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Author: Subject: Attempting anhydrous ethanol with CaO
highpower48
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[*] posted on 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.
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Keras
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[*] posted on 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]
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Sulaiman
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[*] posted on 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.
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nimgoldman
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[*] posted on 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.
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Keras
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[*] posted on 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.
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nimgoldman
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[*] posted on 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?
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macckone
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[*] posted on 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
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Keras
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[*] posted on 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?
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unionised
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[*] posted on 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...
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Keras
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[*] posted on 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]
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CaptainPike
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[*] posted on 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
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nimgoldman
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[*] posted on 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]
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macckone
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[*] posted on 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?
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[*] posted on 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%.
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[*] posted on 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?
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[*] posted on 22-3-2021 at 16:44


Tapioca. It is used industrially to dry ethanol.
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[*] posted on 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.
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