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Abstract

Response surface methodology was successfully employed in the optimization of the production of lubricating oil from re-refined used lubricating oils. The re-refined lubricating oil was obtained from caustic treatment and vacuum distillation of used automotive gasoline engine lubricating oils. A 2³ factorial design augmented with seven experimental points to form an orthogonal central composite design (CCD) to accommodate all second order effects was employed in this study. Lubricating oil additives namely oxidation/corrosion inhibitor, detergent and dispersant were used as independent variables. The extent of deterioration of the lubricating oil was investigated using neutralization number, sludge deposition and corrosion of carbon steel as responses. Optimal additive levels of 0.99 % (v/v) oxidation/corrosion inhibitor, 1.33 % (v/v) detergent and 3.0 % (v/v) dispersant; were used with a blend of re-refined used lubricating oil and virgin bright lube stock in the ratio 3:1 to obtain an SAE 40 grade lubricating oil suitable for automotive gasoline engines.