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Magpie
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salting out
In jharmon12's thread about forcing ethanol out of E-85 fuel there was some discussion about the possibility of salting out ethanol from water. A
YouTube indicated that this is indeed possible using K2CO3 as salt. Then I read somewhere that any salt can be used. Since this technique is going
to be very important to an upcoming separation, I conducted some preliminary experiments.
My experiments were conducted by dissolving the salt in 10mL of water. This was then mixed with 10mL of Everclear (95 vol% ethanol in water). A few
drops of diluted food coloring was added to better show any phase separation.
In my 1st experiment NaCl was added to the water to saturation, 26wt%. As can be seen in the picture below this resulted in no phase separation.
Instead adding the alcohol just caused most all of the salt to precipitate.
In the 2nd experiment I added 10g of pottery grade K2CO3. This did cause a nice clean phase separation to quickly form, as shown.
In the 3rd experiment I added 1.2g of K2CO3. Again a nice clean separation quickly resulted but only to a limited extent with most of the water
remaining in the upper alcoholic layer.
In the 4th experiment I added 11.7g of K2CO3 which I estimate is very near saturation. Again a clean separation was quickly obtained. The water
level came up to the original water level before mixing as indicated by the black magic marker line.
I'm quite pleased with the results of the separations using K2CO3. I have also read that (NH4)2SO4 is an effective salt for such separations.
Comments, questions, and suggestions are welcomed.
The single most important condition for a successful synthesis is good mixing - Nicodem
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S.C. Wack
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I've noted that potassium carbonate, only, is used in manuals going at least as far back as Norris. For other alcohols as well.
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Magpie
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To test (NH4)2SO4 effectiveness for salting out ethanol I prepared 10mL of water with 7.7g of said salt added. It did not work at all, in fact the
salt all came out of solution even more dramatically than did the NaCl.
[Edited on 19-5-2013 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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papaya
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Wonderful, never thought this is even possible with ethanol, what is the purity (concentration) of alcohol obtained this way?
Also I want to ask question there not to open a new thread - how to salt out acetone from water? I know this must be simple and the reason is I have
some water waste from experiments which contains a lot of acetone, so I added NaCL to it up to saturation - no separation occurs. To test idea - I
took s test tube with half NaCl/water solution and added acetone. First it formed layers, but after shaking it mixed and some solid started to
precipitate (must be NaCl). So even at high concentrations of acetone this didn't work and I'm surprised, because I've heard many times about easy
salting out of acetone, my question is what to do? Can I use NaHCO3 instead of K2CO3 ?
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papaya
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NaOH is quite expensive for this, of course you can regenerate it if you have only acetone and water and no other salts. What else works for acetone ?
Also why potassium salt - there's something special for it?
edit: I replied this to someone who it seems removed the post 
[Edited on 19-5-2013 by papaya]
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garage chemist
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I have used K2CO3 in the past for drying alcohols and ketones after synthesis. Specifically cyclopentanol, cyclopentanone and 2-methyl-2-butanol.
It works very well for quickly removing large quantities of water, but it is not a very strong desiccant. It leaves a little water in the organic
liquids even if they are left in contact with fresh solid K2CO3 for a long time, evident by a small amount of azeotrope with water coming over as
forerun upon distillation.
K2CO3 cannot be replaced by Na2CO3, NaHCO3 or NaOH. Its alcohol-water separating powers are unique among the alkali carbonates and hydroxides.
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papaya
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Quote: Originally posted by garage chemist  |
K2CO3 cannot be replaced by Na2CO3, NaHCO3 or NaOH. Its alcohol-water separating powers are unique among the alkali carbonates and hydroxides.
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Where can I read about practical aspects of out salting in chemistry?
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amazingchemistry
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Why is it that only only some salts work with some solutions and others don't? In another thread, it was suggested that aluminum phosphate would be
good at salting out colloidal iron, but other salts wouldn't and from what I remember just plain old table salt works when you're trying to get rid of
a chloroform-water emulsion. Why the specificity?
Edit: Perhaps you should have handled one variable at a time. Maybe by trying out different salts, each at saturation concentrations? Do other K salts
work? Do other CO3 salts work?
[Edited on 19-5-2013 by amazingchemistry]
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papaya
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Destabilization of colloidal solutions with salts relies on the process of ionic adsorption to the surface of colloidal particles thus neutralizing
net charge and facilitating aglomeration - multivalent ions work better here for obvious reasons. But salting out is a different story, where I
believe different ability for coordination of solvent molecules plays important role, I'm not sure about the theoretical side, I wanted some practical
information on it, like is it described in textbooks for distillation, recrystallization, etc.
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BromicAcid
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The solution is going to just do whatever is thermodynamically favorable. There are two reactions competing:
Salt<sub>solid</sub> + EtOH<sub>(H2O)</sub> <----> Salt<sub>(aq)</sub> + EtOH<sub>(H2O)</sub>
<---> Salt<sub>(aq)</sub> + EtOH
If the ethanol is going to more strongly coordinate than the salt then the salt will crash out as the water molecules solvating the ions become more
bound up with the ethanol. If the salt however forms a stronger complex than the ethanol then the water molecules will be more associated with the
salt and the ethanol will be ousted from the solution.
At least that is how I was looking at it. I'm sure someone could do the calculations of the solvent cages (water as a ligand) and determine the
actual difference in energy between the two and determine possible candidates that would salt out the ethanol.
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papaya
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OK, now explain me on this basis if K2CO3 works but not Na2CO3, so K+ binds to water stronger than ethanol or Na+, right? Then why sodium salts are
more hygroscopic than potassium in general?
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papaya
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Judging from solubility temperature dependence the curve for KCL is steeper than for NaCl, this should mean KCL dissolution is more endothermic, thus
hydration of K+ is weaker than Na+ (greater ionic radius?), am I right?
[img] http://www.sciencegeek.net/Chemistry/taters/graphics/solubil... [/img]
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Magpie
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Here's the result of one more test of salting out ethanol with K2CO3. 23.4g of K2CO3 was dissolved in 20mL of water. To this was mixed 3.75mL of
Everclear (95vol% ethanol). This was prepared to yield a mix ~15vol% in ethanol. As can be seen the phase separation was good. The black line
indicates the original salt water level before mixing with the Everclear..
Attachment: phpVIRNBU (69kB)
This file has been downloaded 1500 times
The single most important condition for a successful synthesis is good mixing - Nicodem
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S.C. Wack
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In the course of some work involving potassium fluoride, it was observed that this substance would salt out ethyl alcohol from aqueous
solution...It is well known that the higher alcohols, acetone, and many other organic liquids can be precipitated from their aqueous solutions by
addition of various salts. Potassium carbonate seems to be the only substance which is capable of salting out methyl alcohol, while the carbonates and
hydroxides of sodium and potassium, sulphates of sodium, ammonium, cadmium, manganese, iron (ferrous), cobalt, nickel, magnesium and zinc, alum,
sodium phosphate, thiosulphate and silicate, potassium phosphate, citrate and nitrate, ammonium nitrate and ammonium citrate are all capable of
producing two layers in solutions of ethyl alcohol under certain conditions. The phenomenon of salting out or the formation of layers is not confined
exclusively to organic compounds in water solution, as Proctor found that ammonia is salted out and forms two layers with a strong solution of either
potassium carbonate or sodium silicate. Newth recently rediscovered the salting out of ammonia by the carbonate.
http://books.google.com/books?id=nccmAQAAMAAJ&pg=PA3
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papaya
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Sodium silicate sounds good to me as containing polymeric anion, it's pity I don't have it to try with acetone, also it's obtainable in solution as a
glue in big quantities..
[Edited on 20-5-2013 by papaya]
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Nicodem
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| Quote: Originally posted by papaya | | I know this must be simple and the reason is I have some water waste from experiments which contains a lot of acetone, so I added NaCL to it up to
saturation - no separation occurs. To test idea - I took s test tube with half NaCl/water solution and added acetone. First it formed layers, but
after shaking it mixed and some solid started to precipitate (must be NaCl). So even at high concentrations of acetone this didn't work and I'm
surprised, because I've heard many times about easy salting out of acetone, my question is what to do? Can I use NaHCO3 instead of K2CO3 ?
|
Since I do not believe you as much as I believe my experience, I tested the miscibility of saturated brine and acetone. 10 mL of each were mixed to
give two liquid layers (11.5 mL of the lower phase and about 8.5 mL of the upper phase) and some NaCl precipitate. I think you either did not reach
saturation of NaCl or your mixture contains little acetone. Less concentrated aqueous NaCl does not result in phase separation. For example, adding 7
mL of water to the described 10 mL brine + 10 mL acetone mixture resulted in one single liquid layer with all the NaCl precipitate redissolving.
| Quote: | | Where can I read about practical aspects of out salting in chemistry? |
A article on the topic of salting out organic solutes with salts has been posted here. The topic has also been discussed for specific cases elsewhere on the forum.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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papaya
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"I think you either did not reach saturation of NaCl or your mixture contains little acetone." Well first I tried to add NaCL to my mixture (already
acetone + water, acetone concentration was low) and dissolved as much salt as possible this ended in nothing. Then to test idea as I wrote i took test
tube, prepared NaCL solution (sorry, I can't speak with numbers, because when doing this micro-test never thought it'll be necessary but I believe I
made concentrated solution), then added acetone, I believe on 50/50 volume basis. First it formed layers, then I saw some turbid crystalline coated
drops are falling down from acetone layer (it's like acetone wrapped in NaCL crystalls, more dense than liquid). I shaked test tube for some seconds
and layer separation disappeared and NaCL precipitation started. Also my acetone is stated to be 99.5% purity, I cannot explain the differences
between our tests.
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Bot0nist
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Redo your test and post accurate data and measurments. If you want others to repeat your attemp, you must be more specific. This is science. Keep a
notebook with notes of everything, also, get a 1/10th gram accurate digital scale. about $20 online, or your local head shop. completely indespinable
to the amature chemist on a budget...
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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papaya
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OK, now I did the test once again, taking 5ml of water, to that I added excess salt (lot's of it undissolved) and then I added 5ml acetone - phase
separation took place even after shaking, however I added acetone at once, now I realize it could be more interesting to add drop by drop and see if
this occurs immediately.
Here's it: 
I wouldn't say this is a practical way, must look for a better salt..
EDIT: §"For the sake of that and for people on dialup", I constrained my image to 800x600. 
[Edited on 20-5-2013 by papaya]
[Edited on 21-5-2013 by papaya]
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Magpie
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The links provided by S.C. Wack and Nicodem are very informative - thank you. S.C. Wack's reference shows that KF can yield an upper layer having
93.75% ethanol for the system ethanol-water-KF. For the system ethanol-water-K2CO3 an upper layer with 90.35% ethanol can be attained. Although I
would like to use KF, pottery grade K2CO3 is likely more economical and available. It also doesn't have KF's toxicity.
If I had some KF I would do some experimentation. But all I have is a large supply of NaF. However, it has much less solubility than KF. It seems
there may indeed be something special about K+. I know that potassium soaps are more soluble than those of Na+, and are used to make the liquid hand
soaps.
papaya: please see vulture's advisory on posting photo's:
http://www.sciencemadness.org/talk/viewthread.php?tid=7568
you can edit this if you do it within 24hrs of your post
[Edited on 20-5-2013 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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papaya
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Liquid soaps are different story, their liquid state must be is of the reason as it is for ionic liquids - larger ions interact weaker hence melting
point is low.
Strange, but following the link provided by Nicodem an article says, that Na+ salts must be best (Li excluded)? Then why K2CO3?
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Adas
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Anhydrous CaCl2 works well for removing water. You can always heat it to make it anhydrous again.
Rest In Pieces!
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papaya
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We don't want to remove water (well we do), we want to cause phase separation, though these may be related somehow..
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Adas
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| Quote: Originally posted by papaya | | We don't want to remove water (well we do), we want to cause phase separation, though these may be related somehow.. |
When there is nothing useful in the water phase, you can just remove the water and distill the rest off.
Rest In Pieces!
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amazingchemistry
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Does anyone have access to butyl alcohol and its isomers? It'd be interesting to see a comparison of the salting out effects of a salt that works with
n-butanol when you try and use it with the isomers. My guess is that it'll go in this order (from more salting out to less salting out): n-butanol
> isobutanol > s-butanol > t-butanol. This is based on boiling point (as a rough indicator of the strength of intermolecular forces). I'm
sure some scientific article already exists for this, but this is a little less exciting than running an experiment  . Also, is there anything on systems that use more than one salt? Are the effects of
different salts roughly additive? What about ternary salts? Do they even work? As you can see I'm getting a bit excited about this topic. Sadly, I
don't really own any glassware or chemicals (yet!) so I can't run rigorous experiments myself.
One last note: Since KCO3 seems to work at salting out alcohols, would adding a mixture of baking soda and no-salt (KCl) work to turn a big volume of
a moderately alcoholic drink into a little volume of essentially hard liquor (after decanting and such)? Forgive the unscientific question, but that
sounds like a really cool party trick
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