INVESTIGATION OF THE PHYSICOCHEMICAL PROPERTIES OF RECOVERED OIL BY DETERMINING THE OPTIMAL AMOUNTS OF ACIDS AND ADSORBENTS IN THE USED OIL RECYCLING PROCESS

Abstract. This study explores the purification methods of used lubricating oils from internal combustion engine lubrication systems using hydrochloric acid (HCl), nitric acid (HNO₃), sulfuric acid (H₂SO₄), acetic acid (CH₃COOH), and trichloroacetic acid (CCl₃COOH). The research focuses on the physical and physicochemical properties of the treated oils, including kinematic viscosity, viscosity index, density, flash and pour points, water content, total acid number, and infrared (IR) spectroscopy analysis. The results indicate that treatment with acetic and trichloroacetic acids improved the physical and physicochemical properties of the oil, achieving characteristics comparable to new lubricants. Treatment with sulfuric and nitric acids allowed for 70–80% restoration of the oil’s properties; however, an increase in the acid content in the adsorbent composition was observed when used to enhance color improvement. In the case of hydrochloric acid treatment, the oil’s properties were partially restored, and it was found that unactivated bentonite could yield positive results for improving the color. The findings suggest that the proposed oil regeneration process can partially meet the demand for fresh lubricants and contribute to reducing the overall cost of oil production.