How is used oil purified?

Used oil is purified through processes like filtration, centrifugation, and vacuum dehydration. The oil is first heated to lower viscosity, making it easier to filter out contaminants such as dirt, metal particles, and sludge. Filtration and centrifugation remove solid particles, while vacuum dehydration eliminates water and dissolved gases. Some used oils, like transformer oil, may also undergo chemical treatment to remove acids and other degradation products.