Study on the impact of environmental pressure on the diffusion kinetic characteristics of CH₄ in coal

The influence of environmental pressure on the diffusion kinetic characteristics of methane in coal is investigated. Three typical coal samples with high, medium, and low degrees of metamorphism are selected, and the CH₄ desorption characteristics under standard atmospheric pressure and above atmospheric pressure are measured. The diffusion coefficient is obtained based on the single-pore diffusion model. Furthermore, using the macromolecular structure models of coals, the influence of environmental pressure on the diffusion kinetic characteristics is simulated. The results show that the CH₄ desorption process conforms to the Langmuir EXT model, with a fitting coefficient of over 0.99. When environmental pressure increases from atmospheric pressure to 0.20 MPa, the desorption and diffusion of CH₄ are significantly inhibited, and the maximum reduction in the ultimate desorption amount reaches 32.48%. The diffusion coefficient decreases with the increase in environmental pressure, and the reduction extent correlates with the pore structure characteristics of the coal. The self-diffusion coefficient, corrected diffusion coefficient, and transfer diffusion coefficient of CH₄ all decrease with the increase in environmental pressure, which is consistent with the experimental trend. This study reveals the mechanism of the effect of environmental pressure on inhibiting the CH₄ desorption-diffusion process, and the research results can provide a theoretical basis for the improvement of the gas diffusion theory and the prevention and control of gas disasters.