What is the process for used oil purification?

The process for used oil purification typically involves:

Heating the oil to reduce viscosity.
Filtration to remove solid particles and sludge.
Vacuum dehydration to remove water and dissolved gases.
Centrifugation to separate heavier contaminants.
Chemical treatment to neutralize acids and remove oxidation products. After purification, the oil is tested for quality and can be reused or further refined.