Sciencemadness Discussion Board

Attempting anhydrous ethanol with CaO

nimgoldman - 16-8-2018 at 13:08

I am trying to produce about a liter of anhydrous ethanol. I tried different methods but all have failed (molecular sieves lead to huge losses as they get covered with EtOH; drying agents such as MgSO4 or CaSO4 don't work at all; magnesium cannot be used on azeotropic alcohol as there is too much water).

The forum posts I read give mixed opinions to every method so I reverted to the old and proven method - refluxing with calcium oxide.

One writeup says to add 200 g of CaO per liter of alcohol. I had 1 400 ml so I added 240 grams of CaO.

Unfortunately, this amount makes magnetic stirring impossible even with a large and powerful stirrer.

Overhead stirrer cannot be used in a reflux setup (lack of insulation) so I hoped the CaO will smooth out boiling. No bumping happened and I continued refluxing for about 8 hours (the writeup I read advised to reflux 24 hours but I already used 12 blocks of ice and not having more).

Unfortunately, there is some brown burnt stuff because of lack of stirring - see image.

I proceeded to vacuum filtration but it's also a real pain. It slowed down and the stuff is in no way dry - it's a wet pudding, refusing to filter. The air always finds its way in, breaking the vacuum so I have to mix it with spatula from time to time, only to get few more drops. The process is tedious.

I am afraid I will lose over 50% of ethanol using this method, not to mention the calcium oxide, which is hard and expensive for me to obtain, even more than molecular sieves.

I wonder how this CaO method should be done correctly since it seems impossible to reflux such amount of CaO in alcohol without problems and it's not possible to filter it without losing huge amounts of ethanol.

I feel lost as I already spent three months and liters of carefully distilled ethanol in my pursuit of anhydrous ethanol for syntheses. I don't want to buy it since I want to find a way to make it myself (it is regulated and taxed - purchasing it as an individual is shady).

Maybe the only efficient way would be to use smaller amount of CaO, say, 100 grams per liter of alcohol, so it can be stirred. It won't produce anhydrous ethanol, but the last two or so percent water could be removed using molecular sieves. This might get the better from both worlds.

Any tips for making anhydrous ethanol without losing huge amounts of it?

DSC_0382.JPG - 275kB DSC_0386.JPG - 241kB DSC_0388.JPG - 224kB DSC_0392.JPG - 199kB

[Edited on 16-8-2018 by nimgoldman]

happyfooddance - 16-8-2018 at 13:35

Have you tried potassium carbonate?

WGTR - 16-8-2018 at 13:38

The first thing that jumps out at me is that you can try a filtering aid, like diatomaceous earth, on the Buchner funnel. It might help keep your lime from clogging the filter paper, at least for a while.

Another out-of-the-box wild idea is to try filling a wide-mouthed container with your alcohol, and then float a smaller container in the middle that contains your CaO. Then seal the lid, of course. Assuming that the water and alcohol will have their own respective vapor pressures, it may take quite a while for all of the water to leave the alcohol and react with the CaO. Maybe you could put a stir bar in the container to help keep the alcohol stirred up. Keep in mind that I have not tried anything like this; it may just be a dumb idea.

JJay - 16-8-2018 at 13:51

I've never tried this because around here CaO is apparently a rare commodity used only in labs, but you might try distilling off the ethanol. I suspect that if you don't use a heating bath, it will bump like crazy.

Magpie - 16-8-2018 at 14:05

Slaked lime, Ca(OH)2, can be found at the garden store and at Ace Harware as pickling lime. This can be calcined to CaO at 500-600°C for an hour.

CaO will reduce 95% ethanol (Everclear) to 99% ethanol per Vogel (forum library). This is then made anhydrous w/3A mole sieves.

nimgoldman - 16-8-2018 at 14:13

Quote: Originally posted by happyfooddance  
Have you tried potassium carbonate?


I haven't tried this one but I've read this causes only physical separation by creating a concentration gradient. The CaO removes the water chemically by reacting with it.

It seems I blindly followed one writeup without doing more research. From more searches it seems that alcohol with CaO has to be left to sit for several days (or maybe reflux for 24 hours will suffice) and then carefully distilled using a water bath and a drying tube to avoid atmospheric moisture suck-up. Only the middle fraction is taken.

It seems this CaO method still leads to huge losses of ethanol, even more than with molecular sieves. So I will probably stick with the sieves or try the calcium oxide drying just as a future experiment.

So the official methods doe snot include any filtering - the ethanol should be directly distilled and water bath is probably used to prevent overheating from excess lime sitting in the flask.

happyfooddance - 16-8-2018 at 14:35

Quote: Originally posted by nimgoldman  
Quote: Originally posted by happyfooddance  
Have you tried potassium carbonate?


I haven't tried this one but I've read this causes only physical separation by creating a concentration gradient. The CaO removes the water chemically by reacting with it.


Water isn't chemically bound to etOH, so all you need is a physical separation.

Edit: Alternatively, you can use K2CO3 as a first stage and your calcined lime (you did calcine it, right?) as a second stage, and thus can get by with using less... Might fix your problem.

[Edited on 8-16-2018 by happyfooddance]

JJay - 16-8-2018 at 14:48

I've wondered about using Portland cement, but I don't relish the idea of chipping concrete out of a flask.

S.C. Wack - 16-8-2018 at 20:06

The contents of the flask don't need to be liquid or stirred or filtered (shaken perhaps)...it looks like if the drying was a success the vacuum filtration would have wetted it. It seems not so unsensible to be heating the pot to dryness after adding the lime (or adding alcohol to the lime)? One may want more than a water bath.

Acids for residue. The lime residue. Maybe the brown color has an explanation. Has this azeotropic ethanol been checked for color after refluxing with some other base such as KOH flake?

[Edited on 17-8-2018 by S.C. Wack]

LMNts - 17-8-2018 at 01:01

If you have access to toluene or benzene you could try to distill off the water azeotropically with it. I have never tried this method myself though.

Loptr - 17-8-2018 at 09:36

Quote: Originally posted by LMNts  
If you have access to toluene or benzene you could try to distill off the water azeotropically with it. I have never tried this method myself though.


Ethanol and toluene form an azeotrope that boils at 76.7*C. Ethanol and water form an azeotrope that boils at 78.2*C, where as Ethanol by itself boils at 78.37*C.

There isn't enough of a temperature difference for it to make any difference.

walruslover69 - 17-8-2018 at 09:37

Why don't you just use molecular sieves and distill the ethanol off them?

LMNts - 17-8-2018 at 10:31

Quote: Originally posted by Loptr  
Quote: Originally posted by LMNts  
If you have access to toluene or benzene you could try to distill off the water azeotropically with it. I have never tried this method myself though.


Ethanol and toluene form an azeotrope that boils at 76.7*C. Ethanol and water form an azeotrope that boils at 78.2*C, where as Ethanol by itself boils at 78.37*C.

There isn't enough of a temperature difference for it to make any difference.


Here is the source: http://www.separationprocesses.com/Distillation/DT_Chp06c06.htm. I should have mentioned it before.

With toluene a ternary azeotrope is made which distills at 74.4 °C which should make enough of a difference to do a fraction distillation.

On the azeotrope tables page of wikipedia some more ternary azeotropes with water and ethanol are listed. Benzene even forms a 64.9 °C azeotrope.

nimgoldman - 1-9-2018 at 09:31

I have access to toluene and it might be doable with a 60 cm Vigreux column. However, the temperature control on my heating mantle seems not sensitive enough (jumps occassionally) so the benzene approach seems more viable.

I don't have access to benzene but make some from sodium benzoate and see.

Deathunter88 - 1-9-2018 at 21:32

Woah woah woah, you guys are making it way too complicated here. Either distill the slurry directly, or if there is too much bumping then just let the solution settle for a day a two and decant. I have done it before, easy, no fuss.

Alternatively, just go buy some molecular sieves.

RogueRose - 1-9-2018 at 22:03

Quote: Originally posted by Deathunter88  
Woah woah woah, you guys are making it way too complicated here. Either distill the slurry directly, or if there is too much bumping then just let the solution settle for a day a two and decant. I have done it before, easy, no fuss.

Alternatively, just go buy some molecular sieves.


Wow, this reply kind of shows the state of the Internet. The OP's very first sentence says he tried molecular sieves and he lost a lot of ethanol. IDK if it is more than other amounts but loss of alcohol when drying is always an issue.

To the OP, I had the same problem and tried a number of different methods, all reported to be "a great way" to dry ethanol, but they seemed to suck IMHO.

I finally tried anhydrous copper sulfate and had excellent success. The thing about using CuSO4 instead of something like K2CO3 is the hydrates that are formed with CuSO4 - which is a pentahydrate instead of a monohydrate - it can accept 5x the water per molecule compared to potassium carbonate. It also has the great characteristic of changing color to tell you when it is "full" (hydrated).

There are a couple of ways to do it, I have a thread on this, it should be in the search results. You have to powder the CuSO4 (dry it first) then I used a mesh strainer to filter the powder into a funnel full of 100-110F ethanol. It will produce heat as it absorbs water. Shaking or stirring helps A LOT in the process, as well as keeping it warm (going to 140 F seems to speed it up).

You need to realize that you are going to loose a good bit to retention on the surface of the drying agent. You could distill this off if you wanted, then dissolve the remaining CuSO4 in water.

There is another compound that looks promising for drying though I can't say if it works, from looking at the characteristics and reports, it should work well as it is insoluble in ethanol, it also accepts 11 - 16 water molecules per molecule, which means it is can dry a lot of ethanol for a relatively small molar amount - you'd need 11-16x as much K2CO3 to dry the same amount of ethanol - and a lot more ethanol stuck to all that carbonate. The compound I'm talking about is TriSodium Phosphate (Na3PO4) and can be found in many local hardware store paint sections (make sure it isn't the "substitute"). I have some and heated in an oven, and it looses at least 1/2 it's weight in water, and it doesn't seem to dissolve in alcohols - though I havent' used it for drying yet.

Good luck, this can be a PITA until you find a method you like. I'd suggest staying away from CaO as it has relatively poor drying capability compared to CuSO4 or Na3PO4 - because it has a 1:1 water ration vs the 5:1 or 11/16:1 of the other compounds.

Sulaiman - 2-9-2018 at 00:57

The simplest method of drying an azeotropic ethanol/water mixture seems to be to use 3A sieves, per the OP

Loss of product is not a major concern because
. even with losses we should get fairly cheap dry ethanol
. the 'lost' ethanol could be recovered in dilute form for re-distillation when the sieves are de-hydrated for re-use ?

RogueRose - 2-9-2018 at 01:17

Quote: Originally posted by Sulaiman  
The simplest method of drying an azeotropic ethanol/water mixture seems to be to use 3A sieves, per the OP

Loss of product is not a major concern because
. even with losses we should get fairly cheap dry ethanol
. the 'lost' ethanol could be recovered in dilute form for re-distillation when the sieves are de-hydrated for re-use ?


That is a good point, to dry the sieves in a distillation setup. I had thought of heating the wet sieves (or salts) in a distillation setup but not drying them completely in it but I guess you could switch the receiver flask when the temp rises about 180 or so as much of that would be lower strength alcohol.

Deathunter88 - 2-9-2018 at 06:43

Quote: Originally posted by RogueRose  
Quote: Originally posted by Deathunter88  
Woah woah woah, you guys are making it way too complicated here. Either distill the slurry directly, or if there is too much bumping then just let the solution settle for a day a two and decant. I have done it before, easy, no fuss.

Alternatively, just go buy some molecular sieves.


Wow, this reply kind of shows the state of the Internet. The OP's very first sentence says he tried molecular sieves and he lost a lot of ethanol. IDK if it is more than other amounts but loss of alcohol when drying is always an issue.


I believe the problem with the internet/this forum is the exact opposite of what you're saying. People on this forum (especially recently) seems to have lost the ability to give straightforward answers, especially towards new members who are just trying to get something done. Azeotropic distillation with benzene or toluene!??? Are you freaking serious? Or using concrete? Both posters even mentioned they never tried either of those methods. I'm not sure how replies like these are in any way helpful to someone new to the hobby. Now this isn't targeted at you, but it's something that I really hope can change.

I'm not saying experimentation with novel methods shouldn't be encouraged, but they deserve their own threads with some testing done by the person who made the claim, not thrown out onto a thread as a way to help someone achieve something practical.

Now, I recommend the OP revisit molecular sieves. If you're losing too much ethanol from using them on a liter scale, then you are adding way too much or you are using something other than the 3A type, and ethanol is getting adsorbed into them alongside water. 10-20% by weight is plenty, just enough to cover the bottom of the container with an even layer (1-2cm).

S.C. Wack - 2-9-2018 at 12:11

Well said. BTW about new members...many of them are strongly suspected of being really only a few, so it takes a lot to get interested in responding to posts/threads that fit their profile, even though I'm in it for the bored postwhoring.
Quote: Originally posted by nimgoldman  
One writeup says to add 200 g of CaO per liter of alcohol. I had 1 400 ml so I added 240 grams of CaO...(the writeup I read advised to reflux 24 hours]


"...put 10 liters of 92% alcohol and 2000 g. of good lime in the 12-liter flask of the [reflux] apparatus last described. After refluxing for 24 hours, alcohol of 99% concentration can be obtained [by distillation], with a loss of only about 4% of alcohol actually present."

Now is the time to hit it with the 3A. IMHO there's no point in making perfectly dry impure alcohol, and even if from vodka the azeotrope should be distilled with a little 50% sulfuric acid, before the lime.

fusso - 2-9-2018 at 14:14

Quote: Originally posted by Deathunter88  
Quote: Originally posted by RogueRose  
Quote: Originally posted by Deathunter88  
Woah woah woah, you guys are making it way too complicated here. Either distill the slurry directly, or if there is too much bumping then just let the solution settle for a day a two and decant. I have done it before, easy, no fuss.

Alternatively, just go buy some molecular sieves.


Wow, this reply kind of shows the state of the Internet. The OP's very first sentence says he tried molecular sieves and he lost a lot of ethanol. IDK if it is more than other amounts but loss of alcohol when drying is always an issue.


I believe the problem with the internet/this forum is the exact opposite of what you're saying. People on this forum (especially recently) seems to have lost the ability to give straightforward answers, especially towards new members who are just trying to get something done. Azeotropic distillation with benzene or toluene!??? Are you freaking serious? Or using concrete? Both posters even mentioned they never tried either of those methods. I'm not sure how replies like these are in any way helpful to someone new to the hobby. Now this isn't targeted at you, but it's something that I really hope can change.

I'm not saying experimentation with novel methods shouldn't be encouraged, but they deserve their own threads with some testing done by the person who made the claim, not thrown out onto a thread as a way to help someone achieve something practical.

Now, I recommend the OP revisit molecular sieves. If you're losing too much ethanol from using them on a liter scale, then you are adding way too much or you are using something other than the 3A type, and ethanol is getting adsorbed into them alongside water. 10-20% by weight is plenty, just enough to cover the bottom of the container with an even layer (1-2cm).
Actually I guess if you have asked OP to revisit molecular sieves instead of buying it in the former post then RR wouldn't roast you.

Btw concerning new members, maybe we can have streety analyse the members' registration dates for us and post the results in "reporting spam" thread.

JJay - 2-9-2018 at 14:53

Portland cement contains calcium oxide; I mentioned it after the issues with the OP's procedure had already been discussed. The idea of using it was more of a supplementary exercise type comment (or just making conversation). While a successful writeup using Portland cement for dehydrating ethanol might well deserve its own thread, no claims have been made regarding it.

I do think that berating people on other people's threads over non-scientific issues is really counterproductive, but ethanol purification threads get contentious at times.

Herr Haber - 3-9-2018 at 03:20

Quote: Originally posted by Deathunter88  


Now, I recommend the OP revisit molecular sieves. If you're losing too much ethanol from using them on a liter scale, then you are adding way too much or you are using something other than the 3A type, and ethanol is getting adsorbed into them alongside water. 10-20% by weight is plenty, just enough to cover the bottom of the container with an even layer (1-2cm).


Same thought here.
Maybe OP's sieves are of questionnable quality ?

[Edited on 9-3-2018 by Texium (zts16)]

highpower48 - 3-9-2018 at 07:52

From Macroscale and Microscale Organic Experiments by Williamson 4th edition.

It suggests using Calcium Oxzide to dry ethanol. If your wet ethanol is at least 95%, it suggests using benzene.

highpower48 - 3-9-2018 at 07:57

According to Macroscale and Microscale Organic Experiments by Williamson 4th edition.

Use calcium oxide for drying ethanol. If it's at least 95% is suggests using benzene.

highpower48 - 3-9-2018 at 08:04

Sorry if this posts more th a once, was having an issue with the quick reply function


According to Macroscale and Microscale Organic Experiments by Williamson 4th edition.

Use calcium oxide for drying ethanol. If it's at least 95% is suggests using benzene.

Keras - 7-9-2018 at 03:12

Did someone already mention Calcium hydride? Calcium hydride sucks water and gives out hydrogen. It’s used as a desiccant. Wikipedia even states it’s used with alcohols.



[Edited on 7-9-2018 by Keras]

Sulaiman - 7-9-2018 at 03:35

Calcium hydride is neither cheap nor easily available,


Speculation only ... not tried
using a water absorbant/adsorbant material that can be re-used with no overall loss of ethanol such as bran or tapioca may be better overall
e.g. https://www.purdue.edu/newsroom/research/2011/110913LadischT...
i.e. any ethanol retained by the fermentable material will be returned to the next fermentation.
I doubt that absolutely dry ethanol will be produced
but it would remove most of the water
requiring less of whatever agressive / expensive dehydration material is required.

nimgoldman - 7-9-2018 at 04:05

Thanks. I found the issue was that one have to reflux with CaO for full 12 hours or more OR leave CaO in alcohol for several days with occassional swirling.

Then it should be distilled over CaO and only middle fraction is taken - no filtering.

Another possible issue was that my CaO was not freshly ignited and I don't know how long it sat in the container, it might picked up some moisture.

So I reverted to molecular sieves but I will give it a shot later.

Keras - 7-9-2018 at 22:28

Quote: Originally posted by Sulaiman  
Calcium hydride is neither cheap nor easily available.


I’d had a quick look this summer on Ebay and there was some chap in China selling that for a few bucks. But it seems to have gone away.

Why not use the more available and cheaper calcium carbide then? Water will be transformed into ethylene and you get slaked lime that you can easily filter out.

nimgoldman - 8-9-2018 at 05:38

Quote: Originally posted by Keras  
Quote: Originally posted by Sulaiman  
Calcium hydride is neither cheap nor easily available.


I’d had a quick look this summer on Ebay and there was some chap in China selling that for a few bucks. But it seems to have gone away.

Why not use the more available and cheaper calcium carbide then? Water will be transformed into ethylene and you get slaked lime that you can easily filter out.


I haven't heard about using calcium carbide for drying ethanol. Do you have a source reference?

macckone - 8-9-2018 at 08:04

Commercial methods are:
Distilling 95% alcohol with benzene - not suitable for human consumption and requires a very high reflux ratio
Drying with molecular sieves - suitable for human consumption if sieves are food grade
Drying with CaO - if CaO is suitable for human consumption after distilling is suitable
Drying with cellulose - usually used for fuel grade - literally kiln dried corn cobs
For ultra dry use iodide activated magnesium as described in 'Purification of laboratory chemicals' by Armarego et al.
Also activated aluminum amalgam from the same source.

Potassium carbonate is the simplest and easiest with the least loss but it has to be pretty high percent to work. You can't use off the shelf vodka or mash for salting out. There is another thread that covers getting it over 95%.

http://www.sciencemadness.org/talk/viewthread.php?tid=61746

Keras - 9-9-2018 at 11:09

Quote: Originally posted by nimgoldman  

I haven't heard about using calcium carbide for drying ethanol. Do you have a source reference?


No. This is a wild guess based on what everyone knows of calcium carbide reacting with water. Besides, if calcium hydride is used to suck water (producing Ca(OH)2), why calcium carbide wouldn't work?

unionised - 9-9-2018 at 12:50

Carbide is used- but it's hazardous. Acetylene (Not ethylene, BTW) isn't nice stuff to work with.

https://www.jstor.org/stable/2993231?seq=1#metadata_info_tab...

Keras - 11-9-2018 at 00:23

Quote: Originally posted by unionised  
Carbide is used- but it's hazardous. Acetylene (Not ethylene, BTW) isn't nice stuff to work with.

https://www.jstor.org/stable/2993231?seq=1#metadata_info_tab...


Agreed. As I said, it was a wild guess. I had considered the possibility of acetylene dissolving in alcohol, but didn't mention it.

Also this article

[Edited on 11-9-2018 by Keras]

CaptainPike - 14-9-2018 at 10:19

Quote: Originally posted by RogueRose  


[…]

I finally tried anhydrous copper sulfate and had excellent success. The thing about using CuSO4 instead of something like K2CO3 is the hydrates that are formed with CuSO4 - which is a pentahydrate instead of a monohydrate - it can accept 5x the water per molecule compared to potassium carbonate. It also has the great characteristic of changing color to tell you when it is "full" (hydrated).

[…]


I liked this. I haven't used it yet for drying ethanol, but I did bake some down to at least the dihydrate in a conventional oven – white powder.
Here's the MSDS for the one I bought:

ZEP ROOT KILL MSDS

nimgoldman - 14-9-2018 at 13:52

Quote: Originally posted by Herr Haber  
Quote: Originally posted by Deathunter88  


Now, I recommend the OP revisit molecular sieves. If you're losing too much ethanol from using them on a liter scale, then you are adding way too much or you are using something other than the 3A type, and ethanol is getting adsorbed into them alongside water. 10-20% by weight is plenty, just enough to cover the bottom of the container with an even layer (1-2cm).


Same thought here.
Maybe OP's sieves are of questionnable quality ?

[Edited on 9-3-2018 by Texium (zts16)]


These are 3A sieves from a reputable vendor (Carl Roth). They were very expensive. I have reactivated them beforehand (4 hours at 250 °C and 100 mbar of vacuum).

I used 5 grams of sieves per gram of water. Lower sieves:water ratio resulted in incomplete drying (the resulting alcohol was 97-98%).

Last time I used 5:1 ratio, lost 100 ml of ethanol (from liter of solution) and still got only 98%, not 99%.

I don't know why this process is so lossy...

[Edited on 14-9-2018 by nimgoldman]

macckone - 14-9-2018 at 15:05

5g per 1g of water is about right. Seives absorb 20% of their weight. 3a should not absorb alcohol, even 4a should not. Alcohol is about 5a. There should be about 45ml of water in 1000ml of azeotropic and 250g of seives should absorb that. Is your alcohol actually azeotropic?

nimgoldman - 15-9-2018 at 07:55

Quote: Originally posted by macckone  
5g per 1g of water is about right. Seives absorb 20% of their weight. 3a should not absorb alcohol, even 4a should not. Alcohol is about 5a. There should be about 45ml of water in 1000ml of azeotropic and 250g of seives should absorb that. Is your alcohol actually azeotropic?


Now I am unfortunately never able to get above 93.5-94% even with multiple distillations with a 60 cm Vigreux column.

I use 2L heating mantle with a thermometer probe and usually have to heat the solution to 79-81 °C to push the vapours up to the still head.

I tried insulating the column but it does not help much if at all.

Unfortunately the heating mantle sometimes go crazy and has a hard time keeping a constant temperature.

Overall the distillation is extremely slow, like 1 drop per 2 seconds. I don't know if it should be that way. If I make it quicker, like 1-2 drops per second, then the resulting alcohol is only up to 94%.

Fyndium - 22-3-2021 at 13:06

So, about that portand cement..

Has anyone actually tried it or know of a successful use for dehydrating ethanol with it?

digga - 22-3-2021 at 16:44

Tapioca. It is used industrially to dry ethanol.

pneumatician - 25-3-2021 at 18:52

What you call "dry etanol" or "100% eta." is what a alcoholometer say, pure obvious :-)

in reality when you get 98, 99, 100% etanol is only a primitive standard measure far from real dry etanol. The 100% etanol continue contain more than 60% of water, so pure etanol in an alcoholometer need to say something like 160% :-)

no more, no less.

MrDoctor - 23-9-2024 at 23:28

drying ethanol using copper sulfate only works when going from anhydrous, to monohydrate. any lower hydrates that form (indicated by a stronger blue) will compete for water with ethanol, where absolute ethanol ultimately wins out.

Magnesium sulfate is similar. when OP says it "didnt work" they probably did what i and many others did and added the magnesium sulfate, then distilled with it inside. magnesium sulfate loses its water readily by heat.
What you do is add enough anhydrous magnesium sulfate such as that there isnt enough to dissolve in the water. depending on how dry you want it, add a slight molar excess based on the specific hydrate you wish to form, and youll subsequently get something like 98%, 99% and/or 99.5% dry ethanol. you FILTER out the magnesium, just like you do the copper, then distill to eliminate contaminants and dissolved solids.

you can during this distillation seperate the ethanol into azeotropic and pure, or you can try eliminating the water with magnesium with iodine/ultrasonication, you can use other methods of destroying water molecularly too, like CaO, though it will require re-filtration.

azeotropic distilation with toluene is good if trace toluene isnt going to be an issue, but regardless you still have to store over molecular sieve to finish it off. those sieves will impose a tax, and the only way to get around it is to start from 99.5% instead of making them soak up a whole 5%.

Lastly, members on the forum have demonstrated using potassium carbonate to seperate the water from ethanol, to a degree which it was impossible to descern wether or not it was close to, or actually absolute ethanol. you can decant this, otherwise invest in a sep funnel.
Once again, a certain amount of carbonate must be used such as that there is more carbonate than water present to form hydrate with. in this case the hydrate extends well into the liquid state, much like how water does with calcium chloride. basically though this just means, if you arent sure, add way more than neccesary, and if its going to clog your sep funnel, then i guess keep a little wet ethanol seperate, or water, to help dissolve your excess before seperating. what i read btw was that the starting ethanol was everclear, or possibly some sort of vodka. or perhaps both. so potassium carbonate was able to get absolute starting from as low as 30% (if i recall correctly).

Sulaiman - 24-9-2024 at 09:11

Quote: Originally posted by pneumatician  
What you call "dry etanol" or "100% eta." is what a alcoholometer say, pure obvious :-)

in reality when you get 98, 99, 100% etanol is only a primitive standard measure far from real dry etanol. The 100% etanol continue contain more than 60% of water, so pure etanol in an alcoholometer need to say something like 160% :-)

no more, no less.
multiple times I have fermented sugar, done a simple distillation and then a fractional distillation,
sometimes followed by drying with sieves,
at all stages my (cheap Chinese) alcohol hygrometers gave expected readings,
eventually up to somewhere between 99 and 100% ABV.
Why do you think 60% water ?
Is your hygrometer in proof degrees or similar?

clearly_not_atara - 24-9-2024 at 10:29

Perhaps a stupid question, but why not a polyphosphate?

CaO and other highly basic drying agents will produce ethoxide, which can react with atmospheric oxygen. Many, many attempts at producing ethoxide without sodium (which generates a blanket of H2) result in it turning brown and becoming difficult to crystallize.

But e.g. Na5P3O10 ("sodium triphosphate", widely used in laundry detergents) should react fully and is not that basic AFAIK:
Na5P3O10 + 2 H2O >> 2 Na2HPO4 + NaH2PO4

Unlike Mg sulfate hydrates, I strongly doubt that absolute ethanol will dehydrate sodium hydrogen phosphates.

[Edited on 24-9-2024 by clearly_not_atara]

MrDoctor - 24-9-2024 at 17:15

Quote: Originally posted by clearly_not_atara  
Perhaps a stupid question, but why not a polyphosphate?
[Edited on 24-9-2024 by clearly_not_atara]


http://www.sciencemadness.org/talk/viewthread.php?tid=61746&... not triphosphate, tripotassium. functionally dry ethanol was produced.

in this thread i think others had difficulty in reproducing the results.

Of course its not like most people actually have pure LR ethanol in the first place.


i swear this subject requires a dedicated thread or post just of different ways confirmed to work and maybe, a note about the quality of product, the pros and cons, etc, like the benzene from benzoates page got.

if ethoxide is the desired product theres a patent for drying ethanol by using a dean stark like arrangement where the refluxed distillate passes down through a different chamber before returning, loaded with either 3A or alumina, to eliminate water without using oxides or alkali metal.

K3PO4 has been tested
potassium carbonate, done
3A needs no explanation but, done
toluene/benzene azeotrope ala old textbook, done
adding dried NaCl to improve the output when distilling hardware store spirits, in preparation for breaking the azeotrope, done
magnesium to reduce traces, thats in a few textbooks as a standard method
magnesium sulfate, copper sulfate, hell even calcium sulfate, done on the forum
activated alumina is an industrially used adsorbent for ethanol specifically
simply drying the ethanol just a lil bit, and using the ethanols own azeotrope to dry itself, done.
silica gel has been refferenced in textbooks, its ok but its strength lies in the fact it can be left in solution since its so unreactive to a lot of things.
and of course, CaO, it works good but, has its own challgenges. personally id see it as more of something where it can undenature the ethanol and then be disposed of after filtering, i dont know though how reactive it is towards ketones, or glass when heated though. when you factor its other properties in, suddenly it becomes a bit more favorable depending on the situation.

Precipitates - 24-9-2024 at 19:05

For me it's not generally the method - but how many times you do it.

If I want a really dry product, I triple dry.

I like copper sulphate as its colour depends on the amount of water present - white if none, green if a little bit/slight solubility in the solvent, or blue if lots of water present, and can be used with acidic chemicals.

[Edited on 25-9-2024 by Precipitates]

Keras - 25-9-2024 at 00:23

Wouldn't phosphorus pentoxide do the job? Or would it react with ethanol, converting it to… well, ethylene?

Precipitates - 25-9-2024 at 00:59

According to the wiki it will react - I'm not sure of the products though (I guess it depends on the conditions).

chornedsnorkack - 25-9-2024 at 04:37

Quote: Originally posted by Precipitates  
According to the wiki it will react - I'm not sure of the products though (I guess it depends on the conditions).


Obvious alternatives, analogous to reactions with concentrated sulphuric acid, about which there is an active recent thread: