2015
DOI: 10.1021/ef502672d
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Comparative Study of the Aromaticity of the Coal Structure during the Char Formation Process under Both Conventional and Advanced Analytical Techniques

Abstract: Six coal samples of different rank, five southern hemisphere and one northern hemisphere, were studied using both conventional and advanced analytical techniques: scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), carbon nuclear magnetic resonance (C NMR), and X-ray diffraction (XRD). Apart from SEM that was used to study the coal to char morphology, the other analytical techniques were used to determine the molecular structural parameter of coal, specifically, the aromaticity,… Show more

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Cited by 35 publications
(27 citation statements)
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“…The two medium rank coals converged to the same value of 13.86 nm (139 Å) while the two high rank coals converged to the same value of 13.00 nm (130 Å) at the highest pyrolysis temperature of 700˚C. It is evident that the convergence to the same value by coals of same rank is a clear display of the mechanism of devolatilization and a demonstration of a decreasing anisotrophy tendency of the coals with increasing pyrolysis temperature as expected due to the complex character in coal and coal chars [23] [32] [38]. Coals of same rank seem to exhibit same devolatilization mechanisms that lead to more aromatic structure of the coal matrix where the size and the thickness of the carbon sheets increase with the heating temperature [41] [42].…”
Section: Resultsmentioning
confidence: 94%
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“…The two medium rank coals converged to the same value of 13.86 nm (139 Å) while the two high rank coals converged to the same value of 13.00 nm (130 Å) at the highest pyrolysis temperature of 700˚C. It is evident that the convergence to the same value by coals of same rank is a clear display of the mechanism of devolatilization and a demonstration of a decreasing anisotrophy tendency of the coals with increasing pyrolysis temperature as expected due to the complex character in coal and coal chars [23] [32] [38]. Coals of same rank seem to exhibit same devolatilization mechanisms that lead to more aromatic structure of the coal matrix where the size and the thickness of the carbon sheets increase with the heating temperature [41] [42].…”
Section: Resultsmentioning
confidence: 94%
“…This could be attributed to the washing off of the alkaline and alkaline earth metals in the low rank coals that aids coal reaction [38] and the inactivity of the active minerals present in the high rank coals [39]. Though considerable variation was seen in the values of the specific surface area between coals from low to high pyrolysis temperature, the results fit well with published rank trends [40], and when the conventional properties (proximate and ultimate analyses data) are put into consideration [38]. As can also be seen in Table 3 and Figure 2, the radius of gyration (a parameter proportional to the surface area) increased gradually with increasing pyrolysis temperature and was more pronounced for the low rank coals.…”
Section: Resultsmentioning
confidence: 99%
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“…The carbon structure in the coke matrix, which has a non-graphitic and turbostratic scaffold, can capture inorganic impurities such as metals. The dimensions of graphiticcrystallite in the coke matrix is characterized by the interlayer spacing (c/2 = half the hexagonal lattice c-axis), the thickness of hexagonal packing (L c = crystallite dimension in the c-axis direction) (Feret 1998;Lu et al 2001;Sonibare et al 2010;Mollick et al 2015), the spread of carbon basal plane (L a = crystallite dimension in the a-axis direction) (Sonibare et al 2010;Mollick et al 2015), aromaticity (Sonibare et al 2010;Odeh 2015), coke rank (Yoshizawa et al 2001;Sonibare et al 2010), graphitation degree (Mollick et al 2015) and number of carbon rings (Belenkov 2001) and grapheme layers (Mollick et al 2015), which are determined from X-ray diffraction (XRD) patterns. Not only the bond strengths are not fixed along the crystallographic directions, but also a variety of voids, defects and cross-links are present in the coke matrix.…”
Section: Introductionmentioning
confidence: 99%
“…7,8 The contents of volatiles and oxygen-containing chemical groups are much higher compared with those of the high rank coals. [9][10][11] These structure features make the lignite suffer several defects during utilization, including high content of water and volatiles, low caloric value, the lower ignition temperature, and more prone to spontaneous combustion in air. 12 These disadvantages limit the utilization of lignite to some extent.…”
Section: Introductionmentioning
confidence: 99%