Characteristics of Athabasca bitumen fractions using fluorescence microscopy : Residuum/asphaltene/coke/solids. Characterization in petroleum processing

Unsaturated organic compounds, such as aromatics, resins and asphaltenes, are primarily responsible for the fluorescence of crude oils. Fluorescence of crude oils and their fractions is initiated by electron energy absorption during UV excitation. Excitation causes a transition from a ground state energy level to an excited state energy level (BΨ B * orbital). Intermolecular quenching increases with aromatic condensation and crosslinking polymerization. Fluorescence emissions progressively shift to shorter and shorter wavelengths with increasing dilution of aromatic hydrocarbons with saturate hydrocarbons. An increase in UV fluorescence intensity from asphaltenes through resins to aromatics with decreasing wavelength was shown by Pieri et al. The increase was attributed to the lower degree of fluorescence quenching and a lower potential for electron delocalisation and intermolecular interaction among the aromatic molecules. The number of rings within aromatic molecules also influenced this phenomenon. UV spectroscopy has been used as a tool for the rapid screening of organic compounds in heavy petroleum products. Fluorescence microscopy has also been applied recently for the determination of hydrocarbon types in petroleum distillates and heavy oils. The method was shown to be sensitive and precise, particularly on measuring the concentration of saturates and aromatics. The objective of this study was to elucidate the relationship between the aromatic composition spectra of Athabasca bitumen vacuum bottoms fractions and their fluorescence microscopy.