Kinetic study of catalytic hydrogenation of O-nitroanisole to O-anisidine in a microchannel reactor

Hydrogenation reactions are ubiquitous in the fine chemicals and pharmaceutical industries. The hydrogenation of o-nitroanisole to o-anisidine in methanol was selected as a model three-phase reaction for kinetics study in a packed-bed microchannel reactor using Pd metal supported on zeolite as a catalyst. The kinetics of three-phase hydrogenation reactions in conventional slurry or batch reactors is often limited by mass transfer of hydrogen through the liquid due to the limited solubility of hydrogen in organic substrates and solvents. These reactions are also highly exothermic, therefore adequate temperature control is of primary importance to reduce side reactions and to prevent thermal runaway conditions. The use of a microchannel reactor for such reactions provides improved mass and heat transfer rates which may ensure that the reaction operates close to intrinsic kinetics. In the present study, the rate data in the intrinsic kinetic regime were analyzed and found to be well represented by L-H type rate equations. Kinetic experiments were also conducted in a semi-batch reactor under similar reaction conditions as the microchannel reactor. The performance of the packed bed microchannel reactor was compared to that of the semi-batch reactor by evaluating the mass transfer resistance in each system.