated to develop a technique for recycling fluorine element. By adding KMnO4 to the system, quasi-complete mineralization of the ionic liquids was achieved at 300 °C. When [Me3PrN][(CF3SO2)2N] was reacted for 18 h with 158 mM KMnO4, F–, SO42–, and NO3– yields were 98, 98, and 91%, respectively, and the amount of total organic carbon (TOC) was below the detection limit. [C3mpip][(CF3SO2)2N] was also almost completely mineralized via the same treatment, affording F–, SO42–, and NO3– yields of 94, 97, and 96%, respectively, with no detectable TOC. The rest of the nitrogen atoms were well accounted for by the formation of NO2–. Compared with a previous reported method using FeO, our approach reduces the reaction temperature for complete mineralization by 76 °C and suppresses the formation of environmentally undesirable CHF3.