Fluorine recovery through alkaline defluorination of polyvinylidene fluoride

Abstract

The establishment of technological approaches for the defluorination of waste fluoropolymers and recovery of eliminated F^– may contribute to the development of fluorine recycling routes. In this study, we investigated the effects of alkalinity, phase transfer catalyst (PTC) concentration, reaction temperature, and solvent types on the defluorination of polyvinylidene fluoride (PVDF) by alkaline wet processing. The rate of defluorination of PVDF in 4.0 M sodium hydroxide (NaOH) and 50 mM tetrabutylammonium bromide (TBAB) under aqueous conditions reached 89.2%. In addition, the defluorination reaction proceeded faster in solvents such as diethylene glycol (DEG) and triethylene glycol (TEG) than in water because of the high affinity between PVDF and these diols. To investigate the feasibility of developing a fluorine recycling route, the defluorination of a photovoltaic (PV) backsheet and subsequent CaF₂ precipitation from the eliminated F^– was examined. A total of 88.3% of F contained in the PV backsheet was recovered as CaF₂, which satisfied the quality standards of commercial fluorspar. This study demonstrated that alkaline wet processing is effective for the defluorination of PVDF and that the establishment of a F recycling route along the F supply chain may be feasible.