Alumina bulk components

Adsorption column cleanup procedures have been designed to cope with two types of interferences the coextracted bulk components comprising predominantly lipids and coextracted organochlorine pesticides (described under fractionation). Alumina columns normally provide an excellent cleanup of PCBs from bulk components such as lipids. 

The process of isolation finally adopted by the former authors consists in precipitating as reineckates the water-soluble bases contained in a methyl alcoholic extract of the curare. The mixed reineckates are further purified, by solution in acetone and precipitation with water as often as may be necessary. The product so cleaned represents the bulk of the biological activity of the crude drug the mother liquors may contain curine (p. 374), which indicates a menisperm as one of the components of such curares. The mixed reineckates are then fractionated chromato-graphically over alumina and the components isolated as chlorides by the use of silver sulphate and barium chloride in succession. This process has been modified in detail by Schmid and Karrer, who have also found that with their curare, the more soluble reineckate fraction includes less potent quaternary alkaloids. 

Upon dissolving Al into liquid Ga, the alumina layer that instantly forms from exposure to air or water at the surface is either discontinuous or porous. In either case the surface of the Ga-Al liquid is not passivated. As a result, when water contacts the surface of the liquid, Al atoms at the surface split the water, liberating hydrogen and heat with the formation of alumina. Since the liquid is fluid, the alumina cannot form a bonded layer at the liquid surface that would passivate pure, solid Al. Instead, the alumina is swept away by convection or agitation as a suspension of alumina particles in the water. The surface of the liquid alloy is now depleted of Al. This depleted region at the surface is replenished via diffusion or convection of Al from the bulk to the surface where it continues to split water. This process continues until all of the Al in the liquid alloy is converted to alumina. To summarize, liquid Al-Ga alloys rich in Ga split water because the Al component is not passivated as it is in solid pure Al. 

Adsorption in water treatment is a robust technique for removing water-soluble ions, especially when these ions exist in water at low concentrations. Coincidentally, fluoride ions exist in some groundwaters at low concentrations, which are above the permissible limits. The principle behind this technique is that a component (fluoride in our case) is transported by diffusion from the bulk phase to the solid surface where it is bound at the surface or interface between two phases by either chemical or physical forces [35], Numerous investigations have focused on surface adsorption as a means of removing fluoride from water. As a result of these studies various water treatment plants using treatment media such as activated alumina or bone char have been constructed and are in use in several countries. One example is a water purification plant in Kansas that utilizes activated alumina [36], Several other smaller fluoride treatment facilities are scattered all over India, Kenya and Tanzania, among other nations. 

Heterogeneous catalysts are solid materials that sometimes consist of the bulk material itself, for example, acid zeolite catalysts [10] or fused catalysts [11], Or in other cases of an active component or components deposited, as a rule, on a highly developed area support, for example, silica, alumina, carbon or in some cases a zeolite. The function of the support is to enhance the catalyst properties, for example, the stability of the active component or components, or in some cases to be even included in the catalytic reaction, for example, by providing acidic sites in bifunctional zeolite catalysts [10],... 

The state of tin in Pt/Sn/alumina catalysts was investigated bv Li and Shia (25) via Mossbauer spectroscopy (i/9Sn enriched isotopes) and XPS. The former technique indicated the presence of Sn+, Sn+2 and Sn, in proportions that depended on the method of preparation, but in all cases the Sn+4 component dominated. These conclusions were confirmed by the XPS experiments. Additional TPR tests on the reduced catalyst and on samples exposed to air showed that reoxidation of Pt/Sn/alumina reduced preparations was rather slow, confirming our EXAFS observations. The presence of zero valent tin in similar preparations, using the acetone complexation procedure, was recently confirmed by Li, Stencel and Davis (12) in an extended XPS investigation. For reduced samples, with a Pt Sn ratio 1 5, these authors estimated that approximately 68% of the tin was in the metallic state. However, they observed that exposure of the sample to air for 10 minutes entirely eliminated the XPS detectable Sn°. Their data also indicated that upon reduction, chlorine migrated from the surface to the alumina. Thus, XPS which measures surface composition indicates a higher sensitivity to oxidation than was demonstrated by our EXAFS experiments, which is a bulk diagnostic. 

Figure 44 presents a scanning electron micrograph of a capsule in which alumina particles are encapsulated in crosslinked polyacrylamide. Table 20 lists under PLA1 the amounts of the components involved in the preparation of these capsules. The capsules have a polyhedral shape and their sizes are larger (around 5 pm) and more uniform than the polymer latexes free of solid particles. Some of the cells of the gel coalesce during polymerization, forming bulk phases. As a result, some unencapsulated solid particles were also observed. 

Another interesting example of using a chemisorbent (Na20 supported on alumina) in a PSA process is direct removal and recovery of bulk CO2 from a wet hi temperature feed gas without pre-drying or cooling the feed [21]. A gas stream at 200 C containing 10 mole % CO2 and an inert component (dry basis), and which is saturated with water, can be treated to simultaneously produce a CO2 depleted stream (<3% CO2) and a CO2 enriched gas (99+%) without removing the water. The PSA cycle steps consist of (a) adsorption at... 

Co-precipitation. - The preparation of supported catalysts by the coprecipitation of metal ions with the support ions usually produces an intimate mixing of catalysts and support. An example of this technique is the coprecipitation of metal ions with aluminium ions to produce a precipitated alumina gel containing the metal hydroxide. This precipitate when calcined produces a refractory support with active component dispersed throughout the bulk as well as at the surface. However, in the preparation of multi-component catalysts, it is possible under improper conditions to obtain a heterogeneous product because of the different solubility products of the constituents. Care should be taken therefore to avoid this undesirable situation by appropriate forethought. 

Klissurski et al. [87] have examined the combustion of acetone, toluene and styrene by zinc-cobalt spinel oxides supported on alumina. Catalysts were prepared by co-precipitation with sodium carbonate from a mixed zinc/cobalt nitrate solution at pH 9. The supported catalyst was prepared by deposition of the precursor on Y-AI2O3 from a suspension in dimethylformamide and water. The supported precursor was dried at 150°C and calcined at 300°C to produce the catalyst. The bulk and supported catalysts both showed the formation of zinc cobaltite spinel structures which were thermally stable. Microreactor studies at 15,000 h- space velocity showed that the components of a mix of acetone, toluene and styrene were destroyed at 225°C, 280°C and 350°C respectively. The VOC concentrations were not specifically expressed but it is assumed that they... 

In Chapter 3, Busca summarizes the current state of knowledge of aluminas, the various polymorphs of which constitute some of the most commonly used catalyst components. The author starts with a discussion of the bulk structures of transition aluminas, which are the intermediate phases formed in the thermal transformation of aluminum oxyhydroxides into the thermodynamically most stable modification, a-alumina. Crucial are the definitions of the various phases, which are based on the methods of preparation rather than on the structural properties. The understanding of many alumina structures is incomplete, and progress, even with modem analytical methods and theory, is hampered by the defective and disordered nature of these materials. The stabilities of the various phases are governed by both thermodynamics and kinetics, either of which can be affected by impurities. The uncertainties in the surface stmctures are even greater than those of the bulk stmctures. Numerous models of alumina surface stmctures have been formulated over decades, but the tme stmctures seem to become even more elusive. Busca concludes his chapter with a list of research needs. 

Fig. 16 Shear stress and shear distance vs time for AIMD simulations of bulk alumina shear to induce slip along the [2130] /(OOOl) direction and plane (a) moving the x and y components of the c vector along the slip direction at a rate of 0.5 A s or (b) by increasing the external stress applied along the slip direction at a rate of 2.5 GPa s...

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