Optimization of Base Oil Recovery from Used Lubricating Oil through Extraction-adsorption using Response Surface Methodology

Response surface methodology, based on the central composite design, was successfully applied to study the optimum conditions and the statistical effects of the variables on base oil recovery from used lubricating oil using a two-step process for oil recovery: solvent extraction with 1-butanol compared to methyl ethyl ketone, followed by adsorption using activated clay. 1-Butanol was found to be more effective than methyl ethyl ketone for oil extraction and sludge removal. The optimum conditions for oil extraction were determined to be a 1-butanol-to-oil ratio of 3.2:1 at 57ºC and a mixing speed of 600 rpm. The removal of sludge was achieved at 12.08% by weight. Residual contaminant adsorption from the extracted oil was optimized using 55% activated clay by weight, stirred at 200 rpm 130°C. The physical properties of the treated oil were analyzed, revealing a specific gravity of 0.84, a viscosity index of 144, and a color reduction from 8.0 to 1.0. The chemical properties were analyzed by IR spectroscopy, showing reduced nitration, oxidation, sulfation, total base number, and the absence of water. Additionally, the GC-MS composition analysis of the treated oil revealed that 99.64% of the oil was composed of alkanes, with a trace amount of aromatic compounds and no naphthalene or polycyclic aromatic hydrocarbons (PAHs). The elemental content analysis by atomic emission spectroscopy showed that the residue was less than 1 ppm. As a result of the recovery under optimum conditions, the treated oil has chemical and physical characteristics that make it suitable for repurposing as base oil in industrial applications.