Distribution of vanadyl complexes and free radicals in asphaltenes fractions from electron paramagnetic resonance

Structural characterization of asphaltenes in complex systems is in the focus of scientific and industrial interests since many years. Asphaltenes isolated from the high-viscous Ashal'cha oil (2500 mPas) were studied. Five asphaltene fractions were obtained by stepwise extraction with an alcohol-benzene solvent with different alcohol contents after precipitating the asphaltenes from the oil with hot isooctane. Redistribution of paramagnetic centers between the fractions of asphaltenes is revealed by electron paramagentic resonance (EPR) while no significant changes in EPR spectral parameters are found. The results can be used for tracking the asphatenes formation as well as following the changes of their supramolecular structure.