Runningbear
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Separating DCM and methanol
If you have a mixture of DCM and methanol and you plan to separate them using fractional distillation, could you add anything to the mixture to help
make the separation cleaner? (assuming you didn't plan to save the methanol). Or is the temp difference enough to make the fractions very clean.
thanks in advance,
Runningbear
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JohnWW
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Have you looked on Google for any data suggesting whether DCM and methanol form an azeotrope?
P.S.: They DO, unfortunately, form an azeotrope! See http://www.solvent--recycling.com/azeotrope_1.html , which says:
Component A: Dichloromethane
Component B: Methanol
Boiling Point A: 40 °C
Boiling Point B: 64.5 °C
Azeotrope Boiling Point: 37.8 °C
Azeotrope Wt.% A: 92.7 %
This means that it is a constant-minimum-boiling-point azeotrope, like water-ethanol, preventing further purification by only distillation beyond
92.7% dichloromethane.
[Edited on 11-10-09 by JohnWW]
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entropy51
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Quote: Originally posted by Runningbear  | If you have a mixture of DCM and methanol and you plan to separate them using fractional distillation, could you add anything to the mixture to help
make the separation cleaner? (assuming you didn't plan to save the methanol). Or is the temp difference enough to make the fractions very clean.
thanks in advance,
Runningbear |
Since you don't want the methanol, why not just wash the methanol out with water? Doesn't get much cleaner than that. You can then dry the DCM and
distill it.
There's at least one thread on this, in one of which Magpie described his method. Best to look at it.
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Runningbear
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thanks guys,
I have tried the wash with water Entrophy, but there is some type of emulsifier present that is creating three layers, the middle layer being this
messy soap like mixture. It's reducing the yield on the DCM from 87% to about 20%.
I thought there might be another option but I may have to go back and experiment with different wash techniques.
thanks,
Runningbear
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entropy51
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Runningbear, that's the reason I suggested consulting that other thread. You said CH3OH and CH2Cl2, no mention of other junk being present. I
thought about mentioning it, but didn't. Sorry, I should have known better, but took you literally.
Do a quick distillation so that both CH3OH and CH2Cl2 distill over. Don't distill too close to dryness, or the other crap will mess up your flask.
(You could even try putting a little mineral oil in the pot to keep the junk from sticking to the distillation flask, just an idea, I haven't tried
it.)
Wash the distillate, now free of emulsifier with water to remove the CH3OH.
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mr.crow
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How much methanol should you put back in when its distilled? To prevent it from turning into phosgene
So its
1) Crude distill
2) wash with water to get rid of ~10% methanol
3) dry with CaCl2
4) fractional distill
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entropy51
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| Quote: Originally posted by mr.crow | How much methanol should you put back in when its distilled? To prevent it from turning into phosgene
So its
1) Crude distill
2) wash with water to get rid of ~10% methanol
3) dry with CaCl2
4) fractional distill |
CH2Cl2 won't turn into phosgene when distilled, with or without CH3OH. Just don't distill to dryness (not ever, not anything).
Yes, that's a procedure that works for some of the commercial mixtures, but it might depend on what else is in the mix.
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mr.crow
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Oh I mean putting methanol in for storage, sry
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entropy51
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Sorry, I misunderstood. I've put ethanol in CHCl3 to prevent COCl2 formation, but I've never heard of needing in in CH2Cl2. Maybe I'm missing
something. I think even CHCl3 may not really need it if kept tightly closed, cool and dark, but I do it anyways. I guess it couldn't hurt, but I
would use very little, certainly less than 1%.
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Runningbear
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thanks entrophy. The answer is kind of obvious when you spell it out like that
Runningbear
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