Heinrich
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Water removal from ionic liquid
Hey guys, i've been lurching on this forum for ages now so i thought i'd finally sign up an account as i have a problem i can't seem to solve myself.
Any input/thoughts/ideas would be greatly appreciated.
I'm making an ionic liquid, in this case a near-eutectic mixture of carbamide (urea), acetamide and magnesium perchlorate. All of these chemicals are
solid at room temperature, however it forms a liquid when mixed at right ratios, thanks to thermodynamics (it also exhibits signs of supercooling
under 20C which is pretty cool). The purpose for this liquid is to function as an electrolyte in a Mg-ion battery prototype that i am developing.
This means that the liquid cannot contain any traces of water at all (as this will immediately react with Mg and ruin the battery).
I've tried various methods of removing water, such as pre-drying of raw materials and also boiling the ready-made liquid in a glove box. Furthermore,
i have tried adding molecular sieves (4A) which ended badly, and i have also tried pre-reacting all water with Mg, but this releases hydroxides into
the liquid which has a very negative effect. I've also tried ordering high-purity chemicals, but that didn't help much (i'm doing my work in China-
"anhydrous" means "max 2%" apparently)
I have a limited lab at my disposal, but i really don't know enough organic chemistry to come up with a solution on my own. Any suggestions would be
greatly appreciated 
Cheers,
Heinrich
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Saerynide
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Maybe try the freeze drier or vacuum oven?
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Heinrich
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I tried using a vacuum furnace at near-melting points for all the 3 materials for 48 hours, with some improvement however not enough.
Freeze drier might work, hadn't thought of that, but unfortunately i don't have one available and my budget is rather stretched. Any other
suggestions?
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Saerynide
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Borrow the freeze drier from the institution next door haha.
Or maybe mix the materials with solvents that forms azeotropes and distill off the solvents taking with them the water?
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Heinrich
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Normally that's what i would have done, but here in China that's not how things work (and trust me i'm getting the hell outta here- however, equipment
is dirt cheap, vigreux columns goes for ~1 USD, considering starting import company to Europe). In fact, there is a group at the institution next door
working on the same project as i am, but cooperation is not an option. Terrible if you ask me.
I'll look into possible azeotropes but that process is going to be a bitch considering how hygroscopic the solution is, are you sure it's even
possible?
Thanks for reply 
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Saerynide
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I'm not entirely sure the azeotrope thing is possible. I've never tried. I'm not an organic chemist either. I'm a chemical engineer. I just
thought about it based on the reasoning that if you have wet things like glass that you want to dry faster, you wash them with acetone or EtOH and the
solvent takes away the water and leaves your stuff dry. But maybe the materials are too hydroscopic for that? I forgot to mention that maybe before
you strip the solvent, dry the solution with a drying agent first to remove as much water as possible?
But I mean, urea is cheap, so you can try it first and if it doesnt work, there isn't much to lose 
Or grind the materials to powder under an inert atm and then vac and bake again and for even longer? I use the vac oven all the time and it can take
several days to drive off the water.
But I think the freeze drier does a better job of making things anhydrous than the vac oven, in my experience. My product that comes out of the
freeze drier is light and fluffy whereas the vac oven product is a bit crystaline still.
[Edited on 3/14/2011 by Saerynide]
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Nicodem
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You would better try drying the urea and acetamide first (for example, in a desiccator over P2O5 under vacuum), because once you mix them with
Mg(ClO4)2 you get a hygroscopic mixture which sounds like much more difficult to dry.
Then, if you want to try drying it azeotropically you should use a solvent which dissolves the ionic liquid, like propanol or isopropanol, for
example. Toluene might not do much as it is immiscible and thus can only take away the amount of water limited by the partial pressure above the ionic
liquid (which is close to zero due to hygroscopicity). But even with azeotropic drying you might later have troubles removing the traces of the
alcohol used (though urea and acetamide should coordinate Mg2+ better than propanol, it is still an equilibrium).
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Heinrich
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Thanks for further suggestions. I'll hit the equipment store to see if i can find a vacuum desiccator. They should be retardedly cheap here. I'll use
P2O5 as you suggest Nicodem. Would it be an idea to combine with molecular sieves?
I'll look further into the solution with azeotropes but i am generally against adding anything directly to the compound, as you say, it will most
likely leave some traces and that's most definitely going to be noticed in a battery cell when using a sensitive potentiostat.
I've been fiddling with the idea of doing an electrolysis to remove the water (that's more along the lines of what i do, i'm a materials scientist),
but it would have to be done before addition of the perchlorate. I might try adding some MgSO4, it should dissolve just enough to allow for an
electrolysis of the water.
Thanks again
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Saerynide
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Our lab's giant vacuum desiccator imploded a couple months ago, shortly after I put in my samples... Good thing it was in the fume hood. I'd be wary
about buying a cheapo no brand one, especially from Mainland
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froot
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Won't Mg dehydrate acetamide to acetonitrile? If so this is where your water problem may be.
Hope I make sense, lets see.
What I'm seeing here is that urea and acetamide forms a deep eutectic solvent - media for ion transport, while the Magnesium perchlorate provides the
active ions in the cell chemistry.
What would the benefits of this solvent be in comparason to commonly used solvents like ethyl carbonate used in Li cells? Ion solubility? Could you
use acetonitrile instead?
I am veryinterested in new and simpler battery ideas and busy doing research myself in anhydrous cell chemistries. Busy looking into developing a K
ion cell at the moment.
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Heinrich
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@Saerynide: Tell me about it, these things can be really dangerous. But then again- if you can get a 20L desiccator + silica gel for a grand total of
~20 USD, it's kinda worth the risk. I mean, how much are these in the US? In Norway, where i'm originally from, i believe they would go for about
2-500 USD depending on size. Anyway it's great for cheap labware like beakers, pipettes and basic organic glassware, but anything involving vacuum
or accurate measurements for volume i'd probably chose to go for some more reliable stuff.
@froot: I'm terrible at organic chem, but i believe that the acetamide can withstand dehydration from Mg, even when it is polarized anodically. I did
an exposure test (in a glove box) where i put some Mg strips into the liquid- bubbles formed, most likely hydrogen (or chlorine if perchlorate is
involved). A few hours later, i removed the oxidized Mg-strip and put in a new, freshly polished one, this time there was no reaction. The
near-eutectic composition i employ contains 0.57 mole fraction acetamide, so if that's the case, the reaction would have continued. Also, it would
probably get more liquid, as acetonitrile is quite fluent at RT (ionic liquid is viscous). Instead, my liquid turns more viscous.
The electrolyte i'm using is basically just a reproduction of two articles written by S. Sampath, India. You can search them up, they're published in
Journal of Power Sources, 2010 and Electrochemistry Communications, 2009, search for key words "room temperature molten electrolytes".
I believe that the perchlorate is far more involved in the reduction of the MP than the Urea, as a binary ionic liquid between acetamide and
perchlorate is also possible. I've tried both, and i find that addition of urea makes it far less viscous.
I am in fact not used to room temperature ionic liquids so i can't say much about carbonate, but most likely it will have a positive effect on
conductivity. What about the decomposition potential? Wouldn't want any CO2-buildup during charging. Seen button cell batteries explode, it can be
some nasty shit. I have never worked with acetonitrile (and frankly, we don't have the proper equipment to do thorough analysis of electrolytes, so
i wouldn't want to begin either )
I am a huge fan of sodium and potassium based batteries. They should be way easier than Mg-ion batteries, the double charge obstacle is a real bitch
to overcome. Also, finding Na and K conducting electrolytes should be far easier, and it should be possible to make low temperature batteries (-50C)
with decent efficiencies & capacities.
Use of RT molten salts (ionic liquids) is considered a very promising field for future electrolytes in Li/Mg(Na/K,etc) battery cells. They're safer
and exhibit a wider electrochemical window. And best of all you have no *#!ing electrolyte leak through the rubber seals! Do let me know if you
believe we can benefit from each others experiences with battery cells.
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