bromosapien
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fractionating at reduced pressure, DIY packed column?
Hello nerds! So, I have begun learning vacuum distillation. I like to learn reasoning and mechanics behind the techniques so feel free to just point
me to good learning material that can answer my questions. As just a hobbyist, my first attempt testing my setup went reasonably well, but I’d like
to learn how to improve separation and efficiency.
As far as fractionating, I have so far only tried a vigreux at atmospheric pressure, and it hasn’t really given me the results i’m looking for.
how would you recommend a hobbyist proceed? I’ve read that a packed column is a great option. Can I use a vertical liebig condenser for this, and
connect vacuum to the condenser ports for insulation? I have some broken glassware i could crush and sift into bead-sized chunks, or probably other
stuff that would work (open to ideas). Then I just need a way to prevent it from falling in the flask, perhaps a straight vacuum takeoff with the
stopcock closed and a piece of screen?
What are the considerations for using fractionating columns like packed columns when reducing at lower pressure? is it different than atmospheric, why
if so?
Thanks in advance.
[Edited on 23-7-2024 by bromosapien]
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Sulaiman
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For fractional distillation at atmospheric pressure,
fractionating efficiency is mainly determined by the surface area of gas:liquid interface, and reflux ratio.
Area: wall(s) of column plus packing material.
A packed Vigreaux column works well,
Broken glass is ok but it is likely to cause 'channeling', I use small glass spheres.
Stainless steel wool/scrubber has more surface area so it's good, if not incompatible with your distillate.
Reflux: commonly implemented in two different techniques;
1) preferred is a thermally insulated packed column with a reflux condenser and partial take off head on top.
2) simpler but not as efficient is a packed un-insulated column.
Being un-insulated the wall(s) of the column cause reflux.
An insulated column without a reflux condenser is useless.
I suggest that you try 2) then 1) before attempting a reduced pressure fractionation.
PS a packed column is often referred to as a Hempel column.
CAUTION : Hobby Chemist, not Professional or even Amateur
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bromosapien
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Thanks! so for the insulated setup, I have one of these:
https://www.prismresearchglass.com/product/adapter-distillat...
Would this work for what you were describing above the column? With a reflux condenser?
If not, can you point me toward a hobbyist-friendly diagram or overview of this type of setup?
For now I will try just packing my un-insulated vigreux to see if separation imporves enough. Thanks again
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Rainwater
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Mood: indisposition to activity
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I got one for about half that price with 24/40 joints from
https://www.sciencemadness.org/whisper/viewthread.php?tid=71...
Still in use. 5ft insulated packed column, big reflux condencer, 3-way adapter with takeoff valve, 45 sweep, graham condenser, vacuum adapter and
addition funnel. Use the vacuum adapter, graham condencer and a peristaltic pump to vapor lock the liquid and control the reflux ratio.
Customer wanted to reclaim solvent from an automated paint booth. All the exhaust flows through a chiller and is condenced then fractionally
distilled.
"You can't do that" - challenge accepted
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