Chemical composition of used motor oils
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During engine operation, lubricating oil accumulates not only insoluble contaminants, but also soluble products of aging such as “resins” and also heavier substances that cannot be desorbed from silica gel by alcohol- benzene or acetone—benzene mixtures. The relative content of hydrocarbon groups is thereby reduced, mainly through “dilution” of the oil by aging products. The ratio of components in the total paraffinic—naphthenic and aromatic fractions of the oil is changed only slightly by operation in the engine.
According to the infrared spectra, the paraffinic-naphthenic fractions of new and used oils do not differ substantially from each other.
The aromatic fractions of the used oil, in contrast to the fractions of the new oil, contain oxygen groups that can be removed only by catalytic hydrotreating.
Oxygen groups in the aromatic fractions are detrimental to the thermal-oxidative stability of the oil.
KeywordsAlcohol Acetone Benzene Hydrocarbon Infrared Spectrum
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