Chapter 9 Electron Spin Resonance Study of Bituminous Substances and Asphaltenes

Chang, Hung-Li; Wong, Gary K.; Lin, Jiunn-Ren; Yen, Teh Fu

doi:10.1016/s0376-7361(09)70280-8

Cited by 38 publications

(48 citation statements)

References 55 publications

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“…EPR measurements clearly confirm the presence of unpaired electrons in all the investigated systems, according to previous studies [16,37]. The X-band EPR spectra of the bituminous signals consist of two non-overlapping EPR signals, one centered at about 3480 G due to vanadyl ions (spin 7/2), and the second in a range between 3510 and 3530 G associated to organic radicals (see Figure 3 for the asphaltene fractions).…”

Section: Epr Spectroscopy Investigationsupporting

confidence: 86%

“…The objective of the present work is the investigation carried out by Electron Paramagnetic Resonance (EPR) and Dynamic Shear Rheology (DSR) of the effects of the aging process of bituminous binders modified with antioxidant agents obtained by natural resources. Bitumen manifests EPR spectra due to organic radicals [15][16][17] whose signal shape is susceptible to changes in the oxidative state, and vanadyl ions VO 2+ [18] associated with porphyrin species, which instead appear to be unaffected by oxidative treatments. Here we will focus our attention on the two most representative components present in the bitumen, namely, asphaltenes and maltenes [19].…”

Section: Introductionmentioning

confidence: 99%

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Effects of Natural Antioxidant Agents on the Bitumen Aging Process: An EPR and Rheological Investigation

Rossi¹,

Caputo²,

Ashimova³

et al. 2018

Preprint

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Bitumen aging is the major factor which contributes to the deterioration of the road pavement. Oxidation and volatilization are generally considered as the most important phenomena affecting aging in asphalt paving mixtures. The present study was carried to investigate whether various antioxidants provided by natural resources such as phospholipids, ascorbic acid as well as lignin from rice husk, could be used to reduce age hardening in asphalt binders. A selected bituminous material was modified by adding 2 % w/w of the anti-aging natural additives and subjected to accelerated oxidative aging regimes according to the Rolling Thin Film Oven Test (RTFOT) method. The effects of aging were evaluated based on changes in sol-gel transition temperature of modified bitumens measured through Dynamic Shear Rheology (DSR). Moreover, changes of Electron Paramagnetic Resonance (EPR) spectra were monitored on the bituminous fractions asphaltene and maltene separated by solvent extraction upon oxidative aging. The phospholipids-treated binder exhibited the highest resistance to oxidation and the lowest age-hardening effect compared to the other tested anti-oxidants. The combination of EPR and DSR techniques represents a promising method for elucidating the changes in associated complex properties of bitumen fractions promoted by addition of free radical scavengers borrowed by green resources.

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Section: Epr Spectroscopy Investigationsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Effects of Natural Antioxidant Agents on the Bitumen Aging Process: An EPR and Rheological Investigation

Rossi¹,

Caputo²,

Ashimova³

et al. 2018

Preprint

View full text Add to dashboard Cite

show abstract

“…The unresolved hyperfine interactions from many different chemical environments caused the main absorption to appear as a single broadened absorption. 17,23,24 In some materials anisotropic effects could also contribute to broadening of the absorption, as in the case of coal. 24 Although the dominant Landég values were in the range of 2.0025−2.0037, as reported in Table S4, inspection of Figure S4 reveals that a second smaller absorption with a g value of ∼2.015.…”

Section: Discussionmentioning

confidence: 99%

Uncatalyzed Hydrogen Transfer during 100–250 °C Conversion of Asphaltenes

2017

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The reactivity and reactions of asphaltenes were explored over the temperature range 100−250°C following reports of reactivity and meaningful free radical content in asphaltenes. This study employed industrial pentane precipitated asphaltenes from Athabasca oilsands bitumen. The presence of free radicals in the asphaltenes feed was confirmed. On heating the asphaltenes to 150°C, the aromatic hydrogen content increased relative to the feed by a factor 1.12. It was also found that on heating the asphaltenes to 150°C the n-heptane insoluble fraction increased from 67% to 75%. Almost no gas phase products were produced. The observed changes were ascribed to hydrogen transfer reactions and addition products formed by combination reactions. Direct evidence of hydrogen transfer reactions taking place in the asphaltenes was obtained through the use of the model systems, α-methylstyrene and cumene, as well as anthracene and 9,10-dihydroanthracene. The extent of hydrogen transfer was of the order 1.8 mg H/g asphaltenes in 1 h at 250°C. Asphaltenes also caused dimerization of model compounds, providing indirect evidence that free radical combination reactions took place in the asphaltenes. Interpretation relying on thermodynamic arguments combined with experimental results indicated that at 250°C the reactive species in asphaltenes were incapable of abstracting hydrogen by hydrogen transfer that had bond strengths (based on homolytic bond dissociation energy) exceeding around 353 kJ mol −1 . Using similar arguments, it was deduced that the ratio of reactive species in asphaltenes capable of abstracting hydrogen with bond strengths in the range around 315−353 kJ mol −1 , compared to transferable hydrogen in asphaltenes with a bond strength less than 315 kJ mol −1 was about 2:1.

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“…For example, the free-radical concentrations of 9 Â 10 18 /g-asphaltene and 2 Â 10 17 /g-resin have been reported, showing the dramatic decline in free-radical content as the PAHs become smaller. 57 Consequently, if free radicals dominated our signal, it is very unlikely that a very light crude oil with <1% resin and no asphaltene would have almost-identical excited-state spectra as a crude oil with >10% resin and Figure 10. The singlet (S) and triplet (T) manifold.…”

Section: Articlementioning

confidence: 97%

Triplet Electronic Spin States of Crude Oils and Asphaltenes

et al. 2011

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The resolution of asphaltene nanoscience is becoming increasingly important for a variety of purposes. One key molecular attribute of the asphaltenes is the size distribution of their polycyclic aromatic hydrocarbons (PAHs). Comparison of measured spin singletÀsinglet absorption and emission transitions with exhaustive molecular orbital (MO) calculations on 523 PAHs indicates that asphaltene PAHs have a population centroid of ∼7 fused rings. To further test this understanding of asphaltene PAHs, it is desirable to consider the dynamics of triplet states. Nevertheless, triplet-state spectroscopy is complex, especially on polydisperse materials such as asphaltenes. For validation, we compare simple expectations for asphaltenes against both experimental and theoretical results. Measurements were conducted on crude oil and asphaltene samples of dramatically different heavy end content to identify specific transitions being investigated. Experimental results include spectra at several wavelengths, lifetimes in the presence and absence of molecular oxygen, and temperature effects. Specifically, we use classic techniques [Horrocks and Wilkinson, Proc. R. Soc. London A 1968, 306, 257À273] to measure tripletÀtriplet spectra for crude oils and asphaltenes. These are compared with corresponding MO calculations. Again, using classic methods [Guzeman et al., J. Chem. Soc. Faraday Trans. 1973, 69, 708À720], quenching effects of asphaltene triplet states by molecular oxygen are measured and compared with simple diffusion expectations. The temperature dependence provides further stringent testing. Spectral comparisons versus crude oil composition rule out significant spectral contributions from free radicals. Simple expectations regarding triplet-state spectroscopy of asphaltenes and crude oils apply and corroborate previous conclusions from singlet-state spectroscopy of crude oils and asphaltenes. The data herein are consistent with asphaltene PAHs being relatively large (e.g., 7 fused rings); this, in turn, is consistent with the predominance of a single PAH per asphaltene molecule (the "island" molecular architecture). Smaller PAHs dominate the triplet transitions for the crude oil samples and optical wavelengths used herein.

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Chapter 9 Electron Spin Resonance Study of Bituminous Substances and Asphaltenes

Cited by 38 publications

References 55 publications

Effects of Natural Antioxidant Agents on the Bitumen Aging Process: An EPR and Rheological Investigation

Effects of Natural Antioxidant Agents on the Bitumen Aging Process: An EPR and Rheological Investigation

Uncatalyzed Hydrogen Transfer during 100–250 °C Conversion of Asphaltenes

Triplet Electronic Spin States of Crude Oils and Asphaltenes

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