Zibo XiangRun Environment Engineering Co., Ltd.Adsorption occurs at the surface of an adsorbent. Special materials have been developed with a high surface area for this purpose. These are various forms of:
- activated carbons,
- activated aluminas
- silicas.
Adsorbents typically have an effective surface area of several hundred m2/gram.
Commonly used adsorbents:
Commonly used adsorbents include activated carbon, alumina, silica gel and the molecular sieves 13X, 5A and 4A. The number refers to the approximate effective pore size in Angstrom.
Activated carbon :
Activated carbon is used for the adsorption of hydrocarbons, but this is generally not a reversible process. Activated carbon adsorbs oxygen, and so is used to produce nitrogen from compressed air in a nitrogen pressure swing adsorption plant.
Activated Alumina :
Activated Alumina is used for the adsorption of water vapour at ambient temperature.
Silica gel :
Silica gel is also used for low temperature adsorption of hydrocarbons and carbon dioxide.
Classes of adsorbent:
Carbon, alumina and silica gel adsorbents are termed amorphous because they have a broad distribution of pore sizes and depend for their selectivity on the difference in surface attraction for different molecules. A second class of adsorbent termed crystalline has a narrow distribution of pore sizes and uses a small pore opening to also control the selectivity of adsorption. These adsorbents are called molecular sieves.
Molecular sieve :
Molecular sieves are a class of crystalline solids called zeolites. They are formed from a mixture of aluminates and silicates. By varying the relative amounts of aluminate and silicate in the manufacture of the porous crystals different size molecular scale cavities can be formed. The openings between the crystal cavities are of molecular size and so are capable of sieving or filtering action on a molecular scale. Only molecules smaller than a certain size can pass between the cavities and become attached to adsorption sites within the cavities.
Molecular sieve 13X :
Molecular sieve type 13X is used for combined water and CO2 removal. Sometimes an alumina layer precedes the 13X for water removal and the 13X removes the CO2 only.
Molecular sieve 5A :
Molecular sieve 5A is effective for hydrocarbon removal. It can adsorb small unsaturated molecules such as acetylene, propylene and ethylene. Neither propane nor methane/ethane are removed by 5A.
Molecular sieve 4A
Molecular sieve 4A is used primarily for water removal from argon.
Other types of adsorbent
Other special adsorbents are used for specialist applications. Examples are carulite, hopcalite and palladium catalyst which can be used to remove traces of carbon monoxide and hydrogen (by conversion to CO2 and water respectively) from air. The CO2 and water molecules are then adsorbed by a layer of molecular sieve.
Another is the use of alumina adsorbent coated with active copper, which can adsorb carbon monoxide from reformer gas. The carbon monoxide is subsequently desorbed under vacuum as a product stream. This is a chemi sorption process.
Zibo Xiangrun professionally manufacture activated alumina and molecular sieve. Our surface area of activated alumina is 350㎡/g. In air seperation and compressed air industry, the dew point can be -55℃. XR101 activated alumina is an efficient desiccant for deep drying.
