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REFRIGERANTS Are


HFOs PFAS?


Asks Professor Dick Powell of Refrigerant Solutions.





When I use a word,” Humpty Dumpty said in rather a scornful tone, “it means just what I choose it to mean— neither more nor less.” Lewis Carroll: Alice through the


Looking Glass. Perhaps less scornful than Humpty Dumpty, the


governments of five European states, Germany, Sweden, Denmark, the Netherlands and Norway, have re-iterated their 202O request that the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulation extends the term, PFAS, (Per- and Poly-Fluoro-Alkyl Substances) to other fluorinated compounds. (In this context ‘poly’ does not refer to polymers, but to partially fluorinated compounds.) PFAS are presently characterised by their highly fluorinated carbon chains, notably derived from perfluoro-octanoic acid (CF3 (CF3


(CF2 (CF2 )6CO2 )7SO3 H) and perfluoro-octane sulfonic acid H), salts of which have been used as surfactants. Since their introduction in the 1950s, the PFAS have been


used in a wide range of applications such as polymeric anti- stain surface coatings, fire-fighting foams and the manufacture of PFTE (polytetrafluoroethylene). Thirty years ago, concern was raised about the long-term toxicity of PFAS when it was noted they were bioaccumulating in shellfish and subsequently in other organisms, including humans. Further studies have suggested links to diseases such as increased cholesterol levels, cancers and type-2 diabetes. Authoritative overviews by the US Government EPA and National Institute of Health can be found at https://www.epa.gov/pfas/basic-information-pfas and https://pubmed.ncbi.nlm.nih.gov/29498927/. While concern about PFAS has so far only affected the refrigeration and HVAC industries indirectly, the situation could be changed by the five states now proposing that PFAS to include any compound that contains a trifluoromethyl (CF3-) or difluoromethylene (-CF2-) group. This would encompass all the major HFCs and HFOs refrigerants. Is this justifiable? What are the implications? Before addressing these questions, I had better declare my


own experience and interests, enabling the reader to better judge any bias in my opinions. By industrial experience, I have been a fluorine chemist for over 50 years. I have worked for


24 December 2021 • www.acr-news.com


short periods on PFAS, fluoropolymers, fluorinated inhalation anaesthetics and fluorochemical intermediates. But the major part of my career has been spent on HFCs refrigerants and more recently on HFOs, carbon dioxide and hydrocarbon refrigerants – volatile chemicals, either singly or in mixtures, that in my view can all contribute to the transition to low impact cooling and heat pump technologies in a nett carbon neutral world. The principal justification for classifying HFCs and HFOs as ‘PFAS’ appears to be their ability to degrade by atmospheric oxidation to trifluoroacetic acid (CF3


CO2 H), which is carried to


the Earth’s surface by rainwater in dilute solution. (When it reaches the ground trifluoroacetic acid will be converted to salts of the trifluoroacetate anion CF3


CO2 -. For convenience in this


note I shall use TFA to refer to both the acid and its anion.) In contrast to HFOs and HFCs, PFAS are large, heavy molecules generally of low volatility, at least compared to TFA, HFCs and HFOs and are proven to bioaccumulate in humans with evidence they can have a negative impact on health. How does TFA compare? As a chemist, I might pedantically describe TFA as a simple PFAS, but I would appreciate that its properties as a small molecule are likely to be very different from the large molecules that have previously been designated as PFAS.


The scientific evidence about the impact of TFA on the biosphere has been expertly reviewed by UNEP (https:// ozone.unep.org/sites/default/files/2019-08/TFA2016.pdf). Perhaps the most astonishing finding is that it is a naturally occurring chemical found in oceans at depths where 14C dating proves there has been no mixing with surface layers for over 1000 years, so have received no contamination from anthropomorphic TFA. Measurements suggest that its formation may be associated with deep ocean vents where volcanic lava containing fluoride is ejected as the continental plates split apart. Despite efforts to find mechanisms for the natural destruction of TFA, none has been discovered. But ‘absence of evidence is not evidence of absence’. My guess is that natural biotic or abiotic TFA destruction does exist and that it is probably occurring in ocean where natural TFA is generated.


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