2 replies to this topic

[middy08]

I'm a mechanical engineering student working on a continuous distillation column for ethanol as a design project. I am trying to decide what to use for the packing, as I've decided this is the direction I need to head in. I've heard from some fairly shady sources that you can use something as common as marbles, however in all of the texts that I have referred to and all of the more legitimate internet sites, I've found different types of rings, saddles or meshes made of ceramics, metals or plastics. What is the difference; why use the more complex versus the marbles? Also what would be suggested for a cost effective packing material (remember student budget)?

Thanks very much.

[Adriaan]

Suppose you use marbles as the filling; as they are near perfect globes they would take up a VERY significant amount of the space in the column. It would be more effective to use short lengths of (small diameter) tube as they provide far more surface area per volume and create a more irregular flow AND do not stack as efficiently as globes do (resulting in more useable volume).

As to the material used; I would avoid plastics (thermoplasts, yech, use a thermoHARDER! In a heated process such as destillation it would be unwise to use a thermoplast. The ethanol or whatever is fouling the ethanol could react with the plastic too AND the plastic can absorb chemicals).

As you are on a budget maybe you could use a very cheap packing material; clean(ed) glass shards. Available for free if your university has a laboratory, probably < wink > students can be SO clumsy with pipettes.

[djack77494]

middy,
As you have guessed, we don't use different types of rings, saddles or meshes made of ceramics, metals or plastics without good reason. When you look into selecting packing, you make your selection based on packing performance (and cost). You're interested in mass transfer performance, or how efficient the packing will be in effecting mass transfer. This is related to the surface area or m^2 of surface / m^3 of packing volume. You will also be interested in the packing's hydraulic performance or what pressure losses can be expected in flow through a bed of packing. There are other considerations as well, such as strength.

I'm not a good source for pricing. I know that a wide variety of shapes and materials is available. Polypropylene is probably on the lower end of the price range, while stainless steel is more likely on the high end.

HTH,
Doug