désulfurer

A technical, industrial verb: to desulfurize, to remove sulfur or sulfur compounds — used in winemaking (désulfurer un vin, removing excess sulfites) and in heavy industry (désulfurer un carburant, du charbon). Outside these specialist contexts, an everyday speaker has little reason to use it.

• Le vigneron désulfure son vin avant la mise en bouteille. — The winemaker removes excess sulfites from the wine before bottling.
• L'usine désulfure le pétrole brut avant raffinage. — The plant desulfurizes the crude oil before refining.
• De nouvelles normes obligent à désulfurer davantage les carburants. — New standards require fuels to be desulfurized more thoroughly.

This is strictly a chemistry/industry term about sulfur compounds — don't stretch it as a general word for 'purify' or 'clean,' which would sound like a category error outside a technical context.