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<p>With the deepening of China’s energy structure optimization, the development of coalbed methane (CBM) is imperative. Nanoscale pores have a momentous impact on the occurrence state and migration performance of CBM. The macromolecular structure of coal controls the distribution characteristics of nanoscale pore structure, and its alteration has a modifying effect on the morphology and size of these pores. Microwave–LN2 freeze–thaw (MLFT) technology is an effective technology for enhancing permeability. This study investigated the influence mechanism on the structural evolution characteristics of coal macromolecules based on X-ray diffraction and Raman spectroscopy. The results indicated that, after fracturing, the density of cross-link bond and proportion of aromatic structures of coal macromolecules increase, which promoted the displacement, directional stacking and parallel arrangement of aromatic layers. After treatment, the aromaticity of the modified coal samples increased by 58.6% to 83.5%, and <i>L</i><sub><i>a</i></sub>/<i>L</i><sub><i>c</i></sub> ultimately increased by 35.6%. With the condensation and aromatization of macromolecular structure, the microcrystal structural units tended to flatten and molecular chains became ordered, thereby enhancing pore size and space volume, which promotes desorption and seepage efficiencies of gas in coal. This study contributes to the understanding of the microstructural evolution of coal under MLFT and provides theoretical support for this technology optimization and the development strategy of CBM resources.</p>

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Potential Impact of Macromolecular Structure and Nanoscale Pore on Coal Matrix Subjected to Microwave–LN2 Freeze–Thaw Cycles

  • 期刊论文

  • 发表日期：

    2026年2月18日

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  • Xi Wu,
  • He Li,
  • Huihui Liu,
  • Quanle Zou,
  • Jiexin Lu,
  • Junhui Mou,
  • Baiquan Lin,
  • Wei Yang,
  • Jieyan Cao

摘要

With the deepening of China’s energy structure optimization, the development of coalbed methane (CBM) is imperative. Nanoscale pores have a momentous impact on the occurrence state and migration performance of CBM. The macromolecular structure of coal controls the distribution characteristics of nanoscale pore structure, and its alteration has a modifying effect on the morphology and size of these pores. Microwave–LN2 freeze–thaw (MLFT) technology is an effective technology for enhancing permeability. This study investigated the influence mechanism on the structural evolution characteristics of coal macromolecules based on X-ray diffraction and Raman spectroscopy. The results indicated that, after fracturing, the density of cross-link bond and proportion of aromatic structures of coal macromolecules increase, which promoted the displacement, directional stacking and parallel arrangement of aromatic layers. After treatment, the aromaticity of the modified coal samples increased by 58.6% to 83.5%, and La/Lc ultimately increased by 35.6%. With the condensation and aromatization of macromolecular structure, the microcrystal structural units tended to flatten and molecular chains became ordered, thereby enhancing pore size and space volume, which promotes desorption and seepage efficiencies of gas in coal. This study contributes to the understanding of the microstructural evolution of coal under MLFT and provides theoretical support for this technology optimization and the development strategy of CBM resources.