Changes in the hydrocarbon composition of used marine motor oils

This study focuses on the analysis of used marine engine oils by gas chromatography–mass spectrometry (GC-MS), which makes it possible to identify chemical degradation, oxidation products, fuel contaminants, and additives and thereby assess the degree of oil degradation and the effectiveness of its recycling. The objective of the study was to investigate changes in the chemical composition of marine engine oil during service. Fresh and used samples of Shell Rimula 15W-40 and TPEO 12/40 oils were analyzed. A comparative analysis of the chemical composition of fresh and used oils revealed the predominance of initial hydrocarbons in fresh oil, a sharp increase in oxygen-containing compounds in used oil, the appearance of nitrogen-containing compounds in used oil, changes in aromatic and polycyclic aromatic hydrocarbons, and the appearance of organohalogen compounds. Analysis of the GC-MS data clearly demonstrates that used marine engine oil is a complex mixture resulting from deep chemical transformation of the base oil and additives. The content of oxygenand nitrogen-containing compounds, including oxidation and nitration products, increases sharply; condensed aromatic structures formed as pyrolysis products appear; and the proportion of light hydrocarbons decreases. These changes indicate the need for timely oil replacement, since its functional properties, including viscosity, base number, and detergency, deteriorate significantly, while accumulated aging products may cause corrosion and deposits in the engine. The study concludes that GC-MS is an effective method for monitoring lubricant characteristics and determining the degree of lubricant degradation in engines .