Color Degradation of Lubricating Base Oil Fraction Induced by Sunlight Irradiation

摘要

The behavior of color degradation of lubricating base oil in sunlight was investigated at ambient temperature, using UV-vis, FT-IR and fluorescence spectroscopy. Color of the oils turned from pale yellow to dark brown, and the amount of sediments formed increased with increasing sunlight irradiation. The color change was different, depending on the season of irradiation and/or the characteristics of sunlight and ambient temperature. The intensity of fluorescence emission spectra of the irradiated oil decreased in comparison with that of the original oil, indicating that those having emission of fluorescence spectra, and polynuclear aromatic compounds with three to five fused-ring cause color degradation. The sediments formed during irradiation comprised mainly aromatic compounds with carbonly, carboxyl, and hydroxyl groups. Neither a significant change in color nor formation of sediments was detected in the degassed oil, but change in color and formation of sediments were observed in the original oil. It may therefore be concluded that both dissolved oxygen and the polynuclear aromatics in oil are indispensable for the color degradation induced by photo-irradiation.