N-alkylation of aniline with ethanol over an industrial niobic acid catalyst – influence of water formation on kinetics and selectivity

The reaction of aniline with ethanol was carried out over an industrial niobic acid catalyst in a fixed bed reactor at atmospheric pressure and 220–260 °C. The main products, N-ethylaniline and N,N-diethylaniline were formed consecutively. A kinetic study including a model discrimination between several Hougen/Watson type rate equations led to an Eley/Rideal mechanism, where the reaction of gas phase aniline with adsorbed ethanol is the rate determining step. As second adsorbing agent, water inhibits the reaction in higher partial pressures. N-alkylation was the main reaction observed but the addition of water decreased the selectivity and up to 15% C-alkylated products were found. The apparent activation energies for the first and second N-ethylation are 85.6 and 70.7 kJ/mol, respectively. The high equilibrium constants indicate a nearly irreversible reaction.