Activated alumina is a porous aluminum oxide material characterized by its high specific surface area, porous structure, and strong surface activity. Its effectiveness as an adsorbent stems from its strong affinity for water molecules, certain polar gas and liquid molecules, and fluoride ions. Its primary applications include:

1. Gas Drying: This is the most important and widespread application.

   • Industrial Gas Drying: Used to dry air, nitrogen, oxygen, hydrogen, carbon dioxide, natural gas, cracked gas, acetylene, propane, flue gas, etc. It can deeply dry gases to very low dew points (e.g., -70°C or lower).

   • Refrigeration System Drying: Used in air conditioning and refrigeration systems (e.g., automotive AC, household refrigerators, industrial cold storage) to adsorb moisture from refrigerants (like R134a, R410a, R404a), preventing ice formation and corrosion.

   • Instrument Air Drying: Provides dry, clean air for precision instruments and pneumatic control systems.

   • Natural Gas Drying: Removes water from natural gas before extraction, processing, and pipeline transmission to prevent hydrate formation and pipeline corrosion.

2. Liquid Drying (Dehydration):

   • Petrochemical Industry: Deep drying of organic liquids like aromatics (benzene, toluene, xylene), olefins, gasoline, kerosene, lubricating oils, transformer oils, etc., to remove trace water.

   • Solvent Drying: Drying polar solvents such as ethanol and isopropanol.

   • Refrigerant Drying: Removes moisture during refrigerant production and filling.

3. Fluoride Removal from Drinking Water & Wastewater:

   • Activated alumina exhibits selective adsorption for fluoride ions (F⁻). It is a commonly used and effective adsorbent for treating high-fluoride drinking water (preventing endemic fluorosis) and fluoride-containing industrial wastewater (e.g., from aluminum electrolysis, electronics, glass, phosphate fertilizer production). Once saturated, it can be regenerated (typically using alum solution or sodium hydroxide solution) to restore its adsorption capacity.

4. Acidic Gas Removal:

   • Capable of adsorbing and removing acidic components from gases, such as hydrogen sulfide (H₂S), sulfur dioxide (SO₂), and hydrogen chloride (HCl). While its capacity may be lower than specialized desulfurizers (e.g., zinc oxide), it is still used in specific operating conditions.

5. Selective Adsorption & Separation (Chromatography):

   • Due to its surface acidity/basicity and polarity, activated alumina is widely used as a stationary phase (adsorbent) in chromatographic separation (column chromatography) for purifying and separating organic compounds (e.g., alkaloids, steroids, vitamins, fats), especially in column and thin-layer chromatography.

   • Used in the petroleum industry for the separation of certain hydrocarbons.

6. Catalyst Carrier:

   • Though not strictly a direct "adsorbent" application, its excellent adsorptive properties (high surface area, pore structure, surface characteristics) make it an extremely important and widely used catalyst carrier. It effectively supports and disperses active metal components (e.g., cobalt, molybdenum, nickel, platinum, palladium) and is extensively used in numerous catalytic processes like hydrotreating, hydrocracking, reforming, dehydrogenation, and the Claus sulfur recovery process.

Summary of Activated Alumina's Core Advantages as an Adsorbent:

• High Specific Surface Area and Pore Volume: Provides abundant adsorption sites.

• Good Mechanical Strength and Abrasion Resistance: Suitable for fixed-bed operations, resistant to attrition.

• Excellent Thermal Stability: Can be used and regenerated at elevated temperatures.

• Strong Affinity and High Capacity for Moisture: Especially effective for deep drying.

• Selective Adsorption for Fluoride Ions: Virtually irreplaceable in defluoridation applications.

• Controllable Surface Acidity/Basicity: Useful for selective adsorption and as a catalyst carrier.

• Regenerability: Adsorbed substances can be desorbed through heating (dehydration) or treatment with specific solutions (e.g., regeneration after fluoride removal), restoring most of its adsorption capacity for cost-effective reuse.

Therefore, activated alumina plays a vital role in gas and liquid drying/purification, environmental fluoride removal, chromatographic separation, and as a catalyst support material.