Effect of structure and thermal properties of a Fischer Tropsch catalyst in a fixed bed
Résumé
A 2D G-S pseudo-homogeneous steady-state plug flow, non-isobaric and non-isothermal model is used to investigate the effects of operating conditions and catalyst thermal properties on the behaviour of a multi-tubular fixed bed for Fischer–Tropsch synthesis. This simulator allows observing, quantifying and discussing the influences of the gas velocity, the tube diameter, the type of catalyst used (monolithic foam or extrudates) and the heat conductivity of the support (alumina or silicon carbide). The observed responses are the effective thermal parameters of the catalytic bed, the radial and axial temperature profiles and the global performances of the reactor (yield, productivity and selectivity). Thermal properties of the support exhibit a strong influence when low fluid velocities and/or large tube diameters are employed. Because of the high void fraction of a foam structure these effects are less pronounced than with packed beds. This structural difference allows a wider range of operating conditions in terms of fluid velocity and tube diameter but underlines the necessity to tune the void fraction of a foam bed to obtain the best compromise between its volumetric catalytic activity and a good thermal behaviour.