Pseudoboehmite properties

The large majority of activated alumina products are derived from activation of aluminum hydroxide, rehydrated alumina, or pseudoboehmite gel. Other commerical methods to produce specialty activated aluminas are roasting of aluminum chloride [7446-70-0], AIQ calcination of precursors such as ammonium alum [7784-25-0], AlH2NOgS2. Processing is tailored to optimize one or more of the product properties such as surface area, purity, pore size distribution, particle size, shape, or strength. 

Using such procedures, high purity pseudoboehmite is produced (PURAL01, Condca Chemic, Brunsbuttel). With this type of microcrystallinc pseudoboehmite spheres of y-alumina can be manufactured. PURAL can also be extruded to pellets with binders and then subjected to calcination to prepare y-alumina. The cx-trudation of various aluminum hydroxides and oxide hydroxides with binders to pellets is covered in Ref. [44], The properties of the different aluminum hydrox-... 

The procedure for the preparation of alumina spheres is as follows. Pseudo-boehmite powder (AIOOH.2H2O) is dispersed in an aqueous solution of urea and a monovalent inorganic acid, e.g. HNO3. The type of powder or powder mixture may exert considerable influence on the properties of the sol and the end product [12]. The type of acid which is used for the peptization of the pseudoboehmite powder is not very important [12], so nitric acid is used, being the most suitable one. 

Alumina promoted FCC catalysts are commercially viable if, and only if, the alumina component produces the desired properties without detrimentally affecting the attrition resistance and the cracking activity of the finished catalyst particle. Previous work (8.9.11) indicated that attrition resistant catalysts containing alumina could be formed only if a highly dispersed, pseudoboehmitic alumina was used. Other studies have demonstrated catalytic performance improvement without determining the attrition character of the catalyst (1-7). 

Boehmite type aluminas from hydrolysis of aluminum alkoxides are typically not fully crystallized. This is reflected in a broader X-ray pattern as well as in an overstoihcimetric water content. These so-called pseudoboehmites are of the same structure as boehmite, but have additional water incorporated in the crystal. There are different theories about the exact structure of pseudoboehmite [7]. However, the widely accepted model is that the additional water molecule are located between the boehmite layers (figure 6). The amount of additional water uptake can be adjusted by the processing conditions and determines the properties of an alumina to a great extent. 

The impact of crystallinity, however, goes beyond surface area and porosity properties. Phase transition temperatures and thermal stability of a product also change with the size of the primary crystals. This is demonstrated in figure 8, showing a typical phase transition diagram for a material of small and large crystallites, representing pseudoboehmite and boehmite alumina. 

The poorly crystallized pseudoboehmite, for instance, exhibits good adsorptive properties for phosphates and arsenates in aqueous streams. 

Leveque J-M., Estager J., Draye M., Cravotto G., Boffa L. Benrath W. (2007) Synthesis of Ionic Liquids Using Non-Conventional Activation Methods An Overview, Monatsh. Chem., vol.138, n°ll, p>p.ll03-1113 (August 2007), ISSN 0026-9247 Li DY, Lin YS, Li YC, Shieh DL, Lin JL (2007) Synthesis of mesoporous pseudoboehmite and alumina templated with l-hexadecyl-2/3-dimethyl-imidazolium chloride. Microporous Mesoporous Mater., vol.108, n°l-3, pp.276-282, (February 2008), ISSN 1387-1811 MacFarlane D.R., Sun J., Meakin P., Fasoulopoulos P., Hey J. Forsyth M. (1995). Structure-property relationships in plasticized solid polymer electrolytes, Electrochimica Acta, International symposium on polymer electrolytes, vol.40, n°13-14, pp. 2131-2136, (October 1995), ISSN 0013-4686... 

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