Fluorine, one of the smallest atoms of the elements in the periodic table, brings impressive properties to tens of thousands of products. Adding an atom of fluorine into a drug molecule can make it more potent by slowing its breaking down in the body. The electrolytes used to shuttle ions through lithium-ion batteries are fluorine-containing materials. Refrigerants for keeping food fresh, medicines safe and buildings cool, often contain fluorine, as do propellants used to release gases in asthma inhalers and fire extinguishers. Fluorine is also a key component in the stable polymers used for non-stick cookware coatings and waterproof materials.
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But fluorine’s ability to add stability has a dangerous legacy: ‘forever chemicals’, or per- and polyfluoroalkyl substances (PFASs), that have infiltrated every inch of Earth, from breastmilk to the snowy heights of Mount Everest. Some of the most problematic PFASs that have been used in non-stick cookware and waterproof coatings, as well as other applications, are toxic to humans, disrupting hormones and causing problems for parts of the body such as the liver and thyroid.
Getting fluorine into products also relies on a hazardous, energy-intensive process that takes the mineral fluorite — commercially known as fluorspar and with the chemical name calcium fluoride — and heats it with concentrated sulfuric acid to make hydrogen fluoride (HF): an extremely corrosive poisonous gas that forms hydrofluoric acid when dissolved in water. This allows the fluorine locked in the mineral to become reactive. “I would argue that HF is probably one of the most dangerous chemicals that we produce on this planet,” says Veronique Gouverneur, a chemist at the University of Oxford, UK.
The conundrum of balancing fluorine’s immense utility with the hazards of isolating and using it is something that chemists have grappled with for centuries. But the sheer ubiquity of fluorine-infused chemicals, and the growing realization that many compounds are having lasting ill effects on the environment and human health, is spurring a wave of research projects exploring alternatives to current processes and products.
Ground up
Gouverneur wants to tackle problems with fluorine chemistry at the start of the process: before fluorite has even been treated. “Calcium fluoride is not soluble in water or organic solvents, so it’s very difficult to do chemistry directly with calcium fluoride,” she says. In 2023, however, chemists in her lab worked out a way to release fluorine from fluorspar without needing to make HF: by using physical force1. Grinding fluorspar and a potassium phosphate salt together creates friction, which provides the energy needed to make the reaction happen. This mechanochemistry approach is being commercialized by a start-up, Fluorok, based in Oxford and co-founded by Gouverneur. “It’s really a paradigm shift,” says Gouverneur, “because now I can prepare Lipitor [a commonly used drug for lowering cholesterol that contains fluorine] in my lab, from this”, holding up a lump of fluorspar.
Her group has also used the mechanical approach to break up PFASs and regain valuable raw materials. By milling PFASs with potassium phosphate salts, they were able to make potassium fluoride (KF) and dipotassium monofluorophosphate (K2PO3F), fluoride salts that are commonly used by the chemicals industry2.
Fluorok’s chief executive and co-founder, Gabriele Pupo, explains that a big determiner of the company’s early success will be whether he can persuade people that its technology can offer an alternative route. “Everybody remains with the idea there is only one path to make these materials: through HF,” he says. Taking away the need to use a gas as hazardous as HF is not only safer but cheaper too, Pupo says. “Every time you have to deal with something highly corrosive, extremely toxic, very difficult to handle,” he says. “Our process is considerably lower cost compared to the industry standard.”
Other researchers are trying to make fluorine chemistry a circular process, where end-of-life fluoropolymers or other fluorinated chemicals can be transformed back into the useful starting materials that they were built from in the first place.
University of Oxford researchers are hunting for more sustainable ways to work with fluorine.Credit: Thomas Player/University of Oxford
Mark Crimmin, an organometallic chemist at Imperial College London, worked out a way to make fluorine chemistry circular almost by accident. “We ended up discovering some reactions that broke down carbon–fluorine bonds in molecules,” he says3. The next step was to see what their bond-breaking reactions could be applied to.
Crimmin’s development led to chemistries that can modify existing fluorochemicals so they can be used in other new syntheses. The first is what Crimmin calls a ‘transfer fluorination’ process, which treats widely used refrigerant hydrofluorocarbons (HFCs) with a potassium base (rather than the strong acid used in fluorite-to-HF processes) and creates potassium fluoride, a useful starting material for lots of other fluorine chemicals4. For now, this process isn’t fully circular, Crimmin explains, “because the fluorochemicals are so stable, you’ve got to pay an energy cost in order to break them down”.
Crimmin’s second approach, which he calls ‘HF shuttling’, involves taking a hydrogen and a fluorine atom out of one molecule — in this case, waste polyvinylidene fluoride (PVDF) — and with the help of a catalyst, transfer those atoms over to a different molecule, to create a fluoroalkyne, a type of molecule that is used to make agrochemicals, pharmaceuticals and many other fluorochemicals5. PVDF is used as a coating in lithium-ion batteries, and Crimmin is working with a battery recovery company to recycle PVDF from spent batteries and recycle the fluorine content without having to re-form fluorite.
Of course, moving such processes beyond the lab, from working with substances in the tens of grams to tonnes, is far from straightforward. One barrier is working on real-world systems, Crimmin says. “Getting our hands on the true waste streams is an ongoing challenge,” he says. “One of the general challenges of academic labs is that we deal with pristine substances” whereas actual waste substances will probably contain impurities or mixtures of fluorine chemicals.
Crimmin is working with A-Gas, an international company based near Bristol, UK, that makes and manages refrigerants. A-Gas has teams that recover spent refrigerants from industrial and commercial settings before purifying them to sell back to the market. Crimmin is in discussions with the company to get hold of the waste refrigerants before they are reused. “We’re interested in the alternative, which is taking those waste products and then turning them into other fluoride chemicals,” he says.
Tipping point
With such promising work on fluorine chemistry emerging from laboratories, a key question is how large-scale industry can be persuaded to invest more time and money into turning nascent innovations into game-changing solutions.
Strong regulation of the chemical industry can trigger change, with efforts to tackle the hole in the ozone layer being a prime example of a success story. The Montreal Protocol, signed in 1987, banned several ozone-depleting chlorofluorocarbons (CFCs), which had been widely used before then as refrigerants and propellants. It was later updated in 2007 to phase out hydrochlorofluorocarbons (HCFCs), which initially were used as an alternative to CFCs. Since these measures were brought in, the ozone hole has shrunk, but one knock-on effect is that replacement HFC refrigerants are potent greenhouse gases. HFCs were added to the protocol in 2016 with a goal of reducing them by 80–85% by the late 2040s.
Specific regulations designed to restrict PFASs vary between regions. The most concerning types of PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which have been used in non-stick coatings and heat-resistant materials, are already banned or severely restricted in Europe and the United States because of their persistence in the environment, their link to cancers and other health concerns, and their contamination of drinking water. In Canada, concerns that alternative, unrestricted PFASs are replacing the banned substances has led to a proposal that all PFASs be classified as controlled chemicals.
For industry, PFAS regulations have forced some changes, although the public perception that PFASs are environmentally catastrophic is now also having an impact on reducing their use, says Shababa Selim, a senior technology analyst at IDTechEx, a research consultancy in Cambridge, UK.
Industry-based efforts to deal with the hazards posed by fluorine chemistry do seem to be growing in response to mounting public concern and legal cases around the impact of PFASs. So far, chemical companies have settled lawsuits to the tune of millions of dollars for environmental and health problems associated with historic exposure to PFASs.
