Alumina basic concepts

The basic concept of a H2 PSA process is relatively simple. The impurities from the H2-containing feed gas mixture are selectively adsorbed on a micro- and meso-porous solid adsorbent (zeolites, activated carbons, silica and alumina gels) at a relatively high pressure by contacting the feed gas with the solid in a packed column of... 

The basic concept of a TSA drying process consists of (a) selective adsorption of trace or dilute water from the contaminated fluid mixture by flowing the fluid over a packed column of alumina particles while withdrawing a dry product stream until the water concentration at the column effluent rises to a predetermined value and then (b) thermal desorption of the adsorbed water by heating the column with a relatively dry fluid stream. The adsorbent is repeatedly used in a cyclic manner by carrying out steps (a) and (b). More than one adsorbent column is required for continuous processing of the wet feed fluid stream and production of a dry fluid stream. 

Pyrene and dinaphthylpropane fluorescent probes have been used to investigate the structural details of adsorbed layer of SDS at the alumina-water interface. This study supports the basic concepts of hemimicellization. Adsorption isotherm turns out to be S-type. The values of microviscosity of adsorbed layer and normal micelle are 90 to 120 and 8 cP, respectively. The mobility of the probe... 

Conclusions on the structure of aluminosilicate melts are mainly based on the interpretation of physico-chemical properties, such as density and viscosity, in terms of composition, particularly of the x(Ca0)/x(Al203) ratio. The basic idea was the concept that in melts with the ratio x(Ca0)/x(Al203) > 1, all the Al(III) atoms are in tetrahedral coordination and that the octahedral coordination of Al(III) atoms occurs only at ratios x(Ca)/x(Al203) < 1, i.e. at the excess of alumina with respect to CaO. 

LNA, which is an acid, can adsorb on alumina via acid-base interaction or hydrogen bonding. The structural formula of LNA and those of other organic dispersants are given in Fig. 2. The interaction between the solvent and LNA cannot be responsible for the viscosity curves because the most basic solvent, tetrahydrofuran (THF) [11], would interact with LNA the most. The acid-base interaction is based on Drago s work on Lewis acid-base interaction energies [12]. Fowkes [2,13,14] expanded the concept to ceramic processing. The relative acidity and basicity of solvents used are listed in Table 1. The ceramic powders used are listed in Table 2. 

This concept has been transferred to corundum fibers. The experimental fiber, PRD-166, is an example of a zirconia-corundum fiber. PRD-166 is polycrystalline and contains 80 wt.% a-alumina and 20 wt.% yttria-stabilized zirconia and it is slurry spun, like Fiber FP [19] [61]. Zirconia-corundum fibers can be prepared by the slurry route, the slurry being an aqueous suspension of fine alumina particles, to which are added a basic aluminum salt (such as aluminum chlorohydroxide), zirconyl acetate and yttrium chloride hexahydrate. After... 

The most common approach to surface modification with transition aluminas is through control of the thermal treatment. As shown in Figures 5 and 7, it is quite easy to alter the total surface Lewis and Bronsted acidity and basicity via control of the hydroxyl concentration. To some extent this technique has been used since the early 1950s, particularly in chromatographic aluminas. The so-called Brockmann scale for rating aluminas is based on thermal history, and commercial materials are available today in the various Brockmann grades. Only recently has the concept been applied to large scale adsorption systems. 

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