Structural characterization of crude oil asphaltenes by infrared spectroscopy (FTIR). Application to photo-oxidation

Photo-oxidation of asphaltenes, the most recalcitrant crude oil fraction to weathering processes was studied in ten petroleums of different geographic and geochemical origins. Isolated asphaltenes were exposed in vitro to UV and visible light for time durations up to 11 months, and studied by FTIR spectroscopy. FTIR spectra presented similar patterns before and after light exposure, except in the 1800-1600 cm(-1) range, in which variations were suggestive of an overall increase in carbonyl groups. Several structural indices were computed from area ratios of specific IR bands, and allowed to characterize asphaltene spectra in terms of oxidation, aromaticity, aliphaticity, ramification, alkyl chain length, substitution and aromatic CH and sulfoxide amounts. Only oxidation and aliphaticity indices displayed significant variations after light exposure. (C) Academie des sciences/Elsevier, Paris.