Liquid Phase hydrogenation of nitrobenzene over an industrial Ni/SiO 2 supported catalyst Jose ´ Relvas a,b, * , Rui Andrade b , Filipe Gama Freire a , Francisco Lemos a , Paulo Arau ´jo b , Ma ´rio Jorge Pinho b , Clemente Pedro Nunes b , Fernando Ramo ˆa Ribeiro a a IBB – Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Te ´cnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b CUF – Quı ´micos Industriais, S.A., Quinta da Indu ´stria, 3860-680 Estarreja, Portugal Available online 22 January 2008 Abstract The catalytic hydrogenation of nitrobenzene using a commercial nickel catalyst supported on silica was studied in a three-phase batch laboratory scale stirred tank reactor. Reaction mixture samples were analyzed by gas chromatography. The aim of the work consists in obtaining a fully functional and practical mathematical model of the reaction kinetics that is easy to implement and able to describe the reaction progression in a wide range of conditions. The effects of temperature, pressure and nitrobenzene concentration for a given catalyst concentration were studied. The model that was obtained is able to describe all the experiments with just one set of parameters and helped to describe and explain phenomena that were observed in an industrial system; the results obtained indicated the possibility of the catalyst surface changing with time by contact with the reaction mixture. # 2007 Elsevier B.V. All rights reserved. Keywords: Hydrogenation; Nitrobenzene; Modelling; Kinetics; Aniline production 1. Introduction Aniline is a valuable compound for the plastic, rubber processing, herbicides and dyes and pigments industries. The catalytic hydrogenation of nitrobenzene, which is used for the production of aniline, can be performed through several processes which can be divided into two major groups: vapour- phase and liquid-phase processes. Both are currently used in the industry with very high yields (around 99%) [1–6]; despite these high yields, in the interest of process optimization, the complex kinetic behaviour of this reaction has been extensively studied in the last 50 years, both in gas [5,7,8] and liquid phases [4,6,9–18]. The liquid phase transformation implies the existence, in the reactor, of three distinct phase, which increases the process complexity, and several studies have been published on this three-phase reaction process, in particular, on the kinetics of the hydrogenation of nitrobenzene to aniline using a laboratory scale stirred tank reactor where the solid catalyst is suspended in the liquid reactants [6,10,11]; this type of reactors has been demonstrated as being a useful tool to obtain kinetic information for this reaction. More recently studies concerning the detailed mechanism, i.e. describing the formation of the intermediates in the hydrogenation of nitrobenzene to aniline [13] has been published. The reaction, within the range of conditions under which it was studied in this work, shows a very high selectivity and, thus, this study has been restricted only to the rate of the main reaction, although it will be extended to include secondary products in the future. With the technological advances in the last few years and with the help of more and more powerful computers, the chemical industry has now an increased capability to improve and optimize its production processes by resorting to more detailed and accurate mathematical models. These models require the use of reliable kinetic information and, in particular, the use of kinetic rate laws and mechanisms that area able to www.elsevier.com/locate/cattod Available online at www.sciencedirect.com Catalysis Today 133–135 (2008) 828–835 * Corresponding author. E-mail address: relvas@ist.utl.pt (J. Relvas). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.11.050