EPR and Fluorescence Spectroscopy in the Photodegradation Study of Arabian and Colombian Crude Oils

Abstract

EPR and fluorescence spectroscopy were used to evaluate the degradation of crude oils of different origins that were submitted to photochemical weathering under tropical conditions. The EPR spectra obtained showed signals of the paramagnetic species: the vanadylVO2+ion and organic free radicals. A decrease in linewidth of free radical signals was observed for both oils irradiated for 100 hours with sunlight of 350 W/m2. The reduction in the linewidth of the free radical of 9.8% in Arabian oil and 18.5% in Colombian oil, as well as the decrease in radical numbers, indicated photochemical degradation, especially in Colombian oil. The linewidth narrowing corresponding to free radicals in the irradiated oils occurred due to the rearrangement among radicals and aromatic carbon consumption. The irradiated oils showed a reduction in the relative intensity of fluorescence of the aromatics with high molecular mass, polar aromatics, and asphaltene. The fluorescent fraction was reduced by 61% in Arabian oil and 72% in Colombian oil, corresponding to photochemical degradation of crude oil aromatic compounds.

Proton–Radical Interaction in Crude Oil—A Combined NMR and EPR Study

“…The diversity of g -values in oil disperse systems is, among other reasons, attributed to the spin–orbit coupling of unpaired electrons and the existing heteroatoms. The value of the g -factor is higher than typical values reported in the literature (see refs and and the Introduction section), reflecting the low aromaticity in the environment of the free radical in the high-molecular components of the oil under study. Furthermore, the presence of phenoxy radicals partially localized in aromatic systems due to the oxygen might be the reason for the observed high value of the g -factor. , …”

Tar Balls from Deep Water Horizon Oil Spill: Environmentally Persistent Free Radicals (EPFR) Formation During Crude Weathering

“…Figure 1) centered at 3454 G, characterized by a g value of 2.0035 and the ΔH p-p of 5.1 G. The parameters of the spectrum recorded were consistent with the radical species observed in the crude oil and originating from asphaltene species. 20,21 The spin number of detected radicals (6.7 × 10 18 spins/g of sample) was in the range of the number of radicals present in pure asphaltenes. 22 Unlike other reports, no spectral features were observed typical for the presence of metal centers, often present in asphaltenes from crudes.…”

Photochemical degradation of crude oil: Comparison between direct irradiation, photocatalysis, and photocatalysis on zeolite

“…In different studies of oil dispersed in seawater, it was found that the synchronous fluorescence decreased with irradiation [8][9][10][11]. Photochemical weathering of Brazilian petroleum was evaluated by using EPR spectroscopy showing a partial destruction of the asphaltenic fraction of the oil [12].…”