Rogeryermaw
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Azeotropic Distillation
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.
I've been doing a lot of reading on breaking azeotropes and azeotropic distillation. example: ethanol forms an azeotrope with water at 96.4% at which
no more water can be separated by distillation with out an entrainer such as benzene. according to what i have read, if you can get the concentration
of the alcohol above the azeotropic percentage you can then distill the rest of the water out. my question is: say you had a bottle of everclear. now
suppose you had a small bottle of 100% pure ethanol. if you mixed the two that should, in theory, raise the concentration and break the azeotrope
allowing for continued distillation. is this correct? any help is greatly appreciated. what techniques have some of you used for this purpose? sodium?
molecular sieves? MgSO4 or hydroxides? any links to tables regarding this will also be much appreciated.
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unionised
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I don't think there's a thread about azeotropes in general; but there is at least one about that particular azeotrope.
http://www.sciencemadness.org/talk/viewthread.php?tid=7379#p...
Anyway, if you added a little pure alcohol to the azeotrope you could distil it and get pure alcohol; but only as much as you added so there would be
no point.
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gsd
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The Ethanol(Boiling point 78.4 Deg C) & Water (Boiling point 100 Deg C) Azeotrope ( Boiling Point 78.2 Deg C) contains 95.63% ethanol and 4.37%
water (by weight).
In simple distillation of this mixture, the azeotropic point is a point of inflection. If your starting mixture has a ethanol content in between o and
95.63 wt %, then in an ideal distillation process the top product will have 95.63 % ethanol and 4.37 % water whereas the bottom product will be 100 %
water.
Now if your starting mixture has a ethanol content in between 95.63 wt % and 100 then after the distillation, the BOTTOM product will
be 100 % ethanol and TOP product will be 95.63 % ethanol and rest water.
Please Note that the Amount of top and bottom product will depend on initial compositon.
In order to break the azeotrope you will have to add third component like benzene for azeotropic distillation or a salt like CaCl2 for "Salting out"
the ethanol.
You can also use the process pervaporation (http://en.wikipedia.org/wiki/Pervaporation) to reach beyond the azeotropic concentration.
gsd
[Edited on 20-9-2010 by gsd]
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Rogeryermaw
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thank you for your quick responses. i wasn't really optimistic it would be that easy but basic info sources don't go into this detail.
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peach
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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]
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Rogeryermaw
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if you are referring to homer's stills exploding i think it was homer vs. the 18th amendment in season 8 episode 18 (funny you bring it up cuz i
watched that one last night) but distilling under vacuum? that i can do. just so happen to have a vacuum port distillation adapter. i think i will
give that a try. i doubt it will matter too much for my purposes but you never know when anhydrous conditions mean the difference between a successful
experiment and disaster (especially in syntheses with hydrazine). thank you much for the info. this will come in handy!
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peach
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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]
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not_important
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For EtOH a water aspirator gives sufficiently low pressures (somewhere around 70..100 mmHg IIRC) to get 99+ percent EtOH, a small amount of molecular
sieves will finish the job w/o too much expense.
Some other azeotropes can't be handled that way, others required increased pressures; exact method will depend n what the mix is.
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Rogeryermaw
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is it the 4A zeolite that absorbs water? can anyone point me to a publication where all this data is collected? there has to be a collected work about
anhydrous solvents/drying solvents somewhere. i have collected several little bits of info but most of it is about either this solvent or that
chemical...no collection of works about the subject as a whole. i am sure i'm just missing something...
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peach
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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]
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Rogeryermaw
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thank you peach! now that is info i can use. excellent links as always!
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dann2
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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
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Rogeryermaw
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it will take a better chemist than me to fully answer your question. the different alcohols have different boiling points and i don't believe methanol
forms an azeotrope with water but it may with benzene.
check out the links peach put up. there is some very good data there.
[Edited on 29-9-2010 by Rogeryermaw]
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peach
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I suspect that's going to shift it at least partly to what you're after, if it doesn't get all of it you could try drying over a strong base. I can't
answer specifically because I don't know enough about what you're trying to do or what with. I also don't tend to use entrainers.
Can you not simply boil off the water / alcohols and then re-dissolve?
You're not getting all the water out of there with hydrochloric in there, not without the hydrochloric trying to leave as well. Waterless hydrochloric
is of coarse hydrogen chloride (a gas at room temperature, so it won't hang around once the water is gone, if that's the aim).
[Edited on 29-9-2010 by peach]
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Panache
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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 |
placing some molecular sieves into a soxhlet thimble and then refluxing the mixture as if you were extracting it should do the trick, i often use it
when i want to remove water but do not want to have to remove everything else first. I think the methanol will be a big problem here though, depending
on how much you have, you might just end up refluxing that all day and not bringing any water with it.
As for Mr Rogermauxxxx, i have an excellent PhD thesis from some scandinavian chap on all things azeptropic etc, the intro chapter is concise and
brings you up to speed well and the research chapters are very enlightening, however the pdf is 3.8meg and i can't post it up (2meg limit, forgot it
was 1998 still, whats less than 2meg these days). Can anyone please tell me a way around this, compressing it further might lose too much detail and
make the document unsearchable and hence useless. well almost useless.
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peach
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Use rapidshit, or google for another; "file hosting"
I wouldn't mind a read of that.
I like the soxhlet idea. I was thinking about soxhlets earlier. I keep seeing them and thinking, mmmmm maybe. But don't have enough use for one right
now to warrant the cha-ching. Then realized I could make a mock soxhlet with the 500ml pressure equalizing funnel. Fill the solvent flask with
slightly less solvent than it takes to reach the side arm on the funnel, let it go up, open the tap. Or just leave the tap permanently dripping. It
will require that I'm sat next to it or check back on it, but damn... that's not too hard. I have a bunch of solenoids I could use to drain the funnel
every now and again if I was getting all technical on it.
{edit} actually, over filling the solvent flask may make things easier, as it'll ensure it never runs dry. Just need to make sure it's not boiling off
at a rate where there'll be 'problems' in the side arm (flooding / splashing).
[Edited on 29-9-2010 by peach]
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aonomus
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I'm wondering if there is an easy way to take 'dirty' pottery store alumina, wash it, dry it, activate it, and then use that to pack columns for a
SPS. I'd be weary of the impurities making their way into solvents, but there has to be a cheaper way to get alumnia to do such a column?
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peach
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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.
Stills for each solvent are expensive and waaaay too prone to the old fireball trick to be running at home for each solvent on a regular basis.
I'm sure with some digging a suitable, everyday replacement can be found. OTC drying agents are a bit more noble a cause than OTC iodine, red P and
ephedrine replacements.
I saw some Alumina furnace tube liners on one of the sell sites last night. £650 for one. Shiiiiiiiiiiiiiiiii-it.
[Edited on 30-9-2010 by peach]
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bbartlog
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As regards activated alumina, you can get it from some water filters - ones designed for defluoridation, for example item 1014 here: http://www.aquasmart.com/filters.html. Likely a lower price can be found, that's just the first example I found via google. I have the alumina
from a used cartridge similar to the one shown. I cut it open and washed twice each with dilute NaOH and acetic acid to get rid of adsorbed gunk
(mostly iron compounds I think), then baked.
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arghh
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| 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] |
Activated alumina is used in aquarium phosphate removers. One brand is SeaChem PhosGuard. Here is a link to their FAQ:
http://www.seachem.com/support/FAQs/PhosGuard.html
Strangely, it doesn't mention solvent purifying, gas drying or making cryogenic absorption vacuum pumps. On google shopping, I saw one place that had
it for $38 for a 4 liter container or $13 for a 1 liter container. It can probably be had for somewhat more OTC at a pet or aquarium store.
Braur also has a synthesis for aluminum hydroxide gel on page 1652 from aluminum ethoxide. Heating dehydrates to alumina gel. The synthesis for the
ethoxide didn't look all that bad as long as you have and don't mind working with HgCl2. So if you don't have anhydrous ethanol all you need to make
it is Al turnings, HgCl2, I2 and ..... anhydrous ethanol ... DoooH! By the way, does anyone know of a suitable substitute for the HgCl2 for this?
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The WiZard is In
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| 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. |
------
Ethanol. I would be so bold as to suggest a simpler method - it is in
Brauer — Handbook of preparative inorganic Chemistry p. 26 The
book (both volumes) are in the forms library, and a 'hole bunch
of other sites.
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