Tools for Predicting Emulsification Capacity of Crude Oil Exposed to Sunlight: Impact of Photoproduced Carboxylic Acids on Emulsion Stability

The role of acids in the formation of emulsions from sunlight exposed petroleum is not well understood. To elucidate the impact of sunlight on the formation of emulsions from petroleum, Macondo, its surrogate and NIST 1619b and 2717a were separately exposed to simulated sunlight for up to 48 hours as a film dispersed into a quartz dish, or a film spread on water. Emulsion stability was scored from 0-5. All exposures demonstrated a correlation between emulsion stability and sunlight exposure with no observable emulsification in absence of photoproduction due to sunlight exposure. Aqueous studies of DOCHC (dissolved organic carbon produced from the partitioning of hydrocarbons from oil into the water) via TOC, fluorescence, conductivity, and pH probes revealed the impact of photopartitioning on emulsification capacity such that emulsion stabilities of sunlight exposed oil on water increased with conductivity. The pH of DOCHC decreased with shifts toward higher wavelengths in fluorescence excitation and emission as larger, more highly oxidized photoproducts partitioned into the water. Since conductivity is dependent upon hydrogen ion concentration in pure water, a bottle test for petroleum emulsion stability was used to investigate the impact of carboxylic acids on emulsion stability. Findings demonstrated that emulsion formation was inhibited in absence of photoproduced carboxylic acids. Studies in which oil volume was kept constant, while acid concentration was varied between 0 and 1 molar were conducted in absence of sunlight. High concentrations of straight chain alkyl acids or branched alkyl acids formed weak emulsions while cyclic aromatic acids produced moderate to strong emulsions at lower concentrations. Solid phase extraction of irradiated oil and subsequent MAPS (modified aminopropyl silica) fractionation demonstrated a correlation between emulsion stability, aromaticity, and the mass of extracted acids since larger aromatic acids formed stronger emulsions than did smaller saturated acids. The impact of photoproduced acids on the emulsion stability of sunlight exposed petroleum highlights the significance of carboxylic acids to the formation of emulsions from oil spilt in the environment since carboxylic acids support emulsion stability. Consequently, further investigation of the impact of photoproduced carboxylic acids on the fate spilt oil is required