Compositional Changes in Hydrotreated Naphthenic Oil under Ultraviolet Radiation

Abstract

Compositional changes of hydrotreated naphthenic oil during ultraviolet (UV) radiation were studied in detail. First, liquid–solid chromatography was used to separate the initial oil and the UV-irradiated oil into three different fractions: saturates, aromatics, and polars. Then, each fraction's compositional changes were evaluated using a series of instrument technologies including gas chromatography-mass spectroscopy (GC-MS), infrared spectroscopy (IR), atmospheric pressure chemical ionization mass spectroscopy (APCI/MS), and X-ray photo electron spectroscopy (XPS), respectively. The results show that after UV radiation, the UV-irradiated sample exhibited a decrease in saturates concomitant with an increase in the aromatic and polar fractions. For saturates and aromatics, the UV-irradiated sample exhibited a decrease in alkanes, diaromatics, and polyaromatics concomitant with an increase in other aromatics. The UV light had no significant effect on the cycloalkanes. For polars, a relatively large amount of oxygen-containing compounds, such as hydroxyl, carbonyl, and carboxyl groups, was formed in the presence of UV light. XPS data show that a type of S 2pa compound in the initial oil disappears and could be converted to SO4 2−. No obvious changes of molecular weight distribution were observed. A part of polar compounds in the UV-irradiated oil might come from aromatic photooxidation in the initial oil.