Cracking catalyst data

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... 

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

This method has been applied (M5) for modeling the vapor-phase rate of dehydration of secondary butyl alcohol to the olefin over a commercial silica-alumina cracking catalyst. Integral reactor data are available at 400, 450, and 500°F. Two models considered for describing this reaction are the single site... 

Independence from cracking catalyst composition has been shown by adding cerium and alumina to cracking catalyst (25). The data on Table I demonstrate this. 

Two sets of experiments were made to show the effect of steaming temperature on stability. In the first set, steaming was done non-interactively. Cerium/alumina additive was steamed (100% steam, 1 atm) for 5 hours in a fixed bed from 1200 to 1450 F. SO2 removal ability was then measured on these steamed samples diluted with cracking catalyst. The data in Figure 14 show that, for steamings done separate from cracking catalyst, losses of SO2 removal ability are small but become more pronounced above 1350 F. 

These data were obtained by mixing the SOx additive with a low alumina cracking catalyst and steaming at 1400°F in 100% steam in a fixed bed for 5 hours. The concentration of additive was adjusted so that the initial activity was approximately the same for all materials. (The amounts were the same as those used for the regenerability test.) The SO2 removal ability was then measured before and after steaming and the % loss calculated. The average deviation was 7%. 

Our SOx test work was done with samples which were fully promoted with Davison CP-3 Combustion Promoter (7.4 pounds per ton of cracking catalyst, 0.37%). The only exception is the data in Table II which shows the effect of not using combustion promoter. 

These results on commercially-aged samples show that silica is transported from the cracking catalyst particles to the Additive R particles during commercial-unit aging, just as it is during a laboratory steam deactivation. More Importantly, the data show that silica deactivates Additive R in a commercial unit (loss of SOx capability) just as it does in a laboratory deactivation. 

Because of the ease of experimentation batch-solids devices are much preferred however, they can only be used when deactivation is slow enough (in the order of minutes or longer) so that sufficient data on the changing fluid composition can be obtained before exhaustion of the catalyst. When deactivation is very rapid (in the order of seconds or less) then a flowing-solids system must be used. Cracking catalysts whose activity half-lives can be as short as 0.1 second fall into this class. 

The catalytic cracking of four major classes of hydrocarbons is surveyed in terms of gas composition to provide a basic pattern of mode of decomposition. This pattern is correlated with the acid-catalyzed low temperature reverse reactions of olefin polymerization and aromatic alkylation. The Whitmore carbonium ion mechanism is introduced and supported by thermochemical data, and is then applied to provide a common basis for the primary and secondary reactions encountered in catalytic cracking and for acid-catalyzed polymerization and alkylation reactions. Experimental work on the acidity of the cracking catalyst and the nature of carbonium ions is cited. The formation of liquid products in catalytic cracking is reviewed briefly and the properties of the gasoline are correlated with the over-all reaction mechanics. 

Figure 1. Metal level trends in equilibrium fluid cracking catalysts (FCC). Data based on Davison analysis of samples from 96% of fluid units in the USA and Canada.

Transmission electron micrographs and XPS results have been used to show that a catalyst, with a high silica content in the matrix, prevents nickel dispersion (16,18). In fact, in a FCC with a Si-rich (Si/Al = 4.3) surface, XPS data has indicated that calcination and steaming cause nickel (and vanadium) migration to the cracking catalyst surface where nickel sinters. As a result, nickel crystallites 50... 

The value of Do used to calculate the data in Table IV was obtained from direct measurement of the diffusion of hydrogen in the catalyst by the porous plug method (1, p. 189, method b). The value used was for the spherical beads of cogelled silica-alumina cracking catalyst used in the experiments to be reported here. The catalyst contained 10% AI2O3 by weight and had a surface area of 350 m.2/g. The value of the effective diffusivity of the catalyst particle for H2 at 27°C. (DHj) was found to be 7 X 10-3 cm.2/sec. The value of the effective diffusivity of the catalyst particle for cumene Dc, at reaction temperature was calculated from this measured hydrogen diffusivity by the equation... 

This paper reviews literature data on model fluid cracking catalysts (FCC) and reports results of spectroscopic studies performed in our laboratories for catalysts in which vanadium has been passivated by tin. Mossbauer spectroscopy, luminescence, x-ray powder diffraction and electron paramagnetic methods have been used to monitor vanadium-tin interactions in all the catalysts studied. 

Of particular mention and of widespread interest throughout the petrochemical industry has been the Committee s success in obtaining round robin results on testing fluid cracking catalysts. Overcoming a natural desire not to share data or methods, industry representatives developed a standard method to determine the weight percent conversion of gas oil in a fixed bed microactivity unit. 

For residence times below 0.15 s. Mg is more effective than Ca at reducing the yield of volatile matter. This may be due to the 30% higher Mg loading. In the total residence time of the reactor, however, Ca and Mg reduced the volatile matter yield equally. Tanabe ( 5) has reported Ca to be a better polymerization and/or cracking catalyst than Mg. The data in Figures 2 and 3 imply that in the... 

Figure 1 shows the matrix surface area of conunercially aged Ecat for four types of cracking catalyst. Each set of data represents one type of cracking catalyst deactivated in different conunercial FCC units. The four types of catalysts were chosen fOT their wide range of matrix surface areas. Although the fresh catalyst matrix surface area for each catalyst type is similar, the equilibrium matrix surface area decreases by as much as fifty percent with increasing Na The variation of matrix surface could be attributed to other... 

The application of IR spectroscopy to catalysis and surface chemistry was later developed in the fifties by Eischens and coworkers at Texaco laboratories (Beacon, New York) in the USA [7] and, almost simultaneously, by Sheppard and Yates at Cambridge University in the UK [8]. Mapes and Eischens published the spectra of ammonia chemisorbed on a silica-alumina cracking catalyst in 1954 [6], showing the presence of Lewis acid sites and also the likely presence of Br0nsted acid sites. Eischens, Francis and Pliskin published the IR spectra of carbon monoxide adsorbed on nickel and its oxide in 1956 [9]. Later they presented the results of an IR study of the catalyzed oxidation of CO on nickel at the First International Congress on Catalysis, held in Philadelphia in 1956 [10]. Eischens and Pliskin also published a quite extensive review on the subject of Infrared spectra of adsorbed molecules in Advances in Catalysis in 1958, where data on hydrocarbons, CO, ammonia and water adsorbed on metals, oxides and minerals were reviewed [11]. These papers evidence clearly the two tendencies observed in subsequent spectroscopic research in the field of catalysis. They are the use of probes to test the surface chemistry of solids and the use of spectroscopy to reveal the mechanism of the surface reactions. They used an in situ cell where the catalyst sample was... 

Three particle systems were examined by image analysis and their aspect ratio and particle size distributions were measured [197,198]. The data were then used as a reference method for neural networking using a Malvern Mastersizer X and concentrations from 2 g f to 60 g I" . Particle shapes ranged from an ellipsoidal cracking catalyst, needle shaped asbestos and monoclinic sucrose crystals. 

Typical data on representative samples of fresh commercial cracking catalysts are shown in Table XI. In the case of silica-magnesia, practically the entire surface area and pore volume are contributed by small pores in... 

Catalytic hydrogenation of ethylene by nickel- or copper-impregnated cracking catalyst is taken here for comparison. Figure 67 shows typical experimental A or values taken under a constant superficial gas velocity Uq by varying A ,. Curve LGG is based on the data by Lewis et al. (LI 2), GK by Gilliland and Knudsen (G7), and FKM those by Furusaki et al. (F18). The calculation ofA R will be explained later. The dotted curves are calculated by the two-phase consecutive model (TCM) and by the bubbling bed model (BBM) for Ug = 20 and 25 cm/sec, where the mean bubble size is 4.5 cm and the wake fracticm / = 1.0. 

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