N i Yi 11112016 P rinciples Remove dissolved gases from a liquid Performed under reduced pressure It takes advantage of the pressure dependence of gas solubility in a liquid Lowering the pressure of the gas above the liquid causes the solubility of the dissolved gas in the liquid to decr ID: 659869
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Slide1
Freeze-Pump
T
haw
for degassing
N
i Yi
11/11/2016Slide2
Principles
Remove dissolved gases from a liquid
Performed under reduced pressure
It takes advantage of the pressure dependence of gas solubility in a liquid. Lowering the pressure of the gas above the liquid causes the solubility of the dissolved gas in the liquid to decrease
The dissolved gas is released from the liquid as a bubbleSlide3
Safety Carefully
check
all glassware for cracks or defects (Vacuum suitable glassware: round bottom, not conical)
D
o
not fill the ampoule >
60%
E
nsure that Young’s tap creates an effective seal
U
se
a vacuum
gauge
Person performing this procedure must be in the vicinity of the vessel at all times and alert neighbors in the lab to the procedure
N
ever
open the ampoule to argon during freezingSlide4
Glassware required
Solvent should be stored preferably in a Young’s flasks rather than a
Schlenk
flask
Teflon tap provides a better seal
The greased joint seal of a
Schlenk flask can degrade over timeSlide5
Method
It is important not to fill the solvent ampoule to more than 60% of its volume (to avoid the build-up of an overpressure
)
If an argon atmosphere is used, the solvent ampoule must be sealed and the
S
chlenk
line tap closed, prior to freezing (otherwise gas can be condensed, this presents a significant risk of overpressure)
The solvent ampoule should be kept inside the
dewar
of liquid nitrogen until all of the solvent has frozen
N
ote: this picture is for demonstration, please use the ampoule when you are degassing a large amount
of solventSlide6
Method
Quickly open and then shut vacuum to apply partial static vacuum as it is freezing.
Place under dynamic
vacuum
for 10-15 min
once completely frozen.
Remove ampule from liquid nitrogen, and close tap to vacuum.
Always be aware of vacuum gauge in case of any leaks.
N
ote: this picture is for demonstration, please use the ampoule when you are degassing a large amount
of solventSlide7
Method
Keep the fume cupboard sash lowered as far as possible whilst warming
The flask is to remain closed under static vacuum as it is warmed with occasional application of dynamic vacuum until the solvent has completely melted.
Repeat x3 for general needs
After the last cycle the flask is backfilled with N
2
/
Ar
at room temperature
Dry solvents can be stored over suitable drying agents, such as molecular sieves to prolong their life.
N
ote: this picture is for demonstration, please use the ampoule when you are degassing a large amount
of solvent