Direct amination of dodecanol with NH3 over heterogeneous catalysts. Catalyst screening and kinetic modelling

The direct amination of dodecanol with ammonia to dodecylamine was investigated over carbon supported ruthenium, palladium, platinum, iridium and osmium catalysts. The influence of ammonia and hydrogen pressures was investigated. It was found that ammonia pressure did not influence the reaction, while extra hydrogen in the reaction mixture was beneficial for dodecanol conversion and dodecylamine selectivity. A dodecylamine yield of 83.8% was achieved with Ru/C catalyst at 150 °C, 4 bar ammonia and 2 bar hydrogen after 24 h reaction.

Zero reaction order in ammonia typically implies that the rate limiting step is not related to amination, but rather to a preceding dehydrogenation step. Experimentally observed unusual positive order in hydrogen in dehydrogenation was related to deactivation by surface coking. Partial surface regeneration requires presence of hydrogen, thus explaining a positive reaction order towards this reactant. A detailed analysis of kinetic regularities, which due to specificity of the reaction mechanism could be done separately for activity and selectivity, allowed advancing a mathematical model adequately describing experimental observations.