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This post was last edited by I am kind on 2016-8-9 09:39. Adsorbents can be classified based on factors such as pore size, particle shape, chemical composition, and surface polarity. Examples include coarse-pore and fine-pore adsorbents, powdered, granular, and strip-shaped adsorbents, as well as carbon-based and oxide-based adsorbents, polar and non-polar adsorbents, etc. Commonly used adsorbents include various activated carbon adsorbents made from carbon-based materials, as well as adsorbents based on metal and non-metal oxides (such as silica gel, alumina, molecular sieves, natural clays, etc.). The main indicators for evaluating adsorbents include: the adsorption capacity for various gaseous impurities, wear rate, bulk density, specific surface area, and compressive strength. It is used to remove toxic gases, refine petroleum and vegetable oils, prevent viruses and molds, recover gasoline from natural gas, and decolorize vinegar and other dark-colored substances. 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. Silica gel is a hydrophilic, polar desiccant that is primarily used for drying, as well as for the separation of gas mixtures and petroleum components. Silica gel used in industry is divided into coarse-pore and fine-pore types. 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. The properties of activated alumina 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 reactivity of its pore channel surface, it is also known as active alumina. It has a strong affinity for water and is an adsorbent used for the deep drying of trace amounts of water. Activated carbon is produced 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; after removing volatile components, usually at temperatures below 700°C, 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. Zeolites are characterized by their molecular sieve properties, featuring uniform pore sizes such as 3A0, 4A0, 5A0, and 10A0 pores. 4A0 zeolite with a 4A0 pore size can adsorb methane and ethane, but not n-alkanes 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-alkanes and isoparaffins. Carbon molecular sieves are essentially a type of activated carbon. What sets them apart from ordinary carbon-based adsorbents is that the pore sizes of their 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 more than 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 lead 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 primarily serve as transport channels, while the micropores function 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 achieved success in the field of air separation for nitrogen production, and they also hold great potential for other gas separations. In the chemical industry, molecular sieves are used as solid adsorbents; the substances adsorbed by them can be desorbed, and molecular sieves can be regenerated after use. It is also used for the drying, purification, separation, and recovery of gases and liquids. Starting in the 1960s, they were used as cracking catalysts in the petroleum refining industry, and today a variety of molecular sieve catalysts suitable for different catalytic processes have been developed.