The trend towards scaling down reactors, in particular for research applications, causes a change in hydrodynamics of multiphase systems. The catalyst packing in a small reactor exhibits properties which we cannot predict by extrapolating large-particle trickle-bed data. The reason is that capillary and viscous forces rather than convection become increasingly predominant in the micrometer range. Research on the hydrodynamics of powder-packed beds showed the importance of the volumetric ratio of the gas and liquid flows. For a decreasing liquid fraction in the feed, bypass of the gas increases exponentially. This can reduce conversion and, as a consequence, disguise kinetics data when part of the reactants can evaporate to the gas phase. The conclusion on the hydrodynamics work is: plug-flow behaviour in micro-packed beds is possible if a certain gas-liquid ratio is maintained. (Van Herk et al. 2005) The degree to which a catalyst is diluted in the bed is an important factor in catalyst performance testing. If on one hand the catalyst bed is diluted too much, some of the reactants may pass through the bed without getting in contact with the catalyst. On the other hand, if the catalyst is not diluted enough, the high concentration of the active catalyst may cause non-plug flow behaviour and radial temperature profiles. In our high-throughput unit, we could investigate these general aspects of catalyst packing and dilution for micro-packed beds. In this talk, I will demonstrate the design and the best operating conditions for miniature-packed beds, based on a combination of cold-flow hydrodynamic experiments and reactive tests.

References Van Herk D., Kreutzer M.T., Makkee M. and Moulijn J.A., Cat. Today, 106 (2005) 227-232.