The impacts of stress on the chemical structure of coals: a mini-review based on the recent development of mechanochemistry

Hou, Quanlin; Han, Young‐Kyu; Wang, Jin; Dong, Yijing; Pan, Jienan

doi:10.1016/j.scib.2017.06.004

Cited by 50 publications

(37 citation statements)

References 61 publications

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“…Coal deformation types are classified as brittle deformation, brittle-ductile deformation, and ductile deformation, involving more than ten series of TDCs such as fragmented coal, flax seed coal, scaled coal, and mylonitized coal (Ju et al, 2004;Jiang et al, 2010;Cheng and Lei, 2021). Different tectonic deformation mechanisms have significant effects on the nanopore structure and macromolecular structure of coal (Hou et al, 2012;Pan et al, 2015;Hou et al, 2017;. TDC has a larger total pore volume (TPV) and total specific surface area (TSSA) than original structure coal (OSC).…”

Section: Introductionmentioning

confidence: 99%

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

Ren

Weng

et al. 2022

Front. Earth Sci.

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Pore is the main adsorption and desorption space of coalbed methane (CBM). Pore size configuration and connectivity affect the adsorption/desorption hysteresis effect. Using tectonically deformed coal (TDC) and original structure coal of medium- and high-rank coal as the research objects, through the N2/CO2 adsorption experiment to analyze the pore size distribution and connectivity of different scales. We investigate the control mechanism of heterogeneous evolution in the key pore scales against adsorption/desorption hysteresis characteristics during coal metamorphism and deformation by combining the CH4 isothermal adsorption/desorption experiment under 30°C equilibrium moisture. The findings indicate that the super micropores (<2 nm) are mainly combination ink bottle-shaped pores and have worse connectivity as the degree of metamorphism and deformation increases. The super micropores occupy the vast majority of pore volume and specific surface area; its pore size distribution curve change presents an “M” bimodal type and is mainly concentrated in two pore segments of 0.45–0.70 nm and 0.70–0.90 nm. The effect of ductile deformation exerts a significantly greater effect on super micropores than brittle deformation. The exhibited adsorption–desorption characteristics are the result of the combined effect of the unique pore structure of the TDCs and different moisture contents. The presence of a large number of super micropores is the most important factor influencing the degree of gas desorption hysteresis. The “ink-bottle effect” is the primary cause of gas desorption hysteresis. For CBM development, some novel methods to increase desorption and diffusion rate at the super micropores scale should be considered.

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Section: Introductionmentioning

confidence: 99%

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

Ren

Weng

et al. 2022

Front. Earth Sci.

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“…In addition, we infer that flash-heating mechanisms reported by Kaneki and Hirono (2019) may play a minor role, as the structural and Raman parameters are both insensitive to applied effective normal stress. As a result, we infer that the improvement of molecular structure and maturity observed in our experiments is caused by shear deformation (i.e., strain localization in the shear bands) associated with strain energy (Hou et al, 2017). Similarly, an improvement of the molecular structure of anthracite coal was also observed in creep compaction experiments at axial strain rates of 1.3 × 10 −6 -1.3 × 10 −4 s −1 performed at a confining pressure of 500 MPa and temperatures of 300-600 • C (Ross and Bustin, 1990;Ross et al, 1991).…”

Section: Development Of the Molecular Structure And Maturity Of Coal ...mentioning

confidence: 54%

Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at slow slip rates

et al. 2020

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Abstract. Previous studies show that organic-rich fault patches may play an important role in promoting unstable fault slip. However, the frictional properties of rock materials with nearly 100 % organic content, e.g., coal, and the controlling microscale mechanisms remain unclear. Here, we report seven velocity stepping (VS) experiments and one slide–hold–slide (SHS) friction experiment performed on simulated fault gouges prepared from bituminous coal collected from the upper Silesian Basin of Poland. These experiments were performed at 25–45 MPa effective normal stress and 100 ∘C, employing sliding velocities of 0.1–100 µm s−1 and using a conventional triaxial apparatus plus direct shear assembly. All samples showed marked slip-weakening behavior at shear displacements beyond ∼ 1–2 mm, from a peak friction coefficient approaching ∼0.5 to (nearly) steady-state values of ∼0.3, regardless of effective normal stress or whether vacuum-dry or flooded with distilled (DI) water at 15 MPa pore fluid pressure. Analysis of both unsheared and sheared samples by means of microstructural observation, micro-area X-ray diffraction (XRD) and Raman spectroscopy suggests that the marked slip-weakening behavior can be attributed to the development of R-, B- and Y-shear bands, with internal shear-enhanced coal crystallinity development. The SHS experiment performed showed a transient peak healing (restrengthening) effect that increased with the logarithm of hold time at a linearized rate of ∼0.006. We also determined the rate dependence of steady-state friction for all VS samples using a full rate and state friction approach. This showed a transition from velocity strengthening to velocity weakening at slip velocities >1 µm s−1 in the coal sample under vacuum-dry conditions but at >10 µm s−1 in coal samples exposed to DI water at 15 MPa pore pressure. The observed behavior may be controlled by competition between dilatant granular flow and compaction enhanced by the presence of water. Together with our previous work on the frictional properties of coal–shale mixtures, our results imply that the presence of a weak, coal-dominated patch on faults that cut or smear out coal seams may promote unstable, seismogenic slip behavior, though the importance of this in enhancing either induced or natural seismicity depends on local conditions.

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“…Then, both ring opening and chain dissociation are possible by the mechanical stretching of molecules. 28,61,62 Therefore, the C−S cleavages in thiophene are possible during the superfine comminution. More efforts are needed for further elucidating the bond cleavage behaviors during the comminution both experimentally and theoretically in the future.…”

Section: Resultsmentioning

confidence: 99%

Chemical Properties of Superfine Pulverized Coal Particles. Part 4. Sulfur Speciation by X-ray Absorption Near-Edge Structure Spectroscopy

et al. 2020

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Exploring the transformation mechanisms of sulfur during the superfine comminution plays a crucial role in constructing a coal macromolecular model and developing clean coal technologies. In this work, the occurrences of sulfur in raw coal were quantitatively analyzed by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The sulfur forms in two typical rank coals were compared, and the influence of particle size on the transformation of sulfur was elucidated. Furthermore, the mechanochemical effect on sulfur speciation during the superfine comminution was focused on. The final results indicate that HN coal contains more thiophene with ring structures, while sulfate is the dominant sulfur form in NMG coal. In addition, pyrite can be easily oxidized to sulfate and elemental S, while sulfide, sulfoxide, and sulfone are susceptible to transformation to thiophene during the coalification. It is worth noticing that during the superfine comminution, the organic sulfur shows a decreasing trend, while the inorganic sulfur shows the opposite, suggesting that a conversion from organic to inorganic sulfur exists due to the mechanochemical effect. In addition, two conversion pathways of sulfur are concluded, i.e., sulfide → sulfoxide → sulfone and thiophene → sulfoxide → sulfone → sulfate, which further elucidate the sulfur transformation mechanisms in coal. As the particle size decreases, there is an evident decline for sulfide and thiophene, while pyrite, elemental S, and sulfate generally increase. As for sulfoxide and sulfone, different tendencies are observed in HN and NMG coals due to the complex oxidation processes. The combined application of XANES and XPS is recommended for better characterization of the sulfur speciation and distribution due to the different probing depths in coal particles. This research provides a comprehensive understanding of the mutual transformation between organic and inorganic sulfur in coal. The elucidation of sulfur migration pathways can further promote the exploitation of more valuable desulfurization methods.

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The impacts of stress on the chemical structure of coals: a mini-review based on the recent development of mechanochemistry

Cited by 50 publications

References 61 publications

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at slow slip rates

Chemical Properties of Superfine Pulverized Coal Particles. Part 4. Sulfur Speciation by X-ray Absorption Near-Edge Structure Spectroscopy

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