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Differences in Macromolecular Structure Evolution during the Pyrolysis of Vitrinite and Inertinite Based on In Situ FTIR and XRD Measurements

Author

Listed:
  • Meng Zhao

    (College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China)

  • Anmin Wang

    (College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China)

  • Daiyong Cao

    (College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China)

  • Yingchun Wei

    (College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China)

  • Liqi Ding

    (College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China)

Abstract

An accurate understanding of molecular structure evolution during pyrolysis is essential for the clean utilization of coal. In this study, middle-rank coal was taken as the research subject, and vitrinite and inertinite samples were stripped from coal using a hand picking and sink–float separation process. In situ Fourier transform infrared (FTIR) spectroscopy and in situ X-ray diffraction (XRD) were performed to compare the macromolecular structure changes between vitrinite and inertinite during pyrolysis. The results show that the aromaticity (I), the polycondensation degree of aromatic rings (DOC), the average lateral sizes (L a ) of basic structure unit (BSU), and the stacking heights (L c ) of BSU in both vitrinite and inertinite during pyrolysis increase continuously with increasing temperature. The values of these parameters for inertinite are higher than those of vitrinite, suggesting that the aromatization degree of inertinite has always been higher than that of vitrinite. In situ FTIR spectroscopy shows that the macromolecular structure evolution of vitrinite and inertinite could be divided into three stages based on temperature: 30–200 °C, 200–300 °C, and 300–500 °C. The content of C–O–C, aromatic C=O, O–H groups, and aromatic ring C=C gradually decreases, while that of the CH 2 in aliphatic hydrocarbons increases between 30 °C and 200 °C. The 200–300 °C stage is mainly filled by the synergistic effects of aliphatic and aromatic groups. The content of aliphatic groups, C–O–C groups, aromatic C=O, and aromatic ring C=C of both vitrinite and inertinite decreases greatly. The 300–500 °C stage is dominated by the aromatization and condensation of macromolecules. The substituents of the aromatic system gradually detach, leading to an increase in I and DOC. From 30 °C to 1000 °C, in situ XRD results reveal a difference in macromolecular structural evolution between vitrinite and inertinite. The arrangement of aromatic layers in vitrinite tends to be ordered during pyrolysis, whereas there are no significant changes in the inertinite. However, the aromatic layers of inertinite are always more compact than that of vitrinite. In addition, the aliphatic side chains of inertinite are more stable than that of vitrinite during the pyrolysis process.

Suggested Citation

  • 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.
    • Handle: RePEc:gam:jeners:v:15:y:2022:i:15:p:5334-:d:869478
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    References listed on IDEAS

    as
    1. Zhao, Jingyu & Wang, Tao & Deng, Jun & Shu, Chi-Min & Zeng, Qiang & Guo, Tao & Zhang, Yuxuan, 2020. "Microcharacteristic analysis of CH4 emissions under different conditions during coal spontaneous combustion with high-temperature oxidation and in situ FTIR," Energy, Elsevier, vol. 209(C).
    2. 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.
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