Solid effects on gas-liquid mass transfer in three-phase slurry catalytic hydrogenation of adiponitrile over raney nickel

Abstract

Many three-phase catalytic reactions are limited by gas-liquid mass transfer. Previous works have found the transfer rate to be increased by the presence of fine catalyst particles. Most of the studies concerned active carbon particles in aqueous media. This paper intends to point out and to explain this effect in the case of catalytic hydrogenation of adiponitrile over Raney nickel particles. The experiments based on pressure variation due to the hydrogen absorption in a stirred batch reactor point out clearly an increase of k 1a at an optimum catalyst loading. This positive effect is reduced at high stirring speed and turns back to a small negative effect when using inert particles. The enhancement of gas-liquid mass transfer by particles is maximum when a layer of water is physisorbed at the catalyst surface. The water located at the solid surface could induce a better adhesion of the particles to the bubble. The total gas-liquid mass transfer could be enhanced when using particles with high hydrogen adsorption capability, by a “shuttle” or a “bridge” effect. The solid particles act as hydrogen carriers. These assumptions have been further supported by original experiments involving the same equipment and measurements with a simultaneous reaction. A model which takes into account particles adhesion at the interface has been set up and is in good agreement with the experiments.