mycotheologist
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Simple fractional distillation setup
I don't have any proper, packable columns but I have a 2 condensers. First one is a B49/52 (or something like that I don't remember the exact figures)
liebig condenser and the second one is a 14/23 Allihn condenser. Could I setup a fractionating apparatus by connecting the Allihn condenser,
vertically, to the boiling flask. Then I attach a still-head to the top of the Allihn condenser and use the liebig as the receiving condenser. Should
I do it like that, or the other way round with the larger condenser as the column? I suspect I'm going to have terribly slow distillations due to the
Allihn condenser small joints.
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Magpie
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I use a Hemple column as a fractionating column as it has 3 small indents near the bottom that support the packing. Other than that the Hemple is
just like a West (or Liebig) condenser.
I've never heard of using an Allihn as a fractionating column and it may be very inefficient. I would go the other way. However, the pooling of
condensate in the Allihn "bubbles" may, or may not, be a problem depending on your separation goals.
[Edited on 21-3-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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peach
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Packing an Allihn and using it vertically is likely to cause it to flood with the constrictions in it (the distillate ends up stuck in the column, as
a liquid, gurgling away and not separating correctly). It may flood so well it lifts it's self out of the joint with the pressure building up
underneath it; the vapour will then end up in the air. If you try wiring it together or rigidly clamping it, and it does flood, it may burst the flask
with the pressure having nowhere to go.
Without packing, the distillation will run, but you likely won't get great separation with such a simple path in the way.
It really isn't a great combination. If you use the Liebig as the column (which is fine), you'd then have the Allihn as the condenser. If it's at a 45
degree angle, you'll end up with big puddles sitting in it, which somewhat voids the point of doing a fractional distillation.
Are you sure about those joint sizes? Do you mean 45/50? Either way, one of those is process glass size (for doing five -> 100l litres) and the
other is mini/micro (for doing 5 -> 250ml).
What are you distilling and how much of it? Is this a one off or are you asking generally?
[Edited on 21-3-2012 by peach]
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mycotheologist
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I'm asking generally but the problem I have in mind is fully separating nitromethane from methanol. I distilled the methanol but it smells of
nitromethane. I'd also like to be able to concentrate dilute solutions to their azeotropic compositions without having to do multiple distillations.
For example, if I want to concentrate a 10% solution of HCl to 22%, God knows how many times I'd have to distil with a simple apparatus. I'll invest
in a column one of these days.
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peach
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Methanol and nitromethane form an azeotrope with each other, so they can't be fully separated by column distillation alone.
If you do buy a column, don't get one larger than a foot or ft and a 1/2 because they start getting difficult to handle when the apparatus ends up a
meter tall with a kilo of liquid moving around.
[Edited on 22-3-2012 by peach]
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