A fraction to fraction study of photo-oxidation of BAL 150 crude oil asphaltenes

Sun light plays an important role in the degradation of oil spilled at sea or ground surface. Nevertheless, the efficience of photo-oxidation as a weathering process was hardly studied in asphaltenes, the most recalcitrant of petrogenic contaminants. Asphaltenes precipitated from Blend Arabian Light crude oil topped at 150 degrees C were exposed to UV and visible light sources for time durations up to 140 days, analyzed globally, then fractionated by sequential elution solvent chromatography. FTIR spectroscopy, elemental analysis, NMR, UV-fluorescence, GC and GC/MS analyses were implemented to investigate structural changes potentially induced by photo-oxidation. No obvious effect could be detected by overall approaches, whereas fraction to fraction analyses evidenced significant variations in the gravimetric distribution of asphaltene constituents, accompanied by changes in functionality linked to limited oxidation processes. Under our experimental conditions, most observed changes were suggestive of an increase in carbonyl, phenolic, sulfoxyde and carboxylic groups after light exposure, without significant alteration of the hydrocarbon skeletons of polyaromatic and alkyl compounds associated with the asphaltene matrix.