Difference between absorbption/adsorbption/sorption 3

[kuki]

I have found that this terms are often misused. What is in fact the difference between absorb, adsorb and sorp? What are the inverse processes of them: desorb/desorp?

 

[MortenA]

Absorption is a mass transfer operation wherease adsorption is a surface reaction as far as i understand it.

Eg: air (or other gasses) can be absorbed in water
solvents (and other gasses) can be adsorped on activated charcoal.

Best regards

Morten

 

[sciguyjim]

Absorption occures when something soaks up another material within its structure. So sponges absorb water.
Adsorption is a surface effect. Cut aluminum in a vacuum has bare aluminum atoms exposed. The instant air is admitted to the vacuum, some oxygen is adsorbed onto the bare metal and instantly forms a layer of aluminum oxide.
Sorption, I think, is a generic term referring to any action similar to either of the above actions. For example, if you had to mention the effect but it was unknown which action is actually happening.

 

[quark]

scyguyjim is correct. Sorption is commonly used for both absorption and adsorption.

Adsorption is a superficial phenomenon. An example is moisture adsorption by desiccants.

An example for absorption is water absorption by sponge.


Regards,


Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[MortenA]

Are you sure water is absorbed into a sponge (yes i know thats what you say) - but from a chemical point of view isnt it a lot like gas beeing adsoped on activated carbon? The water isnt really integrated in to the sponge but occupies vacant space between in the sponge internal?

Is coffee brewing extraction or absorption - or is extration a combination of absoption and filtering/separation in the same process?

Best Regards

Morten

 

[kuki]

Thanks a lot people!
I have found something that matches with what scyguyjim said:
"Sorption is the common term used for both absorption and adsorption, describing adherence of chemical substances to particles. Absorption is the incorporation of a substance in one state into another of a different state (e.g., liquids being absorbed by a solid or gases being absorbed by water). Adsorption is the physical adherence or bonding of ions and molecules onto the surface of another molecule. Unless it is clear which process is operative, sorption is the preferred term.

Regards.

 

[sciguyjim]

MortenA, You asked:
"Are you sure water is absorbed into a sponge (yes i know thats what you say) - but from a chemical point of view isnt it a lot like gas beeing adsoped on activated carbon? The water isnt really integrated in to the sponge but occupies vacant space between in the sponge internal?

Is coffee brewing extraction or absorption - or is extration a combination of absoption and filtering/separation in the same process?"

I have never heard of water soaking into a sponge described as anything but absorption. You are correct about the water occupying the vacant spaces in the sponge, but on a microscopic scale, it also soaks into the substance of the sponge. Now, this could be occupying microscopic spaces here too, but, when talking about the sponge as a whole, it is considered to be absorption.

A similar thing would be water soaking into a towel made of synthetic fibers. The fibers themselves, being plastic basically, don't absorb water into their structure, the water is held between the fibers. We call this absorption too.

It probably depends, to some extent, on whether we're talking about liquids or gases. Water soaks into a towel, but if the towel were dessicated then exposed to water vapor, the vapor would adhere to the surfaces of the fibers. In this case it would be adsorption.

Activated carbon is called "activated" because it is produced in a way that gives it a very large surface area. Substances can be held, not only on the surface, but inside the granuals too. However, this has been determined to be a surface phenomenon (whether inside or out), so it is adsorption.

Coffee brewing is a combination of first, absorption of water into the granuals, then solvation of some solids into the water, then extraction of solvated material away from the insoluble granuals, then, finally, filteration of granuals from the water.

 

[kuki]

Yes, sciguyjim, for me it's clear.
About the inverse processes: desorption is obviously the inverse of sorption; what about the inverse of absorption and adsorption?... maybe it's just a question of english, but should it be deabsorption and deadsorption?

Regards.

 

[sciguyjim]

Kuki, simply saying desorption is accurate regardless of the type of sorption. Concerning sponges and the like, some people prefer the term "dripping" (ha ha). Jim.

 

[quark]

Kuki!

Disorption is not antonym for sorption but for adsorption. And absorption and adsorption are not chemical reactions but physical. (It is actually attractive, adhesive force)
Yeah sponge absorbs water.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[sciguyjim]

That's right Quark, sorption involves intermolecular forces like surface tension, hydrogen bonding, dipole moments and more. There has to be an attraction between a liquid and the ad(ab)sorber for the liquid to "wet" the material.

The closest sorption comes to being a chemical reaction would be with certain hygroscopic chemicals that can first absorb water, then incorporate it into their chemical and crystal structure. Typically, heat is used to return the crystals to their dessicated form.