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:

Adsorbent

Applications

Drying of gases, refrigerants, organic solvents, transformer oils
Desiccant in packings and double glazing
Dew point control of natural gas

Drying of gases, organic solvents, transformer oils
Removal of HCl from hydrogen
Removal of fluorine in alkylation process

Nitrogen from air
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

Oxygen from air
Drying of gasses
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
Removal of acetylene, propane and butane from air
Separation of xylenes and ethyl benzene
Separation of normal from branched paraffins
Separation of olefins and aromatics from paraffins
Recovery of carbon monoxide from methane and hydrogen
Drying of refrigerants and organic liquids
Pollution control, including removal of Hg, NOX and SOX
Recovery of fructose from corn syrup

Polymers & Resins

Water purification
Recovery and purification of steroids, amino acids
Separation of fatty acids from water and toluene
Separation of aromatics from aliphatics
Recovery of proteins and enzymes
Removal of colours from syrups
Removal of organics from Hydrogen peroxide

Treatment of edible oils
Removal of organic pigments
Refining of mineral oils
Removal of polychlorinated biphenyls (PCBs)

 

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