Application of frequency modulation spectroscopy to shock tube studies of elementary amidogen reactions.

摘要

The reaction of NH₂ with NO plays an important role in the Thermal De-NOx process and reburning. In the Thermal De-NOx process, NO₂ is an important intermediate, and the NH₂ + NO ₂ reaction plays a key role in recycling NO₂ back to NO and in N₂O formation. While there are multiple pathways for both reactions, leading to different products, only two product channels for each reaction are dominant: NH2+NO=NNH+OH R1a NH2+NO=N2+H2O R1b NH2+NO2=N2O+H 2OR2a NH2+NO2=H2NO+NO R2b ; In the present study, the overall rate coefficients (k₁ = k_1a + k_1b, k₂ = k_2a + k_2b ) and branching ratios (α₁ = k_1a/k ₁, α₂ = k_2a/k₂) of the NH ₂ + NO and NH₂ + NO₂ reactions have been determined using a shock tube facility and frequency modulation spectroscopy of NH ₂.; Using the frequency modulation absorption technique, a significant improvement in NH₂ detection can be achieved. An equivalent absorption detection limit of 0.01% and 0.003% was achieved for non-resonant and resonant type electro-optic modulators, respectively. Due to the sensitive detection of NH₂ radicals, the initial concentration of the reactants can be lowered and consequently the influence of secondary reactions is reduced.; For high temperature experiments to determine k₁, NH ₂ radicals were produced by thermal decomposition of monomethylamine, CH₃NH₂ (MMA). For the low temperature experiments, benzylamine, C₆H₅CH₂NH₂ (BA) was used as a source of NH₂. The measured NH₂ traces were interpreted using a detailed reaction mechanism. The MMA and BA data are consistent with lower temperature data from other studies.; To obtain the branching ratio, α₁, NH₂ radicals were produced by photolysis of NH₃ at low temperatures (1700K) and pyrolysis of BA at high temperatures (>1800K). In excess NH₃, the NH₂ trace was mainly sensitive to the branching ratio. The measured branching ratios increased from 0.40 at 1340K to 0.66 at 2159K, and were in good agreement with results of the theoretical work.; For experiments on reaction R2a and R2b, BA was used as a thermal source of NH₂ radicals. The IR emission from N₂O was monitored to determine the branching ratio, α₂. The measured α ₂-value was 0.17 ± 0.04 for the temperature range 1319–1493K, which is consistent with the results of lower temperature studies.