High-temperature n.m.r. analysis of aromatic units in asphaltenes and preasphaltenes derived from Victorian brown coal

Masuda, Kaoru; Okuma, Osamu; Nishizawa, Takashi; Kanaji, Mariko; Matsumura, Toshiro

doi:10.1016/0016-2361(95)00261-8

Cited by 22 publications

(11 citation statements)

References 8 publications

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“…To determine the average number of methyl groups bonded directly to the aromatic Aguacate asphaltene PAH core (MG in eq 4), the integration in the region of 20.42−21.75 ppm 46 (aromatic α-CH 3 ; see Table 5) in the 13 C SPE NMR spectrum is used. The integration of 0.01 multiplied by the total number of carbon atoms in the chemical formula of the Aguacate asphaltene (see eq 2) gives a total of 0.73 methyl group directly bonded to the aromatic core (Table 5).…”

Section: Determination Of the Average Structuralmentioning

confidence: 99%

“…NMR has proven to be a powerful tool in the determination of asphaltene structures, as shown in the recent review by Ok and Mal . Solution- and solid-state NMR have been used to study asphaltene structure. − Fergoug and Bouhadda studied structural parameters of the asphaltenes derived from the Algerian Hassi Messoud oilfield using 1 H and 13 C liquid NMR, finding that the PAH region contains seven fused aromatic rings (7FAR). Scotti et al concluded, from a liquid-state 1 H and 13 C NMR study, that the most probable number of fused aromatic rings in asphaltene PAHs is seven.…”

Section: Introductionmentioning

confidence: 99%

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Experimental and Theoretical Approach To Determine the Average Asphaltene Structure of a Crude Oil from the Golden Lane (Faja de Oro) of Mexico

et al. 2020

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The structural parameters and average molecular structures of the asphaltenes obtained from the Aguacate oilfield, located in the Golden Lane of Mexico, have been investigated combining experimental analysis and molecular simulation. The average molecular structural parameters of the polycyclic aromatic hydrocarbon (PAH) region, average number of fused aromatic rings (nFAR), average structural isomers in the polydispersity of the PAH core, average architecture, average molecular weight, and substituents in the PAH core have been determined by means of 13 C single-pulse excitation (SPE) nuclear magnetic resonance (NMR) in combination with 13 C distortionless enhancement by polarization transfer (DEPT)-135°experiments, 1 H NMR, X-ray photoelectron spectroscopy, fluorescence emission, and matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry. The total energy of the PAH isomers and their fluorescence emission are calculated with density functional theory and ZINDO/S, respectively. The PAH region structural parameters determined are (a) Y-carbons (C Y ) or internal triple bridgehead aromatic carbons, (b) external peripheral aromatic carbon atoms at the junction of two fused rings (C AP3 ), (c) aromatic carbon atoms bonded to hydrogen atoms (C AH ), (d) aromatic carbon atoms bonded to heteroatom (C AX ), (e) aromatic carbon atoms bonded to hydrogen at the β position with respect to the heteroatom (C AHβX ), and (f) substituted aromatic carbon atoms (C A-Caliph ). The 13 C NMR chemical shift ranges used for the different structural carbon atoms in the PAH core were obtained from our previous study [

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Section: Determination Of the Average Structuralmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental and Theoretical Approach To Determine the Average Asphaltene Structure of a Crude Oil from the Golden Lane (Faja de Oro) of Mexico

et al. 2020

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“…The topological characteristics of benzenoid PAHs have previously been extrapolated to the aromatic ring region of asphaltenes, , but the effect of the presence of different number of resonant sextets in the PAH structures was not taken into account in the differentiation of possible structural isomers.…”

Section: The Aromatic Fused Region In Asphaltenesmentioning

confidence: 99%

HOMO−LUMO Gap as an Index of Molecular Size and Structure for Polycyclic Aromatic Hydrocarbons (PAHs) and Asphaltenes: A Theoretical Study. I

2002

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Theoretical calculations are presented for the effect on the HOMO−LUMO gap due to the successive addition of aromatic rings and their different distributions, isomers, for polycyclic aromatic hydrocarbons (PAHs). The study is based on ZINDO/S calculations. PAHs with 1−14 fused aromatic rings (FAR) are considered. The results of these calculations are addressed to a currently existing controversy regarding the number of FAR in asphaltene structures. Asphaltenes are considered as polycyclic aromatic compounds similar to PAHs but containing heteroatoms and alkyl side chains. The theoretical results are compared with fluorescence emission (FE) experimental data. It is found that the asphaltene experimental FE range does not necessarily correspond to different chromophores with different number of FAR but may be different isomers with the same number of FAR. Also, the effect of the presence of alkyl chains and heteroatoms in the asphaltene structures on the HOMO−LUMO gap is almost negligible. We conclude that the FAR region in asphaltenes has PAH chromophores with 5−10 fused rings. The 100% compactness (circular) PAH structures, beyond 10 fused rings, and the 0% compactness (linear or zigzag) PAH structures are not possible for asphaltenes. Relationships between the HOMO−LUMO gap and structural parameters for PAH chromophores in asphaltenes were found. The effect of the number of FAR and Clar sextets, the compactness, and longest dimension on the HOMO−LUMO gap of PAHs is evaluated.

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“…On a weight basis, PA produces a viscosity about twice that of AS fraction . Therefore, up until now, the structure of PA has remained generally unknown, though its chemical composition, such as elemental compositions and functional groups, had been extensively investigated by the elemental analyses, nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), and so forth. − For example, Yoshida et al studied the formation and chemical structure of PA in coal hydrogenolysis by solid state cross-polarization magic angle spinning 13 C NMR spectroscopy and found that there are aromatic rings of from 1 to 3–5 per condensed aromatic ring system. By comparison of the structural features of AS and PA, Baltisberger et al suggested that PA contains more condensed aromatic molecules, and the majority of the PA lies in a range from 600 to 2500 amu.…”

Section: Introductionmentioning

confidence: 99%

Structural Characterization and Aggregation of the Subfractions of Preasphaltene from Direct Coal Liquefaction

et al. 2014

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Preasphaltene (PA) defined as tetrahydrofuran (THF) soluble and toluene insoluble is an important intermediate product of direct coal liquefaction (DCL). Investigating the structure of PA not only can improve the DCL technology but also can help us understand the structure of coal. In this paper, two types of PAs from the DCL residue of 6 t/d Shenhua process developing unit (PDU) and the products of a batch hydroliquefaction in an autoclave were first separated into different subfractions by the column chromatography. Then, the obtained subfractions were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet−visible spectroscopy (UV) and fluorescence spectroscopy (FL), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and gel permeation chromatography (GPC), respectively. The results indicate that the PA from DCL mainly exists in the form of aggregates. Two different PAs show similar distribution of subfractions, but the PA(B) obtained by the batch liquefaction displays larger molecular weight than the PA(A) from Shenhua PDU technology. A molecule of PA contains two or more aromatic nuclei (fluorophors). Subfractions I−III consist of smaller fused aromatic nucleus than the other subfractions. In general, their intermolecular aggregations increase from subfraction I to VII, and the aggregation of PA(A) subfractions is stronger than that of corresponding PA(B) subfractions.

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High-temperature n.m.r. analysis of aromatic units in asphaltenes and preasphaltenes derived from Victorian brown coal

Cited by 22 publications

References 8 publications

Experimental and Theoretical Approach To Determine the Average Asphaltene Structure of a Crude Oil from the Golden Lane (Faja de Oro) of Mexico

Experimental and Theoretical Approach To Determine the Average Asphaltene Structure of a Crude Oil from the Golden Lane (Faja de Oro) of Mexico

HOMO−LUMO Gap as an Index of Molecular Size and Structure for Polycyclic Aromatic Hydrocarbons (PAHs) and Asphaltenes: A Theoretical Study. I

Structural Characterization and Aggregation of the Subfractions of Preasphaltene from Direct Coal Liquefaction

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