Modeling the Decomposition of Nitromethane, Induced by Shock Heating

Abstract

The decomposition of nitromethane was studied over the temperature range 1000−1100 K in reflected shock waves. CH3NO2 and the reaction products were analyzed by gas chromatography. The derived gross rate constant and activation energy for the disappearance of CH3NO2 is consistent with that of Glänzer and Troe. A reaction mechanism consisting of 99 chemical reactions was developed to simulate the experimental data of the present study and that of Hsu and Lin. Good agreement between experiments and simulations was achieved. It appears that significant amounts of CH3NO2 are destroyed through secondary reactions that involved highly reactive free radicals (H, OH, and CH3), suggesting the need for redeterming the true unimolecular decay rate constant for CH3NO2. For improvement of the performance of the model, several other rate constants also need to be determined. The final section is a preliminary report on a spectrophotometric technique for measuring the loss of nitromethane due to pyrolysis by recording its absorption of UV radiation, directed axially along a small diameter shock tube. Although only semiquantitative data were obtained, this novel procedure merits discussion.

Nitromethane dissociation: Implications for the CH3 + NO2 reaction

“…The more recent of these studies, most of which involve detailed chemical kinetic modeling, indicate that the pyrolysis chemistry of nitromethane is much more complex than assumed by Glänzer and Troe, with secondary reactions consuming a major fraction of both CH 3 NO 2 and NO 2 . The two recent shock tube studies by Zaslonko et al [26] and by Zhang and Bauer [27] are consistent with the high and low pressure limit rate constants for (R1) determined by Glänzer and Troe [9]. However, Zhang and Bauer [27] point out that a redetermination of the rate constant for reaction (R14) should be undertaken.…”

“…The two recent shock tube studies by Zaslonko et al [26] and by Zhang and Bauer [27] are consistent with the high and low pressure limit rate constants for (R1) determined by Glänzer and Troe [9]. However, Zhang and Bauer [27] point out that a redetermination of the rate constant for reaction (R14) should be undertaken.…”

“…Unimolecular rearrangement of nitromethane to methyl nitrite, CH NO EF CH ONO 3 2 3 has been suggested [41] to be competitive with the simple bond fission (R1), but theoretical work [42,43] points to a high energy barrier for the isomerization pathway, making it negligible under conditions of interest. More important are secondary reactions of CH 3 NO 2 with the radical pool [27]. The major steps to be considered are,…”

“…Furthermore, the reaction is in the fall-off region under most conditions of practical interest, and the fall-off behavior may not be described with sufficient accuracy by the simple Lindemann expression used in modeling (e.g. [7,27]). In the present work, selected shock tube data [9,21,27] on thermal decomposition of nitromethane are analyzed in terms of a detailed reaction mechanism.…”

“…[7,27]). In the present work, selected shock tube data [9,21,27] on thermal decomposition of nitromethane are analyzed in terms of a detailed reaction mechanism. The purpose has been to reexamine the rate constants for the reactions as well as the ther-CH ϩ NO 3 2 mochemistry for CH 3 NO 2 .…”