Reclaiming used lubricating oil

A process for the production of an essentially ash free oil stock from a lubricating oil containing ash-forming components comprising:

• (1) contacting said lubricating oil with an aqueous solution of a treating agent comprising an ammonium salt capable of reacting with the ash forming components and rendering them removable under conditions sufficient to disperse said agent in said lubricating oil and react said agent with ash-forming components of said lubricating oil;
• (2) removing a major portion of the water from the mixture resulting from combining said aqueous solution and said lubricating oil;
• (3) separating solids from the oil resulting from step (2) to obtain a partially purified oil;
• and
• (4) vacuum distilling the partially purified oil with steam dilution in a fractionation column to obtain a plurality of boiling range oil fractions characterized by the fact that said fractionation column is divided into three sections of a total drawoff tray positioned in a lower portion of the column and a partial drawoff tray positioned in an upper portion of the column and a heavy sidedraw fraction is withdrawn from the total drawoff tray, a light sidedraw fraction is withdrawn from the partial drawoff tray, an overhead fraction is withdrawn from the top of the column, further characterized in that a portion of the oils in the overhead fraction is recycled above said partial drawoff tray to provide additional reflux, a first portion of the oils in the heavy sidedraw fraction is recycled below said total drawoff tray, and a second portion of the oils in the heavy sidedraw fraction is recycled above said total drawoff tray in an amount sufficient to assure that the total drawoff tray is not drawn dry.