Coal-based cryptocrystalline graphite is an intermediate phase formed during the transformation of highly metamorphic anthracite into crystalline graphite. In order to explore the relationship between the graphitization degree of coal-based cryptocrystalline graphite and its physical properties from macromolecular structure to provide a theoretical basis for industrial application, samples were tested by X-ray diffraction, electrochemistry, and thermal conductivity and compared with standard graphite (SG) and artificial thermal simulation graphitized samples. The results show that with the increase of graphitization degree and the growth of microcrystalline structure, the electrical impedance of cryptocrystalline graphite decreases, the conductivity increases, the specific capacity of initial discharge increases, and the thermal conductivity increases, which gradually approach the electrical and thermal properties of crystalline graphite. The linear equations between impedance and L_a and L_c are y = -0.42x + 70.44 and y = -1.87x + 70.62, and the correlation coefficients are 0.93 and 0.88. The linear equations between thermal conductivity and the horizontal extension length (L_a) and vertical stacking thickness (L_c) are y = 0.09x + 1.36 and y = 0.4x + 0.76, the correlation coefficients are 0.82 and 0.84., and the reduction of microcrystalline parameters d₀₀₂ and the increase of L_a and L_c lead to a direct improvement of physical properties. Artificial thermal simulation samples also show the same regularity, but their physical properties are lower than those of natural evolution samples. Short-term high-temperature simulation is different from long-term magma heat and pressure, and the growth of graphite microcrystals is more complete under long-term geological conditions, resulting in better physical properties.

Maceral composition is one of the key factors affecting the liquefaction and gasification of coal, which has attracted extensive attention of researchers working on coal chemical industry. To elucidate the impact of vitrinite and inertinite in coal on pyrolysis products, vitrinite and inertinite were extracted from a single coal sample and mixed to create six samples with varying vitrinite/inertinite ratios. The samples were subjected to thermogravimetry coupled online with mass spectrometry (TG–MS) experiments, and the Fourier transform infrared spectrometry (FITR) experiment was used to determine the macromolecular structures before and after the TG–MS experiments. The results show that the maximum mass loss rate is proportional to the vitrinite content and inversely proportional to the inertinite content, and increased vitrinite content accelerates the pyrolysis process and shifts the pyrolysis peak to low temperatures. Based on FTIR experiments, the sample’s CH2/CH3 content, representing the length of aliphatic side chains, decreases significantly after pyrolysis, and the greater the loss of CH2/CH3, the greater the intensity of organic molecule production, indicating that aliphatic side chains are likely to yield organic molecule products. The aromatic degree (I) of samples rises sharply and steadily with increasing inertinite content. After high-temperature pyrolysis, the polycondensation degree of aromatic rings (DOC) and relative abundance of aromatic and aliphatic hydrogen (Har/Hal) within the sample increased significantly, indicating the thermal degradation rate of aromatic hydrogen content is much lower than that of aliphatic hydrogen. When the pyrolysis temperature is lower than 400 °C, the higher the inertinite content, the easier it is to produce CO2, whereas an increase in vitrinite leads to an increase in CO production. At this stage, the “–C–O–” functional group is pyrolyzed to produce CO and CO2. When the temperature exceeds 400 °C, the CO2 output intensity of vitrinite-rich samples is much higher than that of inertinite-rich samples, while the CO output intensity of vitrinite-rich samples is lower, and the higher the vitrinite content, the higher the peak temperature of CO gas production of samples, indicating that when the temperature exceeds 400 °C, the increase of vitrinite inhibits CO production and promotes CO2 production. At this stage, the reduction of each sample’s “–C–O–” functional group after pyrolysis is positively correlated with the maximum CO gas production intensity, and the reduction of each sample’s “–CO” functional group after pyrolysis is positively correlated with the maximum CO2 gas production intensity. As a result, the “–C–O–” functional group is more likely to produce CO, whereas the “–CO” functional group is more likely to be pyrolyzed to CO2. Hydrogen is primarily produced during the polycondensation and aromatization processes, and its production is proportional to the dynamic DOC values after pyrolysis. The higher the I value after pyrolysis, the lower the maximum gas production peak intensity of CH4 and C2H6, which indicates that increasing the aromatic proportion is detrimental to CH4 and C2H6 production. This work is expected to provide theoretical support of the liquefaction and gasification of coal with different vitrinite/inertinite ratios.

This paper reports the mineral compositions and geochemical characteristics of the No. 5⁻² high-sulfur coal (Taiyuan Formation) from Dongpo Mine, Weibei Coalfield, Shaanxi, Northern China via transmitted and reflected light microscopy, scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray fluorescence spectrometry (XRF). We also confirmed the input of intermediate-felsic volcanic ashes into the Taiyuan Formation coals in Dongpo Mine, Weibei Coalfield. The results show that Dongpo coals are enriched in Ga and Li compared to the average values for world hard coals, and they are depleted in Al₂O₃ compared to Chinese coals. The coal low temperature ash contains kaolinite, illite, quartz, calcite, pyrite, and to a lesser extent, chlorite, plagioclase, dolomite, ankerite, and apatite. The concentration anomalies of Ga and Li in No. 5⁻² high-sulfur coal were not caused by the Benxi Formation Bauxite, but by the influence of multiple geological factors. The Middle Proterozoic moyite from the Yinshan Oldland led to the slightly higher Ga and Li contents of the No. 5⁻² coal than those in world hard coals. Input of synchronization volcanic ash, injection of hydrothermal fluids during the syngenetic or early diagenetic stages and influence of seawater further contributed to the Ga and Li enrichment of the No. 5⁻² coal.

In order to study the evolution of the mechanical properties and macromolecular structures in different macerals of tectonically deformed coal (TDC), vitrinite and inertinite samples were handpicked from six block TDCs in the same coal seam with an increasing deformation degree (unaltered, cataclastic, porphyroclast, scaly and powdery coal). The micro mechanical properties were tested by the nanoindentation experiment and the macromolecular structures were measured using ¹³C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results show that the range of hardness and elastic modulus of inertinite is 0.373–1.517 GPa and 4.339–12.158 GPa, respectively, which is significantly higher than that of vitrinite with values of 0.278–0.456 GPa and 4.857–7.810 GPa, respectively. From unaltered coal to powdery coal, the hardness of vitrinite and inertinite gradually decreases, with the difference between these macerals becomes smaller and the elastic modulus of vitrinite shows an increasing trend, while that of inertinite was more variable. Both the NMR and FITR results reveal that the macromolecular structure of inertinite has similar structural transitions as vitrinite. As the degree of deformation increases, the aliphatic side chains become shorter and the aromaticity is increasing. Macromolecular alterations caused by tectonic stress is expected to produce defects in the TDCs, therefore there should be more interspacing among the macromolecular groups for the extrusion of macromolecules caused by the indenter of the nanoindentation experiment, thereby reducing the hardness. The elastic modulus of coal is believed to be related to intermolecular forces, which are positively correlated to the dipole moment. By calculating the dipole moments of the typical aromatic molecular structures with aliphatic side chains, the detachment of the aliphatic side chains and the growth of benzene rings can both increase the dipole moment, which can promote elastic modulus. In addition, the increasing number of benzene rings can create more π-π bonds between the molecules, which can lead to an increase in the intermolecular forces, further increasing the elastic modulus.

The Juhugeng mining area in the Qilian Mountains is the only district of China where terrestrial gas hydrate has been found. This paper aimed at studying the gas migration for gas hydrates based on fluid inclusion and apatite fission track experiments with samples being collected in both the hanging wall (Triassic strata, non-hydrocarbon source rocks) and footwall (Jurassic strata, hydrocarbon source rocks) of drilling cores. Fluid inclusions are found in both the hanging wall and footwall, and are characterized by two generations: the first generation includes gaseous and liquid hydrocarbon fluid inclusions with the homogenization temperature of concomitant saline water inclusions being 83–115°C, and the second generation includes gaseous fluid inclusions with the concomitant homogenization temperature of saline water inclusions being 115–149 °C, suggesting two periods of gas migration. Combining with the reconstruction of the burial and thermal histories, the gas migration history can be elaborated as follows: (1) In the Late Paleogene period (>30 Ma), the gas in the footwall migrated to the hanging wall because of the thrusting of Triassic strata, with the temperature being more than 110 ± 10°C (derived from apatite fission track results), corresponding well with the homogenization temperature of the saline water inclusions of the first generation being 115–149 °C; (2) In the Late Neogene to Quaternary (<8 Ma), the study area were impacted by the intensive faults, leading to the second gas migration with a good match between temperature lower than 110 ± 10°C (derived from apatite fission track results) and the homogenization temperature of saline water inclusions in the second generation (83–115 °C), and the geological age of the second gas migration can be restricted from 8 to 1.8 Ma. The permafrost was formed in Quaternary, so the controversial gas hydrate formation pattern can be determined that the gas should be accumulated before the permafrost was formed.