Structural Dependence of Photogenerated Transformation Products for Aromatic Hydrocarbons Isolated from Petroleum

Previous work has suggested a potential structural dependence for the formation of oil- and water-soluble photoproducts from the simulated solar irradiation of petroleum. Aromatic species in petroleum are thought to play a role in the type and amount of transformation products as a result of their ability to act as chromophores and promote photochemical reactions. To investigate the effect of the aromatic ring number on the formation of photoproducts from petroleum, we subject an Arabian heavy crude oil to a previously developed HPLC-3 method, which fractionates oil based on the number of aromatic rings. All five aromatic ring fractions (1-ring to 5+ rings) produce abundant oil- and water-soluble photoproducts with high oxygen content and similar chemical composition upon photoirradiation in the laboratory, despite large differences in aromaticity in the starting material. The 3- and 4-ring fractions produce the highest amount of dissolved organic carbon, which is quantified by non-purgeable organic carbon analysis. We investigate photoinduced fragmentation, oxidation, and potential polymerization as key processes in the formation of water-solubles from starting material containing different numbers of aromatic rings. As a result of the high amount of sulfur in Arabian heavy crude oil, sulfur-containing photoproducts (OxS1) are also investigated.