Sciencemadness Discussion Board

Vacuum distillation - can it alone break azeotrope? Simple media bottle setup for alcohols & solvents

RogueRose - 24-12-2017 at 23:42

I had the need to evaporate off a good bit of a solution of methanol & a salt as well as maybe try distilling some ethanol as dry as possible and I don't have good glassware available at the moment but I have good glass media bottles (they are botosillicate & have used them with heat before) with hose barbs in the caps which will allow for hooking up a vacuum pump. I also have about 10 ft of copper tube (1/4" soft tubing) and the hose to go with it.

I've never done vacuum distillation and know to put the vacuum on the side after the condenser.

I put some sand in the bottom of a pan, added hot tap water, placed the bottle w/ methanol in it and hooked everything up and within about 7-10 seconds it was boiling/bubbling ferociously. Some of the methanol ended up getting into the vacuum hose line (the condensate outlet & vacuum inlet in the cap may have been too close).

I had to stop because this seemed to be happening to quickly and I didn't know if the bubbling (filled the bottle) would bring over some of the salt.

I could do the distillation by heat very easily but I thought I'd practice the vacuum method b/c I want to try some 50-96% ethanol (I have various concentrations to clean up) and see if I can get 100%, but I wasn't sure if it requires a fractional distillation column AND vacuum or if vacuum & heat will do it alone.

I'll post some pics of the setup later as it is really simple and can be replicated with just about any glass bottle (many products like milk come in thick 1/2 gal glass bottles if you need larger size) and when doing solvents with vacuum can probably be done with a hot water bath.


Well I hope everyone is having a great day!

[Edited on 25-12-2017 by RogueRose]

PirateDocBrown - 25-12-2017 at 04:00

Methanol-water is not azeotropic.

But, no, vacuum distillation cannot break an ethanol-water azeotrope. use a drying agent on the wet ethanol.

happyfooddance - 25-12-2017 at 10:13

Yes, vacuum does in fact break the ethanol azeotrope. You don't need tremendous vacuum to get around it, either. I know that there is info on the web saying both that it does and that it doesn't, but I can confirm from experience. You need to start with near azeotropic etOH. If it comes over at around 17° C and slowly, it tends to be pretty dry. I heat on a warm water bath.

Edit: More relevant to your post, yes you will need a column, and more importantly an ebulliator or magnetic stirring, but even though I have done this in the past, it is neither practical nor efficient/timely. A much better way to dry alcohol is with CaO as per Vogel or similar.

[Edited on 12-25-2017 by happyfooddance]

SWIM - 25-12-2017 at 15:37

CaO is a great way to get dry ethanol from azeotropic to 100%, I can attest to that too.

Sudden boiling with vacuum distillation can be a problem.
Common practice is to apply the vacuum before heating the boiling flask, and It's best to heat in a water or oil bath that has a higher level than the level of the liquid in the flask as this help to control bumping.

Stirring or a bubbler will likely be needed as happyfooddance said above.

If you don't want to establish vacuum before heating, or have to break and re-establish vacuum during a distillation you can use an air bleed to slowly increase the vacuum to avoid boil-overs. (like a needle valve controlled vent in the vacuum line)

I usually use a thermostatic water or oil bath as heat for vacuum distillations as you can set it to only heat to 15-20 degrees above the expected boiling point of your solution under vacuum and avoid the danger of things getting out of hand. For careful fractionations under vacuum I will sometimes set the bath temp as little as 10C above the expected boiling temperature, although I will raise it during the distillation if necessary.

For solutions over about 80% alcohol I often dry them to 95% by adding potassium carbonate. It absorbs the water and forms 2 layers so you just pour the alcohol off. Then you can re-generate your potassium carbonate for re-use by just roasting it in an oven. I suspect doing this with lower proof alcohol would require an awful lot of carbonate and not be worth doing, but I haven't tried that.

RogueRose - 25-12-2017 at 21:22

I think I'll finally try making some CaO and have both CaCO3 and Ca(OH)2. I'm guessing that the hydroxide would be the best choice to dehydrate but is there anything special that should be done? I was looking at using a cast iron pan/bowl and heating on a propane burner. Is that sufficient?

NEMO-Chemistry - 26-12-2017 at 01:58

Quote: Originally posted by RogueRose  
I think I'll finally try making some CaO and have both CaCO3 and Ca(OH)2. I'm guessing that the hydroxide would be the best choice to dehydrate but is there anything special that should be done? I was looking at using a cast iron pan/bowl and heating on a propane burner. Is that sufficient?

HI RR
CAO needs time and high temp (850C), I did this this the other night to get a small amount. In my case an open coal fire at home, small stainless steel crucible (mine is a cooking thing!!).

The coals where glowing almost white and the fire not easy to get near. I wore welders gloves and a full face shield, i put the crucible right in the fire amongst the coals, left for about 2 hours.

The crucible glowed a deep red after ages, the amount of calcium carbonate shrank down (it was powder). It worked but only just, i wasnt impressed TBH.

I think in future i am going to buy it, it seems to take alot of heat and a fair bit of time, i think propane burner would be a pain! Also propane here is £15 for 3.8kg (smallest size bottle for regulator), you would need to keep moving the flame all around the container.

I think it would take alot of gas to get it too 850C and keep it there, the CO2 dosnt want to come off easy!

I havnt tried CAO to dry Ethanol, but i have added water, how do you stop the Ethanol from boiling off? CAO gets hot when it meets water?? Even an ice bath would have a hard time wouldnt it?

[Edited on 26-12-2017 by NEMO-Chemistry]

[Edited on 26-12-2017 by NEMO-Chemistry]

unionised - 26-12-2017 at 04:07

Quote: Originally posted by PirateDocBrown  
Methanol-water is not azeotropic.

But, no, vacuum distillation cannot break an ethanol-water azeotrope. use a drying agent on the wet ethanol.

Yes it can.
Pressure distillation does it better, but isn't practical for amateur chemistry.

RogueRose - 26-12-2017 at 04:57

Quote: Originally posted by NEMO-Chemistry  
Quote: Originally posted by RogueRose  
I think I'll finally try making some CaO and have both CaCO3 and Ca(OH)2. I'm guessing that the hydroxide would be the best choice to dehydrate but is there anything special that should be done? I was looking at using a cast iron pan/bowl and heating on a propane burner. Is that sufficient?

HI RR
CAO needs time and high temp (850C), I did this this the other night to get a small amount. In my case an open coal fire at home, small stainless steel crucible (mine is a cooking thing!!).

The coals where glowing almost white and the fire not easy to get near. I wore welders gloves and a full face shield, i put the crucible right in the fire amongst the coals, left for about 2 hours.

The crucible glowed a deep red after ages, the amount of calcium carbonate shrank down (it was powder). It worked but only just, i wasnt impressed TBH.

I think in future i am going to buy it, it seems to take alot of heat and a fair bit of time, i think propane burner would be a pain! Also propane here is £15 for 3.8kg (smallest size bottle for regulator), you would need to keep moving the flame all around the container.

I think it would take alot of gas to get it too 850C and keep it there, the CO2 dosnt want to come off easy!

I havnt tried CAO to dry Ethanol, but i have added water, how do you stop the Ethanol from boiling off? CAO gets hot when it meets water?? Even an ice bath would have a hard time wouldnt it?

[Edited on 26-12-2017 by NEMO-Chemistry]

[Edited on 26-12-2017 by NEMO-Chemistry]


Well the wiki page states that the hydroxide decomp's at 580C so that is a good bit lower than 850C, that is why I thought it better, but IDK if there is something I'm missing about the process.

As far as keeping the temp down, maybe setup the alcohol in a distillation setup and allow the heat to pass it over? Or maybe add it much slower?

BTW, I tried anhydrous MgSO4 and it does not break the azeotrope but it may have dried it to about 96%. I did not reflux but I did allow it to sit with an excess for about 8 months (just put it on a shelf and came back to it...).

NEMO-Chemistry - 26-12-2017 at 06:25

wikipedia says 850C

https://en.wikipedia.org/wiki/Calcium_oxide

https://www.wikihow.com/Make-Quicklime

NEMO-Chemistry - 26-12-2017 at 06:27

Quote: Originally posted by RogueRose  
Quote: Originally posted by NEMO-Chemistry  
Quote: Originally posted by RogueRose  
I think I'll finally try making some CaO and have both CaCO3 and Ca(OH)2. I'm guessing that the hydroxide would be the best choice to dehydrate but is there anything special that should be done? I was looking at using a cast iron pan/bowl and heating on a propane burner. Is that sufficient?

HI RR
CAO needs time and high temp (850C), I did this this the other night to get a small amount. In my case an open coal fire at home, small stainless steel crucible (mine is a cooking thing!!).

The coals where glowing almost white and the fire not easy to get near. I wore welders gloves and a full face shield, i put the crucible right in the fire amongst the coals, left for about 2 hours.

The crucible glowed a deep red after ages, the amount of calcium carbonate shrank down (it was powder). It worked but only just, i wasnt impressed TBH.

I think in future i am going to buy it, it seems to take alot of heat and a fair bit of time, i think propane burner would be a pain! Also propane here is £15 for 3.8kg (smallest size bottle for regulator), you would need to keep moving the flame all around the container.

I think it would take alot of gas to get it too 850C and keep it there, the CO2 dosnt want to come off easy!

I havnt tried CAO to dry Ethanol, but i have added water, how do you stop the Ethanol from boiling off? CAO gets hot when it meets water?? Even an ice bath would have a hard time wouldnt it?

[Edited on 26-12-2017 by NEMO-Chemistry]

[Edited on 26-12-2017 by NEMO-Chemistry]


Well the wiki page states that the hydroxide decomp's at 580C so that is a good bit lower than 850C, that is why I thought it better, but IDK if there is something I'm missing about the process.

As far as keeping the temp down, maybe setup the alcohol in a distillation setup and allow the heat to pass it over? Or maybe add it much slower?

BTW, I tried anhydrous MgSO4 and it does not break the azeotrope but it may have dried it to about 96%. I did not reflux but I did allow it to sit with an excess for about 8 months (just put it on a shelf and came back to it...).


Easy simple cheap dry Ethanol is a bit of a holy grail :D.

Trouble is it requires more effort than it costs to buy it, even at silly UK prices!

unionised - 26-12-2017 at 07:43

Quote: Originally posted by NEMO-Chemistry  
wikipedia says 850C

https://en.wikipedia.org/wiki/Calcium_oxide

https://www.wikihow.com/Make-Quicklime


Wiki says both.
"When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa (normal atmospheric pressure), which decomposes calcium hydroxide into calcium oxide and water"
https://en.wikipedia.org/wiki/Calcium_hydroxide


"Calcium oxide is usually made by the thermal decomposition of materials, ... in a lime kiln. This is accomplished by heating the material to above 825 °C"

https://en.wikipedia.org/wiki/Calcium_oxide

NEMO-Chemistry - 26-12-2017 at 08:14

Surely thats a mistake? At those temps wouldnt Hydroxide decompose into Carbonate? I know with calcium carbonate based minerals you heat until they are red, from my own experience the other night in a hot coal fire, i cant see dry calcium oxide being made under 850C.

The fire was too hot to get near for long, and yet the crucible was in it for ages and glowing red, but it took a couple of attempts to get anything like the Oxide.....

Some i purchased a while back (all gone now), reached 290C when i added a little water to it. Just seems odd to dehydrate Ethanol using something that gets that hot in water, obviously depends on amount used and amount of Ethanol being dried, but i would think decent cooling is an absolute must?

Fulmen - 26-12-2017 at 08:22

Unionseed: Read both sources again. 825°C is for calcium carbonate, 512°C is for calcium hydroxide.

happyfooddance - 26-12-2017 at 08:31

How can hydroxide decompose into carbonate, please tell?

Edit: Drying etOH with CaO isn't a high art, isn't expensive, and isn't dangerous (unless you are prone to hurt yourself regardless). The heat evolved has less to do with the amount of ethanol than with the ratio of CaO to water. You should be starting with ethanol that has less than 5% water.

I don't think drying ethanol is any sort of a holy grail. Drying solvents is just something that has to be done.

[Edited on 12-26-2017 by happyfooddance]

RogueRose - 26-12-2017 at 09:26

Well I just did some Ca(OH)2 on a propane burner and SS pot (started with cast iron but it's too thick). IDK what temp it was at, but I don't think it was any where near 850C.

Here it says hydroxide deomp's at 580C..
https://en.wikipedia.org/wiki/Calcium_hydroxide

The problem is that it is really dusty. IDK if it can be done by not stirring it occasionally but it seems like it needs to b/c it insulates pretty well, so the Ca(OH)2 on the top takes a while to heat.

I was thinking of making something with an old heater or old toaster oven element or using Ni-chrome like wire. I'd think that either the carbonate or hydroxide would be non-conductive, though I'll have to check that and see if it will short nichrome.

I think the nichrome would be better, basically make a circle or square and have a wire every 5-10mm and wind back and forth from side to side, making evenly spaced rows. All that would be needed is a post at the end (finishing nail?) and a heat resistant non-conductive base (clay?). Put the carbonate/hydroxide in and allow to cook for XX minutes , allow to cool, remove finished product.

Temps should be doable with any of the resistance wires: Nichrome, Kanthal, Titanium, etc.

NEMO-Chemistry - 26-12-2017 at 09:35

Quote: Originally posted by happyfooddance  
How can hydroxide decompose into carbonate, please tell?

Edit: Drying etOH with CaO isn't a high art, isn't expensive, and isn't dangerous (unless you are prone to hurt yourself regardless). The heat evolved has less to do with the amount of ethanol than with the ratio of CaO to water. You should be starting with ethanol that has less than 5% water.

I don't think drying ethanol is any sort of a holy grail. Drying solvents is just something that has to be done.

[Edited on 12-26-2017 by happyfooddance]

Why ask me?? Isnt like I know much about chemistry!! My guess was simple, from what it said and the fact the OXIDE picks up CO2 from the air very easily, i assumed at those temps it would become carbonate.

What is Calcium Hydroxide without water but with CO2? Heating it to 850 drives off the CO2 according to wiki, so my assumption cant be that far off can it??

Equally Rose, the other link i gave says to heat a mineral to red glow, this sounds alot less than 850C, i measured my coal fire right by the coal itself. The temp was around the 900C mark (hard to tell as it was real quick (too hot) ). The colour of the coal was almost white yellow.

The other sign to look for with powder is loss of volume, apparently 1.8kg leaves 1kg oxide, so its safe to assume you would notice a decrease in volume.

unionised - 26-12-2017 at 09:47

Quote: Originally posted by Fulmen  
Unionseed: Read both sources again. 825°C is for calcium carbonate, 512°C is for calcium hydroxide.

Read the thread again.
Quote: Originally posted by RogueRose  
I think I'll finally try making some CaO and have both CaCO3 and Ca(OH)2. I'm guessing that the hydroxide would be the best choice to dehydrate but is there anything special that should be done? I was looking at using a cast iron pan/bowl and heating on a propane burner. Is that sufficient?


Also, read my nickname again.

unionised - 26-12-2017 at 09:49

Quote: Originally posted by NEMO-Chemistry  
Surely thats a mistake? At those temps wouldnt Hydroxide decompose into Carbonate?

Not unless someone is doing nuclear physics.

happyfooddance - 26-12-2017 at 09:51

Calcium hydroxide does indeed attract CO2, but not when you approach the temperatures that will remove it. Also, I am assuming that y'all are using closed containers as all good preps for CaO exclude CO2, also, from 550 degrees on you should be quitting water, and your can/crucible will be filled with mostly water vapor and have a slight positive pressure, even if very little, enough to prevent CO2 from entering in measurable quantities.

NEMO-Chemistry - 26-12-2017 at 10:48

Quote: Originally posted by happyfooddance  
Calcium hydroxide does indeed attract CO2, but not when you approach the temperatures that will remove it. Also, I am assuming that y'all are using closed containers as all good preps for CaO exclude CO2, also, from 550 degrees on you should be quitting water, and your can/crucible will be filled with mostly water vapor and have a slight positive pressure, even if very little, enough to prevent CO2 from entering in measurable quantities.

No i am using an open crucible, i wouldnt use a closed one at any temp in my house...

TBH if this means I got to buy the stuff then so be it. I am sure your right, but for me with my luck, not a chance i will heat stuff up in my lounge in a closed container :D.

RogueRose - 26-12-2017 at 10:55

At one point when I had the hydroxide heated to about 1100F, it flowed like water, it was really interesting to see this. There was a little bubbling and it looked similar to boiling liquids, or heating baking soda to washing soda. It was pretty apparent when the hydroxide had lost it's water as the behaviour of the powder changed noticeable from highly flow-able (almost uncontrollable if stirred) to a more rigid powder, though still settled evenly in vessel.

happyfooddance - 26-12-2017 at 11:00

A piece of foil over the top might suffice, though it will burn if too close to the coals. Closed container is not the same as a closed system... You have literally no chance of a catastrophic pressure increase with this sort of set-up, maintaining a slight positive pressure is okay. But, you should really try to find or make an outdoors, out-a-window set-up to do this, I agree...

NEMO-Chemistry - 26-12-2017 at 11:16

Quote: Originally posted by happyfooddance  
A piece of foil over the top might suffice, though it will burn if too close to the coals. Closed container is not the same as a closed system... You have literally no chance of a catastrophic pressure increase with this sort of set-up, maintaining a slight positive pressure is okay. But, you should really try to find or make an outdoors, out-a-window set-up to do this, I agree...


So wait for Noah to sod off with the ark then!

I have some thick foil, i didnt think of that sorry. Even a lid placed over the top might do the trick....

Rose it sounds like you had better luck than me, i didnt get any fluid at all.

The carbonate from Hydroxide was a total guess from a noob! I stand corrected gents.

I got a new mini propane torch, i might try that but doubt it has the power. The problem for me really is, Calcium Oxide isnt hard to get and its only around £8 per kg. that makes it really hard to justify not buying it.

Then again Chloroform is only £12 for 2.5ltr to buy, but £45 on top for shipping :(

happyfooddance - 26-12-2017 at 11:24

Quote: Originally posted by NEMO-Chemistry  


The problem for me really is, Calcium Oxide isnt hard to get and its only around £8 per kg. that makes it really hard to justify not buying it.


Exactly. There is no place on earth where CaO should be restricted or expensive. It is a great drying agent, depending on how dry it is when it gets to you... I, too, would like to make CaO out of the carbonate and the hydroxide, but it is too cheap on its own for me to justify at the moment.

NEMO-Chemistry - 26-12-2017 at 11:28

Quote: Originally posted by happyfooddance  
Quote: Originally posted by NEMO-Chemistry  


The problem for me really is, Calcium Oxide isnt hard to get and its only around £8 per kg. that makes it really hard to justify not buying it.


Exactly. There is no place on earth where CaO should be restricted or expensive. It is a great drying agent, depending on how dry it is when it gets to you... I, too, would like to make CaO out of the carbonate and the hydroxide, but it is too cheap on its own for me to justify at the moment.


The trouble is the curiosity effect! Or the madness part of science madness

happyfooddance - 26-12-2017 at 11:34

Quote: Originally posted by NEMO-Chemistry  


The trouble is the curiosity effect! Or the madness part of science madness


Agreed. Which is why I have done this many times before, and can say with surety: buy your CaO. :)

[Edited on 12-26-2017 by happyfooddance]

RogueRose - 26-12-2017 at 13:22

I didn't mean that I ever saw fluid. I meant that the powder was acting like a fluid the way it flowed. It swashed around and acted every way that a liquid would act when it was de-watering at about 1100F.. Really neat to watch.

aga - 26-12-2017 at 13:33

Break out a few dollars and get some glass from China.

There's a reason why most people do that - it is cheap and works better.

You CAN try to make your own, but the results are generally not so good :
http://www.sciencemadness.org/talk/viewthread.php?tid=30497#...

NEMO-Chemistry - 26-12-2017 at 13:39

Quote: Originally posted by aga  
Break out a few dollars and get some glass from China.

There's a reason why most people do that - it is cheap and works better.

You CAN try to make your own, but the results are generally not so good :
http://www.sciencemadness.org/talk/viewthread.php?tid=30497#...

He wants dry Ethanol, this is about drying Ethanol after its been distilled (unless i got it completely???).