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.