Studying the internal mass transfer phenomena inside a Ni/Al2O3 catalyst for benzene hydrogenation

The mass transfer phenomena occurring inside Ni/Al2O3 catalytic extrudates have been studied for the liquid-phase hydrogenation of benzene. The experiments were conducted in a bench scale trickle-bed reactor at 17 bar absolute pressure and temperatures between 70 and 150 °C. Kinetic, thermodynamic and hydrodynamic effects have previously been examined [K.C. Metaxas, N.G. Papayannakos, Ind. Eng. Chem. Res. 45(21) (2006) 7110–7119]. Temperature gradients inside the particle and across the liquid film surrounding catalyst particles have been checked and verified as absent. Concentration profiles of hydrogen and benzene show firstly that are consumed close to the surface of the extrudate and secondly to be in large excess along the particle radius. Catalyst particle tortuosity is estimated to be 3.75, very close to the value of 3.56 extracted from a statistical model based on nitrogen sorption hysteresis data. The effectiveness factor lies in the range of 0.19–0.35, implying strong diffusion limitations. The passivation of catalyst surface is posed as a solid reason for the modification of the true activation energy of the reaction occurred while moving from crushed catalyst particles to catalytic extrudates.