A two-stage coupling process for the recovery of base oils from used lubricating oils

This study aims to apply a two-stage solvent extraction and adsorption principles for base oil recovery from used lubricating oils (UBO). Methyl-ethyl ketone was utilized as the solvent for extraction and activated carbon (AC) from unripe plantain peels as the adsorbent. The activities of the solvent to oil proportions from 1:1 to 5:1 on lube oil recovery were analyzed in terms viscosity of the oil, total base number (TBN) of lubricating oil, and percent weight of metallic contents removal from used oil. The results confirm that solvent to oil ratio of 3:1 gave excellent efficiencies relating the UBO to a treated base oil (TBO) with the highest removal of contaminants, increased viscosity, high TBN after the two-stage treatments. The results after solvent extraction at varying temperatures of 30, 45, 60 °C showed the TBN increased to 32% (10.21 mgKOH/g from an initial UBO value of 6.90 mgKOH/g) at 60 °C extraction temperature. After the adsorption stage, the removal of metallic contaminants at the 60 °C extractive temperature and AC 15 wt% loading was 91% for calcium and over 91% for zinc. The optimum solvent to oil ratio of 3:1 at 60 °C yielded a base oil with a kinematic viscosity of 90.23 centiStokes, a flashpoint of 203 °C, the density of 0.909 g/ml and sulphur content of 0.64 wt%. This refined base oil obtained had close similarities with fresh Ram SN500 base oil.