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Understanding the molecular structure characteristics of coal at the molecular level is of great significance to realize the rational utilization and efficient conversion of coal. This paper gives insights into the acquisition of characterization parameters of coal molecular microstructure by testing and analyzing the long flame coal from Qinggangping (QGP) Coal Mine through proximate analysis, ultimate analysis, vitrinite reflectance determination, fourier transform infrared Spectroscopy test (FTIR), X-ray photoelectron epectroscopy test (XPS), carbon nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The results show that benzene rings in the QGP coal are mainly connected in a disubstituted way, accounting for 36.48%. Oxygen atoms mainly exist in the oxygen-containing functional groups such as the ether C–O, C=O and –COO. Aliphatic hydrocarbons in the aliphatic group are mainly of symmetrical -CHx stretching vibration. Hydroxyl groups are mainly composed of OH–OH and OH–O hydrogen bonds, accounting for 29.21% and 21.53%, respectively. Nitrogen atoms exist in the form of C4H5N. The coal molecular is mainly of aromatic carbon structure, where the ratio of bridge aromatic carbon to peripheral carbon is 0.198. There are benzene, naphthalene and anthracene in the coal molecular structure, and the former two chemicals play a dominating role. According to the analysis results, the molecular formula of the QGP coal is finally determined as C205H181O29N3S. On this basis, the two-dimensional and three-dimensional macromolecular models are constructed with the assistance of simulation software. In addition, the 13C-NMR spectra and densities of the constructed molecular models are calculated, which verifies the rationality of the models. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant. [ABSTRACT FROM AUTHOR]

Understanding the molecular structure characteristics of coal at the molecular level is of great significance to realize the rational utilization and efficient conversion of coal. This paper gives insights into the acquisition of characterization parameters of coal molecular microstructure by testing and analyzing the long flame coal from Qinggangping (QGP) Coal Mine through proximate analysis, ultimate analysis, vitrinite reflectance determination, fourier transform infrared Spectroscopy test (FTIR), X-ray photoelectron epectroscopy test (XPS), carbon nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The results show that benzene rings in the QGP coal are mainly connected in a disubstituted way, accounting for 36.48%. Oxygen atoms mainly exist in the oxygen-containing functional groups such as the ether C–O, C=O and –COO. Aliphatic hydrocarbons in the aliphatic group are mainly of symmetrical -CHx stretching vibration. Hydroxyl groups are mainly composed of OH–OH and OH–O hydrogen bonds, accounting for 29.21% and 21.53%, respectively. Nitrogen atoms exist in the form of C4H5N. The coal molecular is mainly of aromatic carbon structure, where the ratio of bridge aromatic carbon to peripheral carbon is 0.198. There are benzene, naphthalene and anthracene in the coal molecular structure, and the former two chemicals play a dominating role. According to the analysis results, the molecular formula of the QGP coal is finally determined as C205H181O29N3S. On this basis, the two-dimensional and three-dimensional macromolecular models are constructed with the assistance of simulation software. In addition, the 13C-NMR spectra and densities of the constructed molecular models are calculated, which verifies the rationality of the models. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant. [ABSTRACT FROM AUTHOR]

To prevent and control the coal seam gas disaster affected by the reverse fault, we performed gas seepage tests, which consider stress-loading and unloading schemes, to investigate the stress change and coal permeability of the mining coal with reverse fault. The experimental results show that the mechanical behavior and permeability change of the mining coal are related to the distance between the coal and the reverse fault. The stress concentration coefficient of the coal body gradually increases. The closer is the distance between the coal and the reverse fault, the larger are the deviatoric stress peak and strain. In comparison with the coal sample M1 that is 5 m away from the reverse fault, the deviatoric stress peak and axial strain of the coal sample M3, 35 m away from the reverse fault, increase by 40.74% and 26.73%, respectively. In this stage, the permeability of M1, M2, and M3 coal samples increases by 22.1%, 28.0%, and 36.7%, respectively. In another stage, the stress concentration coefficient of coal increases to the peak and then decreases, causing the deviatoric stress peak and strain of coal to rise first and then fall. In comparison with the coal sample M4 that is 65 m away from the reverse fault, the deviatoric stress peak and axial strain of coal sample M6, 5 m away from the reverse fault, decrease by 29.48% and 5.55%, respectively. The permeability of coal samples M4, M5, and M6 increases by 23.6%, 37.2%, and 20.8%, respectively. Based on the gas seepage test results, we established the permeability model of mining-induced coal under the influence of a reverse fault, with consideration of the volume changes of coal fractures induced by adsorption and desorption. In the model, the variations of permeability in both stages of the prepeak and postpeak were deduced, which was verified with the experimental data. The verification results demonstrate that the proposed model has the capacity to predict the permeability evolution of mining coal under the influence of a reverse fault. [ABSTRACT FROM AUTHOR]

• Effects of ultrathin (thickness ≈ 1 m) igneous sill intrusion on high volatile bituminous coal were comprehensively investigated. • Differences between the ultrathin and ordinary igneous intrusion on coal's properties were compared. • How to use the changing trend of thermal affected coal's physical and gas desorption characteristics as signs for the hard-detectable small igneous intrusion as well as outburst risk were discussed. As the one of the most catastrophic mining hazards, coal and gas outburst seriously threatens the mining safety of collieries. Previous studies indicate that lots of outbursts are closely related to igneous intrusion. Thus, to further understand the influence of igneous intrusion on coal's physical properties and outburst risk (especially the impacts from ultrathin igneous sill intrusion, which is hard to be detected underground), the combined analyses of petrographic, proximate, pore structure and methane ad/desorption are applied. Results indicate that with the approaching to the ultrathin igneous sill, physical properties of coal change significantly. Due to thermal evolution effect from intrusion, metamorphic grade of coal increases from the high volatile bituminous coal (Ro = 0.6949) of unaffected normal region to the low volatile bituminous coal (Ro = 1.6684), and the altered range of thermal evolution zone is larger than 3 times of the sill thickness but of which the range of strong thermal evolution zone only reaches 0.8 times of the sill thickness. Within the thermal evolution zone: moisture content of coal decrease while the ash content increase when approaching to the sill; micropore volume and specific surface area of the coal are nearly unchanged in the weak thermal evolution zone but reduced in the strong thermal evolution zone, however, methane adsorption capacities of the coal are generally enhanced when comparing to the normal region sample; the transition pores and mesopores pore of the sample close to distal boundary of thermal evolution zone is seriously suppressed (which are 49.21–68.32 % and 20.14–63.31 % of the normal sample, respectively). By comprehensively considering the impact of igneous intrusion on coal, coal locates near the distal boundary of strong thermal evolution zone (about 0.5 times of sill thickness away from the intrusion boundary) seems to have the most serious threat of outburst risk. Additionally, the moisture, ash contents and the gas desorption property of coal has the feasibility to be used as the signs for the hard-detectable small-scale igneous intrusion ahead during roadway tunneling process. Meanwhile, due to the correlation between igneous intrusion and outburst, which can also be regarded as the early warning indicator for outburst prevention. [ABSTRACT FROM AUTHOR]