Comparison of performance of microreactor and semi-batch reactor for catalytic hydrogenation of o-nitroanisole Sunitha Tadepalli * , Dongying Qian, Adeniyi Lawal New Jersey Center for Microchemical Systems, Department of Chemical, Biomedical and Materials Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, United States Available online 5 April 2007 Abstract 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 mm 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 10 0 and 10 2 s. # 2007 Elsevier B.V. All rights reserved. Keywords: Catalytic hydrogenation; Fixed-bed microreactor; Semi-batch reactor; Reactor modeling; Kinetics; Mass transfer analysis 1. Introduction Catalytic hydrogenation has evolved as a key process for the manufacture of fine chemicals and pharmaceuticals constituting about 10–20% of all the reactions in the pharmaceutical industry [1]. For example, catalytic hydro- genation of nitro compounds is important in the synthesis of drugs such as Viagra, Zyvox, Agenerase [2] and antimalarial drugs [3]. Similarly, hydrogenation of 2,4-dinitro toluene to toluene diamine is an important step in the production of polyurethane [3] and in the manufacture of TDI (toluene di-isocyanate), a fine chemical [4]. The diverse applications of catalytic hydrogenation lead to significant advances in the way these reactions are conducted in the pharmaceutical and fine chemical industries. Various types of reactor designs such as trickle bed [5], fixed bed [6] and slurry [4,7] reactors have been used in commercial operation. The types of reactor systems used for multi-phase hydrogenation reactions depend upon the type of reaction and the phase behavior of the catalyst and the reactants. All three- phase processes involve steps of gas–liquid, liquid–solid and intra-particle mass transfer and chemical reaction. The relative importance of these individual steps depends upon the type of contact between these phases provided by the reactor system. Therefore, the choice of the reactor is important for optimum performance. In the pharmaceutical industry, most of the multi-phase hydrogenation reactions are conducted in large slurry batch or semi-batch reactors, where the catalyst is suspended in the liquid, which is continuously agitated with a stirrer. The interest in slurry batch reactors derives from their industrial importance in the manufacture of important intermediates for dyes, agrochemicals and pharmaceuticals, often produced on a large industrial scale [3]. Also, the laboratory semi-batch reactor or www.elsevier.com/locate/cattod Catalysis Today 125 (2007) 64–73 * Corresponding author. Tel.: +1 201 216 5332. E-mail address: stadepal@stevens.edu (S. Tadepalli). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.01.076