De-ashing lubricating oils

Claim 1

In a process for the production of an essentially ash-free oil stock from a lubricating oil containing ash-forming components wherein the process comprises: (a) contacting said lubricating oil with an aqueous solution of a treating agent comprising a suitable ammonium salt under conditions sufficient to dispense said agent in said lubricating oil and to react said agent with ash-forming components of said lubricating oil; (b) removing a major portion of the water from the mixture resulting from combining said aqueous solution and said lubricating oil; (c) heating at least a portion of the product resulting from step (b) in the temperature range of about 300° to about 420° C. for a period of time sufficient to increase the amount of ash-forming components that can be removed from the oil; (d) cooling the product from step (c) to a temperature in the range of about 100° to about 180° C.; and (e) separating solids from the product of step (d); the improvement comprising conducting step (c) by passing the oil from step (b) into a soaking vessel containing a large volume of said oil having a soaking temperature in the range of about 300° C. to about 420° C. before the oil from step (b) is heated to a temperature higher than 200° C. and passing portions of said large volume of oil through a heating coil wherein said oil is heated to a temperature in the range of 300° C. to 420° C. and recycled to said soaking vessel wherein the residence time for the oil in said soaking vessel is such that the fouling of the heating coil is less than it would be if the oil from step (b) were heated to the same temperature by being passed directly through the heating coil.