Desiccants are substances or chemicals that absorb and attract moisture from the air, resulting in desiccation (dryness) in the surrounding atmosphere. Desiccants are used in packaging to prevent moisture damage to items in packages during shipping. They are widely used in the food, manufacturing, logistics and pharmaceutical industries. For example, in the food industry, a box of new vitamins is frequently sealed with a small mesh bag labeled “Desiccant, Do Not Eat.” Inside the packet are hygroscopic beads (commonly Silica or Activated Alumina) that absorb moisture and protect the item during transportation and storage, keeping the products dry and preventing corrosion.
The shelf life of desiccants is determined by the packaging environment in which they are used, but most desiccants have a shelf life of one to three years and can be reused upon regenerating them.
Here are some ways to reuse Desiccants.
1. Silica Gel
Silica Gel is a traditional and safe moisture absorbing desiccant commonly used in the healthcare and electronics industries to adsorb moisture. Adsorption is when water in the air is absorbed between the microscopic pores as the air passes through them, which is made possible by the high surface area of the Silica Gels. The absorbers are made of oxygen and silicon atoms and have nanometer-sized voids.
When the Silica Gel absorbs moisture, it transitions from an active to an inactive state. When this occurs, the Silica Gel must be reactivated before it can be used again.
To reactivate the Silica Gel, pour the saturated Silica Gel beads into a thin layer on a baking sheet before baking for 15 minutes at 79.4°C in a preheated oven. The heat from the oven will absorb moisture from the Desiccant pack, helping to reactivate the Silica Gel. After removing the Desiccant bag from the oven, please place it in a zip lock bag to keep away moisture, and the Desiccant pack will be ready for use when needed.
2. Molecular Sieve
Molecular Sieve is the most commonly used desiccant for dehydrating, purifying, and separating specific gases and liquids. It is widely used in filtration systems to reduce humidity levels due to its ability to absorb up to 22% of its weight and withstand temperatures as high as 300°C.
Due to water adsorption from carrier gas or samples, the separating power of Molecular Sieves can gradually decrease, which means that the Molecular Sieve will not work as well as it did the first time, and regeneration is required.
The methods for regenerating Molecular Sieves include:
- Pressure change (oxygen concentrators).
- Heating and purging with a carrier gas (ethanol dehydration).
- Heating under a high vacuum.
Although some Molecular Sieves that remove alcohols and aromatic hydrocarbons use force to regenerate the sieve, most water-adsorption Molecular Sieves are usually regenerated by heating.
Depending on the Molecular Sieve type, regeneration temperatures range from 175°C to 315°C. Most industrial applications require temperatures ranging from 121°C to 232°C.
3. Activated Alumina
Activated Alumina is used in a variety of heavy industrial applications, including catalyst adsorption and fluoride removal. Activated Alumina has a surface area greater than 200m2g and can adsorb many substances, including gases and liquids, without changing their shape or structure. As a result, Activated Alumina works well as a desiccant adsorbent. It is also commonly used to remove fluoride, arsenic, and selenium from water. Moreover, due to its toughness, the adsorbent is ideal for use in high-pressure applications.
A compressed air dryer is required to regenerate an Activated Alumina Desiccant. A heatless or heated compressed air dryer restores the Activated Alumina by using hot air or gas. The heat evaporates the small water vapours and droplets trapped inside the tiny holes of Activated Alumina. Activated Alumina can also be regenerated by baking it at temperatures ranging from 149°C to 204°C. Once the Activated Alumina Desiccant is restored, it can be reused multiple times.
4. Activated Clay
Activated Clay is primarily used in industrial packaging to protect products. Activated Clay is an excellent substitute for Silica Gel in all traditional packaging applications because of its high efficiency, dehydrating properties, and low cost. It is also available in three varieties: Sodium Bentonite, Calcium Bentonite, and Potassium Bentonite.
Activated Clay is a porous mineral that has been dried to create an adsorbent material with a high adsorption capacity at average temperature and relative humidity levels. The Clay retains its structure as it becomes saturated and can be easily reactivated for reuse by heating.
The adsorbent material’s main disadvantage is its ability to absorb moisture at low temperatures. Temperatures as low as 50°C may start the process of releasing moisture back into the environment. This adsorbent material property helps reactivate the Clay but may cause issues in high-temperature applications. As a result, when choosing this material for moisture protection, exercise caution.
Activated Clay is safe to handle and dispose of as it is chemically inactive and non-toxic. Moreover, Clay is usually less expensive than adsorbents like Silica Gel or Molecular Sieves.
5. Activated Carbon
Activated Carbon is a type of graphite with a random, flawed structure with a wide range of pore sizes, resulting in a high surface area and the highest physical adsorption forces. Activated Carbon is also a cost-effective method for treating large volumes of low-polluting gas or water, and it is commonly used in water, air, and gas treatment, as well as odor control.
Before reusing Activated Carbon:
- Allow it to dry completely if the Activated Carbon has become damp due to absorbing atmospheric moisture.
- Preheat the oven to 149°C and spread the Carbon in a single layer on a baking sheet.
- Bake the Activated Carbon for one hour at 149°C to remove odours and impurities.
- Allow the Activated Carbon to cool completely before placing it in an open shallow dish to remove odours. After it has been cooled completely, it can be reused multiple times.
Desiccants are an excellent choice for packaging that keeps moisture out of products while they are being shipped or stored. They are widely used in the manufacturing, food, and pharmaceutical industries and can be used repeatedly to protect items from moisture damage.