RogueRose
International Hazard
Posts: 1585
Registered: 16-6-2014
Member Is Offline
|
|
Vacuum Distillation & other vacuum uses
I was always confused as to how vac distill worked as I thought the dist pot was put under vacuum (the pot with the liquid to be distilled) and always
wondered how the constant creation of vapor didn't nullify the vacuum.
Now I see that the vacuum is placed on the receiving flask which means that no vapor reaches it (theoretically) as it condenses before reaching flask.
Are there any alternatives to this standard setup or is that the only workable method.
I have also been looking at various reactions where heating a compound to X degrees will work best under vacuum (because the vac temp lowers BP to
compound isn't damaged). Can the same type of vacuum unit be used as the distillation setup?
Are there any other applications where a vacuum is used to help the reaction?
|
|
|
BromicAcid
International Hazard
Posts: 3227
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
If the distillation flask was not under vacuum then it would not boil. The boiling point occurs when the vapor pressure of the liquid is the same as
the pressure over the liquid. So although you are pulling vacuum from your receiver your distillation flask is under vacuum. Of course the hope is
to condense all the vapors before they make it to your pump but they may not all be stopped along the way to your receiver and for fairly volatile
things your receiver may be hot enough to allow them to continue to evaporate.
With regards to alternative setups it depends on what you are trying to accomplish.
For your last point are you talking about a thermally sensitive compound and continually stripping it off under vacuum as it is formed?
|
|
|
Zephyr
Hazard to Others
Posts: 341
Registered: 30-8-2013
Location: Seattle, WA
Member Is Offline
|
|
I have a similar question I am hoping someone can answer; could the vacuum be applied and then turned off and sealed before the is applied? I am
hoping this could work because it would greatly reduce the fumes that reach the pump, but I suspect its not that easy?
Thanks.
|
|
|
Detonationology
Hazard to Others
Posts: 362
Registered: 5-5-2015
Location: Deep South
Member Is Offline
Mood: Electrophillic
|
|
Quote: Originally posted by Pinkhippo11  | I have a similar question I am hoping someone can answer; could the vacuum be applied and then turned off and sealed before the is applied? I am
hoping this could work because it would greatly reduce the fumes that reach the pump, but I suspect its not that easy?
Thanks.
|
This only works for reactions that do not produce much off-gassing, and only for a short time before the pressure equalizes.
“There are no differences but differences of degree between different degrees of difference and no difference.” ― William James
|
|
|
RogueRose
International Hazard
Posts: 1585
Registered: 16-6-2014
Member Is Offline
|
|
As an example, I need to evap the water from an ammonium sulfate solution without boiling as the sulfate decomposes at 212F to bisulfate. So if I
could reduce the pressure and lower BP, that would allow me to do this without decomp to bisulfate. Reducing pressure to lowest BP would be great!
To do this, what kind of equipment is needed? Is the only way to do it a standard distillation setup?
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
For water evaporation use an aspirator or an aspirator pump. The use of a trap is recommended although in practice these are usually absent. These
questions are pretty basic and the topic is covered in all or almost all lab manuals. Vogel has a decent treatment of the subject. So does Organic
Chemistry Lab Survival Manual. Read and learn.. read an learn. I don't know why this would be a new topic.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
Hey Bromic! Keep writing! Creative endeavors go beyond organic synthesis. Congratulations on your continuing efforts.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
