Molecular Sieve- A Brief Introduction
Molecular Sieves, like Silica Gel,
are well-known desiccants used mainly for removing vapour molecules from oil,
liquid and natural gas streams. Available in balls, beads and pellet form,
these desiccants are nowadays more preferred to Silica Gel and Activated
Alumina because they can absorb humidity molecules in a better manner.
Molecular Sieves are also economically viable as they can take in more moisture
molecules in lesser period of time and this helps in saving money.
Molecular Sieves are much in demand
due to their uniform pore crystalline structure. This added with their large
surface area speeds up the absorption process to a large extent. Molecular
Sieves work by using the size exclusion principle. When water molecules come in
contact with the Molecular Sieve, only those molecules which fit into the pores
are absorbed while the larger molecules pass through. The pore size of
Molecular Sieves are in the range of 3,4,5 and 10 Angstroms. When the
absorption process is going on depending on the pore size, the water molecules
will be absorbed or move forward. This is one of the biggest benefits of using
Molecular Sieves as desiccants for removing water vapour.
The main difference while using
Molecular Sieve and other desiccants like Silica Gel and Activated Alumina is
that in Molecular Sieves, the absorbed molecules get trapped while in the
others, the absorbed molecules are free to move away. This is why when
Molecular Sieves are used, the water molecules are retained in the pores,
freeing the remaining area of moisture.
Molecular Sieves pellets are widely
used in drying oil and liquid gas streams and solvent drying because this
desiccant can hold 22% of its own weight in water. Molecular Sieve beads also
witness much demand because their absorption qualities are much superior to
other desiccants. These qualities include adsorption possible based on
molecular size, molecular affinity for the sieve crystal surface and finally
the shape of the molecule.
Molecular Sieve Beads/Pellets in Solvent Drying
Among all the Molecular Sieves
beads in use, the Molecular Sieve type 3A is generally used to dry dehydration
solvents for electron microscopy. The solvents, which are generally made free
from moisture molecules are the most commonly used ones like acetone, ethanol,
and methanol. They are generally used in electron microscopy embedding work
using epoxy resins, so it becomes very important that they have no traces of
moisture in them. This is where the role of Moisture Sieve Beads and Pellets
become crucial as they will remove all the traces of humidity from the
solvents. What better way of solvent drying that Moisture Sieve beads and
pellets.
When the bottles containing the
solvents are opened, there are chances that they will pick up moisture from the
surroundings so that is why Molecular Sieves are used to dry up the solvents.
These dried solvents are used in the final stages of dehydration and embedding.
The solvent and the water will be quickly adsorbed onto the molecular sieve
surfaces as the small pores can only access the smaller water molecules.
