What is the difference between physical desiccant and chemical desiccant?

The principle of physical desiccant is to physically adsorb water molecules in its internal pore structure; the principle of chemical desiccant is to chemically absorb water molecules and change their chemical structure to become another substance.
Example 1: Silica gel desiccant is a kind of physical desiccant. Silica gel desiccant is usually prepared by reacting sodium silicate and sulfuric acid, and after a series of post-treatment processes such as aging and acid foaming. Silica gel desiccant is an amorphous substance, and its appearance is generally colorless, blue, orange and transparent bead-shaped particles. There are many pores extending in all directions inside. The principle of moisture absorption is to use these pores to adsorb water molecules in the air into its structure. in.
There are two common silica gel desiccants:
1. Fine-pored silica gel desiccant:
The product has a white, translucent glass body in appearance. Mainly used for drying and moisture-proof, can be used as catalyst carrier and dehydration refining of organic compounds. Because of its high bulk density and obvious moisture absorption effect under low humidity. It can be used as an air purifier to remove moisture from the air to control air humidity. It is also widely used in sea transportation, and can also be used as a dehumidification between two parallel sealing glass plates, which can maintain the transparency of the glass.
2. Coarse-pored silica gel desiccant:
The product is white in appearance and has three types: lump, spherical and micro-spherical. The moisture absorption effect is more obvious in the environment of higher relative humidity. It is commonly used as dehydrating agent, desiccant, catalyst carrier, and can remove organic acid and water in transformer insulating oil. In addition, because of its large pore size, it is also a raw material for further processing of silica gel.
Example 2: Quicklime desiccant is a kind of chemical desiccant. The main component of quicklime desiccant is calcium oxide. Usually the preparation method is to calcinate natural rock with calcium carbonate as the main component at high temperature to decompose to produce Carbon dioxide and calcium oxide. Its water absorption capacity is achieved through chemical reaction (CaO + H2O ==== Ca(OH)2 ), which becomes another substance calcium hydroxide after absorbing water, so it is a chemical desiccant. The water absorption of quicklime desiccant is irreversible. Regardless of the humidity of the external environment, it can maintain a moisture absorption capacity greater than 35% of its own weight. It is more suitable for low-temperature storage. It has excellent drying and moisture absorption effects and is low in price. However, due to the explosion of quicklime desiccant in recent years, children have been injured. Occurrence, so this kind of desiccant has gradually been eliminated.