Do you know what activated alumina is? And what is the application for different alumina?
You will know more details in the following blog：
1, what is activated alumina?
Activated alumina is a white porous substance made of aluminum hydroxide AI(OH)3 by high temperature roasting and dehydration, mostly in the shape of spheres with molecular formula Al2O3*nH2O (0<n<0.8).
2, what the difference between different alumina?
Aluminum hydroxide is a kind of polycrystalline substance, which can be obtained under different temperature treatment with different lattice of alumina. Depending on the manufacturing process, alumina is divided into
- low-temperature alumina, which will form transition state crystals with a large internal active surface at activation temperatures below 600℃ The different forms of alumina include ρ-alumina, χ-alumina, η-alumina and γ-alumina;
- high-temperature alumina at activation temperatures from 900 to 1000℃, which include κ-alumina, θ-alumina, δ-alumina and α-alumina.
When the activation temperature is lower than 600℃, transition state crystals with a large internal active surface will be formed, and the crystal structures that can be used for gas separation are χ-ρ-type and, γ-type;
There are more than 8 forms of alumina now, and their properties and applications are different, and they can be used as adsorbents, catalysts carrier.
3, The application of activated alumina
Due to the presence of hydroxyl active center and higher concentration of acidic point on the surface of activated alumina, it is a polar adsorbent.
Low temperature alumina is mostly used for gas drying, and its water absorption capacity under low water vapor pressure is inferior to molecular sieve; under high water vapor pressure, it is inferior to silica gel. However, compared with silica gel, activated alumina has good heat and water resistance, easy to be regenerated for many times, good strength; lower regeneration temperature and lower price compared with molecular sieve;
Therefore, it is always the main variety of gas desiccant in industry.
χ-ρ type activated alumina can also be used for desulfurization of petroleum gas, hydrogen chloride removal from catalytic reforming units and purification of fluorine containing waste gas;
High temperature alumina is often used as carrier of catalyst.
A typical preparation process of activated alumina is as below. After drying and removing the free water, AI(OH)3 is crushed to micron-sized particles, then quickly roasted and dehydrated in a high-temperature furnace, and the binder is added as the basic raw material for forming, mixed evenly, and then shaped in a ball forming machine.