Investigation of the mechanism of the hydrodenitrogenation of n-hexylamines over sulfided NiMo/γ-Al2O3

The hydrodenitrogenation (HDN) of n-hexylamine, dihexylamine, and trihexylamine was studied between 300 and 340 °C, 3 and 5 MPa total pressure, 5 and 20 kPa amine pressure, and 10 and 150 kPa H2S pressure over a sulfided Ni–Mo/γ-Al2O3 catalyst. The conversion increased with the H2 pressure and decreased with increasing partial pressure of the hexylamines. The conversion of hexylamine and dihexylamine decreased slightly with H2S pressure, but that of trihexylamine increased substantially. The contributions of elimination and nucleophilic substitution to the HDN were determined by the initial product selectivities at short weight time. The initial alkene selectivities were low and accounted for only a minor part of the n-alkylamine conversion. Since the hexene/hexane branching ratio in the HDN of the alkylamines was almost equal to that in the hydrodesulfurization of pentanethiol in the presence of an alkylamine, it was concluded that the majority of hexene in the HDN of the hexylamines originates from hexanethiol. Nucleophilic substitution of the hexylamines with H2S to give an alkanethiol is the predominant HDN reaction of all three n-hexylamines.