Siddique Kamal, Altarawneh Mohammednoor, Gore Jeff, Westmoreland Phillip R, Dlugogorski Bogdan Z
School of Engineering and Information Technology, Murdoch University , 90 South Street, Murdoch, WA 6150, Australia.
Dyno Nobel Asia Pacific Pty Ltd. , Mt. Thorley, NSW 2330, Australia.
J Phys Chem A. 2017 Mar 23;121(11):2221-2231. doi: 10.1021/acs.jpca.6b12890. Epub 2017 Mar 9.
This contribution investigates thermokinetic parameters of bimolecular gas-phase reactions involving the amine (NH) radical and a large number of saturated and unsaturated hydrocarbons. These reactions play an important role in combustion and pyrolysis of nitrogen-rich fuels, most notably biomass. Computations performed at the CBS-QB3 level and based on the conventional transition-state theory yield potential-energy surfaces and reaction rate constants, accounting for tunnelling effects and the presence of hindered rotors. In an analogy to other H abstraction systems, we demonstrate only a small influence of variational effects on the rate constants for selected reaction. The studied reactions cover the abstraction of hydrogen atoms by the NH radical from the C-H bonds in C-C species, and four C hydrocarbons of 2-methylbutane, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-2-butene, and 3-methyl-1-butyne. For the abstraction of H from methane, in the temperature windows 300-500 and 1600-2000 K, the calculated reaction rate constants concur with the available experimental measurements, i.e., k/k = 0.3-2.5 and 1.1-1.4, and the previous theoretical estimates. Abstraction of H atom from ethane attains the ratio of k/k equal to 0.10-1.2 and 1.3-1.5 over the temperature windows of available experimental measurements, i.e., 300-900 K and 1500-2000 K, respectively. For the remaining alkanes (propane and n-butane), the average k/k ratio remains 2.6 and 1.3 over the temperature range of experimental data. Also, comparing the calculated standard enthalpy of reaction (ΔH°) with the available experimental measurements for alkanes, we found the mean unsigned error of computations as 3.7 kJ mol. This agreement provides an accuracy benchmark of our methodology, affording the estimation of the unreported kinetic parameters for H abstractions from alkenes and alkynes. On the basis of the Evans-Polanyi plots, calculated bond dissociation enthalpies (BDHs) correlate linearly with the standard enthalpy of activation (ΔH°), allowing estimation of the enthalpy barrier for reaction of NH with other hydrocarbons in future work. Finally, we develop six sets of the generalized Arrhenius rate parameters for H abstractions from different C-H bond types. These parameters extend the application of the present results to any noncyclic hydrocarbon interacting with the NH radical.
本文研究了涉及胺基（NH）自由基与大量饱和及不饱和烃的双分子气相反应的热动力学参数。这些反应在富氮燃料（尤其是生物质）的燃烧和热解过程中起着重要作用。在CBS - QB3水平上基于传统过渡态理论进行的计算得出了势能面和反应速率常数，同时考虑了隧穿效应和受阻转子的存在。与其他氢提取系统类似，我们发现变分效应对所选反应速率常数的影响较小。所研究的反应涵盖了NH自由基从C - C物种中的C - H键以及2 - 甲基丁烷、2 - 甲基 - 1 - 丁烯、3 - 甲基 - 1 - 丁烯、3 - 甲基 - 2 - 丁烯和3 - 甲基 - 1 - 丁炔这四种C烃中提取氢原子的过程。对于从甲烷中提取H，在300 - 500 K和1600 - 2000 K的温度区间内，计算得到的反应速率常数与现有的实验测量值相符，即k/k = 0.3 - 2.5和1.1 - 1.4，也与先前的理论估计值相符。在现有的实验测量温度区间（分别为300 - 900 K和1500 - 2000 K）内，从乙烷中提取H原子的k/k比值分别为0.10 - 1.2和1.3 - 1.5。对于其余的烷烃（丙烷和正丁烷），在实验数据的温度范围内，平均k/k比值分别为2.6和1.3。此外，将计算得到的反应标准焓（ΔH°）与烷烃的现有实验测量值进行比较，我们发现计算的平均绝对误差为3.7 kJ/mol。这种一致性为我们的方法提供了一个精度基准，有助于估计从烯烃和炔烃中提取H的未报告动力学参数。基于埃文斯 - 波拉尼图，计算得到的键解离焓（BDH）与标准活化焓（ΔH°）呈线性相关，这使得在未来的工作中能够估计NH与其他烃反应的焓垒。最后，我们针对从不同C - H键类型中提取H开发了六组广义阿伦尼乌斯速率参数。这些参数将当前结果的应用扩展到了与NH自由基相互作用的任何非环状烃。
