萃取改造对煤体多尺度孔隙结构与甲烷吸附动力学的影响机制

Mechanism of extraction modification on multiscale pore structure and methane adsorption kinetics in coal

  • 摘要: 水力化技术作为煤层瓦斯治理的重要手段,常辅以有机化学抑制剂注入,通过抑制瓦斯的吸附行为来提升煤层瓦斯的抽采效率。为了探明有机试剂对煤体理化性质的改造作用及甲烷吸附动力学行为受到有机组分的影响机制,利用有机试剂二氯甲烷(DCM)、四氢呋喃(THF)、N,N-二甲基甲酰胺(DMF)和乙醇(EA)对试验煤样进行有机组分萃取和孔隙结构改造,综合采用傅里叶变换红外光谱(FT-IR)、场发射扫描电子显微镜(SEM-EDS)、拉曼光谱(Raman)、X射线光电子能谱(XPS)、13C核磁共振(13C-NMR)等表征手段和低压N2、低温CO2流体侵入法等孔隙分布测试手段对萃取改性前后的煤体物理及化学结构进行定性定量分析,探索基于微孔填充的积分优化模型的计算结果与萃取改造前后煤体对甲烷吸附的影响机制。结果表明:萃取改造作用导致高变质程度的无烟煤中有机组分发生不同程度变化,其中DMF的改造效果较强,其含氧官能团相对含量锐减,导致了煤的甲烷吸附能力降低(最大程度可从空白对照组的26.536 4 cm3/g降至DMF处理后的10.983 0 cm3/g);同时萃取改造作用改变了煤的孔隙结构,即中、大孔相对增加,微孔相对降低。通过优化微孔填充理论,解释了化学结构改变导致甲烷吸附量衰减作用机制;同时,利用分子模拟手段,通过径向配位分布函数定量对比了萃取改造下煤体限域效应强弱,获得了微孔填充与有机组分改变的内在关系,从微观化学角度解释了甲烷在煤体内部的吸附倾向。

     

    Abstract: Hydraulic stimulation, as a pivotal technique for coalbed methane control, is frequently integrated with organic chemical inhibitors to enhance gas drainage efficiency by suppressing methane adsorption through competitive adsorption mechanisms. To explore the modification effects of organic reagents on the physicochemical properties of coal and the mechanisms influencing methane adsorption kinetics due to organic components, experiments were conducted using organic reagents (DCM, EA, THF, and DMF) to extract organic components from coal samples and modify their pore structure. A comprehensive qualitative and quantitative analysis of the physical and chemical structure of the coal before and after modification was performed using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM-EDS), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (13C-NMR characterization techniques), along with low-pressure N2 and low-temperature CO2 fluid invasion methods for pore distribution testing. The study investigates the impact mechanism of the modified coal on methane adsorption through calculations based on an integrated optimization model of micropore filling. The results indicated that the extraction process led to varying degrees of change in the organic components of high-metamorphic bituminous coal, with DMF showing the strongest effect. The relative content of oxygen-containing functional groups significantly decreased, resulting in reduced methane adsorption capacity of the coal (from 26.536 4 cm³/g in the control group to 10.983 0 cm³/g after DMF treatment). Additionally, the extraction process altered the pore structure of the coal, increasing the relative amount of mesopores and macropores while decreasing micropores. The mechanism behind the decrease in adsorption capacity due to chemical factors was elucidated by optimizing the micropore filling theory. Concurrently, molecular dynamics simulations were employed to quantitatively assess the confinement effects in extraction-modified coal systems via radial distribution function (RDF) analysis. This approach revealed the intrinsic relationship between micropore-filling behavior and the reorganization of organic components, providing a microscopic chemical interpretation of methane adsorption propensity within the coal matrix.

     

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