Biochemscientist - 21-10-2012 at 15:25
Can column chromatography be used for the separation or purification of liquids and solvents? For instance, can ethanol be separated from water or
from acetone via column chromatography? Why or why not?
kristofvagyok - 21-10-2012 at 15:35
NO.
For liquids sure but the liquid should have specific properties e.g.: 2chlorotoluene could be separated from 2 nitrotoluene.
The other thing is that column chomatography works with small amount of the purifing chemicals. E.g.: we needed to clean 60g azulene and we used a
170cm tall and nearly 20cm diameter column.
The third thing is that the separation is not as You think. We add a mixture and we add a solvent system what will cause that our mixture will flow
with different speed on the column.
Fourth: WHY IS THIS IN THE ORGO SECTION?
Fifth: Ethanol could be separated from water in a few hundred way, read a bit.
Sixth: column chromatography is not for continuous separation.
Biochemscientist - 21-10-2012 at 16:30
Ethanol and water do have specific properties. They are different molecules with different molecular weights, different polarities, etc. I am already
aware that there are plenty of other suitable methods which can be used to separate or purify liquids. My goal with this post was not to determine the
best possible method for such a purification, but to determine whether column chromatography can be used to separate solvents and other liquids.
I chose water and ethanol merely as an example. Since water is more polar than ethanol, wouldn't the water cling to a polar stationary phase more than
the ethanol, thus causing the ethanol to elute first?
Is anyone here capable of explaining to me the underlying chemical reasons why this would or would not work, rather than just replying "yes" or "no"?
Thanks.
phlogiston - 21-10-2012 at 17:20
Sure, you would easily be able to separate water and ethanol by chromatography. However, ask yourself what would be the composition of the mobile
phase?
Imagine injecting a sample containing both water and ethanol onto a suitable column. What would you then use to elute them from the column? You'd get
two peaks, one of water and one of ethanol, each of which contains a tiny amount of either compound, and both of which will contain whatever solvent
you used to elute them from the column.
To separate a useful quantity, you'd need to repeat this many, many, many, many, many (ad nauseum) times. Distillation is much more practical and
cheap and doesn't involve a third solvent.
[Edited on 22-10-2012 by phlogiston]