H-Atom-Forming Reaction Pathways in the Pyrolysis of Furan, 2-Methylfuran, and 2,5-Dimethylfuran: A Shock-Tube and Modeling Study

Abstract

The methyl-substituted furan derivatives 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) are often discussed as alternative fuels. Despite the large number of mechanistic studies on the pyrolysis and oxidation of 2-MF, 2,5-DMF, and unsubstituted furan (F), detailed kinetic investigations of the initial reaction steps are scarce. In this work, we report on shock-tube studies with detection of hydrogen atoms by atom resonance absorption spectroscopy to investigate the thermal decomposition of F, 2-MF, and 2,5-DMF. Hydrogen atom concentration-time profiles were recorded behind reflected shock waves at temperatures between 1200 and 1900 K and pressures between 0.7 and 1.6 bar with Ar as the bath gas. The recorded profiles were compared with results from kinetic simulations performed on the basis of a joint F/2-MF/2,5-DMF oxidation mechanism recently published. Kinetic parameters for a small number of reactions with high sensitivities for the formation and consumption of H atoms were adapted by taking values from other references to improve the agreement of the experimentally determined and simulated concentration-time profiles. In this way, an adequate description of the H atom concentration-time profiles for all three furan derivatives with the joint mechanism could be achieved. On the basis of this adapted mechanism, the formation pathways of H atoms in the pyrolysis of all three furan derivatives were identified and analyzed. It turned out that the formation of H atoms in the case of 2-MF and 2,5-DMF is governed by a competition between H split-off from the methyl group(s) of the reactant molecule as well as from the primary ring-opening product. In the case of F, only decomposition steps of the ring-opening product are relevant. The adapted mechanism is given in machine-readable form for modeling purposes, and the alterations made are discussed.

Ab-initio studies of thermal unimolecular decomposition of furan: A complementary deterministic and stochastic master equation model

“…The mechanism for the formation of propargyl (C3H3) radicals is proposed to be via formyl allene (INT3) → C3H3 + HCO (P3) by Tian et al 36 while Sendt et al 35 proposed via the formation CH3CCH (P2) → C3H3 + H pathway. The proposed pathway via CH3CCH resonates well with the conclusion of recent works by Cheng et al (2017) 98 and by Weber et al 32 who pointed out that C3H3 radical is mainly formed from C3H4 isomers rather than from furan directly. Moreover, Urness and co-workers 31 determined the fraction of propargyl (C3H3) radical to propyne (CH3CCH) using a silicon carbide microtubular reactor and found that the [C3H3]/[CH3CCH]) branching ratio (increasing from ~2% at 1500 K to ~10% at 1600 K over the pressure range of 100-300 Torr).…”

“…[b] 7.9×10 14 0.00 35164.7 P4 → Furan [c] 1.7×10 -10 0.00 0.0 P5 → Furan [c] 1.7×10 -10 0.00 0.0 [a] Units of [s −1 ] for first-order reactions and [cm 3 molecule −1 s −1 ] for second-order reactions. [b], [c] Taken from the works of Sendt et al 31 and Tian et al 32 , respectively, for the barrierless channels.…”

“…The gas-phase thermal reactions of furan were studied by several groups both experimentally 18,[21][22][23][24][25][26][27][28][29][30][31][32] and theoretically. [33][34][35][36] In a recent single pulse shock tube study, Guarneri et al 37 assessed the efficiency of furan as a model oxygenated reburn fuel for the reduction of NO, and found that NO removal by furan is as effective as propene.…”

“…Also, their mechanism was successfully validated against the species time histories of Fulle et al 25 work on furan pyrolysis. Recently, Weber et al 32 studied the pyrolysis reactions of furan, 2-MF and 2,5-DMF in shock-tube experiments behind reflected shock waves over the temperature of 1200 -1900 K and pressures between 0.7 and 1.6 atm. Above 1600 K, the authors found that the original kinetic mechanism proposed by Liu et al 29 severely underpredicted their experimentally measured H-atom concentration-time profiles.…”

3-Bromopyridine-Heterogenized Phosphotungstic Acid for Efficient Trimerization of Biomass-Derived 5-Hydroxymethylfurfural with 2-Methylfuran to C21 Fuel Precursor

“…HPAs (heteropoly acids) with superb strong acidity are extensively used as economic and environmental catalysts in organic synthesis [28][29][30][31][32]. In particular, phosphotungstic acid (HPW, H 3 PW 12 O 40 ) has a tetrahedral PO 4 core in the center of the anion structure, surrounded by twelve WO 6 polyhedra via oxygen atoms to link each other, which exhibits excellent catalytic activity for upgrading biomassderived compounds into different valuable chemicals and biofuels [33,34].…”