Chemicals that contain the element fluorine and are widely used in pharmaceuticals, fertilisers and batteries can now be made through a process that is safer and takes less energy than how these substances have been manufactured for centuries.
Fluorine in most fluorochemicals comes from chunks of salt called fluorspar where the element is bound to calcium. Fluorspar crystals are mined then treated with a strong acid at a high temperature to create hydrogen fluoride gas which can then be used in the remaining steps of fluorochemical production.
However, hydrogen fluoride is very toxic which makes the whole process hazardous to both the environment and human health. Calum Patel at the University of Oxford and his colleagues wanted to make fluorochemicals without using it at all.
Their idea was to grind fluorspar and a potassium phosphate salt into a powder instead of reacting it with acid. They placed the two salts in a stainless-steel jar together with a small steel ball, then used a machine called a ball mill to shake the jar for a few hours.
As the jar moved, the steel ball repeatedly hit the salts, grinding them like a hands-free mortar and pestle. This also caused a chemical reaction that produced a new powdery compound that the researchers named Fluoromix.
The researchers could then make compounds that contain fluorine by combining Fluoromix with water and other chemical ingredients. To confirm that this could be work in place of using the dangerous hydrogen fluoride gas as a source of fluorine in reactions that produce fluorochemicals, they used Fluoromix to make over 50 different ones, including some that are necessary ingredients for drug compounds, fertilizers and antibiotics.
Patel says that the milling process his team used is new in fluorine chemistry but has been widely used as a more environmentally friendly approach in other chemical manufacturing processes, like for creating parts for novel batteries. This it because it works at room temperature so it makes the process less energy-intensive than both producing and using hydrogen fluoride.
David O’Hagan at the University of St. Andrews in the UK says that the new method could bring about a change in an industry that is still using methods that go back to the 1600s. “It is in a very positive way surprising that you can avoid hydrogen fluoride, and hydrogen fluoride has led to many industrial accidents and deaths. To me, this looks like it could be the beginning of something new for this industry,” he says.
“This seems like a breakthrough, making direct use of fluorspar in this way is something of a Holy Grail that has had virtually no success so far,” says James Clark at the University of York in the UK. He says that the researchers now need to work out how exactly the new method stacks up against more traditional approaches, in terms of price and how well it can be adapted for very large, industrial quantities of fluorspar.