The pyrolysis of 2-methylfuran: a quantum chemical, statistical rate theory and kinetic modelling study

Abstract

Due to the rapidly growing interest in the use of biomass derived furanic compounds as potential platform chemicals and fossil fuel replacements, there is a simultaneous need to understand the pyrolysis and combustion properties of such molecules. To this end, the potential energy surfaces for the pyrolysis relevant reactions of the biofuel candidate 2-methylfuran have been characterized using quantum chemical methods (CBS-QB3, CBS-APNO and G3). Canonical transition state theory is employed to determine the high-pressure limiting kinetics, k(T), of elementary reactions. Rice-Ramsperger-Kassel-Marcus theory with an energy grained master equation is used to compute pressure-dependent rate constants, k(T,p), and product branching fractions for the multiple-well, multiple-channel reaction pathways which typify the pyrolysis reactions of the title species. The unimolecular decomposition of 2-methylfuran is shown to proceed via hydrogen atom transfer reactions through singlet carbene intermediates which readily undergo ring opening to form collisionally stabilised acyclic C5H6O isomers before further decomposition to C1-C4 species. Rate constants for abstraction by the hydrogen atom and methyl radical are reported, with abstraction from the alkyl side chain calculated to dominate. The fate of the primary abstraction product, 2-furanylmethyl radical, is shown to be thermal decomposition to the n-butadienyl radical and carbon monoxide through a series of ring opening and hydrogen atom transfer reactions. The dominant bimolecular products of hydrogen atom addition reactions are found to be furan and methyl radical, 1-butene-1-yl radical and carbon monoxide and vinyl ketene and methyl radical. A kinetic mechanism is assembled with computer simulations in good agreement with shock tube speciation profiles taken from the literature. The kinetic mechanism developed herein can be used in future chemical kinetic modelling studies on the pyrolysis and oxidation of 2-methylfuran, or the larger molecular structures for which it is a known pyrolysis/combustion intermediate (e.g. cellulose, coals, 2,5-dimethylfuran).

2-methylfuran Oxidation in the Absence and Presence of NO

“…This model has been used in recent studies addressing the ignition phenomena of 2-MF [14,15]. Continuing with this work, Somers et al [20] described, in a more complete way, the ab initio calculations in which their original model [19] was based. Here the authors used more rigorous Rice-Ramsperger-KasselMarcus (RRKM) theory calculations coupled with an energy grained Master Equation (ME) solution to account for the influence of pressure on reaction rate constants.…”

“…The authors also add to this sub-mechanism an H-atom addition reaction on the C2 site of 2-MF, yielding 1,3-butadiene (CH 2 CHCHCH 2 ) and the HCO radicals. Finally, 3) mechanism 3 incorporates to the base mechanism developed in our group, the 2-MF sub-mechanism from Somers et al [20], in which an ab initio study was carried out to calculate kinetic parameters for the 2-MF sub-mechanism, and accounts for the influence of pressure on reaction rate constants. The SENKIN computer code from the CHEMKIN package [37] was used to simulate the experimental data.…”

Advanced Biofuels and Beyond: Chemistry Solutions for Propulsion and Production

“…[163] This knowledge has led to the formulation of reaction classes and associated rate rules for alcohols,a ldehydes,a nd carbonylic species, which permit the further development of mechanisms for such compounds. [167,168] Quite recently,c hemical mechanisms have also been developed for fuels from second-generation processes and beyond, including larger alcohols, [164,165] ethers, [169] and ketones, [170,171] and as ubstantial amount of work has been devoted to the furans [172][173][174][175][176][177][178] and tetrahydrofurans,w hich are in the focus of the present Review. [69,179,180] It is interesting to understand how macroscopic properties such as derived cetane numbers (compare Section 2a nd Figure 1) for advanced biofuels relate to the chemical kinetics mechanisms,s ince such understanding can substantially support strategies for fuel design.…”

Recent Trends in the Production, Combustion and Modeling of Furan-Based Fuels

“…Another furanic fuel, 2-MF, has been studied using quantum chemical calculations [115][116][117]. Davis and Sarathy [115] employed composite computational methods to determine the bond dissociation energies (BDEs) for the C-H bond in 2-MF, the enthalpies of reaction and barrier heights of a number of possible initiation reactions.…”

“…Furthermore, a new reaction type, referred to as Waddington concerted elimination, was reported. Furthermore, Somers et al [116] calculated the potential energy surfaces for 2-MF pyrolysis, high-pressure rate constants, k(T), and pressure-dependent rate constants, k(T, p), of elementary reactions. The main pathway for unimolecular decomposition of 2-MF was found to be via H-atom transfers through singlet carbene species, which further undergo ring opening to produce C 5 H 6 O isomers.…”