Activated alumina is an extremely useful material used in multiple industrial settings, from gas purification to catalytic reactions in the petrochemical industry. This unique porous substance is produced through thermal treatment – or “calcination” – of aluminum hydroxide.
Activated alumina has an immense surface area and intricate network of pores, which enables it to absorb a range of different substances for various uses.
Moisture Adsorption
Activated alumina has an exceptional molecular spacing and pore structure that enables it to attract water molecules, making it a key component of air purification, where it can remove harmful pollutants, allergens and volatile organic compounds from indoor environments.
Deodorizer and purifier of industrial air, activated carbon can also help deodorize and purify it, while its ability to absorb sulfur compounds that cause unpleasant odors is useful in waste treatment and management.
Activated alumina has long been used as an effective desiccant in the oil and gas industry to protect pipelines from corrosion by extracting moisture from hydrocarbon liquids and gases, thus improving operational efficiency and product quality.
Importantly, an activated alumina system’s adsorption capacity may be negatively impacted by contamination and fouling. Fouling refers to build-up of impurities on its surface while contamination leads to gradual decreases in dynamic capacity adsorption rates.
One way to ensure optimal performance is by monitoring contaminant levels using a test kit that measures water treated rather than time in service. Once contamination reaches maximum removal capacity, establishing a maintenance schedule based on water treated can ensure minimal downtime when replacing an adsorption device when needed.
Fluoride Removal
Activated alumina is an efficient sorbent for fluoride removal from drinking water. It can be utilized at either point-of-entry or point-of-use water treatment devices to safely filter harmful ions out of solutions, and even help treat source water with high total dissolved solids (TDS) or sulfate concentration. In contrast to corundum (alpha-Al2O3) which only has limited exchange capacities, activated alumina has an expansive surface area for absorption that attracts fluoride ions electrostatically.
To improve its fluoride adsorption properties, activated alumina was modified by adding alum during its sol formation step. To test it in batch adsorption studies as a function of dose, contact time, stirring rate, initial fluoride concentration and initial fluoride concentration; MIAA had an up to 1.35 times greater capacity compared with regular immobilized activated activated alumina.
MIAA was also tested as a filter media for natural mineral waters, with positive results in terms of safety for use, provided that water samples were subjected to leaching tests (EN 12902). These tests ensure that no impurities would enter the water that exceeded limits specified in Commission Directive 2003/40/EC on constituents of natural mineral waters or regulations set by national legislation.
Catalytic Activity
Activated alumina has many industrial uses thanks to its special properties. These include acting as an adsorbent, desiccant and catalyst. Most frequently it is employed in oil refineries as a Claus catalyst in sulfur recovery operations by absorbing hydrogen sulfide molecules and keeping them out of the environment by virtue of its excellent thermal, chemical, mechanical stability, large surface area and exceptional absorption abilities.
Before activated alumina products can be introduced into a reactor for use as catalysts, they must undergo certain preprocessing steps that ensure their viability as catalysts. These include the aging of the agglomerates through recrystallization of pseudoboehmite, bayerite and gibbsite aluminum hydroxides into gamma alumina – this helps strengthen agglomerates while simultaneously altering phase chemistry for enhanced catalytic performance.
The activated alumina catalyst must also be capable of withstanding the rigorous operating conditions inherent to Claus process, specifically high temperatures, different amounts of chemicals, cyclic operations and low rates of side reactions, selective decline and toxicity. Furthermore, it must have great thermal and mechanical stability with large specific surface area as well as numerous active sites.
Molecular Sieve
Activated alumina is an exceptionally porous material with superior moisture-absorbing capabilities, made by heating aluminium hydroxide at high temperatures, extracting bound water molecules, and creating an extensive network of pores that are controlled during calcination and activation processes with specific parameters controlling their size for preferential absorption of gas or liquid molecules.
This pore structure is critical to activated alumina’s desiccant property, as it allows the product to effectively remove moisture from gases, vapours and liquids. Furthermore, its importance plays an important role in industrial applications as it improves process efficiency and product quality.
Molecular sieves are used in gas purification applications to remove impurities such as carbon dioxide and sulfur compounds that contribute to corrosion, while also being utilized by automotive emissions control systems to capture trace contaminants harmful to the environment.
Molecular sieve 3A, with its 3 Angstrom kinetic pore diameter, is often used to dry natural gas as well as various gases and liquids with its 3-Arnstrom kinetic pore diameter pore size pore structure pore diameter; particularly effective at absorbing hydrogen and helium. Meanwhile, 13X sieve has 10-Anstrom kinetic pore diameter structure which can also absorb hydrocarbons and alcohol; this method may also be utilized to dehydrate ethanol to meet fuel grade specifications at less cost than steam distillation would allow.