Alumina pellet

Specific. surface of solid spheres of 0.1 mm (0.0039 in) dia is 0.06 mVml (18,300 ftVfF) and a porous activated alumina pellet has about 600 mVml (1.83 X 10 ftVfF). Other considerations aside, a large surface is desirable because the rate of reaction is proportional to the accessible surface. On the other hand, large specific surface means pores of small diameter. 

The catalyst employed consisted of platinum deposited on the external surface of 1/8 x 1/8 in. cylindrical alumina pellets. The data below were obtained in run C-127S. Determine the composition at the exterior surface of the catalyst. 

Erroneous use of aluminium instead of alumina pellets in a hydrogen chloride purification reactor caused a vigorous exothermic reaction which distorted the steel reactor shell. 

Fig. 6 (a) 2-D 7) maps, (b) their 1-D central cross sections, and (c) the 1-D profiles of hexachloroplatinate dianion distributions obtained by electron probe analyzer measurements. S-2 and S-3 identify different porous alumina pellets, both prepared with an egg-shell distribution of hexachloroplatinate dianion the dianion is located towards the external surface of the pellet). S-2 and S-3 differ in terms of their nominal diameter and their pore-size and surface-area characteristics. Reprinted with permission from ref. 24. Copyright (2000) American Chemical Society. 

All the experimental data in Table 6.1 refer to pure gases. Separation experiments, in which surface diffusion is the separation mechanism, are scarcely reported. Feng and Stewart (1973) and Feng, Kostrov and Stewart (1974) report multicomponent diffusion experiments for the system He-Nj-CH in a y-alumina pellet over a wide range of pressures (1-70 bar), temperatures (300-390 K) and composition gradients. A small contribution of surface diffusion (5% of total flow) to total transport could be detected, although it is not clear, which of the gases exhibits surface difiusion. The data could be fitted with the mass-flux model of Mason, Malinauskas and Evans (1967), extended to include surface diffusion. 

The reaction between deuterium and 1-butyne, 2-butyne, 1,2-butadiene, and 1,3-butadiene, respectively, was conducted in a flow system at near ambient temperatures. The catalyst (0.03 wt % palladium on alumina) was prepared by impregnating hard alumina pellets with palladium chloride so that the metal was probably confined to an outer shell of each particle. 

The hardware used for the hydrogenation of benzene is shown in Figure 4—2. The basic parts are three or four reactors in a series plus a separation section at the end. The reactors are vessels filled with catalysts in the form of charcoal or alumina pellets that are coated with one of the above metals. The catalyst is packed loosely enough that the feed can flow through, top to bottom, by gravity. 

The reactor is a vessel with beds of solid catalyst. Most commercial processes use a catalyst called kieselguhr, which is phosphoric acid deposited on a silica/alumina pellet. Because of the weight of the pellets, supported beds at multiple levels in the vessel are used so the bottom layers wont be crushed.-... 

After heating, the EB is mixed with superheated steam and fed to the first stage reactor. Both the first and second stage reactors are packed with a catalyst of metal oxide deposited on an activated charcoal or alumina pellets. Iron oxide, sometimes combined with chromium oxide or potassium carbonate, is commonly used. 

Compressed oxygen, and fresh and recycled ethylene, are heated, mixed, and then passed through a reactor with fixed beds of catalyst— silver oxide deposited on alumina pellets. In recent years the catalyst has been improved by the addition of promoters and inhibitors. (Promoters—in this case compounds of alkali or alkaline rare earth metals—enhance the activity of the catalyst inhibitors—in this case chlorine compounds—chloroethane, or vinyl chloride, reduce its rate of activity decline.)... 

A11 operating cost based on 0.10/kW, 1.50/lb of conditioned alumina pellets, and labor costs of 30/hr. Vendor-supplied values. 

In the second example, the selective oxidation of propylene to propylene oxide (PO) was investigated with a huge library of y-alumina pellets impregnated with various single metals, binary metal combinations and catalyst loadings [40],... 

When samples of unknown behavior are tested, investigators will often line the bottom of the casing (under the specimen) with alumina pellets or platinum foil. This will protect the casing against accidental specimen melting. Platinum foil can be used as an interface between pushrod/specimen and speci-men/casing back in order to protect against inadvertent reaction. The expansion of the known thickness of platinum used must then be corrected for in the specimen expansion data. 

Figure 3. TPO (a) and ESR (b) evidence of carbonaceous deposits produced on Si02-Al20, (25%) during cyclohexene hydrogenation while fluidised in the reactor [7] at 296-393K with (—) and without (——) Pt/alumina pellets. In TPO the samples were heated in (VN2 at 5K.min l.

Au/Fe203 has been formed within the pores of alumina pellets to facilitate their use in a prototype reactor.6... 

Figure 11. Nickel profile in a y-alumina pellet after 26.75 h. Reprinted with permission from Chu etal. [34],...

Spatially resolved Raman spectroscopy has provided insights into the physicochemical processes that determine the distribution of the H2PMoOi iCoOV active phase in alumina pellets (Bergwerff et al., 2005). Molybdenum and cobalt complexes were found to diffuse through the pore structure of the alumina pellets at different rates the transport of cobalt complexes was fast, whereas molybdenum complexes required several hours to reach an equilibrated distribution. Spatially resolved Raman monitoring provides information about how preparation conditions affect the distribution of molybdenum ions (Bergwerff et al., 2005). 

Van de Water et al. (2005a,b) developed a design for spatially resolved UV-vis spectroscopy. The fiber optical probe remains in a fixed position, while the specimen is moved by moving the platform with the cell. The spatial resolution is reported to be 100 /im. The apparatus was used to follow the impregnation of an alumina pellet with solutions containing nickel ions, chromate, or polyoxometallates. 

The liquid is initially distributed by means of four small 1/16" pipes. An inert bed, realized with inert alumina pellets, ensured preheating, liquid saturation and an uniform distribution of both fluids. The reactor is provided with an axial thermocouple well. A sliding thermocouple can be moved along the bed axis allowing to measure the axial temperature profile and to check the isothermal operation of the reactor. 

Although several standard test methods have been developed for the chemical analysis of catalysts only small samples of supported platinum and palladium reference materials are available. Zeolites have been characterized for zeolite area, unit cell dimensions, and relative x-ray diffraction intensity. The crush strength of alumina pellets has also been determined. As the needs of catalyst users and producers change so will the materials characterized. To the extent that adequate amounts of material can be donated, standard test methods developed, and round robin tests performed Committee D-32 on catalysts will continue to make them available through NIST as reference materials. 

Senkan and Ozturk (52) reported the synthesis and screening of a 66-member discrete heterogeneous catalyst library L7, containing Pt, Pd, and In, for the dehydrogenation of cyclohexane to benzene at 300 °C. The structure of L7 and its synthesis are reported in Fig. 11.8. Sixty-six jxrrous alumina pellets (30 mg each) were shaped into 0.3-cm-diameter, 0.1-cm-high cylinders (step a), then immersed in aqueous HCl solutions containing the 66 appropriate mixtures of InCh, PdCli, and HiPtCle (step... 

Figure 2 (a) Deactivation of Pt/silica (D) in isothermal cyclohexene hydrogenation under conditions mentioned in the text in the reactor shown in (b). (c) Ruidised bed reactor in which entered at 1 and passed by 1.7%Pt/alumina pellets and fluidised 3g silica-alumina powder thereon (which also received QHiq/Nj entering at a low rate at 2) in which the activity of the silica-alumina shown in (d) was recorded at 323K. These data were measured in the absence (O ) and the presence ( C first run 9 second run) of the Pt/alumina pellets, and after the removal of these pellets ( ). The dependence of the activity (d) of this silica-alumina on the weight of pellets used in retesting is shown in (e)... 

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