High-Field (3.4 T) ENDOR Investigation of Asphaltenes in Native Oil and Vanadyl Complexes by Asphaltene Adsorption on Alumina Surface

Abstract

Vanadyl porphyrin complexes in asphaltenes from heavy (Karmalinskoye) oil and in asphaltene films obtained as a result of adsorption on the surface of aluminum oxide were studied by electron paramagnetic resonance (EPR) and double electron-nuclear resonance (ENDOR) in the W-band frequency range (microwave frequency of 95 GHz, magnetic field of 3.4 T). Mims ENDOR spectra from 1H and 27Al nuclei are observed. ENDOR spectra are different for native oil and asphaltenes from one side and the adsorbed samples from the other side while no significant changes in X- (microwave frequency of 9 GHz) or W-band EPR spectra are found. The results allow supposing that vanadyl porphyrin complexes (at least in the studied asphaltene films) participate in the formation of asphaltene aggregates through the functional groups rather than π−π interactions. The data show the feasibility of the commercial pulsed ENDOR approaches for the investigation of crude oils and their constituents under external influence.