Study of the Reasons for Discoloration of Hydrotreated Naphthenic Lube Base Oil under Ultraviolet Radiation

In this paper, the reasons for discoloration of hydrotreated naphthenic lube base oil were studied in detail. To define compositional factors associated with the color deterioration, first liquid-solid chromatography was used to separate hydrotreated naphthenic base oil into five different fractions, i.e., saturates, monoaromatics, diaromatics, polyaromatics, and polars. Then the sensitivity of each fraction to ultraviolet radiation was evaluated through ultraviolet radiation testing. The results of the tests indicate that polyaromatics and polars are the main precursor of color and deposits, respectively, and the compositions of two fractions were characterized by a series of instrument technology including elemental analysis, gas chromatography-mass spectrometry, and X-ray photoelectron spectroscopy.