title: Hydrogen Abstraction from Hydrocarbons by NH2.
abstract: This contribution investigates thermokinetic parameters of bimolecular gas-phase reactions involving the amine (NH2) 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 NH2radical from the C-H bonds in C1-C4species, and four C5hydrocarbons 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., kcalculated/kexperimetal= 0.3-2.5 and 1.1-1.4, and the previous theoretical estimates. Abstraction of H atom from ethane attains the ratio of kcalculated/kexperimetalequal 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 kexperimental/kcalculatedratio remains 2.6 and 1.3 over the temperature range of experimental data. Also, comparing the calculated standard enthalpy of reaction (ΔrH°298) with the available experimental measurements for alkanes, we found the mean unsigned error of computations as 3.7 kJ mol-1. 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 (Δ⧧H°298), allowing estimation of the enthalpy barrier for reaction of NH2with 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 NH2radical.
authors.affiliation: School of Engineering and Information Technology, Murdoch University , 90 South Street, Murdoch, WA 6150, Australia.
authors.forename: Kamal
authors.initials: K
authors.lastname: Siddique
authors.affiliation: School of Engineering and Information Technology, Murdoch University , 90 South Street, Murdoch, WA 6150, Australia.
authors.forename: Mohammednoor
authors.identifier: http://orcid.org/0000-0002-2832-3886
authors.initials: M
authors.lastname: Altarawneh
authors.affiliation: Dyno Nobel Asia Pacific Pty Ltd. , Mt. Thorley, NSW 2330, Australia.
authors.forename: Jeff
authors.initials: J
authors.lastname: Gore
authors.affiliation: Department of Chemical and Biomolecular Engineering, North Carolina State University , Raleigh, North Carolina 27695-7905, United States.
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Westmoreland
authors.affiliation: School of Engineering and Information Technology, Murdoch University , 90 South Street, Murdoch, WA 6150, Australia.
authors.forename: Bogdan Z
authors.initials: BZ
authors.lastname: Dlugogorski