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Information about Desiccant

A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container.

Commonly encountered pre-packaged desiccants are solids, and work through absorption or adsorption of water, or a combination of the two. Desiccants for specialised purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules.

Pre-packaged desiccant is most commonly used to remove humidity that would normally degrade or even destroy products sensitive to moisture. Silica gel, calcium sulfate, montmorillonite clay, and molecular sieves are commonly used as desiccants.

Rice is a common "low-tech" alternative, frequently used for example in salt-shakers to maintain ity of table-salt for effective pouring or shaking. Rice, however, is not a good general purpose desiccant since, unless immersed in an organism-hostile environment like pure salt, over time may be eaten by creatures that might in turn pollute the product that is being preserved. Salt itself is another effective desiccant, used for millennia in preparation of dried foodstuffs.

Toxicity

A desiccant may be chosen for a particular task based not only on its effectiveness at drying, but also perhaps for any natural antibiotic/fungicidal/pesticidal effect, or for a lack of harmful effect on humans -- for instance salt has a natural antibiotic and anti-fungal effect and is not harmful to humans when consumed in moderate quantities, hence its popular use a drying agent in preparation of dried foods.

Desiccants may also incorporate secondary substances in order to achieve such antibiotic etc properties. These may be mineral, synthetic, or herbal in origin, and vary in toxicity toward humans.

Chemical reactivity

Because of their common use in preservation, usually it is desirable for a desiccant to be substantially chemically stable or chemically inert, and a number of useful desiccants with this property have been identified and are in common use, such as silica gel, chalk- and clay-based desiccants.

Performance efficiency

One measure of desiccant efficiency is the ratio (or percentage) of water storeable in the desiccant, relative to the mass of desiccant (ie weight).

Another measure is the residual relative humidity of the air or other fluid being dried.

The performance of any desiccant varies with temperature and both relative and absolute humidity. To some extent the performance can be described, but most commonly the final choice of which desiccant best suits a given situation, and how much of it to use, and in what form, is made based on testing and experience.

Coloured saturation indicators

Often some sort of humidity indicator is included in the desiccant to show, by color changes, the degree of water-saturation of the desiccant. One commonly used indicator is cobalt chloride (CoCl2). Anhydrous cobalt chloride is blue. When it bonds with two water molecules, (CoCl2•2H2O), it turns purple. Further hydration results in the pink hexaaquacobalt(II) chloride complex [Co(H2O)6]Cl2.

Most useful desiccants can be recycled by thermally-induced drying, for example in a conventional kitchen oven.

Drying of solvents

See also:
Desiccants are also used to dry solvents, typically used for moisture free reactions (e.g. the Grignard reaction). While various desiccants are used in a variety of ways, the method generally involves stirring the desired solvent with the drying agent.

Often, the drying agent will react with moisture to form an insoluble solid in the solvent being dehydrated, thus the precipitate can be removed by filtration. For more demanding applications, requiring very pure, anhydrous solvents a distillation rig is used to remove moisture and other impurities simultaneously.

References

Lavan, Z.; Jean-Baptiste Monnier, Worek, W. M.; 1982, "Second Law Analysis of Desiccant Cooling Systems", Journal of Solar Energy Engineering, Vol. 104, pp. 229-236.

See also

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Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption.

Hygroscopic substances include honey, glycerin, ethanol, methanol, concentrated sulfuric acid, methamphetamine, and concentrated
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Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately-well sealed container.
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Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. This is a different process from adsorption, since the molecules are taken up by the volume, not by surface.
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Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorbate).
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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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Humidity is the amount of water vapor in a sample of air compared to the maximum amount of water vapor the air can hold at any specific temperature. Absolute humidity, relative humidity and specific humidity are different ways to express the water content in a parcel of air.
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Silica gel is a granular, porous form of silica made synthetically from sodium silicate. Despite the name, silica gel is a solid.

Silica gel is most commonly encountered in everyday life as beads packed in a semi-permeable plastic.
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Calcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite (the nearly anhydrous form), it is used as a desiccant. While natural, unrefined calcium sulfate is a translucent, crystalline white rock, a form sold under the name Drierite®
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Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a
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Clay is a naturally occurring material, composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried or fired.
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A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

Molecules small enough to pass through the pores are adsorbed while larger molecules are not.
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RICE is a treatment method for soft tissue injury which is an abbreviation for Rest, Ice, Compression and Elevation.[1][2][3] When used appropriately, recovery time is usually shortened and discomfort minimized.
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low-technology may be that it can be practiced or fabricated with a minimum of Capital investment by an individual or small group of individuals; and that the knowledge of the practice can be completely comprehended by a single individual, free from increasing specialization and
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salt shaker is a small container filled with salt used to sprinkle it onto food. They were invented in the 19th century. Salt shakers have a hole or several holes at the top which are small enough to require a shaking action to get an appreciable amount of salt out.
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Salt is a mineral essential for animal life, composed primarily of sodium chloride. Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt.
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Drying is a method of food preservation that works by removing water from the food, which prevents the growth of microorganisms and decay. Drying food using the sun and wind to prevent spoilage has been known since ancient times.
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antibiotic is a chemotherapeutic agent that inhibits or abolishes the growth of micro-organisms, such as bacteria, fungi, or protozoans. The term originally referred to any agent with biological activity against living organisms; however, "antibiotic" now is used to refer to
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Fungicides are chemical compounds used to prevent the spread of fungi or plants in gardens and crops, which can cause serious damage resulting in loss of yield and thus profit.
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worldwide view.
A pesticide is a substance or mixture of substances used for preventing, controlling, or lessening the damage caused by a pest.[1] A pesticide may be a chemical substance, biological agent (such as a virus or bacteria), antimicrobial,
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A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties.
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Synthetic is usually used in the sense of synthesis, the combination of two or more parts, whether by design or by natural processes. It can also be used as in many stuff:
  • Synthetic chemical or synthetic compound, produced by Chemical synthesis

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A herbal is a book, often illustrated, that describes the appearance, medicinal properties, and other characteristics of plants used in herbal medicine.

See also

  • Herbal (Music Venue in Shoreditch, London)
  • Herbalism (herbal medicine)
  • Herbal liqueurs

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In English, to be inert is to be in a state of doing little or nothing.

In chemistry, the term inert is used to describe something that is not chemically active. The noble gases were described as being inert because they did not react with the other elements or themselves.
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In mathematics, a percentage is a way of expressing a number as a fraction of 100 (per cent meaning "per hundred"). It is often denoted using the percent sign, "%". For example, 45 % (read as "forty-five percent") is equal to 45 / 100, or 0.45.
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Mass is a fundamental concept in physics, roughly corresponding to the intuitive idea of "how much matter there is in an object". Mass is a central concept of classical mechanics and related subjects, and there are several definitions of mass within the framework of relativistic
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weight is a measurement of the gravitational force acting on an object. Near the surface of the Earth, the acceleration due to gravity is approximately constant; this means that an object's weight is roughly proportional to its mass.
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Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water.

Definition

The relative humidity of an air-water mixture is defined as the ratio of the partial pressure of water vapor in the mixture to the
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Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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Humidity is the amount of water vapor in a sample of air compared to the maximum amount of water vapor the air can hold at any specific temperature. Absolute humidity, relative humidity and specific humidity are different ways to express the water content in a parcel of air.
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Humidity is the amount of water vapor in a sample of air compared to the maximum amount of water vapor the air can hold at any specific temperature. Absolute humidity, relative humidity and specific humidity are different ways to express the water content in a parcel of air.
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