Molecular sieves are crystalline metal aluminosilicates having a threedimensional interconnecting network of silica and alumina tetrahedra Water is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size ID: 654168
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Slide1
Activation of molecular sievesSlide2
“Molecular sieves are crystalline metal aluminosilicates having a three-dimensional interconnecting network of silica and alumina tetrahedra
.
Water is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size.A 4 to 8-mesh sieve is normally used in gasphase applications, while the 8 to 12-mesh type is common in liquidphase applications. The powder forms of the 3A, 4A, 5A and 13X sieves are suitable for specialized applications.”
What are molecular sieves?
What do we use them for?
Removing trace amounts of water from both normal solvents and deuterated solvents.Slide3
Required Apparatus: Solvent bomb fitted with a Youngs tap
Schlenk
line (with a dewar of liquid nitrogen/solid CO2 on the trap, daytime/nighttime) and vacuum gauge.Heating mantle with working temperature probeHeating beads
Blast shieldPPE (lab coat, safety glasses, gloves)Associated risks:
Working under reduced pressure – risk of implosionHandling liquid nitrogen – cold burns
Working at elevated temperatures (200
o
C) - Hot burnsManaging riskSlide4
Procedure
Before set up:
Check all glassware for cracks/defects, if you see any then do NOT use itRemove all flammables/valuable samples from your fumehoodInform group members in the local area of procedure to be carried out
Fill solvent bomb with hot molecular sieves (in the oven for at least 24 hours) about half full and leave in oven until ready
Set
up:
Ensure
schlenk
line is on with liquid nitrogen
dewar and is pulling a good vacuum (5.0 x 10-2 mbar at least)
Attach bomb with sieves to your line, securely clamped and in an empty glass dish on a heating mantleFill glass dish with heating beads, ensuring good coverage of the bomb and above the level of the molecular sieves once full.
Fit a heating probe in the beads and set the temperature probe to 200 oC.
Put the bomb under vacuum and place blast shield in front of the set up. Allow to heat to temperature and leave overnightSlide5
3. Cooling down
The next day, once the vacuum has returned to the original level, turn off the heating and leave to cool to room temperature under vacuum.
Put molecular sieves in glovebox and leave sealed to avoid absorption of any water traces.