MS molecular sieves are aluminosilicates containing oxides of alkali metals and divalent metals, distinguished by a strictly regular structure of the internal structure. They have a porous structure, consisting of many different cations, such as Na+, K+, Ca2+, Mg2+ and others. and their free spaces are filled with water particles.
The main structural elements of zeolite molecular sieves are tetrahedral SiO4 units. Their general structural formula is as follows:
Me2/n O ∙ Al2O3 ∙ xSiO2 * yH2O
Me – alkali metal cation,
n –valency of the alkali metal.
Tetrahedrons form a three-dimensional spatial form by grouping together with common oxygen atoms. The basic structures include cubes (8 tetrahedrons), hexagonal pyramids (12 tetrahedrons) and cubooktahedra (24 tetrahedrons). Some of the atoms of the silicon element are replaced with an aluminum atom, creating a negative charge with this combination (due to the lower valency of aluminum). In the unoccupied porous structure of zeolites, apart from elemental water, metal cations of groups I and II are located, which balance the electric charge. The internal structure creates a system of channels, the shape of which affects the adsorption properties of materials. The channels can form non-intersecting channels of equal size, two-dimensional channel systems and three-dimensional intersecting channel systems.
Molecular sieves are adsorptive materials with a high selective adsorption capacity and the ability to separate mixtures based on differences in the size and shape of adsorbed molecules. The main division of molecular sieves is based on the effective pore diameter. We distinguish the following materials:
- Molecular sieve 3A (effective pore diameter 3 Å)
- Molecular sieve 4A (effective pore diameter 4Å)
- Molecular sieve 5A (effective pore diameter 5Å)
- 13X Molecular Sieve (effective pore size 10Å)