Characterisation and Analysis of Used Lubrication Oil: Implications for Performance and Efficiency

The present work demonstrates a two-step process for effectively recovering and restoring used SAE 20W40 lubricating oil through thermal vacuum distillation and chemical treatment with Zinc Dialkyl Dithiophosphate (ZDDP). The vacuum distillation process removes moisture, volatiles and degraded fractions, and the ZDDP additive replaces broken-down antiwear and oxidative stability characteristics. Untreated, treated, and virgin oils underwent a complete physicochemical characterisation including density, viscosity, viscosity index, flash point, fire point, pour point, specific gravity and Total Acid Number. This indicates that the physicochemical properties of the treated oil were like those of the commercial SAE 20W40 oil. Among them, the Total Acid Number decreased from more than 10 to 2 mg KOH/g, while the viscosity index experienced a significant improvement. In addition, an economic analysis of costs estimated the treatment process to be cost-effective at approximately 25-40 % lower cost per litre than virgin oil at market rates. This demonstrates the viability and sustainability of the re-refinement integrated into industrial uses and the recovery of lubricants from municipalities. Major Findings: The two-stage treatment enhanced performance by increasing viscosity from 167 cP to 266 cP and raising the viscosity index from 51 to 81. TAN decreased from >10 to ~2 mg KOH/g, indicating improved chemical stability. Enhanced flash/fire points and a reduced pour point (–18 °C) confirm suitability for extreme thermal conditions.