Desiccant

Drying agents are substances that are water or (more rarely) deprive other solvents. The water can be chemically bonded, for example sulfuric acid, calcium chloride or phosphorus pentoxide, or the drying may be accomplished by adsorption, such as on molecular sieves, or bentonite. A distinction is made between static and dynamic drying. The static drying is the substance to be dried, the drying agent is added and removed again, wherein the dynamic drying flows through the gaseous or liquid substance to be dried, the drying agent.

Desiccants are used in industry to dry materials over the production to protect against unwanted end products wetting, or as a chemical agent to physically induced release of water or condensation. This serves the durability of a product, as well as corrosion and thereby undesired changes of a material surface can be avoided.

The drying agent most commonly used is air, more air with low relative humidity. One speaks of air drying. This is used in almost all areas artisanal or industrial production.

Examples:

• Drying of wood for musical instruments, or the furniture industry.
• Drying food as a means of preservation ( dried fruit, dried mushrooms, Pastirma ).
• Drying of textiles on the clothesline.
• Fluidized bed drying of sodium chloride ( salt).

Often chemical compounds with unique internal structure can be used as a drying agent. They are used to protect high-quality components or components of a product against corrosion or condensation of water vapor. Such agents are, for example, silica gel or zeolites. In the organic chemistry laboratory often anhydrous sodium sulfate or magnesium sulfate may be used as a drying agent. These include due to their chemical and structural nature of a water molecules and change thereafter by intermolecular forces its spatial molecular structure. Water molecules can thus no longer escape from the structure and remain bound. By heat treatment, this drying agent can be regenerated, the bound water is driven off and the desiccant can be reused. Blue gel is also made of silica gel, however, contains an indicator dye, which indicates the degree of water absorption (blue = dry or moist pink = ). Orangegel also based on silica gel as a desiccant, it is used only one other indicator to display further use.

For particularly high demands on the dryness of solvents (for example, diethyl ether ) of sodium wire is dried with freshly squeezed ( bare ). Here, the sodium reacts irreversibly to form sodium hydroxide and hydrogen gas escaping with water residues.

Further drying means commonly used are: alumina ( regenerated ), calcium, calcium hydride, calcium oxide, calcium sulphate ( regenerated ), potassium carbonate ( regenerated ), potassium hydroxide, copper sulphate, lithium hydroxide, sodium hydroxide.

Examples:

• Dry attitude of optical, precision mechanical and electronic components during transport within the packaging
• For keeping dry enclosed volumes ( housing, optical components, laser)

There were also attempts to silica gel for buoyancy compensation to be used in airships to be replaced by water absorption from the air, the mass of fuel consumed.