Quantum chemistry and chemical kinetics of large straight-chain hydrocarbons in aviation kerosene

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Quantum chemistry and chemical kinetics of large straight-chain hydrocarbons in aviation kerosene

 

Author: Zhu, Yajie
Title: Quantum chemistry and chemical kinetics of large straight-chain hydrocarbons in aviation kerosene
Degree: M.Sc.
Year: 2016
Subject: Hydrocarbons.
Airplanes -- Fuel.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Engineering
Pages: viii, 73 pages : illustrations (some color)
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2917041
URI: http://theses.lib.polyu.edu.hk/handle/200/8610
Abstract: In straight-chain alkanes, each carbon is bound to its two neighbors and to two hydrogen atoms, except the two terminal carbon nuclei, bound to only one carbon atom and three hydrogen atoms. Hydrogen abstraction reactions, in which a hydrogen atom is abstracted by a radical from a molecule, often play the important role as chain propagation reaction in the oxidation of straight-chain alkanes. For the abstraction reactions of straight-chain alkanes by hydrogen radical, there are multiple attacking positions, conventionally identified by α, β and so on. The quantum chemistry and chemical kinetics of these reactions are the focus of the present study. The geometry optimization and vibrational frequency calculation on the potential energy surface of studied reactions were conducted by using B3LYP/6-311++G(d,p) method. For high-level energy barrier (EB) and heat of reaction (HR) calculations, we used three different methods, such as [QCISD(T)/CBS]₁, [QCISD(T)/CBS]₂ and ONIOM. For the tested straight-chain alkanes from methane to n-hexane, the errors for EB and HR are below 0.1kcal/mol by comparing these three methods. Rate coefficients for hydrogen abstraction reactions were calculated based on the transition state theory and by using two methods to deal with low-frequency torsional modes: the 1-D hindered rotor method and the Truhlar's Multi-structure method, the comparison of the results quantified by the ratio of calculated pre-exponential factor by using these two approximations, can be up to almost one order of magnitude. The rate coefficients obtained by using the multi-structure method show good agreement with those by the 1-D hindered rotor method under low temperatures, while the formers are slightly higher than the latters under high temperatures.

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