Patent ID: 8088276

Claim:
A method of re-refining used oil comprising the steps of: processing the used oil to remove select constituents of the used oil; introducing liquefied propane into the used oil to form an oil/propane mixture; processing the oil/propane mixture in an extraction process that includes a plurality of extraction towers linked in series, wherein each extraction tower has an inverted cone shape to promote enhanced removal and recovery of undesired components that settle in the tower and are discharged to a storage container; and transferring the oil/propane mixture from the last extraction tower in the series to at least one propane recovery tower where propane is withdrawn from the mixture and the used oil is ready for further processing, wherein the method further includes the steps of distilling the oil in a distillation apparatus after the propane extraction process; withdrawing at least a portion of at least one distillate fraction from the distillation apparatus; delivering at least a portion of the at least one withdrawn distillate fraction to at least one other distillation apparatus arranged in series for withdrawing at least a portion of at least one distillate fraction from the at least other distillation apparatus; and delivering at least a portion of the at least one withdrawn distillate fraction to a hydro-fining process, wherein the oil is heated prior to introduction to the distillation apparatus and the at least one withdrawn distillate fraction is heated after withdrawal from the distillation apparatus and prior to introduction to the at least one other distillation apparatus.