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Desiccant

December 07, 2023

For the use of chemicals in agriculture to aid harvesting, see crop desiccation.

A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. They are commonly encountered in foods to retain crispness. Industrially, desiccants are widely used to control the level of water in gas streams.

Canisters are commonly filled with silica gel and other molecular sieves used as desiccant in drug containers to keep contents dry.
Silica gel in a sachet or porous packet

Types of desiccants edit

Main article: List of desiccants

Although some desiccants are chemically inert, others are extremely reactive and require specialized handling techniques. The most common desiccant is silica gel, an otherwise inert, nontoxic, water-insoluble white solid. Tens of thousands of tons are produced annually for this purpose.[1] Other common desiccants include activated charcoal, calcium sulfate, calcium chloride, and molecular sieves (typically, zeolites). Desiccants may also be categorized by their type, either I,II,III,IV, or V. These types are a function of the shape of the desiccant's moisture sorption isotherm.

Alcohols and acetones are also dehydrating agents. Development of desiccants made of treated rice husks is a promising use of waste agricultural products.[2]

Performance efficiency edit

One measure of desiccant efficiency is the ratio (or percentage) of water storable in the desiccant relative to the mass of desiccant.

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.

Colored saturation indicators edit

 
Indicating silica gel

Sometimes a 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.

Applications edit

One example of desiccant usage is in the manufacture of insulated windows where zeolite spheroids fill a rectangular spacer tube at the perimeter of the panes of glass. The desiccant helps to prevent the condensation of moisture between the panes. Another use of zeolites is in the "dryer" component of refrigeration systems to absorb water carried by the refrigerant, whether residual water left over from the construction of the system, or water released by the degradation of other materials over time.

Bagged desiccants are also commonly used to protect goods in barrier-sealed shipping containers against moisture damage: rust, corrosion, etc.[3][4] Hygroscopic cargo, such as cocoa, coffee, various nuts and grains, and other foods[5] can be particularly susceptible to mold and rot when exposed to condensation and humidity. Because of this, shippers often take measures by deploying desiccants to protect against loss. Pharmaceutical packaging often includes small packets of desiccant to keep the atmosphere inside the package below critical levels of water vapor.

Desiccants induce dryness in any environment and reduce the amount of moisture present in air. Desiccants come in various forms and have found widespread use in the food, pharmaceuticals, packing, electronics and many manufacturing industries.

Air conditioning systems can be based on desiccants, as drier air feels more comfortable and absorbing water itself removes heat.[6]

Desiccants are used in livestock farming, where, for example, new-born piglets are highly susceptible to hypothermia owing to their wetness.[7]

Drying of solvents edit

 
Toluene is heated under reflux with sodium and benzophenone to produce dry, oxygen-free toluene. The toluene is dry and oxygen free when the intense blue coloration from the benzophenone ketyl radical is observed.
Main article: Air-free technique

Desiccants are also used to remove water from solvents, typically required by chemical reactions that do not tolerate water, e.g., the Grignard reaction. The method generally, though not always, involves mixing the solvent with the solid desiccant. Studies show that molecular sieves are superior as desiccants relative to chemical drying reagents such as sodium-benzophenone. Sieves offer the advantages of being safe in air and recyclable.[8][9]

See also edit

References edit

  1. ^ Otto W. Flörke, et al. "Silica" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Weinheim: Wiley-VCH, . doi:10.1002/14356007.a23_583.pub3.
  2. ^ Emdadi, Z (2014). "Feasibility Study of Using Rice Husk and its Treated Forms with Alkali Solution as a Desiccant Material, Project 2695-9" (PDF). WSEAS TRANSACTIONS ON ENVIRONMENT AND DEVELOPMENT. 10. Retrieved 20 November 2023.
  3. ^ Rollo, P (1996). A Protective packaging evaluation involving a high barrier film lamiation, desiccants and oxygen absorbers (MSc). Rochester Institute of Technology. Retrieved August 8, 2021.
  4. ^ MIL-D-3464E, MILITARY SPECIFICATION: DESICCANTS, ACTIVATED, BAGGED, PACKAGING USE AND STATIC DEHUMIDIFICATION, 1987, retrieved August 8, 2021
  5. ^ Hirata, T (1985). "Simulation of Moisture and Chlorophyll Changes in Dried Laver, Porphyra Yezoensis, in a Desiccant-Enclosing Packaging System". Nippon Shokuhin Kogyo Gakkaishi. 32 (4): 266–273. doi:10.3136/nskkk1962.32.4_266. S2CID 101082998. Retrieved 11 August 2021.
  6. ^ Daou, K; Wang, Xia (2005). "Desiccant cooling air conditioning: a review". Renewable and Sustainable Energy Reviews. 10 (2): 55–77. doi:10.1016/j.rser.2004.09.010.
  7. ^ Vande Pol, Katherine D.; Tolosa, Andres F.; Shull, Caleb M.; Brown, Catherine B.; Alencar, Stephan A S.; Ellis, Michael (2020). "Effect of method of drying piglets at birth on rectal temperature over the first 24 h after birth1". Translational Animal Science. 4 (4): txaa183. doi:10.1093/tas/txaa183. PMC 7672461. PMID 33241187.
  8. ^ Chai, Christina Li Lin; Armarego, W. L. F. (2003). Purification of laboratory chemicals. Oxford: Butterworth-Heinemann. ISBN 978-0-7506-7571-0.
  9. ^ Williams, D. Bradley G.; Lawton, Michelle (2010). "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants". The Journal of Organic Chemistry. 75 (24): 8351–8354. doi:10.1021/jo101589h. PMID 20945830. S2CID 17801540.

Further reading edit

  • Lavan, Z.; Jean-Baptiste Monnier & Worek, W. M. (1982). "Second Law Analysis of Desiccant Cooling Systems". Journal of Solar Energy Engineering. 104 (3): 229–236. doi:10.1115/1.3266307.
  • S. Sadik; J. W. White (1982). "True potato seed drying over rice". Potato Research. 25 (3): 269. doi:10.1007/BF02357312. S2CID 41039047.

December 07, 2023
desiccant, chemicals, agriculture, harvesting, crop, desiccation, desiccant, hygroscopic, substance, that, used, induce, sustain, state, dryness, desiccation, vicinity, opposite, humectant, commonly, encountered, packaged, desiccants, solids, that, absorb, wat. For the use of chemicals in agriculture to aid harvesting see crop desiccation A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness desiccation in its vicinity it is the opposite of a humectant Commonly encountered pre packaged desiccants are solids that absorb water Desiccants for specialized purposes may be in forms other than solid and may work through other principles such as chemical bonding of water molecules They are commonly encountered in foods to retain crispness Industrially desiccants are widely used to control the level of water in gas streams Canisters are commonly filled with silica gel and other molecular sieves used as desiccant in drug containers to keep contents dry Silica gel in a sachet or porous packet Contents 1 Types of desiccants 1 1 Performance efficiency 1 2 Colored saturation indicators 2 Applications 3 Drying of solvents 4 See also 5 References 6 Further readingTypes of desiccants editMain article List of desiccants Although some desiccants are chemically inert others are extremely reactive and require specialized handling techniques The most common desiccant is silica gel an otherwise inert nontoxic water insoluble white solid Tens of thousands of tons are produced annually for this purpose 1 Other common desiccants include activated charcoal calcium sulfate calcium chloride and molecular sieves typically zeolites Desiccants may also be categorized by their type either I II III IV or V These types are a function of the shape of the desiccant s moisture sorption isotherm Alcohols and acetones are also dehydrating agents Development of desiccants made of treated rice husks is a promising use of waste agricultural products 2 Performance efficiency edit One measure of desiccant efficiency is the ratio or percentage of water storable in the desiccant relative to the mass of desiccant 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 Colored saturation indicators edit nbsp Indicating silica gelSometimes a 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 Applications editOne example of desiccant usage is in the manufacture of insulated windows where zeolite spheroids fill a rectangular spacer tube at the perimeter of the panes of glass The desiccant helps to prevent the condensation of moisture between the panes Another use of zeolites is in the dryer component of refrigeration systems to absorb water carried by the refrigerant whether residual water left over from the construction of the system or water released by the degradation of other materials over time Bagged desiccants are also commonly used to protect goods in barrier sealed shipping containers against moisture damage rust corrosion etc 3 4 Hygroscopic cargo such as cocoa coffee various nuts and grains and other foods 5 can be particularly susceptible to mold and rot when exposed to condensation and humidity Because of this shippers often take measures by deploying desiccants to protect against loss Pharmaceutical packaging often includes small packets of desiccant to keep the atmosphere inside the package below critical levels of water vapor Desiccants induce dryness in any environment and reduce the amount of moisture present in air Desiccants come in various forms and have found widespread use in the food pharmaceuticals packing electronics and many manufacturing industries Air conditioning systems can be based on desiccants as drier air feels more comfortable and absorbing water itself removes heat 6 Desiccants are used in livestock farming where for example new born piglets are highly susceptible to hypothermia owing to their wetness 7 Drying of solvents edit nbsp Toluene is heated under reflux with sodium and benzophenone to produce dry oxygen free toluene The toluene is dry and oxygen free when the intense blue coloration from the benzophenone ketyl radical is observed Main article Air free technique Desiccants are also used to remove water from solvents typically required by chemical reactions that do not tolerate water e g the Grignard reaction The method generally though not always involves mixing the solvent with the solid desiccant Studies show that molecular sieves are superior as desiccants relative to chemical drying reagents such as sodium benzophenone Sieves offer the advantages of being safe in air and recyclable 8 9 See also editDesiccator Humidity buffering Humidity indicator card Moisture sorption isotherm Solar air conditioning Oxygen scavenger oxygen absorber Sorbent Volatile corrosion inhibitor Cromer cycleReferences edit Otto W Florke et al Silica in Ullmann s Encyclopedia of Industrial Chemistry 2008 Weinheim Wiley VCH doi 10 1002 14356007 a23 583 pub3 Emdadi Z 2014 Feasibility Study of Using Rice Husk and its Treated Forms with Alkali Solution as a Desiccant Material Project 2695 9 PDF WSEAS TRANSACTIONS ON ENVIRONMENT AND DEVELOPMENT 10 Retrieved 20 November 2023 Rollo P 1996 A Protective packaging evaluation involving a high barrier film lamiation desiccants and oxygen absorbers MSc Rochester Institute of Technology Retrieved August 8 2021 MIL D 3464E MILITARY SPECIFICATION DESICCANTS ACTIVATED BAGGED PACKAGING USE AND STATIC DEHUMIDIFICATION 1987 retrieved August 8 2021 Hirata T 1985 Simulation of Moisture and Chlorophyll Changes in Dried Laver Porphyra Yezoensis in a Desiccant Enclosing Packaging System Nippon Shokuhin Kogyo Gakkaishi 32 4 266 273 doi 10 3136 nskkk1962 32 4 266 S2CID 101082998 Retrieved 11 August 2021 Daou K Wang Xia 2005 Desiccant cooling air conditioning a review Renewable and Sustainable Energy Reviews 10 2 55 77 doi 10 1016 j rser 2004 09 010 Vande Pol Katherine D Tolosa Andres F Shull Caleb M Brown Catherine B Alencar Stephan A S Ellis Michael 2020 Effect of method of drying piglets at birth on rectal temperature over the first 24 h after birth1 Translational Animal Science 4 4 txaa183 doi 10 1093 tas txaa183 PMC 7672461 PMID 33241187 Chai Christina Li Lin Armarego W L F 2003 Purification of laboratory chemicals Oxford Butterworth Heinemann ISBN 978 0 7506 7571 0 Williams D Bradley G Lawton Michelle 2010 Drying of Organic Solvents Quantitative Evaluation of the Efficiency of Several Desiccants The Journal of Organic Chemistry 75 24 8351 8354 doi 10 1021 jo101589h PMID 20945830 S2CID 17801540 Further reading editLavan Z Jean Baptiste Monnier amp Worek W M 1982 Second Law Analysis of Desiccant Cooling Systems Journal of Solar Energy Engineering 104 3 229 236 doi 10 1115 1 3266307 S Sadik J W White 1982 True potato seed drying over rice Potato Research 25 3 269 doi 10 1007 BF02357312 S2CID 41039047 Retrieved from https en wikipedia org w index php title Desiccant amp oldid 1186518737, wikipedia, wiki, book, books, library,

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