Four Chinese bituminous coals were analyzed using X-ray diffraction, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy, and the relationships between structural parameters and coal rank were then established. X-ray diffraction analysis reveals that amorphous and crystalline carbon types exist in coals, and average stacking heights and lateral sizes of the layer structures are various. Good correlations between coal crystalline volume, aromaticity and maximum vitrinite reflectance exist, reflecting their level of maturity. The Fourier-transform infrared spectroscopy analysis shows that A-factor, reflecting the coal hydrocarbon-generating potential, decreases with the increase of maximum vitrinite reflectance. Meanwhile, small values of C-factor and C=O/C=C show little amount of C=O components in coal samples. A good correlation between CH2/CH3 and R0 indicates that the length of aliphatic chains declines with the increase of coal rank. X-ray photoelectron spectroscopy analysis shows that the relative amounts of C–C and C–O groups rise with the increase of R0 value. The higher the R0 is, the lower the amount of C vacancy exists, which results in coal reactivity decreasing, all of which suggest that the variety of coal structure mainly depends on the coal rank.
Bituminous coals Carbon structure Functional groups Coal rank
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This work was supported by the National Natural Science Foundation of China (Grant No. 51474042 & 51774061) and the Fundamental Research Funds for Central Universities (Grant No. 106112017CDJQJ138801). The authors also acknowledge the support provided by the Fund of Chongqing Science and Technology (Project No. cstc2018jscx-msyb0988).
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