Stacking Columns for Ethanol Fractionation - Snyder vs Vigreux

[MoleMan]

I am fractionally distilling ethanol out of solution.
I have done this with a Snyder column (3-ball)and most of my fraction came over between 79°+ and 83°.
I am wanting to improve upon this and am thinking about stacking a Vigreux in there.

Should the assembly have the Snyder on the top or the bottom?

 

[chemisttree]

Were all three balls chattering throughout the distillation? If not you might have had a column that was flooding. If they were, it probably doesn't matter how you place the vigreux column but I would place it on top of the snyder and be careful of flooding. The longer the column, the more likely you will need to insulate it to be able to maintain a distillation.

 

[MoleMan]

Thanks for the reply.

To answer your question. Yes the Snyder was insulated with the ol paper towel/Al foil-sandwich wrap. It chattered away for hours.

I am now running the Vigreux column separately to see what temp the ethanol comes over at. I expect it to be slightly higher as I have read that a Snyder is more efficient than a Vigreux.

If I could stack columns instead of multiple passes it would be nice.

What are your thoughts on efficiency, 200mm Vigreux vs. 3-ball Snyder.

 

[chemisttree]

I think the Vigreux would have more theoretical plates but technique will determine the actual efficiency. Don't distill too fast. Temperatures can fluctuate if the pot is overfull, there is bumping and if the pressure in the lab changes. Opening the lab door or sliding up the hood's screen can have some big effects on atmospheric pressure in the lab and the hood.

 

[DrBob]

I use a 3-stage Snyder column regularly, and the time it takes to the separation is literally half that required for a Vigreaux colummn of twice the length...and, the Snyder column does a far better job of separation! It would seem that a 3-stage Snyder beats a two-foot Viugreaux.

DrB