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Macromolecular Structure Controlling Micro Mechanical Properties of Vitrinite and Inertinite in Tectonically Deformed Coals—A Case Study in Fengfeng Coal Mine of Taihangshan Fault Zone (North China)

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  • Anmin Wang

    (Department of Energy Geology, College of Geoscience & Surveying Engineering, China University of Mining & Technology, Beijing 100083, China
    Shandong Key Laboratory of Depositional Mineralization & Sedimentary Mineral, Shandong University of Science and Technology, Qingdao 266510, China)

  • Daiyong Cao

    (Department of Energy Geology, College of Geoscience & Surveying Engineering, China University of Mining & Technology, Beijing 100083, China)

  • Yingchun Wei

    (Department of Energy Geology, College of Geoscience & Surveying Engineering, China University of Mining & Technology, Beijing 100083, China)

  • Zhifei Liu

    (Department of Energy Geology, College of Geoscience & Surveying Engineering, China University of Mining & Technology, Beijing 100083, China)

Abstract

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 13 C 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.

Suggested Citation

  • Anmin Wang & Daiyong Cao & Yingchun Wei & Zhifei Liu, 2020. "Macromolecular Structure Controlling Micro Mechanical Properties of Vitrinite and Inertinite in Tectonically Deformed Coals—A Case Study in Fengfeng Coal Mine of Taihangshan Fault Zone (North China)," Energies, MDPI, vol. 13(24), pages 1-23, December.
    • Handle: RePEc:gam:jeners:v:13:y:2020:i:24:p:6618-:d:462517
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    References listed on IDEAS

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    1. Katarzyna Godyń & Barbara Dutka & Monika Chuchro & Mariusz Młynarczuk, 2020. "Synergy of Parameters Determining the Optimal Properties of Coal as a Natural Sorbent," Energies, MDPI, vol. 13(8), pages 1-17, April.
    2. Qiang Chen & Jin Jing & Jun Liu & Jianhui Long & Sheng Zhang, 2019. "Productivity Evaluation of Coalbed Methane Well with Geophysical Logging-Derived Tectonically Deformed Coal," Energies, MDPI, vol. 12(18), pages 1-15, September.
    3. Jun Lu & Yun Wang & Jingyi Chen, 2018. "Detection of Tectonically Deformed Coal Using Model-Based Joint Inversion of Multi-Component Seismic Data," Energies, MDPI, vol. 11(4), pages 1-17, April.
    4. Xin Wang & Tongjun Chen & Hui Xu, 2020. "Thickness Distribution Prediction for Tectonically Deformed Coal with a Deep Belief Network: A Case Study," Energies, MDPI, vol. 13(5), pages 1-14, March.
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    Cited by:

    1. Meng Zhao & Anmin Wang & Daiyong Cao & Yingchun Wei & Liqi Ding, 2022. "Differences in Macromolecular Structure Evolution during the Pyrolysis of Vitrinite and Inertinite Based on In Situ FTIR and XRD Measurements," Energies, MDPI, vol. 15(15), pages 1-18, July.

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