【Weekly Topic】{November 28, 2011} What are the common types of adsorbents?

Commonly used adsorbents include activated carbon, silica gel, molecular sieves, and activated alumina.

Activated carbon, silica, molecular sieves, activated alumina, carbon molecular sieves, activated carbon fibers

This post was last edited by fuwasi on 2011-11-30 at 13:27. Reply 1# QQNeverGivesUp. Common adsorbents include diatomaceous earth, activated carbon, activated clay, silica gel, molecular sieves, etc

What I have seen are activated carbon, silica gel, molecular sieves, and activated alumina.

Commonly used adsorbents in industry include silica gel, activated alumina, activated carbon, molecular sieves, etc. There are also adsorbent materials developed for the selective adsorption of specific components. The success of gas adsorption separation depends to a large extent on the properties of the adsorbent; therefore, selecting an appropriate adsorbent is the primary issue in determining the adsorption process. I. The properties of commonly used adsorbents are outlined as follows: 1. Silica gel It is a hard, amorphous polymeric particle with chain-like and network-like structures; its molecular formula is SiO2·nH2O. It is a hydrophilic, polar adsorbent. It is obtained by treating an aqueous solution of sodium silicate with sulfuric acid to form a gel; after washing away sodium sulfate and drying, glassy silica gel is produced. It is mainly used for drying, as well as for the separation of gas mixtures and petroleum components. Silica gel used in industry is divided into two types: coarse-pored and fine-pored. Under conditions of saturated relative humidity, the adsorption capacity of coarse-pore silica gel can reach over 80% of the weight of the adsorbent; whereas under low-humidity conditions, its adsorption capacity is **lower than that of fine-pore silica gel. 　　Active alumina is produced by heating and dehydrating aluminum hydrates; its properties depend on the structural state of the initial hydroxide. It is generally not pure Al2O3, but rather a partially hydrated, amorphous porous material that contains not only amorphous gels but also crystals of hydroxides. Due to the high activity of its pore channel surface, it is also known as activated alumina. It has a strong affinity for water and is an adsorbent used for the deep drying of trace amounts of water. Under certain operating conditions, its drying depth can reach below the dew point of -70°C. It is made by carbonizing and activating carbon-containing materials such as charcoal, fruit shells, and coal. Activation methods can be divided into two major categories: chemical activation and gas activation. The chemical activation method involves adding chemicals such as zinc chloride and potassium sulfide to the raw material, followed by heating in a non-reactive atmosphere to carry out carbonization and activation. The gas activation method involves heating the activated carbon precursor in an inert atmosphere; typically, volatile components are removed at temperatures below 700°C, after which water vapor, carbon dioxide, flue gas, air, etc., are introduced, and a reaction is carried out at temperatures ranging from 700 to 1200°C to activate it. Activated carbon contains many capillary pore structures, which gives it excellent adsorption capacity. Therefore, its applications are widespread in areas such as water treatment, decolorization, and gas adsorption. 3. Zeolite molecular sieves: Also known as synthetic zeolites or molecular sieves, their general chemical formula is: O.Al2O3.nSiO2.mH2O. Here, M2(Ⅰ) and M(Ⅱ) represent monovalent and divalent metal ions, usually sodium and calcium respectively. n denotes the silica-alumina ratio of the zeolite; silicon comes from sodium silicate and silica gel, while aluminum comes from sodium aluminate and Al(HO)3. These substances react with an aqueous solution of sodium hydroxide to form colloids, which, after drying, become zeolites. Generally, n ranges from 2 to 10, and m ranges from 0 to 9. 　　Zeolites are characterized by their molecular sieve functionality, possessing uniform pore sizes such as 3A0, 4A0, 5A0, and 10A0 fine pores. 4A0 zeolite with a 4A0 pore size can adsorb methane and ethane, but not n-paraffins with more than three carbon atoms. It has been widely used in gas adsorption separation, gas and liquid drying, as well as the separation of n- and isopentane. 4. Carbon molecular sieve 　　It is actually a type of activated carbon as well. What sets it apart from ordinary carbon-based adsorbents is that the pore sizes of its micropores are uniformly distributed within a narrow range; these pore sizes are comparable to the diameter of the gas molecules to be separated. The specific surface area of these micropores accounts for over 90% of the total surface area of the carbon molecular sieve. The pore structure of carbon molecular sieves is mainly organized as follows: large pores have diameters that connect to the outer surface of the carbon particles; transitional pores branch off from the large pores; and micropores branch off from the transitional pores. During the separation process, the macropores mainly serve as transport channels, while the micropores act as molecular sieves. 　　The methods for producing carbon molecular sieves from coal as a raw material include carbonization, gas activation, carbon deposition, and impregnation. Among them, the carbonization method is the simplest, but to produce high-quality carbon molecular sieves, these methods must be used in combination. 　　Carbon molecular sieves have been successful in the field of air separation for nitrogen production, and they also hold great potential for other gas separation applications. II. Other adsorbents, also known as absorbents, are substances that allow active components to adhere to their particle surfaces, converting liquid trace compound additives into solid compounds, which facilitates uniform mixing. Their characteristics include strong adsorption capacity and stable chemical properties. Adsorbents are generally divided into organic and inorganic categories; organic ones include wheat germ flour, defatted corn germ flour, corn cob fragments, coarse bran, soybean flour, as well as grains with high water absorption capacity. Inorganic adsorbents include silica, vermiculite, calcium silicate, etc. The most representative adsorbent is activated carbon, which has excellent adsorption properties but is relatively expensive; it was used in the Songhua River incident to absorb toluene from the water. Next are molecular sieves, silica gel, activated aluminum, polymer adsorbents, and biological adsorbents, among others

Activated carbon, molecular sieves, silica gel, activated aluminum, natural clays, polymer adsorbents, and biological adsorbents, etc

The common adsorbents we use include coke, activated carbon, silica gel, molecular sieves, and activated alumina.

Reply 1# QQNeverGivesUp: activated carbon, silica, zeolite molecular sieves, carbon molecular sieves, activated alumina

Commonly used ones include activated carbon, molecular sieves (mainly 5A and 13X), silica gel (fine-pored), alumina, and copper adsorbents (for purification or removal of CO)

Activated carbon, silica gel, activated alumina, etc.