[curiouscat]

I've a liquid stream with almost 85% of & ~3%  of Methyl Ethyl Ketone (balance being some dissolved high boiling crap).

To strip out this MEK in a batch fractionating still (vacuum) is proving very difficult & long. Does anyone know of any tricks / ideas to speed this up? If not distillation, any other ideas? Reactions?  Azeotropes?

Further, given the ~60 C difference in boiling point would you guys expect it to be so difficult?

We need to bring the MEK to below 0.05% (w/w)

[discodermolide]

Don't use a vacuum. MEK boils at 80°C I would imagine your compound would be higher. With only 3% to remove this is going to take quite a while.
But check thermal stability first especially under extended thermal load.

[curiouscat]

Don't use a vacuum.

Thanks @disco! I'll try that! Wouldn't a vacuum help the relative volatility? That was my understanding.

With only 3% to remove this is going to take quite a while.

That's precisely the problem.

Oh, but it wouldn't be any easier say it were 10% would it?  It's the final target MeOH % being very low that's the problem? Or do I misunderstand this?

[curiouscat]

But check thermal stability first especially under extended thermal load.

We've heated under a moderate vacuum at ~120 C for more than 36 hours with no ill effects. I think the atm. BP is around 150 C.

[discodermolide]

Sure a vacuum would help, but it may hinder the fractionation. Have you tried a thin film evaporation? Can't remember what the machine is called
Have you a molecular still? You could do this quite fast with a three column unit.

[curiouscat]

Have you a molecular still? You could do this quite fast with a three column unit.

No we don't unfortunately. Would be mighty expensive at plant scale too I guess.