Environmentally friendly recovery and characterization of oil from used engine lubricants

The present paper demonstrates the review of some acid processes as well as development of some new solvent processes for reclamation of used lubricating oils. The conventional processes are found to be of low yield (similar or equal to-50%), laborious, time consuming and environmentally hazardous, because of residual acidic sludge. Based on the findings, a new modified Aluminium sulphate-sodium silicate-acid-base method employing a small quantity of acid and giving a high yield (similar or equal to 60%) is proposed. Further, to avoid use of acid, new regeneration processes based on solvent extraction were investigated. They are termed CCl4-alcohol method, Dodecane-alcohol method and Toluene-alcohol method. These processes are not only cost effective in terms of complete solvent recovery, but are rapid, less time consuming, more environmentally friendly and gave a high yield (70-75%). The virgin lubricants (Castrol GTX and Rimula-C) as well as oils recovered by different methods were also characterized physicochemically to determine kinematic viscosity, density, refractive index, carbon distribution, wear scar diameter, % Conradson carbon residue, % ash, % chloride, pour point, etc. Results obtained show that many of the physico-chemical properties of the recovered oils are in good agreement with those of virgin oils. The n.d.M analysis was also performed which shows that virgin oils have 73 +/- 3% paraffinic carbon, 26 +/- 3% naphthenic carbon and about 1% aromatic carbon. The recovered oils also showed nearly the same chemical composition. The UV-Visible spectra of the recovered oils are all similar to those of virgin lubricants. The results suggest that the oils recovered by solvent treatments, particularly Dodecan-alcohol and Toluene-alcohol methods, may serve for lubrication purposes and can be rendered as excellent as virgin lubricants with the addition of certain additives. The proposed methods may be considered as alternative cost effective green techniques for acid reclamation processes and being the motivation of the present investigation.