The challenge is to minimize the size of the wall-coated reactor, i.e. increase the catalyst loading per unit volume, which requires coatings thicker than 10ƒÝm. G.I. Taylor reported that the thickest coating possible occupies 57% of the total cross sectional area, independent of channel diameter. However, Taylor performed his study with a Newtonian fluid in channel diameters ranging from 1.5-4mm . In this work we performed an experimental study to determine the maximum coating thickness feasible for non-Newtonian fluids in channels ranging from 250 to 530ƒÝm in diameter. In contrast to Taylor's findings, our data shows the fraction coated to be dependent on the channel diameter due to inertial effects within the coating fluid. The maximum fraction coated was drastically lowered, e.g. 12% in 250ƒÝm diameter channel.
It is imperative to minimize the effects of surface tension while concurrently minimizing the inertial effects within a given coating structure. We were able to increase the fraction coated by minimizing these effects through careful manipulation of the viscosity of the coating fluid. This is done inherently by using multi-channeled structures, and the resulting coatings are found to be thicker than predicted by the single-channel data .
The presentation will show data on coating multi-channel ceramic microreactors (square channel cross-sections) and multi-bore fused-silica tubing (circular channel cross-sections). The microreactors were coated using a commercial Cu/ZnO/Al2O3 catalyst from BASF and the catalyst reactivity was measured and compared to that in a packed-bed.
This work has been funded by the U. S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0010
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