Efficient Reclamation of Base Oils from Spent Lubricants Using Novel Ternary Solvent Combinations

Abstract

To mitigate the harmful environmental impacts associated with the improper disposal of used engine oils and to reduce dependence on fossil fuel sources, there has been an increasing need to recycle the spent engine oils more extensively than ever. In this work, the recovery of base oils from spent lubricating oils using a novel solvent extraction combination was investigated. Laboratory-scale experiments were conducted on used engine oils collected from different service stations. Two ternary systems were employed in this study for the recovery of base oil from spent lubricants: (a) acetonitrile (35 vol.%), xylene (40 vol. %), and n-heptane (25 vol. %); and (b) dimethyl sulfoxide (DMSO) (35 vol. %), toluene (40 vol. %), and n- hexane (25 vol. %). Various solvent-to-spent lubricant ratios were investigated, especially 1:1, 2:1, 4:1, and 6:1 (wt/wt) under atmospheric pressure. The extraction process was conducted at various temperatures (60, 70, 80, and 90°C) and mixing durations (15, 30, 45, and 60 minutes), with a constant stirring speed of 500 rpm maintained throughout all experiments.  Post extraction, the recovered base oil underwent a bleaching process using hydrogen peroxide followed by activated bentonite. Hydrogen peroxide was applied in varying concentrations (5%, 10%, and 15% v/v %), while the amount of bentonite used ranged from 1 to 5 g/100 mL of oil. The optimal bleaching performance was observed at 15% (v/v) of hydrogen peroxide concentration combined with 5 g of bentonite. The experimental results demonstrated that solvent system (a) yielded the highest base oil recovery rate of 86.6% under the conditions of 70°C, a 6:1 solvent to oil ratio, and a 60-minute extraction time. In contrast, solvent system (b) achieved a maximum recovery rate of 74.4% at 80°C, under the same ratio and extraction duration.