Catalysts alumina content

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. 

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.

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. 

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. 

We explored various possibilities in our efforts to control nickel. Catalysts high in alumina content, especially if a separate inclusion of alumina gel is utilized, did seem to show some improvement. It also appears that in severe conditions such as in the RCC operation, nickel tends to agglomerate, this reducing exposed surface and possibly also embeds in the matrix or zeolite. 

Natural clay catalysts were replaced by amorphous synthetic silica-alumina catalysts5,11 prepared by coprecipitation of orthosilicic acid and aluminum hydroxide. After calcining, the final active catalyst contained 10-15% alumina and 85-90% silica. Alumina content was later increased to 25%. Active catalysts are obtained only from the partially dehydrated mixtures of the hydroxides. Silica-magnesia was applied in industry, too. 

Andreu et ah (11) explained the increased activity (with increasing alumina content of amorphous silica-alumina catalysts) for cracking of sec-butylbenzene by the greater density of acid sites in the high-alumina-content catalysts. Adams et ah (12) proposed that the interaction of several active sites with reactant molecules in mordenite catalysts was partly responsible for the rapid rate of activity loss. 

All these results are easily explained on the basis of structural properties of samples provided by X ray and EPR studies. It was actually pointed out that for low contents of chromium in the catalysts, alumina interacts with the amorphous active phase and favours the stabilization of low coordinate chromium ions... 

Hydrocarbon Trap System. The concept of a hydrocarbon trap or adsorber system is based on molecular sieve hydrocarbon adsorber systems. The temperatures at which hydrocarbon adsorption takes place exist in the auto engine exhaust system during the period of cold start of an automobile when the catalytic control system has not yet reached functional temperature. Zeolites have been reportedly useful for hydrocarbon adsorption (53,169). Zeolites desorb hydrocarbons at temperatures of 400°C, ie, once the catalytic control system is functional. Therefore, hydrocarbons adsorbed by the zeolite can also be desorbed then oxidized by a catalyst. Methods to accomplish cold start hydrocarbon adsorption, heatup of the main catalyst, and desorption have been identified. Some of these systems use exhaust pipe valves to divert the exhaust gases to the hydrocarbon trap for the low temperature portion, and by-pass the gases around the trap after the main catalyst has heated up. One device that uses a heat exchanger is shown in Figure 15 (44). The Si—Al ratio in the zeolite is important, and by lowering the alumina content, the zeolite is rendered more hydrophobic and more able to adsorb... 

Rates of model reactions are more commonly used to determine relative rather than absolute surface acidities and a variety of acid-catalyzed reactions have been used for this purpose (1-3). Xylene isomerization is a particularly well-substantiated model reaction, thanks to work by Ward and Hansford (43). They demonstrated that the conversion of o-xylene to p- and /n-xylenes over a series of synthetic silica-alumina catalysts increases as the alumina content is increased from 1 to 7%. The number of strong Brdnsted acids in each member of the catalyst series was measured by means of infrared spectroscopy. Since conversion of o-xylene was found to be a straight-line function of the number of Br0nsted acids (see Fig. 9), rate of xylene isomerization appears to be a valid index of the amount of surface acidity for this catalyst series. This correlation also indicates that the acid strengths of these silica-alumina preparations are roughly equivalent. 

Activity per Unit Surface Area for Gas Oil Cracking. A second order kinetic conversion parameter (conversion + 100 - conversion) was used (13) to monitor gas oil cracking activity. The activity relationship as a function of surface area and catalyst composition is described in Figure 4. As expected, activity increased linearly with surface area. Activity per unit surface area depended on composition and increased with increasing alumina content. 

Effect of Composition and Pretreatment on Coke and H2 Selectivity. We examined the effect of catalyst composition and pretreatment on the selectivity for coke and H2. Results (Figures 5 and 6) indicate higher yields of coke and H2 at constant conversion for SA-59 relative to catalysts with lower alumina content. Pretreatment conditions influenced coke, H2 yields indirectly by influencing surface area and gas oil conversion. Thus, coke and H2 selectivity was not influenced by pretreatment conditions. We conclude that coke and H2 selectivity does not correlate with the concentration of A1 species of a particular coordination (eg., tetrahedral). 

Breck s preparation of type Y faujasite in die late 1950 s still stands as the outstanding success in zeolite synthesis (2). Type X might have had some catalytic applications but I doubt the International Zeolite Association would exist without the interest and support generated by the catalytic applications of the Type Y materials. It didn t seem that critical at the time after all Breck had reproduced a material which exists naturally. Synthetic counterparts of natural zeolites have been prepared dozens of times since (3). But die extra silica content, or perhaps die diminished alumina content, was enough to give high temperature stability in the acid form and to get zeolites into catalysts for petroleum processes (4). 

Catalyst Fluorination. The adsorption and desorption record and calculated data for a silica-alumina catalyst of low alumina content and a median pore radius of 78 A. were obtained. This indicated a fairly wide distribution of pore sizes in this material. 

Feed and catalysts. A regular Kuwait vacuum gasoil was used as a feed. Its characteristics can be found in Table II. Three commercial cracking catalysts with an increasing rare earth and alumina content, viz. A, B, and C, were tested. All catalyst were presteamed and deactivated to an equilibrium level by its supplier. Larger catalyst particles were removed with a 150 pm sieve. This step is followed by either a calcination or regeneration. Fresh, but pre-steamed catalyst was calcined at 773 K for 1 h, while coked catalyst was regenerated at 873 K for 2 h. 

Alumina (AI2O3). Alnmina is present in several components of the catalyst such as zeolite, clay (kaolin) and active matrices. The alumina content of catalyst can often be used to calculate the degree of exchange when switching to a different catalyst. 

The acidity of the catalyst arises due to interaction of the components (e.g., silica and alumina) during preparation. Pure silica and pure alumina have little or no cracking activity, but the presence of only a few hundredths of a per cent of alumina in silica is sufficient to produce an active catalyst (138,148,320,321). Activity and acidity both increase, up to a certain point, with increased alumina content (320,324). Infrared spectra of ammonia chemisorbed on silica-alumina catalyst indicate that most of the chemisorbed ammonia is in the NHs form, with only a relatively small amount of NH4+ (204). From this evidence it is concluded that most of the catalyst acid is of the Lewis type since, in reacting with a Bronsted acid or a hydrated Lewis acid, the ammonia would be converted to an ammonium ion. 

Platinum and chlorine content also changed. There appeared to be a 14 percent loss in Pt after 96 h, although there was no significant trend with respect to distance. Loss in Pt was unexpected and there is no clear reason for it at this time. Repeat ICP-MS analysis of the fresh catalyst showed <1 percent variability, suggesting that this difference is significant and not due to reproducibility problems. The difference may be due to inaccuracy in the coke measurement, since the measured Pt concentration was corrected to a fresh catalyst . Chlorine content appeared to increase with reactor distance. However, the measured chlorine content only included what was water extractable, and not what might be chemisorbed to the Pt, reacted with the alumina, or part of the coke. 

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