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Author: Subject: Salting out ethanol and distillation
deltaH
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Salting out ethanol and distillation

I happened upon this lab practical, see attached, with references.

In it is described how to salt out ethanol from water using potassium carbonate.

Their pic shows a pretty impressive separation.

I was thinking that this could be a very easy way to lower energy requirements and up the concentration and recovery of alcohol obtained, by the simple act of throwing in K2CO3 in the still. I would use much more than they did though, in fact, I'd throw in enough to make sure one saturates it at 100°C... that would be about 150g K2CO3/100g mash.

Afterwards, the residue can be dried out in the sun in wide open troughs to recycle the potassium carbonate for the next batch, easy peasy.

Also, instead of throwing salt into the still, another option is to use to reduce volumes prior to distilling by decanting and then distilling the organic phase only.

Why is this not done?

Reference:

http://ncsu.edu/project/chemistrydemos/Organic/SaltingOut.pd...

Attachment: Salting out ethanol.pdf (19kB)

[Edited on 8-3-2015 by deltaH]

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I like it. It seems very straightforward.
My first question is why potassium carbonate is used rather than sodium carbonate. The latter is so readily available.

But, yes I agree. It seems like a very simple and efficient procedure. There must be some reason why it is not commonly done. Probably only one way to find out.
deltaH
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Thanks j_sum1.

As far as I can tell, potassium carbonate is used because of its much higher solubility, but you are right, in principle any salt that is very water soluble, inert(unreactive), non-toxic and cheap would do.

Wikipedia's solubility table is an easy way to look such things up for those that want to shake it up

chem_haruka
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Yes,you can separation ethanol from water.
Separation of Alcohol–Water Mixtures Using Salts
www.ornl.gov/info/reports/1982/3445605458670.pdf
j_sum1
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 Quote: Originally posted by chem_haruka Yes,you can separation ethanol from water. Separation of Alcohol–Water Mixtures Using Salts www.ornl.gov/info/reports/1982/3445605458670.pdf
Ok. That's the firsttime I have seen a quaternary phase diagram presented as a tetrahedron. (page 20)
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This method does not work well.

I tried this on a large scale and it was a bit of a disaster. Not only does it require huge amounts of carbonate to get any useful amount of ethanol, but the upper phase often has a significant fraction of water remaining, requiring the process to be repeated several times or followed by distillation.

I did this with a 1.75L bottle of 40% plain bottom-shelf vodka. Recovering the carbonate for reuse failed miserably. The water from the vodka contained traces of organics, enough to cause the carbonate to be contaminated by nasty-smelling char when I attempted to dehydrate it for reuse, ending up a golden brown color.

The first problem could be solved by saturating the aqueous layer with the carbonate, but this is impractical since K2CO3 solubility is 112g per 100g water at 20C. I would have needed something like 1200g of carbonate to separate 700ml of EtOH from the vodka.

Fractional distillation is the way to go, and maybe with a salt like K2CO3 in the still pot to bind the water ionically and improve separation.

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deltaH
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Thanks for the literature chem-haruka.

Thanks for the report Praxichys, some comments and questions:

 Quote: This method does not work well. I tried this on a large scale and it was a bit of a disaster. Not only does it require huge amounts of carbonate to get any useful amount of ethanol, but the upper phase often has a significant fraction of water remaining, requiring the process to be repeated several times or followed by distillation.

It would be great to get some extra info here if you have it please. Specifically, what amount of K2CO3 did you use?

The 'followed by distillation' is strongly recommended because one would also want to reject the heads and tails that contain the impurities from naturally fermented alcohol, anyway.

The residual water is expected, but it MUST be significantly enriched in alcohol. Again, I'd throw the salt straight into the still pot in my principle version, as an aid to distillation.

 Quote: I did this with a 1.75L bottle of 40% plain bottom-shelf vodka. Recovering the carbonate for reuse failed miserably. The water from the vodka contained traces of organics, enough to cause the carbonate to be contaminated by nasty-smelling char when I attempted to dehydrate it for reuse, ending up a golden brown color.

I'd simply leave it in the sun to evaporate. Even on a large scale, this is easily done by digging a shallow trough, placing a large thick black plastic sheet to waterproof it, then pour in the tails, you could do hundreds of litres in this fashion if you wanted to, easily.

*This wouldn't work for mash tails though, only distillitate, though you could put it in a thumper though

 Quote: The first problem could be solved by saturating the aqueous layer with the carbonate, but this is impractical since K2CO3 solubility is 112g per 100g water at 20C. I would have needed something like 1200g of carbonate to separate 700ml of EtOH from the vodka.

Why? 25kg bags of K2CO3 from a chemical supplier is probably cheap and you can reuse it many times unless you use it in raw mash. If it's not easily available on a country-specific basis, we might be able to suggest substitutes that are.

 Quote: Fractional distillation is the way to go, and maybe with a salt like K2CO3 in the still pot to bind the water ionically and improve separation.

My thought here is that this could be the chemical version of a 'thumper'. Something that is really easy to do and can be done with existing still setups, but gives better recovery and concentration.

Perhaps the best way to use this is to put it IN the thumper, not the still, that way the mash residue doesn't foul it up as much and simply evaporation afterwards can be used to recycle the salt.

*****************************************************

Perusing the solubility tables... calcium chloride looks like a good alternative and it's available as de-icer AFAIK?

Also phosphate salts, e.g. monosodium phosphate?

[Edited on 8-3-2015 by deltaH]

Praxichys
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 Quote: Originally posted by deltaH Thanks for the report Praxichys, some comments and questions: Specifically, what amount of K2CO3 did you use?

I used 50% w/w with regard to the water in the ethanol.
 Quote: Originally posted by deltaH The 'followed by distillation' is strongly recommended because one would also want to reject the heads and tails that contain the impurities from naturally fermented alcohol, anyway.

Correct. My plan was to dry with 3A sieves afterward though, so I would then need an intermediate step to remove carbonate before sieving. I could save time and effort by not bothering with carbonate and going right to fractionating.
 Quote: Originally posted by deltaH The residual water is expected, but it MUST be significantly enriched in alcohol. Again, I'd throw the salt straight into the still pot in my principle version, as an aid to distillation.

Also correct, but keep in mind that heat will reduce the hold the K2CO3 has on the water. I have not tried this with carbonate, but this is generally why desiccants are strained before distillation. It will be better than no entrainer at all, but not perfect.
 Quote: Originally posted by deltaH I'd simply leave it in the sun to evaporate. Even on a large scale, this is easily done by digging a shallow trough, placing a large thick black plastic sheet to waterproof it, then pour in the tails, you could do hundreds of litres in this fashion if you wanted to, easily.

Theoretically, yes. However, the reason the K2CO3 works, while other salts do not, is in part caused by the affinity the salt has for water. I do not think K2CO3 is deliquescent, but it must be close. You may have a hard time evaporating the solution without heat.
 Quote: Originally posted by deltaH 25kg bags of K2CO3 from a chemical supplier is probably cheap and you can reuse it many times unless you use it in raw mash. If it's not easily available on a country-specific basis, we might be able to suggest substitutes that are.

True, but I got mine for $5/lb on eBay. It cost me about$10 to salt out 700ml of wet EtOH. For me, setting up a fractionating apparatus and taking the few hours required is free.
 Quote: Originally posted by deltaH Perusing the solubility tables... calcium chloride looks like a good alternative and it's available as de-icer AFAIK? Also phosphate salts, e.g. monosodium phosphate?

CaCl2 will not work because both water and the smaller alcohols can form "hydrates" in the crystal structure. I am not sure about phosphates - it seems interesting to try! With monosodium phosphate you might end up with sodium diethyl phosphate though.

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deltaH
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Thanks Praxichys and good points. I'll try to think of better alternatives.

Once you get over the knee-jerk reaction, would nitrates be a definite no-no?

[Edited on 8-3-2015 by deltaH]

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Everything old is new again:

Shamelessly plugging my attempts at writing fiction: http://www.robvincent.org
deltaH
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Oh crap, missed that, sorry guys.

Would anyone with glassware for distillation try a basic one stage distillation with some vodka and potassium carbonate and report on what's obtained as distillate?

[Edited on 8-3-2015 by deltaH]

deltaH
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A small experiment: anh. zinc chloride + drinking gin

Okay, performed a very simple experiment.

Hypothesis:

Saturating drinking gin with anhydrous zinc chloride will increase the alcohol concentration of the vapours enough to make it flammable.

Experimental:

I incrementally added anhydrous zinc chloride to a small amount of ordinary drinking gin (43% Vol.) until no more would dissolve. This took a lot of zinc chloride and led to a large increase of the solution's volume. No phase separation occurred at saturation. Then I poured some of this on a small ball of cotton wool and attempted to ignite it. Surprisingly, it wasn't flammable.

Discussion:

Zinc chloride is EXTREMELY soluble in water (432g/100ml, Wikipedia), but also in ethanol to a degree. The formation of the aqua complex from the hydration of anhydrous zinc chloride does consume a lot of water, but the resulting solution is diluted by the sheer volumes generated and the net result is that you don't have a large increase in the concentration of alcohol vapours, well not enough to ignite it, anyhow.

Conclusion:

When a salt is extremely soluble, it won't necessarily give you a great benefit of increasing the concentration of alcohol in the vapour at equilibrium.

*********

Now we already know that potassium carbonate works for bringing about a phase separation for ethanol-water, but I want to understand why. It looks like high solubility is not the only thing, it might also have to do with the interactions of the ions themselves, perhaps even their charge density. Understanding this better make allow us to select better salts for this purpose.

I'm thinking perhaps sodium orthosilicate (Na4SiO4) might work better, operating under the assumption that the higher the charge density on the anion, the better.

Problem is that sodium orthosilicate is not trivial to make... one would need to fuse silica gel and sodium hydroxide or carbonate at high temperature

[Edited on 8-3-2015 by deltaH]

Praxichys
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It seems that my earlier failure could be mainly because I did not bring the water solution up to the saturation point with the K2CO3. As noted in the other thread, Magpie received back nearly all of the water after bringing the K2CO3 concentration to something near the saturation point.

Another good point was brought up in the thread regarding the cost of potassium carbonate. It could be made in-situ with super cheap sodium carbonate and KCl.

I will do some experimentation today.

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deltaH
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 Quote: Originally posted by Praxichys It could be made in-situ with super cheap sodium carbonate and KCl.

Yes I saw this, I also thought it was quite smart and the bonus is that the NaCl, not being very soluble, may precipitate, so not a worry there so much that it would have a negative effect.

Tripotassium phosphate could also be a good candidate going on the hypothesis that high charge density on the anion is beneficial. It very basic though, but I don't think that should be a problem. Unfortunately, my phosphoric acid is not at my current premises, but I can remedy that at a later date. I do have potassium hydroxide though, so making some K3PO4 should be easy peasy (once I get to my H3PO4 )

Doing some reading, actually tripotassium phosphate looks like a very good candidate, it's solubility goes up a lot with increasing temperature and it's insoluble in alcohol (like potassium carbonate), plus it's a commercial fertiliser which means it probably can be bought in bulk bags on the cheap.

[Edited on 8-3-2015 by deltaH]

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Don't bother with any of those methods...

3A Zeolite is the easiest way to go, and you want to use it AFTER azeotrope has been reached, not before or during distillation. The cost is too high to fill a boiler.

To pre separate EtOH from water it is easier to freeze the water , an pour off the EtOH. Due to the volatility you really don't want to begin with more that a 40% ABV in a "still".

Controlled lab glassware is a different animal.

The Zeolite will pull out 100% of the water but exposure to air will replace it.

[Edited on 3-8-2015 by Zombie]

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deltaH
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Zeolites are similar to using a desiccant, but it's an expensive way to absorb bulk water. It's great for removing that last little bit almost completely, but what I'm interested in is different. It's a salt you can use with low concentration alcohol that would result in the ability to distil a much higher concentration, simply, but not by desiccation, but by an ion effect reducing the water-ethanol interaction by favouring water-ion interaction.

As I said before, consider it as a 'chemical thumper', not a desiccant.

In fact, the way to use this would be to add the salt to a 'thumper' and not the still pot. In fact, probably even an empty 'thumper' with pure salt and nothing else.

I'll test out my hypothesis if using trisodium phosphate as soon as I can make it. That's also easily scalable because of the availability in bulk as commercial fertiliser (not the kind sold in garden centres, but the kind sold to big farma <<< see what I did there )

[Edited on 8-3-2015 by deltaH]

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Quote:
"Zeolites are similar to using a desiccant, but it's an expensive way to absorb bulk water. It's great for removing that last little bit almost completely, but what I'm interested in is different. It's a salt you can use with low concentration alcohol that would result in the ability to distil a much higher concentration simply."

A properly designed, and run 6 plate 4" column will run Azeotrope in one run.
How much easier can it get?

Distilling is the same physical process no matter what the beginning concentration, and the same final product will always be azeotrope.

Other than a time machine... nothing will change that.

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deltaH
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 Quote: Originally posted by Zombie A properly designed, and run 6 plate 4" column will run Azeotrope in one run. How much easier can it get?

I'm hoping a lot easier than that, equipment-wise. Also don't forget, there might be a significant energy saving as well... but that remains to be seen, of course.

deltaH
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Speaking of energy, a thought just occurred to me. If one employed such a salt in a 'chemical thumper' then ideally you want the salt employed to give off heat on dissolving, else the liquid will just condense without vapours going off. Fortunately, tripotassium phosphate has a heat of fusion of +41.9 cal/g according to the CRC handbook, which is fantastic news. Potassium carbonate is +56.4 cal/g which means that should work even better from a heats point of view.

[Edited on 8-3-2015 by deltaH]

Zombie
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You're beating a dead horse brother.

No matter what you do you need a reflux column.
Yes you can easily scale it down but no matter what you begin with the boil temp. is controlled by the EtOH mole fraction.

The more you raise the ABV, the more energy you need to release the vapor, and get the boiler up to that temp.

There's are couple thousand years of distilling to prove it out.

I suppose you could always chemically separate the water, and do away with distilling all together.

[Edited on 3-8-2015 by Zombie]

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deltaH
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 Quote: Originally posted by Zombie You're beating a dead horse brother. No matter what you do you need a reflux column. Yes you can easily scale it down but no matter what you begin with the boil temp. is controlled by the EtOH mole fraction. The more you raise the ABV, the more energy you need to release the vapor, and get the boiler up to that temp. There's are couple thousand years of distilling to prove it out. I suppose you could always chemically separate the water, and do away with distilling all together. [Edited on 3-8-2015 by Zombie]

Huh? The heat of vapourisation of ethanol is much lower than water, so the higher the ethanol concentration, the LESS energy it takes to vapourise.

Also, separation requires work, so the higher the concentration of the thing you want to enrich, the less work it's going to take to enrich it. To get 0.0001% alcohol solution to 50% is going to take a lot more work than getting a 40% alcohol solution to 50%.

I still think that forming a second phase where the alcohol is of higher concentration would improve distillation significantly, for a simple setup (still plus chemical thumper pot).

Shit, I really need to get away from using this term 'chemical thumper' very bad for PR. Perhaps a 'salt thumper' is better, in that case, might as well call it a Godzilla

[Edited on 8-3-2015 by deltaH]

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I wonder what the the initial concentration if alcohol/water must be in order for salting out to work. I looked but couldn't find any information on the web.
I just tried it using potassium carbonate, calcium chloride and sodium phosphate (seperately) to salt what I believe to be about a 5% EtOH solution with water, sucrose and yeast (lots if contaminates I know) from a fermentation batch I've had going for a week or so. I just wanted to see if there's a way to raise the concentration before distillation. None of them worked.
So does anyone know what the minimal concentration for this to work is?
Normally I just distill first and then salt out most of the rest of the water with potassium carbonate, then distill with anhydrous magesium sulfate to achieve ~97% or so.
If I could salt out before the first distillation that would be great.

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Quote: Originally posted by deltaH
 Quote: Originally posted by Zombie You're beating a dead horse brother. No matter what you do you need a reflux column. Yes you can easily scale it down but no matter what you begin with the boil temp. is controlled by the EtOH mole fraction. The more you raise the ABV, the more energy you need to release the vapor, and get the boiler up to that temp. There's are couple thousand years of distilling to prove it out. I suppose you could always chemically separate the water, and do away with distilling all together. [Edited on 3-8-2015 by Zombie]

Huh? The heat of vapourisation of ethanol is much lower than water, so the higher the ethanol concentration, the LESS energy it takes to vapourise.

Also, separation requires work, so the higher the concentration of the thing you want to enrich, the less work it's going to take to enrich it. To get 0.0001% alcohol solution to 50% is going to take a lot more work than getting a 40% alcohol solution to 50%.

I still think that forming a second phase where the alcohol is of higher concentration would improve distillation significantly, for a simple setup (still plus chemical thumper pot).

Shit, I really need to get away from using this term 'chemical thumper' very bad for PR. Perhaps a 'salt thumper' is better, in that case, might as well call it a Godzilla

[Edited on 8-3-2015 by deltaH]

You are correct. I miss stated that part Less energy...

Now a Salt Station (thumper) may be worth a try.
Or same thing for 3AZeolite.

It would be easy to spot the point of saturation, and amounts could be modified.

I would think an empty column filled with a desiccant, with a RBF below to collect water May work.
The only issue is the column would have to be heated enough to pass EtOH vapor, and cool enough to allow the desiccant to trap / hold the water.

A simple "dryer" in the vapor path.

You still have the issue of the hygroscopic nature of EtOH collecting moisture from the environment to contend with.

I mean otherwise you just start w/ Everclear, and don't bother drying it.

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 Quote: from page 38 6. CONCLUSIONS 1. The best of the three new separation designs uses a beer still to concentrate the feed to 50 wt % solvents, KF salt, and a multipleeffect evaporator for salt recov-ry. mental capital costs ($1.72 x 10 vs$1 76 x 10 ) and iiiu h more favorable incremental operating costs ($2.14 x lot/, vs$4.83 x 10 /y) than the conventional separation. This process has comparable incremental operating costs than the conventional separation. 2. Na2SO4, the best salt for this process, effected good phase separation, while its low water solubility means a low salt addition rate. Addition of this salt can break both the butanol/water and the propanol/ water azeotropes, 3. Evaporation is better thdn precipitation for salt recovery in this process, because of the low salt losses and much lower energy requirements compared with precipitation. 7. RECOMMENDATIONS 1. The use of salt to separate alcoho!/water mixtures is effective, and further investigation is definitely recommended. 2, For the Clostridia fermentation-product separation specifically, a parameteric study should be performed to optimize the separation design presented here. 3. The use of this process in other organic-aqueous separations should be investigated.
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Quote:

"2. Na2SO4, the best salt for this process, effected good phase separation,
while its low water solubility means a low salt addition rate.
Addition of this salt can break both the butanol/water and the propanol/
water azeotropes,"

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