Alumina is an unprocessed material with numerous advantages over silica gel as an desiccant desiccant. These include its superior crushing strength, chemical compatibility and regeneration capability which make it a top choice for drying air and purifying liquids.
Activated alumina is a porous material made from aluminum hydroxide that undergoes controlled activation processes to produce large surface areas with various pore sizes, commonly found in petrochemical and natural gas industries for use in filtering out impurities from gases and vapour streams.
High Surface Area
One of the key characteristics that distinguish alumina as an exceptional material is its high surface area, giving it multiple active sites for adsorption. Activated alumina is produced by treating aluminium oxide (Al2O3) into porous spongelike material with interlinked pores for gas and catalytic adsorption – making it an excellent solution for purifying gases or liquids.
Figure 1d illustrates TEM analysis of mesoporous alumina’s pore size distribution; as can be seen, as-synthesized material was in an aggregated state with particles between 30-40nm in size.
Alumina can take advantage of its high surface area by being utilized in applications like industrial gas adsorption, where its high surface area absorbs moisture, carbon dioxide and sulfur compounds from natural or industrial gases and vapour streams – thus producing higher-quality products while decreasing environmental emissions.
Alumina comes in various forms, from beads and pellets to granules, depending on its application. Although their physical and chemical properties differ slightly, all offer impressive adsorption performances. When handling activated alumina it is vital to wear appropriate personal protection equipment as it may irritate skin or eyes or even cause respiratory problems if inhaled directly.
High Mechanical Strength
Activated alumina is an outstanding desiccant with superior mechanical/crush strength and can withstand elevated temperatures. Its structure is formed through controlled heating of hydrated alumina; when exposed to excess heat, water molecules are expelled as its crystal lattice fractures along planes of structural weakness, leaving well-defined pores with an average pore diameter of 4nm. In comparison to silica gel, activated alumina remains resistant to attrition better while also maintaining its adsorptive capacity much better.
Activated alumina is an excellent gaseous adsorbent, such as for helium, hydrogen, argon and chlorine adsorption; it also has strong affinity with liquids such as kerosene, aromatic compounds and essences. As such, activated alumina is widely utilized as a drying agent in various industrial applications, including gas turbines, chemical processes, air conditioning systems etc.
Alumina adsorption behavior is highly dependent on its aqueous pH conditions. At pH > 7.4 in basic media, its surface becomes negatively charged due to deprotonation and thus hinders anionic dye ions adsorption by colombic repulsion (reaction 1).
Al2O3 is the chemical formula for alumina. This structure consists of two aluminium and three oxygen atoms bonded together in an octahedral structure, along with trace amounts of other elements which may alter its adsorption and catalytic properties depending on its raw materials used during manufacturing; such elements could include silicon dioxide (SiO2), sodium oxide (Na2O), or iron oxide (Fe2O3) as impurities present. Activated alumina typically contains impurities such as silicon dioxide (SiO2), sodium oxide (Na2O), or iron oxide (Fe2O3) as impurities.
High Hydrophilicity
Alumina boasts a large surface area with numerous pores and voids, which enables it to adsorb gases, liquids, and dissolved species effectively. Bulk density typically ranges between 0.6 to 0.8 grams per cubic centimetre for intended uses of Alumina.
It has a strong affinity for moisture, making activated alumina an effective desiccant. Indeed, its water absorption capacity exceeds that of molecular sieve, so activated alumina is frequently employed when large amounts of moisture must be extracted from gas or liquid streams.
The FTIR absorption spectrum of as-synthesized alumina material revealed that after dye ions adsorption, peak intensity at 3457 cm-1 decreased while its position shifted, suggesting interactions between dye ions and AlOH and AlO groups on its surface and AlOH and AlO groups of the dyestuff itself. Furthermore, its E value (chemisorption adsorption rate) is estimated to be below 8 kJ/mol and this indicates its control by chemical rather than physical mechanisms of adsorption.
Adsorption experiments were performed by adding 100 mL of dye solution to 250 mL Erlenmeyer flasks containing 0.1 g of alumina nanoparticles and then varying the times and conditions to find optimal operating parameters for the process of dye adsorption. Results demonstrated that initial concentration and contact time are key variables when it comes to controlling adsorption, with removal percentage increasing as initial concentration drops; furthermore, reused nanoparticles could be reused up to four cycles without losing their capacity of adsorption capacity;
High Stability
Due to its high crush strength, alumina is resistant to attrition and retains more of its adsorption capacity than silica gel, making it an attractive material for use in various applications, including drying-down and dehydration of gases and liquids. Furthermore, activated alumina acts as an excellent desiccant absorbing moisture from the air as well as purifying drinking water by removing fluoride, arsenic, and selenium contaminants – as well as filtering out trace contaminants from gaseous and vapour streams.
Microporous hydrous alumina gels can rapidly lose BET surface area when exposed to water, while mesoporous pseudoboehmite and boehmite-like aluminas tend to be more stable. Soaking hydrous alumina in liquid water produces bayerite phase which has significantly less BET surface area compared to microporous alumina; to maintain integrity it’s often treated with sulphuric acid or sodium hydroxide before being used as an adsorption media.
Batch adsorption experiments were performed to assess the ability of alumina nanoparticles to absorb and desorb Orange G dye (OG) from both real wastewater as well as simulation wastewater, the results showing significant removal performance from both sources. Thermodynamic investigations confirmed spontaneous exothermic OG adsorption on alumina; moreover it can be reused without losing its absorption capacity for at least four cycles without losing effectiveness.