ESR Characterization of Organic Free Radicals in Crude Oil and By‐Products

Piccinato, Marilene Turini; Guedes, Carmen Luı́sa Barbosa; Mauro, Eduardo Di

doi:10.1002/9781119286325.ch3

Cited by 2 publications

(3 citation statements)

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“…A few free radicals observed thus far by nc-AFM on various coal and petroleum asphaltenes fall into this category . Additional radicals of this type were also found in jet fuel, marine diesel, coal tar, petroleum pitch, and soot samples and inferred to be present in high-ranked coals and petroleum mass spectra. , …”

Section: New Hypothesis For Asphaltene Aggregation Via Pancake Bondin...mentioning

confidence: 83%

“…A few free radicals observed thus far by nc-AFM on various coal and petroleum asphaltenes fall into this category. 47 Additional radicals of this type were also found in jet fuel, 94 marine diesel, 88 coal tar, 95 petroleum pitch, 91 and soot 96 samples and inferred to be present in high-ranked coals 97 and petroleum mass spectra. 98,99 The second type of doubly benzylic radicals is σ radicals that are significantly stabilized by delocalization into two aromatic systems confined by a fiveor six-membered ring (Scheme 2b, 6−9).…”

Section: New Hypothesis For Asphaltenementioning

confidence: 92%

“…However, some organic radicals are long-lived, even shelf-stable, and commercially available, such as (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) and α,γ-bisdiphenylene-β-phenylallyl (BDPA). The presence of radical species in petroleum has been known since their detection using electron spin (or paramagnetic) resonance (ESR or EPR) in the late 1950s − and remains a subject of active research today. − They are carbon-centered free radicals based on the g value of 2.0034 ± 0.0004, indicating that a free electron is delocalized in a π system ( g is a spectroscopic splitting factor dependent upon the orbital, and the electronic environment of the electron, g e , is 2.0023 for the free electron). This is easily distinguished from paramagnetic metals, such as the septet peaks, as a result of vanadyl (VO 2+ ) petroporphyrins. , The presence of organic radicals in petroleum is unquestionable, but the featureless single EPR signal does not readily reveal information about their structures. , Much of the structural information that can be provided by EPR on individual radical species is lost, apparently as a result of overlapping signals from a mixture of diverse radicals.…”

Section: New Hypothesis For Asphaltene Aggregation Via Pancake Bondin...mentioning

confidence: 99%

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Mechanisms of Asphaltene Aggregation: Puzzles and a New Hypothesis

et al. 2020

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In petroleum science, asphaltenes are well-known as the most refractory fraction of crude oil and remain infamous for problems in production, transportation, and refining processes. Hence, they have been continuously analyzed and modeled over more than half a century. Defined only by solubility and characterized by an extremely complex and diverse molecular composition, asphaltenes lack discriminative molecular descriptions and definitive chemical characteristics. Most of the historic research has focused on representative structures in an attempt to yield physical and chemical models of asphaltenes, and thus, conflicting theories of bonding structures and aggregation interactions remain. This review focuses on the aggregation behavior of asphaltenes and attempts to rationalize a structure−property relationship to asphaltene aggregate thermal stability. Herein, the chemical and physical bonding properties of asphaltenes and the contradictory interpretations of their nature and composition are examined, particularly as they impact formation and stability of asphaltene aggregates. We propose a new hypothesis involving free radical interactions, i.e., pancake bonding, as an additional significant contributor to the bonding structure and formation of aggregates in asphaltenes that is consistent with the latest findings based on Fourier transform ion cyclotron resonance mass spectrometry and non-contact atomic force microscopy techniques. Various structural features of polycyclic aromatic hydrocarbons contributing to this interaction involving a stable free radical are highlighted, and suggestions for future research are presented.

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