Sciencemadness Discussion Board - salting out

salting out

Magpie - 18-5-2013 at 18:14

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.

S.C. Wack - 18-5-2013 at 18:48

I've noted that potassium carbonate, only, is used in manuals going at least as far back as Norris. For other alcohols as well.

Magpie - 18-5-2013 at 20:14

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]

papaya - 19-5-2013 at 00:51

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 ?

papaya - 19-5-2013 at 01:09

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]

garage chemist - 19-5-2013 at 11:36

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.

papaya - 19-5-2013 at 11:47

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.

Where can I read about practical aspects of out salting in chemistry?

amazingchemistry - 19-5-2013 at 12:09

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]

papaya - 19-5-2013 at 12:30

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.

BromicAcid - 19-5-2013 at 13:14

The solution is going to just do whatever is thermodynamically favorable. There are two reactions competing:

Saltsolid + EtOH(H2O) <----> Salt(aq) + EtOH(H2O) <---> Salt(aq) + 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.

papaya - 19-5-2013 at 13:18

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?

papaya - 19-5-2013 at 13:27

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]

Magpie - 19-5-2013 at 16:28

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 1491 times

S.C. Wack - 19-5-2013 at 17:58

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

papaya - 19-5-2013 at 23:49

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]

Nicodem - 20-5-2013 at 07:33

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.

papaya - 20-5-2013 at 08:10

"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.

Bot0nist - 20-5-2013 at 10:02

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...

papaya - 20-5-2013 at 11:34

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]

Magpie - 20-5-2013 at 15:23

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]

papaya - 21-5-2013 at 01:18

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?

Adas - 21-5-2013 at 01:18

Anhydrous CaCl2 works well for removing water. You can always heat it to make it anhydrous again.

papaya - 21-5-2013 at 01:24

We don't want to remove water (well we do), we want to cause phase separation, though these may be related somehow..

Adas - 21-5-2013 at 10:54

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.

amazingchemistry - 21-5-2013 at 17:19

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

manimal - 23-5-2013 at 23:10

Maybe a poor man's potassium carbonate solution could be made by mixing potassium chloride with sodium carbonate.

papaya - 23-5-2013 at 23:40

KCL may work alone, problem is we didn't really get why K2CO3 and not NaCL or Na2CO3 (from the link provided by Nicodem I only could figure out that NaCL must be much better

)...

Random - 11-6-2013 at 16:15

I tried this with yeast&sugar alcohol solution and wood ashes but didn't encounter anything, I'll try to use food coloring next time.

Organikum - 11-6-2013 at 16:47

Quote: Originally posted by Adas

Anhydrous CaCl2 works well for removing water. You can always heat it to make it anhydrous again.

Just that it has a high affinity to the lower alcohols as well.
And it forms complexes with them.

Welcome to chemistry the non-intuitive home of exceptions!

/ORG

Nicodem - 12-6-2013 at 06:41

Quote: Originally posted by Random

I tried this with yeast&sugar alcohol solution and wood ashes but didn't encounter anything, I'll try to use food coloring next time.

It is obvious you did not understand much about this topic. The food coloring was not added to promote the phase separation. It has nothing to do with the "salting out" phenomena. Magpie added it only to take a more aesthetic picture. Also, I can't see how could you salt out ethanol from such a mixture that only presumably contains ethanol and even if does it must be very diluted (I assume you are talking about some fermentation broth or wine or something similar, because most yeast strains cannot produce ethanol of more than about a dozen % concentration). Also, you need to saturate with K₂CO₃ (not some "wood ash" of undefined composition!).

Random - 13-6-2013 at 14:16

Quote: Originally posted by Nicodem

Quote: Originally posted by Random

I tried this with yeast&sugar alcohol solution and wood ashes but didn't encounter anything, I'll try to use food coloring next time.

I may have written my thoughts the wrong way, I meant to say that maybe phase separation occured, but I didn't notice it. Food coloring makes them more visible.

I used a large excess of wood ash, but still I think that concentration of yeast fermentation broth contains about 10 percent ethanol by rough estamination. I wonder what is the minimum concentration of EtOH that can be salted out by saturating with potash.

Maybe very soluble salts ammonium nitrate would work too?

[Edited on 13-6-2013 by Random]

alka - 23-5-2015 at 13:06

In Salting out separation of amine(weak base)-water(15% amine by weigth) by NaOH salt(18g), aqueous layer contain NaOH and some quantity of amine .While doing titration of aqueous layer, addition of pheonphthaline indicator does not change the aqueous layer to pink, even though NaOH is strong base and also amine is basic in nature. why its happening?? NaOH is not soluble in amine.

turd - 24-5-2015 at 13:42

I don't understand what you are trying to achieve, but quote Wikipedia (https://en.wikipedia.org/wiki/Phenolphthalein):

Quote:

In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes completely colorless above 13.0 pH.

Why not use standard universal pH indicator paper?

byko3y - 6-8-2015 at 17:19

I was thinking that salting out ethanol/isopropanol might be a good way ащк separating non-polar substances from solution. I was that stupid.
In fact you cannot salt out a bare isopropanol with Na2CO3 or NaCl solution - it will just form another homogenous solution. Maybe this solution will have a top part with slightly higher alcohol content and bottom one with lower alcohol content, but there will be no layers. What you really need is anhydrous Na2CO3 or NaCl. And truly, when I add anydrous NaCl to isopropanol solution, I can see the bottom layer which ends right above the solid salt layer. Still the upper layer contains the salt, dissolved in isopropanol-water solution, and you can't remove all the water from it using NaCl.
I just watched the video https://www.youtube.com/watch?v=9kV0bmLVoeo which is actually misguiding and the author has no idea what he talks about. Well, you can get separate layers using NaCl completely dissolved. For that you need another compound, non-polar, which will draw the isopropanol from salt, making it possible for the layers to appear. But still a lot of isopropanol will be dissolved in water, and a lot of water will be present in the alcohol.
So, the dissolved salt actually just shifts the equilibrium, but it will shift nothing if you have a homogenous mixture.
There's such thing as https://en.wikipedia.org/wiki/Hofmeister_series . It describes observation that some salts lead hydrophobic substances to separation, while others may cause them to mix with water. Chlorides lay somewhere in the middle of the series, while both potassium and carbonates favor separation of hydrophobic molecules.
As you might already know (at the first page of the thread), K2CO3 seems to be the only one capable of separation of MeOH from water. I think that probably ammonium carbonate can remove water from ethanol. Hovewer, I have no ammonium carbonate to verify my theory.
Anyway, salting out hydrophobic substances might be a viable alternative to diethyl ether extraction, because diethyl ether is a controlled substance in most countries, but for some reason the theory of alcoholic salting out seems to be poorly known. AFAIK, acetone used to be a good substrate for salting out, but guess what? It's also on the goddamn list.

[Edited on 7-8-2015 by byko3y]

clearly_not_atara - 8-8-2015 at 10:25

The reason NaCO3 doesn't work is the same reason you've never heard of NaOtBu, always KOtBu: alkoxides are sort of covalent, and the more substituted the alcohol, the more covalent the bond. NaOiPr is pretty covalent, but it can still be used as a base. However it's certainly covalent enough that iPrOH readily dissolves Na+. Potassium has much weaker covalent interactions and so does not dissolve as easily.

Ammonium carbonate or ammonium sulfate has a pretty good chance of salting out alcohols, methinks. You can prepare KHCO3 by passing CO2 over KOH, possibly prepared by thermal decomposition of KNO3, which itself is very soluble at high temperatures but nearly insoluble near 0 C. K2CO3 forms by pyrolysis of KHCO3.

[Edited on 8-8-2015 by clearly_not_atara]

byko3y - 8-8-2015 at 14:21

The reason why potassium is used for t-Bu bases is because it interacts with DMSO and HMPA much better than sodium, e.g. solubility of Na2CO3 in DMSO is 1.4g/100ml while it is 4.3 for K2CO3. Although, still I have no idea why there's not reports on NaOtBu-DMSO adduct. Cesium is even better than potassium, but it is more expensive.
There's no need in preparing K2CO3 - most people can easily buy it.

byko3y - 8-8-2015 at 16:19

I've found that acutally sodium alkoxides are more soluble in low polar/nonpolar solvents, e.g. 2% for KOtBu, 7% for NaOtBu, and 25% for NaO-t-pentyl, 13% for NaOtBu in hexane, 38% NaO-t-pentyl in hexane. But, as I've already mentioned, the things go opposite direction when we use a strongly polar solvent polar solvents (DMSO).

clearly_not_atara - 9-8-2015 at 10:54

Yeah, that's because NaOtBu is basically a covalent molecule, thus dissolves preferentially in the nonpolar phase. Some is explained in this patent I found a long time ago when I was wondering why I couldn't just use Mg(OtBu)2 -- short answer, that just doesn't work.

http://www.google.com/patents/US6544446

KOtBu on the other hand is totally ionic. Mg(OMe)2 might be a good base if you need a strong anhydrous base, but I don't know if anyone here has ever successfully isolated it -- the famous procedure is all in situ.

Fyndium - 1-9-2020 at 12:26

According to https://doi.org/10.1021/ac60333a023 CaCl2 at 31.8g per 100g of solution or 4.2M should result in almost total recovery of acetone with 0.6% residual moisture with 2h equilibriation. This extraction could be dried with standard procedure of 25g/L of CaSO4 and distilled pure over 10g/L for pretty anydrous product.

Considering CaCl2 is available as road salt for 50c a kg, it would be an economical method for recovering acetone.

Screenshot_20200901-231627__01.jpg - 644kB

http://revues.univ-biskra.dz/index.php/jaest/article/view/38...

This article also demonstrates the pushing of solvate into an immiscible layer, eg. Extracting acetic acid from water solution with salting. It could provide easier to extract a substance into low boiling phase than distilling the water base directly.

[Edited on 1-9-2020 by Fyndium]

Fyndium - 3-9-2020 at 22:10

A test to confirm NaCl salting out.

47mL of store grade acetone was added into a cylinder with 46mL of water, resulting in a homogenous mixture. 16g of NaCl was added and stirred. A layer started to form slowly on top, and reaches 27mL in 15 minutes, and after 12 hours of sitting, the layer volume was 28mL. The upper layer consists of acetone with unknown amount of water content. Part of the NaCl remains undissolved at the bottom of the cylinder.

59.5% of acetone is therefore separated with NaCl.

I'll do a test with CaCl2 as soon as I get my hands on some.

I also recovered some toluene from a paint thinner, which is stated to contain 50-75% of toluene. 56% of volume remained undissolved after water wash, and the turbid liquid was washed with brine to result in a clear solution. It will be dried with CaSO4 and fractionated later. The water washing was treated with NaCl up to saturation, but no phase separation occured.

VancouverBackyardChemist - 6-9-2020 at 17:07

Has anyone tried salting out acetic acid from vinegar?
I tried this questionable method here: https://chemistry.mdma.ch/hiveboard/acquisition/000478316.ht...
multiple times, testing different salts and solvents, but none of my attempts managed to produce a phase separation. I tried using NaCl and CaCl2 as my salts, and Acetone and Isopropanol as my solvents, but none of these attempts worked. I even added water based food coloring to help me see the organic phase separating out easier, but the mixture's been sitting for 3 months now and there hasn't ever been any separation.

Fyndium - 9-9-2020 at 09:26

Afaik acetic acid per se cannot be salted out, at least with any economical means.

But it can be made less hydrophilic, meaning that it can be extracted with non-water-miscible solvent in a much larger portion as it migrates more readily out from water.