B.D.E
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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]
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CharlieA
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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.
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Sulaiman
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I agree with CharlieA - even though I do not have a Vigreux column.
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)
As fractionating power is linearly related to liquid-gas contact surface area,
you could buy two shorter Vigreux colums and use one or both to suit the situation ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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fusso
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I 2nd this.
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B.D.E
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Knowing that I'm rethinking if it's even worth buying. I Can instead just buy air condenser and use it as Sulaiman suggested.
Btw, combining 100&200mm column would definitely be the worst thing for me. It would be even longer then a regular 300mm column and I don't
believe it will fit inside my fumehood.
Much thanks to everyone, appreciate it ❤️
[Edited on 13-10-2019 by B.D.E]
[Edited on 14-10-2019 by B.D.E]
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Praxichys
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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)
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I have had good luck with glass Raschig rings. They are cheap on eBay and don't have the extreme surface-area-to-volume ratio (and thus, a long time
for he column temperature gradient to stabilize) or heavy weight of glass spheres. I have had issues with column flooding with spheres as well.
Raschig rings are also stronger than the spirals and much cheaper. They appear to simply be chopped bits of glass tube.
They aren't too expensive to buy:
https://www.ebay.com/itm/Glass-Raschig-Rings-Distillation-Co...
But you can make them yourself a lot cheaper by buying a pack of 6mm glass tube and taking them 3 or 4 at a time to a tile saw to chop them into
pieces.
https://www.amazon.com/Ginsberg-Scientific-6MMSLT-24-Flint-T...
[Edited on 14-10-2019 by Praxichys]
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SWIM
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A Hempel with rings or steel wool will give you a LOT better separation than a vig of the same length.
A 200 mm Hempel with glass rings should out perform a good 300 mm Vigreux by a fair margin.
The retention coils mentioned above aren't something I've dealt with.
I look for columns with either spikes or a perforated glass funnel built into the bottom.
The funnels are pretty much just on the fancier columns, but the ones with spikes can be found more easily.
They're mostly from major manufacturers and expensive new, but lots of them turn up used on Ebay.
Some have cooling jackets so they can serve as both a condenser and a Hempel column.
I was cooking up some radiatore the other day and it occurred to me that it would probably make a great column packing.
I could make distilled water for the lab and cook lunch at the same time!
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B.D.E
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Thanks for all the replies.
I Looked into buying some spheres/rings on Ebay, and although they weren't too expensive, the shipping fee was unbelievably high(almost always twice
the price of rings themselves).
Do you think it's possible to just use broken glass from my deceased Vigreux column?
Also, do you think I can just use 6mm clear glass beads instead
(https://www.ebay.com/itm/321001254218)? They are unbelievably cheap and they seems to be a nice hybrid between spheres and rings.
If not I'll probably buy a burner and some 6mm glass tubes and get to work.
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Ubya
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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)
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Sulaiman
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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]
CAUTION : Hobby Chemist, not Professional or even Amateur
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B.D.E
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| Quote: Originally posted by Sulaiman |
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] |
Okay, I think I understand the idea. 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.
Also thanks for the link, I might buy those if the copper mash has hidden flaws that I'm not aware of.
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Sulaiman
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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
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B.D.E
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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.
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Ubya
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| 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) |
i bought a few glass beads at a local "jewelery supplier"(a guy that sells stuff to make jewelry), i don't have a hempel column, so i just packed my
vigreaux column with the beads i bought (plus a few i had already because i didn't buy enough...).
i'm doing a test right now. i tried to fractionate a few weeks ago a solvent i bought, on the lable said only toluene, dcm, methanol, but it was far
from the truth. with my 300mm vigreux column i separated the bulk in a few fractions, 40-60, 60-80, 80-110.
i couldn't get a clear separation, the temperature just kept raising slowing down or going faster, but never being still at a single temperature, so
i had to make big fractions.
next i tried to fractionate each fraction hoping to get a clear separation, but nope.
so i tried now with the packed vigreux column to fractionate the 40-60+60-80 fractions and guess what, just one temperature at a time, right now i'm
still at 54.6°C, acetone (why the fuck they added acetone to their solvent mix and didn't mention it in the label?!)
anyway, the column works, much much better. if anybkdy else has a crappy chinese vigreux column that does shitty separations, packing it helps a lot.
i'll post a picture once i'm finished with the distillation
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feel free to correct my grammar, or any mistakes i make
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