Azeotropic Distillation

You can distill 100% pure ethanol from azeotropic mixtures by running the distillation under something like 75mbar or less of pressure; an aspirator / fridge pump.

This is a very common trick exploited industrially.

They even do the reverse and then rerun some distillations under increased pressures, in a process called 'pressure swing distillation'.

One example I can think of relating to alcohol is producing ethanal. It's usually done right from the ground up industrially, but some people came into possession of huge quantities of fermented alcohol and decided to catalytically convert it to ethanal over hot copper. Then use pressure swing to purify the result.

Changing the pressures alters the way the azeotrope behaves. They produce pretty graphs like this to identify what pressures will work best;



{edit}Forgot to say, 100% pure ethanol is a lot more flammable than drinking alcohol. Explosively so if you have big clouds of it floating round (Ref; Homer, "Eternal moonshine of the Simpson mind", Circa 2007). Proofing alcohol was a name that came about from sailors (and piratey folk) who used to get paid part of their wages in Rum. To check it was strong, they'd try pouring some over gun powder and lighting it. If the gun powder wouldn't burn, they were being horse waggled out of wages (the Rum was dilute and therefore useless for getting drunk with the land lubbin' wenches). The gunpowder was the acid test of the strength, the proof.

{double edit}That shape is also one of the shapes proposed for the universe by Stephen Hawking and friends. I proposed a circle, but he said it looked too much like dividing by 0.

[Edited on 22-9-2010 by peach]

Usually, if you need it over the azeotropic ratio, it also needs to be distilled from sodium wire; since work requiring very dry ethanol is usually anhydrous (entirely hates even traces of water) and wants every drop of water pulling out of it. You won't get that even with vacuum distillation. Don't use TNT.

There are alternatives to sodium that are much safer. For example, the molecular sieves. A lot of uni's and big labs are now switching to Solvent Purification Systems (SPS), which are essentially columns packed with alumina that the solvent is pushed through at 15psi under something like Argon. Sometimes they use an oxygen scavenger (like Q5) as well, to remove dissolved O2. That avoids the glass, the continually boiling litres of flammable solvent, heat sources and sodium. The latter can quite easily end up with people engulfed in balls of fire. And has done in practice.

People say it all the time, but when the end result of that is someone being horrifically scared for life, or dying, one person is enough to warrant ditching the glass. Particularly if that person is a 18-21 year old student the university is the guardian of and who gets to live with it for a long time.

I'm interested in the idea of making SPS systems for home use. They're not complicated at all and the pressures are very low. You can easily buy cheap stainless pipe rated to 4000psi, and these are running at 15.

The only complaint I've seen against these is having the column repacked. But that seems to require 6 months to a few years of use in full scale uni / chem labs. At home, it could last absolutely ages before it needs redoing. It could also be significantly smaller, since we're doing some reactions, sometimes. There aren't 30 students tapping it off every single day.

An accident in disguise;


A very expensive, but probably easily copied at home, SPS array (looks like someone's gone crazy with the Swagelock catalogue );


[Edited on 23-9-2010 by peach]

As I'm aware of things, all of them will absorb water, but the pore size is important to stop them also absorbing what you're trying to dry.

There's a list of what to use to dry what, HERE.

Also, if you haven't seen his blog yet, curly arrow is a kind of online chemistry guru place for all the genuine, in the lab everyday, chemists. He has a good amount of information about drying things, HERE. There's more on there about the topic, in other blog updates. And reading the replies is usually a good idea, because others are giving other information and he's replying, it's not all just 'Great site!' / 'You suck!'

Zeolites are also amazing in terms of what they can do as catalysts, or at least supports for them. The precise pore size, again, determines how well they behave.

Going back to my alcohol mention before. The guys doing that deposit the copper / coper with traces of other things in it on the zeolite by precipitating it out of solution as they give it a stir. The zeolite is microporous, like activated carbon. So the catalyst now has a monumental surface area when compared to a solid lump of copper metal.

The stuff also features lewis acid sites without anything else on there.

I think the precise pore size sieves may actually be synthesized as opposed to dug up, to ensure the pores are the correct size. That can be done hydrothermally in an autoclave (hot + water, like at those hydrothermal vents under the sea).

The things needed to do it aren't actually that complicated. Hydroxide, sulphuric, aluminium sulphate, silicic acid ('sand' acid ). They use something like propylamine as a scaffold, to define the pore dimensions.

Here's an idea for how they do it, if you have an autoclave at home

This is another thing where the US has it better than the UK (We still have all the iodine ), because you can get those pressure canners that would fit a dead body inside on eBay. They won't manage quite the same pressure / temperature as a Parr bomb, but I'm sure I've read about people forming these at autoclave temp/press.

There are also quite a lot of posts about MS's here on SM, just searcherize 'molecular sieve drying' or something similar.

[Edited on 26-9-2010 by peach]

Quote: Originally posted by dann2

Hello, Hope I am not going off topic toooooooo much....... I have a problem similar(ish) to needing to get all the water out of an alcohol mixture. I have a concoction of Ethanol + Methanol (distilled methylated spirits actually) + Tin and Antimony Chlorides and some HCl + water. I want to get rid of all the water. If I simply add some Benzene to the mixture and distill until the Benzene is all in the receiver will the Benzene take the water out with it and leave me with just Alcohols + dissolved solids in the boiling flask. Will it at least take most of the water away? I have no molecular seives and I don't want to add any dehydrating solids as this is not a suitable option for what I am trying to do. TIA, Dann2

Quote: Originally posted by peach

Alumina seems to be an issue for a lot of people. I want some, I know someone else wants some, you'd like some and I think the SPS idea is the way forward for Science Hatters and solvent drying. [Edited on 30-9-2010 by peach]

Quote: Originally posted by Rogeryermaw

First i am sorry for posting a new thread that surely has been beaten to death but i did search and came up with limited answers and nothing really dedicated to breaking azeotropes. if i just missed something please feel free to move this to the proper thread. also if someone could direct me to that thread i would be grateful. thank you.