High alumina silica-aluminas

The catalyst must also have acidity in the matrix in order to reduce the molecular weight of molecules too large to enter the zeolite and in order to also convert heavy-cycle oil to light-cycle oil. Our studies have established that good balance in acidity between the matrix and the zeolite tends to enhance selectivity. A stable matrix acidity is also required, and here a high alumina silica-alumina cogel was selected due to its demonstrated stability in the pre-zeolite era. Certainly many other acidic matrices could probably be substituted. 

Table 2. RELATIVE STABILTIY OF AMORFHOUS AND CRYSTALLINE HIGH-ALUMINA SILICA ALUMINAS...

High-alumina silica/alumina microspheroidal catalyst. 

Year Fireclay High alumina Silica Basic ... 

In oxychlorination. ethylene reacts with dry HC1 and either air or pure oxygen to produce EDC and water. While commercial oxychlorination processes may differ from one another to some extent because they were developed independently by many different vinyl chloride producers, in each case the reaction is carried out in the vapor phase in either a fixed- or fluidized-bed reactor containing a modified Deacon catalyst. Cupnc chloride is usually the primary active ingredient of the catalyst, supported on a porous substrate such as alumina, silica-alumina, or diatomaceous earth. The oxychlorination reaction is highly exothermic (AH = —239 kJ/mol for eq. 3) and requires heat removal for temperature control. 

By conducting the MPV reduction of 27 in refluxing isopropanol at 80°C in the presence of a number of different catalysts, H. van Bekkum et al(32) found that in addition to BEA (in both H- and Na-forms) gamma-alumina, silica alumina and the mesoporous MCM-41 also proved active. These last catalysts, however, give the thermodynamically favoured trans-compound 29 in 80-90% isomeric selectivity, high m-selectivity only being found with BEA (Table 15.4). 

Since catalytic oxidation is a surface reaction, an inexpensive support material is normally coated with the noble metal. The support material can be made of ceramic, such as alumina, silica-alumina, or of a metal, such as nickel-chromium. The support material is arranged in a matrix shape to provide high surface area, low pressure drop, uniform flow of the waste gas through the catalyst bed, and a structurally stable surface. Structures that provide these characteristics are pellets, honeycomb matrices, or mesh matrices. 

Figure i. Comparison of Davison fluid catalysts for cracking west Texas gas oil Lower propylene yields and higher gasoline yields result with molecular sieve XZ-15 vs. high activity silica alumina (5). 

Operationally, the basic difference between the Type X and Type Y structures was largely a matter of thermal stability, although acid strength-related differences in selectivity were also found. While the Type Y zeolite was much more stable, it was also much more expensive. Davison initially marketed their XZ-15 catalyst, containing steam-stabilized Y zeolite admixed with low-alumina silica-alumina, at a price of 800 per ton. This was quite a high price at the time, but despite that, about 15 refiners tried it. At the same time, Filtrol introduced their Grade 800 catalyst, and although they didn t officially claim that it contained molecular sieves, the product distributions clearly pointed to their presence (67). 

A reduction in alumina content enhances acid strength up to a point, but a reduction in physical strength and thermal stability limits the utility of such materials. A breakthrough came with the synthesis of the low-alumina-content zeolites, by the growth of highly regular silica-alumina crystals around bulky quaternary ammonium ions. These materials provide nearly 1 milliequivalent/g of sites of — Hq from 3 to 10 or more, while showing markedly improved thermal stability ... 

Weisz and Miale compared the activity for hexane cracking of a number of zeolites (Table 4.25) with a highly active silica — alumina (10% alumina). The zeolites are at least 10 times as active as amorphous silica —alumina. The catalytic process, however, cannot utilize the activity from a pure zeolite catalyst. The catalyst must be modified to decrease the acid-strength to avoid excessive formation of coke and low molecular weight gases, at the expense of gasoline. Moreover, the catalyst must be able to withstand the thermal and hydrothermal conditions experienced in regeneration. It must also withstand breakup in the mechanical circulation systems. A detailed description of the preparation of industrial catalysts is found in the literature. 

Other Processes. Numerous catalysts have been employed for polymerization, including highly stable silica-alumina (Phillips Pet. Co.), aluminum chloride, boron trifiuoride, and activated bauxite. ... 

The above methods for obtaining D, as well as other ones, are reviewed in Refs. 3-12, and Refs. 7-9 give tables of D values for various adsorbents. For example, D is close to 3 for the highly porous silica gels and close to 2 for nonporous fumed silica and for graphitized carbon black coconut charcoal and alumina were found to have D values of 2.67 and 2.79, respectively [7]. 

Strong acids are able to donate protons to a reactant and to take them back. Into this class fall the common acids, aluminum hahdes, and boron trifluoride. Also acid in nature are silica, alumina, alumi-nosihcates, metal sulfates and phosphates, and sulfonated ion exchange resins. They can transfer protons to hydrocarbons acting as weak bases. Zeolites are dehydrated aluminosilicates with small pores of narrow size distribution, to which is due their highly selective action since only molecules small enough to enter the pores can reacl . 

Inorganic packings (silica, alumina, etc.) are very stable (yet brittle) and show very high pore volumes (i.e, efficiency). However, their chemical stability is very limited and the surface is very active (this is also true for reversed-phase columns), allowing their use in special applications only. 

High-density polyethylene (HDPE) is produced by a low-pressure process in a fluid-bed reactor. Catalysts used for HDPE are either of the Zieglar-type (a complex of A1(C2H5)3 and a-TiCl4) or silica-alumina impregnated with a metal oxide such as chromium oxide or molybdenum oxide. 

A conventional FCC unit can be an olefin machine with proper operating conditions and hardware. Catalysts with a low unit cell size and a high silica/alumina ratio favor olefins. Additionally, the addition of ZSM-5, with its lower acid site density and very high framework silica-alumina ratio, converts gasoline into olefins. A high reactor temperature and elimination of the post-riser residence time will also produce more olefins. Mechanical modification of the FCC riser for millisecond cracking has shown potential for maximizing olefin yield. 

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