A desiccant is a substance that absorbs or adsorbs water to promote or sustain dryness (desiccation). In other words, a desiccant is a hygroscopic material. The opposite of a desiccant is a humectant, which promotes water retention.
Examples of Desiccants
Many products include tiny packets containing silica gel beads. Silica gel is a desiccant that removes moisture because each bead contains numerous pores that attract and hold water. But, there are other common desiccants:
- Silica gel
- Calcium chloride
- Calcium sulfate
- Activated charcoal
- Activated alumina
- Molecular sieves (e.g., zeolites)
- Montmorillonite clay
Most desiccants are solids, but some liquids also remove water from their environment. Examples are acetone and alcohol.
Desiccant Uses
Desiccants protect materials and items that suffer damage from moisture. For example, including packets of desiccants in packaging protects metals and electronics from corrosion, organic fabrics from decay, and dry foods from becoming soggy.
Desiccants preserve dry environments. For example, they are included in sealants in insulated windows so the glass does not get foggy.
Manufacturing uses desiccants during chemical and product manufacturing. In the chemical industry, desiccants help prevent some chemicals from forming their hydrates. In other cases, removing moisture protects against dissolving or chemical reactions with water. Desiccants remove moisture from solvents and gas streams.
Desiccants often serve a dual purpose, as most absorb odors as well as moisture.
Uses Around the Home
When you get silica gel packets, don’t just throw them away. They serve many useful purposes:
- Dry out a wet phone by sealing it in a plastic bag with silica gel packets overnight.
- Toss silica gel packets on the dashboard of a car to defog the windshield quickly.
- Dry flowers so you can keep them as decorations.
- Keep a package inside shoes, drawers, or your gym bag to prevent mildew and reduce odors.
- Store razors in a sealed container with the desiccant and keep them rust-free.
- Protect important documents and old photos. Include a desiccant inside their box.
How to Regenerate Desiccants
Eventually, silica gel packets absorbs all the water they can hold. Regenerate silica gel by baking it in a warm oven (up to 180 °F or 82 °C ). This drives off the water and regenerates the desiccant.
Some other desiccants are easily regenerated, although they need higher temperatures. Bake activated alumina at ~200 °C and zeolite at ~550 °C.
References
- Chai, Christina Li Lin; Armarego, W. L. F. (2003). Purification of Laboratory Chemicals. Oxford: Butterworth-Heinemann. ISBN 978-0-7506-7571-0.
- 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
- Flörke, Otto W., et al. (2008) “Silica” in Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a23_583.pub3
- Lavan, Z.; Monnier, Jean-Baptiste; 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
- Williams, D. B. G.; Lawton, M. (2010). “Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants.” The Journal of Organic Chemistry. 75: 8351. doi:10.1021/jo101589h