3 replies to this topic

[Ebrahim]

Dear all

In activated alumina adsorbents:
1. What is the difference between "attrition loss" and "abrasion loss"?
2. What is the importance of LOI (loss on ignition) on activated alumina adsorbent performance?
3. What is the amount of mesh by converting this unit to inch? (It was in a U.S patent that: "Mesh sizes are U.S standard screen sizes")

Regards

[Art Montemayor]

Ebrahim:

The answers to your specific questions are as follows:

1) "attrition loss" is the loss of material due to the handling or excessive movement of the material due to it composition properties. In other words, the break-up of the material due mostly to its own properties. "abrasion loss" is the loss of material due to the mechanical "rubbing" or the abrasive movement within intself or with other harder components - like the support grids, screens, and vessel walls that are in contact with it. A sudden rush of fluid being adsorbed through the bed can cause a lot of abrasion if the adsorbent bed is not properly held down. That is why I (& others) always advise that the fluids going through an adsorbent fixed bed to be in the downward direction - not in the upward direction - because the latter can cause the bed to "rise" or agitate it such that it stimulates abrasion and subsequent attrition.

2) I have never found any importance of the LOI (loss on ignition) values on activated alumina adsorbent performance. I have no reason to put the adsorbent under flame or afire, so I'm not interested in that scenario. I have a suspicion why that value is tossed around, but it has no value in the implementation of an Adsorption Unit Operation.

3) Mesh, in the popular meaning, means the size of the opening in a screen or a sieve. It determines the nominal size of particles that can "squeeze" through that opening. This is an important value to be aware of when you are primarily interested in retaining or "holding down" a fixed bed of adsorbent (as mentioned in 1), above). It is impossible to convert mesh into "inch" - as you will become aware when you review the excellent reference that Profe has been kind enough to refer you to. Mesh is not an area; it is a measure of two dimensions (usually square). You should not try to define it as an area. Remember your high school trigonometry: the diagonal measure (hypothenuse) is longer than any of the two other sides. It is normally square because it is easier to fabricate screen that way and to standardize it. There are no "patents" on mesh - humans have been making (or weaving) screens since a long, long time ago.