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.