Research project Title: Recycling of used lubricating oil to base oil using solvent extraction and clay adsorption

Abstract

The management of waste lubricating oils is particularly important because of the large quantities are generated through transport and Industrial activities. These waste oils have detrimental effect on the environment if not properly handled, treated or disposed to the environment. Thus, it is imperative to find more environmentally sustainable ways to dispose used lubricating oils through recycling. The main aim of the study was to determine the optimum extraction condition for the extraction of base oil from used lubricating oil. For this, first four different solvents namely ethanol, isopropanol, n-butanol and hexane were examined for maximum oil yield. With the solvent that gives maximum oil yield solvent to oil ratio 1:1, 2:1, 3:1 and 4:1 and extraction time 24hr, 48hr, 72hr and 96hr were considered for optimization. From the experiment it was found that a maximum yield of 74.55% was obtained using n-butanol solvent. On the basis of n-butanol solvent further experimental investigation was performed by implementing full factorial experimental design. According to the study a maximum oil yield of 86% was obtained at 4:1 solvent to oil ratio and 96hr extraction time and a minimum oil yield of 21% was obtained at 1:1 solvent to oil ratio and 24hr extraction time. ANOVA analysis was showed significant effect of solvent to oil ratio and extraction time on oil yield (P value < 0.005). When a solvent to oil ratio increased from 1:1 to 4:1, the oil yield increased from 25.1% to 86% for 96hr extraction time. A sharp increase of percentage oil yield was observed as the solvent to oil ratio increased. On the other hand no significant percentage oil increment was observed with increment of extraction time above 48hr. Therefore, the optimum extraction time is 48hr. Quadratic regression model equation was obtained to describe the effect of operatic conditions on base oil yield. The properties (specific gravity, water content, ash content, kinematic viscosity, viscosity index, flash point, pour point and metal content) of the base oil extracted under a condition that gave maximum oil yield were determined and compared to those of virgin lubricating oil and base lubricating oil. The result obtained indicated that the properties of recycled oil were within the standard of base lubricating oil. Therefore, the recycled oil can be used as base oil which is the fundamental component in manufacturing of different types of lubricating oil. Based on the preliminary feasibility study, the production process was found to be feasible at 3:1 solvent to oil ratio with rate of return on investment equal to 22.4% and payback period of 2.8 years. According to the study also the process is not economically feasible for solvent to oil ratio more that 3:1 and therefore, the optimum solvent to oil ratio is 3:1.