Modeling and comparison of acetophenone hydrogenation in trickle-bed and slurry airlift reactors

The performance behavior of a trickle-bed and a slurry airlift reactor has been studied, in case of an exothermic complex multistep reaction. Liquid-phase hydrogenation of acetophenone over a Rh/C catalyst has been performed using both continuous reactors. Mathematical models have been developed and simulations compared with experimental data. Modeling the airlift reactor is easy because it has been operated under conditions where there are no significant mass transfer limitations. Conversely, the trickle-bed model incorporates wall heat transfer, external and internal mass transfer resistances coupled to Langmuir-Hinshel-wood-type kinetics, and shows that: (1) available correlations for gas-liquid transfer are not satisfactory, (2) partial wetting of the catalyst is most probably an important process, (3) internal diffusion limitations are important. Finally, the trickle-bed and airlift reactor performances have been rigourously compared in terms of productivities and yields, and the effect of various parameters discussed. Differences observed concerning the yields have been attributed to the influence of back mixing in airlift reactor and pore diffusional effects in the case of a trickle-bed. The choice of an optimal technology remains an open problem especially when exothermic and complex reactions are to be carried out. (C) 1997 Elsevier Science Ltd.