Recovery of Base Oil from Used Oil through Solvent Extraction Followed by Adsorption: A Review

Base oil is the major component of lubricating oil, which is present in its original form and used lubricating oil in a sufficient amount. This review article focuses on the recovery of base oil from used oil through solvent extraction followed by adsorption. Different solvents and various solvent-to-oil ratios are studied. Solvent selection is based on its ability to selectively dissolve the base oil from used oil and to reject the impurities in the solution. The percentage yield and quality of extracted oil usually depend upon the nature of the solvent, solvent-to-oil ratio, and nature of impurities. Various solvents and solvent-to-oil ratios are studied. However, results show that methyl ethyl ketone (MEK) is the best solvent because it gives the maximum sludge removal, is more easily recovered, and also has a low cost. A two-phase system occurs after adequate mixing of solvent and oil. Before solvent addition, oil is dehydrated to remove water present as impurities, and then light hydrocarbons are removed using vacuum distillation. After solvent addition, the extracted phase is separated, leaving behind the sludge phase, which consists of aggregates of impurities. The solvent is evaporated from the extracted phase. The extracted oil is put in contact with a suitable adsorbent to absorb the aromatic contents and heavy metals in it. In the end, additives are added to the recovered oil for the formulation of a new lubricant.