Anthracite and coal-based graphite (CBG) samples were collected at varying distances from a granite intrusion. Optical microscopy, X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structural evolution of CBG at different scales. The results indicated differences in the graphitization rates of coal macerals and crystallization degree of different graphite-like particles. Differentiated graphitization of coal was caused by deformation, which led to the discontinuous distribution of CBG. This indicates that samples located at the same distance from the intrusion were graphitized to different degrees or that CBG with a similar graphitization degree occurred at varying distances from the intrusion. A possible mechanism for graphitization is strain-induced graphitization, where the local stress concentration leads to preferred orientations of the basic structure units (BSUs), as well as the motion and rearrangement of structural defects, resulting in the formation of a locally ordered structure. The graphitization degree is enhanced as the local graphite structure spreads.

Two vitrinite- and inertinite-rich anthracites from Daliuta and Hujiahe, Shannxi, China, were heated to temperatures to 2900°C. The aim of this study was to investigate the difference of graphitization behavior between vitrinite and inertinite. X-ray diffraction, Raman spectroscopy, and HRTEM analysis were applied to characterize the graphitized products. Graphitization behaves as two aspects, namely crystallization and reorganization of structures. The results show that graphitization temperature for vitrinite is lower than inertinite. Besides, the graphitization of vitrinite is characterized by homogenous crystallization and reorganization of structures. The two processes are likely simultaneous during graphitization. However, the graphitization of inertinite is described by a heterogenous process. A mutation appears both in crystallization and reorganization process and the two processes are non-synchronous during graphitization.

To gain insights into the spectroscopy characteristics from coal to graphite, we investigated different metamorphic degrees of coal-based graphite which were collected from Hunan Province China. In this paper, by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, graphite with different metamorphism degrees has been characterized to explore the evolution of macromolecular structure of organic matter during graphitization. The results show that with the increase of metamorphism degree, the 002-diffraction peak of the series of samples gradually shrinks and narrows, and the peak intensity becomes stronger, indicating that the microcrystalline structure gradually becomes regular and ordered. As the degree of graphitization increase, the uniformity of particle size in coal samples observed gradually increases, and the morphology becomes more regular, transitioning from disordered and irregular shapes to a structured large-scale flake pattern. The crystallinity improves, and the massive coal particles gradually coalesce into large plate crystals, with the inter-particle pores gradually closing. The graphite structure becomes increasingly evident. The FTIR spectra show that as the degree of graphitization increases, the peak at 1,581 cm⁻¹ corresponding to C=C vibrations gradually intensifies. Some inert functional groups are retained throughout the graphitization process. The pores between coal particles gradually close, and the morphology of graphite particles becomes more regular and ordered. Additionally, during the graphitization process, structures similar to carbon nanotubes may develop. Throughout the structural transformation from coal macromolecules to graphite crystals, the size of the sp² planar domains in single-layer graphene increases, and the lattice structure of carbon atoms gradually enlarges. These findings contribute to a comprehensive understanding of the properties and characteristics of coal-derived graphite, and can provide theoretical reference and basis for the metallogenic mechanism of coal-derived graphite and the efficient utilization of coal.

Tectonically deformed coal exhibits significantly different gas adsorption-desorption characteristics from primary structure coal due to intense coal mass deformation, making it a research hotspot in coalbed methane development and gas disaster prevention and control. To explore the differences in the competitive adsorption mechanisms of CH ₄ and CO ₂ between mylonitic coal and primary structure coal, this study took No. 8 coal from the Zhuxianzhuang Mining Area as the research object. Based on experimental results, molecular models of mylonitic coal (C ₂₁₄ H ₁₅₉ N ₃ O ₂₀ ) and primary structure coal (C ₂₀₈ H ₁₅₂ N ₂ O ₁₈₎ were constructed respectively. Isothermal adsorption simulations of single-component and mixed gases of CH ₄ andCO ₂ at different ratios were carried out using molecular dynamics methods. The results show that the adsorption of CH ₄ and CO ₂ in both types of coal belongs to physical adsorption, with stronger adsorption capacity under low temperature and high pressure. Under the same conditions, the adsorption capacity and adsorption heat of CO ₂ are higher than those of CH ₄ , and the adsorption advantage of CO ₂ in mylonitic coal is more prominent. This is closely related to the more complete aromatic ring conjugated π-electron system, abundant oxygen-containing functional groups and a higher proportion of ultramicropores in mylonitic coal. With strong polarity and small kinetic diameter, CO ₂ molecules are more prone to interact with π-electrons and produce the “pore-filling effect”. In mixed gas adsorption, the total adsorption capacity and interaction energy of both coal types increase with the rise of CO ₂ molar fraction. Although the adsorption selectivity coefficient of CO ₂ to CH ₄ decreases, it is always greater than 1, and the selectivity coefficient of mylonitic coal is higher. The energy distribution curve of CO ₂ shifts to adsorption sites with low interaction energy, while that of CH ₄ shows the opposite trend, and the shift amplitude of gas molecular curves in mylonitic coal is larger. In addition, the interaction energy of mylonitic coal is dominated by van der Waals force, accounting for a higher proportion than that of primary structure coal. Its CH ₄ adsorption heat also has a larger fluctuation range, reflecting a stronger competitive adsorption capacity for CO ₂ . The research findings provide a theoretical basis for mine gas prevention and control and efficient coalbed methane development.