Mass transfer and kinetics of the three-phase hydrogenation of a dinitrile over a Raney-type nickel catalyst

Abstract

The hydrogenation kinetics of a dinitrile over a Raney-type nickel catalyst was evaluated from experiments performed in a fed-batch operating autoclave at 320– 355 K and 2– 7 MPa hydrogen pressure. This complex catalytic reaction consists of two main parts: almost 100% selective hydrogenation of the dinitrile to the corresponding aminonitrile and consecutive hydrogenation to either the desired primary diamine or to pyrrolidine via ring formation. An extensive study has been made on the effects of mass transfer in the applied slurry-type reactor for this reaction. The gas–liquid mass transfer is enhanced by the presence of catalyst particles, and at typical hydrogenation conditions, k L a values up to 1.0 s −1 can be reached. A Sherwood correlation for the three-phase reactor showed that important parameters in the gas–liquid mass transfer are stirrer speed and the density and viscosity of the solvent. The kinetic experiments were performed in absence of mass and heat transfer limitations. The kinetic data were modeled using two rate models based on Langmuir–Hinshelwood kinetics, assuming the reaction of dissociatively adsorbed hydrogen and nitrile compound as rate-limiting step. The first model involved competitive adsorption between hydrogen and organic compound and the second model was based on non-competitive adsorption. Both models successfully described both reaction parts. The reaction of dinitrile to aminonitrile is nearly 100% selective due to the relatively strong adsorption of the dinitriles as compared to the aminonitriles. By increasing the hydrogen partial pressure, higher yields of primary amine can be obtained. The models predict that operating in the mass-transfer regime at relatively high temperatures reduces the formation of the primary diamine.