Sciencemadness Discussion Board

Separate EtOH and IPA

Fyndium - 17-9-2020 at 03:17

I have a solution that contains an unknown portion of isopropyl and ethyl alcohols, former being major component. I was thinking of recovering IPA because the solution is very cheap compared to pure IPA, but I'm unsure if it is possible to separate these without special equipment or some very expensive treatment?

ArbuzToWoda - 17-9-2020 at 03:54

You'd need some very careful fractional distillation. They don't form azeotropes according to I suppose ethanol is a bit more polar so you could try something like adding CaCl2 to keep it in solution? That's just an idea that rushed through my mind, no clue if it would work.

Tsjerk - 17-9-2020 at 05:23

I wouldn't start trying to separate these two, it is just really hard. What do you need the IPA for? If it is for solvent use, just use the mixture.

Heptylene - 17-9-2020 at 07:04

Perhaps with a packed column and distillation head you can manage some separation but it would take a long time and IPA is still pretty cheap considering the labor involved with distillation.

Fyndium - 17-9-2020 at 09:31

I suppose spinning band distillation would be only reliable method to separate them due to their almost identical BP. When I have compounds that have less than 5C bp I usually just consider distilling them apart futile, or if it would be carried out, it would need a meter long column with 10+:1 reflux ratio and very careful cuts and most likely at least one redistillation.

I'm not very sure if IPA and EtOH are quite similar in their dissolving capabilities, otherwise it doesn't really matter. I think I just buy the pure IPA and pay a little extra. I considered this more of a challenge in the first place than an actual money saving thing.

macckone - 17-9-2020 at 10:11

That kind of column is common in distilling ethanol.
I have one made of copper for medicinal purposes.
I use rings for packing.

But how about a chemical method.
potassium carbonate with 3 parts water and 7 part alcohol mix (assuming dry),
should selectively allow separation of isopropyl and ethanol.
I have not tried it but it should work as ethanol is much more soluble in water with potassium carbonate than isopropanol.

Another tactic is converting the isopropyl alcohol to isopropyl chloride,
any ethanol converted to the chloride will evaporate quickly (12C) while the isopropyl chloride boils around 35C.
This could form azetropes so look those up.
Converting isopropyl chloride back to the alcohol is trivial.

A third tactic is to find something that forms an azetrope with one component.
Water and benzene for an azetrope with ethanol that allows drying of ethanol.

[Edited on 17-9-2020 by macckone]

arkoma - 17-9-2020 at 16:55

Quote: Originally posted by macckone  

I have one made of copper for medicinal purposes.

Mines glass, with copper mesh packed in a claisen to catch those nasty sulfur compounds. Strictly medicinal.

Thanks for the chemical separation tips, too.

Syn the Sizer - 18-9-2020 at 06:41

My one though is, and it is a bit of a process. Use Fischer Esterification to produce esters, I compared a couple of the EtOH and IPA esters and their boiling points are usually further apart that the 2 alcohols.

Fractional distillation to seperate the esters and hydrolyze back to the alcohol and respective carboxylic acid. Of course you need to remove H2O to push the reaction forward but I really believe you would have an easier time separating the esters.

I personally wouldn't bother separating but I get 4L of 99% IPA for $30CDN and 2.5L of 80% EtOH for $40CDN, so for me seperation of the mixed alcohol is more a project to see if I can do it.

Fyndium - 19-9-2020 at 00:45

For what I can record, I can get solvent grade IPA for about 8€ per liter and ethanol in the form of car wash fluid that distills over at 78C at less than 2€ per liter, so yes, this was more for an experimental point of view. It appears that it is totally not worth doing it, but if there was an easy way like salting them apart..

Syn the Sizer - 19-9-2020 at 04:54

I would say yes and no, not as A source for the reagents, but chemistry is fun so to attempt it as a fun project is worth it just for the experience and just to say you did it lol. I personally would attempt the ester method as it seems the most fun to me.

To be honest I may mix some EtOH and IPA in quantitative amounts and see how much I can recover just for the hell of it.

Fyndium - 19-9-2020 at 21:42

The experience is what I'm looking into. You learn only by doing and repeating, and developing in this will eventually lead into a good routine where you can just do things because you have experience on the smallest of the detail that makes you not fail so easily.

And once you master the skill of being able to separate and purify almost anything, things get a lot more interesting. It may not be of interest to separate such cheap compounds, but when you come up in a situation where you want to isolate a high value substance, you may already know how to do it because you have the experience. Apparently more than half of entire chemistry is basically isolating and purifying substances, the synthesis phase itself is more of a minor detail.

unionised - 20-9-2020 at 03:11

A strong solution of magnesium sulphate or sodium chloride won't mix with IPA, but it will mix with EtOH.

It's possible that washing with salt water will remove ethanol preferentially.

However, unless you have a GC or something handy, it's not going to be easy to tell.

More a matter of speculation than any practical use.