Multifrequency (9 and 95 GHz) EPR study of stable radicals in asphaltenes fractions of oils and bitumen

Abstract

© Published under licence by IOP Publishing Ltd. Structural characterization of asphaltenes in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. Various analytical tools and approaches are used for that. We present the results of our study of asphaltene fractions A1 and A2 with the predominantly "island" type and "archipelago" type asphaltene molecules by conventional and pulsed electron paramagnetic resonance (EPR) at X-band (9 GHz) and W-band (95 GHz) with aim to expand the abilities of EPR technique for asphaltene characterization. Shift to the higher frequencies allows to separate spectrally the contributions from paramagnetic complexes of different origin, define the EPR parameters more accurately comparing to the conventional X-band EPR. Application of pulsed techniques allows (at least partially) to separate the radicals in time domain. Features of the obtained spectra are described. Electronic relaxation times are found to be different for stable "free" radical for A1 and A2 fractions. We suggest that the obtained results can be used for investigation of various petroleum systems.