Abstract: A process is provided for removing contaminants from waste lubricating oil. The waste oil is contacted with one or more of the pretreatment chemicals ammonium sulphate, ammonium bisulphate, ammonium dihydrogen phosphate, diammonium phosphate, calcium hydrogen phosphate, phosphoric acid, calcium sulphate, aluminum sulphate, and magnesium sulphate. The contacting step is performed at a temperature of at least about 650.degree. F. The oil mixture is then filtered to remove the contaminants. The pretreatment chemical is preferably added in the absence of water, thereby reducing the amount of water to be removed from the oil.

Abstract: A double-walled drill pipe, having a plurality of outer pipe lengths connected end-to-end and a plurality of inner pipe lengths connected end-to-end and concentrically disposed within the outer pipes and defining an annular fluid flow passageway and a return flow passageway, is provided with an inner pipe support arrangement for minimizing stresses applied to the inner pipe lengths when blows are applied to the outer pipe lengths to drive a cutting bit. Each outer pipe length is provided with a ledge on its inner surface to provide a seat for an abutment on the outer surface of its adjacent inner pipe. When a blow is applied to the outer pipe lengths, the outer pipe is forced downwardly but due to inertial effects, the inner pipe unseats and is permitted to fall under its own weight. A resilient shock ring may be positioned on the length to cushion the fall of the inner pipe and provision may be made to limit axial displacement between the inner and outer pipes.

Abstract: A process is provided for removing contaminants from waste lubricating oil. The previously untreated waste oil is contacted with decolorizing clay and the mixture is heated to and retained for a period of time at a temperature in the range of about 650.degree.-725.degree. F., to render the mixture filterable. The product clay-oil mixture is cooled and filtered to produce an oil filtrate reduced in contaminants. The clay contacting step may optionally be performed in a hydrogen atmosphere. The oil product can be used for non-critical uses or further upgraded by conventional methods.

Abstract: A process is provided for removing metal contaminants from used lubricating oil. The used oil is contacted with an aqueous solution of aluminum sulphate and ammonium sulphate at elevated temperature to form compounds of the metal contaminants in an aqueous phase which is phase separable from the oil. An oil product reduced in metal contaminants is thereby produced which is suitable as a cheap fuel or lubricant.