A comparative analysis of the trickle-bed and the monolithic reactor for three-phase hydrogenations

Based on numerical simulations, a quantitative comparison is made between the performance of a conventional trickle-bed reactor (TBR) and a monolithic reactor (MR). The model reaction considered is a consecutive, three-phase hydrogenation for which the kinetics can be described using a rate equation of the Langmuir-Hinshelwood-Hougen-Watson (LHHW) type. A mathematical model is formulated for both the TBR and the MR based an literature correlations. The volumetric space-time yield (STY,), the selectivity towards the intermediate product and the pressure drop are taken as the main performance criteria, For the model system considered here, the selectivity of the intermediate product was found to be higher for the MR over almost the whole range of variables studied. STY, is higher for TBR with particles of less than 2 mm diameter, but the pressure drop for such small particles is high. For larger spherical particles it is possible to reach comparable or higher STY. using MR. The use of a shell catalyst in the TBR was also considered and it was found that by using large particles with a thin shell of active material, the selectivity as well as the catalyst load were comparable to those of the MR. The pressure drop in the MR is always low and sufficient flow rates can be obtained from the hydrostatic pressure alone. This implies that it is possible to operate at zero net pressure drop, which makes internal recirculation of gas very simple.