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Regeneration of used motor oil by supercritical carbon dioxide

This study was aiming at regeneration of used motor oil (UMO) by separation of engine wear residues (lees) using supercritical carbon dioxide. The experiments were carried out at 35-65 MPa of pressure and 70-80 o C of temperature. The UMO purification from lees was achieved by the use of sand as porous media filter at lower temperature. The samples extracted at 70 o C were clean, transparent and reddish-brown. Similar clean samples were obtained at 80 o C at 45 MPa only. The temperature effect was mainly revealed in its impact on the purification of the extracted used motor oil samples, while the cumulative recovery after three runs varied from 50 % to 60 % in the pressure range of 45-65 MPa at both temperatures after three runs. The complex interplay between the solubility and the kinetics of the process requires further study. The proposed method can be an alternative to the existing methods of cleaning used motor oil.