Hi There,
I am trying to remove water from EMIM TFSI, I need to do electrochemistry on the ionic liquid afterward, so I need it very pure. I want to try using vacuum heating. What temperature and pressure do you recommend?
I also already followed the discussion on this forum but I still did not get my answer. Somebody mentioned freeze-drying which is quite easy to do for me, I was wondering if anyone has any info on that as well.
Thanks,
Dear Sima,
I'm not fully familar with EMIM TFSI, but have a done a little web research to see that it's not that nice to handle, is dense at 1.5g/ml and imiscible with water. What I can't find is a boiling point, but the freezing point is about +15°C. Also, I see the "store under inert gas" note.
Given the challenge of safety with many warnings over the MSDS to not inhale and be careful, I guess we must think about this in how we process it.
Depending on the volume of sample that you have, then various routes could be open to you.
I would be cautious about rotary evaporation here, the tumbling action may create aerosols and generally a rotary is not great at removing water unless really leak tight, all depends on the equipment you have at your disposal.
Freeze drying would work, you would solidify the EMIM product as the water freezes so be careful about formation of dust when you let the air back into the system. If you have access to one, use a system with shelves (not a flask dryer) as you have more control. Freeze the sample to below say -10°C with the shelf, then apply the vacuum when you have a solid sample. Then, before letting the air back in you can rise the shelf temperature to thaw the product. Also, a good shelf freeze dryer will let you connect an inert gas, and, if you need store and you put the product in vials, can close the vials with only inert gas inside. Typically, vacuum level would be 100mTorr for water to sublime at -40°C, but you'd be better off going higher, say to 200mTorr, or above. Challenge of deep vacuum is when the EMIM will sublime.
Alternatively, a centrifugal evaporator would be relatively fast, as the system spins that samples the EMIM will sing and water float. The best centrifugal evaporators also have an inert gas purge option. Benefit here is that you can boil water at a low temperature (not sublime it) using a less deep vacuum, therefore less chance to boil EMIM.
Common to all methods - caution ... what is the boiling point of EMIM, you don't want to start boiling / subliming it.
Hope this helps you chose the route ahead.
Regards
Rob
Thanks so much Rob, I only have access to flask freeze dryer unfortunately. However, the melting point of the salt is -16 C which would turn into liquid quickly after I remove it fro the freezer. I was not able to sublime it. And unfortunately I do not have access to that high of vacuum which is required which made this more challenging.
70-75 oC, 30 to 48 hr, with as high a vacuum as you have available. A turbo pump is best. A simple freeze dryer is not adequate. No it does not readily sublime - the vapour pressure is very low. [J. Chem. Eng. Data 2015, 60, 1408]
An alternative is to dry it isopiestically in an evacuated desiccator with clean, small pieces of sodium metal in a second container in the desiccator. This is very slow however & may take weeks, depending on the initial water content. And you must take care with sodium metal.
Dear Sima,
Here is maybe the answer that you wanted. We have used highly pure BMIM NTf2 as a medium for acidity measurement as well as, more recently, for electrochemical determination of oxidation potential for some commonly seen organic compounds. OK, Firstly, we always prepare the IL by ourself by ion exchange approach, or metathesis method, then the water in the ILs was removed by heating these ILs (not all, but for aprotic ILs this is OK, some of protic ILs may use a lower temp) around 60 deg C under high vacuum with agitation (you will need a very good oil pump, such as Edwards, etc) for overnight, normally by this way, the water content of less than 15-20 ppm can be achieved, which is monitored by Karl-Fisher machine. We have applied the BMIM NTf2 prepared by this way for the electrochemical purposes, so far we have not found any trouble due to the presence of 10-20 ppm of trace water.
Hope this may help,
Best Wishes,
Pengju Ji
- Badges
- Science topic
- Similar topics
- Chemistry
- Electrochemistry