(32c) Catalytic Hydrogenation of Aromatic Nitro Compound in a Micro-Reactor

In this work, a three phase solid catalyzed hydrogenation reaction of aromatic nitro compound was studied in a microreactor as a model pharmaceutical reaction. In the pharmaceutical industry, hydrogenation reactions constitute about 15-20% of the reactions and are generally carried out in batch reactors. Hydrogenation of nitro compounds falls under the class of reactions with fast kinetics on noble-metals, and is usually limited by external mass transfer in batch reactors. Besides, these reactions are highly exothermic in nature which necessitates effective heat removal. Ineffective mass transfer and non-uniform temperature distribution in the batch reactor can have deleterious effects on reactor performance including the formation of undesired side products. The use of microreactor for such reactions provides improved mass and heat transfer rates which may ensure that the reaction is close to intrinsic kinetics.

The main objective of this study is to compare the performance of the microreactor with a batch reactor using this model reaction. For this purpose, experiments were conducted in a packed bed micro-reactor and also in a semi-batch reactor. Internal and external mass transfer limitations were examined and kinetic experiments conducted in both reactor systems. Different rate laws using different mechanisms from the literature were considered to fit the experimental data. The mass transfer coefficient in the microreactor was found to be orders of magnitude greater than that in the semi-batch reactor. Furthermore, the effects of various operating conditions on the performance of the two reactor systems were investigated, and their performance measured by the space-time yield.