bromosapien
Harmless
Posts: 7
Registered: 2-6-2024
Member Is Offline
|
|
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]
|
|
|
Sulaiman
International Hazard
Posts: 3630
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
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
|
|
|
bromosapien
Harmless
Posts: 7
Registered: 2-6-2024
Member Is Offline
|
|
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
|
|
|
Rainwater
National Hazard
Posts: 859
Registered: 22-12-2021
Member Is Offline
Mood: indisposition to activity
|
|
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
|
|
|
bromosapien
Harmless
Posts: 7
Registered: 2-6-2024
Member Is Offline
|
|
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]
|
|
|
Rainwater
National Hazard
Posts: 859
Registered: 22-12-2021
Member Is Offline
Mood: indisposition to activity
|
|
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
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
