Electron Spin Resonance of Slowly Rotating Vanadyls–Effective Tool to Quantify the Sizes of Asphaltenes in Situ

Abstract

The approach for quantitative estimation of asphaltene sizes in crude oils in situ via precise simulation of electron spin resonance (ESR) spectra of the slowly rotating VO2+-containing fragments was developed. The method is based on the correlation between the size of the paramagnetic particles and their characteristic rotational time that can be determined by ESR in situ while incomplete averaging of anisotropic hyperfine interactions is observed. The precise simulation of the ESR spectra of heavy molecules, labeled naturally with vanadyl ions, allows one to find their size distribution in crude oils. In particular, the method is demonstrated to be an effective tool for the quantitative determination of the asphaltene sizes in different oil fractions in situ.

Asphaltenes: Separations, structural analysis and applications

“…It was proved that VO 2 + influenced the formation of asphaltene aggregates since VO 2 + was only a few nanometers away from free radical of asphaltene polyaromatic condensed nuclei by analyzing twelve different kinds of asphaltenes using high-frequency (W-band, ν MW ≈ 94 GHz) pulsed EPR spectroscopy [153] . Asphaltene sizes could be quantitatively estimated in situ by correlating paramagnetic particle size with the responding rotational time using ESR [154] . Besides, ESR could offer the transformation between anisotropic and isotropic vanadium and 14 to 20 kcal/mol was needed to associate a metallo-complex with asphaltenes, which was calculated by adding vanadyl indicators to asphaltenes [7] .…”

“…The mechanism by which the incident radiation acts on asphaltene makes them essentially different [11] , as shown in Table S4. But with any of the three techniques, scattering pattern produced by radiation could give an unambiguous determination of sizes and ships of asphaltene components, like semi-crystalline structure of asphaltene aggregates, described as a prolate ellipsoid or a sphere or an oblate cylinder building a dense, or fractal physical network [11,70,154] . SAXS analysis revealed that the size was nearly 2 nm for asphaltene nanoaggregates and about 5 nm for nanoaggregate clusters [81] .…”

Identify Similarities in Diverse Polycyclic Aromatic Hydrocarbons of Asphaltenes and Heavy Oils Revealed by Noncontact Atomic Force Microscopy: Aromaticity, Bonding, and Implications in Reactivity

“…The presence of stable free radical species in native asphaltenes has been reported since the1960s, 50 when free radicals were detected by electron spin resonance (ESR) spectroscopy and remained a subject of active research. [51][52] Therefore, detection of these odd-carbon number PAHs might provide a clue to the presence of these types of free radicals and their structures.…”

Molecular Dynamics and Proton Hyperpolarization via Synthetic and Crude Oil Porphyrin Complexes in Solid and Solution States

“…Due to the paramagnetic properties of the vanadyl ion VO 2+ , various electron paramagnetic resonance (EPR) techniques such as electron spin echo envelope modulation (ESEEM), electron–nuclear double resonance (ENDOR), and hyperfine sublevel correlation spectroscopy (HYSCORE) are widely applied to study the structure and properties of ligands of synthetic and crude oil vanadium compounds. ,− Surprisingly, complementary to the ENDOR hyperfine approach, dynamic nuclear polarization (DNP) is only sporadically applied for the porphyrin complexes. DNP, in turn, is a hyperpolarization technique to increase the sensitivity of NMR experiments and to study the details of electron–nuclear interactions.…”