Spectroscopic Study on the Evolution of Coal Molecular Structure During CO2 Storage
GAO Fei1, 2, LIN Wan1, JIA Zhe1, BAI Qi-hui1, LIU Jing1, WANG Yi-fan1, LI Wei-ying3
1. School of Safety Science and Engineering, Liaoning Technical University, Huludao 125100, China
2. Liaoning Technical University-Mine Thermal Power State Key Laboratory of Prevention and Control, Ministry of Education, Huludao 125100, China
3. PetroChina Jinxi Petrochemical Company, Huludao 125001, China
Abstract:This study examines the impact of CO2 storage on the pore and molecular structures of coal in unminable coal seams. Low-temperature liquid nitrogen adsorption, low-temperature CO2 adsorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy (Raman) experiments were employed. The evolution rules of pore structure, surface functional groups, macromolecular structure, and microcrystalline structure of coal after CO2 adsorption at different pressures were investigated. The results showed that, after CO2 adsorption, the cumulative specific surface area and cumulative pore volume of micropores decreased. In contrast, the cumulative specific surface area and cumulative pore volume of mesopores and macropores increased. The average pore size of micropores increases overall, and the micropores in the pore structure transition to a direction that favors mesopores and macropores. At the same time, the total content of aromatic hydrocarbons in coal decreased, the aromatic layer spacing d002 increased, the microcrystalline stacking height Lc, the average number of crystal stacking layers n, the aromaticity fa decreased, the content of oxygen-containing functional groups and hydroxyl groups increased, the content of —CH2— decreased, the content of —CH3 increased slightly, and the CH3/CH2 value increased. It shows that after the adsorption of CO2 by coal, the large aromatic structure developed to the small aromatic structure, the branched chain on the aromatic ring gradually became shorter and increased, the aromatic microcrystalline structure was destroyed, and the aromatic layer was more loosely accumulated, resulting in a decrease in the degree of crystallization. With the increase of CO2 adsorption pressure of coal, the peak position difference d(G-D) between D peak and G peak decreases, the intensity ratio ID/IG, half peak width of D peak (FWHM-D), half peak width of G peak (FWHM-G) and WD/WG values increased, and the peak area ratio AS/Atotal, AS/AD, AD/AG, A(GR+VL+VR)/AD values representing the defect structure also increased, it indicates that after coal adsorbed CO2 under different pressure, the macromolecular structure in coal expanded and cracked, the proportion of graphite structure decreased and the proportion of impurity structure increased. The coal structure as a whole develops in the direction of increasing disorder. The research results provide a theoretical basis for the influence of geological storage of CO2 on the microscopic properties of coal. The research results provide a theoretical foundation for understanding the impact of geological CO2 storage.
高 飞,林 菀,贾 喆,白企慧,刘 婧,王一凡,李伟英. CO2封存过程煤分子结构演化规律的光谱研究[J]. 光谱学与光谱分析, 2025, 45(06): 1791-1800.
GAO Fei, LIN Wan, JIA Zhe, BAI Qi-hui, LIU Jing, WANG Yi-fan, LI Wei-ying. Spectroscopic Study on the Evolution of Coal Molecular Structure During CO2 Storage. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(06): 1791-1800.
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