Near 100% Isopropyl Alcohol from 70% Rubbing Alcohol

[lumberjack]

Here is a way to get near 100% Isopropyl Alcohol from 70% Rubbing Alcohol. Just add a half a cup or so of table salt to 32 fl oz bottle of 70% and shake well. You should see two separate layers appear, one that is a NaCl, H20 mixture and the other will be your high concentrated Isopropyl.

(won't there be an equilibrium estabished with H2O in both layers? - kingspaz)

[nbk2000]

Maybe by using multiple iterations, you could bring down the water percentage, but I doubt you could get it near anhydrous with only salt.

Azetropic distillation with something like toluene, xylene, or such, with a dean-stark trap would be more effective. Besides which, you can buy 91% very easily, and 99% too.

Though it never hurts to know how to do it yourself. :)

[Rosco Bodine]

Anhydrous Sodium Sulfate should also do the job nicely , and
Anhydrous Magnesium Sulfate ( baked dry Epsom Salt )
would likely work also , perhaps Anhydrous Sodium Carbonate
( baked dry washing soda ) as well . Which would be best ,
I don't know . Would have to check and see which has a
favorable insolubility in the resulting dried alcohol , just do
a few spot tests by evaporation of samples on a watch glass
and go from there .

Indeed isopropanol does show the property of phase separation
with salts soluble in the water which is present , or with other
liquids which may have a greater affinity for the water , than
for the isopropanol . Hydrazine Hydrate is one of those liquids .
I noticed the same peculiar phase separation when I was testing
different alcohols for extracting freebased hydrazine hydrate from
a slurry with sodium sulfate . Methanol extracted the aqueous
hydrazine hydrate nicely , but isopropanol just wouldn't mix with
the aqueous phase , even when agitated into an emulsion , it
was like mixing toluene and water , separated on standing into
two imiscible phases .

So you definitely can "salt out" a whole lot of the water from
an isopropanol phase containing water , along with whatever
likes being "brine" in that water better than being in the alcohol .

[megalomania]

You know, you can buy anhydrous isopropyl alcohol in the form of fuel line anti-freeze (isoheet). Salting out is certainly a good way to improve your percentage of alcohol, but I would not think you could get much beyond the high 90's percent wise.

[Rosco Bodine]

The final dehydration of solvents and also the maintenance
of solvents in anhydrous condition while in storage is often done
by use of dessicants which are relatively insoluble in the solvent .
Some of the dessicants may chemically react with any moisture ,
like calcium oxide for example , while others like Drierite may
absorb the moisture to form a hydrated salt . I have a couple
of liters of ethanol stored over a dessicant , same for some
benzene . The dessicants will get the moisture content down to
a very low percentage of maybe a few hundreths per cent .

[FUTI]

I think that I once had seen a result of a similar method but it used ammonium-sulfate or urea. Mega it really does make good result in water removal and alcohol concentration. I once found a 10L bottle with remains (not saturated enough) of this and I didn't know what is inside. It smelled like ethanol so I give it a try and redistilled it. Imagine mine face when the residue in the distiling flask started to crystalise out of solution upon cooling. In that case it was ammonium-sulfate.
EDIT : Of course noting can't match with CaO or molecular sieves.

[Bugger]

According to Perrys Chemical Engineers Handbook, chapter 13, isopropanol forms a constant minimumboiling-point azeotrope with water which has 31.46% water and boils at 80.37ºC. This would be the commercial "rubbing alcohol".

The use of table salt and other hygroscopic ionic solids, soluble in water but only slightly so in organic solvents, is bound to leave small quantities of these solids dissolved in the isopropanol. As with the large-scale industrial production of pure ethanol, I am sure that the large-scale industrial method for preparation of pure isopropanol would involve distillation from a ternary mixture to which something like benzene or toluene is added to the water-isopropanol mixture. The triangular ternary phase diagram required to design a still for this would probably be in the International Critical Tables, which are hard to get hold of;Perryhas nothing about this ternary system.

Of course, the reduced-water mixture after treatment with table salt or other ionic solid could be subsequently redistilled to leave behind the dissolved solid, but this would be adding an additional step, adding to the cost.

Bugger.

[FUTI]

Yes most water removal goes through a benzene Dean-Stark azeotropic removal. If you have UV spectrophotometer you can test the one you have on the shelf easy. I bet you can find the UV absorption of benzen easily. But recently it has been a trend to some firms to switch to a zeolite based dehydation technics. It is fine job since it can remove some other small molecules like methanol.

[lumberjack]

Thank you very much Rosco for your input. I think it will prove to be very helpful. This is probably a dumb question so don’t laugh. When you talk about storing a solvent over a desiccant, does this mean that you just add the desiccant to the solvent storage container allow it to settle and then store it that way? Is that all there is to it?

[Rosco Bodine]

Yeah it's that simple . For a particular solvent there is probably
at least a couple of choices of dessicant that will do nicely at
absorbing the water , while having a solubility in the dried solvent
that is so low as to introduce only insignificant contamination of
the solvent itself with any dissolved dessicant . You have to
consider what the solvent will be used for to decide if the trace
of any contamination will interfere with its use . Often the
trace contamination of the solvent by a dessicant is not any
problem , but the presence of water is undesirable , and that is
the scenario where this method would be useful .

[Doug]

If you are just after high purity isopropyl alcohol, most electronics suppliers sell it by the litre at around 99.7% purity. You may also want to try printers suppliers. It's reasonably cheap as well.

Of course, if you are doing it for scientific endeavour, then please accept my apologies and carry on.

[chochu3]

Add salt to rubbing alcohol and then add either anhydrous MgSO4 or NaCO3. This will do the trick. It's also better if you use the 70% and greater concentration as the 50 percent leaves you with using more reagents and leaves you with less isopropanol.

[zxxyxzxzz]

intresting subject. perhaps after adding the salt ( and when the layers form ), you could siphon the iso and repeat the procedure?

[Match]

Wouldn't placing the solution in the freezer work to extract the water?

(please excuse my rudimentary chemistry knowledge)

[DMSOnMyVeins]

Wouldn't placing the solution in the freezer work to extract the water?


Is this purpose to make the alcohol cold? Certainly you aren't implying that you'll be increasing the percentage of alcohol by placing the sol. in the freezer.

[festergrump]

I believe he's talking about freezing the water in the solution so it can be extracted as ice, much in the same way you can do with mash or homemade wine to achieve better alcohol concentration.

I've never tried this myself (no need :rolleyes: ), but it seems like it might work with lesser effort than the aforementioned technique.

[DMSOnMyVeins]

Concentrated solutions of alcohol are used as ANTI-FREEZE. Your household freezer couldn't possibly begin to work to purify alcohol/water solutions with high concentrations of alcohol. This may work with low percentage alcoholic solutions like beer or wine, but not with 70% isoPrOH

As for me, I use sodium chloride followed by separation of the alcohol layer followed by vacuum distillation of the alcohol over anhydrous magnesium sulfate. Works great for me.

Always use a cobalt chloride test strip to determine if the alcohol is anhydrous.

[Match]

Wouldn't placing the solution in the freezer work to extract the water?

(please excuse my rudimentary chemistry knowledge)


Oops, I meant once the solution had been separated into two layers.

[c.Tech]

How are you planing on separating the alcohol from water (in layers) when it’s
miscible in water?

And if you had layers why freeze when you could use a simple separatory funnel?

[megalomania]

The process of separating different chemicals by freezing is called fractional crystallization. This is a quite difficult procedure that requires carefully controlled cooling. This might work better with more dilute solutions, but it gets more complicated with less water.

Ever freeze sugared iced tea in a water bottle? The sugared portion freezes later than the water creating a core of unsweetened ice surrounded by a highly sweetened ice portion. When this melts the sweetened portion goes first due to freezing point depression and it being on the warmer outer part of the bottle. If you drink your partially melted tea it will be sweeter, but then the last bit will be largely unsweetened. This is fractional crystallization at work.

Quite coincidentally, I was looking for IsoHeet about a week ago at wal-mart, but they don’t seem to carry it anymore, just the methyl alcohol Heet brand.

[Cobalt.45]

Quite coincidentally, I was looking for IsoHeet about a week ago at wal-mart, but they don’t seem to carry it anymore, just the methyl alcohol Heet brand.
If you have an O'Riley's Auto Parts store nearby, check with them.

[nbk2000]

The local dollar store has both types.