Previous attempts to model both low-temperature atmospheric and supercritical water oxidation of methylamine have failed due to a lack of elementary kinetics for peroxy radical reactions involving methylamine and its free-radical derivatives [1]. We have explored the potential energy surface (PES) for the reaction of CH2NH2 + O2 using ab initio quantum chemical calculations with the CBS-QB3 method [2]. While the PES is similar to its hydrocarbon analogue, CH3CH2 + O2, there are discernable differences both in kinetics and mechanisms due to the presence of the nitrogen atom. Using the information from the PES, we have computed reaction rate constants from transition state theory. These rate constants are then used as input to improve an existing detailed chemical kinetic model (DCKM) [1] to describe the homogeneous oxidation of methylamine under both atmospheric and supercritical water conditions. In the case of atmospheric methylamine oxidation, we probe the effect of the low-temperature peroxy-radical reactions and water concentration on the fundamental kinetics and mechanisms at 350°C, with particular attention given to the yet unexplained large experimental ammonia yields [3]. For methylamine supercritical water oxidation, we model reactivity at 683 K and 249 atm. In both cases, we use our mechanistic simulations to determine global reaction orders and activation energies. Reaction pathway and sensitivity analyses are used to identify the main routes of chemical transformations and most important elementary reactions during both types of homogeneous methylamine oxidation.
(1) Benjamin, K.M.; Savage, P.E. Ind. Eng. Chem. Res. 2005, 44, 9785.
(2) Montgomery, J.A., Jr.; Frisch, M.J.; Ochterski, J.W.; Petersson, G.A. J. Chem. Phys. 1999, 110, 2822.
(3) Cullis, C.F.; Willsher, J.P. Proc. R. Soc. London Ser. A 1951, 209, 218.