Oxidative Mineralization of Poly[vinylidene fluoride-co-2-(trifluoromethyl)acrylic acid] Copolymers in Superheated Water

Abstract

The decomposition of functional fluoropolymers poly­[vinylidene fluoride-co-2-(trifluoromethyl) acrylic acid] copolymers, [poly­(VDF-co-MAF)], in superheated water was investigated as the first example of the decomposition of these copolymers aimed at recycling the fluorine element. Such statistical copolymers were prepared from the conventional radical copolymerization of VDF and MAF in two different feed molar ratios leading to different VDF/MAF molar ratios (90/10 and 58/42 molar percentages). Their degradation was achieved in the presence of two oxidizing agents. By the use of KMnO4 (25–158 mM), these poly­(VDF-co-MAF) copolymers efficiently generated F– ions and resulted in low total organic carbon (TOC) content in the reaction solutions. Specifically, when the copolymer containing a 90 mol % VDF was treated with aqueous KMnO4 (158 mM) at 250 °C for 6 h, the F– yield reached 83% and the remaining amount of TOC decreased to 4% of the carbon atom amount in the initial copolymer. Likewise, for the same treatment of the other copolymer (58 mol % VDF), the F– yield reached 90% while the remaining TOC ratio was 4%. Compared to KMnO4, H2O2 induced a lower copolymer mineralization. Adding Ca­(OH)2 to the solutions from superheated water treatment with KMnO4 and a subsequent washing procedure gave pure CaF2.

Recycling and the end of life assessment of fluoropolymers: recent developments, challenges and future trends

“…Compared to the above-mentioned method (combination of H 2 O 2 and subcritical water), the reaction temperature to achieve complete mineralisation was reduced by 50 °C. Furthermore, these authors examined the formation of CaF 2 154,155 from the reaction solutions to close the loop on the fluorine element, given that CaF 2 is the source for all the fluorinated compounds.…”

“…Hori's team is currently studying the mineralisation process of various FPs by subcritical water 149 (i.e., superheated water) as high-pressure liquid water in the temperature range of 100 1C and its critical temperature, 374 1C (while supercritical (sc) water is defined as water at temperature and pressure higher than the critical point: 374 1C and 22.1 MPa, respectively). [149][150][151][152][153][154][155] Given that under these conditions, the water displays high diffusivity, low viscosity and ability to hydrolyze many organic compounds including biomass, reactions using subcritical or sc water are considered environmentally benign in chemical engineering with the aim of developing a technique for the recycling of fluorine element.…”

“…Compared to the above-mentioned method (combination of H 2 O 2 and subcritical water), the reaction temperature to achieve complete mineralisation was reduced by 50 1C. Furthermore, these authors examined the formation of CaF 2 154,155 from the reaction solutions to close the loop on the fluorine element, given that CaF 2 is the source for all the fluorinated compounds. This strategy was further extended to the mineralisation of various copolymers such as ETFE (efficiently mineralised in sc water at 380 1C in the presence of an excess amount of O 2 150 or a lower temperature in the presence of H 2 O 2 ), 151 VDF-containing copolymers, 154 poly(VDF-ter-HFP-ter-TFE) fluoroelastomer 152 and perfluorosulfonic acid (PFSA) membranes 149 (usually involved in ion-exchange polymer membranes, PEMFC, chloro-alkali process to produce chlorine and sodium hydroxide from brine, desalination for drinkable waters, etc.…”

Copolymers of vinylidene fluoride with functional comonomers and applications therefrom: Recent developments, challenges and future trends

“…This strategy was extended to the mineralization of poly(VDF-co-MAF) copolymers [234] and poly(VDF-ter-HFP-ter-TFE) fluoroelastomer [233].…”

“…3). [191,234,235,243] (where CSM and SolvaySP stand for cure site monomer and Solvay Specialty Polymers, respectively).…”