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PrussianBlue
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Alternative Ethanol Drying Agent
This has probably already been answered somewhere, but I can't seem to find it. Can potassium carbonate be substituted with sodium carbonate for
ethanol drying? I also have some copper sulfate and basic copper carbonate, but not in expendable quantities.
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LearnedAmateur
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I don’t see why not, sodium carbonate is insoluble in ethanol. Also, you can reuse copper sulphate after drying the ethanol, you don’t have to
throw it out, and can simply be recrystallised if you think it could’ve been contaminated.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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JJay
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I've tried using potassium carbonate as a drying agent for 95% ethanol, and it didn't seem to work very well. I didn't observe any clumping or other
qualitative changes in the potassium carbonate. After standing overnight, the ethanol became very slightly more concentrated, or perhaps I only
witnessed measurement error. Perhaps with extended drying times or stirring it could be gotten to work well, but my experience with potassium
carbonate as a drying agent for ethanol was not very satisfactory.
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Tsjerk
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@ JJay; My guesses are these;
Your ethanol was more than 95%
You added so much drying agent you didn't observe clumping
Your carbonate was not dry
I always used potassium carbonate for many organic solvents, always worked like a charm, in ten minutes max. I don't think I ever used it for ethanol
though.
I don't see why sodium carbonate couldn't be used as long as you use enough of it.
I like to keep a stash of a salt per solvent, after drying I let the solvent vape of and after some time I "recharge" the salt in the microwave.
Usually, for extractions I just filter (before evaporation/drying). If you want your solvent nice and clean you can distill and do the same
evaportation/drying to reuse.
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JJay
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Quote: Originally posted by Tsjerk  | @ JJay; My guesses are these;
Your ethanol was more than 95%
You added so much drying agent you didn't observe clumping
Your carbonate was not dry
I always used potassium carbonate for many organic solvents, always worked like a charm, in ten minutes max. I don't think I ever used it for ethanol
though.
I don't see why sodium carbonate couldn't be used as long as you use enough of it.
I like to keep a stash of a salt per solvent, after drying I let the solvent vape of and after some time I "recharge" the salt in the microwave.
Usually, for extractions I just filter (before evaporation/drying). If you want your solvent nice and clean you can distill and do the same
evaportation/drying to reuse.
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Your inferences are reasonable. The ethanol was azeotropic (about 95.5%). I let about two liters stand over about 100 grams of potassium carbonate
overnight. Afterward, it measured 96.0%. The potassium carbonate was straight out of a freshly opened package, and it claims to be 99% food grade, but
I am not 100% sure that it is anhydrous. I still have more than 4 kg of it. I've used it to dry trichloromethane with better success and visible
clumping, but trichloromethane is not nearly as hydrophilic as ethanol.
I'll try again after drying the potassium carbonate in an oven to see if it works better. I am actually planning on making some ether this weekend, so
I might actually get to that this evening. That said, I think molecular sieves are probably a better bet than potassium carbonate, but it would be
nice to confirm once and for all whether potassium carbonate can take ethanol well above azeotrope dryness.
I do happen to know that the most common form of sodium carbonate available is the monohydrate, which fluffs off of decahydrate crystals at room
temperature and moderate humidity. I imagine that anhydrous sodium carbonate makes an effective drying agent for ethanol, although I doubt it can
absorb more than one molecule of water per molecule of sodium carbonate unless the ethanol is very wet.
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JJay
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I'm going to try:
3A molecular sieves
Copper sulfate
Potassium carbonate, oven dried
Sodium carbonate, oven dried
Anything else that is readily available that I probably have sitting around that I should try?
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PrussianBlue
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CaCl2?
[Edited on 3-24-2018 by PrussianBlue]
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Dr.Bob
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food grade K2CO3 is likely not very anhydrous, so limited drying ability. I would do 3A sieves first, as they hold a lot of water, then use the
Copper sulfate for the finishing pass. I used it as a drying agent a while back, and it has to be very dry to start (not blue, but whitish), and it
took a bit. The sieves are much easier to re-dry eventually, although you will loose some ethanol to them, as they hold a lot. They are best dried
under vacuum and heat, or just heated really hot and then cooled in a desiccator or sealed bottle.
Aluminum oxide, aka alumnia, is used commercially for drying ethanol, if it is well activated by drying well under heat/vacuum, it hold a lot of water
as well, and holds up less alcohol, typically. Good luck.
I prefer my ethanol at about 5-40% in water. But it is a great solvent, and theoretically quite green, safe, and cheap.
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PrussianBlue
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I have an old bottle of Fisherbrand Boileezers that I believe are made of alumina. Would powderizing some of these and oven-drying them be worth my
effort?
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JJay
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It's a powerful drying agent, but it is soluble in alcohols.
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JJay
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| Quote: Originally posted by Dr.Bob |
I prefer my ethanol at about 5-40% in water. But it is a great solvent, and theoretically quite green, safe, and cheap. |
I like mine flavored with juniper berries in a martini glass with the vermouth never even removed from the refrigerator. But yes, it is one of the
most readily accessible solvents and one of the most useful.
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Sulaiman
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I remember (probably) reading somewhere here on SM about using dried rice or bran or some similar cheap organic source. ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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RogueRose
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| Quote: Originally posted by JJay | I'm going to try:
3A molecular sieves
Copper sulfate
Potassium carbonate, oven dried
Sodium carbonate, oven dried
Anything else that is readily available that I probably have sitting around that I should try? |
I'd try anhydrous Mag sulfate. It can absorb 7 water molecules so it should be pretty good at drying compared to sodium carbonate and it is easily
attainable. If you do try this, I suggest heating the ethanol and even the MgSO4 to about 120-140 before mixing. This seemed to help A LOT when I
dried my ethanol with CuSO4 (which absorbs 5 water molecules or about 40% of it's weight in water). CuSO4 works well for ethanol and IPA both
starting from about 91% and getting 100% alcohol!
In both cases (ethanol & IPA) the CuSO4 started out pinkish/greyish and then turned white as it absorbed some water and then light blue and then
a strong blue.
If you are drying with any of these I suggest powdering them (coffee grinder?) as if it is clumps it is MUCH slower in drying. I used a tea strainer
and anything that was caught didn't go in and was ground some more. Much more efficient than having small clumps of drying salt(s).
[Edited on 3-24-2018 by RogueRose]
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Dr.Bob
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I'm pretty sure that small amounts of MgSO4 can dissolve in ethanol, so that might work best if distilled afterwards, depending on how critical your
work is. If you let the salts dry out well after used, they should be able to be heated and redried, just maybe start outside incase they still hold
ethanol, as that could be exciting in an oven.
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S.C. Wack
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Potassium carbonate is used to dry alcohol, to 90%, based on the mutual insolubility of conc. ethanol and conc. potassium carbonate. It's debatable
whether it's wisely used otherwise, or the sodium salt at all AFAIK.
CaSO4 dehydrated at 225C has been recommended for further drying, before distilling and treatment with a final drying agent. The capacity is quite low
(to the hemihydrate) but even so it's no stranger to the art.
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PrussianBlue
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I think I'll give MgSO4 and alumina (assuming I can powderize and dry some Boileezers) a try. If I can only attain around 95% EtOH, will
this still act to stabilize chloroform or does that require absolute?
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RogueRose
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| Quote: Originally posted by Dr.Bob | | I'm pretty sure that small amounts of MgSO4 can dissolve in ethanol, so that might work best if distilled afterwards, depending on how critical your
work is. If you let the salts dry out well after used, they should be able to be heated and redried, just maybe start outside incase they still hold
ethanol, as that could be exciting in an oven. |
I think I recall the same about MgSO4 but it is a very small amount.
From what I've read about CuSO4, it is totally insoluble in ethanol and IDK about IPA but it seems to be the same. I'll report back when I get my
distillation setup as I have about 1L that was dried with CuSO4 from 91% to 100%.
As for being re-usable, I know the CuSO4 works very well after the first drying. The nice thing is once you grind it into a very fine powder, it goes
back to that very easily if it is dried on an open plate/dish and not compacted while drying. This saves a lot of time when re-using it! The odd
thing is that my CuSO4 turns pinkish when anhydrous which I've read it is supposed to be white/grey. It does turn white/grey a minute or two after
putting the ethanol in it so it seems that maybe the white may be either a hemi-hydrate or monohydrate as I know I've seen CuSO4 listed as having a
monohydrate and possibly trihydrate form though they are more rare.
As far as cost goes, I'd have to say it's tough to beat the CuSO4 in how much it will dry per gram used. IIRC 1 mole is 160g anhydrous and 250g
pentahydrate - so for every 100g (of anhydrous) it can absorb 56g of water which is a major factor when dealing with ethanol that can be left behind
adhereing to the drying salt. Using something that only absorbs 1 mole of water, you have to use 5x as much compared to CuSO4 which means much more
left behind when filtering off. Even when using strong vacuum filtration with CuSO4 I estimated about 10-15% loss due to adhesion to the salt. Next
time I will weigh my salt post filtration and then once it has dried (of the remaining ethanol).
If one were to use a carbonate, much more would be required and much more would remain adhereing to the salt. Now this can be over-come with
distillation of the salt post filtration, but if that isn't an option, then a salt with a higher hydrate form should be looked at.
As for Na2CO3, it is listed as slightly soluble in alcohols. I've seen it form the decahydrate in water (it forms somewhat clear large crystals) when
making a saturated solution from anhydrous carbonate.
MgSO4 is listed as slightly soluble in alcohols the same as Na2CO3. But the thing is that it should form the heptahydrate in the alcohol, which means
7 mole's of water! 120g anhydrous vs 246g for the heptahydrate. That means for every gram used you can absorb a little more than 1g of water! It
also forms lower hydrates so that is a good thing while drying as well.
MnSO4 is another one I'm interested in looking at as it is totally insoluble in ethanol and only "very slightly soluble" in methanol. I'm curious
about IPA. This would be a very good choice as well as the color change will indicate how strongly it has hydrated and it will pull 7moles
(heptahydrate) as well as the MgSO4. The MnSO4 can also be used to dry ether as it is insoluble in ether (as per wiki..)
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unionised
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It depends.
One important difference is that a solution of potassium carbonate will not mix with alcohol, so you can "salt out" alcohol with potassium carbonate,
but not with sodium carbonate.
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LearnedAmateur
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| Quote: Originally posted by RogueRose |
I'd try anhydrous Mag sulfate. It can absorb 7 water molecules so it should be pretty good at drying compared to sodium carbonate and it is easily
attainable |
If we’re going off the water of crystallisation then Na2CO3 would be better because it forms a decahydrate as opposed to the heptahydrate of MgSO4,
so that’s another 3 molar equivalents of water absorbed. Sodium carbonate becomes anhydrous at around 100C whereas it takes double that to fully dry
magnesium sulphate, so that’s something to consider if you’re starting from Epsom Salts. It’s still a reasonable option though, but I think here
the carbonate would win out, especially since it’s cheaper (anhydrous for both, IME) and can be used as a common reagent too.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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RogueRose
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| Quote: Originally posted by PrussianBlue | | I think I'll give MgSO4 and alumina (assuming I can powderize and dry some Boileezers) a try. If I can only attain around 95% EtOH, will
this still act to stabilize chloroform or does that require absolute? |
I can tell you with 100% certainty that CuSO4 works extremely well for this and I've used MgSO4 as well with much poorer results. I used a large
excess of anhydrous MgSO4 (not powdered, but fairly fine) and about 92% EtOH and after over a year sitting there, it is still at about 96%. I used at
least 4-5x the needed MgSO4 to dry the 3L of EtOH and I was sad at the reaction. I shook it 4-5x a day for 4 months, then once every few days for 4
months, then once a month the last 6-7 months. I'm thinking had I heated both, it would have worked much faster.
When I dried with CuSO4 (that was VERY fine powder), both started at 120F, enough heat was generated to boil the EtOH while in the bottle (glass media
bottle). It also dried it in about 5-6 mins using 450g anhydrous and 900ml 92% EtOH. It also leaves pure ethanol after and filtering through the
CuSO4 (once to extract first washing, then run through again to filter cloudyness out) left me with crystal clear EtOH.
If I were to try again, I'd powder the MgSO4 and heat both the salt and EtOH, but only if I was going to distill afterwards, otherwise I'd use the
CuSO4.
Just a thought. I know I was in your shoes for some time and didn't know what to believe from the different postings, so I tried them out myself. I
also tried corn meal and it left me with a yellow, gelatenous mess (no liquid left!)that I still need to re-distill and I started with ~94% EtOH.
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happyfooddance
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| Quote: Originally posted by Sulaiman | I remember (probably) reading somewhere here on SM about using dried rice or bran or some similar cheap organic source. ?
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Corn meal is used industrially in some places, to this day.
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RogueRose
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It may be used to break azeotrope but I don't think it is used as a "soaking" method. From what I have read it is often used in the distillation
column (or maybe even condensor - though I'd see the column working better) where the alcohol is in vapor and it may be easier to strip the water.
I'll show some pics of what the process does when using it like standard salt drying, it's a mess that looks a lot like jello.
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happyfooddance
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| Quote: Originally posted by RogueRose |
It may be used to break azeotrope but I don't think it is used as a "soaking" method. From what I have read it is often used in the distillation
column (or maybe even condensor - though I'd see the column working better) where the alcohol is in vapor and it may be easier to strip the water.
I'll show some pics of what the process does when using it like standard salt drying, it's a mess that looks a lot like jello.
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This is correct, but it is used only in the column, the condenser will not work, liquid etOH would just coat the sludge. Careful grain size selection
and careful column packing are needed to prevent blockage of vapor (and subsequent pressure build-up and potential explosion).
I don't think it would be practical or efficient at home. The only reason this method has been developed and used extensively is because, in America,
corn ethanol is a huge industry, and corn is the cheapest drying agent for a corn ethanol operation. It is basically free; they grow more corn than
they can sell or use.
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JJay
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Right now I'm entertaining an unexpected guest, but as soon as she takes off, I'm getting started.
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aga
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What alternative is required other than K3PO4 ?
How quickly people forget.
http://www.sciencemadness.org/talk/viewthread.php?tid=61746&...
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