Vigreux column: 200mm vs. 300mm

So my 300mm Vigreux column just broke and I'm looking to buy a new one. Because the 300mm length was a serious pain in my ass to handle, I considering buying the 200mm length instead.

Does anyone know how much of a step down it would be to "cut off" those 100mm, in regards to the quality of separation?(for most mixtures)

Thanks, Ben


Edit: The 300mm has 8 "steps" vs the 200mm who has 6 "steps".


[Edited on 12-10-2019 by B.D.E]

To a first approximation, you might say the HETP (height equivalent to a theoretical plate) will be reduced by 25% ({8-6}/8) or 33% ({300-200}/300. But from what I recall from various readings, a Vigreaux column is not all that efficient for fractional distillations anyway. They are probably just a good way to keep "splash over" from bumping or too vigorous boiling getting into the distillate. This is just my 2 cents (and is probably not even worth that much ). I would go with the shorter column just for the sake of convenience.

Quote: Originally posted by Sulaiman

you could buy two shorter Vigreux colums and use one or both to suit the situation ?

Quote: Originally posted by Sulaiman

I've only used Hempel columns (air condenser(s) packed with stainless steel wool if compatible with distillate, or 6mm dia. glass spheres otherwise) (the glass spirals required for the glass spheres are uncommon, expensive and fragile)

Quote: Originally posted by B.D.E

...do you think I can just use 6mm clear glass beads instead (https://www.ebay.com/itm/321001254218)? ...

Quote: Originally posted by Sulaiman

Quote: Originally posted by B.D.E   ...do you think I can just use 6mm clear glass beads instead (https://www.ebay.com/itm/321001254218)? ... I think that the holes would cause significant holdup, and make cleaning and drying much more difficult. The flat faces would rest against each other reducing the effective area. So glass spheres would be better e.g. https://www.ebay.com/itm/Outer-diameter-2-5-12MM-Laboratory-... They are effectively infinitely re-usable. Broken glass pieces from a vigreux column (or any column or flask etc.) would tend to stack against each other reducing area, and gas flow would be very uneven, bypassing liquid:gas interface area, and probably allowing condensed liquid to fall a long way down the walls, all of which would reduce fractionating efficiency. P.S. If I ever get a suitable saw, I like the idea of cutting rings from glass tubing as it should be significantly more efficient than spheres. [Edited on 18-10-2019 by Sulaiman]

Quote: Originally posted by B.D.E

... How about Copper mash? https://ebay.com/itm/Fermfast-Solid-Copper-Mesh-Roll-For-Pac... Unlike iron it's non reactive with most liquids, it's cheap, relatively uniform in structure and definitely porous enough for gas movement...

I've not tried copper, but ethanol distillers seem to like it as it reduces some of the sulphurous byproducts of fermentation.
http://homedistiller.org/wiki/index.php/Boka_Reflux_Still_-_...

Stainless steel in the form of pot scrubbers is compatible with many distillates,
e.g. https://www.ebay.com/itm/Stainless-Steel-Scourer-Wire-Pot-Di...VwAAOSwENVb5TCE

Alright then, copper mash it is!(I am also buying the hollow beads, just because they're cheap af ).

I'm really happy that I asked this question. Not only that I now have a better overall understanding of fractional distillation, I also learned a new and more efficient method for doing it

Sorry if was a bit spoon fed towards the end.


Thanks again for everyone who replied, I really appreciate it.

Quote: Originally posted by Ubya

well they are cheap, you could try using them, they won't be the best but better than an empty column (i have a 30cm vigreaux column, i regret buying it)