TY - JOUR
T1 - An experimental and theoretical study of toluene pyrolysis with tunable synchrotron VUV photoionization and molecular-beam mass spectrometry
AU - Zhang, Taichang
AU - Zhang, Lidong
AU - Hong, Xin
AU - Zhang, Kuiwen
AU - Qi, Fei
AU - Law, Chung King
AU - Ye, Taohong
AU - Zhao, Pinghui
AU - Chen, Yiliang
N1 - Funding Information:
FQ is grateful for the funding supports from Chinese Academy of Sciences, Natural Science Foundation of China under Grant No. 20533040, National Basic Research Program of China (973) under Grant No. 2007CB815204 and Ministry of Science and Technology of China under Grant No. 2007DFA61310. The participation of CKL was sponsored by the US Air Force Office of Scientific Research. We thank Mr. Tao Yuan and Mr. Huijun Guo for their generous help in the experimental work.
PY - 2009/11
Y1 - 2009/11
N2 - 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 (C16H10), containing many radicals (CH3, C3H3, C5H3, C5H5, C7H5, C7H7, C9H7, C11H7 and C13H9) and isomers, such as C3H4 (propyne and allene), C4H4 (vinylacetylene and 1,2,3-butatriene), C5H5 (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C6H4 (3-hexene-1,5-diyne and benzyne), C6H6 (benzene and fulvene), C7H8 (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 C7H8 → C7H7 and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C7H8 → C6H5 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 C2H2 is so high that many aromatics are formed through the hydrogen-abstraction/C2H2-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 (C5H5) was determined to be a major product of the decomposition of toluene.
AB - 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 (C16H10), containing many radicals (CH3, C3H3, C5H3, C5H5, C7H5, C7H7, C9H7, C11H7 and C13H9) and isomers, such as C3H4 (propyne and allene), C4H4 (vinylacetylene and 1,2,3-butatriene), C5H5 (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C6H4 (3-hexene-1,5-diyne and benzyne), C6H6 (benzene and fulvene), C7H8 (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 C7H8 → C7H7 and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C7H8 → C6H5 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 C2H2 is so high that many aromatics are formed through the hydrogen-abstraction/C2H2-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 (C5H5) was determined to be a major product of the decomposition of toluene.
KW - Molecular-beam mass spectrometry
KW - PAHs
KW - Quantum mechanical calculation
KW - Toluene pyrolysis
KW - Tunable synchrotron VUV photoionization
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U2 - 10.1016/j.combustflame.2009.06.001
DO - 10.1016/j.combustflame.2009.06.001
M3 - Article
AN - SCOPUS:70349180835
SN - 0010-2180
VL - 156
SP - 2071
EP - 2083
JO - Combustion and Flame
JF - Combustion and Flame
IS - 11
ER -