煤成烃反应机制的红外光谱证据

FTIR study of hydrocarbon generation reactions of coal

张爽 姚素平 尹宏伟

ZHANG Shuang YAO Suping YIN Hongwei

南京大学 地球科学与工程学院, 南京 210046

School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210046, China

应用傅里叶变换红外光谱（FTIR）分析及计算机分峰拟合技术，对不同温度下热模拟煤样的脂肪族、芳香族官能团含量及其化学结构热演化特征进行了精细表征与分析。研究表明，除了热裂解反应，脂肪族芳构化反应与芳香族缩聚反应在煤成烃过程中同样占有重要地位。煤样脂肪氢及芳香氢的含量变化均为多种不同类型化学反应综合作用的结果，单一的官能团含量分析并不能准确反映煤的成烃反应机制及潜力。进一步对煤样脂肪族及芳香族化学结构热演化特征分析发现，煤成烃初期以活化能较低的长链脂肪族结构断裂脱落、生成液相产物为主，并在325℃到达生油高峰；325~400℃阶段，前期断裂脱落的长链脂肪族结构除了进一步热裂解生成气态烃产物，还有相当一部分发生了芳构化反应，导致煤样芳香氢含量升高。随着热模拟温度的升高，芳环上的短链脂肪族取代基首先从苯环β位开始断裂脱落，发生甲基化作用；随后甲基、桥键等在高温作用下进一步从苯环上断裂脱落，发生去甲基化作用。煤成烃过程中芳香族缩聚反应具有明显的阶段性，其中300~400℃阶段主要为脂肪族芳构化产物的缩聚。而煤样原有芳香族结构由于芳环取代基及桥键的阻碍作用，其缩聚反应则依赖去甲基化作用的进行，主要发生在500~600℃高温阶段。

The thermal evolution characteristics of bulk coal as well as chemical structural characteristics of aliphatic and aromatic groups within an artificially matured coal series were characterized and analyzed combining the FTIR analysis with a computer curve-fitting method. The results showed that except for thermal cracking reactions, the aromatization reactions of aliphatic structures and the condensation reactions of aromatic structures also played important roles in the hydrocarbon formation of coal. Both contents of aliphatic hydrogen and aromatic hydrogen were subjected to more than one type of chemical reaction. Functional group analysis alone cannot accurately reflect the mechanism of hydrocarbon generation reactions and the hydrocarbon generation potential of coal. Further investigations on the thermal evolution characteristics of aliphatic and aromatic chemical structures indicated that the initial phase of hydrocarbon generation of coal is dominated by the formation of oil products due to the prior cleavage of long-chain aliphatic groups with lower bond energies. The highest yield of oil products is reached at 325℃. Except for generating gaseous hydrocarbons via further thermal cracking, a significant proportion of long chain aliphatic structures are involved in aromatization reactions in the range of 325-400℃, leading to the increased content of aromatic hydrogen of coal. With increasing temperature, the short chain aliphatic substituents begin to cleave from the β-position to aromatic rings, indicating the methylation of aliphatic substituents. At higher temperature stage further demethylation takes place with the breaking of methyl and bridged bonds connected to aromatic rings. The condensation reactions during hydrocarbon formation of coal take place in stages. The lower temperature phase in the range of 300-400℃ is dominated by the condensation of aromatization products. Due to the steric hindrance of substituents and bridged bonds, the condensation between the primary aromatic structures of coal mainly takes place along with the demethylation effect in the range of 500-600℃.

“十三五”国家科技重大专项“东濮凹陷油气富集规律与增储领域”（2016ZX05006-004）资助。

https://doi.org/10.11781/sysydz201804538