Sciencemadness Discussion Board

Using a rotovap as a crude form of fractional distillation?

SuperOxide - 9-2-2025 at 12:23

This is probably a very amateur question, but I was curious just how feasible it is to separate volatile mixtures using a rotary evaporator.

Obviously I wouldn't be able to switch out collector flasks, and the "fractioning" power would be somewhat limited. But if I were to use something like a bump trap with a coarse frit in it, or even a very short extension packed with some steel or glass wool, that would give some fractioning power. Then I would know the vacuum pressure and can monitor the vapor temperature before the condenser (if the condenser has a port for it).

I'm sure someone here has tried it, I'm curious how it worked out. How far apart do the boiling points need to be to make this feasible?

Sulaiman - 10-2-2025 at 10:28

The number of effective plates for a fractionating column is a linear function of the surface area of liquid-vapour contact,
and a .non-linear function of reflux ratio

it would be fairly simple to add surface area
(eg as you described, steel or glass wool in an extension tube)

for reflux you could use air cooling (like a Vigreaux column)
but the fractionation will be poor (like a Vigreaux column)
in my opinion, a packed Vigreaux column performs very well due to the indentations directing liquid flow from the column walls to the column centre
but this needs a reflux condenser.

For fine fractionation you need an insulated packed column with a reflux condenser.

Suppose that you can arrange for surface area and reflux
you would have very poor fractionation if the column is not vertical
because otherwise you will get a lot of channeling.
(liquid would just flow back to the pot bypassing most of the column packing)

IF I had a rotovap
I would rather buy a cheap distillation kit, than risk damage or wear to my rotovap

SuperOxide - 10-2-2025 at 16:15

Quote: Originally posted by Sulaiman  

Suppose that you can arrange for surface area and reflux
you would have very poor fractionation if the column is not vertical
because otherwise you will get a lot of channeling.
(liquid would just flow back to the pot bypassing most of the column packing)

I haven't heard of "channeling" before, Interesting.

Quote: Originally posted by Sulaiman  

IF I had a rotovap
I would rather buy a cheap distillation kit, than risk damage or wear to my rotovap

Im not so sure that wear would be an issue if I tried it once or twice. I was just curious if anyones tried it before. But I do see your point.

Thanks for the reply!