Molecular sieves are synthetic zeolitic materials with specific and identical structures followed by pore size. It is also preferably capable of adsorbing gases and liquids depending on molecular size and polarity.
The pore diameters of molecular sieves are usually similar in size to small molecules and therefore large molecules cannot penetrate or be adsorbed while smaller molecules can.
Zeolites are naturally occurring porous crystalline solids that belong to a class of chemicals known as aluminosilicates (minerals composed of aluminium, silicon and oxygen). Zeolites are useful additives for heavy metal binding.
Zeolite has a unique three-dimensional molecular structure based on the combination of [AlO4]5- and [SiO4]4-tetrahedra. Their structure contains regular channels and co-arranged cations and water molecules.
In a molecular sieve, the Natural water of hydration is removed by heating to produce uniform cavities which then selectively adsorb the molecules of a specific shape and size. The ångströms (Å) or nanometres (nm) are the diameters to examine a molecular sieve. Molecular sieves may be microporous, mesoporous or microporous.
- Microporous substances have pore diameters of much less than 2 nm (20 Å)
- Macroporous substances have pore diameters of more than 50 nm (500 Å);
- The mesoporous class lies within the centre with pore diameters between 2 and 50 nm (20–500 Å).
There are main types of molecular sieve: 3A, 4A, 5A, and 13X. Furthermore, the same is based on the chemical formula of the molecule and decide the pore size of the molecular sieve.
WHAT ARE THE USES OF MOLECULAR SIEVE?
Splitting up the molecules on the basis of their shape & size, the Molecular sieves are beneficial to dry gases and liquids. However, the splitting is deployed on the polarity of the molecules (charge separation) if two molecules are proportionately minute to fit into the pore. Like gel chromatography (Gel chromatography, also known as gel filtration in analytical chemistry) is a method of separating chemicals by using the difference in the rate through which they pass through a porous semi-solid layer.
They are also useful in Water vapour removal from hydrocarbon and alcohol vapours.
In lab supplies, molecular sieves are used to dry solvents, for isolating compounds and drying reaction starting materials. "Sieve" has proven to outperform traditional drying methods that often use aggressive desiccants.
1. 3A Molecular Sieves
Creation: 3A molecular sieves are produced through cation alternate of potassium for sodium in 4A molecular sieves
- 3Å molecular sieves are used to dry a variety of materials such as ethanol, air, refrigerants, natural gas and unsaturated hydrocarbons. The latter include cracked gases, acetylene, ethylene, propylene and butadiene. Indirectly used to produce an array of products such as pharmaceuticals, chemicals, foods, etc, the 3Å molecular sieves are also used to take off the water from ethanol and further being directly utilized as a biofuel.
2. 4A Molecular Sieves
Creation: 4A sieves function the precursor to 3A and 5A sieves through cation change of sodium for potassium (for 3A) or calcium (for 5A)
- 4Å molecular sieves are broadly used to dry laboratory solvents. They can soak up water and different molecules with a crucial diameter much less than four Å together with NH3, H2S, SO2, CO2, C2H5OH, C2H6, and C2H4. It is broadly used within the drying, refining and purification of beverages and gases (together with the guidance of argon).
- Mainly preferred for static dehydration in closed liquid or gas systems e.g., in the packaging of drugs, electric-powered additives and perishable chemicals; water scavenging in printing and plastics structures and drying saturated hydrocarbon streams.
3. 5A Molecular Sieves
Creation: 5A molecular sieves are produced via way of means of cation change of calcium for sodium in 4A molecular sieves
- Five ångström (5Å) molecular sieves are frequently applied for the purification of gas streams and within the chemistry laboratory equipment for setting apart compounds and drying response beginning materials.
- They include tiny pores of a unique and uniform size and are particularly used as an adsorbent for gases and liquids.
- They also can be used to split combinations of oxygen, nitrogen and hydrogen, and oil-wax n-hydrocarbons from branched and polycyclic hydrocarbons.
- Mainly utilised for static dehydration in closed liquid or gas structures, e.g., in the packaging of drugs, electric-powered additives and perishable chemicals; water scavenging in printing and plastics structures and drying saturated hydrocarbon streams.
4. 13X Molecular Sieves
Creation: The 13X molecular sieve is the sodium shape of zeolite X and has a far larger pore starting than the sort A crystals, with a powerful pore diameter of 10 angstroms.
- Type 13X gives more advantageous adsorption overall performance over the kind A zeolite, and it could eliminate impurities too huge to healthy into the kind A zeolite crystal cages. It is likewise frequently used to split nitrogen from the air to provide a high-purity oxygen stream.
- Utilised for desulfurization, desiccation and purification of petroleum gas and natural gas, Molecular sieves are preferred for laboratory usage due to their excellent adsorbing capacity.
Molecular sieves are a salient part of laboratory equipment and have influenced almost every product imaginable in some way. From the insulated glass units to the production of steel and air-conditioner filter cores of automobiles to the fuel ethanol and oxygen for breathing apparatus, molecular sieves are a part of our daily life.
Also Read: Types of Tubes Used in Science Laboratories