Impacts of CO₂/CH₄/N₂ adsorption/desorption on the macromolecular structure of anthracite: Insights from in situ Raman spectroscopy

Authors

WANG Tian, School of Resources and Environment, Henan Polytechnic University, Jiaozuo 454003, ChinaFollow
PAN Jienan, School of Resources and Environment, Henan Polytechnic University, Jiaozuo 454003, ChinaFollow
LI Meng, School of Resources and Environment, Henan Polytechnic University, Jiaozuo 454003, China
WANG Kai, School of Resources and Environment, Henan Polytechnic University, Jiaozuo 454003, China
TANG Zhuyun, No.156 Coalfield Geologic Exploration Team, Coalfield Geology Bureau of Xinjiang Uygur Autonomous Region, Urumqi 830009, China
CHENG Nannan, School of Resources and Environment, Henan Polytechnic University, Jiaozuo 454003, China
HOU Quanlin, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

Abstract

Objective and Methods The adsorption/desorption of coalbed methane (CBM) not only induces the macroscopic deformations of coals but also significantly alters their macromolecular structures, with different gases exhibiting greatly varying mechanisms and influence degrees. Utilizing an independently developed in situ laser Raman spectroscopy system, this study revealed the differential structural responses and mechanisms of anthracite under CO₂, CH₄, and N₂ injection. Results and Conclusion Experimental results indicate that gas injection led to notable blue shifts in the D₄, D, D₃, and G peaks characterizing the microcrystalline structures of coals. In contrast, red shifts were observed during desorption, with the structures failing to recover completely. With an increase in the adsorption pressure, the A-to-G area and intensity ratios (A_D/A_G and I_D/I_G, respectively), as well as the full width at half maximum (FWHM) of the D peak, increased significantly. These results indicate reduced microcrystalline sizes, decreased degrees of structural order, and increased defects. Among the studied gases, CO₂ induced the most substantial structural variations, with the influence degrees of the three gases decreasing in the order of CO₂, CH₄, and N₂. These microstructural variation patterns provide a molecular-scale theoretical basis for enhanced CBM recovery in deep coal seams via CO₂/N₂ injection and the geological sequestration of CO₂.

Keywords

anthracite, adsorption deformation, Raman spectrum, gas injection, macromolecular structure, expansion/contraction

DOI

10.12363/issn.1001-1986.25.02.0110

Recommended Citation

WANG Tian, PAN Jienan, LI Meng, et al. (2025) "Impacts of CO₂/CH₄/N₂ adsorption/desorption on the macromolecular structure of anthracite: Insights from in situ Raman spectroscopy," Coal Geology & Exploration: Vol. 53: Iss. 8, Article 5.
DOI: 10.12363/issn.1001-1986.25.02.0110
Available at: https://cge.researchcommons.org/journal/vol53/iss8/5

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