干酪根主要由碳、氢、氧组成,是原油和天然气的主要成分。干酪根热解是产生清洁能源的有效方法。本工作利用ReaxFF分子动力学(MD)方法模拟了三种干酪根的热解反应过程,研究其微观机理和产物分布。结果表明,三类干酪根的热解产物显着依赖于分子结构、温度和反应时间。随着温度升高,气态烃以及轻油和重油馏分减少,其中小分子碎片聚合形成新的分子碎片。在等温条件下,随着反应的进行,热解碎片中的某些组分发生聚合,从而产生新的轻油和重油。此外,还利用量子化学分析揭示了干酪根热解机理。首先,C-O、C-N、C-S结构等弱键被分解,生成大的碳和一些重质页岩油碎片。其次,环烷烃和长链烷烃分解,生成大量轻质页岩油和气态烃。最后发生芳环中C=C的分解,发生轻质和重质页岩油的二次分解,以及短链烷烃的进一步分解。此外,氢气(H 2 )的产生发生在热解反应的后期。 C-H键分解形成氢自由基,随后相互碰撞,形成H 2分子。 干酪根的热解和化学分析可以明确确定烃类物质的类型和含量,为页岩气和页岩油的勘探、开发和利用提供科学数据。
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ReaxFF Molecular Dynamics Study on the Microscopic Mechanism for Kerogen Pyrolysis
Kerogen is mainly composed of carbon, hydrogen, and oxygen, which are the main components of crude oil and gas. The pyrolysis of kerogen is an efficient method to generate clean energy. In the present work, the pyrolysis reaction process of three types of kerogen is simulated using ReaxFF molecular dynamics (MD) methods to study the microscopic mechanism and the distribution of products. The results indicated that the pyrolysis products of the three types of kerogen significantly depend on the molecular structures, temperature, and reaction time. As the temperature increases, the gaseous hydrocarbon and the light and heavy oil fractions decreased, where small molecular fragments polymerized to form new molecular fragments. For an isothermal temperature, with the reaction proceeding, some component polymerization of the pyrolyzed fragments occurred, resulting in the generation of new light oils and heavy oils. Moreover, quantum chemical analysis was employed to reveal the kerogen pyrolysis mechanism. First, the weak bonds such as C–O, C–N, and C–S structures were decomposed to generate large carbon and some heavy shale oil fragments. Second, the cycloalkanes and long-chain alkanes were decomposed to generate a large amount of light shale oil and gaseous hydrocarbons. Finally, the decomposition of C═C in the aromatic ring, the secondary decomposition of light and heavy shale oils, and the further decomposition of short-chain alkanes occurred. In addition, the production of hydrogen (H2) occurred at the late stage of the pyrolysis reaction. Hydrogen radicals were formed by the decomposition of C–H bonds and subsequently collided with each other, resulting in the formation of H2 molecules. The pyrolysis and chemical analysis of kerogen can clearly determine the type and content of hydrocarbon substances, providing scientific data for exploration, development, and utilization of shale gas and shale oil.