An experimental and theoretical study of toluene pyrolysis with tunable synchrotron VUV photoionization and molecular-beam mass spectrometry

Journal Article · Sun Nov 15 00:00:00 EST 2009 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2009.06.001· OSTI ID:21235975

Zhang, Taichang ^[1]; Zhang, Lidong; Hong, Xin; Zhang, Kuiwen; Qi, Fei ^[1]; Law, Chung K ^[2]; Ye, Taohong; Zhao, Pinghui; Chen, Yiliang ^[3]

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1. National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029 (China)
2. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States)
3. Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, Anhui 230027 (China)

An experimental study of toluene pyrolysis (1.24 vol.% toluene in argon) was performed at low pressure (1.33 kPa) in the temperature range of 1200-1800 K. The pyrolysis process was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). Species up to m/z = 202 (C{sub 16}H{sub 10}), containing many radicals (CH{sub 3}, C{sub 3}H{sub 3}, C{sub 5}H{sub 3}, C{sub 5}H{sub 5}, C{sub 7}H{sub 5}, C{sub 7}H{sub 7}, C{sub 9}H{sub 7}, C{sub 11}H{sub 7} and C{sub 13}H{sub 9}) and isomers, such as C{sub 3}H{sub 4} (propyne and allene), C{sub 4}H{sub 4} (vinylacetylene and 1,2,3-butatriene), C{sub 5}H{sub 5} (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C{sub 6}H{sub 4} (3-hexene-1,5-diyne and benzyne), C{sub 6}H{sub 6} (benzene and fulvene), C{sub 7}H{sub 8} (toluene and 5-methylene-1,3-cyclohexadiene) and so on, were identified from near-threshold measurements of photoionization mass spectra, and the mole fraction profiles of the pyrolysis products were evaluated from measurements of temperature scan. Experimental results indicate that the reaction C{sub 7}H{sub 8} {yields} C{sub 7}H{sub 7} and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C{sub 7}H{sub 8} {yields} C{sub 6}H{sub 5} and subsequent reactions gradually become competitive and important with increasing temperature. Furthermore the barriers of the decomposition pathways of toluene and benzyl radical determined by quantum mechanical calculation are in good agreement with the initial formation temperatures of the species. Based on the mole fractions and formation temperatures of the detected pyrolysis species, a simple reaction network is deduced. At relatively high temperatures, H-abstraction is prevalent and the mole fraction of C{sub 2}H{sub 2} is so high that many aromatics are formed through the hydrogen-abstraction/C{sub 2}H{sub 2}-addition (HACA) mechanism. Moreover the reactions of benzyl with toluene/benzyl/phenyl/propargyl radicals to directly produce larger aromatics should play an influential role in PAH formation. Meanwhile the five-member-ring recombination mechanism also plays an indispensable role in the aromatics growth, as cyclopentadienyl radical (C{sub 5}H{sub 5}) was determined to be a major product of the decomposition of toluene. (author)

• OSTI ID: 21235975
• Journal Information: Combustion and Flame, Vol. 156, Issue 11; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
TOLUENE
FAR ULTRAVIOLET RADIATION
POLYCYCLIC AROMATIC HYDROCARBONS
PROPARGYL RADICALS
PYROLYSIS
BENZYL RADICALS
MASS SPECTROSCOPY
BENZENE
SYNCHROTRON RADIATION
MOLECULAR BEAMS
PHOTOIONIZATION
ARGON
TEMPERATURE RANGE 1000-4000 K
PRESSURE RANGE KILO PA
ALLENE
QUANTUM MECHANICS
PROPYNE
HYDROGEN
MASS SPECTRA
PYROLYSIS PRODUCTS
TEMPERATURE DEPENDENCE
ISOMERS
COMBUSTION KINETICS