Decomposition of Perfluorinated Ion-Exchange Membrane to Fluoride Ions Using Zerovalent Metals in Subcritical Water

Abstract

The decomposition of Nafion NRE-212, a typical perfluorinated ion-exchange membrane used for fuel cells, in subcritical water was investigated. This is the first report of the decomposition of a perfluorinated ion-exchange membrane aimed at the development of a technique to recover the fluorine component for waste treatment. Although the membrane showed little decomposition in pure subcritical water, the addition of several zerovalent metals to the reaction system accelerated the membrane decomposition to F− ions, and the acceleration increased in the order Al < no metal < Zn < Cu ≪ Fe. When the membrane and iron powder were heated in subcritical water at 350 °C for 17 h, 73.2% of the fluorine content in the initial membrane was successfully transformed into F− ions. In addition to F− ions, trifluoroacetic acid and HCF(CF3)OC2F4SO3− were also detected in the reaction solutions as intermediates, and CO2 and CF3H were detected in the gas phase. Time profiles of the products suggest that one pathway of the decomposition of the membrane proceeded by decomposition of the pendant-chain part, followed by decomposition of the polymer backbone.