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.