Abstract Coalbed methane (CBM) is mainly adsorbed in coal reservoir. To explore the methane (CH4) adsorption mechanism in coal, this paper investigated the relationships among CH4 adsorption characteristics and microstructure and chemical composition of the coal samples through different solvent treatments. The results indicate that after THF and CH3CH2OH treatments, aromatic and aliphatic functional groups decline significantly as hydrocarbon low molecular weight compounds are dissolved, while oxygen-containing functional groups show a remarkably increase after acid solvent treatment. However, it can be found that the inter-layer spacing (d002) and stacking height (Lc) values of the basic structure unit of coal show enlarged characteristics, except for the residue treated by CH3COOH. The macropore content of coal samples under THF treatment increases greatly and the micropores all but disappear, while other samples show an increase. Actually, chemical structure also contributes to nanopore structure. Both the specific pore volume and specific surface area show an opposite trend slightly with microcrystalline structure parameters, while the d002 value gives a ‘U’ shape distribution for pore structure parameters. Further, combined with adsorption curves, adsorption potential theory and Clausius-Clapeyron equation, the adsorption capacity and adsorption heat indicate a physical adsorption process. However, there is no perfect correlation among microcrystalline structure parameters, pore structure distribution and CH4 adsorption. On the other hand, low molecular weight compounds such as aromatic hydrocarbons and aliphatic hydrocarbons combined to macromolecular structures by non-covalent bonds, are easy to form competitive adsorption with CH4 molecule by occupying CH4 adsorption sites. Meanwhile, these aromatic and aliphatic structures as the non-polar functional groups on the surface of coals can also promote CH4 adsorption, but the polar oxygen-containing functional groups (especially –OH and C–O) weaken CH4 adsorption capacity greatly. Totally, the more complex the chemical composition of coal surface is, the more important it is on CH4 adsorption.

中文翻译：

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煤的微观结构和化学成分对甲烷吸附的影响

摘要 煤层气（CBM）主要吸附在煤储层中。为探究煤中甲烷(CH4)的吸附机理，本文研究了不同溶剂处理后煤样的CH4吸附特性与微观结构和化学成分之间的关​​系。结果表明，经过THF和CH3CH2OH处理后，芳香族和脂肪族官能团随着烃类低分子量化合物的溶解显着下降，而含氧官能团在酸溶剂处理后显着增加。但可以发现，煤的基本结构单元的层间距（d002）和堆积高度（Lc）值表现出放大的特征，但经过CH3COOH处理的残渣除外。THF处理后煤样的大孔含量大大增加，微孔几乎消失，而其他样品则呈增加趋势。实际上，化学结构也有助于纳米孔结构。微晶结构参数的比孔容和比表面积都显示出略微相反的趋势，而 d002 值给出了孔结构参数的“U”形分布。此外，结合吸附曲线、吸附势理论和克劳修斯-克拉佩龙方程，吸附容量和吸附热表明了物理吸附过程。然而，微晶结构参数、孔结构分布和CH4吸附之间没有完美的相关性。另一方面，芳香烃、脂肪烃等低分子化合物通过非共价键结合成大分子结构，通过占据CH4吸附位点，容易与CH4分子形成竞争吸附。同时，这些作为煤表面非极性官能团的芳香族和脂肪族结构也能促进CH4的吸附，但极性含氧官能团（特别是-OH和C-O）大大削弱了CH4的吸附能力。总的来说，煤表面化学成分越复杂，对CH4吸附的影响就越大。这些芳香族和脂肪族结构作为煤表面的非极性官能团也能促进CH4的吸附，但极性含氧官能团（特别是-OH和C-O）大大削弱了CH4的吸附能力。总的来说，煤表面化学成分越复杂，对CH4吸附的影响就越大。这些芳香族和脂肪族结构作为煤表面的非极性官能团也能促进CH4的吸附，但极性含氧官能团（特别是-OH和C-O）大大削弱了CH4的吸附能力。总的来说，煤表面化学成分越复杂，对CH4吸附的影响就越大。