Active Aluminum oxide

Product Description:

Physicochemical parameters

General description

Active aluminum oxide (also known as AOA, activated aluminum oxide, active aluminum oxide, activated aluminum oxide, adsorbent, and alumogel) has the chemical formula _Al2O3 and is a white or cream-colored granular substance with a microporous structure and a smooth surface. AOA is odorless. Due to its incredible hardness and mechanical strength _, active aluminum oxide is resistant to abrasion, corrosion, and high temperatures.

Industrially, active alumina is produced by calcining gibbsite, the raw material for which is bauxite, at 400–600°C. In the Bayer process, bauxite is converted into sodium aluminates by the action of alkali. After washing and separation, the "red mud" (containing impurities such as iron and silicon oxides) is removed, yielding gibbsite, which is then used in the production of aluminum oxide.

The quality of activated alumina is determined by the ratio of gibbsite and boehmite, two chemical compounds with different crystallochemical properties, in the bauxite ore. When large gibbsite grains obtained in this process are thermally dehydrated without the use of specialized technologies, the resulting active alumina has a low specific surface area and small pore volume, due to the presence of inactive boehmite, whose content reaches up to 40%. We offer our customers only active alumina produced using a process that produces AOA with a large surface area, high specific pore volume, and exceptionally high adsorption properties. Axens developed AxSorb A and AxSorb D active alumina grades using a special "flash process" technology, which precisely defines the ratios necessary to produce various grades of activated alumina with the desired combination of adsorption capacity and desirable physical parameters such as crushing strength and abrasion resistance.

Adsorption with activated alumina is one of the primary methods for removing water from air or gas streams. It is used to avoid unwanted liquid and ice formation and associated problems with corrosion and catalyst fouling in a variety of processes, including air conditioning and industrial gas drying. Activated alumina is ideal for drying compressed air or gases with high relative humidity.

Adsorption capacity remains the key parameter of activated alumina used to evaluate adsorbent performance. Adsorption capacity depends on the reactivity of surface sites and is measured as the volume of water adsorbed per unit surface area. Activated alumina with improved high porosity exhibits a large specific surface area and high adsorption capacity per unit mass. Even when saturated with water, AOA appears and behaves like a dry material. Furthermore, activated alumina is inert to most liquids and gases. Activated alumina is ideal for use in petrochemical product purification due to its high resistance to fouling by olefin polymerization products.

The specific heat of adsorption of activated alumina at the most active sites is very high. This makes activated alumina an extremely effective desiccant and allows for extremely low water dew points near these sites. As relative humidity increases, water adsorption at less active sites increases.

To create adsorption centers, a large internal surface area is required due to pores (capillaries). Active alumina has become the most popular adsorbent due to its surface chemical properties and the ability to produce it with precisely defined pore sizes:

• Macropores (>500 A) to enhance diffusion into the pore system.
• Mesopores (50–500 A) for absorption of medium-sized molecules.
• Micropores (< 50 A) for absorption of small molecules such as water.

Active alumina has a significant advantage over other desiccants: neither capillary condensation nor the presence of free water destroys its structure. These processes occur at the surface, which determines the reaction rate.

Adsorbents in industry face stringent requirements, particularly in air drying, where customers require high gas velocities and pressures, as well as frequent regeneration. Low cost, chemical and physical stability, regeneration capability, and high water absorption capacity are factors that have contributed to the widespread use of activated alumina. We supply AxSorb grades of activated alumina from the French manufacturer Axens, meeting these requirements:

• 1. AxSorb A is a bead-shaped adsorbent with a diameter of 2-5 mm. The adsorbent's parameters are optimized for use in cleaning or drying applications.
• 2. AxSorb D (Drying) comes in beads with diameters of 2–5 and 4–8 mm. This type of active aluminum oxide is specifically designed for air drying. The smooth surface of the AOA beads provides improved mechanical properties. Extremely high abrasion resistance and strength, combined with a large surface area and high adsorption capacity, give AxSorb D the properties necessary for safe operation in the harshest drying conditions.

Axens AxSorb activated alumina can be used to dry most streams, including liquids. Liquids are typically dried in an upflow mode to ensure better distribution across the activated alumina bed. Alumina can be regenerated using either dried product vapor or a dry gas such as methane. In practice, when drying liquids with activated alumina, the contact time is much longer than when drying gases, as the moisture content per unit volume of the stream is higher. For some liquids, effective drying can be achieved with a contact time of 1 minute or less.

The porosity of AxSorb activated alumina is controlled through a carefully controlled production process, allowing for favorable and gentle operating conditions during drying and regeneration.

Axens AxSorb aluminum oxide materials are highly resistant to abrasion and fracture. This is due to the production technology and the spherical shape of the particles. Spherical particles offer excellent strength and abrasion resistance, perfectly suited to operating conditions. Furthermore, the spherical shape allows for compact and uniform loading with extremely low subsequent shrinkage. Higher flow rates and taller apparatuses can be used.

The most important parameter of active alumina remains hydrothermal aging. AxSorb adsorbents with a high specific surface area exhibit good surface properties that remain virtually unchanged over time. This is a clear advantage over alumina-based materials offered by competitors. Axens' AxSorb aluminum oxide grades have gained wide recognition for their exceptional stability, combined with excellent physical properties and extremely high adsorption capacity.

Axens AxSorb activated alumina materials, supplied in ball form, feature extremely low pressure drops compared to the same volumes of granules or extrudates. Their excellent loading properties virtually eliminate the risk of channeling, which is often observed with granules. This AxSorb activated alumina can be used in very tall apparatuses, as pressure drops are low, and the extremely durable balls eliminate the risk of crushing or abrasion.

AOA is non-flammable. According to Directive 1999/45/EC, activated alumina is not classified as hazardous to health.

Appearance

In appearance, activated aluminum oxide appears as white or cream-colored granules with a smooth surface and a microporous structure. The diameter of the activated aluminum oxide beads AxSorb A is 2-5 mm, while AxSorb D is 2-5 mm and 4-8 mm, respectively.

Package

Active aluminum oxide is supplied in industrial packaging:

Transportation and storage conditions

Active aluminum oxide is recommended to be transported and stored under the following conditions:

• Activated aluminum oxide is transported by all available modes of transport in accordance with the rules for the transportation of goods;
• AOA must be stored in unopened factory packaging, in a dry, ventilated area and on pallets, avoiding dust formation and spraying into the atmosphere.

Subject to transportation and storage conditions, the guaranteed shelf life of activated aluminum oxide is 3 years.

Application areas

Active aluminum oxide is widely used in industry:

• In the chemical industry, activated alumina is used as a catalyst carrier (catalytic reforming), a catalyst and a drying agent, a derivative for mixed catalysts;
• Active aluminum oxide is used as a hydrophilic sorbent, since its properties are similar to those of fine-pored silica gel;
• In the gas and oil refining industry, AOA is necessary for drying various liquids (oil, gasoline, hexane), gases (air, natural gas, liquefied petroleum gas, carbon dioxide);
• activated aluminum oxide is used in the purification of industrial oils from oxidation products;
• when preserving equipment, active aluminum oxide is used at the static drying stage;
• AOA is used in chromatography.