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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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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bromosapien
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Quote: Originally posted by Rainwater  | 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. |
That was just the only place I could find a picture of the exact kind of adapter I got, which actually came in a huge box of a ton of other glassware
and chemistry stuff that I paid very little for 
Anyhow I have read and reread your reply with a lot of mind's eye effort, and done a good amount of googling about, and I'm still not confident that I
understand the setup you are describing nor how to use it like you are describing. It sounds awesome though! If you have time can you elaborate, or
send me somewhere I can learn it in detail?
[Edited on 29-7-2024 by bromosapien]
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Rainwater
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https://library.sciencemadness.org/library/books/vogel_pract...
Page 98 in the book(page 121 of the pdf file)
So the basic setup uses a vapor lock to prevent fluid from traveling down the graham condenser. (To all the liebig lovers, bet you didnt know the
graham was made for this)
Using a peristaltic pump to control the pressure in the collection vessel. You can directly control how much fluid is taken off the reflux stream
Heres some doodles
 
Edit: updated drawing and added smarky remarks
[Edited on 30-7-2024 by Rainwater]
"You can't do that" - challenge accepted
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bromosapien
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Cool! finally a reason to get a graham... thank you
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RustyShackleford
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| Quote: Originally posted by Rainwater | https://library.sciencemadness.org/library/books/vogel_pract...
Page 98 in the book(page 121 of the pdf file)
So the basic setup uses a vapor lock to prevent fluid from traveling down the graham condenser. (To all the liebig lovers, bet you didnt know the
graham was made for this)
Using a peristaltic pump to control the pressure in the collection vessel. You can directly control how much fluid is taken off the reflux stream
Heres some doodles
Edit: updated drawing and added smarky remarks
[Edited on 30-7-2024 by Rainwater] |
The whole point of proper column distillation is that a part of the condensed distillate is returned to the boiler. If the condensed fluid is
prevented from returning it seems like a rather pointless waste of heat. In your described setup there is no reason to include the pump at all, since
all the reflux occurs by the heat transfer and back flow inside the graham, not due to the condenser above.
[Edited on 14-8-2024 by RustyShackleford]
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Rainwater
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?
The graham takes no part in the reflux. In theory it does not even need to be cooled.
The reflux condencer at the top of the picture that is cropped off provides the only condensation.
The pump is used to create pressure difference in the receiving flask.
This is used to control the takeoff rate.
Next time I build it, i will record a demo of the operation.
"You can't do that" - challenge accepted
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bromosapien
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I'll have a go at it, perhaps i'll share footage as well if i get anywhere... check back in a month
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