Thermal decomposition of benonitrile: A combined single-pulse shock tube-aras investigation

Abstract

A combined atomic resonance absorption spectrometry and single-pulse shock tube investigation on the thermal decomposition of benzonitrile was performed behind reflected shocks in pressurized driver shock tubes. The single-pulse shock tube experiments covered the temperature range 1350–1750 K at overall densities of ∼×10 −5 mol/cm 3 and the ARAS measurements covered the range 1500–1900 K at approximately the same densities. The resonance absorption measurements were done to provide rate parameters for two key reactions in the system: (1) C 6 H 5 CN→C 6 H 4 CN·+H· and (2) C 6 H 5 CH+H·→ products. The values obtained were k 1 =7.6×10 15 exp(−16×10 3 / RT ) s −1 and k 2 =2.2×10 14 exp(−12.6×10 3 / RT ) cm 3 mol −1 s −1 , where R is expressed in units of cal/(K mol). GC analyses of postshock samples obtained in the single-pulse shock tube experiments revealed the presence of the folowing decomposition products: C 2 H 2 , C 4 H 2 , C 6 H 6 , HCN, CH≡C−CN, C 6 H 5 ≡CH, and C 6 H 5 −C 6 H 5 . The overall rate constant for benzonitrile decomposition (in terms of a first-order constant) is given by k total =1.15×10 14 exp(−87.8×10 3 / RT )s −1 . A reaction scheme containing 21 species and 32 elementary reaction was constructed to account for the experimental roduct disribution. The results of the computer simulation show that the decomposition of te open l -C 6 H 4 CN· radical is somewhat slower than the decomposition of l -C 6 H 5 . . Arrhenius rate parameters for the product of the decomposition products decomposition of l -C 6 H 5 . . Arrhenius rate parameters for the production rates of the decomposition products are given and a discussion of the mechanism is presented.