Normal alumina

Alumina has been used in a similar manner. Normally, alumina is added to an aqueous solution of PCC in water, prepared by mixing chromium trioxide, hydrochloric acid (6N) and pyridine. Removal of water leads to the formation of alumina particles covered by PCC, described as PCC on alumina, which is commercially available. Alternatively, it has been described that best results are obtained when alumina and PCC are finely ground in a mortar.231 The alumina not only helps in the work-up by allowing an easy filtering of the chromium-containing by-products, but also accelerates the oxidation with PCC.229a... 

Data from Kirk-Othmer [1]. Normally alumina reduction pots are operated on the acid side (i.e., a net AlFs NaF mole ratio of 1.2 to 1.5 1). 

For a 125,000 ampere cell the metal production capacity is 810-910 kg/day. Normally, alumina additions are made to each cell at about four hourly intervals. However, if the alumina consumption in any one cell exceeds the addition rate and the alumina content of the electrolyte drops to about 2% alumina or less, there is a sudden rise in the cell operating voltage to about 50 V. This is caused by polarization of the anode from the near stationary film of carbon monoxide and carbon dioxide on its surface [1]. This situation, called the anode effect, is detected via a 50-60 V light wired in parallel to each cell in a multicell potline. Normal cell operating voltages are too low to cause bulb incandescence, but when an anode effect occurs the light of the affected pot comes on to alert the operators to correct the situation. 

Modern GPPS is produced by continuous bulk and solution processes developed in the mid-1950s by major PS producers, BASF, Dow Chemical, Monsanto, Union Carbide, and others. In the modern continuous GPPS process, as the one shown in Figure 13.6, styrene monomer is continuously fed to a packed column (normally alumina, silica gel, or clay) to remove moisture, impurities, and inhibitor, blended with recycled styrene monomer, peroxide initiator (normally dialkyl or diacyl peroxides, such as di-fert-butyl peroxide, dicumyl peroxide, or fert-butyl peroxibenzoate utilized at low concentrations [I] <0.5% w/w in the feed), chain transfer agent (normally aliphatic... 

Since the collected samples were of alumina in an aluminium producing plant, the effects of such peaks of fines on the alumina s transportability on air-slides was studied at POSTEC. Mixtures numbered from 1 to 5 where number I was alumina containing much fines and number 5 was normal alumina, were used for capacity tests in a 12 meters air-slide. The mixtures were analysed for size distribution and tested in a fluidisation tester. The results are shown in Fig. 5. 

The process of chromatographic separation is illustrated in the following experiment, in which a wider tube than usual is employed to give a reasonably rapid separation within the time normally available to students. The alumina employed is the usual active alumina as supplied by dealers. 

A second Mobil process is the Mobil s Vapor Phase Isomerization Process (MVPI) (125,126). This process was introduced in 1973. Based on information in the patent Hterature (125), the catalyst used in this process is beHeved to be composed of NiHZSM-5 with an alumina binder. The primary mechanism of EB conversion is the disproportionation of two molecules of EB to one molecule of benzene and one molecule of diethylbenzene. EB conversion is about 25—40%, with xylene losses of 2.5—4%. PX is produced at concentration levels of 102—104% of equiHbrium. Temperatures are in the range of 315—370°C, pressure is generally 1480 kPa, the H2/hydrocatbon molar ratio is about 6 1, and WHSV is dependent on temperature, but is in the range of 2—50, although normally it is 5—10. 

Refractory Linings. The refractory linings (2,3) for the hearth and lower wads of furnaces designed for melting ferrous materials may be acidic, basic, or neutral (see Refractories). Sdica has been widely used in the past, and is stid being used in a number of iron and steel foundries. Alumina, a neutral refractory, is normally used for furnace roofs and in the wads for iron foundries, but basic brick can also be used in roofs (4). 

Gainum (HI) Ga203 is the single gallium oxide that is stable under normal conditions. Like alumina, it exists iu several crystalline forms. The... 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

Molten aluminum is removed from the cells by siphoning, generally daily, into a cmcible. Normally the metal is 99.6—99.9% pure. The principal impurities are Ee, Si, Ti, V, and Mn, and come largely from the anode, but also from the alumina. 

Activated alumina is a relatively innocuous material from a health and safety standpoint. It is nonflammable and nontoxic. Fine dusts can cause eye irritation and there is some record of lung damage because of inhalation of activated alumina dust mixed with siUca [7631-86-9] and iron oxide [1317-61 -9] (30). Normal precautions associated with handling of nuisance dusts should be taken. Activated alumina is normally shipped in moisture-proof containers (bags, dmms, sling bins) because of its strong desiccating action. 

Refractories. Calcined alumina is used in the bond matrix to improve the refractoriness, high temperature strength/creep resistance, and abrasion/corrosion resistance of refractories (1,2,4,7). The normal, coarse (2 to 5 )J.m median) crystalline, nominally 100% a-Al202, calcined aluminas ground to 95% —325 mesh mesh are used to extend the particle size distribution of refractory mixes, for alumina enrichment, and for reaction with... 

Various catalytic materials promote dehydrochlorination including AlCl (6,91), AICk-nitrohenzene complex (114), activated alumina (3), and FeCl (112). Chlorination in the presence of anhydrous aluminum chloride gives hexachloroethane. Dry pentachloroethane does not corrode iron at temperatures up to 100°C. It is slowly hydrolyzed by water at normal temperatures and oxidized in the presence of light to give trichloroacetyl chloride. 

Complete removal of water from the pyrolysis gas is achieved with molecular sieve dryers. Typically, there are two dryers one is in normal operation while the other is being regenerated. The dryers are designed for 24 to 48 hours between successive regenerations and high pressure methane heated with steam at 225°C is the preferred regeneration medium. Activated alumina was used in older plants, but it is less selective than molecular sieves (qv). 

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

Diffusion within the largest cavities of a porous medium is assumed to be similar to ordinary or bulk diffusion except that it is hindered by the pore walls (see Eq. 5-236). The tortuosity T that expresses this hindrance has been estimated from geometric arguments. Unfortunately, measured values are often an order of magnitude greater than those estimates. Thus, the effective diffusivity D f (and hence t) is normally determined by comparing a diffusion model to experimental measurements. The normal range of tortuosities for sihca gel, alumina, and other porous solids is 2 < T < 6, but for activated carbon, 5 < T < 65. 

These super-alloys are remarkable materials. They resist creep so well that they can be used at 850°C - and since they melt at 1280°C, this is 0.72 of their (absolute) melting point. They are so hard that they cannot be machined easily by normal methods, and must be precision-cast to their final shape. This is done by investment casting a precise wax model of the blade is embedded in an alumina paste which is then fired the wax bums out leaving an accurate mould from which one blade can be made by pouring liquid super-alloy into it (Fig. 20.4). Because the blades have to be made by this one-off method, they are expensive. One blade costs about UK 250 or US 375, of which only UK 20 (US 30) is materials the total cost of a rotor of 102 blades is UK 25,000 or US 38,000. 

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