Detailed kinetic study of anisole pyrolysis and oxidation to understand tar formation during biomass combustion and gasification

Milena Nowakowska (1) , Olivier Herbinet (1) , Anthony Dufour (2) , Pierre-Alexandre Glaude (1)

1 KinCom
2 GREENER

Received 4 September 2013 Received in revised form 21 November 2013 Accepted 28 November 2013 Available online 31 December 2013 Keywords: Anisole Pyrolysis Oxidation Tars Biomass Kinetic modeling 1. Introduction Environmental concerns such as the control of greenhouse gas emissions have led to an increased interest in the use of renewable energy. Biomass is widely used in combustion but can also be uti- lized in more advanced applications such as the production of a synthesis gas (syngas, a mixture of CO and H2), which can be used for the production of liquid fuels such as Fisher-Tropsch or meth- anol. Lignocellulosic biomass may be a promising feedstock through the gasification processes [1,2], but tar is also formed dur- ing gasification [3]. The tar content in the product gas is the major cumbersome and problematic parameter in the gasification pro- cesses [4]. Tar represents a complex mixture of over 100 com- pounds [5,6]. It leads to fouling, coke deposition, and catalyst deactivation. Hence, tar conversion or removal is one of the main challenges for the successful development of commercial gasifica- tion technologies and has been extensively studied [7,8]. Evans and Milne [5] defined three main classes of tars: primary tars (low temperature, oxygenated) and secondary and tertiary tars (benzene, polycyclic aromatic hydrocarbons--PAHs, etc.). In com- bustion and gasification reactors, the heaviest (tertiary) tars are ⇑ Corresponding author. Fax: [phone]. E-mail address: [e-mail] (P.-A. Glaude). abstract Anisole was chosen as the simplest surrogate for primary tar from lignin pyrolysis to study the gas-phase chemistry of methoxyphenol conversion. Methoxyphenols are one of the main precursors of PAH and soot in biomass combustion and gasification. These reactions are of paramount importance for the atmospheric environment, to mitigate emissions from wood combustion, and for reducing tar formation during gasification. Anisole pyrolysis and stoichiometric oxidation were studied in a jet-stirred reactor (673-1173 K, residence time 2 s, 800 Torr (106.7 kPa), under dilute conditions) coupled with gas chromatography-flame ionization detector and mass spectrometry. Decomposition of anisole starts at 750 K and a conversion degree of 50% is obtained at about 850 K under both studied conditions. The main products of reaction vary with temperature and are phenol, methane, carbon monoxide, benzene, and hydrogen. A detailed kinetic model (303 species, 1922 reactions) based on a combustion model for light aromatic compounds has been extended to anisole. The model predicts the conversion of anisole and the formation of the main products well. The reaction flux analyses show that anisole decomposes mainly to phenoxy and methyl radicals in both pyrolysis and oxidation conditions. The decomposition of phenoxy radicals is the main source of cyclopentadienyl radicals, which are the main precursor of naphthalene and heavier PAH in these conditions.

Mots clés: Anisole; Pyrolysis Oxidation; Tars; Biomass; Kinetic modeling

Domaines: Génie des procédés; Chimie théorique et/ou physique

Milena Nowakowska, Olivier Herbinet, Anthony Dufour, Pierre-Alexandre Glaude. Detailed kinetic study of anisole pyrolysis and oxidation to understand tar formation during biomass combustion and gasification. Combustion and Flame, 2014, 161, pp.1474-1488. ⟨10.1016/j.combustflame.2013.11.024⟩. ⟨hal-00991550⟩