Reclaiming used lubricating oils

A process for the production of an essentially pure lube oil stock from a used lubricating oil containing ash-forming and additive components which comprises:

• (a) contacting said used lubricating oil with an aqueous solution of a treating agent consisting essentially of an ammonium salt selected from the group consisting of ammonium sulfate, ammonium bisulfate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and mixtures thereof, said treating agent being present in an amount at least sufficient to react with essentially all of the metal constituents in said used lubricating oil, wherein said contacting is carried out at a temperature in the range of from 60.degree. to 120.degree. C. and a pressure in the range of 1 atmosphere to 250 psia and wherein said agent is kept in contact with said used lubricating oil for a time sufficient to disperse said agent in said used lubricating oil and to react said agent with essentially all the ash-forming metal components of said used lubricating oil;
• (b) removing a major portion of water and light hydrocarbon components from the resulting aqueous reaction mixture from step (a) by maintaining said mixture at a temperature in the range of 110.degree. to 140.degree. C. and a pressure in the range of 5 to 25 psia for a period of time sufficient to effect removal of a major portion of water and light hydrocarbons therefrom;
• (c) separating the oil phase from the residual mixture consisting essentially of used lubricating oil and reacted treating agent resulting from step (b) by filtration;
• (d) heating the resulting filtered oil from step (c) to a temperature in the range of 200.degree. to 480.degree. C;
• (e) contacting the resulting heated oil from step (d) with at least one adsorbent selected from the group consisting of activated carbon, silica gel, clay, bauxite and alumina in a contacting zone;
• (f) hydrotreating the resulting oil from step (e) by contacting said oil with hydrogen and a hydrotreating catalyst at a temperature in the range of 200.degree. to 430.degree. C. and at a pressure in the range of 150 to 3000 psia;
• (g) stripping the resulting hydrotreated oil from step (f) in a stripping zone maintained at a temperature in the range of about 280.degree. to 395.degree. C. and at a pressure in the range of atmospheric to 50 psia;
• and thereafter
• (h) recovering the resulting stripped oil from said stripping zone as a product of the process.