GREEN MATTERS


An acid attack on HFOs O


By Professor Dick Powell.


As far as I know, TFA precursor products that fall outside the Montreal Protocol are not being proposed for inclusion in the European PFAS


regulations. Why then should HFO refrigerants be singled out for special treatment?


ver the past 25 years as environmental regulations have become stricter, I have helped develop refrigerant blends for retrofi tting into existing units. Initially the objective was the replacement of ozone depleting products, notably R22. For the last decade, I have focused on replacements for high GWP HFC blends, especially R404A and R410A. In seeking appropriate products, I have variously used fl uorocarbons, originally HFCs now HFOs, hydrocarbons and carbon dioxide. No single refrigerant is a perfect match for all applications, but appropriately formulated blends can provide the optimum balance between safety to the user while minimising environmental impact and providing good energy effi ciency.


I make no distinction between so-called ‘natural’ and


‘synthetic/chemical’ refrigerants. As a chemist, I recognize that all these products are presently sourced from large, conventional chemical plants or fossil fuel refi neries. I appreciate that carbon dioxide, ammonia and hydrocarbons occur naturally, but this simplistic view alone cannot be a rational justifi cation for their desirability as refrigerants. Sulfur dioxide and methyl chloride are also ‘natural’ but they have long been rejected as refrigerants. The risks presented by hazardous, ‘natural’ refrigerants


can be reduced by adopting safety measures such as leak detection and ventilation to dissipate the gases into the environment, with adequate training for service engineers. But the regularity of accidents involving long-used ammonia suggests it is diffi cult to entirely eliminate risks. HFOs provide an alternative to hazardous refrigerants, combining intrinsically low risk at point of use with very low GWPs, but, when they appeared 20 years ago, they were attacked by environmental activists because they were ‘synthetic/chemical’. Yet, despite such adverse aspersions end-users have recognised the intrinsic value of low hazard HFOs which have replaced high GWP HFCs in a variety of applications. But in recent years opponents, have renewed attacks on HFOs because they generate trifl uoroacetic acid (TFA, CF3


CO2 H) when degraded in the atmosphere by hydroxyl


radical, and have required The European Chemicals Agency to include HFOs in proposed regulations controlling PFAS (per/ poly-alkyl-substances). I refer to trifl uoroacetic acid in this article as ‘TFA’, but this abbreviation should also be taken to include its anion trifl uoroacetate CF3


CO2 - and its salts.


Although I have discussed this issue in previous articles, I think its implications are potentially very serious, so I off er no apologies for returning to it here. In my view regulators are in danger of excluding low hazard HFOs based on the ill-advised whims of green activists who have decided that only so-called ‘natural’ refrigerants are acceptable. The political proponents of this policy appear to dismiss the recent authoritative UNEP report that includes a detailed appraisal of the scientifi c evidence for the impact of trifl uoroacetic acid on the global


22 June 2024 • www.acr-news.com


environment: Environmental Eff ects of Stratospheric Ozone Depletion, UV Radiation, and Interactions with Climate Change 2022 Assessment Report. This weighty document is not bedtime reading, even for a chemist. But it contains one key, unequivocal statement backed by extensive explanation underpinned by references to peer reviewed articles published in reputable scientifi c journals: ‘The increases in trifl uoroacetic acid concentrations due to replacements of the ozone-depleting substances are not expected to pose signifi cant risk to humans or the environment at the present time. Trifl uoroacetic acid (TFA) continues to be found in the environment, including in remote regions, although concentrations are so low that they are currently very unlikely to have adverse toxicological consequences for humans and ecosystems. The accumulated amount of TFA is expected to increase because of the planned replacement of ODS with short-lived fl uorinated chemicals. However, based on projected future use of these precursors of TFA, no harm is anticipated. There is a large uncertainty associated with the magnitude of other sources of TFA (e.g., which do not fall under the purview of the Montreal Protocol. Trifl uoroacetic acid has biological properties that diff er signifi cantly from the longer chain polyfl uoroalkyl substances (PFAS) and inclusion of TFA in this larger group of chemicals for regulation would be inconsistent with the risk assessment of TFA.’ (UNEP EEAP 2022 Assessment Report, p 25). As far as I know, TFA precursor products that fall outside the Montreal Protocol are not being proposed for inclusion in the European PFAS regulations. Why then should HFO refrigerants be singled out for special treatment? The UNEP report does acknowledge that the Organization for Economic Cooperation Development (OECD) has proposed a defi nition of PFAS that would include TFA, which clearly disagrees with the scientifi c evidence provided by UNEP. ‘PFASs are defi ned as fl uorinated substances that contain at least one fully fl uorinated methyl or methylene carbon atom (without any H/Cl/Br/Iatom attached to it), i.e., with a few noted exceptions, any chemical with at least a perfl uorinated methyl group (−CF3) or a perfl uorinated methylene group (− CF2−) is a PFAS’. ‘The ‘noted exceptions’ refer to a carbon atom with a H/Cl/Br/I atom attached to it.’ (Environmental Science & Technology 2021 55 (23), 15575-15578). This defi nition includes TFA and essentially all CF3-containing


precursor products, giving the impression that all should be regulated, and I presume by implication could be phased-out I do not object to carbon dioxide, ammonia and


hydrocarbon refrigerants competing against HFO refrigerants, but it must be under regulatory regimes that even-handedly refl ect their diff ering advantages, hazards and environmental impact, based on the best presently available scientifi c evidence.


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