广泛分布在我国西北部的富油煤，是一种煤、油、气属性兼备的特殊矿产资源，具有高油气属性。作为富油煤形成的基础，成煤背景的差异性导致不同沉积盆地、不同沉积层位的煤焦油产率不同，本质应归因于其原始分子结构在热解过程中的演化行为特点。本研究以鄂尔多斯盆地延安组以及三塘湖盆地八道湾组煤样为研究对象，结合热失重分析以及原位热解红外光谱对四个不同焦油产率的煤样进行研究。

研究结果表明：（1）分别选择覆水程度依次加深、还原性依次增强的干燥森林沼泽、潮湿森林沼泽、低位泥炭沼泽和强还原泥炭沼泽成煤背景的煤样，后三种均为富油煤且其亚甲基结构相对含量显著高于其他脂肪族结构，表现为脂肪族侧链结构的长度更长且支链化程度更低。（2）基于热解失重率（TG）和失重速率（DTG）分析，随着成煤背景还原性的增强，在高于350 ℃热解阶段煤的失重程度增强、活化能增强，且具备更多可断裂的C_al-C_al、C_al-H、C_al-O以及C_al-N键（约占总裂解量的30-60%）；随着升温速率的提高，煤的失重程度降低，煤中C_al-C_al、C_al-H、C_al-O以及C_al-N键的断裂程度增高。（3）基于原位热解红外光谱分析，在350 ℃之前，各煤样CH₂和CH结构协同裂解的程度一致，CH/CH₂值趋于平缓；在350 ℃后的分解程度加剧阶段，CH₂、CH结构主导着富油煤中脂肪族结构含量的演化，其分解程度与煤焦油产率呈良好对应性。随着成煤背景还原性的增强，在350 ℃热解阶段交联反应相对更弱，富氢的化学键断裂程度增强。到500 ℃后，具有强还原性成煤背景的富油煤CH结构减少量多，CH₂结构相对富集，脂肪族结构表现出弱交联；而具有弱还原性成煤背景的煤游离端CH₃结构断裂明显，CH₂结构迅速减少，CH结构相对富集，脂肪族结构表现出强交联。

Tar-rich coal, which is widely distributed in Northwest China, is a unique mineral resource known for its high oil and gas properties. The variance in coal-forming environments gives rise to varying coal tar yields across different sedimentary basins and layers. The evolution of the original molecular structure during pyrolysis is largely influenced by these characteristics. This study focused on coal samples from the Yan'an Formation in the Ordos Basin and the Badawan Formation in the Santanghu Basin. Four coal samples with different tar yields were analyzed using thermogravimetric analysis and in-situ pyrolysis infrared spectroscopy.

The study results indicated that: (1) The coal samples were selected based on sedimentary backgrounds of dry forest swamp, wet forest swamp, low peat swamp, and strong reduction peat swamp, with increasing water coverage and reducibility. The last three samples are tar-rich coal, with a significantly higher relative content of CH₂ structure compared to other aliphatic structures. This indicated that the aliphatic side-chain structures of tar-rich coal are longer and less branched. (2) Based on thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis, it was found that as the reducing nature of the coal-forming environment increases, there is a higher degree of weight loss during the pyrolysis stage above 350 ℃. Additionally, the activation energy also increases and there are more breakable C_al-C_al, C_al-H, C_al-O, and C_al-N bonds being formed (approximately 30-60% of the total breakage amount). On the other hand, as the heating rate increases, the degree of weight loss of coal decreases while the breakage degree of C_al-C_al, C_al-H, C_al-O, and C_al-N bonds in coal increases. (3) Based on in-situ pyrolysis infrared spectroscopy analysis, it was found that before 350 ℃, the degree of synergistic cracking of CH₂ and CH structures in various coal samples remains consistent, and the CH/CH₂ ratio levels off. However, during the intensified decomposition stage after 350 ℃, the evolution of aliphatic structures in tar-rich coal is mainly dominated by CH₂ and CH structures, with the degree of decomposition closely correlated with coal tar yield. As the reducing nature of the coal-forming environment increases, the degree of cross-linking reaction is relatively weaker at about 350 ℃ pyrolysis stage, leading to an increased breakage of hydrogen-rich chemical bonds. By 500 ℃, a stronger reducing coal-forming environment results in a greater decrease in CH content in tar-rich coal, with CH₂ becoming relatively enriched and aliphatic structures showing weak cross-linking. Conversely, in coal sample with a weaker reducing coal-forming environment, cleavage of terminal CH₃ becomes evident, CH₂ rapidly decreases, CH becomes relatively enriched, and aliphatic structures exhibit strong cross-linking.

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