Statistical Model for Re-Refining of Used Lubricating Oil by Solvent Extraction and Bentonite Clay Adsorption Method

Abstract

Lubricating oils are widely using for reducing friction and wear by interposing a film of material between rubbing surfaces, but these oils lose their properties after a certain period of use. For protection from environmental pollution and the economic side, used oil can be recycling and purifying by various methods. Solvent extraction+ clay adsorption technique is one of the cheapest, competitive, and most efficient processes experienced in the recycling of used lubricating oils. After vacuum filtration of the oil is distilled by vacuum distillation and extracted by Methyl Ethyl ketone as a solvent. Bentonite clay (400 gm) is activated by mixing (100 ml) diluted sulfuric acid under 100 °C for 4 hours. The extracted oil is treated by activated clay (Clay/Extracted oil =%15 wt) at (120°C) with mixing speed (500 rpm) for 90 minutes. However, the capability of this process largely depends on the optimum condition of each parameter in the recycling process. For this purpose, the experiments of three variables (Temperature, mixing speed, extracted solvent/oil ratio) at three levels for the extraction process are designed by Design-Expert software. The optimum condition for the extracted process is (Solvent/used oil=3, Temperature =58 °C, mixing speed =710 rpm) confirmed by ANOVA. The recovered oil with 72% yield is analyzed in the laboratory, found it very close to base oil specifications.