Sciencemadness Discussion Board

Drying IPA - easiest method

Runningbear - 14-4-2010 at 23:03

I want to dry IPA (91% ethanol) using a drying agent. Preferably something I can heat or buy dry, that can be added to the bottle and will store OK in the bottle for use at a later date.

And I want to be relatively certain I have about 99% pure ethanol.

Can anyone suggest the best drying agent(s) to use for this purpose? Is 99% purity realistic without distillation and drying combined?

There are plenty of threads on drying agents here but none address my specific requirements.

thanks in advance,

Runningbear

JohnWW - 15-4-2010 at 01:31

It is not clear whether what you have is isopropyl alcohol or ethanol.

Runningbear - 15-4-2010 at 04:22

Sorry, I said ethanol but it is in fact C3H8O.

Skyjumper - 15-4-2010 at 04:48

IPA = Isopropyl alcohol (:

entropy51 - 15-4-2010 at 17:36

Quote: Originally posted by Runningbear  
There are plenty of threads on drying agents here but none address my specific requirements.
You sure about that, bear?
Quote: Originally posted by leu  
JACS 54 1445 (1932)

Note on the Preparation of Absolute Isopropanol
BY LEWIS E. GILSON
During several years of biochemical research the writer has found many instances where isopropanol could be substituted for ethanol in laboratory work. It is cheap and there are no restrictions governing its use; nor is it likely to be an object of theft. The commercial 91% azeotropic mixture was used instead of 95% ethanol and found to be fully equal or superior to the latter as a solvent or extracting medium. Absolute isopropanol was used in place of absolute ethanol.

Absolute isopropanol is easily prepared. The 91% grade is shaken with 10% of its weight of commercial flake sodium hydroxide, separated from the aqueous layer which forms, then shaken with a little more sodium hydroxide, decanted and distilled. The product obtained mixes with eight volumes of carbon disulfide, xylene or petroleum ether without the slightest trace of turbidity.

Dilute isopropanol can be concentrated by shaking with dry sodium chloride. Water is removed as a saturated layer of brine. The upper layer contains about 87% isopropanol and 2-3% of sodium chloride. While distilling, an additional quantity of brine separates. The distillate has so nearly the composition of the 91% azeotropic mixture that it can be used as such without further treatment. Or, after shaking the dilute isopropanol with sodium chloride and separating, it can be treated directly with sodium hydroxide and the absolute grade prepared.

:cool:

Runningbear - 18-4-2010 at 18:17

thanks entropy51, much appreciated.




[Edited on 19-4-2010 by Runningbear]

redox - 7-4-2011 at 16:56

2-propanol forms an low-boiling ternary azeotrope with water and methyl ethyl ketone.
An alternate way of drying IPA would be through adding MEK to 91% IPA and distilling until anhydrous.

"it is not clear whether it is alcohol or ethanol"

ChemProdigy808 - 13-2-2012 at 01:37

If you don't understand that ethanol is an alcohol hence "ol" then I wouldn't recommend carrying out process.

Pulverulescent - 13-2-2012 at 01:53

If you can't even read a post correctly, then I . . .

P

AirCowPeaCock - 13-2-2012 at 20:29

Quote: Originally posted by redox  
2-propanol forms an low-boiling ternary azeotrope with water and methyl ethyl ketone.
An alternate way of drying IPA would be through adding MEK to 91% IPA and distilling until anhydrous.


How do you intend to separate the MEK from isopropanol? If he doesn't want to distil, I doubt he has an apparti for such, let alone for fractal distillation.

DougTheMapper - 15-2-2012 at 09:24

Jesus, how many times does this topic have to come up? Throw a bunch of NaCl into it and wait for it to layer out. Extract layer of iPrOH, dry over anhydrous MgSO4, CaCl2, whatever; filter out the desiccant.

This iPrOH will be quite dry, well over the 99% spec you're shooting for. The distillation part is recommended to remove the tiny amounts of dissolved desiccants. However, considering your definition of 1% impurities as 'good enough', the amount of dissolved solids should be more than tolerable in your situation.

So, breaking out the spoon:

-Throw a bunch of rock salt into the 91% isopropanol container. Shake vigorously, let it stand for a couple hours to separate into layers.

-Use a syringe, syphon, etc. to remove isopropanol form the saturated NaCl solution.

-Bake epsom salts (MgSO4) or calcium chloride ice melter in the oven on high for a couple hours, let cool, crush.

-Mix isopropanol with the desiccant, shake, wait, repeat for a few hours.

-Filter out the desiccant. Distill (optional) to remove any dissolved desiccant which will be much less than 1% by weight.

Also, UTFSE! http://tinyurl.com/drying-isopropanol

[Edited on 15-2-2012 by DougTheMapper]

Bot0nist - 15-2-2012 at 16:10

Quote: Originally posted by DougTheMapper  
Jesus, how many times does this topic have to come up? Throw a bunch of NaCl into it and wait for it to layer out. Extract layer of iPrOH, dry over anhydrous MgSO4, CaCl2, whatever; filter out the desiccant.

This iPrOH will be quite dry, well over the 99% spec you're shooting for. The distillation part is recommended to remove the tiny amounts of dissolved desiccants. However, considering your definition of 1% impurities as 'good enough', the amount of dissolved solids should be more than tolerable in your situation.

So, breaking out the spoon:

-Throw a bunch of rock salt into the 91% isopropanol container. Shake vigorously, let it stand for a couple hours to separate into layers.

-Use a syringe, syphon, etc. to remove isopropanol form the saturated NaCl solution.

-Bake epsom salts (MgSO4) or calcium chloride ice melter in the oven on high for a couple hours, let cool, crush.

-Mix isopropanol with the desiccant, shake, wait, repeat for a few hours.

-Filter out the desiccant. Distill (optional) to remove any dissolved desiccant which will be much less than 1% by weight.

Also, UTFSE! http://tinyurl.com/drying-isopropanol

[Edited on 15-2-2012 by DougTheMapper]



Ummm, IIRC, calcium chloride is not a suitable desiccant for alcohols.

DougTheMapper - 17-2-2012 at 08:22

Quote:
Ummm, IIRC, calcium chloride is not a suitable desiccant for alcohols.


The halogenation of alkanes using a chloride salt is an SN1 reaction and does not proceed at an appreciable rate with primary and secondary alcohols.

Isopropyl chloride is usually prepared by refluxing isopropanol in HCl with ZnCl2 as a catalyst. At room temperature, simply mixing isopropanol with anhydrous CaCl2 is not going to give any appreciable yield since CaCl2 has a much stronger ionic bond than ZnCl2 and no strongly acidic conditions are present to protonate the alcohol.

I wouldn't dry tert-butanol with it, but this method works fine for ethanol and isopropanol in my experience. If anything, you have to deal with increased solubility over MgSO4.

EDIT: Here's a JACS article about making absolute ethanol with CaCl2 and CaO: http://pubs.acs.org/doi/abs/10.1021/ja01656a048

[Edited on 17-2-2012 by DougTheMapper]

Lambda-Eyde - 17-2-2012 at 08:30

That's not what Bot0nist refers to. Calcium chloride forms complexes with simple alcohols.

DougTheMapper - 17-2-2012 at 08:46

o_O

Yikes, I didn't know that. Perhaps my alcohols aren't as dry as I thought...

Mr. Wizard - 17-2-2012 at 10:56

Quote: Originally posted by DougTheMapper  
o_O

Yikes, I didn't know that. Perhaps my alcohols aren't as dry as I thought...


Been there, done that ;)

"It's what you learn after you know it all that counts. "
John Wooden

killswitch - 31-3-2012 at 10:05

What about drying isopropanol with anhydrous copper sulfate? Would that be too acidic? I ask because copper sulfate (unlike magnesium sulfate) offers an obvious indicator by way of color change for when it has fully hydrated, and would perhaps be less soluble in alcohol than magnesium sulfate.

[Edited on 31-3-2012 by killswitch]

subsecret - 24-7-2013 at 15:20

If you do decide to distill IPA, please be careful as it can form peroxides.

testimento - 24-7-2013 at 15:52

When I purified my otc isopropanols I simply poured a pile of salt into the liquid and heated it to boiling. The water layer was not separated within half an hour after mixing and stirring, but the layer became apparent only after the mixture was brought to boiling temp. I distilled about 90% of the IPA over and discarded the residues including salt, water and impure leftovers of IPA. Because I used simple distillation, not fractionation, the purity is probably not nearly 99%, but I only made an experiment then. IPA could be dried with CaCl as well, as mentioned before, it will not form any appreciable amounts of collateral substances at STP with short exposure times that are required to make it mostly dry.

Lotus - 24-7-2013 at 16:36

If you distill IPA purity of azeotrope will be around 82% max. Easiest is salting out with NaCl then slow distillation to remove salt. MgSO4 is soluble in iso therefore would not be first choice in to simplify procedure.

Rich_Insane - 25-7-2013 at 13:10

I use sodium hydroxide to dry my isopropanol.... If you need really, really dry IPA, wasn't there something in Vogel about using magnesium metal (or was it sodium?) to approach >99% concentration of the alcohol (in Vogel, it was ethanol).

ElectroWin - 25-7-2013 at 14:14

Quote: Originally posted by Rich_Insane  
I use sodium hydroxide to dry my isopropanol.... If you need really, really dry IPA, wasn't there something in Vogel about using magnesium metal (or was it sodium?) to approach >99% concentration of the alcohol (in Vogel, it was ethanol).


yeah i seem to recall he used sodium metal to dry ethanol.

Sublimatus - 25-7-2013 at 14:56

The procedure described for "super-dry ethanol" uses magnesium. It's on the 401st page of the fifth edition.

MrHomeScientist - 28-3-2014 at 12:07

Quote: Originally posted by entropy51  

Note on the Preparation of Absolute Isopropanol
BY LEWIS E. GILSON
During several years of biochemical research the writer has found many instances where isopropanol could be substituted for ethanol in laboratory work. It is cheap and there are no restrictions governing its use; nor is it likely to be an object of theft. The commercial 91% azeotropic mixture was used instead of 95% ethanol and found to be fully equal or superior to the latter as a solvent or extracting medium. Absolute isopropanol was used in place of absolute ethanol.

Absolute isopropanol is easily prepared. The 91% grade is shaken with 10% of its weight of commercial flake sodium hydroxide, separated from the aqueous layer which forms, then shaken with a little more sodium hydroxide, decanted and distilled. The product obtained mixes with eight volumes of carbon disulfide, xylene or petroleum ether without the slightest trace of turbidity.

Dilute isopropanol can be concentrated by shaking with dry sodium chloride. Water is removed as a saturated layer of brine. The upper layer contains about 87% isopropanol and 2-3% of sodium chloride. While distilling, an additional quantity of brine separates. The distillate has so nearly the composition of the 91% azeotropic mixture that it can be used as such without further treatment. Or, after shaking the dilute isopropanol with sodium chloride and separating, it can be treated directly with sodium hydroxide and the absolute grade prepared.


I'm currently using this method to dry some 91% IPA as much as possible. I poured roughly 100mL (79.1g) into a small bottle and added 10% of its weight in NaOH (7.9g), capped it, and shook vigorously for a few minutes (venting often). After allowing to settle overnight, there are two very distinct layers with lots of undissolved NaOH prills. I'm hopeful that beyond pulling the majority of the water into the lower layer, the remaining prills should dry the IPA even further over a few days of standing. I plan to decant and store the alcohol in another bottle. I don't think distillation is really necessary for my purposes.

My question now is, how would I go about testing the water content? I'd try sodium but I believe it also reacts with the alcohol, so it might give false positives.

Magpie - 28-3-2014 at 15:34

Here's a couple methods that were recommended in my 1960s organic lab manual for ethanol. I don't see why they wouldn't be good for IPA also:

1. Place 1 mL of your dried IPA in a small test tube. Add a little CuSO4. If it stays white this would indicate that no water is present. If it turns blue, it's forming a hydrate.

2. Place 1 mL of your dried IPA in a small test tube. Add a little CaC2 (calcium carbide). If you see tiny bubbles of H2 then that indicates the presence of water.

Acid Scavenger - 28-3-2014 at 21:41

Distilling it would be a very easy step to skip over. You are SO close, why stop now?

MrHomeScientist - 29-3-2014 at 05:02

Thanks Magpie, those are both easy methods that I should have thought of! I have both of those reagents. I think CaC2 will be the way to go, since I'd have to dehydrate my copper sulfate first.

As for distilling, I suppose there's no reason not to. It's just a bit of a hassle to set up the apparatus, water pump, etc.

blogfast25 - 29-3-2014 at 06:18

MrHS:

I'm not speaking from experience here but I think only substantial amounts of water in IPA would give those 'positives' (although for 5 % and over it should work). But conventional drying methods like salting, drying over anh. MgSO4 (Epsom salt) and distillation, should give very low water contents in your end product.

[Edited on 29-3-2014 by blogfast25]

S.C. Wack - 29-3-2014 at 08:38

Quote: Originally posted by MrHomeScientist  
, water pump, etc.


No ones saying anything really about a water pump...what's the solubility of NaOH in IPA? You may be in a position to tell us...

Is there a known factual basis for the usual recommendations of drying with sodium and magnesium sulfates? I guess it depends on the definition of dry...they seem to be mentioned mostly due to the non-reactivity, but it would be interesting to compare with calcium sulfate.

[Edited on 29-3-2014 by S.C. Wack]

blogfast25 - 29-3-2014 at 11:29

S.C.:

Good point. Most of use would dry IPA with the methods discussed here and take a BP. If it's close enough to the tabled value, most would be happy with that. But truly anhydrous IPA may be a much more difficult thing to achieve. And once below a certain level you'll need Karl Fisher (or maybe some GC?) to measure it.

forgottenpassword - 29-3-2014 at 12:32

IPA forms an azeotrope with water so you can dry it further by boiling off a small amount sufficient to carry away the residual water.

MrHomeScientist - 29-3-2014 at 13:01

Quote: Originally posted by S.C. Wack  

No ones saying anything really about a water pump...what's the solubility of NaOH in IPA? You may be in a position to tell us...

Water pump for the condenser, as in to condense the low-boiling vapors of isopropanol.

As for solubility I don't know. I suppose I'd need to take my "dry" IPA, stir in NaOH prills, and decant, dry, and weigh the remainder. The fact that it's so hygroscopic would complicate measurements, though.

Magpie - 29-3-2014 at 13:58

Quote: Originally posted by blogfast25  
...
I'm not speaking from experience here but I think only substantial amounts of water in IPA would give those 'positives' (although for 5 % and over it should work)....


You may well be right here. The context of my lab manual was a comparison of the results for 95% ethanol and absolute ethanol.

I prepare absolute ethanol by using 3A mole sieves on 95% ethanol. The product is good enough for Grignards.

vmelkon - 29-3-2014 at 14:02

Quote: Originally posted by Magpie  
2. Place 1 mL of your dried IPA in a small test tube. Add a little CaC2 (calcium carbide). If you see tiny bubbles of H2 then that indicates the presence of water.


What reaction takes place to produce H2?
Perhaps you means acetylene (ethyne) is produced as the CaC2 reacts with the water and you also get Ca(OH)2.

S.C. Wack - 29-3-2014 at 14:28

Quote: Originally posted by MrHomeScientist  

As for solubility I don't know.


If you distill your IPA, you'll get a good guess. Aha! on the water pump...I think nothing of it to the point where my fountain pump is in its bowl in yucky half-evaporated water pretty much 24/7 including right now. It shouldn't be a big deal to hook up if you use surgical tubing.

CuSO4 bluing would be easy enough to test with HEET/isoheet/$60.30 per liter Sigma IPA, and drops of water.

Magpie - 29-3-2014 at 17:10

Quote: Originally posted by vmelkon  

What reaction takes place to produce H2?
Perhaps you means acetylene (ethyne) is produced as the CaC2 reacts with the water and you also get Ca(OH)2.


Yes, I meant acetylene.

blogfast25 - 30-3-2014 at 05:33

Magpie:

In my experience commercial CaC2 is fairly sluggish, even with pure water (it is after all a hard calcined product). Small amounts of water in an inert matrix will further reduce reactivity. In short: it may take quite some time before any acetylene bubbles form.

nimgoldman - 9-6-2020 at 14:26

Sorry for bumping the thread, I wanted to clarify how much salt is actually needed...

Assume 1 000 g of 50 wt% IPA, that is 500 g IPA + 500 g water.

Of the 500 g water, I calculated about 70 g should go into azeotrope as we cannot salt beyond that. The azeotrope is: 70 g water + 500 g IPA as this gives the composition: 87.7% IPA : 12% water.

The remaining 430 g of water would contain about 150 g NaCl (saturated brine).

From this it seems only about 150 g NaCl is needed to salt out a kilogram of 50% IPA.

This seems acceptable as removing the bulk of water saves us from extremely time and energy-consuming fractional distillation...

I would still distill after drying IPA, but the pre-drying with NaCl seems to greatly speed up the process.

Fery - 10-6-2020 at 01:46

The water/NaCl phase still contains some amount of IPA. When having larger volumes, it is worth of distilling the IPA even from water phase. I processed 5 L of 70% IPA and distillation of the bottom brine layer boosted the yield by 20%.
https://www.sciencemadness.org/whisper/viewthread.php?tid=14...
Using only NaCl for salting out, I achieved density 0,829 g/ml = 85,5 wt %.
I did not dry it further using NaOH to anhydrous IPA.
I used 1 kg of NaCl for that experiment, which was sufficiently enough, not the all NaCl dissolved, but it is better to have some excess of NaCl.
Also the upper IPA layer contained some NaCl (which revealed as a distillation residue) - very likely caused by the H2O present.