|
Molecular Sieves are types of desiccants that have differing properties from those of silica gel. These materials are synthetically produced of highly porous crystalline substance made of metal-alumino silicates. The appearance is of tiny opaque pinkish beads made of several internal cavities interconnected by window openings of accurate diameters. Importance of Diameters in Molecular Sieves The precise diameters in sieves are the only distinct classifications that stand apart from the rest of the materials. The diameters are measured in Angstroms units measuring – 3A, 4A, 5A, and 10A (also known as 13 X). If the molecules are of smaller diameters than the above stated cavity openings, then the process of adsorption occurs in the substance. If there are larger molecules present in the material, the process of adsorption is excluded. And in some other cases, molecules of greater polarity are preferentially adsorbed. It is for such reasons these sieves prove ideal for adsorption of water from air and liquids as water molecules are both small and polar. What’s its Chemical Composition? The basic material of its composition is zeolite. Zeolite is originated from the family of hydrated alumino-silicate material that consists of various alkali and alkaline-earth metals. Zeolite is highly valued because of its ready nature of transforming into artificial crystals with well-defined pore size and uniformity. This quality strongly adsorbs water and carefully controls the pore sizes. Molecular sieves are crystalline substances that have a three dimensional intertwined network of alumina and silica tetrahedra. The presence of natural water is extracted from the network by the effect of heating in turn forming a uniform cavity that carefully adsorbs the molecules of a specific size. You can consider the working of this desiccant as a sponge, which on heating dehydrates and sheds the water content causing no damage to the crystal structure. The further points will tell you the number of ways these desiccants differ from the silica gel. Reasons for Differing from Silica Gel • Their performance as being moisture absorbers is more effective at temperatures above 25°C than that of silica gel. • They reduce the water vapor to extremely lower levels as compared to silica gel. This makes it useful in atmospheres which have dry products. • The rate of adsorption of water vapor is faster than that of silica gel. Molecular sieves are quite sensitive in nature, and thus are used to extract undesired tastes and odors from food and beverage products. They are long known for their other efficient uses such as drying capacity and allowing isolation of required products from various condensation reactions in synthetic organic procedures. Practically, these desiccants are used in anything and everything related to laboratory work to heavy manufacturing to petroleum refining.
Related Articles -
Molecular, Sieves,
| 
