Enhanced ignition of biomass in presence of NOx

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Enhanced ignition of biomass in presence of NOx ⁎

Ibukun Oluwoyea, Bogdan Z. Dlugogorskia, , Jeff Goreb, Phillip R. Westmorelandc, Mohammednoor Altarawneha a b c

School of Engineering and Information Technology, Murdoch University, 90 South Street, Murdoch WA 6150, Australia Dyno Nobel Asia Pacific Pty Ltd, Mt Thorley, NSW 2330, Australia Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695-7905, USA

A R T I C L E I N F O

A BS T RAC T

Keywords: Fire chemistry Sawmill Explosion Ignition Biomass Wood Dust Morpholine Sensitisation NOx Nitration reaction Nitrosation reaction Density functional theory (DFT)

Accumulation of combustible biomass residues on hot surfaces of processing machineries can pose fire hazards. In addition, the presence of nitrogen oxides (NOx) from plant equipment alters the local conditions, aggravating the propensity for low temperature ignition risks. This study presents an experimental study on a relative effect of NOx on ignition temperature of morpholine, an important surrogate of biomass, to reveal the sensitising role of NOx in ignition of biomass fuels and to gain mechanistic insights into the chemical aspect of this behaviour in fire. The experiments employed a flow-through tubular reactor, operated at constant pressure and residence time of 1.01 bar and 1.0 s, respectively, and coupled with a Fourier-transform infrared spectroscope. For a representative fuel-rich condition (Φ=1.25), the concentration of NOx as small as 0.06% lowers the ignition temperature of morpholine by 150 °C, i.e., from approximately 500 °C to 350 °C. The density functional theory (DFT) calculations performed with the CBS-QB3 composite method, that comprises a complete basis set, characterised the dynamics and energies of the elementary nitration reactions. We related the observed reduction in ignition temperature to the formation of unstable nitrite and nitrate adducts, as the result of addition of NOx species to morphyl and peroxyl radicals. Furthermore, the reaction of NOx with lowtemperature hydroperoxyl radical leads to the formation of active OH species that also propagate the ignition process. The present findings quantify the ignition behaviour of biomass under NOx–doped atmospheres. The result is of great importance in practical applications, indicating that safe operation of wood-working plants requires avoiding trace concentration of NOx within the vicinity of biomass residues. This can be facilitated by proper (and separate) venting of engine exhausts.

1. Introduction Thermal interaction of biomass with oxides of nitrogen (NOx, mainly NO and NO2) has important practical implications. While such interaction serves the intended industrial purposes in low-emission combustion technologies [1–3], it has an unintended consequence of degrading the safety of organic dust-producing plants. One reason for this is the particular way in which NOx reacts with hydrocarbons, by accelerating their oxidation process [4,5]. In other words, NOx enhances the ignition of combustible materials, and this effect is generally referred to as sensitisation via nitration reactions [6–10]. The addition of NO and/or NO2, to fuel-oxygen systems, significantly alters the overall kinetics by turning the usual low-temperature chainterminating steps of formation of peroxyl (RO2) radicals into a chainpropagating step [5]. Premature ignition of biomass particles, as a result of the sensitising

⁎

effect of NOx gases, can lead to unexpected fires and dust explosions. The latter occur upon direct exposure of combustible dust clouds (dispersed in air at concentrations above the flammability limit) to an ignition source, such as electrical or electrostatic sparks, overheated powder particles, hot surfaces, etc., within a certain degree of confinement [11–14]. Wood dusts in the timber industry display the same potential to explode as coal powders in underground mining operations [15,16]. Minor quantities of NOx (e.g., from diesel engines) promote the primary ignition of small wood particles. These enflamed particles prompt the formation of dust clouds creating conditions for secondary deflagration or detonation. In fact, the industrial safety literature presents numerous examples of explosions and fire accidents in woodprocessing plants, for example, sawmills [11,17–19]. Biomass dusts form during harvesting, sizing, transportation, preparation, storage, as well as through usage in combustion plants. Fire hazard arises when the dust sediments (and suspensions) accumulate on hot surfaces of

Corresponding author. E-mail addresses: [email protected] (I. Oluwoye), [email protected] (B.Z. Dlugogorski).

http://dx.doi.org/10.1016/j.firesaf.2017.03.042 Received 15 February 2017; Received in revised form 19 March 2017; Accepted 22 March 2017 0379-7112/ © 2017 Elsevier Ltd. All rights reserved.

Please cite this article as: Oluwoye, I., Fire Safety Journal (2017), http://dx.doi.org/10.1016/j.firesaf.2017.03.042

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rate of O2 to maintain the fuel-oxygen equivalence ratio Φ of 1.25 (i.e., moderately fuel rich condition, also corresponds to oxygen-fuel equivalent ratio λ=0.8) as per the following stoichiometric reaction:

Nomenclature T To Po X Absi AbsT

temperature (K) ambient temperature; 298.15 K ambient pressure; 1.01 bar fuel conversion bar initial concentration bar outlet concentration bar

C4H9NO + 5·75O2 = 4CO2 + 4·5H2O + 0·5N2

We introduced and maintained a premixed charge of the fuel and oxidiser at constant residence time of 1.0 s in the reaction zone, at ambient pressure Po of 1.01 bar, by regulating the flowrate. Charles’ temperature-volume relationship served to adjust the gas flow rates metered by the mass flow controllers (MFC, operated at the room temperature To) but preheated just before the reactor entry. Similarly, we employed a mass balance to convert the flow rate of the fuel needed for the predefined concentration at isothermal reaction temperature, into the corresponding set-values at room temperature. The relatively small volume of the annual space of zones 1 and 3 (Fig. 1) makes a minor contribution to the overall reaction in the system. The volume of the preheating and cooling-down zones amounts to 4% of the reaction zone. Fourier transform infrared (FTIR) spectroscopy facilitated online monitoring of product species exiting the tubular reactor. The setup incorporated an electrically heated transfer line (3.175 mm ID×300 mm) linking the reactor to a small volume (100 mL) 2.4 m path-length online gas sampling cell (Pike) placed inside the FTIR compartment. The spectrometer averaged 64 accumulated scans per spectrum at 1 cm−1 resolution. Both the sample line and the sampling cell operated at 140 °C, to avoid the condensation of volatile products prior and during the analysis.

Greek Φ λ

(1)

fuel-oxygen equivalent ratio oxygen-fuel equivalent ratio

electrical, and mechanical devices, such as conveyers, dryers, hot bearings and other machineries [20]. Although, the storage conditions in silos aggravate the propensity for low temperature ignition [21–23], local conditions, such as NOx presence from plant equipment, constitutes a contributing factor. Examples of biomass-related fire incidents involved storage facilities and power plants [24]. The complex nature of biomass necessitates the use of representative model compounds to gain an understanding of the ignition, combustion and pyrolysis of biomass-derived fuels. These model compounds include hetero-element species, also known as surrogates, embodying the well-defined N- and O-functionalities within their structures [25–27]. Morpholine (C4H9NO, 1-oxa-4-aza-cyclohexane) represents an excellent surrogate species for an oxygen and nitrogencontaining biofuel, due to its unique heterocyclic structure, wellcharacterised and studied behaviour, and a wide range of industrial applications. Its N-, C-, and O-content correspond to that revealed by ultimate analysis of typical biomass feedstocks. Furthermore, morpholine is widely used as an impregnating agent for fruit, cardboard, and paper, and as a fuel additive. The molecule also bears structural resemblance to ethanol, dimethyl ether, ethyl amine, and dimethyl amine [26]. Several investigations have described its decomposition, combustion, ignition and flame characteristics [26,28–33]. Accordingly, the present work focuses on experimental and theoretical aspects of initiation of thermal decomposition of morpholine, as a model for oxygen and nitrogen-containing compounds present in real biomass fuel, exposed to NOx-laden atmosphere. Our results offer insights into the low-temperature nitration reactions that govern the interaction of biomass with NOx. The conclusions drawn from the present work apply equally to herbaceous, woody and/or chaff biomass.

2.2. Computational methods Gaussian 09 suite of programs [39] served to study the structures of reacting species, transition states, reaction products, as well as the dynamics and energetics of the nitration reactions themselves.. The complete-basis-set CBS-QB3 [40] composite method afforded all structural optimisations, reaction enthalpies, as well as vibrational frequencies, using the tight convergence criteria and rigid-rotor/ harmonic-oscillator approximations. In agreement with previous studies [30,33], the adopted computational method offers an accurate evaluation of thermochemical properties of all species studied herein. The accuracy limit of the computational basis set (CBS-QB3) usually settles within the mean absolute deviation of 6 kJ/mol from experimental values of gas-phase enthalpy [41–45]. To confirm this, we have computed the absolute mean error to be 4.5 kJ/mol for bond dissociation enthalpies (BDH) of selected nitrogenated heterocyclic compounds (Table 1). Furthermore, the reported exothermicity of O2 addition to omorphyl (152 kJ/mol) and, m-morphyl (136 kJ/mol) concur with the literature values of 148 and 136 kJ/mol, respectively [32].

2. Applied methodologies 2.1. Materials and experimental setup

3. Results and discussion Fig. 1 provides a schematic representation of the experimental setup in which a digital syringe pump delivered the reactant fuel (morpholine; TCI, purity > 99.0%, 2.6–1.4 μL/min) into the preheated combined stream of helium, NOx and oxygen gases flowing through the system at combined rates of between 730 and 390 mL/min (at STP). The concentration of morpholine in the diluted stream amounted to 1000 ppm on molar basis. An electrically heated three-zone horizontal split furnace accommodated the quartz reactor tube, and ensured a well-defined isothermal reaction zone (cf. Fig. 1). The current experimental rig represents a typical bench-scale flow-through tubularreactor system employed in similar gas-phase kinetic studies [34– 38]. The reactor operated at nominal Reynolds numbers of 7.8 (at 300 °C)–2.8 (at 800 °C), indicating a laminar flow regime with an average hydrodynamic entry length of approximately 0.9% of the total reaction zone (300 mm). We maintained NOx concentration at 620 ppm (600 ppm of NO and 20 ppm of NO2), adjusting the flow

3.1. Effect of NOx on ignition temperature of morpholine As illustrated in Fig. 2, the IR spectrum of vaporised morpholine (e.g. at 300 °C) contains CH2 stretches (2840–2955 cm−1), CH2 scissors (1455 cm−1), CH2 wagging (1321 cm−1), and oxazines signatures of CO-C symmetric stretches (1237 cm−1, 1062 cm−1), asymmetric C-N-C stretching (1320 cm−1) and aromatic N-H wag (712 cm−1). Previous studies on thermal decomposition of morpholine [28–33] have demonstrated the vulnerability of the heterocyclic ring that readily opens up into linear adducts via homolytic cleavages and/or β-scissions at elevated temperatures. Hence, we selected one of the aromatic group frequencies at 1132 cm−1 to compute the fuel conversion, as indicated in Eq. (2):

⎛ Absi − AbsT ⎞ X=⎜ ⎟ × 100% Absi ⎝ ⎠ 2

(2)

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Fig. 1. Schematic representation of experiment rig. Symbol “T” denotes thermocouples.

where Absi denotes the initial concentration (proportional to absorbance value at 1132 cm−1) at the reactor inlet, and AbsT stands for the concentration of the fuel at the reactor outlet. This band represents a

characteristic vibration of morpholine that does not appear in any of the product species. Fig. 3a,b,c, and d depict the IR profiles of exhaust gases from

Table 1 Comparison of the calculated CBS-QB3 BDH with the literature values for selected heterocyclic hydrocarbons. Bracketed values in italics correspond to the results an alternative highlevel composite G4 method. The second last column assembles the experimental estimates obtained from photoacoustic calorimetry (PAC), acidity–oxidation potential measurements (AOP) and shock tube (ST) techniques, as well as one computational value calculated at the G2(MP2) level of theory.

Heterocyclic species

Homolytic BDH reaction

Calculated CBS-QB3 (and G4) BDH (kJ/mol)

Experimental [46,47] and theoretical [48] BDH (kJ/mol)

Absolute error (kJ/mol)

393.8 (386.6)

393.3 PAC

0.5 (6.7)

377.1 (371.0)

384.9 ± 8.4 PAC

7.8 (13.9)

381.9

385.0 ± 10.0 PAC

3.1

451.1 (444.3)

N/A

N/A

385.9 (377.9)

377.0 ± 10.0 PAC

8.9 (0.9)

387.1 (387.6)

384.3 Theory

2.8 (3.3)

505.6 (498.2)

495.4 ± 4.2 ST

10.2 (2.8)

403.0 (397.4)

405.8 AOP

2.8 (8.4)

Morpholine

(376.0)

(9.0)

Piperidine

Pyrrolidine

Pyrrole

Mean absolute error

3

4.5 (5.6)

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is similar to that experienced in other types of fuels [4,5,7–10,34–36]. For instance, Bendtsen et al. [4] reported that the presence of NO or NO2 lowered the onset temperature for oxidation of methane (CH4) by 250 °C, at shorter residence time of 200 ms. This implies that, with an adequate heat/ignition source, NOx can initiate premature atmospheric combustion of biomass residues. The present measurements indicate that, safe operation of wood-working plants requires avoiding trace concentration of NOx within the vicinity of dust-prone areas. This can be facilitated by proper (and separate) venting of engine exhausts. 3.2. Initial steps in nitration of morpholine The initial reaction of NO/NO2 with biomass produces nitro and nitro species (Reactions 3 and 4) which then decompose to generate two new radical species RO· and NO2/NO3. The latter, chain-branching reactions, underpin the sensitising effect of NO/NO2 [49]. Reaction (5) expresses the bimolecular O-abstraction [7].

Fig. 2. IR spectrum of vaporised morpholine. I: CH2 stretches (2840–2955 cm−1), II: CH2 scissors (1455 cm−1), III: CH2 wagging (1321 cm−1), IV: oxazines signatures of C-OC symmetric stretches (1237 cm−1, 1062 cm−1), V: asymmetric C-N-C stretches (1320 cm−1), VI: aromatic N-H wag (712 cm−1), and VII: selected group frequency (1132 cm−1).

experiments involving He, He-NOx, He-O2, and He-O2-NOx, respectively. The additional low-temperature peaks (1755–1960 cm−1) appearing in experiments for He-NOx and He-O2-NOx bath gases correspond to NO. The figures elucidate the structural identities of the products exiting the reactor. At relatively low temperatures (denoted by black-coloured spectra), the fuel remains unchanged, i.e., no detectable chemical addition, decomposition, or isomerisation reactions occur. However, as the operating temperature increases, morpholine converts into acetylene (C2H2), ethylene (C2H4), formaldehyde (CH2O), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2), hydrogen cyanide (HCN) and ammonia NH3, depending on the composition of the inlet gas mixture (indicated in red in Fig. 3). NOx concentration of 620 ppm, selected for experiments, represents that of untreated diesel engine exhausts. Fig. 4 plots the fuel conversion, as well as the extrapolated onset ignition temperatures for all experiments. The presence of NOx inhibits the decomposition of morpholine under pyrolytic conditions. Under oxidative environment (i.e., in presence of O2), NOx reduces the ignition temperature by 150 °C, i.e., from 500 °C to 350 °C. The trend

R+NO→RNO

(3)

R+NO2→RNO2

(4)

R+NO2→RO+NO

(5)

Oxidative environments allow the bimolecular H-abstraction by triplet oxygen to form HO2 radicals (see Fig. 5a), opening channels for the formation of peroxyl adducts (Reaction 6), an important combustion intermediates [50–54]. Reactions 7 and 8 describe the subsequent interaction of oxides of nitrogen with the peroxyl radicals. R+O2→ROO·

(6)

ROO+NO→RO+NO2

(7)

ROO+NO2⇌ROONO2

(8)

The thermal stability of peroxynitrate (RO2NO2) depends on the chemical nature of the R backbone [55,56]. It can dissociate back into peroxyl adduct, or preferably form alkoxy radical via Reaction 9 [57]: ROONO2→RO+NO3

(9)

Fig. 3. IR profile of morpholine decomposition at different temperatures, in He (a), He-NOx (b), He-O2 (c) and He-O2-NOx (d) atmospheres. Black coloured spectra correspond to morpholine, with functional identities as described in the text of the paper. Red coloured spectra indicate obvious conversion to product species.

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Fig. 4. Conversion profile of morpholine, at the reactor outlet, at different temperature and atmospheres (left). The points have been connected by basis-spline function, as guide to the eye, and extrapolated for determination of the onset ignition temperatures (right). The two tangential lines indicate an example of extrapolation of the onset ignition temperature for HeNOx condition.

nitrous acid (HNO2) also dissociates and/or reacts with H/O radicals to form OH species.

Previous studies [35,38] described the importance of low temperature chemistry in understanding the sensitisation effect of NOx during oxidation and ignition of hydrocarbons. In fact, these calculations confirmed that, modelled results remain incomplete, as well as insensitive (to the effect of NOx) without the inclusion of the lowtemperature initiation in the overall mechanism. Work is underway in our laboratory to produce a kinetic mechanism describing the initiation reaction responsible for the enhanced ignition of morpholine by NO/ NOx. In the present context, initial decomposition of morpholine involves abstraction and direct dissociation (under pyrolytic condition) of H atom and formation of three morphyl radicals, namely, o-morphyl, mmorphyl and p-morphyl, depending on the relative position of the radical site to the oxazine O atom. Fig. 5 illustrates the enthalpies (ΔrH°298) of these reactions, and of the barrierless addition of molecular (triplet) oxygen. HO2 radical remains highly stable at low temperatures. However, NO reacts with HO2 according to Reaction 10 [58–60], generating OH, an active propagating radical sustaining the oxidation process. Reactions 11 [61,62] and 12 [63,64] illustrate the interaction of NO2 with HO2. The

HO (10)2+NO→OH+NO2;

k(T) = 3·5×10–12 [cm3/molecule s] exp(250/T)

HO2+NO2→HO2NO2; 298.15)−3·1

k(T) = 2·1×10–31

HO2+NO2→HNO2+O2;

k(296 K) = 5·0×10–16 [cm3/molecule·s] (12)

[cm6/molecule2·s]

(T/ (11)

The appearance of radical sites (Fig. 5) enables subsequent addition reactions. Fig. 6 depicts the addition of NO/NO2 to morphyl radicals under inert atmosphere, such as that of He-NOx. These reactions proceed without a barrier, and lead to formation of C-nitroso and nitro species, respectively. The nitro products convert into more thermodynamically stable tautomers (i.e., aci forms) by migration of α-H atom (i.e., from the ipso carbon atom) to the nitro group. The nitroso and nitro compounds, except for nitromethane, are highly stable [65,66], and this explains why we observe no reduction to the onset temperature of decomposition of morpholine under the He-NOx atmosphere. Along the same line of inquiry, Venkatesh et al. [67] also reported

Fig. 5. Radical initiation of morpholine decomposition by H-abstraction (a) and H-dissociation (b) and formation of peroxyl adducts. Reaction enthalpies (ΔrH°298) and Gibbs energies (ΔrG°298, in bold and italic) are reported in kJ/mol at 298.15 K (25 °C).

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Fig. 6. Pyrolytic nitration of morpholine with NOx. Reaction enthalpies (ΔrH°298) and Gibbs energies (ΔrG°298, in bold and italic) are reported in kJ/mol at 298.15 K (25 °C). The reversibility signs indicate the preferred reaction direction based on thermodynamic stabilities.

4. Conclusions

higher inert decomposition temperatures for 2- and 4-nitroimidazoles, relatively to that of imidazole. The authors have demonstrated that, the underlying Arrhenius constants remain relatively large for the nitro compounds. In presence of O2, hydrocarbons degrade along the peroxyl (ROO·) corridor [50,51,68] into oxidation products, such as aldehydes, epoxides, oxetanes, ketones and hydroxyl, with the first step often involving the isomerisation (ROO·→·R′OOH). However, under NOxcontaining atmosphere (e.g. He-O2-NOx), as shown in Fig. 7, NO and NO2 attach attache to the outer oxygen atom of peroxyl species, leading to formation of unstable organic peroxynitrites and peroxynitrates, respectively. The addition channels release considerable amount of energy. The heat feedback from the exothermicity of these reactions compensates the endothermicity of reactions of Fig. 4, sustaining the ignition process. Analogous reactions constitute the major sink for ROO· in urban areas with high levels of NOx concentration [69–71]. From a kinetic viewpoint, considering the typical rate parameters for the addition of NO/NO2 to peroxyl species [72,73], and the representative NOx level (i.e., ca 620 ppm), the bimolecular addition reactions predominate over unimolecular isomerisation of ROO· adducts.

This paper presented new results from experimental measurements and theoretical calculations on the ignition of a representative biomass surrogate, due to sensitising effect of NOx. Approximately 620 ppm of NOx reduces the ignition temperature of morpholine by 150 °C under a characteristic fuel-rich condition. The formation of organic nitrites and nitrates plays an important role in decreasing the ignition temperature of fuel in NOx-laden oxidative environments, but has negligible contributions in pyrolytic decompositions. The addition reactions exhibit significant exothermicity. The physical insights of these results demonstrate that an appreciable concentration of NOx (e.g. from diesel-engine machineries) can instigate premature ignition of biomass, heightening the fire risks of wood-working plants. Safe standard operating procedures should encourage proper (and separate) venting of engine exhausts from dust sediments. Further studies at varying fuel-oxygen equivalence ratio, and NOx concentrations will help elucidate the limit of the sensitising effect. Measurements of the ignition induction time involving actual biomass should provide further insights into this behaviour. We recommend other experimental

Fig. 7. Oxidative nitration of morpholine with NOx. Reaction enthalpies (ΔrH°298) and Gibbs energies (ΔrG°298, in bold and italic) are reported in kJ/mol at 298.15 K (25 °C). Bracketed digit implies corresponding trans conformation.

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Technol. 134 (2015) 372–377. http://dx.doi.org/10.1016/j.fuproc.2015.02.019. [23] Á. Ramírez, J. García-Torrent, A. Tascón, Experimental determination of selfheating and self-ignition risks associated with the dusts of agricultural materials commonly stored in silos, J. Hazard. Mater. 175 (2010) 920–927. http:// dx.doi.org/10.1016/j.jhazmat.2009.10.096. [24] M. Todaka, W. Kowhakul, H. Masamoto, M. Shigematsu, Thermal analysis and dust explosion characteristics of spent coffee grounds and jatropha, J. Loss Prev. Process Ind. 44 (2016) 538–543. http://dx.doi.org/10.1016/j.jlp.2016.08.008. [25] Q. Ren, C. Zhao, Evolution of fuel-N in gas phase during biomass pyrolysis, Renew. Sustain. Energy Rev. 50 (2015) 408–418. http://dx.doi.org/10.1016/ j.rser.2015.05.043. [26] K. Kohse-Höinghaus, P. Oßwald, T.A. Cool, T. Kasper, N. Hansen, F. Qi, C.K. Westbrook, P.R. Westmoreland, Biofuel combustion chemistry: from ethanol to biodiesel, Angew. Chem. Int. Ed. 49 (2010) 3572–3597. http://dx.doi.org/ 10.1002/anie.200905335. [27] A. Lucassen, K. Zhang, J. Warkentin, K. Moshammer, P. Glarborg, P. Marshall, K. Kohse-Höinghaus, Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels, Combust. Flame 159 (2012) 2254–2279. http://dx.doi.org/10.1016/j.combustflame.2012.02.024. [28] P. Nau, A. Seipel, A. Lucassen, A. Brockhinke, K. Kohse-Höinghaus, Intermediate species detection in a morpholine flame: contributions to fuel-bound nitrogen conversion from a model biofuel, Exp. Fluids 49 (2010) 761–773. http:// dx.doi.org/10.1007/s00348-010-0916-y. [29] A. Lucassen, P. Oßwald, U. Struckmeier, K. Kohse-Höinghaus, T. Kasper, N. Hansen, T.A. Cool, P.R. Westmoreland, Species identification in a laminar premixed low-pressure flame of morpholine as a model substance for oxygenated nitrogen-containing fuels, P. Combust. Inst. 32 (2009) 1269–1276. http:// dx.doi.org/10.1016/j.proci.2008.06.053. [30] A. Lucassen, N. Labbe, P.R. Westmoreland, K. Kohse-Höinghaus, Combustion chemistry and fuel-nitrogen conversion in a laminar premixed flame of morpholine as a model biofuel, Combust. Flame 158 (2011) 1647–1666. http://dx.doi.org/ 10.1016/j.combustflame.2011.02.010. [31] M. Altarawneh, B.Z. Dlugogorski, A mechanistic and kinetic study on the decomposition of morpholine, J. Phys. Chem. A 116 (2012) 7703–7711. http:// dx.doi.org/10.1021/jp303463j. [32] P.P. Dholabhai, H.-G. Yu, Exploring the ring-opening pathways in the reaction of morpholinyl radicals with oxygen molecule, J. Phys. Chem. A 116 (2012) 7123–7127. http://dx.doi.org/10.1021/jp3014496. [33] S. Li, D.F. Davidson, R.K. Hanson, N.J. Labbe, P.R. Westmoreland, P. Oßwald, K. Kohse-Höinghaus, Shock tube measurements and model development for morpholine pyrolysis and oxidation at high pressures, Combust. Flame 160 (2013) 1559–1571. http://dx.doi.org/10.1016/j.combustflame.2013.03.027. [34] J.H. Bromly, F.J. Barnes, R. Mandyczewsky, T.J. Edwards, B.S. Haynes, An experimental investigation of the mutually sensitised oxidation of nitric oxide and n-butane, Symp. (Int. ) Combust. 24 (1992) 899–907. http://dx.doi.org/10.1016/ S0082-0784(06)80107-4. [35] J.H. Bromly, F.J. Barnes, S. Muris, X. You, B.S. Haynes, Kinetic and thermodynamic sensitivity analysis of the NO-sensitised oxidation of methane, Combust. Sci. Technol. 115 (1996) 259–296. http://dx.doi.org/10.1080/ 00102209608935532. [36] J.H. Bromly, F.J. Barnes, P.F. Nelson, B.S. Haynes, Kinetics and modeling of the H2-O2-NOx system, Int. J. Chem. Kinet. 27 (1995) 1165–1178. http://dx.doi.org/ 10.1002/kin.550271204. [37] P. Glarborg, D. Kubel, P.G. Kristensen, J. Hansen, K. Dam-Johansen, Interactions of CO, NOx and H2O under post-flame conditions, Combust. Sci. Technol. 110–111 (1995) 461–485. http://dx.doi.org/10.1080/00102209508951936. [38] P.F. Nelson, B.S. Haynes, Hydrocarbon-NOx interactions at low temperatures— 1.Conversion of NO to NO2 promoted by propane and the formation of HNCO, Symp. (Int.) Combust. 25 (1994) 1003–1010. http://dx.doi.org/10.1016/S00820784(06)80737-X. [39] M. Frisch, G. Trucks, H.B. Schlegel, G. Scuseria, M. Robb, J. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, Ge Petersson, Gaussian 09, in: Gaussian 09, Gaussian, Inc. Wallingford, CT, 2009. [40] Jr.J.A. Montgomery, M.J. Frisch, J.W. Ochterski, G.A. Petersson, A complete basis set model chemistry. VI. Use of density functional geometries and frequencies, J. Chem. Phys. 110 (1999) 2822–2827. http://dx.doi.org/10.1063/1.477924. [41] J. Bugler, K.P. Somers, J.M. Simmie, F. Güthe, H.J. Curran, Modeling nitrogen species as pollutants: thermochemical influences, J. Phys. Chem. A 120 (2016) 7192–7197. http://dx.doi.org/10.1021/acs.jpca.6b05723. [42] E.K. Pokon, M.D. Liptak, S. Feldgus, G.C. Shields, Comparison of CBS-QB3, CBSAPNO, and G3 predictions of gas phase deprotonation data, J. Phys. Chem. A 105 (2001) 10483–10487. http://dx.doi.org/10.1021/jp012920p. [43] J.M. Simmie, A database of formation enthalpies of nitrogen species by compound methods (CBS-QB3, CBS-APNO, G3, G4), J. Phys. Chem. A 119 (2015) 10511–10526. http://dx.doi.org/10.1021/acs.jpca.5b06054. [44] J.M. Simmie, K.P. Somers, Benchmarking compound methods (CBS-QB3, CBSAPNO, G3, G4, W1BD) against the active thermochemical tables: a litmus test for cost-effective molecular formation enthalpies, J. Phys. Chem. A 119 (2015) 7235–7246. http://dx.doi.org/10.1021/jp511403a. [45] Z. Zeng, M. Altarawneh, I. Oluwoye, P. Glarborg, B.Z. Dlugogorski, Inhibition and promotion of pyrolysis by hydrogen sulfide (H2S) and sulfanyl radical (SH), J. Phys. Chem. A 120 (2016) 8941–8948. http://dx.doi.org/10.1021/acs.jpca.6b09357. [46] Y.-R. Luo, Handbook of Bond Dissociation Energies in Organic Compounds, CRC press, 2002. [47] D. Wayner, K. Clark, A. Rauk, D. Yu, D. Armstrong, C.−H. Bond Dissociation,

parameters for assessing the risk of biomass ignition, e.g., thermogravimetrically-derived apparent activation energy (Ea) and the temperature of maximum rate of weight loss (TMWL) [20,22,23,74]. The thermochemical parameters of low-temperature intermediates identified herein will facilitate the development of an improved reaction mechanism. Acknowledgement This study has been funded by the Australian Research Council (ARC) and Dyno Nobel Asia Pacific, with grants of computing time from the National Computational Infrastructure (NCI) and the Pawsey Supercomputing Centre in Perth, Australia. I.O. thanks Murdoch University for the award of a postgraduate scholarship. References [1] L.D. Smoot, S.C. Hill, H. Xu, NOx control through reburning, Prog. Energy Combust. Sci. 24 (1998) 385–408. http://dx.doi.org/10.1016/S0360-1285(97) 00022-1. [2] B. Adams, N. Harding, Reburning using biomass for NOx control, Fuel Process. Technol. 54 (1998) 249–263. http://dx.doi.org/10.1016/S0378-3820(97)00072-6. [3] P. Maly, V. Zamansky, L. Ho, R. Payne, Alternative fuel reburning, Fuel 78 (1999) 327–334. http://dx.doi.org/10.1016/s0016-2361(98)00161-6. [4] A.B. Bendtsen, P. Glarborg, K. Dam-Johansen, Low temperature oxidation of methane: the influence of nitrogen oxides, Combust. Sci. Technol. 151 (2000) 31–71. http://dx.doi.org/10.1080/00102200008924214. [5] Y. Tan, C. Fotache, C. Law, Effects of NO on the ignition of hydrogen and hydrocarbons by heated counter flowing air, Combust. Flame 119 (1999) 346–355. http://dx.doi.org/10.1016/S0010-2180(99)00064-4. [6] P.G. Ashmore, B.P. Levitt, Further studies of induction periods in mixtures of H2, O2 and NO2, Symp. (Int. ) Combust. 7 (1958) 45–52. http://dx.doi.org/10.1016/ S0082-0784(58)80017-X. [7] C.L. Rasmussen, A.E. Rasmussen, P. Glarborg, Sensitizing effects of NOx on CH4 oxidation at high pressure, Combust. Flame 154 (2008) 529–545. http:// dx.doi.org/10.1016/j.combustflame.2008.01.012. [8] P. Dagaut, F. Lecomte, S. Chevailler, M. Cathonnet, Mutual sensitization of the oxidation of nitric oxide and simple fuels over an extended temperature range: experimental and detailed kinetic modeling, Combust. Sci. Technol. 148 (1999) 27–57. http://dx.doi.org/10.1080/00102209908935771. [9] P. Dagaut, J. Luche, M. Cathonnet, The low temperature oxidation of DME and mutual sensitization of the oxidation of DME and nitric oxide: experimental and detailed kinetic modeling, Combust. Sci. Technol. 165 (2001) 61–84. http:// dx.doi.org/10.1080/00102200108935826. [10] G. Dayma, K.H. Ali, P. Dagaut, Experimental and detailed kinetic modeling study of the high pressure oxidation of methanol sensitized by nitric oxide and nitrogen dioxide, Proc. Combust. Inst. 31 (2007) 411–418. http://dx.doi.org/10.1016/ j.proci.2006.07.143. [11] T. Abbasi, S.A. Abbasi, Dust explosions – Cases, causes, consequences, and control, J. Hazard. Mater. 140 (2007) 7–44. http://dx.doi.org/10.1016/j.jhazmat.2006.11.007. [12] P.D. Amyotte, An Introduction to Dust Explosions: Understanding the Myths and Realities of Dust Explosions for a Safer Workplace, Butterworth-Heinemann, 2013. [13] K.L. Cashdollar, Overview of dust explosibility characteristics, J. Loss Prev. Process Ind. 13 (2000) 183–199. http://dx.doi.org/10.1016/S0950-4230(99)00039-X. [14] J. Cross, D. Farrer, Dust Explosions, Springer, US, 2012. [15] K.L. Cashdollar, Coal dust explosibility, J. Loss Prev. Process Ind. 9 (1996) 65–76. http://dx.doi.org/10.1016/0950-4230(95)00050-X. [16] A. Gillies, S. Jackson, Some investigations into the explosibility of mine dust laden atmospheres, Coal Oper. Conf. Wollongong (1998) 626–640. [17] S. Callé, L. Klaba, D. Thomas, L. Perrin, O. Dufaud, Influence of the size distribution and concentration on wood dust explosion: experiments and reaction modelling, Powder Technol. 157 (2005) 144–148. http://dx.doi.org/10.1016/ j.powtec.2005.05.021. [18] National Fire Protection Association, NFPA 654: standard for the prevention of fire and dust explosions from the manufacturing, processing, and handling of combustible particulate solids, in. National Fire Protection Association, NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. Massachusetts, 2005. [19] National Fire Protection Association, NFPA 664: standard for the prevention of fires and explosions in wood processing and woodworking facilities, in: National Fire Protection Association, NFPA 664: Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, Massachusetts, 2007. [20] Y.S. Chin, L.I. Darvell, A.R. Lea-Langton, J.M. Jones, A. Williams, Ignition risks of biomass dust on hot surfaces, Energy Fuels 30 (2016) 4398–4404. http:// dx.doi.org/10.1021/acs.energyfuels.5b02622. [21] U. Krause, Fires in Silos: hazards, Prevention, and Fire Fighting, John Wiley & Sons, 2009. [22] J.M. Jones, A. Saddawi, B. Dooley, E.J.S. Mitchell, J. Werner, D.J. Waldron, S. Weatherstone, A. Williams, Low temperature ignition of biomass, Fuel Process.

7

Fire Safety Journal xxx (xxxx) xxx–xxx

I. Oluwoye et al.

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55] [56]

[57] [58]

[59]

[60]

[61]

jp035905o. [62] R. Atkinson, D.L. Baulch, R.A. Cox, J.N. Crowley, R.F. Hampson, R.G. Hynes, M.E. Jenkin, M.J. Rossi, J. Troe, Evaluated kinetic and photochemical data for atmospheric chemistry: volume I - gas phase reactions of Ox, HOx, NOx and SOx species, Atmos. Chem. Phys. (4) (2004) 1461–1738. http://dx.doi.org/10.5194/ acp-4-1461-2004. [63] G.S. Tyndall, J.J. Orlando, J.G. Calvert, Upper limit for the rate coefficient for the reaction HO2+NO2→HONO+O2, Environ. Sci. Technol. 29 (1995) 202–206. http://dx.doi.org/10.1021/es00001a026. [64] S. Sander, D. Golden, M. Kurylo, G. Moortgat, P. Wine, A. Ravishankara, C. Kolb, M. Molina, B. Finlayson-Pitts, R. Huie. Chemical kinetics anSander d photochemical data for use in atmospheric studies evaluation number 15., in: Chemical kinetics and photochemical data for use in atmospheric studies evaluation number 15‘, Jet Propulsion Laboratory, National Aeronautics and Space Administration, CA, Pasadena, 2006. [65] P.D. Bailey, K.M. Morgan, Organonitrogen Chemistry, Oxford University Press, Oxford, 1996. [66] H. Goldwhite, Chapter 6 - Nitrogen derivatives of the aliphatic hydrocarbons, in: S. Coffey (Ed.)Chapter 6 - Nitrogen Derivatives of the Aliphatic Hydrocarbons, Elsevier, Amsterdam, 1964, pp. 93–164. http://dx.doi.org/10.1016/B978044453345-6.50475-2. [67] M. Venkatesh, P. Ravi, S.P. Tewari, Isoconversional kinetic analysis of decomposition of nitroimidazoles: friedman method vs Flynn–Wall–Ozawa method, J. Phys. Chem. A 117 (2013) 10162–10169. http://dx.doi.org/10.1021/jp407526r. [68] M. Altarawneh, B.Z. Dlugogorski, E.M. Kennedy, J.C. Mackie, Theoretical investigation into the low-temperature oxidation of ethylbenzene, P. Combust. Inst. 34 (2013) 315–323. http://dx.doi.org/10.1016/j.proci.2012.06.066. [69] S.M. Aschmann, W.D. Long, R. Atkinson, Pressure dependence of pentyl nitrate formation from the OH radical-initiated reaction of n-pentane in the presence of NO, J. Phys. Chem. A 110 (2006) 6617–6622. http://dx.doi.org/10.1021/ jp054643i. [70] R. Atkinson, J. Arey, Atmospheric degradation of volatile organic compounds, Chem. Rev. 103 (2003) 4605–4638. http://dx.doi.org/10.1021/cr0206420. [71] J. Sehested, O.J. Nielsen, T.J. Wallington, Absolute rate constants for the reaction of NO with a series of peroxy radicals in the gas phase at 295 K, Chem. Phys. Lett. 213 (1993) 457–464. http://dx.doi.org/10.1016/0009-2614(93)89142-5. [72] R. Atkinson, Gas-phase tropospheric chemistry of volatile organic compounds: 1, Alkanes alkenes, J. Phys. Chem. Ref. Data 26 (1997) 215–290. http://dx.doi.org/ 10.1063/1.556012. [73] J. Eberhard, C.J. Howard, Rate coefficients for the reactions of some C3 to C5 hydrocarbon peroxy radicals with NO, J. Phys. Chem. A 101 (1997) 3360–3366. http://dx.doi.org/10.1021/jp9640282. [74] A. Saddawi, J.M. Jones, A. Williams, C. Le Coeur, Commodity fuels from biomass through pretreatment and torrefaction: effects of mineral content on torrefied fuel characteristics and quality, Energy Fuels 26 (2012) 6466–6474. http://dx.doi.org/ 10.1021/ef2016649.

Energies of alkyl amines: radical structures and stabilization energies, J. Am. Chem. Soc. 119 (1997) 8925–8932. http://dx.doi.org/10.1021/ja971365v. Y. Feng, L. Liu, J.-T. Wang, S.-W. Zhao, Q.-X. Guo, Homolytic C−H and N−H bond dissociation energies of strained organic compounds, J. Org. Chem. 69 (2004) 3129–3138. http://dx.doi.org/10.1021/jo035306d. I. Oluwoye, M. Altarawneh, J. Gore, H. Bockhorn, B.Z. Dlugogorski, Oxidation of polyethylene under corrosive NOx atmosphere, J. Phys. Chem. C 120 (2016) 3766–3775. http://dx.doi.org/10.1021/acs.jpcc.5b10466. F. Battin-Leclerc, Detailed chemical kinetic models for the low-temperature combustion of hydrocarbons with application to gasoline and diesel fuel surrogates, Prog. Energy Combust. Sci. 34 (2008) 440–498. http://dx.doi.org/10.1016/ j.pecs.2007.10.002. I. Oluwoye, M. Altarawneh, J. Gore, B.Z. Dlugogorski, Oxidation of crystalline polyethylene, Combust. Flame 162 (2015) 3681–3690. http://dx.doi.org/10.1016/ j.combustflame.2015.07.007. W.J. Pitz, C.J. Mueller, Recent progress in the development of diesel surrogate fuels, Prog. Energy Combust. Sci. 37 (2011) 330–350. http://dx.doi.org/10.1016/ j.pecs.2010.06.004. J.M. Simmie, Detailed chemical kinetic models for the combustion of hydrocarbon fuels, Prog. Energy Combust. Sci. 29 (2003) 599–634. http://dx.doi.org/10.1016/ S0360-1285(03)00060-1. J. Zador, C.A. Taatjes, R.X. Fernandes, Kinetics of elementary reactions in lowtemperature autoignition chemistry, Prog. Energy Combust. Sci. 37 (2011) 371–421. http://dx.doi.org/10.1016/j.pecs.2010.06.006. F. Kirchner, A. Mayer–Figge, F. Zabel, K. Becker, Thermal stability of peroxynitrates, Int. J. Chem. Kinet. 31 (1999) 127–144. F. Kirchner, L.P. Thüner, I. Barnes, K.H. Becker, B. Donner, F. Zabel, Thermal lifetimes of peroxynitrates occurring in the atmospheric degradation of oxygenated fuel additives, Environ. Sci. Technol. 31 (1997) 1801–1804. http://dx.doi.org/ 10.1021/es9609415. S. Jagiella, F. Zabel, Reaction of phenylperoxy radicals with NO2 at 298 K, PCCP 9 (2007) 5036–5051. http://dx.doi.org/10.1039/b705193j. G.S. Tyndall, R.A. Cox, C. Granier, R. Lesclaux, G.K. Moortgat, M.J. Pilling, A.R. Ravishankara, T.J. Wallington, Atmospheric chemistry of small organic peroxy radicals, J. Geophys. Res. Atmos. 106 (2001) 12157–12182. http://dx.doi.org/ 10.1029/2000jd900746. S. Zhou, I. Barnes, T. Zhu, I. Bejan, T. Benter, Kinetic study of the gas-phase reactions of oh and NO3 radicals and O3 with selected vinyl ethers, J. Phys. Chem. A 110 (2006) 7386–7392. http://dx.doi.org/10.1021/jp061431s. T. Gierczak, E. Jimenez, V. Riffault, J.B. Burkholder, A. Ravishankara, Thermal decomposition of HO2NO2 (peroxynitric acid, PNA): rate coefficient and determination of the enthalpy of formation, J. Phys. Chem. A 109 (2005) 586–596. http:// dx.doi.org/10.1021/jp046632f. L.E. Christensen, M. Okumura, S.P. Sander, R.R. Friedl, C.E. Miller, J.J. Sloan, Measurements of the rate constant of HO2+NO2+N2→HO2NO2+N2 using nearinfrared wavelength-modulation spectroscopy and UV− visible absorption spectroscopy, J. Phys. Chem. A 108 (2004) 80–91. http://dx.doi.org/10.1021/

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