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unionised
International Hazard
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In this instance, yes.
edit
sorry the last post was a bit curt I'm blaming a bad hangover.
[Edited on 28-8-2005 by unionised]
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protem
Harmless
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Interesting notion - apparently according to wikipedia (ethanol)
" At pressures less than atmospheric pressure, the composition of the ethanol-water azeotrope shifts to more ethanol-rich mixtures, and at pressures
less than 70 torr (9.333 kPa) , there is no azeotrope, and it is possible to distill absolute ethanol from an ethanol-water mixture. While vacuum
distillation of ethanol is not presently economical, pressure-swing distillation is a topic of current research. In this technique, a reduced-pressure
distillation first yields an ethanol-water mixture of more than 96% ethanol. Then, fractional distillation of this mixture at atmospheric pressure
distills off the 96% azeotrope, leaving anhydrous ethanol at the bottoms."
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unionised
International Hazard
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It seems to have taken a while but someone has finally spotted that you can separate alcohol from water by distillation without adding any chemicals
whatsoever. Azeotropic composition is pressure dependent.
I thought the change was the other way round i.e. that increasing the pressure led to a higher alcohol content. Does anyone else have any data on
this?
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Panache
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so thats whats happening
i buy cheapish barrels of wine from small wineries and vac distil off the ethanol and have always wondered why i can intially get an extremely dry
ethanol (albeit contaminated with wine flavoinoids) cf/ running the distillation at atmoshperic.
shit now i better go and research this.
As an add on to the thread it makes seperation of closely boiling fractions simplier if you do the distillation under pressure, i clean the vac
distilled ethanol up this way vs slow distillation up a large column. this increased pressure really contains impurities and the neat spirit i get out
doesn't require filtration through carbon to dilute into an acceptable vodka.
you need to use all stainless over course, as pressure and glass don't really go well, although i imagine if one carefully fibreglassed ones glass
setup it would allow for some pressure to be applied.
anyways i'll try to quantify the water/ethanol azetropic behaviour under diminished pressure and post my results.
All should be aware that pressure gradients through a vac distillation setup exsist and the reading on your manometer does not represent the pressure
above the boiling liquid unless it is connected via a large bore (ie half of your condensor diameter) tube that feeds directly to above your boiling
liquid. Likewise digital manometers, utilising the conductance of the atmosphere within the vacuum, are less usefull IMO than mercury based ones as
they require claibrating against whatever you happen to be distilling and they hate water.
anyway blah blah, i'm bored, watching a distillation 5 days a week can do that to you, glad i just found this site it's all over the place and
ace
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alchemist3096
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| Quote: | Originally posted by Al Koholic
What if one were to mix with 95% ethanol, some ethyl acetate for example. Say enough to suck up all the water on hydrolysis. Could you simply reflux
this solution, hydrolysing the ethyl acetate into ethanol and acetic acid, drying the solution out in the process? |
Usually what I have seen used for a drying agent is anhydrous calcium chloride. If a moderate amount is added to the solvent/reagent and allowed to
sit for a minimum of 24 hours, the salt can be either decanted or filtered off leaving dry solvent/reagent (e.g. for Grignard reaction). This would
probably be less problematic than using something like ethyl acetate.
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Klute
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CaCl2 can't be used to dry short-chained alcohols as it reacts with them forming solid adducts.
I obtain my anhydrous ethanol from 96% industrial denaturated ethanol, which is cheap, by leaving 1L of it over ~50g NaOh overnight, then add ~150g
of CaO ( unslacked lime) from a gardenig store, and reflux with CaCl2 guard for 12H. The denaturants self condense (everythign turns yellow/orange).
Then the Ethanol is distilled in a dried, guarded simple distn setup, with molecular seives in the receptor, until only the Ca(OH)2 paste is left
(don't distill to dryness!). About ~200mL of ethano; are lost to this paste, but it's cheap.
The ethanol is left in the receptor and protected from atmospheric moisture, I personnaly keep it under Argon after having degassed it (3X
vacuum-argon cycles). Be carefull when handling it, it's very hygroscopic, ideally use glass syringes. Anhydrous CuSO4 stays white when added to it.
Sufficiently dry for any conventional uses IMHO.
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