What are Desiccants?
Desiccants are substances and agents made up of hygroscopic material that helps keep things dry. Desiccants remove moisture from the air to create and maintain a moisture-free environment.
Moist and damp environments can cause damage to electronics, clothing, cosmetics, medications, vitamins, and various other products. Moisture creates an environment that promotes bacteria, mould, fungus, and degradation. Moreover, moisture in electronics can cause long-term damage and corrosion. However, Desiccants can help to prevent this damage.
Desiccants’ primary function is to facilitate and maintain low-humidity environments by absorbing excess moisture in the air. Common applications include storage, transportation, and maintenance facilities for various products and materials. Desiccants can also keep everything from military weapons to gym shoes dry.
Desiccants are not toxic or harmful. Hence, popular Desiccants such as Silica Gel are commonly used to keep things dry as it works incredibly well at keeping things dry. Desiccants, in addition to metals, can protect paper from humidity, preserve art and display cases, and slow silver.
Various Types of Desiccants
Desiccant packets can be found in various consumer products, from shoeboxes to vitamins. Desiccants are tiny silica gel packets or small cylindrical canisters in the packaging. The following are some of the most common Desiccants:
- Silica Gel (typically found in small “bead” form)
- Activated Carbon
- Activated Alumina
- Activated Clay
- Molecular Sieve
Silica Gel is a safe traditional Desiccant commonly used to adsorb moisture in the healthcare and electronics industries. Adsorption is when water in the air is absorbed between the microscopic pores as the air passes through them, possibly due to its large surface area. The absorbers have nanometer-sized voids and tridimensional oxygen and silicon atoms structure. Silica Gel xerogel is the liquid or gas material that fills the voids or pores. Due to its physical properties, silica Gel is a good drying agent for preventing corrosion, contamination, spoilage, and mould growth in various commodities and products.
Silica Gel is a polymeric colloidal silicic acid that has been partially dehydrated. Silica Gel has an amorphous microporous structure with pore opening sizes ranging from 3 to 60 angstroms. These interconnected pores create a large surface area that attracts and holds water via adsorption and capillary condensation, allowing Silica Gel to absorb up to 40% of its weight in water.
Silica Gel works extremely well at temperatures below 25°C. However, it may release moisture into the air at high temperatures. Nonetheless, Silica Gel is popular due to its non-corrosive and non-toxic nature.
Activated Carbon, also known as Activated Charcoal or Activated Coal, is a type of graphite. Unlike graphite, Activated Carbon has a random, flawed structure with wide pore sizes, resulting in a high surface area and the highest physical adsorption forces. As a result, Activated Carbon is a cost-effective method for treating large volumes of low-polluting gas or water. Activated Carbon is commonly used in water, air, gas treatment, and odour control.
Many carbons adsorb small molecules. The iodine number is the most fundamental parameter used to characterise Activated Carbon performance. The iodine number measures the activity level (a higher number indicates a greater degree of activation) and is commonly reported in mg/g (typical range 500–1200 mg/g). The iodine number can also measure the micropore content of Activated Carbon (0 to 20 or up to 2 nm) obtained through iodine adsorption from the solution.
Activated Alumina is a porous, solid form of Aluminium Oxide (Al2O3) used in heavy industrial applications for various purposes, including catalyst adsorption and removing fluoride and other pollutants.
Activated Alumina has a high specific surface area and good moisture absorption and has been widely used in the petrochemical, food, and air-conditioning industries. It has a high specific surface area (300 m2/g) and a more than 50% moisture absorption rate. Activated Alumina can also be professionally developed to improve performances in specific industrial applications, making it a cost-effective solution to many pressing environmental problems. Activated Alumina can regain moisture adsorption through regeneration, also known as desorption.
Compared to Silica Gel, Activated Alumina had a higher coefficient of performance (COP) and a faster dynamic response. As a result of its unique properties, Activated Alumina differs from Silica Gel in many ways.
Activated Clay is an absorbent aluminium phyllosilicate clay containing a high concentration of the element montmorillonite. It is commonly used to protect products in industrial packaging. Activated Clay is a good alternative to Silica Gel in all conventional packaging applications due to its high efficiency, dehydrating properties, and low cost. Activated Clay is available in three varieties: Sodium Bentonite, Calcium Bentonite, and Potassium Bentonite.
Activated Clay can be activated for use as a Desiccant through careful drying. Activated Clay will regenerate successfully for repeated use at low temperatures without significant deterioration or swelling. However, as temperatures rise, this property causes the Activated Clay to release moisture into the container readily. Activated Clay is inexpensive and effective within the average temperature and relative humidity ranges. There may be some variation in performance as it is a naturally occurring material.
Molecular Sieve is made up of microporous aluminosilicate materials such as zeolites. Molecular Sieve has customisable pore openings that allow specific molecules to separate by absorbing molecules smaller than the width of the pore openings while excluding the rest. As a result, it is the most recommended Desiccant for dehydrating, purifying, and segregating specific gases and liquids.
Molecular Sieve is commonly used in filtration systems to reduce humidity levels due to its ability to absorb up to 22% of its weight and be used in temperatures as high as 300°C. Moreover, because of the varying pore sizes, the product applications of each type of Molecular Sieve differ, making the nature of Molecular Sieves particularly versatile because they can be used for various purposes.
The internal adsorptive surface area of a Molecular Sieve is 700 to 800 square meters per gram (half the total volume of the crystals) due to its uniform network of crystalline pores and empty adsorption cavities. Molecular Sieve has a higher unit cost due to its comprehensive range of adsorptive capabilities.
Desiccants of various types can be used for a variety of purposes. For instance, Desiccants can also be used in filter-like breathers to prevent contamination. Thus, it is good to know the types available and their characteristics to choose the best suitable desiccant for use.