Photooxidation of Crude Oils

Photooxidation is a potentially significant process in the degradation of crude oil spilled at sea. Moreover, a fundamental understanding of the effect of photochemical degradation on crude oil is a prerequisite for providing an accurate description of the recent history and potential fate of oil spilled in a marine environment. In this report we examine the effect of ultraviolet illumination on crude oil using a variety of techniques including gas chromatography/mass spectroscopy and X-ray absorption spectroscopy. The saturated compounds are resistant, but the aromatic compounds are particularly sensitive to photooxidation. Greater size and increasing alkyl substitution increase the sensitivity of aromatic compounds to photochemical oxidation. The photooxidized products appear in the resin and polar fractions as determined by thin-layer chroma tography. Thus, the effect of photooxidation is distinctly different from that of biodegradation, where larger and more substituted compounds are more resistant to degradation. Perhaps surprisingly, X-ray absorption spectroscopy indicates that the aliphatic sulfur compounds are more readily oxidized than the thiophenic compounds with the sulfur being oxidized to sulfoxides, sulfones, sulfonates, and sulfates in approximately equal amounts.