recycling oil in car engine

Heating would drive off any fuel/light ends. I believe they add sulfuric acid to cause flocculation - detergents/dispersants/VI improvers become insoluble removing soot/other particles as they drop out. There are solvents, short chain alcohols and ketones that will accomplish the same thing without the acid - filtration then evaporation of the diluted used oil leaves one with basestock, filtered out additives/soot and condensed solvents for reuse.

thanks a lot for your answers.
i want to do this experiment in a lab but without adding acid, could you please tell me what are exactly formula (solvents, short chain alcohols and ketones).
i know how to do it with acid but i don't know what should i add instead of acid?

Been awhile since I did the tests
Isobutyl acetate (IBA), methyl hexyl ketone (MHK) and methyl ethyl ketone (MEK) all worked to varying degrees. Believe I thinned the used oil 1:4 with solvent - passed through fine filter (0.2 micron) or centrifuged to get rid of soot. Beginning used oil dark, opague - resulting oil brown to amber. Evaporate off solvent or add some water to cause the solvent (water soluble) and oil to separate so that majority of oil can be poured off- believe oil lighter. IBA and MHK left alot of the additives intact (oil brown) - oil viscosity similar to new whereas MEK dropped most of the additives, oil amber with much lower viscosity. Believe isoamyl alcohol and pentanol/hexanol also worked