The diffusion of methane (CH₄) from coal, which is a crucial factor affecting the production of coalbed methane, exhibits dependence on pore structure. In the present study, the effects of pore structure of different coal ranks on the diffusion coefficient of CH₄ from coals were investigated. The CO₂ sorption, CH₄ isotherm sorption and desorption experiments as well as fractal theory were carried out to evaluate the micropore structure of low- to high-rank coals and the characteristics of CH₄ diffusion. The results revealed that the specific surface area (SSA), pore volume (PV) and fractal dimension (D_f) associated with micropores in coal showed a trend of first decrease and then increase with increase in coal rank, and their SSA and PV were controlled mainly by pore diameters of 0.55–0.6 nm, 0.8–0.83 nm and 1.2–1.3 nm. The micropore structure of high-rank coal was relatively more developed. The Langmuir volume (V_L) also showed a trend of first decrease and then increase with increase in coal rank. The SSA, PV and D_f associated with micropores influenced strongly the CH₄ adsorption capacity of coal. In addition, the CH₄ quantity diffused, and initial diffusion coefficient (D₀) showed a trend of first decrease and then increase with increase in coal rank. The differences among the diffusion coefficients of coals of different ranks are attributed mainly to variations in pore structures. As the SSA, PV and D_f of the micropores increased, the D₀ and D_150s also increased. Pore structure has a certain effect on the diffusion coefficient in a short time. The tortuosity of different rank coals was different, and the length of the diffusion channel of CH₄ in the coal was also different. With increase in tortuosity, the diffusion amount of CH₄ decreased exponentially. The research results are conducive to improving the relevant theory of gas migration in coal and are of great significance to the safe mining of coalbed methane.

_{煤中甲烷（CH 4} ）的扩散是影响煤层气生成的关键因素，它表现出对孔隙结构的依赖性。在本研究中，研究了不同煤级的孔隙结构对CH ₄从煤中扩散系数的影响。通过CO ₂吸附、CH ₄等温吸附和解吸实验以及分形理论，评价了低至高阶煤的微孔结构和CH ₄扩散特性。结果表明，比表面积（SSA）、孔容（PV）和分形维数（D _f) 与煤中微孔伴生的微孔随煤阶的增加呈先减小后增大的趋势，其 SSA 和 PV 主要受 0.55~0.6 nm、0.8~0.83 nm 和 1.2~1.3 nm 的孔径控制。高级煤的微孔结构相对较发达。朗缪尔体积（V _L）也随着煤阶的增加呈现先下降后上升的趋势。与微孔相关的SSA、PV和D _{f强烈影响煤的CH 4}吸附能力。此外，CH ₄扩散量和初始扩散系数（D ₀)随着煤阶的增加呈现先下降后上升的趋势。不同煤级煤扩散系数的差异主要是由于孔隙结构的变化。随着微孔的SSA、PV和D _f增加，D ₀和D _{150 s}也增加。孔结构在短时间内对扩散系数有一定的影响。不同等级煤的曲折度不同，煤中CH ₄扩散通道的长度也不同。随着曲折度的增加，CH _{4的扩散量}成倍下降。研究成果有利于完善煤中瓦斯运移的相关理论，对煤层气安全开采具有重要意义。