1,3-丁二烯热裂解的动力学计算与模型研究

Kinetic Calculation and Modeling Study of 1,3-Butadiene Pyrolysis

1,3-丁二烯是碳氢燃料燃烧和裂解过程中生成的一种重要产物,也是形成多环芳烃(PAHs)的一种重要前驱体。目前,关于1,3-丁二烯燃烧实验以及机理的研究较多,但是其热裂解机理的研究较少。本文在B3LYP/CBSB7水平下对1,3-丁二烯裂解过程中相关反应的反应物、产物以及过渡态进行了几何结构优化和频率计算,并通过组合方法CBS-QB3计算得到了单点能和热力学参数。对于紧致过渡态的反应和无能垒反应,分别采用过渡态理论(TST)和可变反应坐标过渡态理论(VRC-TST)计算其高压极限条件下的反应速率常数。计算得到的反应速率常数与已有文献报导的结果吻合较好。通过量子化学计算,对Hidaka等人提出1,3-丁二烯的热裂解机理模型进行了更新和改进:更新后的机理模型包含45个物种和224步反应,并对更新后的机理模型进行了模拟验证。结果表明,更新的机理模型能更好地预测1,3-丁二烯激波管裂解实验过程中C_2H_2、1-丁烯-3-炔(C_4H_4)以及苯(C_6H_6)主要产物的浓度分布,为进一步完善核心机理(C_0-C_4)模型提供了可靠的热、动力学参数。

1,3-Butadiene is an important product in combustion and pyrolysis of hydrocarbon fuels and it is also an important precursor to form polycyclic aromatic hydrocarbons（PAHs）. Currently, a variety of experimental and mechanism studies have been performed on 1,3-butadiene oxidation. However, few studies about pyrolysis mechanism of 1,3-butadiene have been done. In this work, the optimization of the geometries and the vibrational frequencies for the reactants, products, and transition states of the relevant reactions in 1,3-butadiene pyrolysis have been performed at the B3LYP/CBSB7 level. Their single point energies and the thermodynamic parameters are also calculated by using the composite CBS-QB3 method. The high-pressure limit rate constants for tight transition state reactions and barrierless reactions are obtained by transition state theory and variable reaction coordinate transition state theory, respectively. The calculated rate constants in this work are in good agreement with those available from literature. Furthermore, the mechanism of Hidaka et al. is updated with replacing the calculated rate constants of reactions in this work to simulate the shock tube experiment results of 1,3-butadiene pyrolysis and the updated mechanism consists of 45 species and 224 reactions. It can be seen that the updated mechanism can improve the concentration profiles of the main products, ethylene, 1-butylene-3-acetylene, and benzene in 1,3-butadiene pyrolysis. It can also provide reliable kinetic and thermodynamic parameters to further improve the core mechanism of C0-C4 species.