Once released, petroleum undergoes transformation (weathering) that includes physical processes that modify its native composition (water washing and evaporative losses) and chemical processes (largely oxidative, photo-oxidation and biodegradation) that generate new, increased oxygen-containing chemical functionalities in the released oil. The transformation alters both the structure and chemistry of the petroleum, and thus significantly changes the native oil’s physical properties (density, viscosity, surface tension, etc.). Combined, these changes are responsible for the formation of oil mats, thick emulsions, and differing sheen morphologies observed in oil spills that affect oil transport, fate, and spatial distribution. Weathering processes that most influence these changes are evaporative loss of the light ends (topping) and generation of surface active (interfacially active) oxygen-containing species through photo-oxidation. Recent advances in analytical instrumentation have exposed tens-of-thousands of oxygen-containing transformation products, and established methodologies for their detailed molecular-level characterization. Specifically, a novel method to isolate interfacially active species from hydrocarbon matrices allows for the identification of species responsible for emulsion formation. For the first time, emulsion-causing species can be isolated and analyzed prior to emulsion formation. Interestingly, unaltered crude oils that form stable emulsions in oil production/refining are shown to contain oxygen-containing species similar to those molecular-level compositions identified in photooxidized crude oils. Thus, photo-oxidation appears to generate interfacially active species in situ from the largely hydrocarbon matrix of crude oil. We hypothesize that these species are largely responsible for thick emulsions/mousses observed on the gulf surface after the Deepwater Horizon oil spill.
In response to research theme ii, we aim to combine the photo-chemistry expertise of Dr. Matthew Tarr (University of New Orleans) with the analytical, petroleum emulsion, and data analysis capabilities of Dr. Ryan Rodgers and Dr. Yuri E. Corilo (both Florida State University) to address the following: (1) what interfacially active species are generated during photo-oxidation? (2) what is their effect on stable emulsion formation? (3) How does this composition change with increased irradiation times? (4) What is the predominate oxygen-containing functionality (aldehyde, ketone, hydroxyl, carboxylic acid) that contributes to stable emulsion formation, and how does that change with the initial oil composition?
The current proposal will irradiate a light (Macondo surrogate), medium, and heavy crude oil for different time periods. To these photo-microcosm samples, we will add a collection of previously collected field samples (sheen, mousse, sediment extracts, and tar balls). The FSU patented “Wet Silica Method” will be used to isolate interfacially active species from photo-irradiated crude oils and field samples. Previous results reveal that although these isolated species account for less than 1 wt.% of the crude oil, they alone are responsible for stable emulsion formation, and are largely composed of oxygen-containing species similar to those identified in photo-irradiated crude oils. Since the method allows clean isolation of interfacially active species, their ability to form stable emulsions in seawater can be directly measured with simple bottle tests. Detailed molecular-level information is provided by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Attribution of chemical functionality within the interfacial materials and their importance in stable emulsion formation is afforded by previous methods developed for DEEP-C and a carboxylic acid fractionation technique developed by FSU, called MAPS. Thus, the molecular composition, chemical functionality, and importance to emulsion formation of all transformation products are revealed. Since these highly oxygenated species are not native to the parent crude oil, confident assignment of the mass spectral data by previously developed algorithms can be difficult. Dr. Corilo is a world expert in complex mixture software development, and creator of PetroOrg, a commercial software platform for petroleum data analysis/visualization, used by most of the world’s largest oil companies. We will deliver a software platform specifically aimed at processing mass spectral data from environmentally transformed crude oils that will be provided to the scientific community free of charge. It will contain a photo-oxidation database that will be populated with all data obtained in this project. Given the importance of emulsification in the fate, transport, and cleanup of spilled oil, it is essential to comprehensively understand the emulsification process, its temporal change, and relation to field samples/observations, including previously unaddressed/critical photochemical inputs.