Sciencemadness Discussion Board - Alternative Ethanol Drying Agent

Alternative Ethanol Drying Agent

PrussianBlue - 23-3-2018 at 04:24

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.

LearnedAmateur - 23-3-2018 at 05:28

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.

JJay - 23-3-2018 at 06:18

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.

Tsjerk - 23-3-2018 at 08:34

@ 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.

JJay - 23-3-2018 at 16:53

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.

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.

JJay - 23-3-2018 at 16:59

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?

PrussianBlue - 23-3-2018 at 17:33

CaCl₂?

[Edited on 3-24-2018 by PrussianBlue]

Dr.Bob - 23-3-2018 at 17:54

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.

PrussianBlue - 23-3-2018 at 18:11

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?

JJay - 23-3-2018 at 18:22

Quote: Originally posted by PrussianBlue

CaCl₂?

[Edited on 3-24-2018 by PrussianBlue]

It's a powerful drying agent, but it is soluble in alcohols.

JJay - 23-3-2018 at 18:30

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.

Sulaiman - 24-3-2018 at 02:02

I remember (probably) reading somewhere here on SM about using dried rice or bran or some similar cheap organic source. ?

RogueRose - 24-3-2018 at 04:24

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]

Dr.Bob - 24-3-2018 at 05:08

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.

S.C. Wack - 24-3-2018 at 06:15

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.

PrussianBlue - 24-3-2018 at 06:37

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?

RogueRose - 24-3-2018 at 06:37

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..)

unionised - 24-3-2018 at 06:43

Quote: Originally posted by PrussianBlue

Can potassium carbonate be substituted with sodium carbonate for ethanol drying?

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.

LearnedAmateur - 24-3-2018 at 06:50

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.

RogueRose - 24-3-2018 at 06:52

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.

happyfooddance - 24-3-2018 at 09:18

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. ?

Corn meal is used industrially in some places, to this day.

RogueRose - 24-3-2018 at 10:05

Quote: Originally posted by happyfooddance

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. ?

Corn meal is used industrially in some places, to this day.

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.

happyfooddance - 24-3-2018 at 12:53

Quote: Originally posted by RogueRose

Quote: Originally posted by happyfooddance

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. ?

Corn meal is used industrially in some places, to this day.

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.

JJay - 24-3-2018 at 12:54

Right now I'm entertaining an unexpected guest, but as soon as she takes off, I'm getting started.

aga - 24-3-2018 at 15:01

What alternative is required other than K₃PO₄ ?

How quickly people forget.

http://www.sciencemadness.org/talk/viewthread.php?tid=61746&...

PrussianBlue - 24-3-2018 at 17:37

Aga, what are the easiest sources of KOH and Phosphoric acid? KOH doesn't seem terribly expensive on ebay and I found a 35-45% phosphoric acid source (https://www.homedepot.com/catalog/pdfImages/ac/ac25e93c-5593...), but I'm wondering if there's an easier way. My reasoning behind the previously discussed options is that I already have them or can very easily obtain them locally.

aga - 25-3-2018 at 00:44

I got my KOH online.

The H₃PO₄ is/was green agricultural grade stuff.

XeonTheMGPony - 25-3-2018 at 04:44

Go to any local spa place and ask for a spa flush, usualy it is near pure phosphoric acid with perhaps a bit of dye in it, but every where is different so read the bottle

PrussianBlue - 25-3-2018 at 18:33

Has anyone ever tried and/or heard of this? Probably isn’t very cost-effective, but interesting nonetheless.

CD5CDE11-63B5-4F36-B95C-CE11310432D2.jpeg - 133kB

JJay - 27-3-2018 at 16:48

Ok, I am finally getting started on this....

JJay - 29-3-2018 at 16:38

Oven drying my potassium carbonate resulted in little change in texture aside from some clumping at the bottom of the mixture (so it was not anhydrous).

Adding oven-drived potassium carbonate to a vial of quintuple distilled 191 proof rum resulted in some minimal clumping and a small but perceptible temperature increase. I'm drying out some copper sulfate....

JJay - 29-3-2018 at 19:08

My copper sulfate is discoloring the ethanol. I think it contains an impurity... ferrous sulfate, perhaps. Ugh...

RogueRose - 3-4-2018 at 14:05

Quote: Originally posted by JJay

My copper sulfate is discoloring the ethanol. I think it contains an impurity... ferrous sulfate, perhaps. Ugh...

Mine was like this as well when I dried with CuSO4, maybe not quite as bad but it was cloudy and a brownish color. Even if there is some FeSO4, very little would dissove in the ethanol unless there is a lot of water in the ethanol you are trying to dry.

You need to filter the ethanol through the CuSO4 and it will probably be cloudy. Then run it through the CuSO4 again and it should remove the cloudyness, that is what I did and mine is extremely clear.

How fine was the CuSO4 you used? Was it powdered or just small crystals. The filtration should work if it was powdered.

Another option would be passing it through a little bit of activated carbon powder if the CuSO4 doesn't filter it out.

What temp did you dry the sulfate to and what color was it?

Is the alcohol the rum you started with, the 191 proof? Was it clear or did it retain some color if it was amber to start with?

[Edited on 4-3-2018 by RogueRose]

JJay - 3-4-2018 at 17:46

Quote: Originally posted by RogueRose

Hmm... you raise a good point... ferrous sulfate probably wouldn't turn green under those conditions either....

I am pretty sure my CuSO4 was not quite pure because I could see some grey/brown discoloration in it after I dehydrated it before I powdered it.

I always wondered why recrystallizing CuSO4 was such a popular experiment

I checked the ethanol with a hydrometer right before the experiment. It came in at 191 proof. The ethanol is clear and has low odor. I haven't treated it to remove ketones, esters, aldehydes, acids, etc., but I expect that they are present in very low amounts.

[Edited on 4-4-2018 by JJay]

RogueRose - 3-4-2018 at 21:02

Quote: Originally posted by JJay

Quote: Originally posted by RogueRose

The discoloration is totally normal for CuSO4. Did you dry it in an oven? I've done it under a broiler and by just baking it at 500 - 550F.. The decomp point of CuSO4 is about 1040F so I doubt I've ever gotten it that hot. I thought I was getting some CuO on the top where it was exposed to the broiler, but the same happened when I baked it, the top got brown.

The odd thing is mine turns pinkish-grey when it is dehydrated, then when exposed to air for a few hours, it turns white (which is supposed to be the anhydrous color), then I get a very light blue, then the normal blue of the pentrhydrate. I believe there is a monohydrate as well which may be the white/light blue.

Like I said, filter the ethanol through the sulfate, twice, and I think you will have good results. When I used vacuum I pulled about 20% more ethanol out of the sulfate as it adheres to the salt and when under vacuum it becomes a texture somewhat like mildy damp sand - it is a strange texture, feels damp, but is totally dry (no water, just EtOH that evaporates quickly).

Reusing the sulfate is really easy after you have powdered it and used it to dry. Just heat and then it crushes to powder again very easily.

MrDoctor - 13-9-2022 at 23:26

is it totally neccesary to dry it ALL the way though? i recently had a conversation with someone that told me, above 95% only the 95% azeotrope boils out, meaning that you can seperate something like 98% into an almost equal volume of anhydrous and 95%, and just repeat the process using easily regenerated simple desiccants. i cant find any literature that confirms this, but i also cant find any explicit information to the contrary either, and they swear to the success in a few applications that do demand >99% ethanol.

I realize it might not be a substitute but it does appear to eliminate the need for an unreasonable degree of thoroughness, for quickly deriving absolute EtOH from 95% hardware store spirits. I was only entertaining this line of thought at all because my 3A sieves are a VERY long way away and i just ran out of absolute EtOH

pneumatician - 18-9-2022 at 12:46

Pop-Sci

[Edited on 18-9-2022 by pneumatician]

PirateDocBrown - 19-9-2022 at 08:38

For methanol or ethanol, powdered magnesium, let the hydrogen evolve, then distill off the alcohol from the MgO residue in the pot.

Store on sieves.

[Edited on 9/19/22 by PirateDocBrown]

Dr.Bob - 20-9-2022 at 11:19

I know that mole sieves and alumnia are used commercially for drying ethanol now, few places use benzene azeotrope, due to hazards.

Mateo_swe - 4-10-2022 at 09:22

Quote: Originally posted by aga

What alternative is required other than K₃PO₄ ?

How quickly people forget.

http://www.sciencemadness.org/talk/viewthread.php?tid=61746&...

The K₃PO₄ method sounds very nice but how hard is the salt to make from KOH and Phosphoric acid?

From the thread:
"K3PO4 was prepared by reacting 3 mol equivalents of KOH with phosphoric acid.
This is a bitch to get to crystallise and dry, however determined boiling and a couple of hours in an oven @ 130 C worked to yield dry white powder (the hydrated crystal lumps are rock hard, a bit like Al Sulph)."

Do one need to pulverize the rock hard K3PO4 before the ethanol dehydration?

Maybe its easier to use the CuSO4 method, it seems very straightforward and i have read many successful attempts using this method.
And it doesnt need to be distilled afterwards, just filter and its ready for use or storage over some dried 3A mol sieves.

Dr.Bob - 4-10-2022 at 15:53

You can still buy Trisodium phosphate at many hardware stores as TSp, but some have been swapped with other compounds. I think in Cal, they sell something useless as "TSP" like sodium bicarb.

Bedlasky - 4-10-2022 at 16:48

But don't forget that Na3PO4 is usually sell as dodecahydrate.