为研究黄陇煤田低阶煤在煤化作用过程中孔隙系统与分子结构的演化规律及对煤层气吸附/解吸的影响，采集黄陇侏罗纪煤田延安组样品作为研究对象，通过低温液氮吸附、扫描电镜、傅里叶红外光谱分析、¹³C核磁共振分析、X射线光电子能谱分析、X射线衍射分析及煤层气的吸附/解吸实验等技术手段，分析了镜、暗煤在物质组成、孔隙结构、分子结构、吸附能力等方面的差异，揭示了煤化作用对镜、暗煤的孔隙与分子结构演化的控制机理。通过本文的研究获得以下认识：

（1）物质组分方面，镜煤水分、挥发分和镜质组含量高于暗煤；灰分、固定碳、惰质组含量则低于暗煤。随煤化作用程度增高，氧元素含量降低，H/C比减小。煤中的矿物以石英和高岭石为主，暗煤的矿物种类多，且含量高于镜煤。

（2）煤中存在植物组织孔、气孔等不同成因类型孔隙。镜煤孔容低于暗煤，比表面积高于暗煤，暗煤的中孔的数量更多，孔径更大，连通性更好，镜煤微孔更为发育。镜煤孔隙分形维数D₁值与暗煤接近，D₂值大于暗煤，两者孔隙非均质性差异小，镜煤的孔隙表面起伏比暗煤大。镜、暗煤的孔隙演化规律相似，整体可分为3个阶段：第一阶段R_o<0.6%，此时各孔径段的孔隙都较为发育、煤基质结构松散，以上覆岩层的物理压实为主；第二阶段0.6%o<0.65%，压实作用增强，中孔数量快速减少，由于微孔对压实作用的滞后效应和有机质热解生气作用产生气孔使微孔占比增加；第三阶段R_o>0.65%，煤分子结构趋于紧密有序，致使各孔径段的孔隙数量均减少。

（3）分子结构方面，煤中主要元素碳、氧、氮的存在形式为C-C/C-H、C-O、COOH、C=O、吡啶型氮和吡咯型氮。镜、暗煤中C=C、CH₃等结构的含量并无明显差异，镜煤的含氧官能团数量少于暗煤。煤化作用过程中，分子结构的支链化程度减小，COOH、C=O数量减少，脂肪侧链、含氧官能团逐渐脱落，芳碳率和芳香度增大，芳香结构数量增多，微晶结构的延展度增大，堆砌度减小，芳香片层直径变大，面网间距的变化不明显，煤分子结构由松散、混乱趋于有序、致密发展。

（4）吸附/解吸方面，相同温压条件下，镜煤由于微孔更加发育，吸附甲烷能力强于暗煤，吸附热更大。解吸滞后现象总是存在，温度升高利于解吸而不利于吸附，但解吸滞后受孔隙结构和吸附热等因素的共同控制。煤化作用程度增加，甲烷的吸附量先增大后减小，这与第一次煤化作用跃变有关。

（5）分子结构、孔隙结构对吸附甲烷能力的影响方面，煤分子结构的支链化度、延展度越高，羟基越少，吸附能力越强。镜煤吸附能力与芳香度和芳碳率呈正相关关系，暗煤则呈负相关。吸附量与羰基和羧基含量的关系以11%为转折点，低于11%时吸附量随碳氧双键含量增加而减小，高于11%时恰好相反。镜、暗煤的甲烷吸附量与总孔容，总比表面积和分形维数D₁呈正相关，镜煤甲烷吸附量与D₂呈负相关，暗煤甲烷吸附量与D₂则呈正相关。

In order to study the characteristics and evolution law of pore system and molecular structure of low-rank coal in Huanglong coalfield during the coalification and the effect on CBM adsorption/desorption. The coal seams of the Yan'an Formation in the Jurassic coalfield of Huanglong were collected as the research object. By using N₂ adsorption tests, SEM, FTIR, ¹³C-NMR, XPS, XRD and adsorption/desorption experiment of CBM to analyze the differences between vitrain and durain in terms of material composition, pore structure, molecular structure and adsorption capacity. Revealing the control principle of coalification on the pore and molecular structure of vitrain and durain. The following conclusions are obtained through the research of this paper:

(1) In terms of material components, the content of moisture, volatile matter and vitrinite in vitrain is higher than durain, while the content of ash, fixed carbon and inertinite in vitrain is lower than durain. With the increase of coalification degree, the content of oxygen element decreases and the H/C ratio decreases. The minerals in coal are mainly quartz and kaolinite, and the types and contents of minerals in durain are higher than vitrain.

(2) There are different types of pores in coal, such as plant tissue pores and gas pores. The pore volume of vitrain is lower than durain, and the specific surface area of vitrain is higher than durain. The number of macropores in durain is larger, the pore aperture is larger, and the connectivity is better, and the micropores of vitrain are more developed. The fractal dimension D₁ of vitrain is close to durain, and its D₂ is larger than durain. The difference in pore distribution heterogeneity between vitrain and durain is small, and the pore surface fluctuation of vitrain is larger. The pore evolution law of vitrain and durain is similar, and the whole process can be divided into three stages: ①R_o<0.6%. The pores of each aperture are relatively developed, the coal matrix is loose, and external force is main physical compaction of the overlying strata. ②0.6o<0.65%. The compaction effect is enhanced, the number of mesopores and macropores is rapidly decreased. The number of micropores increases due to the hysteresis effect of micropores on compaction and the generation of pores by the pyrolysis of organic matter. ③R_o>0.65%. The coal molecular become tight and the compaction make the number of pores continue to decrease.

(3) In terms of molecular structure, the main elements carbon, oxygen and nitrogen in coal exist in the form of C-C/C-H, C-O, COOH, C=O, pyridinic nitrogen and pyrrolic nitrogen. There is no significant difference in some chemical structure number such as C=C, CH₃ between vitrain and durain. The oxygen-containing functional groups and ash content of vitrain are less than durain. In the process of coalification, the branched degree decreased, the number of COOH and C=O decreases, and the aliphatic chains and oxygen-containing functional groups in the coal molecular structure fall off. The aromatic carbon rate and aromaticity increase, the number of aromatic structure increases, and the coal molecular structure develops from loose and chaotic to orderly and dense. The ductility becomes higher, stacking degree becomes lower. The diameter of the aromatic fragment is bigger, and the distance between adjacent aromatic fragment decreases. In addition, the change of molecular structure is also tortuous and staged, which showed the parameters such as the branched degree, aromatic carbon rate and aromaticity are not completely linearly related to R_o.

(4) In terms of adsorption and desorption characteristics, under the same temperature and pressure, vitrain has more developed micropores, and its adsorption capacity for methane is stronger than durain, also its adsorption heat is larger. The pore sealing ability of vitrain is stronger, the desorption rate is lower, and the pore connectivity of durain is better, so the desorption efficiency is higher than vitrain. The phenomenon of desorption hysteresis always exists. The high temperature is favorable for desorption but not for adsorption, but the desorption hysteresis is jointly controlled by factors such as pore structure and adsorption heat et al. As the coalification degree increases, the adsorption capacity of methane first increases and then decreases, which is related to the first coalification jump.

(5) In terms of the influence of molecular structure on the adsorption capacity of methane, the higher the branched degree and ductility of the coal molecular structure, the less hydroxy groups, and the high adsorption capacity. The adsorption capacity of vitrain was positively correlated with aromaticity and aromatic carbon rate, while that of durain was negatively correlated. The adsorption capacity of vitrain and durain both increased with the increase of ductility. The relationship between the adsorption capacity and the carbonyl and carboxyl group content takes 11% as the turning point. When the carbon-oxygen double bond content is lower than 11%, the adsorption capacity decreases with the increase of the carbon-oxygen double bond content, and it is opposite when the carbon-oxygen double bond content is higher than 11%. The methane adsorption capacity of vitrain and durain was positively correlated with total pore volume, total specific surface area and fractal dimension D₁. The methane adsorption capacity of vitrain was negatively correlated with D₂, while the methane adsorption capacity of durain was positively correlated with D₂.

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