Adsorbent Types Essay

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Types of adsorbents Major types of adsorbents in use are: activated alumina, silica gel, activated carbon, molecular sieve carbon, molecular sieve zeolites and polymeric adsorbents. Most adsorbents are manufactured (such as activated carbons), but a few, such as some zeolites, occur naturally. Each material has its own characteristics such as porosity, pore structure and nature of its adsorbing surfaces. Pore sizes in adsorbents may be distributed throughout the solid. Pore sizes are classified generally into 3 ranges: macropores have "diamaters" in excess of 50-nm, mesopores (also known as transitional pores) have "diameters" in the range 2 - 50-nm, and micropores have "diameters" which are smaller than 2-nm. Many adsorbent materials, such as carbons, silica gels and aluminas, are amorphous and contain complex networks of inter-connected micropores, mesopores and macropores. In contrast, pores in zeolitic adsorbents have precise dimensions. Typical applications of commercial adsorbents: Silica Gel Drying of gases, refrigerants, organic solvents, transformer oils Desiccant in packings and double glazing Dew point control of natural gas Activated Alumina Drying of gases, organic solvents, transformer oils Removal of HCl from hydrogen Removal of fluorine in alkylation process Carbons Hydrogen from syngas Ethene from methane and hydrogen Vinyl chloride monomer (VCM) from air Removal of odours from gases Recovery of solvent vapours Removal of SOX and NOX Purification of helium Clean-up of nuclear off-gases Water purification Zeolites Oxygen from air Removing water from azeotropes Sweetening sour gases and liquids Purification of hydrogen Separation of ammonia and hydrogen Recovery of carbon dioxide Separation of oxygen and argon Removl of acetylene, propane and butane from air Separation of xylenes

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