ABSORPTION ACCOMPANIED WITH CHEMICAL-REACTION IN TRICKLE-BED REACTORS

A new development in the field of internals in packed columns is the u se of structured packing types. Recently, a new structured packing typ e coated with a thin alumina layer (KATAPAK(TM)) has been developed. I n this report, the results of an experimental and theoretical study co ncerning the possible applicability of this new packing material for h ydrogenation processes in a trickle-bed reactor is presented. The pall adium catalyzed hydrogenation of alpha-methylstyrene is used as a mode l reaction to study hydrodynamics and mass transfer characteristics in a trickle-bed reactor under reactive conditions. Conversions at sever al process conditions are measured in a pilot plant in which 3 mm sphe res as well KATAPAK(TM) is applied as packing materials. A comparison of the results of some physical absorption experiments with the result s of hydrogenation experiments showed that the resistances in series m odel-in which the total resistance against mass transfer is calculated from the separate resistances-is not valid in systems where heterogen eous reactions at the solid surface can enhance the mass transfer-rate at the gas-liquid interphase. With the aid of a developed trickle-bed reactor model, based on liquid diffusion, simultaneous reaction at th e solid surface and zero volume mixing points,the mass transfer phenom ena in trickle-bed reactors in conditions where the resistances in ser ies model fails can be explained and described. The numerically solved model calculates the hydrogen profiles in the liquid films of the rea ctor and over all single pass conversions at several process condition s. These conclusions are confirmed by the results of the simulation of a model reactor, i.e. the laminar film reactor with a catalytically a ctive wall. From the results of the measurements it could be concluded that in trickle-flow conditions, the application of KATAPAK(TM) does not significantly improve on the overall performance of trickle-bed re actors. The increase of the physical absorption rate due to better mas s transfer characteristics of structured packings compared to dumped p acking types-as reported in literature-will be eliminated to a certain extent in reactive systems due to the enhancement effect of heterogen eous reactions in trickle-flow operation. (C) 1997 Elsevier Science Lt d.