Methanol Purification Help


#1

Hello,
I’m currently using methanol and water as my mobile phases on a separatory hplc. I read all around that methanol and water do not form an azeotrope, but I am finding it hard to separate the two based on boiling (evaporative) points. Have access to both a rotovap and FFE, not much luck getting over 97% purity though. and my 3A molecular sieves aren’t really doing much. Possibly drawing in moisture from the environment(?), I’m going to switch to sealed kegs and post my findings.

If anyone has some tips or pointers on how to better purify my methanol I’d greatly appreciate it. I really need to recover pure methanol so i don’t have to change my method/gradient all the time. If you have any questions on my processes, don’t hesitate to ask.


#2

Have you tested (& regenerated) your sieves?

How are you determining 97% purity?

I would expect 3A sieves or a reflux still head should get the job done.

Liquid Chromatography in a keg I can wrap my head around, but “high performance”?

This I’d like to see!!


#3

They come sealed (and i assume dry, but now it has me thinking). And I weigh them before they go in the methanol, and after they come out of the vacuum oven(250f under vac). Generally I lose some weight if anything, I’m thinking from silica dust particles since I keep them in mesh bags during the soak.:stuck_out_tongue_closed_eyes: . Is there another way to test them?

Yeah, so Im using a hydrometer meant for ethanol… Its probably not ideal, but i figured the densities were so close it shouldn’t skew my results that much. Any pointers there would be duly noted.

Thanks for the suggestion, Ill have to see if they offer a reflux attachment for my rotovaps.

I’m sorry I may have gotten my terminology confused. This is what Im using.
https://www.buchi.com/us-en/products/preparative-chromatography/reveleris-x2-uv

Thanks for your help. This seems a little harder than it should be for me. And it may very well be operator error lol.


#4

see: Molecular sieve beads

Without looking up the densities and doing the math, I suspect that that small difference is making all the difference in the world.

Edit: having looked up the densities of ethanol & methanol , and the temp compensation charts, I suggest you do the same rather than take my word for it.


#5

Are you trying to merhanol back ethanol? Innky use methanol and have been for many yrs, makes my filtering a breeze it pulls more fats at room temp. Just my 2 cents. From what I understand jt doesnt absorb water like etho does


#6

Methanol is hygroscopic just like ethanol.

@ShattersOcleary maybe try using mole sieve that’s meant for removing water from ethanol like this, I’m not sure what makes this different from the regular 3a sieve https://www.deltaadsorbents.com/3a-edg-molecular-sieve-desiccant


#7

methanol and water do form binary azeotropes. it will be hard to separate the two by distillation but it can be done


#8

I would use a big fractional column to distill with. We could probably build one for your rotovap if you want. Then use the good molecular sieves (they should heat when added to the solution).


#9

@ScoobyDoobie I haven’t seen those specific beads. Thanks for the info. Not sure what makes them different from their normal 3a sieves from delta adsorbents I have either.

@goldleaf_scientific Could you maybe elaborate on what kind of fractional column you mean. Just a vigreux column before the cold trap or a secondary coldtrap maybe? Or something more advanced?

@cyclopath Thanks for the link to that post. Good info, ill try baking the beads a little hotter.

Here’s a chart of temperature compensation for methanol using a hydrometer, as a reference for others viewing the post.


#10

You can make a fractionating column out of a long spool and a packing material like stainless scotchbrite pads, the scrubby pads act like the fingers inside a vigreux.
If you have a closed loop system it would only take a second to set the triclamp pieces up like small still to fractionally distill your methanol.


#11

Normally in most rotovaps the vapor duct connect horizontally to the condenser. To purify methanol or any alcohol you would need for that to be vertical and connect to the top of the condenser. Some Buchi models have that feature.
If you put some vigreux on the bottom and then pack it you’ll have a very nice fractional column. We can do some custom glass work if you are interested. This would be an easy retrofit.


#12

A Snyder column seems to fraction volatiles pretty well. I had one for running my reclaimed solvent but broke it after lashing it up as a aersol trap in an experiment testing viability of capturing aersol. I had hoped to run a vaporizer input into the system but the glass buibs of the column broke from it.

Still though it is a very cool piece to watch in action and works a very high efficiency for sovent recovery.