Comparison of performance of microreactor and semi-batch reactor for catalytic hydrogenation of o-nitroanisole

Hydrogenation reactions are ubiquitous in the fine chemicals and pharmaceutical industries. Conventionally, the kinetic studies of hydrogenation reactions are conducted in slurry or batch reactors. The kinetics of fast hydrogenation reactions is often difficult to study in a batch reactor because of the poor mass transfer characteristics of this system. The use of a microchannel reactor for such reactions provides improved mass transfer rates which may ensure that the reaction operates close to intrinsic kinetics. In the present study, a laboratory semi-batch reactor (25 mL) and a packed-bed microreactor (775 μm ID) were evaluated to determine the reactor system that would be best suited for conducting the kinetic study of hydrogenation reactions. For this purpose, hydrogenation of o-nitroanisole to o-anisidine in methanol was selected as a model three-phase reaction. The reaction rates in the two reactor systems were found to be similar under the conditions used for kinetic experiments. Therefore, both batch and microreactors are suitable for studying the kinetics of this reaction. Subsequently, the two reactors were modeled and the modeling results were used to determine the mass transfer coefficients in the two systems under typical operating conditions. The mass transfer coefficients in the microreactor were found to be two orders of magnitude higher than in the semi-batch reactor. This order of magnitude difference in the mass transfer coefficients enables the microreactor to obtain intrinsic kinetics data for fast hydrogenation reactions with half lives in the order of magnitude between 100 and 102 s.