Decomposition of CH 3 NH 2 ${\rm CH}_3{\rm NH}_2$ : Implications for CH x / NH y ${\rm CH}_{\rm {\it x}}/{\rm NH}_{\rm {\it y}}$ radical–radical reactions

Abstract

Experiments on methylamine (${\mathrm{CH}}_3{\mathrm{NH}}_2$) decomposition in shock tubes, flow reactors, and batch reactors have been re-examined to improve the understanding of hydrocarbon/amine interactions and constrain rate constants for ${\mathrm{CH}}_x$ + ${\mathrm{NH}}_y$ reactions. In high-temperature shock tube experiments, the rapid thermal dissociation of ${\mathrm{CH}}_3{\mathrm{NH}}_2$ provides a fairly clean source of ${\mathrm{CH}}_3$ and ${\mathrm{NH}}_2$ radicals, allowing an assessment of reactions of ${\mathrm{CH}}_3$ with ${\mathrm{NH}}_2$ and NH. At the lower temperatures in batch and flow reactors, ${\mathrm{CH}}_3{\mathrm{NH}}_2$ is mostly consumed by reaction with H to form ${\mathrm{CH}}_2{\mathrm{NH}}_2$ + $H_2$; these results are useful in determining the fate of the ${\mathrm{CH}}_2{\mathrm{NH}}_2$ radical. Interpretation of these data, along with flow reactor data for the ${\mathrm{CH}}_3{\mathrm{NH}}_2$/H system at lower temperature, indicates that at temperatures up to about 1400 K at atmospheric pressure and above 2000 K at 100 atm, the ${\mathrm{CH}}_3$ + ${\mathrm{NH}}_2$ reaction forms mainly methylamine. At sufficiently high temperature, H-abstraction to form ${\mathrm{CH}}_4$ + NH and addition–elimination to form ${\mathrm{CH}}_2{\mathrm{NH}}_2$ + H become competitive. The ${\mathrm{CH}}_3$ + NH reaction, with a rate constant close to collision frequency, forms ${\mathrm{CH}}_2\mathrm{NH}$ + H, also leading into the hydrocarbon amine pool. Thus, methylamine can be expected to be an important intermediate in co-combustion of natural gas and ammonia, and more work on the chemistry of ${\mathrm{CH}}_3{\mathrm{NH}}_2$ is desirable.