Catalysts cracking

The hydration of cement paste was investigated as a function of the addition of spent catalyst for catalytic cracking in fluidized bed, in comparison with similar uses of microsilica and fly ashes (38). 

The kinetics of the hydration process was studied by thermogravimetry (TG), differential scanning calorimetry, and spectroscopic methods. The time of setting of freshly prepared pastes and the compressive and bending strengths of sample beams after the 7th day and the 28th day of setting were determined. 

The contents of Ca(OH)2 in the pastes at various times of hydration were determined from the results of the TG studies. Also, the pozzolana nature of the additives has been found out. The ability of combining with Ca(OH)2 was similar in the spent catalyst and the microsilica. In the presence of the spent catalyst, the hydration process was strongly exothermic, which promoted the rapid setting of the cement paste. Calcium carbonate aluminates that are formed in the system, favorably affect the strength of the concrete materials (38). 

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In addition, salts deactivate reforming and catalytic cracking catalysts. 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

Cracking catalysts Crack-tip shielding Crack-wake bndging Cr3Al Crambe Crambe oil Cranb erry... 

ALUMRJUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - ACTIVATED] (Vol 2) Fluid cracking catalysts (FCC)... 

The equivalent nickel content of the feed to the FCCU can vary from <0.05 ppm for a weU-hydrotreated VGO to >20 ppm for a feed containing a high resid content. The nickel and vanadium deposit essentially quantitatively on the cracking catalyst and, depending on catalyst addition rates to the FCCU, result in total metals concentrations on the equiUbrium catalyst from 100 to 10,000 ppm. 

At high metals levels, the coking characteristics of a cracking catalyst can be greatly increased that is, the ratio of contaminant coke to catalytic coke can be quite high. The effect of the contaminant metals on the coke response is affected not only by the level of metals but also by the type of catalyst and the use of a metals passivator. Catalysts, which contain effective metals traps to inhibit the contaminant effects, do produce much less contaminant coke than catalyst without metal traps. 

During the 1980s, antimony was widely used in FCCUs that had a problem with contaminant metals. In the late 1980s, other additives were introduced to combat the contaminant metals, eg. Chevron introduced a bismuth-based additive, which is claimed to provide performance similar to antimony (18). Also in the late 1980s, cracking catalysts were developed with metals traps that appear to be so effective in containing the adverse effects of contaminant metals that additive-type inhibitors are no longer needed (19). 

The H2S comes out with the reactor products, goes through the product-recovery system of the FCCU, and eventually goes to a Claus plant for sulfur recovery. The metal oxide adsorbent recirculates with the spent cracking catalyst back to the regenerator for the next SO adsorption cycle. 

A sample of cracking catalyst in a fixed bed reactor is contacted with gas oil, an ASTM standard feed. Cracked liquid products are analyzed for unconverted material. Conversion is the difference between weight of feed and unconverted product. 

The microactivity test provides data to assess the relative performance of fluid cracking catalysts. ... 

Over the years, thousands of compounds have been tried as cracking catalysts. These compounds fall into two general categories natural and synthetic. Natural catalyst, as the name denotes, is a naturally occurring clay that is given relatively mild treating and screening before use. The synthetic catalysts are of more importance because of their widespread use. Of the synthetic catalysts, two main types are amorphous and zeolitic. 

Catalytic Cracking Catalysts, Chemistry, and Kinetics, Bohdan W. 

Fluid Cracking Catalysts, edited by Mario L. Occelli and Paul O Connor Catalysis of Organic Reactions, edited by Frank E. Herkes The Chemistry and Technology of Petroleum, Third Edition, Revised and Expanded, James G. Speight... 

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