How Does Adsorption Works?

[gladkenn]

Guys,

Activated Carbon, Silica gel, and/or Molecular sieve are just some of the materials that adsorb compounds/chemicals which passes through it. Any idea how this works microscopically?

 

[francesca]

We'll be covering that on Tuesday in my Thermodynamics class.

So far all I can tell you is that there are two types of ADsorption: solvent-motivated, which is entropy driven (eg. hydrocarbons, which are usually hydrophobic, with water - there is expulsion of the solute from one phase and accumulation at the interface of the phase); and sorbent-motivated, which is enthalpy driven (eg. activated carbon and benzene, where the activated carbon surface is attractive to benzene).

More after Tuesday. If you can't wait that long, check out this PowerPoint presentation I cound on Google.

 

[GarySCWSVI]

Adsorption: The physical process occurring when liquids, gases or suspended matter adhere to the surfaces of, or in the pores of, an adsorbent media. It is a physical process which occurs without chemical reaction. It is more of a "stick to" process than a chemical reaction.

Gary Schreiber, CWS VI
The Purolite Co.

 

[gladkenn]

GarySCWSVI,

Does Cation and Anion Exchangers in Water Conditiong Process not of adsorption type? Instead, of absorption?


gladkenn

 

[francesca]

H2G2 to the rescue!

 

[GarySCWSVI]

Basically ion exchange resins are not adsorbents. They cause chemical reactions between ions in a solution and the ions on the resin. Regeneration, or reversal of that process, is a reverse chemical reaction.

There are some adsorbent resins that only work on the basis of adsorption and some that work on the basis of ion exchange and adsorption.

In general, cation and anion exchange resins are used on the basis of the chemical reaction. In special cases, ion exchange resin manufacturers also manufacture adsorbents that look like ion exchange resins and some adsorbents that also have ion exchange functionality.

Some ion exchange resins, particularly the macroporous or macroreticular versions, used in general water treatment also will have some adsorption capability.

Gary Schreiber, CWS VI
The Purolite Co.

 

[dalcazar]

true aDsorbent mediums work by delaying the passage of certain molecules by allowing them thru themselves, this process is normally done by a certain pore size in the medium that allows a molecule of smaller size into the "inner passageways" of the medium and thus momentarily traps it whilst larger molecules must pass around the medium in the interstitial spaces and thus flush much faster.

Adsorption is a means of separating several different kinds of compounds, but the filter itself does not form a chemical bond. It is the principal on which all chromatography works.

In the case of aBsortion there is a physical trapping of the molecule whose retention is desired by formation of some sort of chemical interaction such as ionic bonding.

I always had a hard time remembering which was which when I was learning them so I came up with "aDsorption as in aDhering" which is in effect what happens, whereas absorbing means they are trapped completely like water is aBsorbed by a sponge.