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Author: Subject: Drying 90% Ethanol with Magnesium Sulfate?
The Chemistry Shack
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[*] posted on 6-7-2015 at 09:52
Drying 90% Ethanol with Magnesium Sulfate?


Edit: I have reposted this in the organic chemistry section

I have looked through all of the ethanol and solvent drying threads, but haven't found a definitive answer to this. I distilled some 70% ethanol, and testing the density of the distillate, I found it to be 90% ethanol and 10% water. If this is repeatedly dried with anhydrous MgSO4, will the resulting ethanol need to be distilled? Or will simply filtering off the MgSO4 work well enough (and then storing the product in a parafilm-wrapped bottle to prevent moisture absorption)?

P.S. I don't need completely anhydrous ethanol (If I did I would just reflux over magnesium), but I do want to obtain ethanol above the 96.5% EtOH/4.5% water azeotrope concentration.


[Edited on 6-7-2015 by The Chemistry Shack]




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[*] posted on 6-7-2015 at 10:10


Or, you can buy absolute ethanol:
http://nh.craigslist.org/grq/5086621619.html
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[*] posted on 6-7-2015 at 10:20


That stuff is $80 per gallon, or $21 per liter. The stuff I bought cost $12 and will give me 1.32 L of ethanol, which is a unit cost of $9 per L. So I save a lot of money by distilling the 70% ethanol (also, I dont have to pay shipping, as the local pharmacy has it).



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[*] posted on 6-7-2015 at 10:24
Drying 90 Ethanol with anhydrous MgSO4?


I have looked through all of the ethanol and solvent drying threads, but haven't found a definitive answer to this. I distilled some 70% ethanol, and testing the density of the distillate, I found it to be 90% ethanol and 10% water. If this is repeatedly dried with anhydrous MgSO4, will the resulting product be close to 99% ethanol? Or do I need to fractionally distill the ethanol first up to 96% (I know it would be best to do a fractional distillation anyway, but I want to try and avoid it if I can).
P.S. I don't need completely anhydrous ethanol (If I did I would just reflux over magnesium), but I do want to obtain ethanol above the 96.5% EtOH/4.5% water azeotrope concentration.




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[*] posted on 6-7-2015 at 10:32


I have had mixed results with using magnesium sulfate drying ethanol. I added about 250grams of anhydrous magnesium sulfate to 500ml of 95% ethanol. I shook the bottle and let it stand for 20 minutes. After that I distilled it over and tested it with anhydrous copper chloride. I was disappointed as the copper chloride turned green on contact. It might be that I needed to leave it for longer, or copper chloride is too sensitive to test ethanol for water at say ~98-99% ethanol.

[Edited on 6-7-2015 by Deathunter88]
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[*] posted on 6-7-2015 at 10:45


AFAIK, ethanol solvates the MgSO4.
Suitable drying agents are CuSO4, KOH, CaO, 3Å molecular sieves - those can be easily filtered off even without a need for redistillation (KOH creates some amount of KOEt in the alcohol though).
And of course I forgot about azeotropic distilation with something like benzene.
Deathunter88, did you remove the MgSO4 precipitate after drying but before distillation?

[Edited on 6-7-2015 by byko3y]
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[*] posted on 6-7-2015 at 12:11


CaO (quicklime) is used to dehydrate azeo EtOH.



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[*] posted on 6-7-2015 at 12:28


Above the azeotrope is perfectly doable with just magnesiumsulfate, I think you can go to at least 99%. You only need more of the sulfate if there is more water in there, plus a way to get your ethanol out of the salt. Do you have means to do a vacuum filtration? That always worked great for me.

[Edited on 6-7-2015 by Tsjerk]
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[*] posted on 6-7-2015 at 12:38


Yes I can do a vacuum filtration




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[*] posted on 6-7-2015 at 12:43


Quote: Originally posted by Deathunter88  
I have had mixed results with using magnesium sulfate drying ethanol. I added about 250grams of anhydrous magnesium sulfate to 500ml of 95% ethanol. I shook the bottle and let it stand for 20 minutes. After that I distilled it over and tested it with anhydrous copper chloride. I was disappointed as the copper chloride turned green on contact. It might be that I needed to leave it for longer, or copper chloride is too sensitive to test ethanol for water at say ~98-99% ethanol.

[Edited on 6-7-2015 by Deathunter88]


Since MgSO4 absorbs water in a reversible process:
MgSO4 + 7H2) <-> MgSO4*7H2O
You have to filter it off first before distilling, so that's probably why it didn't work.




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[*] posted on 6-7-2015 at 12:44


Quote: Originally posted by byko3y  
AFAIK, ethanol solvates the MgSO4.


[Edited on 6-7-2015 by byko3y]


Really? I thought MgSO4 was nearly insoluble in ethanol




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[*] posted on 6-7-2015 at 15:49


The Chemistry Shack, I don't have specific number, but I can tell that it's 1% soluble even in diethyl ether, and also:
"Freely soluble in water; freely (and slowly) soluble in glycerin; very soluble in boiling water; sparingly soluble in alcohol."
It has probably something like 3% solubility in 95% ethanol. But anyway it's a shitty dessicant, because magnesium sulfate draws a lot of water into the ethanol.
While CuSO4 is "slightly soluble in ethanol" and 1% soluble in methanol, and this means that you'll get something like 0.5-1% of residual water after drying the ethanol with CuSO4.
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6-7-2015 at 16:37
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[*] posted on 7-7-2015 at 06:53


Quote: Originally posted by byko3y  

While CuSO4 is "slightly soluble in ethanol" and 1% soluble in methanol, and this means that you'll get something like 0.5-1% of residual water after drying the ethanol with CuSO4.


My lab oven only goes up to 450 F, so I can't dehydrate my CuSO4 all the way (it turns into a very faintly blue powder), and I don't want to use the oven in my kitchen to dehydrate it fully.
I'm assuming it will still work as a desiccant, and Ill just have to use more--or will CuSO4 work only if it is fully dehydrated?




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[*] posted on 7-7-2015 at 08:13


Quote: Originally posted by byko3y  

It has probably something like 3% solubility in 95% ethanol. But anyway it's a shitty dessicant, because magnesium sulfate draws a lot of water into the ethanol.


Really? How can anhydrous MgSO<sub>4</sub> 'draw lots of water into the ethanol'?




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[*] posted on 7-7-2015 at 09:58


There is absolutely nothing shitty about magnesium sulfate as long as you use it in the right way.

Solvated magnesium sulfate does not hold any water, hence; dry with a lot of sulfate (it is cheap and recyclable), filter, distill. This way the solid sulfate holds the water, and you get rid of any salts through the distillation.

As The Chemistry Shack says, MgSO4 loses water at the boiling temperature of ethanol.

I once tried to further dry the ethanol obtained this way with fresh (shiny) magnesium turnings, after weeks they where still shiny, not a trace of dullness.

@ The Chemistry Shack; Why don't you use a flame to dry CuSO4? In minutes it goes to complete dryness.

[Edited on 7-7-2015 by Tsjerk]
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[*] posted on 8-7-2015 at 07:56


Tsjerk, I don't know how to tell ya, but... anhydrous ethanol actually reacts with magnesium forming magnesium ethoxide. The reason why it did not react is because THERE'S FEW PERCENTS OF WATER IN YOUR ETHANOL.
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[*] posted on 8-7-2015 at 09:53


Which is why it is used to dry ethanol. It won't react until nearly all of the water is gone.

[Edited on 8-7-2015 by Molecular Manipulations]




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[*] posted on 8-7-2015 at 14:48


You should read you books once again, because magnesium is never used to dry ethanol, but magnesium ethoxide is.
First you mix anhydrous ethanol, magnesium and iodine to make magnesium ethoxide, than you add the ethanol you need to dehydrate.
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[*] posted on 8-7-2015 at 15:21


Quote: Originally posted by byko3y  
You should read you books once again, because magnesium is never used to dry ethanol, but magnesium ethoxide is.
First you mix anhydrous ethanol, magnesium and iodine to make magnesium ethoxide, than you add the ethanol you need to dehydrate.


Yeah, like anyone actually does it that way. Maybe in Dumbass, I mean Donbas... You're a weirdo and always will be.

[Edited on 8-7-2015 by blogfast25]




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[*] posted on 18-11-2017 at 03:58


Wow name calling. Great way to articulate your point.
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[*] posted on 18-11-2017 at 04:00


I use 3-A sieves. They are re-usable and fairly inexpensive on ebay but be cautious with who you buy them from as some are a mix of 3-A and 4-A. Get them from a reputable seller.
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[*] posted on 19-11-2017 at 16:16


Quicklime used to be a standard. Quicklime sadly, is no longer either cheap or readily available. Expensive and hard to find. Also, not easy to have shipped.

Gotta make yer own.

The reaction of Magnesium with Methanol is vigorous. With Ethanol...heating to reflux may be required to kick off the reaction. Some suggest, that drying Ethanol via easily produced Magnesium Methoxide, is a good way to go.

Though to me, it seems that the anhydrous Ethanol produced, must thereafter be contaminated by residual methanol. Quite possibly, a dangerous outcome.
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