Sinha Sourab, Raj Abhijeet
Department of Chemical Engineering, The Petroleum Institute, Abu Dhabi, United Arab Emirates.
Phys Chem Chem Phys. 2016 Mar 21;18(11):8120-31. doi: 10.1039/c5cp06465a.
The role of resonantly stabilized radicals such as propargyl, cyclopentadienyl and benzyl in the formation of aromatic hydrocarbons such as benzene and naphthalene in the high temperature environments has been long known. In this work, the possibility of benzyl recombination to form three-ring aromatics, phenanthrene and anthracene, is explored. A reaction mechanism for it is developed, where reaction energetics are calculated using density functional theory (B3LYP functional with 6-311++G(d,p) basis set) and CBS-QB3, while temperature-dependent reaction kinetics are evaluated using transition state theory. The mechanism begins with barrierless formation of bibenzyl from two benzyl radicals with the release of 283.2 kJ mol(-1) of reaction energy. The further reactions involve H-abstraction by a H atom, H-desorption, H-migration, and ring closure to gain aromaticity. Through mechanism and rate of production analyses, the important reactions leading to phenanthrene and anthracene formation are determined. Phenanthrene is found to be the major product at high temperatures. Premixed laminar flame simulations are carried out by including the proposed reactions for phenanthrene formation from benzyl radicals and compared to experimentally observed species profiles to understand their effects on species concentrations.
诸如炔丙基、环戊二烯基和苄基等共振稳定自由基在高温环境下形成苯和萘等芳烃过程中的作用早已为人所知。在这项工作中，研究了苄基重组形成三环芳烃菲和蒽的可能性。为此建立了一个反应机理，其中反应能量学使用密度泛函理论（采用6-311++G(d,p)基组的B3LYP泛函）和CBS-QB3进行计算，而温度依赖的反应动力学则使用过渡态理论进行评估。该机理始于两个苄基自由基无势垒地形成联苄，并释放出283.2 kJ mol(-1)的反应能量。进一步的反应包括氢原子的氢提取、氢脱附、氢迁移和闭环以获得芳香性。通过机理和生成速率分析，确定了导致菲和蒽形成的重要反应。发现菲是高温下的主要产物。通过纳入从苄基自由基形成菲的提议反应进行预混层流火焰模拟，并与实验观察到的物种分布进行比较，以了解它们对物种浓度的影响。
