Alumina content

Fireclay Refractories. These products are made from clay minerals containing ca 17—45% AI2O2. Pure kaolin has the highest alumina content. 

High Alumina Refractories. The desired alumina content, from 100% to just above 45%, is obtained by adding bauxites, synthetic aluminosihcates, and synthetic aluminas to clay and other bonding agents. These refractories are used in kilns, ladles, and furnaces that operate at temperatures or under conditions for which fireclay refractories are not suited. Phosphate-bonded alumina bricks have exceptionally high strength at low to intermediate temperatures and are employed in aluminum furnaces. High alumina and mullite are used in furnace roofs and petrochemical apphcations. 

Other countries have similar types, some classifications, as in Germany, are based on age-strength levels by standard tests (70). A product made in Italy and Prance known as Perrari cement is similar to Type V and is sulfate-resistant. Such cements have high iron oxide and low alumina contents, and harden more slowly. 

Chemical Raw Material. In addition to use as a catalyst raw material, clays are used or have been extensively studied as chemical raw material. For example, kaolin has been investigated as a raw material for aluminum metal production. Kaolin has a 38 to 40% alumina content and is available in the United States in large quantities whereas the higher alumina bauxite reserves are very limited. The Bureau of Mines has actively carried out research in the aluminum from ka olin area for many years. Activity increases whenever imports of bauxite are threatened by war or other trade intermptions (1,22,23). 

Alumina produced by the Bayer process is precipitated and then calcined [Krawczyk, Ceramic Forum International, 67(7-8), 342-8 (1990)]. Aggregates are typically 20 to 70 [Lm, and have to be reduced. The standard product is typically made in continuous dry ball or vibra-toiy mills to give a product d o size of 3-7 [Lm, 98 percent finer than 45 [Lm. The mills are lined with wear-resistant alumina blocks, and balls or cylinders are used with an alumina content of 80-92 percent. The products containing up to 96 percent AI9O3 are used for bricks, kiln furniture, grinding balls and liners, high voltage insulators, catalyst carriers, etc. 

Fireclays can be dividea into plastic clays and hard flint clays they may also be classified as to alumina content. Firebricks are usually made of a blended mixture of flint clays and plastic clays which is formed, after mixing with water, to the requirea shape. Some or all of the flint clay may be replaced by highly burned or calcined clay, called... 

For many years the most common catalyst was an amorphous or noncrystalline type called 3A. Initially, all 3A catalyst contained 13% alumina and 87% silica. To improve activity maintenance, the alumina content was increased to 25%. Both 13 and 25% alumina grades continue to be used the choice at a given refinery is based on the specific situation. Another amorphous type catalyst, containing silica-magnesia and called 3E, is also used. 

The alumina content, the amount of rare-earth, and the type and amount of zeolite affect catalyst tolerance to vanadium poisoning. 

The alumina content of the E-cat is the total weight percent of alumina (active and inactive) in the bulk catalyst. The alumina content... 

For the same 300-ton inventory unit, assume the alumina (AljOj) contents of the present and new fresh catalysts are 48 wt% and 38 wt%, respectively. Sixty (60) days after the catalyst switch, the alumina content of E-cat is 43 wt%. Determine % changeover ... 

Figure 5-6. Heat capacity of the FCC catalysl as a Sunctron of loo catalyst s alumina content.

The consideration that many zeolite types exist, each with many tunable properties (e.g., pore size and alumina content), leads not only to a wealth of options but also to a high level of complexity. Owing to this complexity and limited understanding of zeolite formation and permeation behavior, a lot of experimental effort is required in this field, slowing down developments toward successful application. 

Recently, Wilson Combe (1991) have studied the reactivity of magnesium, zinc, calcium and strontium boroaluminate glasses towards poly(acrylic acid) solutions. The controlling factor would seem to be the alumina content of these glasses which serves to moderate the setting rate of the cements. 

Silica bricks are manufactured from crushed ganister rock containing about 97 to 98 percent silica. A bond consisting of 2 percent lime is used, and the bricks are fired in periodic kilns at temperatures of 1,500 to 1,540°C (2,700 to 2,800°F) for several days until a stable volume is obtained. They are especially valuable when good strength is required at high temperatures. Superduty silica bricks are finding some use in the steel industry. They have a lowered alumina content and often a lowered porosity. 

In the aluminum electrowinning process a phenomenon called the anode effect is normally encountered when the alumina content in the electrolyte falls below 2%. The anode gets partially covered with a gas blanket and as a consequence, sparking occurs and the cell voltage fluctuates considerably due to frequent breaking and reestablishment of local contact between the anode and the electrolyte. A heavy current passes through the anode area... 

The silica-alumina was supplied by Ketjen with a 13 alumina content. It was vacuum-treated at 1+50°C (I0 5torr) for 15hrs before anchoring the cluster. ... 

During the period 1940-1962, the cracking catalysts used most widely commercially were the aforementioned acid-leached clays and silica-alumina. The latter was made in two versions low alumina (about 13% AI2O3) and high alumina (about 25% AI2O3) contents. High-alumina-content catalysts showed a higher equilibrium activity level and surface area. 

The nature of the acidic sites is still subject of lively discussion. One school of thought, based on a proposition by Thomas (348), attributes the acidity to substitution of AP+ ions for Si + ions in a tetrahedrally linked silica network. Electroneutrality is obtained by addition of protons. Others think that Lewis acid sites, as proposed by Milliken et al. (349), are responsible for the catalytic activity, Gray (350) suggested that only the alumina content was responsible and that a spinel-like phase was formed on heating with protons on certain octahedral positions. 

Cracking Catalyst Composition. Several workers (20-21) have reported differences among cracking catalysts to remove SOx which correlated qualitatively with alumina content. Our work confirmed these reports as shown on Figure 2. Plotted are %S02 removal... 

For cracking catalyst composition, we showed that alumina content is important by showing how catalysts synthesized to contain various amounts of alumina removed SO2. Although for years alumina content has been considered important by the industry, it was difficult to find a conclusive reference showing that fact. 

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