Characterization of the Chemical Structure of Tectonically Deformed Coals

Abstract

Tectonic deformation damages the macromolecular structures of coal. No evidence can be found of tectonically deformed coal (TDC) structures, in which traces of lattice defects exist. In this study, the mechanisms of ductile deformation and the evolution of the molecular structure have been investigated using coal samples collected from one thrust fault in the Qinan Coal Mine of China. Various characterization methods, such as Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) imaging, were employed to explore the macromolecular structure parameters and related information that can be derived from coal subjected to ductile deformation. The results show that the full width at half maximum (fwhm parameter) for D1 of ductile deformation coal is greater than that of brittle deformation coal as a result of its high content of defects in the graphitic structure. The difference in the ratio of the −CH 2 − and −CH 3 functional groups indicates that coals that undergo brittle deformation have a much higher content of aliphatic chains compared to coals that undergo ductile deformation. Defects may result from the breaking of CO bonds in coal macromolecules, given that the maximum energy of broken CO bonds is less. Hence, the content of CO functional groups is less in TDCs than in primary structure coals. Evidently, high shearing stress leads to strong ductile deformation, while brittle deformation is related to the breaking of a series of bonds as a result of tensile stress and direct bond breakage. Ductile deformation, which is more likely to be related to point and line defects, leads to the assessed changes in the carbon structure.

Geochemical Alteration and Mineralogy of Coals under the Influence of Fault Motion: A Case Study of Qi’nan Colliery, China

“…Coal molecular structures can be altered by tectonic stress, including the degradation of oxygen functional groups [28][29][30]130]. FT-IR is an effective method to characterize hydroxyl groups in coal chemical structures.…”

“…TDCs are defined as coals superimposed by tectonic stress [27]. The chemical structure (specifically referring to the organic structure), physical structure and optical characteristics of TDCs are significantly affected by tectonic deformation [27][28][29]. Strong deformation (especially ductile deformation) on coal significantly increases the total volume and specific surface area of pore structures [30][31][32][33][34][35][36].…”

Impact of tectonic deformation on coal methane adsorption capacity

“…Sample N25 was collected from the hanging wall of the fault, while samples N24-2, N26-1, and N27 were collected from the footwall (Figure 1). More details on samples are given elsewhere (Li et al., 2017). We carried out a proximate analysis for these samples using China’s national standards for proximate analysis of coal (GB/T 212–2008).…”

“…Tectonic deformation damages the macromolecular structures of coal. Evidently, high shearing stress leads to strong ductile deformation, while brittle deformation is related to the breaking of a series of bonds as a result of tensile stress and direct bond breakage (Li et al., 2017). Although much effort has been made to understand kerogen structure, it is essential to validate these structures by comparing simulated adsorption isotherms before analyzing gas adsorption mechanisms.…”

Dynamic Characterization during Gas Initial Desorption of Coal Particles and Its Influence on the Initiation of Coal and Gas Outbursts

“…In the view of the fact that the outbursts mainly occur in the TD coal with low mechanical strength, the research shows that the capacity of gas desorption of the TD coal is better than the PU coal [16]. The reasons for their differences have been clearly explained from the microstructures of coals after a detailed literature review [17][18][19][20][21]. The gas initial desorption law of the TD coal conforms to the Venter formula, while the law of the PU coal can be expressed by the Barrel formula or Venter formula [22,23].…”