Collaborative shock tube studies of benzene pyrolysis

Abstract

Three independent shock tube techniques, time-of-flight mass spectrometry (TOF), atomic resonance absorption spectroscopy (ARAS), and laser-schlieren density gradient measurements (LS), were employed to investigate the thermal decomposition of benzene (C6H6 or C6D6) in dilute inert gas mixtures over a wide range of reactant concentration (3–21,000 ppm), total pressure (0.2–3 atm) and temperature (1515–2500 K). The latter two methods were used to derive rate constants for the dissociation of C6H6→C6H5+H and C6H5→C2H2+C4H3 and the overall rate of benzene decomposition that occurred primarily via a direct ring rupture process C6H6→C2H2+C4H4. The ring rupture step was shown to be in the fall-off region. Rate constants subject to fall-off effects were adjusted for particular reaction conditions and used in a mechanism which included steps for acetylene pyrolysis to model the major species, C6H6, C2H2, C4H2, recorded by the TOF experiments, D atom production by ARAS, and density gradient profiles by LS.