Development of Lubricants Using Re-Refined Base Stocks—An Effort toward Circular Economy

Re-refining of used lubricating oil is an economically attractive and effective recycling method that contributes significantly to resource conservation and environmental protection. The effective re-refining process of used lubricating oil undergoes thorough purification to remove contaminants and to produce high yield and good quality base oil suitable for reuse in lubricant formulation. Used lubricating oils have various hazardous materials, these can be processed with safe and efficient methods required to recover high-quality base oil products. Typically, used lubricating oil is a mixture of various types of additives, base oils, and viscometric grades as per the different types automotive and industrial applications. Re-refined base oils can be re-used to produce lubricants such as industrial and automotive lubricants like passenger car motor oils, transmission fluids, hydraulic oils, and gear oils. API classified base oils into two categories namely mineral base oils API Group I–III and synthetic base oils Group IV–V. Re-refined base oils meeting API Group I and II quality standards are mostly produced by re-refiners.

In this article, the author has evaluated lubricating oils: gear oil meeting API GL4 specifications based on 25% re-refined base oil to assess the performance of these lubricants in comparison to conventional base oil-based lubricants. This study includes physicochemical tests, lab performance tests (rust, corrosion, shear stability, and oxidation), and tribological performance tests, i.e., weld load, wear scar diameter, and friction performance by MTM was also evaluated. Test results show similar performance in terms of low temperature, oxidation, and friction performance in 25% re-refined base oil-based lubricant with respect to conventional base oil-based products.