[Cheemistree8889]

How would one go about a fractional distillation in which they would collect ~30 fractions under vacuum?  The fractions themselves do not have to be under vacuum although the fractioning column would need to.  I think I may use a spinning type of distillation column to get a high number of theoretical plates.  Any thoughts on set-up?  I do understand the set-up of a normal fractional distillation, just a little hazy on how to alter it to my needs.

Thanks in advance

[Arkcon]

30 vacuum distilled fractions? Yeouch.  I don't think they make a pig, or a cow with that many vessels.  If they do, it's probably very expensive, or a special order. 

You may have to split your distillate into groups, either 3-4 per fraction, then fractionally distill those.  Or get the first few, stop heat, break vacuum, change the pig, start again.  You'll lose yield, of course.

Consider, do you need to vacuum distill each fraction.  Can you break your analyate up into groups with other separation methods?

[Cheemistree8889]

What about a spinning band column set-up?  I just found out what these were today and pondering the thought.

[Arkcon]

If you're doing a fractional distillation, there are a number of options to enhance plates, like you've mentioned, to insure better fractionation.  Thirty samples is a lot, so that would be useful.

If you're doing a vacuum distillation, you want to remove air from the interior, so the reduction in pressure allows you to distill at lower temperatures.  The system is not under vacuum anywhere unless it is under vacuum everywhere, from boiling flask to column to condenser to receiving vessel, for the duration of the distillation.

If you want 3 or 4 or 5 vacuum fractional distilled fractions (say that 5 times fast) you'll want the receiving flask to be a pig or a cow -- an attachment that allows you to rotate a different flask underneath the condenser with each fraction without breaking vacuum.

I don't believe there exists technology to collect 30 separate fractions without breaking vacuum, is what I was getting at in my first response.

You have 30 fractions to distill?  Think about it, what are their boiling points?  If you evacuate, you may lower their boiling points so much, they may not fractionate, even with the spinning band column.

[Cheemistree8889]

Well what if I can cut off the vacuum to the collection tube?  Wouldn't that work?  Like with a stopcock... Switch the fractions then re-evacuate the collection tube?

[Arkcon]

Well what if I can cut off the vacuum to the collection tube?  Wouldn't that work?  Like with a stopcock... Switch the fractions then re-evacuate the collection tube?

Sure, if they make those, or you can jury rig something like that up.  Beats having to re-evacuate the whole rig.