Mechanochemical mineralization of “very persistent” fluorocarbon surfactants ‒ 6:2 fluorotelomer sulfonate (6:2FTS) as an example

Abstract

Fluorinated organic chemicals have a wide variety of industrial and consumer applications. For long time perfluorooctane sulfonate and perfluorooctanoic acid have been used as precursors for manufacture of such chemicals. However, these C8 chain compounds have been demonstrated to be toxic, persistent, and bioaccumulative, thus inducing their phase-out. Currently, C6 telomer based fluorocarbon surfactants are considered better alternatives to C8 products because of their low bioaccumulability. But, their high persistency suggests that in the near future their concentrations will increase in the environment and in industrial waste. Being a solid state non-thermal technology, mechanochemical treatment is a good candidate for the destruction of emerging C6 fluorotelomers in solid waste. In the present study, 6:2 fluorotelomer sulfonate is effectively destroyed (~100%) in rapid manner (<1 h) by high energy ball milling with KOH. Stoichiometric fluoride formation confirms its entire mineralization, assuring that no toxic by-products are generated. Reaction mechanism and kinetics indicate that effective mineralization of the perfluorinated moiety is obtained thanks to a rapid CF2 “flake-off” process through radical mechanism.

Remediation of poly- and perfluoroalkyl substances (PFAS) contaminated soils – To mobilize or to immobilize or to degrade?

“…Zhang and colleagues (2016a) repeated the same trial with a Chinese PFOS alternative known as F-53B (6:2 chlorinated polyfluoroalkyl ether sulfonate), and they achieved a more rapid rate of degradation due in part to the substitution of a single fluorine with a chlorine on the terminal carbon and the introduction of an ether group. Further work byLu et al (2017) successfully destroyed 6:2 fluorotelomer sulfonate within 60 min, again using KOH as the support. Citing the concerns over the amount of KOH required for matrix support,Cagnetta et al (2017) degraded a range of PFAS compounds and switched the support matrix to La2O3.…”

Reductive Defluorination and Mechanochemical Decomposition of Per- and Polyfluoroalkyl Substances (PFASs): From Present Knowledge to Future Remediation Concepts

“…An MC approach was first reported for the fluorotelomer 6:2-FTS (see Figure 3) in 2017, as complete decomposition was reached in less than one hour of tribochemical treatment with an excess of KOH. Analysis of the reaction pathway clarified that the presence of the significantly weaker C−H bonds (D 0 = 417 kJ/mol) [12] in fluorotelomers leads to an efficient cleavage of the PFAS molecule and thus to faster decomposition times [118].…”

“…Moreover, simple and cost-efficient reagents (CaO, ZVI, KOH, Al 2 O 3, La 2 O 3 , Na 2 FeO 4 , Na 2 S 2 O 8 , etc.) can be applied, yielding significant decomposition and defluorination ratios [113,[118][119][120]127,128]. The process can be easily interrupted for quality control, process monitoring or addition of reagents or additives.…”

The physicochemical and fire extinguishing performance of aqueous film‐forming foams based on a class of short‐chain fluorinated surfactants

“…The toxicity of short‐chain surfactants prepared in this work was found to be less toxic than long‐chain fluorinated surfactants (Supporting information S1). In addition, short‐chain fluorinated surfactants are more cost effective than the traditional long‐chain fluorinated surfactants in terms of their production, consumption, disposal, and degradation (Chen et al, 2018; Lu et al, 2017).…”