Optimisation of Base Oil Regeneration Using Response Surface Methodology From Spent Lubricating Oil Through Binary Solvent Extraction Process

Abstract

Spent lubricating oil (SLO) is a high-pollutant material that requires responsible management. It may cause adverse effects to the environment when dumped into the ground or wastewater streams, resulting in soil and groundwater contamination. This research investigates the regeneration of spent lubricating oil using a binary solvent (hexane and methyl ethyl ketone). The laboratory experiment was based on a central composite design with two levels using response surface methodology. The SLO physicochemical properties gave the following undesired characteristics: low flash point (159^oC), high specific gravity (0.9887), high kinematic viscosity at 40^oC and 100^oC (37.7 cSt and 11.4 cSt), high total acid number (3.9 mg KOH/g) and high colour index (11.0). The experimental run with a solvent-to-oil ratio of 3.99, mixing time of 30 min and agitation speed of 599 rpm was chosen as the optimum combination using statistical analysis. The optimum run yielded 77.20%, ash content 0.29%, and sludge removal percentage 11.25%. The adsorption process using kaolin achieved an 88.88% reduction in zinc ions concentration, while a 46.32% reduction was achieved for iron ions. However, a slight reduction in percentage yield (2.77%) was observed after the adsorption process. The regeneration process gave a yield of 75.06%. Physicochemical parameters of regenerated base oil; specific gravity (0.8699), kinematic viscosity at 40^oC and 100^oC (26.1 cSt and 7.3 cSt), flash point (192^oC) conformed to ASTM standards while total acid number (0.96 mg KOH/g) and colour index (6) were slightly above the required values. The results showed that regenerated base oil has a comparable quality to virgin base oil (SN 150), indicating the process's effectiveness and the possibility of utilising the oil safely.