Pellet partly wetted catalyst

DUDUKOvic AND MILLS Catalyst E ffectiveness in Trickle-Bed Reactors 391 Mathematical Model For Reaction In Partly Wetted Catalyst Pellets... 

Most common in practice is a trickling flow that occurs at relatively low gas and liquid flow rates. Under these conditions in trickle-bed reactors (TBRs) complete liquid films around the particles would break up into partial films, rivulets and droplets and a so-called partial wetting trickling regime exist. It is easier for hydrogen to enter the no wetted or very thin wetted part of partially wetted catalyst pellets because the mass-transfer resistance between a gas and the particle sur-... 

It is instructive to consider first a siiqtler problem, namely that of a reaction on a partly externally but coiqtletely internally wetted catalyst pellet. This case is of Interest in particular for hydrocarbon feeds which presumably readily wet the internal pore structure. Clearly if the kinetic rate is very slow the reduction in the "supply area" i.e. external area wetted through which reactants arrive to the pellet will hardly affect pellet utilization but for higher kinetic rates a reduction in utilization due to Incomplete external wetting should become apparent. 

As previously explained, problems arise from an uneven distribution of the liquid around the catalyst pellets in TBRs In fact only a part of the external particle surface is effectively wetted by the flowing liquid the remaining zones are partly in contact with semistagnant liquid pockets and partly covered by an almost motionless thin film The chosen reaction is not significantly exothermic and the catalyst pores can therefore be assumed completely filled by liquid No particular problem exists if the controlling reactant is fed with the liquid because the most active zones of the catalyst are very likely those characteri- ed by a flowing liquid and the conversion rate increases as the liquid flow... 

---