Hydroxide-ion induced complete mineralization of poly(tetrafluoroethylene-co-hexafluoropropylene) copolymer (FEP) in subcritical water

Abstract

Decomposition of poly(tetrafluoroethylene-co-hexafluoropropylene) copolymer (FEP) in supercritical and subcritical water was investigated with the aim of waste treatment. The efficiency of such decomposition was examined by using either oxidizing agents (O₂, H₂O₂) or an alkaline reagent (KOH). When O₂ was chosen, the highest F^– and CO₂ yields, 75 % and 64 %, respectively, were obtained from a reaction of FEP in supercritical water at 384 °C for 24 h. Under these conditions, traces of CHF₃ were detected in the gas phase, the amount of which decreased with increasing the reaction time. H₂O₂ gave slightly higher reactivity than O₂. In contrast, reactions with KOH induced efficient fluorine mineralization. When FEP reacted in 3.0 M KOH solution at 360 °C for 18 h, the F^– yield reached 98 %. Hence, complete fluorine mineralization was achieved, where very little CO₂ (∼0% yield) and no CHF₃ were generated in the gas phase. Furthermore,¹⁹F NMR spectroscopy and combustion-ion chromatography revealed that the reaction solutions did not contain any organofluorine compounds during the reactions. FEP decomposed, releasing F^– into the reaction solution, resulting in the formation of amorphous carbon in the residue.