Gas Phase Kinetics of Volatiles from Biomass Pyrolysis. Note II: Furan, 2-methyl-furan, and 2,5-dimethylfuran

The aim of this work is to develop and discuss a lumped kinetic mechanism of furan, 2-methyl-furan, and 2,5-dimethylfuran to simulate the pyrolysis conditions, experimentally studied in shock tube and flow reactors and in a wide range of temperature and pressure. The comparisons between experimental data and model predictions support the validity of the lumped kinetic model, but also highlight the need of further experimental measurements in order to better understand the chemistry of these components. Introduction The synthesis of new biofuels through second generation methods of production from biomass is one interesting development in recent times, transforming abundant renewable resources, but not crops destined for human consumption, into liquid transportation fuels [1]. These second generation fuels are very promising, but they require a proper knowledge about the formation of toxic intermediates, and more in general about their combustion and ignition behavior. For these reasons there is a growing interest in the successive gas phase reactions not only of furans, but also of all the volatile species released from biomass pyrolysis [2]. A catalytic strategy for the production of 2,5-dimethylfuran (DMF) from biomass was discussed by Román-Leshkov et al. [3]. Compared to ethanol, the advantages of dimethylfuran as a liquid transportation fuel are a higher energy density, a higher boiling point, and a very low water solubility. Furthermore, the interest toward furans lies in their toxic characteristics. As a matter of facts, aromatic heterocycles such as furan are emitted during traditional fuel and biomass combustion and have been identified as air pollutants. Detailed chemical kinetic models exist to describe the combustion of hydrocarbons, but these are less validated and reliable for oxygenated species such as furans and higher alcohols. Thus, furan appears to be an excellent molecule to study the fundamentals of the unimolecular dissociation of large molecules over a wide range of conditions [4]. Kinetic scheme and numerical methods A semi-detailed kinetic sub-mechanism for the description of furan, methyl-furan, and dimethylfuran pyrolysis is summarized in Table 1. The successive reactions of XXXVI Meeting of the Italian Section of the Combustion Institute the smaller radicals and molecules involved are already considered in the whole oxidation mechanism for hydrocarbon fuels up to C16. The overall kinetic scheme, constituted by ~400 species involved in more than 10000 reactions, is based on a hierarchical modularity [5]. Thermochemical data for most species were obtained from thermodynamic database [6] as well as from the recent work of Sirejan and Fournet [7]. The complete mechanism, including thermo and transport properties, is available online at www.chem.polimi.it/CRECKModeling/. All the simulations were performed with the DSMOKE and OpenSMOKE codes [8]. Table 1. Primary pyrolysis reactions of furan, methyl-furan, and 2,5-dimethylfuran. (Units are mole, l, s, cal) Initiation reactions A E Furan = CO + C3H4 1.30E+15 80000 Furan = C2H2 + CH2CO 2.00E+15 86000 Furan = C3H3+HCO 1.00E+15 86500 2MeFuran = CO + C4H6 2.00E+15 81000 2MeFuran > H + CH2CO + C3H3 1.50E+16 85000 2MeFuran > H + HCCO + C3H4 1.50E+16 85000 DMF = CO + C5H8 2.00E+15 81500 DMF > CO + C2H4 + C3H4 2.50E+15 81500 DMF > CO + C4H5P + CH3 2.50E+16 93000 H-abstraction reactions R + Furan = RH + RFUR 4 H Vinyl type R + 2MeFuran > RH + RMEFUR 3 H Allyl type R + DMF > RH + RDMF 6 H Allyl type Radical Decomposition reactions RFUR > CO + C3H3 3.00E+12 36500 RFUR > CH2CO + C2H 1.00E+13 39000 RMEFUR > CO + C4H5 5.00E+13 30000 RDMF > H2 + C6H5O 3.00E+13 30000 RDMF > H + CyC5H6 + CO 5.00E+13 30000 RDMF > CH3 + CO + C4H4 6.00E+13 30000 RDMF > CH3CO + 2 C2H2 2.00E+13 32000 H addition reactions H + Furan > C2H2 + CH3 + CO 1.00E+10 3000 H + Furan > C2H2 + CH2CHO 1.00E+1