Silica gel: also called silicone rubber, is a kind of high activity adsorption material, is an amorphous substance, its chemical molecular formula is mSiO2 / nH2O. Insoluble in water and any solvent, non-toxic and tasteless, stable chemical properties, in addition to alkali, hydrofluoric acid does not react with any material. According to its nature and composition can be divided into two types of silica gel and inorganic silica gel. 1, organic silica gel is a kind of organic silicon compound. Silicone is mainly divided into four categories: silicone rubber, silicone resin, silicone oil, silane coupling agent. 2, according to the inorganic silica gel pore size divided into big pore silica gel, porous silica, silica gel, silica gel pore type B. Inorganic silica gel according to its use, can also be divided into beer silica gel, pressure swing adsorption silica gel, silicone gel, silica gel desiccant, silica gel, toothpaste, such as silica gel, and so on.