Main Types of Activated Alumina
Briefly introduce the main types of activated alumina.
Main Types of Activated Alumina
Activated alumina is a type of porous, highly dispersed alumina material. Based on differences in crystal structure, preparation process, and applications, it can be classified into several types. The main types are described below.
Classification by Crystal Phase
Activated alumina mainly refers to transition-state alumina such as γ-Al₂O₃, η-Al₂O₃, and χ-Al₂O₃. These crystal phases share common characteristics such as high specific surface area, well-developed pore structure, and a surface rich in hydroxyl groups.
Crystal Phase | Characteristics | Main Uses |
γ-Al₂O₃ | The most commonly used activated alumina, with a specific surface area of 150-300 m²/g and good thermal stability. | Used as a catalyst support and for adsorption and drying. |
η-Al₂O₃ | High specific surface area and small pore size. | Used for high-precision adsorption. |
χ-Al₂O₃ | Obtained from gibbsite through low-temperature dehydration. | Used for special adsorption. |
Classification by Application
From an application perspective, activated alumina can be classified into the following functional types:
Desiccant Type
Primarily aimed at removing moisture (H₂O), its static adsorption capacity for water is typically ≥15% (at 60% relative humidity). Widely used in compressed air drying, natural gas dehydration, and petroleum cracking gas drying, it can lower the gas dew point to below -55℃.
Catalyst Support Type
Its main function is to support the active components of the catalyst (such as platinum, palladium, molybdenum, cobalt, etc.). It requires a specific surface area ≥200 m²/g, a pore volume ≥0.4 cm³/g, and low impurity (Na, Fe, Si) content. Used in petroleum hydrorefining, desulfurization, reforming, and automotive exhaust purification catalysts.
Defluoridation Type
Specifically designed for defluoridation of drinking water, this activated alumina exhibits selective adsorption of fluoride ions. Static defluoridation capacity ≥2.5 mg/g, suitable for drinking water treatment in high-fluoride areas.
Hydrogen Peroxide Type
Used for the regeneration treatment of hydrogen peroxide produced via the anthraquinone process. Requires activated alumina with a high specific surface area and suitable pore structure to effectively adsorb degradation products in the working solution.
High Temperature Resistant Type
Modified with additives (such as lanthanum, cerium, and other rare earth elements) to improve thermal stability, maintaining a high specific surface area at 800-1000℃. Suitable for harsh conditions such as high-temperature tail gas catalytic purification.
Classification by Preparation Process
Fast Dehydration Method: Aluminum hydroxide is rapidly heated to 800-900℃, using instantaneous dehydration to form micropores. Achieves 300-400 m²/g specific surface area.
Slow Dehydration Method: Dehydration at 300-500℃ produces a more regular pore structure but slightly lower surface area.
Acid Method: Aluminum salt solution is neutralized to form gel, then dried and activated. Allows precise pore control but is more expensive.
Fast dehydration is the industrial standard due to high efficiency and low cost. The acid method is used for high-purity or special pore structure products.
Summary
Activated alumina can be classified from multiple dimensions such as crystal phase, morphology, application, and preparation process. γ-Al₂O₃ is the most prevalent crystal phase, spherical and strip-shaped forms are the most common product forms, and desiccants and catalyst supports are the two largest application directions. When selecting a type, the matching of crystal phase, morphology, and specifications must be comprehensively considered based on the specific working conditions, media, pressure, flow rate, and adsorption target.