生物油氧化过程的ReaxFF MD模拟研究—动力学性质、反应机理及替代燃料构建

发布时间：2018-03-14 03:16

本文选题：RP-3　切入点：生物油　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文　论文类型：学位论文

【摘要】：生物油高温氧化微观机制的研究对于生物油的合理利用至关重要。由于生物油组成复杂,且其燃烧过程的温度较高,目前缺乏对其燃烧中间产物的检测方式。量子力学方法是研究燃烧过程时的一种常用理论方法。能对热力学参数进行准确的计算,同时与恰当的反应速率理论结合能得到燃烧的动力学性质。但因考虑电子相关,其计算成本高昂,可计算的体系规模在～100原子数量级,难以对复杂的生物油体系进行进行较为全面的描述。同时量子化学方法研究化学反应微观机制通常需要对反应路径进行预设,这对于复杂的生物油体系而言是一项困难的任务。ReaxFF是一种基于键级的反应分子力场,其与分子动力学结合的ReaxFF MD方法是一种可以对较大体系的化学反应进行描述的方法。该方法在每个模拟时间步用电负性平衡方法更新每个原子上的电荷,较好地考虑了极化作用;可以较好地重现密度泛函方法计算得出的反应势能面。需要特别指出的是,ReaxFFMD方法是一种反应势驱动的方法,无需预设反应路径,这是其应用于复杂体系微观化学反应机制研究的重要优势。ReaxFF MD已被应用于研究复杂体系的热解、燃烧、爆炸、催化过程,并取得了一定的成果,对研究生物油这类复杂体系的化学反应具有一定潜力,也为研究生物油高温氧化微观机制提供了一种新的思路。本论文致力于探索利用ReaxFFMD模拟研究生物油高温氧化反应机理的方法。为了摸索ReaxFF MD对复杂体系燃烧的模拟策略,作者对理论相对成熟的航空燃油RP-3替代燃料模型的高温氧化过程进行了研究。作者在本论文中使用所在课题组自行研发的VARxMD分析工具对RP-3高温氧化模拟过程中的反应物(燃料分子和02)主要产物(C2H4)和自由基(·CH3)随温度和时间的演化信息,并系统地对该过程中的化学反应进行了分析。ReaxFF MD模拟获得的上述物种随时间的演变在数量上与同样条件下CHEMKIN模拟的结果处于同一数量级。VARxMD分析还获得了详细的物种结构信息和化学反应列表,进一步观察模拟得到的反应路径发现其形式和文献的描述一致。通过统计燃料分子的第一个反应发现,其反应类型主要分为分子内断裂反应以及攫氢反应,且前者占主导;不同类型燃料分子引发反应的数量统计也定性展现了模拟条件下反应发生的难易程度。本论文对氧元素相关的反应进行了分析,发现氧分子主要与C1-C3分子发生反应,这可为简化机理提供一定依据。基于反应机理分析获得了 RP-3四组分替代燃料模型高温氧化过程中主要组分正癸烷的初始的化学反应网络。本文构建了一个24组分生物油模型,并对其高温氧化过程进行了 ReaxFFMD模拟研究。得到了燃料分子、氧分子、包括自由基在内的生物油高温氧化初期的主要产物随时间和温度的演化趋势。模拟得到的主要产物与文献报道相符。获得的燃料分子消耗动力学模型能够预测长时间模拟的燃料消耗情况。揭示了生物油中5个代表性组分的初始反应网络。生物油的氧化由攫氢反应或者均裂反应引发,链传播反应包括分子内氢转移、攫氢反应和β断裂反应。不饱和C—C键的氧化、苯酚自由基的缩环反应以及脱羰反应在该体系中较为常见。工作中观察到的反应路径与文献较为符合。本文参考24组分生物油模型的化学种类以及比例和官能团数量信息,构建了 5个6组分生物油替代燃料模型。并用ReaxFF MD方法对所构建的替代模型和24组分模型进行了相同条件下的高温氧化模拟。通过比较模型的元素组成,特别是对模拟替代模型和与24组分模型获得的主要反应物和包括自由基的产物进行比较,对每个替代燃料模型进行了评价。分析发现5个替代燃料模型的元素比与24组分模型均较为接近。比较ReaxFF MD模拟的结果发现,3号模型能较好的预测燃料和氧气分子的演化趋势;4号模型能较好地重现CH2O、C2H2O和·CH3的演化;2号模型能较好的重现CO的演化;5号模型能较好地重现H20的演化。本论文构建的24组分生物油模型对真实生物油的组成和化学结构多样性有更好的表达。对RP-3的4组分替代模型和一个24组分生物油模型的高温氧化过程进行ReaxFF MD模拟所获得的结果展示了一个用ReaxFF MD结合VARxMD分析研究生物油和航空燃油高温氧化反应路径的方法。利用ReaxFF MD模拟、以24组分生物油模型作为基准对所构建的生物油替代组分模型进行评价的方法也是一个新的尝试。
[Abstract]:Study on high temperature oxidation mechanism of bio oil for the rational use of essential oil. The bio bio oil composition is complex, and the higher temperature of the combustion process, the lack of detection of the combustion intermediate product. Quantum mechanics method is a commonly used method of theory research on combustion process. The ability of accurate calculation of thermodynamic parameters at the same time, combined with the reaction rate theory can get appropriate dynamic properties of combustion. But because of considering the electron correlation, the computational cost is high, the scale can be calculated in the system to 100 atomic level, it is difficult for the bio oil system complex are comprehensively described. At the same time quantum chemical methods to study chemical reaction mechanism is usually the need for the reaction path selection, which for the bio oil complex system is a difficult task in.ReaxFF is a key level based on reaction Sub field, ReaxFF MD method combined with the molecular dynamics method is described for a large system of chemical reaction. The method in each simulation time step update charge on each atom with electronegativity balance method, better consider the polarization effect; reaction energy can well reproduce the density functional method the calculated surface. In particular, the ReaxFFMD method is the driving force of a reaction, there is no need to set the reaction path, this is an important advantage of.ReaxFF MD pyrolysis, it was applied to study the complex system of the micro chemical reaction mechanism has been applied to study the complex system of combustion, explosion, and catalytic process. Some results of this kind of complex chemical reaction system of bio oil has a certain potential, but also provides a new way for the research of bio oil oxidation mechanism. The paper induced Methods to explore the use of ReaxFFMD simulation on the reaction mechanism of bio oil oxidation. In order to explore the ReaxFF MD on the simulation strategy of complex system of combustion, high temperature oxidation process of aviation fuel RP-3 theory is relatively mature alternative fuel model is studied. The author's research group used a self-developed VARxMD analysis tool to simulate the reaction process the oxidation of RP-3 in this paper (fuel molecules and 02) main products (C2H4) and free radical (- CH3) evolution with temperature and time, and the system of chemical reaction in the process was analyzed by.ReaxFF MD simulation of the species obtained with the simulation of CHEMKIN and under the same conditions of time the evolution in the number of the results in the analysis of the same magnitude.VARxMD also obtained the species structure information and a detailed list of chemical reactions, the reaction path simulation for further observation The size form and literature described above. Through the first reaction of fuel molecules found in statistics, the reaction types are divided into intramolecular cleavage reactions and hydrogen abstraction reaction, and the former is dominant; counting the number of different types of fuel molecule reactions also shows the difficulty of qualitative reaction under simulated conditions. This the response to oxygen was analyzed, found mainly oxygen molecules react with C1-C3 molecules, which can provide a certain basis for the simplification of the mechanism. The reaction mechanism analysis of chemical reaction network RP-3 four component model of high temperature oxidation of alternative fuels in the process of the main points based on the initial set of n-decane. This paper constructs a the 24 component of bio oil model, and the high temperature oxidation process are studied using ReaxFFMD simulation. The fuel molecules, molecular oxygen, bio oil oxidation, including free radicals The main product of the early evolution trend with time and temperature. The main products are simulated with the reported consistent fuel consumption. The consumption of molecular kinetic model is able to predict long time simulation of fuel. Reveals the bio oil from 5 representative components of the initial reaction network. The oxidation of bio oil by hydrogen abstraction reaction or homolytic reaction initiation, chain propagation reaction including intramolecular hydrogen transfer, hydrogen abstraction reaction and beta scission reaction. Oxidation of unsaturated C - C bond, ring contraction reaction of phenol radical and decarbonylation reaction in this system is more common. The reaction path and observed in the literature work is consistent with this paper. The 24 component of bio oil model chemical species and the proportion and the number of functional groups, constructed 5 6 components of bio oil alternative fuel model. Using ReaxFF MD method to replace the built model and 24 component model. The high temperature oxidation under the same conditions. By comparing the simulation model of elements, especially the comparison of the main reaction products of simulation model and 24 component replacement model and include free radicals, for each alternative fuel model was evaluated. The analysis found 5 alternative fuel elements than the model with 24 component models are more close to the ReaxFF MD. The simulation results show that 3 models can better predict the evolution trend of fuel and oxygen molecules; 4 model can reproduce the evolution of CH2O, C2H2O and CH3; 2 of the CO model can evolve better; the evolution of 5 model to reproduce the H20. This paper constructs 24 component model of bio oil composition has better chemical structure and diversity of the true expression of bio oil. The RP-3 4 component substitution model and a 24 component of bio oil model of high temperature oxidation process The ReaxFF MD simulation results show that a ReaxFF MD combined with VARxMD analysis of bio oil and aviation fuel oxidation reaction path. By using ReaxFF MD simulation method, as the base of bio oil substitute group constructed model to evaluate 24 components of bio oil model is a new try.

【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TE667

【参考文献】