Gudenlau, sorry to go temporarily off-topic...
This is how I figure a chromatography "column" can use a finer adsorbent without increasing the pressure drop nor getting too slow: increase the cross-section and reduce the path length. This must be done in accord with the grain size reduction so that separation stays efficient.
In a first step, the flow can go radially through the adsorbent instead of axially. Then, you can have many inlets and outlets through the adsorbent, say on a chessboard pattern, to define many short paths in parallel. In a remote step, if the inlets and outlets become too thin, they can be shortened and grouped in parallel to arteries and veins.
If the adsorbent is partially sintered to be a porous solid, nothing special to add. But a powder needs to be hold in place. Tubes of porous ceramic could do that, or thin filters hold in good shape by a stronger internal helix of metal, plastic... Besides the coffee filter paper and variations, it's possible to make many small holes in a plastic or metal using a laser, or even by ionizing rays that degrade locally a polymer subsequently etched. All the setup depends on the cleaning needs, supposedly.
But isn't it always done that way?
Marc Schaefer, aka Enthalpy