Commercial catalytic packing for RD processes is done by wrapping: ion-exchange resin beads are sewn into glass-fiber cloth and rolled into bales (CDTech, Passa-dena, Texas) or put into wire mesh or perforated metal sheets (Sulzer, Winterthur, Switzerland, similar to the methods of Koch Engineering or Montz). Fig. 8.1 and Fig. 8.2 show examples [2, 3].
This packing fits the column diameter or a few pieces of packing are arranged across the column diameter; Fig. 8.3 shows an RD column equipped with catalytic bales .
In addition to commercially available packing there are other approaches to wrapping ion-exchange resins. One idea is to use small tetrahedral wire packages: this was also patented by the CDTech company, Fig. 8.4 .
The benefit of wrapping is that a wide variety of catalysts can be used, but production is rather complicated and expensive. The pressure drop is relatively low compared with packed beds, but the mass-transfer characteristics are poorer, leading to longer columns. Filling and removing this packing into and out of the columns causes relatively long shut-off times. The catalyst particles are not anchored to the packing, so they can move. This can lead to abrasion damage, allowing the catalyst to leave the desired section of the column, which can only be prevented by using very fine mesh, but this has adverse effects on mass transfer between the fluid phase and the catalyst.
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