Process for treating used industrial oil

Abstract

A process for rerefining used industrial oil comprising the steps of: (i) contacting said oil with an aqueous solution of the basic salt of an alkali metal to precipitate metal contaminants, polar compounds or particulates from said oil and to neutralize acid that may be present in said oil; (ii) separating bulk water and solid contaminants from said oil; (iii) separating fine particulates and remaining suspended water from said oil; (iv) vacuum drying said oil at a temperature in the range of about 250.degree. F. to about 400.degree. F. and a pressure in the range of about 2 to about 50 torr to remove dissolved water and light hydrocarbons from said oil; (v) contacting said oil with (A) from about 0.1 to about 3% by weight based on the weight of said oil of a polyfunctional mineral acid or the anhydride of said acid and (B) from about 0.1 to about 5% by weight based on the weight of said oil of a polyhydroxy compound, with the proviso that component (B) is in excess of component (A), until substantially all metallic contaminants in said oil have reacted with component (A) or (B) to form reaction products; (vi) separating the reaction products formed in step (v) and any unreacted components (A) or (B) from said oil; (vii) hydrotreating said oil in the presence of hydrogen and a hydrogenation catalyst at a temperature in the range of about 500.degree. F. to about 800.degree. F. to remove residual polar materials and unsaturated compounds; and (viii) stripping said oil to remove light hydrocarbons with boiling point below about 600.degree. F.