The analysis of three representative premium coals by 13C nuclear magnetic resonance

Pan, Vicky H.; Maciel, Gary E.

doi:10.1016/0016-2361(93)90105-b

Cited by 31 publications

(10 citation statements)

References 34 publications

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“…However, there have been questions as to the qualitative reliability of the CP-MAS technique ( 3 , − . These questions come about because the CP-MAS technique can bias non-protonated carbons.…”

Section: Introductionmentioning

confidence: 99%

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

Cook

Langford

1998

Environ. Sci. Technol.

111

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This study uses the analysis of 13 C nuclear magnetic resonance (NMR) spectra and NMR relaxation parameters to study the structure and functional group distribution of a fulvic acid and a humic acid. The spectra and relaxation parameters are obtained with a new cross polarization magic angle spinning (CP-MAS) 13 C NMR technique that gives qualitatively and quantitatively accurate results at higher fields. The analysis of the spectra and relaxation parameters indicates that carbohydrate moieties play a major structural role in the fulvic acid studied and contain the major chemical functionality. This analysis also suggested that the majority of the weakly acid protons may be aliphatic/carbohydrate -OH and not phenolic alcohols, as assigned earlier. Models for the fulvic acid and the humic acid are proposed based on spectra and relaxation parameters obtained. The fulvic acid model consists of three units: (i) large relatively immobile units that are mainly aliphatic in nature and largely unfunctionalized; (ii) relatively unfunctionalized more mobile units that are mainly aromatic in nature; and (iii) and more mobile functionalized units that are mainly carbohydrate in nature. The humic acid model consists of one major immobile unit associated with slightly more mobile functionalized units that are mainly aromatic in nature.

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Section: Introductionmentioning

confidence: 99%

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

Cook

Langford

1998

Environ. Sci. Technol.

111

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“…Woods and their main components (cellulose, lignin, and hemicellulose) have been studied by 13 C CP/MAS NMR by Maciel and co-workers , who have obtained qualitative and quantitative information about wood structure. Coal samples have also been investigated by high-resolution NMR spectroscopy and relaxation studies, leading to the identification of aromatic and aliphatic chemical functional groups, the determination of aromaticity, and the study of the interaction between coal and solvents . New forms of carbonaceous materials, such as amorphous carbons, fullerenes, and nanotubes, have been successfully characterized by 13 C NMR.…”

Section: Introductionmentioning

confidence: 99%

¹³C High-Resolution Solid-State NMR Study of Peat Carbonization

1998

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Peat char samples produced by heat treatments under an inert atmosphere of nitrogen were characterized through 13 C solid-state NMR, allowing the achievement of a detailed picture of the mechanism of carbonization. The treatments were realized at temperatures between 200 and 1000°C, with a controlled heating rate and residence time. NMR spectra were obtained in a home-built spectrometer operating at a field of 2.0 T with the use of high-resolution techniques. The results showed the steps followed during the carbonization process. Initially we observed a degradation of the natural material, with preferential loss of carbohydrates and carboxylic groups. From a heat-treatment temperature of about 500°C upward, the spectra were nearly constituted of only one resonance line with a chemical shift of about 130 ppm (from TMS), typical of aromatic structures. For the most severely treated samples, a decrease in the chemical shift of the resonance line was observed, indicating a deshielding associated with the increase in the electrical conductivity of the material. The structure of these samples was identified as consisting of planes of sp 2 carbon atoms, with a chemical environment similar to graphitic materials but with no long-range spatial order.

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“…Non protonated Aromatic Carbon. The measurement of the fraction of aromatic carbon that is nonprotonated ( f nonprot ) by dipolar dephasing is essential in the determination of the aromatic ring size condensation for carbonaceous materials, such as coal tar pitches. ,− The procedure used here for the SPE dipolar dephasing experiments is essentially the same as that used previously for coals, the only difference being that much longer recycle delays (up to 500 s) were required to take account of the pitch fractions having considerably longer 13 C T 1 s (Table ) than most coals. Figure show the set of spectra obtained from the dipolar dephasing experiment conducted on CTP-6 using SPE with a recycle delay of 440 s. The corresponding set of spectra obtained using CP with a contact time of 5 ms (recycle delay of 5 s) are shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

Structural Uniformity of Toluene-Insolubles from Heat-Treated Coal Tar Pitch As Determined by Solid State¹³C NMR Spectroscopy

et al. 1998

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A suite of coal tar pitches (CTPs) thermally treated to varying degrees and their tolueneinsoluble (TI) fractions have been characterized by solid state 13 C nuclear magnetic resonance (NMR). The nonprotonated aromatic carbon concentrations estimated from dipolar dephasing experiments using cross polarization with a relatively long contact time (5 ms) and the quantitatively reliable single-pulse excitation (SPE) technique were in good agreement and these concentrations were used to deduce the average ring sizes. Complementary information has been obtained from X-ray diffraction and thermogravimetry analysis. An increase in the degree of condensation for the aromatic structure was evident for the whole pitches upon heat treatment, consistent with the increasing concentrations of TIs and published liquid chromatographic results on the toluene-soluble fractions. In contrast, the proportions of nonprotonated and bridgehead/ internal aromatic carbons remained constant over the heat treatment range for the TIs, despite the increase in TI concentration of the CTPs with temperature. Thus, the growth in aromatic ring size appears to be limited by the heat treatment temperature of 380°C used here. Interestingly, the TIs obtained from the parent tar are more condensed than those from the pitches mainly due to the higher concentration of quinoline-insolubles present.

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The analysis of three representative premium coals by 13C nuclear magnetic resonance

Cited by 31 publications

References 34 publications

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

¹³C High-Resolution Solid-State NMR Study of Peat Carbonization

Structural Uniformity of Toluene-Insolubles from Heat-Treated Coal Tar Pitch As Determined by Solid State¹³C NMR Spectroscopy

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The analysis of three representative premium coals by 13C nuclear magnetic resonance

Cited by 31 publications

References 34 publications

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS 13C Nuclear Magnetic Resonance

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS 13C Nuclear Magnetic Resonance

13C High-Resolution Solid-State NMR Study of Peat Carbonization

Structural Uniformity of Toluene-Insolubles from Heat-Treated Coal Tar Pitch As Determined by Solid State13C NMR Spectroscopy

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Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

¹³C High-Resolution Solid-State NMR Study of Peat Carbonization

Structural Uniformity of Toluene-Insolubles from Heat-Treated Coal Tar Pitch As Determined by Solid State¹³C NMR Spectroscopy