Selectivity, of FCC catalysts

Aluminum distribution in zeolites is also important to the catalytic activity. An inbalance in charge between the silicon atoms in the zeolite framework creates active sites, which determine the predominant reactivity and selectivity of FCC catalyst. Selectivity and octane performance are correlated with unit cell size, which in turn can be correlated with the number of aluminum atoms in the zeolite framework. ... 

Catalytic Selectivity of FCC Catalysts Containing Dealuminated Faujasite... 

A complete discussion of FCC catalysts would fill another book. This chapter provides enough information to select the proper catalyst and to troubleshoot the unit s operation. The key topics discussed are ... 

Rare Earth is a generic name used for the 14 metallic elements of the lanthanide series used in the manufacturing of FCC catalyst to improve stability, activity, and gasoline selectivity of the zeolite. 

Thus, a large focus of FCC catalyst research involves control of the density and location of acid sites in order to control product selectivity, product quahty and coke make. In a landmark publication Pines [30] demonstrated how widely spaced framework A1 sites may be utilized to produce high octane gasolines by decreasing hydrogen transfer reactions which in turn results in preservation of olefins. 

FIGURE 11.7 Selected frames of FCC catalyst in the freeboard region of a 6 inch (15 cm) diameter fluidized bed at a superficial gas velocity of 2 ft/sec (0.61 m/sec). Images were collected at 4000 frames per second with a 20 J,s exposure time. 

It is also clear that in the case of FCC with heat removal, the frontier of resid processability can at a certain moment be determined by the coke selectivity of the catalyst, while on the other hand the conversion of resid in a unit without heat removal may also be limited by the metal resistance of a catalyst. 

A few cases of FCC catalyst deactivation are highlighted, specifically addressing the question how to simulate the deactivation phenomena properly, in order to study and estimate the impact on catalyst activity and selectivity. 

Deactivation of FCC Catalysts does not only yield a drop in activity, but usually also a change in selectivity. 

The effect of reversible poisons will be dependent on the catalyst-to-oil, and therefore also of the coke selectivity of the catalyst and the heat balance of the FCC operation. 

Providing catalysts that tolerate the high level of metal contaminants in the resid, while still maintaining high conversion and selectivity, is a key issue of FCC catalyst design. 

Deactivation of FCC catalysts does not only yield a drop in activity, but usually also a change in selectivity. Basically, three types of phenomena should be considered when studying the changes in catalyst activity and selectivity ... 

Experimental Conditions. As the aim of the present study is to understand the intrinsic coke-burning behavior of FCC catalysts, extreme care has been taken in selecting experimental conditions so that no transport resistances influence the results. Minimizing the oxygen axial concentration gradient and obtaining sufficient kinetic data are the two... 

The importance of diffusion restrictions in FCC catalysis is often questioned. Short-contact-time pilot riser experiments confirm that combining zeolites with diffusion-enhancing matrices can result in significant product selectivity and product property improvements. The industrial benefits of a nonzeolite matrix on bottoms cracking in heavy vacuum gas oil (VGO) and resid FCC (RFCC) have also been confirmed in practice. Recently, some new methods have been used to measure the accessibility of FCC catalysts. 

In conclusion, we have shown here that rare earths play an important role in improving the stability of Y zeolite in FCC catalysts. Moreover, by an adequate control of the zeolite rare-earth content, it is possible to control the activity and selectivity of the catalyst by controlling the unit cell size or framework aluminium content of the equilibrated zeolite. 

Union Carbide discovered X Y zeolites but it remained to Plank and Rosinski (1964, Mobil Oil) to apply these zeolites to clay or silica alumina-based FCC catalysts and thereby achieve a considerable boost to activity and selectivity. It is pleasing to note that Plank and Rosinski were introduced to the US patent office inventors Hall of Fame for this discovery (Figures 22-24) Table VI documents of history of FCC catalyst manufacture. 

The traditional Micro Activity Test (MAT) remains the main tool for basic FCC research and catalyst and feedstock evaluation (O Connor and Hartkamp, 1988 Campagna et al., 1986). This test was developed because of its simplicity, reproducibility and quickness of evaluation in comparison to pilot units. The MAT method is an ASTM procedure (ASTM D-3907-80) which comprises a fixed bed of 4 grams of catalyst, operated with continuous oil vapour feed for 75 seconds at a temperature of 482°C under a cumulative catalyst to oil ratio of 3. This specific form of the MAT procedure has not been successful in predicting commercial unit performance and provides only very limited information on selectivity (Carter and McElhiney, 1989 Mauleon and Courcelle, 1985 O Connor and Hartkamp, 1988). In general, catalyst choice based solely on MAT data is questionable and rarely done and it is not suited for simulating commercial operation. Its main use is in the relative comparison of activity of FCC catalysts (Humphries and Wilcox, 1990). 

Teraishi K. Computational study on the product selectivity of FCC zeolitic catalyst. J Mol Catal A 1998 132 73-85. 

As already mentioned, the zeolitic component is the most important component in the FCC catalyst, being able to provide the catalyst with both the convenient activity and selectivity. In FCC catalysts, the zeolite employed is faujasite, or rather, the faujasite zeolite (FAU) structure. The Si/Al ratio of the prepared Y-zeolite is an important feature of such material, in that the higher the Si/Al ratio, the more stable against acid and hydrothermal dealumination the zeolite is. 

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