基于高能自由基化学活化的煤孔隙演化规律及增透机制研究

Coal pore evolution law and permeability enhancement mechanism based on chemical activation by high-energy free radicals

提高煤层渗透率是实现煤层瓦斯高效抽采、防治矿井瓦斯灾害的重要途径。针对瓦斯在煤结构微孔堆积、孔隙渗透率低的问题,提出孔壁反应性消解的煤结构扩孔增容思路,采用活化过硫酸盐生成羟基和过硫酸根等高能自由基活化消解煤有机结构,分析了作用煤体的孔隙分布、孔容、比表面积及孔隙分形特征的演变规律,阐明了煤活性官能团及结构特征参数的变化规律,揭示了煤孔壁芳香结构反应性溶蚀的扩孔增容机制。结果表明,羟基和过硫酸根高能自由基活化作用煤体后,煤样的微孔增加主要集中在0.7nm以下的超微孔,且微孔扩孔作用显著,生成了大量的介孔和大孔,含瓦斯高阶烟煤介孔体积增长了50%以上,大孔体积增长了40%以上。随着煤阶增加,扩孔增容率显著提升,无烟煤介孔体积增长达到了578.91%,大孔体积增长达到了331.37%。煤的比表面积增大均在50%以上,同时处置后煤体分形维数D1增大,孔隙粗糙度增大,增加了孔隙宽度和孔隙连通性。煤侧链的甲基亚甲基含量降低,芳香环含量和芳香度显著增大,阐明了煤孔壁中侧链脂肪烃和低聚合度芳香环反应消解的扩孔增容机制。研究结果为活化过硫酸盐在煤层瓦斯增透抽采中的现场应用提供了理论基础。

Improving coal seam permeability is an important way to achieve efficient coal seam gas extraction and prevent and control gas disasters in mines. Aiming at the problem of gas accumulation in micro-pores of coal structure and low pore permeability,proposes the idea of pore wall reactive dissolution of coal structure to expand pore capacity,adopts activated persulfate to generate hydroxyl and persulfate ion and other high-energy radical activation to dissolve coal organic structure,analyzes the evolution law of pore distribution,pore volume,specific surface area and pore fractal characteristics of treated coal body,elucidates the change characteristics of coal reactive functional groups and structural characteristic parameters,and reveals the mechanism of reactive dissolution of coal pore wall aromatic structure to expand pore capacity. The results showed that after the activation of hydroxyl and persulfate high energy radicals on the coal body,the increase of micropores of coal samples was mainly concentrated in supermicropores below0. 7nm,and the micropore expansion effect was significant,generating a large number of mesopores and macropores,and the pore volume of mesopores of high rank bituminous coal containing gas increased by more than50% and the pore volume of macropores increased by more than40%;with the increase of coal rank,the expansion of pore volume increased significantly,and the increase of mesopore volume of anthracite coal reached578. 91%,and the increase of macropore volume reached331. 37%;the increase of specific surface area of coal were above50%,meanwhile,the increase of fractal dimension D1of the treated coal body,increased pore roughness,increased the pore width and pore connectivity;the methylene content of coal side chains decreased and the aromatic ring content and aromaticity increased significantly,which elucidated the mechanism of pore expansion and capacity increase by the reaction dissipation of side chain aliphatic hydrocarbons and low polymerization degree aromatic rings in the pore wall. The results of the study provide theoretical support for the field application of activated persulfate in coal seam gas permeability enhancement and extraction.