Studies on the Structure of Coals of Different Rank

Abstract

The distribution of hydrogen types in the soluble fractions from the depolymerization of a series of coals has been determined by NMR analysis. The aromatic hydrogen content varies from 20 to 32% of the total hydrogen, and no simple relationship exists with coal rank. β-Paraffinic plus naphthenic hydrogens, the major type, exceed the α-hydrogens and comprise 38-66% of the nonaromatic hydro gens. The most striking variation in the structure of the six coals is the number of methylene bridges. The degree of depolymerization with phenol-BF 3 can be correlated directly with the number of methylene bridges found in the soluble fractions. A general coal structure in accord with our results consists of large units (MW > 4000) and smaller units (MW, 300-600) connected by methylene bridges.Jhe distribution of hydrogen types in coals continues to be a subject of con siderable interest in coal structure studies. Published data indicate that the fraction of aromatic hydrogens usually increases with increasing rank, but the absolute values depend on the specific analytical method used (7). Hydrogen type analysis of a single coal based on the application of NMR spectroscopy to the soluble fraction from depolymerization with phenol-BFa has been re ported by us (3). The conversion of coal to soluble fragments in substantial yields under very mild conditions permits a reliable determination of the hydrogen types by NMR analysis, and these results can be extrapolated to the parent coal with considerable confidence.This procedure has now been extended to a series of coals varying in rank from lignite (70% C) to a low volatile bituminous coal (91% C). In addition to determining the amount of aromatic and aliphatic hydrogens, the aromatic group will be further subdivided into monocyclic and polycyclic types. A more 493 Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 11, 2015 |

Coal as an abundant source of graphene quantum dots

“…The structure of coal is complex [2][3][4][5] ; the simplified composition contains angstrom or nanometre-sized crystalline carbon domains with defects that are linked by aliphatic amorphous carbon 6 . Although research on the chemistry of coal has been reported [7][8][9] , the angstrom-and nanoscale crystalline domains of coal are so small and difficult to access so as to impede their further use in electrical, mechanical and optical applications.…”

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“…1 As a molecular solid, coal has a complex structure. [2][3][4][5] The crystalline carbon within the coal structure consists of abundant irregular, polymerized aromatic hydrocarbon units, such as angstrom-or nanometer-sized crystalline carbon domains that are joined by weak cross-links. 6,7 Compared with crystalline carbon allotropes, so-called lattice solids, such as graphite and diamond that have found applications in areas such as microelectronics, optoelectronics and biomedicine, 8,9 coal is mainly used as a combustible energy resource due to its structural characteristics.…”

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