Reactivity of methyl-substituted indoles

The hydrodenitrogenation (HDN) reactivities of indole (IND) and several methyl-substituted indoles (MINs) were carried out in 35 atm hydrogen and 340°C in a fixed-bed reactor, employing a NiMo/Al2O3 and CoMo/Al2O3 catalyst. Appreciable differences in reactivity were obtained depending on the location of the methyl group in indole. Compared to IND, total conversion and HDN conversion were generally higher when methyl groups were on the aromatic ring, and lower for methyl. groups on the N-ring. Two paths for initial conversion of IND/MINs were deduced, viz a CNH path leading to an intermediate aniline, and a HYD path leading to hydrogenated products. Satisfactory trends were obtained between initial CNH rates and the electrostatic potential on the N atom of the MINs, and between initial HYD rates and the ionization potential of the MINs.; Kinetic studies of the indole HDN reaction network were carried out over both catalysts at 340°C and 35 atm hydrogen by varying the space time and concentration of IND in the feed. A Langmuir-Hinshelwood model consisting of five rate constants and three adsorption constants was successfully adopted to correlate the kinetic data. Due to the strong adsorption of indole, inhibition occurred in subsequent reactions of the HDN network. The different adsorption constants obtained implied that different sites were present for the hydrogenation of the aromatic ring, the cleavage of the C-N bond, and the hydrogenation of unsaturated intermediates. The NiMo catalyst favored the HYD path over the CNH path, while the opposite occurred for the CoMo catalyst. Increasing the H2S partial pressure enhanced the CNH path, resulting in increased total conversion, while the HDN conversion was not changed for the CoMo catalyst; whereas, the HDN conversion was depressed while the CNH conversion was not affected for the NiMo catalyst.; Low material balances were often obtained during the HDN of indole. The loss of indole was attributed to one or more oligomers of IND. Oligomer formation occurred with an alumina support and phosphorus/alumina support, as well as with both catalysts, and was shown to be reversible. Oligomer formation decreased with increase in IND conversion for the catalysts.