Infrared Spectroscopic Analysis of Changes in the Physicochemical Properties and Hydrocarbon Composition of Used Hydraulic Oil During Operation

The article investigates changes in the physicochemical properties and hydrocarbon composition of used L-HL 46 hydraulic oil during operation, comparing it with fresh oil. The samples were analyzed using GOST methods across 12 parameters. As a result of operation, the kinematic viscosity at 40 °C decreased from 46 to 30.56 mm²/s (approximately 33.6%), the viscosity index decreased from 103 to 90, and the flash point dropped from 226 to 212.9 °C, while the acid number increased from 0.5 to 0.8 mg KOH/g. Infrared spectroscopy revealed an approximately 3% decrease in the content of paraffinic and naphthenic hydrocarbons and the occurrence of mild oxidation, while indicating that the chemical composition of the oil's hydrocarbon base remained unchanged. Treatment with alkali and adsorptive purification using Navbahor bentonite did not affect the principal hydrocarbon composition of the oil, indicating that the used oil can be regenerated and reused.