Kinetics for citral hydrogenation was investigated over a Ni/Al2O3 catalyst both in semibatch and in batch mode with respect to the liquid phase. In the former case the liquid phase was pumped out from the reactor continuously, while the amount of catalyst was kept constant during the hydrogenation in the latter case. The idea with liquid phase drainage was to increase the catalyst bulk density with increasing reaction time. The effect of increasing catalyst bulk density on reaction kinetics and selectivity was investigated both qualitatively and quantitatively. The main parameters were hydrogen pressure (5-21 bar) and temperature (50-90 degrees C). The product selectivity, which should theoretically be independent on the changes in catalyst bulk density, varied with varying catalyst bulk density, especially at higher reaction temperatures due to catalyst deactivation. The simplified kinetic model with lumped kinetic and deactivation parameters was applied to the experimental data being able to explain results obtained under semibatch conditions with continuous liquid phase drainage out of the reactor. (c) 2007 Elsevier B.V. All rights reserved.