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<p>The intricate pore structure and ultra-low permeability of lignite severely impede coalbed methane (CBM) extraction efficiency and aggravate the risks of coal and gas outburst, posing great challenges to safe and efficient exploitation of coal resources. Conventional permeability-enhancement techniques, meanwhile, are plagued by environmental concerns and potential structural damage to coal reservoirs. To address these critical issues, this study proposes the biosurfactant rhamnolipid (Rh) as a green permeability-enhancing agent, and systematically investigates its modification mechanism on lignite structure as well as the corresponding dynamic response characteristics of gas desorption. A multi-dimensional characterization was conducted on lignite samples treated with different concentrations of rhamnolipid, integrating techniques such as CT-based 3D reconstruction, scanning electron microscopy (SEM), low-temperature nitrogen adsorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and gas desorption experiments. The results demonstrate that rhamnolipid treatment significantly optimizes the pore-fracture network of lignite. The most pronounced effect was observed at a concentration of 0.5%: Total porosity increased from 6.90% (control) to 11.88% (0.5% Rh), and effective porosity increased from 2.73% (control) to 6.16% (0.5% Rh). The fracture porosity contribution reached 4.88% (0.5% Rh), which is 2.26 times that of the control group (2.16%). The average throat radius expanded from 15.26&#xa0;μm (control) to 29.03&#xa0;μm (0.5% Rh), indicating substantially improved pore connectivity. Moreover, rhamnolipid induced the dissolution of clay minerals and caused expansion and disordering of the coal microcrystalline structure, decreasing the average crystallite stacking height (<i>L</i><sub><i>c</i></sub>) by 56.1% from 8.47&#xa0;nm (control) to 3.72&#xa0;nm (0.5% Rh) and increasing the interlayer spacing (<i>d</i><sub>002</sub>) from 0.359&#xa0;nm (control) to 0.366&#xa0;nm (0.5% Rh). It also significantly increased the peak area of oxygen-containing functional groups on the coal surface, enhancing the hydrophilicity of the coal. These multi-scale synergistic modifications ultimately enhanced the gas desorption markedly. The ultimate gas desorption amount of the 0.5% treated group reached 4.75&#xa0;mL/g (0.5% Rh), a 12% increase compared to the control (4.18&#xa0;mL/g), along with significantly elevated initial desorption velocity and diffusion coefficients. This study clarifies the intrinsic mechanism underlying rhamnolipid-enhanced gas desorption through a synergistic process of physical pore expansion-crystalline structure modulation-chemical modification, providing a insight for the application of biosurfactants in green coal mining.</p>

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Pore Evolution and Gas Desorption Dynamics in Lignite Enhanced by Rhamnolipid: Insights From CT 3D Reconstruction

  • 期刊论文

  • 发表日期：

    2026年3月10日

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  • Xuan Liu,
  • Xiang Fu,
  • Yujie Zhang,
  • Dawei Song,
  • Rongkun Liu

摘要

The intricate pore structure and ultra-low permeability of lignite severely impede coalbed methane (CBM) extraction efficiency and aggravate the risks of coal and gas outburst, posing great challenges to safe and efficient exploitation of coal resources. Conventional permeability-enhancement techniques, meanwhile, are plagued by environmental concerns and potential structural damage to coal reservoirs. To address these critical issues, this study proposes the biosurfactant rhamnolipid (Rh) as a green permeability-enhancing agent, and systematically investigates its modification mechanism on lignite structure as well as the corresponding dynamic response characteristics of gas desorption. A multi-dimensional characterization was conducted on lignite samples treated with different concentrations of rhamnolipid, integrating techniques such as CT-based 3D reconstruction, scanning electron microscopy (SEM), low-temperature nitrogen adsorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and gas desorption experiments. The results demonstrate that rhamnolipid treatment significantly optimizes the pore-fracture network of lignite. The most pronounced effect was observed at a concentration of 0.5%: Total porosity increased from 6.90% (control) to 11.88% (0.5% Rh), and effective porosity increased from 2.73% (control) to 6.16% (0.5% Rh). The fracture porosity contribution reached 4.88% (0.5% Rh), which is 2.26 times that of the control group (2.16%). The average throat radius expanded from 15.26 μm (control) to 29.03 μm (0.5% Rh), indicating substantially improved pore connectivity. Moreover, rhamnolipid induced the dissolution of clay minerals and caused expansion and disordering of the coal microcrystalline structure, decreasing the average crystallite stacking height (Lc) by 56.1% from 8.47 nm (control) to 3.72 nm (0.5% Rh) and increasing the interlayer spacing (d002) from 0.359 nm (control) to 0.366 nm (0.5% Rh). It also significantly increased the peak area of oxygen-containing functional groups on the coal surface, enhancing the hydrophilicity of the coal. These multi-scale synergistic modifications ultimately enhanced the gas desorption markedly. The ultimate gas desorption amount of the 0.5% treated group reached 4.75 mL/g (0.5% Rh), a 12% increase compared to the control (4.18 mL/g), along with significantly elevated initial desorption velocity and diffusion coefficients. This study clarifies the intrinsic mechanism underlying rhamnolipid-enhanced gas desorption through a synergistic process of physical pore expansion-crystalline structure modulation-chemical modification, providing a insight for the application of biosurfactants in green coal mining.