The methylation of aromatic nuclei — I: Implications for the gas evolution
The methylation of aromatic nuclei — I: Implications for the gas evolution
复制标题
芳香核的甲基化 — I：对气体逸出的影响
DOI：
10.1016/j.coal.2019.103302
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发表时间：
2019
影响因子：
5.6
通讯作者：
Lei Tianzhu
中科院分区：
文献类型：
--
作者：
Liu Yanhong;Wu Yingqin;Xia Yanqing;Xing Lantian;Tian Chuntao;Lei Tianzhu
芳香烃是原油和沉积物的重要组成部分。此外，大分子有机质（如干酪根）的结构也是基于芳香核的。各种芳核的早期甲基化和后期去甲基化会影响芳烃以及饱和烃和气态烃的化学成分和碳同位素。本研究的范围是研究芳香核在复杂地质系统中天然气形成和地球化学演化中的作用。模型化合物的使用可以简化复杂体系，选取正二十三烷(n-C23)、正二十四烷(n-C24)和萘(N)作为石蜡和芳烃的模型化合物并进行热解实验。结果表明，在不使用催化剂的情况下，芳香核对气体生成有轻微影响。然而，当温度低于400℃时，在粘土催化作用下，气态组分明显受到芳香核的影响。气态烃中异链烷烃/烷烃的比例因芳香核而降低。由于碳同位素较轻的甲基优先与芳核结合，因此气体产量减少，并且随着温度升高，甲烷 13 C 减少，这与单独石蜡裂解的情况相反。在 II 型和 III 型干酪根形成的热解气体中也可以观察到这种趋势。大分子芳香核与小芳香烃发挥着相似的作用。这些效应主要发生在有机质成熟至高度成熟阶段（古地温≤150℃）。上述探索性实验表明，大量芳香核及其甲基化反应对沉积有机质演化过程中气态烃的分布和碳同位素组成产生重要影响。该研究还为中国西北塔里木盆地深层天然气碳同位素异常（贫~(13C)甲烷和δ13C2-δ13C1值升高）提供了新的解释。
Aromatic hydrocarbons are an important component in crude oil and sediments. Furthermore, the structure of macromolecular organic matter (such as kerogen) is also based on aromatic nuclei. The earlier methylation and later demethylation of various aromatic nuclei would affect the chemical components and carbon isotopes of aromatics as well as saturated hydrocarbons and gaseous hydrocarbons. The scope of the present study was to investigate the role of aromatic nuclei in the formation and geochemical evolution of natural gas in complex geological systems. The use of model compounds could simplify the complex system, andn-tricosane (n-C23),n-tetracosane (n-C24), and naphthalene (N) were selected as model compounds for paraffins and aromatic hydrocarbons and subjected to pyrolysis experiments. The results showed that aromatic nuclei had a slight influence on the gas generation without using a catalyst. However, the gaseous components were substantially affected by aromatic nuclei under the catalysis of clay, when the temperature was lower than 400 °C. The ratios of isoparaffin ton-alkane of gaseous hydrocarbons were reduced by the aromatic nuclei. As carbon isotopically lighter methyls preferred to combine with the aromatic nuclei, the gas productions were reduced, and there was a13C depletion of methane with increasing temperature, which is contrary to the case of paraffin cracking alone. This trend can also be observed in the pyrolysis gases formed from the type II and III kerogens. The macromolecular aromatic nuclei played a similar role with the small aromatic hydrocarbons. These effects would mainly occur in the mature to highly mature stage of the organic matter (the paleo-geothermal temperature is ≤ 150 °C). The above explorative experiments suggested that a large number of aromatic nuclei and their methylation reactions could exert a significant influence on the distributions and the carbon isotopic compositions of gaseous hydrocarbons in the evolution of sedimentary organic matter. This research also provided a new explanation for the carbon isotopic abnormality (the13C-depleted methane and the increasing δ13C2-δ13C1values) of deep natural gas of the Tarim Basin, in northwest China.