Thermal Decomposition of Nitromethane and Reaction between CH₃ and NO₂

Abstract

The thermal decomposition of gaseous nitromethane and the subsequent bimolecular reaction between CH and NO have been experimentally studied using time-resolved cavity-enhanced absorption spectroscopy behind reflected shock waves in the temperature range 1336-1827 K and at a pressure of 100 kPa. Temporal evolution of NO was observed following the pyrolysis of nitromethane (diluted to 80-140 ppm in argon) by monitoring the absorption around 400 nm. The primary objectives of the current work were to evaluate the rate constant for the CH + NO reaction (k) and to examine the contribution of the roaming isomerization pathway in nitromethane decomposition. The resultant rate constant can be expressed as k = (9.3 ± 1.8) × 10(T/K) cm molecule s, which is in reasonable agreement with available literature data. The decomposition of nitromethane was found to predominantly proceed with the C-N bond fission process with the branching fraction of 0.97 ± 0.06. Therefore, the upper limit of the branching fraction for the roaming pathway was evaluated to be 0.09.

Insights into nitromethane combustion from detailed kinetic modeling – Pyrolysis experiments in jet-stirred and flow reactors

“…Hence the bond fission channel is dominating for combustion environments featuring significantly higher pressures in agreement with all of the studies mentioned above and the studies that were reviewed in our recent work [31]. Furthermore, this finding is supported by the later study of Matsugi and Shiina [25] proposing branching ratios of 0.97 and 0.03 in favor of the C-N bond fission channel. Despite its low branching ratio, it is clearly recommended to take into account the roaming type channel in kinetic modeling studies [46].…”

“…The rate constant used in this work is adopted from [22], complemented with the results of [26] and well within the range of available literature data. This choice is supported by the recent studies of Matsugi and Shiina [25] and Vlasov et al [46] and leads to fractions of the roaming type channel from 0.02 to 0.04, increasing with temperature for the conditions studied in this work.…”

“…However, in [31], several recent studies on the thermal CH3NO2 decomposition were not taken into account. In these studies [23,25,[43][44][45], it was suggested that CH3NO2 not only thermally dissociates to CH3 + NO2 but also isomerizes to methyl nitrate (CH3ONO) via a roaming type transition state finally dissociating to CH3O + NO. In 2009, Zhu and Lin [43] studied the CH3NO2 decomposition theoretically and suggested that the channel to CH3O + NO could be detected in experiments.…”

“…Despite its low branching ratio, it is clearly recommended to take into account the roaming type channel in kinetic modeling studies [46]. Therefore, in the present work, we have included this channel using the rate parameters proposed by Matsugi and Shiina [25]. The available kinetic data on the dominating C-N fission channel are summarized in Figure S24 for low and high pressure conditions (see Supplementary material).…”

“…Though studies on nitromethane are not new, there are a number of studies on nitromethane detonation [19][20][21] and nitromethane decomposition [22][23][24][25]. None of these studies took into account the detailed kinetic study of CH3NO2 combustion.…”