The quality of alumina products on the market varies. Inferior products may lead to problems such as low adsorption efficiency, easy pulverization, and short service life. So, how to identify high-quality activated alumina?
Key indicators of high-quality activated alumina
1. Physical properties
(1) Appearance and particle uniformity
• Color: High-quality activated alumina is usually white or slightly red. If the color is yellow, gray or has black spots, it may contain impurities or be aged.
• Shape: Generally spherical or bar-shaped particles with a smooth surface without cracks. Inferior products may have debris, powder or uneven particle size.
• Particle size: Common specifications are 3-5mm (for desiccants) and 1-3mm (for catalyst carriers). The appropriate size should be selected according to the application.
(2) Specific surface area
• Specific surface area directly affects the adsorption capacity. The specific surface area of high-quality products is usually 200-400 m²/g.
(3) Pore volume and pore size distribution
• Pore volume: high-quality products are between 0.3-0.6 cm³/g.
• Pore size distribution: the best adsorption pore size is 2-10 nm (mesopores). If used for gas drying (such as compressed air), micropores of 2-4 nm are more effective; if used as a catalyst carrier, a larger pore size (5-10 nm) is required to improve mass transfer efficiency.
(4) Bulk density
• Too low density may result in insufficient strength, while too high density may result in low porosity.
2. Adsorption performance
(1) Static adsorption capacity
• Under the conditions of 25℃ and relative humidity of 60%, the water adsorption capacity of high-quality activated alumina should be ≥ 15-20%.
• Test method: Weigh the sample after drying at 150℃, expose it to a humid environment for 24 hours, and calculate the weight gain ratio.
(2) Dynamic adsorption capacity
• In industrial applications, it is necessary to test the penetration curve to ensure the stability of adsorption efficiency. Poor-quality products may penetrate early, resulting in reduced drying effect.
3. Mechanical strength
• Compressive strength: The compressive strength of a single particle of high-quality products should be ≥ 50 N (diameter 3-5mm), otherwise it is easy to break and produce dust to clog the equipment.
• Wear rate: Tested by ball milling method, the wear rate should be ≤ 1%, otherwise it is easy to pulverize in a fluidized bed or frequently regenerated environment.
4. Chemical stability
• Acid and alkali resistance: After immersion in a solution of pH 4-9 for 24 hours, the mass loss should be < 5%, otherwise it is easy to dissolve in an acidic or alkaline environment.
• Impurity content: The content of impurities such as Na₂O and Fe₂O₃ in high-quality products is less than 0.5%. High sodium content may cause catalyst poisoning.
5. Regeneration performance
• High-quality activated alumina can be regenerated by heating 200-300 times, and the adsorption capacity will not decrease by more than 20%.
• After regeneration, inferior products may become darker in color, lose strength, or even break.
Common characteristics of inferior activated alumina
1. Fragile: It breaks when pressed lightly, or a large amount of powder is produced after being loaded into the equipment.
2. Low adsorption efficiency: Water absorption rate <10%, or the air dew point does not drop significantly after drying.
3. Poor regeneration performance: The adsorption capacity drops significantly after heating, or the color becomes darker.
4. Many impurities: It becomes turbid or has a peculiar smell after being dissolved in water.
Purchase suggestions
1. Request a quality analysis report: Regular suppliers should provide data such as specific surface area, pore volume, and strength.
2. Small test verification: First purchase a small amount of samples to test the adsorption capacity, strength, and regeneration performance.
Therefore, high-quality activated alumina should have a high specific surface area, a suitable pore size distribution, strong mechanical strength, and good regeneration performance. I hope this article will help you choose activated alumina.
Activated alumina produced by Zibo Xiangrun