Alumina ratio

The product distrihution is influenced hy the catalyst properties as well as the various reaction parameters. The catalyst activity and selectivity are functions of acidity, crystalline size, silica/alumina ratio, and even the synthetic procedure. Since the discovery of the MTG process. 

The zeolites with applications to FCC are Type X, Type Y, and ZSM-5. Both X and Y zeolites have essentially the same crystalline structure. The X zeolite has a lower silica-alumina ratio than the Y zeolite. The X zeolite also has a lower thermal and hydrothermal... 

Figure 3-3. Silica-alumina ratio versus zeolite unit cell size.

Catalyst acid properties depend on several parameters, including method of preparation, dehydration temperature, silica-to-alumina ratio, and the ratio of Bronsted to Lewis acid sites. 

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. 

The exact nature of the zeolite is determined by the reaction conditions, the silica to alumina ratio and the base used. For example zeolite /3, a class of zeolites with relatively large pores, in the range of 0.7 nm, of which mordenite is an example, are usually made using tetraethylammonium hydroxide as the base. This acts as a template for the formation of 12-membered ring apertures (Figure 4.3). 

The ZSM-5 zeolite had a SAR (silica-to-alumina ratio) value of 38 and were supplied by CENPES/PETROBRAS. These samples, as received, were submitted to two ion exchange processes with ammonium chloride solution at 323K for sodium content reduction, followed by calcinations at 773K under dry air flow for transformation to its acid form. 

Soil components, silica, and alumina are solubilized, in low concentration, and can react, or crystallize, to form new clays. In addition, clays from any source change over time and become simpler and simpler. Silica is more soluble than alumina and so the silica alumina ratio decreases over time. Eventually, this leads to deposits of alumina that are used as an aluminum ore for the production of aluminum metal. Although these reactions are considered to be very slow on a human timescale, they do occur. 

Ag exchanged zeolite is used to remove iodine compounds. More recently Ag-LZ-210 , an Ag-exchanged zeoUte-Y adsorbent developed by UOP and having a high silica/alumina ratio (Si/Al > 5), has been used commercially to remove iodide from acetic acid streams [250-252]. 

Mixed matrix membranes with low silica-to-alumina ratio molecular sieves and methods for making and using these membranes. US Patent 7138006 B2. 

Katranas,T.K.,Triantafyllidis, K.S., Vlessidis, A.G., and Evmiridis, N.P. (2007) Propane reactions over faujasite structure zeolites type-X and USY effect of zeolite silica over alumina ratio, strength of acidity and kind of exchanged metal ion. Catal. Lett., 118,79-85. 

It is generally accepted that aluminum deficient structures derived from type Y zeolite alter the extent of hydrogen transfer reactions which ordinarily favor the formation of paraffins and aromatics at the expense of olefins and naphthenes. This octane reducing reaction is controlled principally by the silica/alumina ratio of the zeolite and its rare earth content(1). 

Six kinds of zeolites decatlonlzed-mordenltes and Na-mordenltes with different silica to alumina ratios were used In the present study (Table 1) decatlonlzed mordenltes were prepared from corresponding Na forms. These zeolites were supplied by the Catalysis Society of Japan as reference catalysts. 

The surface silicon concentration at the first saturation was found to decrease with the silica to alumina ratio of zeolite, shown in Table 1. A relatively small concentration on silica was remarkable. Saturated silicon concentration therefore seemed to be correlated with the aluminum concentration of zeolites. 

Because of the consecutive reaction by produced water, the deposition on HN was hardly saturated at 593 K however, it was saturated at room temperature. The saturated silicon concentration on the HM thus measured at room temperature (Table 1) decreased with the silica to alumina ratio of zeolite, similar to that on the NaM. 

It is necessary, however, to maximize the intermediate olefin product at the expense of the aromatic/paraffin product which makes up the gasoline ( ). The olefin yield increases with increasing temperature and decreasing pressure and contact time. Judicious selection of process conditions result in high olefin selectivity and complete methanol conversion. The detailed effect of temperature, pressure, space velocity and catalyst silica/alumina ratio on conversion and selectivity has been reported earlier ( ). The distribution of products from a typical MTO experiment is compared to MTG in Figure 4. Propylene is the most abundant species produced at MTO conditions and greatly exceeds its equilibrium value as seen in the table below for 482 C. It is apparently the product of autocatalytic reaction (7) between ethylene and methanol (8). 

The high silica/alumina ratio zeolites ZSM-5 and ZSM-11 both contain two intersecting channel systems composed of 10-membered oxygen rings. The channels in these zeolites are elliptical, with a free cross-section of 5.5 x 5.1 for the linear channels, and a cross-section of 5.6 x 5.4 for the sinusoidal channels in ZSM-5. The channel structures of these two zeolites are shown in Figure 1. 

A similar experiment was performed with a large crystal (>lp) H-ZSM-5 of 75 silica/alumina ratio, and also with a sample of 1670 1 silica/alumina ratio H-ZSM-5. 

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