Regeneration of used motor oil by supercritical carbon dioxide

S. Rudyk, P. Spirov
Sultan Qaboos University,

Keywords: used motor oil, regeneration, carbon dioxide


Motor oil is used for lubrication in all kinds of cars and engines, which leads to large quantities of used motor oil. 570 million litres of used motor oil are produced every year in the United States of America (USA) alone, and over 50 % of it is recycled. The carcinogenic materials contained in used motor oil may cause both short- and long-term effects if they are allowed to enter the environment through the soil. Over 40% of the USA’s oil pollution comes from improper disposal of motor oil. The re-utilization of used motor oil contributes to the saving and conservation of petroleum natural resources, saving on energy and money used for their production. The used motor oil is a valuable product that can be refined into a base stock for lubricating, transformer and hydraulic oil, or used for heat generation. Extraction of used lubricating oils with supercritical carbon dioxide (SC-CO2) has been proposed as an environmentally friendly process (Krukonis, 1994). The objective of the study on the ability of pure CO2 under supercritical conditions to extract used motor oil from the sand was aiming at two applications: remediation of the contaminated sand by removal of the used motor oil and regeneration of the used motor oil by removal of the pollutants and impurities. The model of contaminated sand was prepared by mixing sand with used motor oil. SC-CO2 extraction was carried out in two runs at 35, 45, 55 and 65 MPa at 70 oC and 80 oC. In the pressure range of 35–65 MPa, the cumulative recovery of used motor oil at 70oC varied from 14–60 %; and at 80 oC ranged from 21–59 %. The total recovery of used motor oil from the sand models at 55–65 MPa was above 80 %. Substantial effect of temperature on recovery was not observed. The temperature effect was in its impact on the quality of the extracted used moto oil samples. A visual inspection of all of the investigated sand models at the end of the experiments at 70 oC revealed that the sand was clean. The dark black color had disappeared, and the sand was dry. At all pressures at 80 oC, the sand was black at the end of the experiments. At higher temperatures, the hydrocarbon part of used motor oil is not separated from the contaminants, a factor which is relevant for the purposes of sand remediation. On the other hand, lower temperatures facilitate the extraction of the hydrocarbon part of used motor oil, which suggests that this method could be employed for the regeneration of used motor oil using SC-CO2. Although the cost of the process has to be yet estimated, the method we describe seems to be fast, easy to manage, does not require special materials such as membranes, and is capable of treating small volumes of used motor oil.