Temperature-dependent oxocarboxylic acid photoproduction from crude oil on water

Abstract

Oxocarboxylic acids are produced when oil is exposed to sunlight and are photo-dissolved in the aqueous phase in oil–water systems, impacting the fate, transport, and impact of spilled oil. However, temperature effects on these reactions are unknown, thus we investigate oxocarboxylic acid photoproduction from irradiated oil–water systems. Oil samples include British Petroleum crude, Deepwater Horizon crude, Maya crude from Mexico, SRM 2717a oil from the National Institute of Standards and Technology, and an Alaskan crude. Oils were spread over water and exposed to simulated sunlight for 6 h at 12, 25, and 35 °C, followed by quantifying oxocarboxylic acid abundance and dissolved organic carbon in the water. Treatment with 2,4-dinitrophenyl hydrazine produced hydrazones, enriched using solid phase extraction and analyzed by using electrospray ionization-tandem mass spectrometry. Results show that temperature and oxocarboxylic acid photoproduction exhibit a complex relationship; however, oil behavior was similar with temperature. Dissolved organic carbon increased with irradiation temperature for photosolubilized oil. Deepwater Horizon oil showed high-temperature sensitivity with dissolved organic carbon production of 12.6 ppm at 35 °C versus 6.0 ppm at 12 °C. Low molecular weight species are easily volatilized, while larger molecules require greater photooxygenation to become substantially water soluble.