Nitrox2
Hazard to Self
Posts: 62
Registered: 10-6-2025
Member Is Offline
Mood: No Mood
|
|
Pear flasks
Why are they used as distillation flasks?
I see how retrieval of a small volume of liquid would be easier in a pear receiving flask but am better trying to understand how the pear flask excels
in usage as a distillation flask.
The pear flask, I've heard, can be better suited for not boiling to dryness, as this is supposed to create bumping.
Here in the picture, is a pear flask with vigreux claisen adapter attached to it. It seems that this would prevent pumping and contamination that
would occur if it were just a simple pear flask with distillation sidearm, as shown below.
Also, the picture of the pear flask with side arm, can this be used to collect a distillate free of contamination from bumping?
Looking for the cheapest way to do a simple short path distillation. The pear flask with sidearm looks promising.
 
[Edited on 13-6-2025 by Nitrox2]
|
|
|
Sulaiman
International Hazard
Posts: 3947
Registered: 8-2-2015
Member Is Offline
|
|
I see that you currently have many ideas buzzing in your head,
I suggest that you explain your requirements clearly if you want specific advice.
Meanwhile,
short path distillation https://en.wikipedia.org/wiki/Short-path_distillation
almost always means that the distillation will be performed at pressure so low that the gas behaves as individual molecules that rarely bump into
rach other and travel in straight lines,
unlke normal or reduced pressure distillations where the gas behaves as a fluid.
Distillation rates are very slow ,
and wide short straight paths are required.
The very low pressure significantly reduces boiling points.
so, any idea that involves narrow paths and/or bends will perform poorly.
______________________
I have a pear shaped flask with Claisen adapter and a short Vigreux column built in, just like in your picture.
Suitable for atmospheric or reduced pressure distillation but not short-path, due to the Vigreux column blocking any straight path, and multiple
bends.
_________________
I have not found any benefit in using pear shaped flasks compared to RBFs.
_________________
Other than requests for recipies for cooks or terrorists,
members will try to help with almost any chemistry related questions,
The most useful advice that I have received is safety related,
there are many unseen hazards in chemistry,
so detailing your intentions is highly recommended.
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
teodor
International Hazard
Posts: 1169
Registered: 28-6-2019
Location: Netherlands
Member Is Offline
|
|
I use pear flasks with distillation arms in small-scale synthesis for purification by distillation, comparing RBF it allows working with smaller
quantities for the same flask volume with minimal loose in the arms also. Also usage of cappilary tube for vacuum distillation is more convenient.
Generally, they are for small-scale because allow to boil the very last ml of liquid.
|
|
|
Dr.Bob
International Hazard
Posts: 2918
Registered: 26-1-2011
Location: USA - NC
Member Is Offline
Mood: Mildly disgruntled scientist
|
|
I typically only use pear shaped flasks for the collection of distillate, which makes it easier to pipette out the collected product. I would not use
one for the distillate. But people will often sell things that are not ideal for your purposes, as not everyone does things the same way. A simple
short path works well for small amounts, but will loss some material no matter how well it is used.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
