Regeneration of used lubricant oil by ethane extraction

Liquid and supercritical ethane has been used as a solvent for the recycling of used lubricant oils. The aim of the work has been to identify the best processing conditions to separate base oil suitable for the formulation of new lubricants, avoiding the coextraction of oxidation products and metallic compounds.The effect of pressure (40–145 kg/cm2) and temperature (25–95 °C) on the separation efficiency and yields has been investigated. In the pressure range analyzed no effect on metallic compounds removal was found. However, it did affect the extraction yields (they increased with pressure) and the separation of oxidation products (removed more efficiently at low pressures). As regards to temperature, at a given pressure the extraction yields were found to be independent of the variable as long as ethane remained as a liquid, but they decreased with increasing temperature with supercritical ethane. As expected, gas ethane could not dissolve base oil at all. On the other hand, at constant pressure metallic and oxidation compounds removal increased as temperature was increased.