Everything about Desiccant totally explained
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 excessive
humidity that would normally degrade or even destroy products sensitive to moisture.
Silica gel,
calcium sulfate,
calcium chloride,
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, isn't 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's 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 isn't harmful to humans when consumed in moderate quantities, hence its popular use as drying agent in preparation of dried foods.
Chemical reactivity
Because of their common use in preservation, usually it's 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 humidity and
absolute humidity. To some extent, desiccant performance can be precisely described, but most commonly, the final choice of which desiccant best suits a given situation, how much of it to use, and in what form, is made based on testing and practical 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 (CoCl
2).
Anhydrous cobalt chloride is blue. When it bonds with two water molecules, (CoCl
2•2H
2O), it turns purple. Further hydration results in the pink hexaaquacobalt(II) chloride complex [Co(H
2O)
6]Cl
2.
Desiccant regeneration
Most useful desiccants can be
recycled by
thermally-induced drying, for example, in a conventional kitchen
oven, or with
solar energy. A cost-effective, low-energy, continuous-cycle desiccant
dehumidifier or desiccant
regeneration system can be easily designed from
off-the-shelf component parts.
Drying of solvents
Desiccants are also used to dry
solvents, typically used for moisture free reactions (for example 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.
Further Information
Get more info on 'Desiccant'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://desiccant.totallyexplained.com">Desiccant Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
