Electron spin resonance study of free radicals in Athabasca asphaltene

Niizuma, Shigeya; Steele, C.Truman; Gunning, H. E.; Strausz, O. P.

doi:10.1016/0016-2361(77)90004-7

Cited by 37 publications

(31 citation statements)

References 9 publications

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“…In GE asphaltenes, radical pairs formation is much lower than in VI, and the trend Idt vs T can be simulated like a single singlet-triplet states. The calculated J st is very similar to the values calculated for other asphaltenes 77 and correspond quite well to a long-range interaction between free spins, according to the apparent absence of fine structure in EPR signal. In VI asphaItenes, the formation of radical pairs is very high as results from the trend of the EPR intensity.…”

Section: Dependence Of Epr Intensity On Temperature and On Oxygen Parsupporting

confidence: 75%

Molecular Structure and Intermolecular Interaction of Asphaltenes by FT-IR, NMR, EPR

Scotti

Montanari

1998

Structures and Dynamics of Asphaltenes

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Section: Dependence Of Epr Intensity On Temperature and On Oxygen Parsupporting

confidence: 75%

Molecular Structure and Intermolecular Interaction of Asphaltenes by FT-IR, NMR, EPR

Scotti

Montanari

1998

Structures and Dynamics of Asphaltenes

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“…This interaction superimposes its effects on the temperature dependence of EPR line intensity to the uninteracting spins which behave as doublets and follow the Cu¡ law. The apparent absence of fine structure of the triplet states is probably due to the inclusion of 0 ~ 1 and -1 --0 transitions in the line width because of a large distance between the free radical sites in the radical pairs [31 ], confirmed by the values of the singlet-triplet separation J calculated in Appendix. At lower temperatures the radical pairs are mainly in singlet states and the EPR line is due to doublets.…”

Section: Discussionsupporting

confidence: 51%

“…This effect is completely reversible and does not depend on the mode of addition of the gas but only on the partial pressure of it. The m 1 = -1/2 perpendicular hyperfine line of VO 2+ signal can be used asa reference standard to normalize the amount of asphaltene powder detected in the different atmosphere, as VO 2 § lines remained unaffected by oxygen [31].…”

Section: Electron Paramagnetic Resonance Spectroscopymentioning

confidence: 99%

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Asphaltene radicals and their interaction with molecular oxygen: an EPR probe of their molecular characteristics and tendency to aggregate

et al. 1998

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The paramagnetic species nature of different geological o¡ asphaltenes are discussed on the basis of Electron Paramagnetic Resonance (EPR) results. Free organic radicals are present in petroleum asphaltenes but their molecular nature is poorly known owing to the multiplicity of their molecular structures which causes the appearance of a single unresolved EPR signal with a linewidth of 4-6 Gauss. In spite of the poorly resolved signals the microwave power dependence of EPR line intensities gives some insights into the nature of the aromatic rings condensation. More aromatic asphaltenes show higher saturation power of the EPR lines: this fact has been explained by a spin exchange mechanism between n-n electronic clouds of adjacent molecules, supported also by some XRD evidences. Moreover, asphaltenes in argon (not paramagnetic gas) show a maximum intensity at much lower microwave power than in oxygen atmosphere (paramagnetic gas); besides, the differences in the saturation behavior for the different asphaltenes are much more evident in oxygen atmosphere. This phenomenon is suggested to be a consequence of a weak spatial complex between aromatic moieties and oxygen molecules that deeply contribute to the relaxation pathway. Synchronous fluorescence spectroscopy confirms the difference in the size of aromatic cores in asphaltenes molecules as supposed on the basis of the saturation mechanism of EPR line intensities.

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“…Oilsand-derived asphaltenes have a high free radical content, of the order 10 18 spins/g, as measured by electron spin resonance spectroscopy [16]. These free radicals might participate in reactions occurring during heating.…”

Section: Heating Effects On Asphaltenes Contentmentioning

confidence: 99%

Low-temperature oxidative asphaltenes liquefaction for petrochemicals: fact or fiction?

Sánchez

Klerk

2016

Appl Petrochem Res

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Asphaltene is the heavy and heteroatom-rich fraction of petroleum that is rejected during a solvent deasphalting process. In patent literature there are claims that state that this material can be converted into an aromatic petrochemical feedstock by oxidative liquefaction at low temperature. To evaluate the validity of these claims, asphaltenes from an industrial solvent deasphalting process were oxidized with dry and water-saturated air at temperatures in the range 45-100°C. Infrared spectroscopy of the oxidized product confirmed that oxygen was incorporated as C=O and C-O. Under all experimental conditions studied little oxidative degradation was observed that would lead to the production of a petrochemical feedstock. Nevertheless, some observations of scientific value were made about the low-temperature conversion of asphaltenes. During autoxidation with dry air, the n-pentane-insoluble fraction increased. On the contrary, when oxidation was conducted with water-saturated air, the formation of additional n-pentane-insoluble material was suppressed. Mild heating of asphaltenes under nitrogen atmosphere also caused the n-pentane-insoluble content to increase. Spectroscopic evidence showed that esters are formed during oxidation at *100°C. The temperature dependence of this reaction was explained and a possible reaction pathway for cycloalkane to ester conversion was presented. Ester selectivity was determined by the competition between hydrogen abstraction and b-scission of the alkoxy radical.

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Electron spin resonance study of free radicals in Athabasca asphaltene

Cited by 37 publications

References 9 publications

Molecular Structure and Intermolecular Interaction of Asphaltenes by FT-IR, NMR, EPR

Molecular Structure and Intermolecular Interaction of Asphaltenes by FT-IR, NMR, EPR

Asphaltene radicals and their interaction with molecular oxygen: an EPR probe of their molecular characteristics and tendency to aggregate

Low-temperature oxidative asphaltenes liquefaction for petrochemicals: fact or fiction?

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