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highpower48
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Sorry if this posts more th a once, was having an issue with the quick reply function
According to Macroscale and Microscale Organic Experiments by Williamson 4th edition.
Use calcium oxide for drying ethanol. If it's at least 95% is suggests using benzene.
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Keras
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Did someone already mention Calcium hydride? Calcium hydride sucks water and gives out hydrogen. It’s used as a desiccant. Wikipedia even states
it’s used with alcohols.
[Edited on 7-9-2018 by Keras]
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Sulaiman
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Calcium hydride is neither cheap nor easily available,
Speculation only ... not tried
using a water absorbant/adsorbant material that can be re-used with no overall loss of ethanol such as bran or tapioca may be better overall
e.g. https://www.purdue.edu/newsroom/research/2011/110913LadischT...
i.e. any ethanol retained by the fermentable material will be returned to the next fermentation.
I doubt that absolutely dry ethanol will be produced
but it would remove most of the water
requiring less of whatever agressive / expensive dehydration material is required.
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nimgoldman
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Thanks. I found the issue was that one have to reflux with CaO for full 12 hours or more OR leave CaO in alcohol for several days with occassional
swirling.
Then it should be distilled over CaO and only middle fraction is taken - no filtering.
Another possible issue was that my CaO was not freshly ignited and I don't know how long it sat in the container, it might picked up some moisture.
So I reverted to molecular sieves but I will give it a shot later.
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Keras
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I’d had a quick look this summer on Ebay and there was some chap in China selling that for a few bucks. But it seems to have gone away.
Why not use the more available and cheaper calcium carbide then? Water will be transformed into ethylene and you get slaked lime that you can easily
filter out.
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nimgoldman
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Quote: Originally posted by Keras  |
I’d had a quick look this summer on Ebay and there was some chap in China selling that for a few bucks. But it seems to have gone away.
Why not use the more available and cheaper calcium carbide then? Water will be transformed into ethylene and you get slaked lime that you can easily
filter out. |
I haven't heard about using calcium carbide for drying ethanol. Do you have a source reference?
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macckone
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Commercial methods are:
Distilling 95% alcohol with benzene - not suitable for human consumption and requires a very high reflux ratio
Drying with molecular sieves - suitable for human consumption if sieves are food grade
Drying with CaO - if CaO is suitable for human consumption after distilling is suitable
Drying with cellulose - usually used for fuel grade - literally kiln dried corn cobs
For ultra dry use iodide activated magnesium as described in 'Purification of laboratory chemicals' by Armarego et al.
Also activated aluminum amalgam from the same source.
Potassium carbonate is the simplest and easiest with the least loss but it has to be pretty high percent to work. You can't use off the shelf vodka
or mash for salting out. There is another thread that covers getting it over 95%.
http://www.sciencemadness.org/talk/viewthread.php?tid=61746
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Keras
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No. This is a wild guess based on what everyone knows of calcium carbide reacting with water. Besides, if calcium hydride is used to suck water
(producing Ca(OH)2), why calcium carbide wouldn't work?
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unionised
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Carbide is used- but it's hazardous. Acetylene (Not ethylene, BTW) isn't nice stuff to work with.
https://www.jstor.org/stable/2993231?seq=1#metadata_info_tab...
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Keras
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Agreed. As I said, it was a wild guess. I had considered the possibility of acetylene dissolving in alcohol, but didn't mention it.
Also this article
[Edited on 11-9-2018 by Keras]
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CaptainPike
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| Quote: Originally posted by RogueRose |
[…]
I finally tried anhydrous copper sulfate and had excellent success. The thing about using CuSO4 instead of something like K2CO3 is the hydrates that
are formed with CuSO4 - which is a pentahydrate instead of a monohydrate - it can accept 5x the water per molecule compared to potassium carbonate.
It also has the great characteristic of changing color to tell you when it is "full" (hydrated).
[…]
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I liked this. I haven't used it yet for drying ethanol, but I did bake some down to at least the dihydrate in a conventional oven – white powder.
Here's the MSDS for the one I bought:
ZEP ROOT KILL MSDS
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nimgoldman
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| Quote: Originally posted by Herr Haber | | Quote: Originally posted by Deathunter88 |
Now, I recommend the OP revisit molecular sieves. If you're losing too much ethanol from using them on a liter scale, then you are adding way too much
or you are using something other than the 3A type, and ethanol is getting adsorbed into them alongside water. 10-20% by weight is plenty, just enough
to cover the bottom of the container with an even layer (1-2cm). |
Same thought here.
Maybe OP's sieves are of questionnable quality ?
[Edited on 9-3-2018 by Texium (zts16)] |
These are 3A sieves from a reputable vendor (Carl Roth). They were very expensive. I have reactivated them beforehand (4 hours at 250 °C and 100 mbar
of vacuum).
I used 5 grams of sieves per gram of water. Lower sieves:water ratio resulted in incomplete drying (the resulting alcohol was 97-98%).
Last time I used 5:1 ratio, lost 100 ml of ethanol (from liter of solution) and still got only 98%, not 99%.
I don't know why this process is so lossy...
[Edited on 14-9-2018 by nimgoldman]
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macckone
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5g per 1g of water is about right. Seives absorb 20% of their weight. 3a should not absorb alcohol, even 4a should not. Alcohol is about 5a. There
should be about 45ml of water in 1000ml of azeotropic and 250g of seives should absorb that. Is your alcohol actually azeotropic?
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nimgoldman
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| Quote: Originally posted by macckone | | 5g per 1g of water is about right. Seives absorb 20% of their weight. 3a should not absorb alcohol, even 4a should not. Alcohol is about 5a. There
should be about 45ml of water in 1000ml of azeotropic and 250g of seives should absorb that. Is your alcohol actually azeotropic?
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Now I am unfortunately never able to get above 93.5-94% even with multiple distillations with a 60 cm Vigreux column.
I use 2L heating mantle with a thermometer probe and usually have to heat the solution to 79-81 °C to push the vapours up to the still head.
I tried insulating the column but it does not help much if at all.
Unfortunately the heating mantle sometimes go crazy and has a hard time keeping a constant temperature.
Overall the distillation is extremely slow, like 1 drop per 2 seconds. I don't know if it should be that way. If I make it quicker, like 1-2 drops per
second, then the resulting alcohol is only up to 94%.
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Fyndium
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So, about that portand cement..
Has anyone actually tried it or know of a successful use for dehydrating ethanol with it?
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digga
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Tapioca. It is used industrially to dry ethanol.
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pneumatician
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Mood: ■■■■■■■■■■ INRI ■■■■■■■■■■ ** Igne Natura Renovatur Integra **
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What you call "dry etanol" or "100% eta." is what a alcoholometer say, pure obvious :-)
in reality when you get 98, 99, 100% etanol is only a primitive standard measure far from real dry etanol. The 100% etanol continue contain more than
60% of water, so pure etanol in an alcoholometer need to say something like 160% :-)
no more, no less.
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MrDoctor
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drying ethanol using copper sulfate only works when going from anhydrous, to monohydrate. any lower hydrates that form (indicated by a stronger blue)
will compete for water with ethanol, where absolute ethanol ultimately wins out.
Magnesium sulfate is similar. when OP says it "didnt work" they probably did what i and many others did and added the magnesium sulfate, then
distilled with it inside. magnesium sulfate loses its water readily by heat.
What you do is add enough anhydrous magnesium sulfate such as that there isnt enough to dissolve in the water. depending on how dry you want it, add a
slight molar excess based on the specific hydrate you wish to form, and youll subsequently get something like 98%, 99% and/or 99.5% dry ethanol. you
FILTER out the magnesium, just like you do the copper, then distill to eliminate contaminants and dissolved solids.
you can during this distillation seperate the ethanol into azeotropic and pure, or you can try eliminating the water with magnesium with
iodine/ultrasonication, you can use other methods of destroying water molecularly too, like CaO, though it will require re-filtration.
azeotropic distilation with toluene is good if trace toluene isnt going to be an issue, but regardless you still have to store over molecular sieve to
finish it off. those sieves will impose a tax, and the only way to get around it is to start from 99.5% instead of making them soak up a whole 5%.
Lastly, members on the forum have demonstrated using potassium carbonate to seperate the water from ethanol, to a degree which it was impossible to
descern wether or not it was close to, or actually absolute ethanol. you can decant this, otherwise invest in a sep funnel.
Once again, a certain amount of carbonate must be used such as that there is more carbonate than water present to form hydrate with. in this case the
hydrate extends well into the liquid state, much like how water does with calcium chloride. basically though this just means, if you arent sure, add
way more than neccesary, and if its going to clog your sep funnel, then i guess keep a little wet ethanol seperate, or water, to help dissolve your
excess before seperating. what i read btw was that the starting ethanol was everclear, or possibly some sort of vodka. or perhaps both. so potassium
carbonate was able to get absolute starting from as low as 30% (if i recall correctly).
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Sulaiman
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| Quote: Originally posted by pneumatician | What you call "dry etanol" or "100% eta." is what a alcoholometer say, pure obvious :-)
in reality when you get 98, 99, 100% etanol is only a primitive standard measure far from real dry etanol. The 100% etanol continue contain more than
60% of water, so pure etanol in an alcoholometer need to say something like 160% :-)
no more, no less. |
multiple times I have fermented sugar, done a simple distillation and then a fractional
distillation,
sometimes followed by drying with sieves,
at all stages my (cheap Chinese) alcohol hygrometers gave expected readings,
eventually up to somewhere between 99 and 100% ABV.
Why do you think 60% water ?
Is your hygrometer in proof degrees or similar?
CAUTION : Hobby Chemist, not Professional or even Amateur
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clearly_not_atara
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Perhaps a stupid question, but why not a polyphosphate?
CaO and other highly basic drying agents will produce ethoxide, which can react with atmospheric oxygen. Many, many attempts at producing ethoxide
without sodium (which generates a blanket of H2) result in it turning brown and becoming difficult to crystallize.
But e.g. Na5P3O10 ("sodium triphosphate", widely used in laundry detergents) should react fully and is not that basic AFAIK:
Na5P3O10 + 2 H2O >> 2 Na2HPO4 + NaH2PO4
Unlike Mg sulfate hydrates, I strongly doubt that absolute ethanol will dehydrate sodium hydrogen phosphates.
[Edited on 24-9-2024 by clearly_not_atara]
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MrDoctor
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http://www.sciencemadness.org/talk/viewthread.php?tid=61746&... not triphosphate, tripotassium. functionally dry ethanol was produced.
in this thread i think others had difficulty in reproducing the results.
Of course its not like most people actually have pure LR ethanol in the first place.
i swear this subject requires a dedicated thread or post just of different ways confirmed to work and maybe, a note about the quality of product, the
pros and cons, etc, like the benzene from benzoates page got.
if ethoxide is the desired product theres a patent for drying ethanol by using a dean stark like arrangement where the refluxed distillate passes down
through a different chamber before returning, loaded with either 3A or alumina, to eliminate water without using oxides or alkali metal.
K3PO4 has been tested
potassium carbonate, done
3A needs no explanation but, done
toluene/benzene azeotrope ala old textbook, done
adding dried NaCl to improve the output when distilling hardware store spirits, in preparation for breaking the azeotrope, done
magnesium to reduce traces, thats in a few textbooks as a standard method
magnesium sulfate, copper sulfate, hell even calcium sulfate, done on the forum
activated alumina is an industrially used adsorbent for ethanol specifically
simply drying the ethanol just a lil bit, and using the ethanols own azeotrope to dry itself, done.
silica gel has been refferenced in textbooks, its ok but its strength lies in the fact it can be left in solution since its so unreactive to a lot of
things.
and of course, CaO, it works good but, has its own challgenges. personally id see it as more of something where it can undenature the ethanol and then
be disposed of after filtering, i dont know though how reactive it is towards ketones, or glass when heated though. when you factor its other
properties in, suddenly it becomes a bit more favorable depending on the situation.
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Precipitates
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For me it's not generally the method - but how many times you do it.
If I want a really dry product, I triple dry.
I like copper sulphate as its colour depends on the amount of water present - white if none, green if a little bit/slight solubility in the solvent,
or blue if lots of water present, and can be used with acidic chemicals.
[Edited on 25-9-2024 by Precipitates]
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Keras
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Wouldn't phosphorus pentoxide do the job? Or would it react with ethanol, converting it to… well, ethylene?
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Precipitates
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According to the wiki it will react - I'm not sure of the products though (I guess it depends on the conditions).
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chornedsnorkack
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Obvious alternatives, analogous to reactions with concentrated sulphuric acid, about which there is an active recent thread:
Ethene
Diethyl ether
Ethyl esters of phosphoric acids. Note that there are more options than in case of sulphuric acids because phosphoric acid is tribasic and
polyphosphoric acids are more stable than polysulphuric ones
Tars. Presumably a side product of a branch to ethene, through acid catalyzed polymerization.
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