Hydrogenation of Nitrobenzene over a Pd/Al sub(2)O sub(3) Catalyst - Mechanism and Effect of the Main Operating Conditions

• Published in: Chemical engineering & technology 2015-09, Vol.38 (9), p.1625-1636
• Main Authors: Couto, Clara Sa, Madeira, Luis M, Nunes, Clemente Pedro, Araujo, Paulo
• Format: Article
• Language: English
• Subjects: Aniline; Byproducts; Catalysis; Catalysts; Formations; Hydrogenation; Nitrobenzenes; Palladium
• ISSN: 0930-7516; 1521-4125
• DOI: 10.1002/ceat.201400468

The catalytic hydrogenation of nitrobenzene (NB) was studied in a three-phase basket reactor with a commercial Pd/Al sub(2)O sub(3) sample as catalyst. The kinetic experiments allowed a better understanding of the mechanism behind the formation of aniline (ANL) and by-products, a topic not yet well comprehended. The effect of some operating conditions was studied and the existence of more by-products than mentioned in the literature was stated; specifically, benzene formation was verified. Both the reaction kinetics and selectivity were found to be strongly dependent on the temperature, while the effect of total pressure is not that pronounced. Moreover, the high selectivity of the catalyst used in the present work was proved, and as such the deep hydrogenation of ANL to form by-products only occurs in considerable extension when the NB concentration in the reaction mixture becomes negligible. The catalytic hydrogenation of nitrobenzene is an important reaction in the production of aniline for the polyurethane industry. The Pd-based catalyst used here is very selective towards aniline at high nitrobenzene concentration, while at low concentrations the formation of by-products is dominant. Benzene production was verified and quantified and added to the reaction network proposed for the formation of aniline and by-products.