How Molecular Sieves Work:
Molecular sieves, because of their
crystalline composition and carefully controlled pore sizes, will yield virtually
water-free products. While both the solvent and the water will adsorb strongly
to the molecular sieve surfaces, the large surface area within the pores is
only accessible to the smaller water molecules, so they are effectively removed
from the solvent. From the table below it can be seen that water (1.93A) will
enter that 3A pore size while acetone (3.08A) will largely be excluded. Water
will be able to occupy the large surface area inside the pores and thus be
removed. If the solvent could also enter the pores, it would compete with
water for the surface area and there would be little or no removal of the
water from the bulk solvent. Type 4A molecular sieve is not suitable for drying
ethanol, methanol, or acetone since the pore size does not exclude these solvents.
|
Molecular radius, nm |
| Water |
0.193 |
| Acetone |
0.308 |
See Solvents: Properties and Drying agents Also see our Humidity Test Strips
How to Use the Sieves:
Running the solvent slowly through
a column of the molecular sieves would be the most effective way to remove
water but, ordinarily, dried sieves are just placed into the bulk solvent
container (about 5%-10% by volume) to remove the water. The easiest is adding
the sieves to your spray bottle. Reusable by just heating the sieves to 250
degrees C for 2 hours to reactivate.
1 lb is approx 3 cups volume of
1/8 inch dia. beads. More than enough for the average hobbyist. 2lbs will
last for years.