beerwiz
Hazard to Others
Posts: 130
Registered: 6-2-2014
Member Is Offline
Mood: No Mood
|
|
Speeding up vacuum distillations - Role of Diameter of Vacuum Intake
Any ideas on how to speed up vacuum distillations? I have large volumes of alcohol to distill and I want to distill it in the least amount of time
under vacuum. Would getting a sub 10 Torr vacuum pump with a larger vacuum intake and a larger diameter vacuum out barb on the glassware do the job
quicker? Any other ideas?
|
|
|
Deathunter88
National Hazard
Posts: 519
Registered: 20-2-2015
Location: Beijing, China
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by beerwiz  | | Any ideas on how to speed up vacuum distillations? I have large volumes of alcohol to distill and I want to distill it in the least amount of time
under vacuum. Would getting a sub 10 Torr vacuum pump with a larger vacuum intake and a larger diameter vacuum out barb on the glassware do the job
quicker? Any other ideas? |
There is no need to use vacuum distillation to distill large amounts of alcohol since it has such a low boiling point. By doing a vacuum distillation
you are just increasing the load on your distillation column, as it now has to be colder to condense the alcohol coming over at a lower temperature.
Instead, increasing your heating ability and length of condenser column (so it doesn't get flooded) is the way to go.
|
|
|
XeonTheMGPony
International Hazard
Posts: 1640
Registered: 5-1-2016
Member Is Offline
Mood: No Mood
|
|
Speed and quality distillation are mutually exclusive, Same for Quality, you do NOT get both, but you may chose any where between the two.
|
|
|
RedDwarf
Hazard to Others
Posts: 166
Registered: 16-2-2019
Location: UK (North West)
Member Is Offline
Mood: Variable
|
|
An ideal vacuum distillation would have zero flow through the barb and vacuum intake once you had reached distillation temperature. Assuming that
you're not bleeding air into the boiling flask to reduce bumping, any flow through the barb is either air leakage (undesirable) or un-condensed
product loss (very undesirable). So increasing the cross sectional area of the pump feed has zero value at this point.
|
|
|
SWIM
National Hazard
Posts: 970
Registered: 3-9-2017
Member Is Offline
|
|
If you're distilling to get the alcohol, the vacuum will be counterproductive in some ways because it will make re-condensing the vapors efficiently
much tougher.
If you have a pump that can withstand alcohol vapors you might be able to just condense it after the pump, but that would take something like a
diaphragm pump with internals that can take the alcohol.
I think the best answer is just a bigger still.
I've got big flasks, but for getting alcohol in a straight run distillation I use a big pressure cooker as a boiler with copper tubing for a
condenser.
Added thoughts about bigger vacuum intakes and barbs:
I don't think they would help much unless what you've got is already very restricted.
The way I see it, you don't really want to pump ANYTHING out of your still during a conventional vacuum distillation.
You just want to maintain a vacuum. If your rig was perfectly airtight, you could just evacuate it and then not even run the pump during distillation.
If the pump has to run you'd want it to only pump out the air that leaks in. Any vapors pumped out are lost.
Of course you can't really do that, but you'd want to limit the pumping to a level that keeps air out of the system.
This would seem to imply that a bigger pump would only help if you either need to draw the boiler down to high vacuum faster, or if the leaks
overwhelm the smaller pump.
Edit: Somehow I managed to fail to read the post right above, which makes the same point I was just guessing at.
[Edited on 10-4-2019 by SWIM]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
