Simple PFAS Destruction Process Disclosed
An article titled Low-temperature mineralization of perfluorocarboxylic acids, Dichtel and Houk, et al., Science, 18 August 2022, Vol 377, Issue 6608, pp. 839-845, DOI: 10.1126/science.abm8868, came out yesterday with a method for defluorination and chain scission of per- and polyfluoroalkyl substances (PFAS). Blessedly, the article is available without charge.
The article describes the mineralization of reactive perfluorocarboxylic anions with NaOH in water and dimethylsulfoxide, DMSO, at 80 to 120 C and ambient pressure.
Ok. If the prefixes “per” and “poly” are unknown to you, read below, otherwise skip ahead.
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First, some clarification of the name “PFAS” for you non-chemists out there. The “P” in PFAS stands for either prefix “poly” or “per”. Both prefixes appear in common use. The prefix “per” is used to abbreviate the name when some atom or fragment is attached at every possible alkyl (see below) carbon connection point in a molecule or specified fragment of the molecule. The much lengthier proper name would have a number of the position of each separate fluorine atom on the molecule. “Per” and “poly” saves everyone from having to trip over a great many tongue-twisting syllables.
Hydrocarbons consist of only hydrogen atoms on a carbon skeleton. Hydrocarbon carbon atoms can have 0 to 3 hydrogen atoms attached to each skeleton atom. The exception would be methane, CH4, which has 4 hydrogen atoms attached. “Alkyl” refers to a subclass of hydrocarbon fragments or molecules that are absent multiple bonds between atoms of a carbon skeleton. A molecule with a carbon skeleton having no multiple bonds between carbon atoms and linked to hydrogen atoms only is called an “alkane”. An alkane fragment that is connected to something else is called an “alkyl” group.
Gasp! So, a perfluoroalkyl molecule or fragment would have 2 or more of its hydrogen atoms replaced with 2 or more fluorine atoms on a given carbon atom (see definition below).
From Wikipedia “According to the Organisation for Economic Co-operation and Development (OECD): “PFASs are defined as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it), i.e. with a few noted exceptions, any chemical with at least a perfluorinated methyl group (–CF3) or a perfluorinated methylene group (–CF2–) is a PFAS.“
The prefix “poly” is much simpler. It is meant to indicate that the word it is attached to has many units of something, as in polyfluoroalkyl, which means many fluorine atoms attached to alkyl carbon atoms.
Outside of the narrow PFAS world, the prefix per in “perfluoroalkyl” would indicate in common usage that the alkyl fragment is completely saturated with fluorine atoms.
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If we were at the bar during happy hour slamming well drinks after a long day of shaking separatory funnels and trying to vacuum distill something useful out of tar, someone might have groused that the PFAS destruction process is simply a process where you heat the piss out of a DMSO mixture of PFAS to destruction. Everyone has thermally decomposed a reaction mixture in the past. We would pause for a moment, shrug our shoulders and say “well, of course that works”. DMSO is a highly polar, high-boiling solvent which supports the formation of ionic decomposition products at elevated temperature. Kendall even did DFT calculations on decomposition mechanisms. Now, that is how to develop a new approach to decomposition! Get out the big stick of quantum mechanical computing power. The rascals Dichtel and Houk published it first so we’d raise our glasses and drink in their honor. Here’s to you, boys and girls!
As we stagger out to the Uber for the ride home, somebody mutters “I wonder how far along the patent application is and who will be the assignee?”