Effects of Metamorphism and Deformation on the Coal Macromolecular Structure by Laser Raman Spectroscopy

Pan, Jienan; Lv, Minmin; Bai, Heling; Hou, Quanlin; Li, Meng; Wang, Zhenzhi

doi:10.1021/acs.energyfuels.6b02176

Cited by 77 publications

(55 citation statements)

References 62 publications

(126 reference statements)

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“…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 molecular structure of anthracite coal was also observed 420 in the 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 at temperatures of 300-600 ℃ (Ross et al (1990;1991).…”

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confidence: 53%

“…CO and/or CH4), while above ~300-400 ℃, the amount of most functional groups would decrease rapidly with the cracking of C-H bonds and C-C bonds, generating much gas (Öztaş and Yürüm, 2000;Zhao et al, 2007;Niu et al, 2016;Kaneki et al, 2018). Besides, high resolution TEM, Raman spectroscopy and FTIR analysis performed on the tectonically deformed coals, which often accumulate many shear strains associated with strain energy, suggest that tectonic deformation can improve the ordering of aromatic structure and reduce the content of hydrogen and 410 oxygen (Ju et al, 2005;Cao et al, 2007;Xu et al, 2014;Pan et al, 2017;Song et al, 2018). Therefore, returning to our experiments, under the PT conditions employed (i.e.…”

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confidence: 99%

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

Fan¹,

Liu²,

Hunfeld³

et al. 2020

Preprint

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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 near 100 % organic content, e.g. coal, and the controlling microscale mechanisms, remain unclear. Here, we report seven velocity stepping (VS) and one slide-hold-slide (SHS) friction experiments 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, using a conventional triaxial apparatus plus direct shear assembly. All samples showed marked slip weakening behaviour at shear displacements beyond ~ 1–2 mm, from a peak friction coefficient approaching ~ 0.5 to (near) steady state values of ~ 0.3, regardless of effective normal stress or whether vacuum dry 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 behaviour 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. This may be controlled by competition between dilatant granular flow and compaction enhanced by presence of water. Together with our previous work on 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 behaviour, though the importance of this in enhancing either induced or natural seismicity depends on local conditions.

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confidence: 53%

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confidence: 99%

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

Fan¹,

Liu²,

Hunfeld³

et al. 2020

Preprint

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“…This result was expected because the char sample with highly active AAEM concentration and low degree of graphitization was believed to be more reactive. 38 , 39 …”

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confidence: 99%

Co-Gasification of Cow Manure and Bituminous Coal: A Study on Reactivity, Synergistic Effect, and Char Structure Evolution

Wang

Song

et al. 2020

ACS Omega

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As special waste biomass, cow manure (CM) is also the main pollutant in agricultural production. The combination of cow manure and coal is conducive to the sustainable development of energy and the solution to pollution problems. This work aims to investigate the co-gasification reactivity and synergy of cow manure and Meihuajing (MHJ) bituminous coal blends at 800–1100 °C using a thermogravimetric analyzer, and the correlation between char gasification reactivity and its structural characteristics is performed. The results indicate that the sensitivity of gasification reactivity to temperature is gradually weakened with the proportion of CM increasing. The synergistic effect on reactivity was observed in the co-gasification process of CM/MHJ. The addition of CM promoted the synergistic effect obviously at the low carbon conversion level, and the inhibitory effect with the CM addition on the order degree of char carbon structure was enhanced during the co-gasification process according to Raman spectroscopy analysis. The addition of CM promoted the porous structure evolutions, which make the pore size distribution and the specific surface developed remarkable. The changes in carbon and pore structures can be well related to the gasification reactivity. The findings in this study would be helpful in the understanding of the co-gasification synergy mechanism of cow manure and coal blends.

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“…The Raman spectra of coal are commonly divided into first-order and second-order regions. Generally, there are two peaks, a defect peak (D peak) and a graphite peak (G peak) (Pan et al., 2017). G peak can be attributed to the in-plane vibration of carbon atoms in graphene sheets (Li et al., 2019).…”

Section: Resultsmentioning

confidence: 99%

Impact of tectonic deformation on coal methane adsorption capacity

Jiang

Zhu

2019

Adsorption Science & Technology

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Tectonic deformation can cause significant changes in the physical and chemical structures of coal by damaging the macrostructure and macromolecular composition. For thorough research on the coal tectonic deformation impacts on gas adsorption capacity, this paper collected and summarized the parameters of experimental adsorption isotherms and coal macerals, conducted proximate and ultimate analyses, and systematically discussed the adsorption properties of different structures of coals and the influence of temperature and pressure on coal adsorption. Furthermore, the semi-quantitative relationships between the structural parameters of coal and its methane adsorption capacity are explored. The results show that (1) due to different tectonic stresses, the molecular and porous structures of different types of tectonic coal exhibit significant differences (e.g. sample N25, which is in a fault zone, has the highest methane adsorption capacity), and (2) coal methane adsorption capacity decreases along with increasing temperature. At a pressure of 12 MPa, primary coal (N32) showed Langmuir volume (VL) values of 15.38, 9.58, and 7.86 cm3/g and Langmuir pressure (PL) values of 3.82, 2.07, and 1.81 MPa at temperatures of 30°C, 50°C, and 70°C, respectively. (3) The Langmuir volume appears to have a linear relationship with parameters ID1/IG, Al/OX, and A-factor, as well as a parabolic curve relationship with fa, thereby illustrating that increases of apparent aromaticity can raise CH4 adsorption on coal.

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Effects of Metamorphism and Deformation on the Coal Macromolecular Structure by Laser Raman Spectroscopy

Cited by 77 publications

References 62 publications

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

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

Co-Gasification of Cow Manure and Bituminous Coal: A Study on Reactivity, Synergistic Effect, and Char Structure Evolution

Impact of tectonic deformation on coal methane adsorption capacity

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