Influence of maceral composition on the structure, properties and behaviour of chars derived from South African coals

Roberts, Mokone J.; Everson, Raymond C.; Neomagus, Hein W.J.P.; Niekerk, Daniel van; Mathews, Jonathan P.; Branken, D.J.

doi:10.1016/j.fuel.2014.10.033

Cited by 91 publications

(57 citation statements)

References 68 publications

(107 reference statements)

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“…Experimental work relevant to molecular models is based on: (i) the characterization of two de-ashed chars, and (ii) constructing a molecular model based on HRTEM data from these chars [45].…”

Section: Chars and Methodologymentioning

confidence: 99%

“…However, the authors acknowledge that if the number of electrons in two structures are different, then one cannot compare the electronic energy directly. In addition to this, the 4x4-carbon ring structure was included to create additional data point, since it was also present in both the vitrinite-and inertinite-rich chars [45]. While this approach was taken, it was noted that the electronic states of the graphene models are greatly dependent on the model size so that the energetic values such as adsorption energies and activation energies are affected, as pointed out by Pham and Truong [59].…”

Section: Dft Computational Methodsmentioning

confidence: 99%

“…The chars were prepared by heating inertinite-and vitrinite-rich South African Gondwana coals of the Permian Age to 1000 in a packed bed reactor, at 20 min -1 , in Nitrogen, maintaining this temperature for 60 min, and then cooling [45]. The Nitrogen flow rate was 1.5 dm 3 min -1 to ensure a rapid escape of volatile matter in an inert atmosphere, and averting secondary reactions [45][46][47].…”

Section: Char Molecular Modelsmentioning

confidence: 99%

“…The Nitrogen flow rate was 1.5 dm 3 min -1 to ensure a rapid escape of volatile matter in an inert atmosphere, and averting secondary reactions [45][46][47]. The chars were de-ashed by HCl-HF treatments [48][49][50][51][52] and characterized using petrographic, HRTEM, NMR and XRD techniques, similar to Roberts et al [45].…”

Section: Char Molecular Modelsmentioning

confidence: 99%

“…Figure 1 shows results from the HRTEM technique, which were used to derive the char models used here [45]. It was postulated that during CO2 gasification, the higher reactive sites such as Cz and Czi, from the 3x3, will preferentially lose H. Anealling during pyrolysis however, may give rise to active sites of lower reactivity as the 3x3 grows to 5x5 sizes, because at high temperatures, and chemically-controlled gasification process, char undergoes thermal annealing in competition with gasification [106][107][108].…”

Section: Dft Reactivity Modelling and The Fukui Functionmentioning

confidence: 99%

See 4 more Smart Citations

Density functional theory molecular modelling and experimental particle kinetics for CO2–char gasification

Roberts

Everson

Domazetis

et al. 2015

Carbon

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Experimental measurements and DFT atomistic modelling were conducted to elucidate the mechanisms for gasification chemistry of char with CO2 gas. The molecular models used were based on experimental representations of coal chars derived from the vitrinite-and inertinite-rich South African coals at 1000 . The HRTEM and XRD techniques were used to construct parallelogram-shaped PAH stacks of highest frequency in the vitrinite-rich (7x7) and intertinite-rich (11x11) char structures. Computations were executed to get the nucleophillic Fukui functions, at DFT-DNP level, to elucidate the nature and proportions of carbon active sites and quantify their reactivity. The DFT-DNP-computed reaction pathways and transition states, to obtain the energy of reaction and activation energies for the gasification reactions of CO2 with active carbon sites were examined. These results were compared with TGA experimental results at 900-980 . The mean nucleophillic Fukui function of the H-terminated char models and active sites located at similar edge positions

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Section: Chars and Methodologymentioning

confidence: 99%

Section: Dft Computational Methodsmentioning

confidence: 99%

Section: Char Molecular Modelsmentioning

confidence: 99%

Section: Char Molecular Modelsmentioning

confidence: 99%

Section: Dft Reactivity Modelling and The Fukui Functionmentioning

confidence: 99%

See 3 more Smart Citations

Density functional theory molecular modelling and experimental particle kinetics for CO2–char gasification

Roberts

Everson

Domazetis

et al. 2015

Carbon

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Emissivity Comparison between Chars and Demineralized Coal Chars under Oxycombustion Conditions

et al. 2018

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Char emissivity of burning particles is an important factor for heat transfer calculations in pulverized fuel boilers. As the chemical composition is known to influence the emissivity in general, a coal sample has been prepared by a leaching method to reduce the mineral content. A flat flame burner was used for the combustion of the particles in oxyfuel atmosphere, providing boundary conditions comparable to pulverized coal applications. The burnout-dependent emissivity of the sample was measured in a defined spectral range and compared with data for an unleached sample of the same coal, indicating that the mineral content has minor effect for the investigated conversion levels, although clear changes in the emissivity show that conversion in general is not negligible.

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Gasification of chars from tetralin liquefaction of < 1.5 g cm−3 carbon-rich residues derived from waste coal fines in South Africa

Uwaoma

Strydom

Matjie

et al. 2021

J Therm Anal Calorim

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Influence of maceral composition on the structure, properties and behaviour of chars derived from South African coals

Cited by 91 publications

References 68 publications

Density functional theory molecular modelling and experimental particle kinetics for CO2–char gasification

Density functional theory molecular modelling and experimental particle kinetics for CO2–char gasification

Emissivity Comparison between Chars and Demineralized Coal Chars under Oxycombustion Conditions

Gasification of chars from tetralin liquefaction of < 1.5 g cm−3 carbon-rich residues derived from waste coal fines in South Africa

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