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How to choose the best desiccant? How much do you know about these scientific principles?
Desiccant is a hygroscopic substance whose main purpose is to stimulate or maintain a dry state around it, which is exactly the opposite of humectant. Common desiccants in daily life usually exist in solid form and can effectively absorb moisture. These desiccants are widely used in food packaging to keep products crisp and fresh, and in industry to control moisture content in gas streams.
Types of desiccant
The most common desiccant is silica gel, which is an inert, non-toxic, white solid that is insoluble in water. Tens of thousands of tons of silicone are produced every year.
In addition to silica gel, other common desiccants include activated carbon, calcium sulfate, calcium chloride, and molecular sieves (usually aluminosilicates). These desiccants can be classified based on different characteristics, such as categories I to V based on the shape of the moisture sorption isotherm. In addition, certain industrial desiccants such as diethylene glycol also play a vital role, as they can effectively absorb moisture from natural gas and reduce the formation of methane hydrates.
Performance efficiency
One measure of desiccant efficiency is the ratio of the moisture it can absorb to the mass of the desiccant. Another key indicator is the residual relative humidity of the medium being dried.
For dry gases, for example, the performance of a desiccant can be accurately described by the dew point of its product. These performance indicators help users make informed decisions when selecting desiccants to meet specific application needs.
Color saturation indicator
Many desiccants will add humidity indicators to show the degree of moisture saturation of the desiccant in the form of color changes. The commonly used indicator is cobalt chloride, which is blue in the anhydrous state and turns purple when reacting with water molecules. With further hydration reaction, a pink cobalt chloride hexahydrate complex will be formed. Although such indicators are effective in use, they also raise health concerns as possible carcinogens.
Application fields
The application of desiccant is mainly in the petrochemical industry. In this industry, natural gas and other hydrocarbons often need to be kept absolutely dry to facilitate handling and transportation. Even trace amounts of moisture can render catalysts used in some petroleum fractionation conversions ineffective. The use of desiccants ensures the stability of industrial processes.
Applications in home and daily life
Desiccant is also widely used in daily life, such as in the manufacture of insulated windows. Molecular sieve spheres are filled with rectangular spacers surrounded by fiberglass to avoid condensation of water vapor between the glasses. In other aspects, desiccants can also be used to protect food, medicine and other moisture-prone goods, reducing the risk of products becoming damp.
For example, when transporting cocoa, coffee, various nuts and grains, in order to prevent mildew and rot, shippers often deploy desiccants to reduce losses caused by moisture. Small packages of desiccant are often included in pharmaceutical packaging to maintain the moisture content of the environment within the packaging below critical levels.
Use in laboratory
In chemistry laboratories, desiccants are used to remove moisture from solvents. Typically, the drying process involves mixing a solid desiccant with a solvent. Compared with chemical desiccants such as sodium phenyl, molecular sieves have advantages in hygroscopic properties, can be used safely in the air, and can be recycled.
Questions worth thinking about
When we review the diversity and uses of desiccants, will we think of the correlation between material selection and use environment that may have been overlooked?
