Silica alumina catalysts bead catalyst

In 1944, Socony-Vacuum Oil Company started manufacture of synthetic silica-alumina catalyst in the form of beads (262). This catalyst was reported to contain about 10% alumina. The bead catalyst gives about the same product distribution as the pelleted synthetic catalyst and was developed primarily to achieve greater physical strength for use in the TCC process. The bead catalyst has also been used in Houdry fixed-bed units (51,171). Subsequently, a harder bead catalyst was developed for use in the air-lift units. The improved bead catalyst consists of approximately 15% alumina and 85% silica and contains 0.003% chromium to minimize afterburning by suppressing formation of carbon monoxide during regeneration (333). 

The synthetic silica-alumina catalysts, TCC Beads, Aerocat, and Diakel, are composed of pores appreciably larger but with average pore radius values almost exclusively in the small pore range of 15 to 25 A. (Ries, Johnson, Melik, and Kreger, 48 Shull, Elkin, and Roess, 57). The complete absence of large pores is indicated for the TCC Beads and the Aerocat Microspheres. In the case of silica-alumina catalysts, the hysteresis loops have considerable breadth and area in contrast to the silica-magnesia isotherms. 

Use the effective diffusivity approach to evaluate the effectiveness factor for the silica-alumina catalyst pellets considered in Illustration 12.2. Assume that the effective diffusivity for cumene in these particles is equal to 1.2 x 10 cm /s, which is a typical value for silica-alumina TCC beads (40). 

The earliest catalyst was made from clay later, synthetic beads from siUca-alumina were introduced. In the early 1960s, catalysts were introduced that employed up to 10% X or Y zeolite in a silica-alumina matrix. 

Fig. 28. The cumulative COj/CO ratio for coke bum-off on spherical catalyst beads versus combustion temperature in air (O) white amorphous silica-alumina ( ) green Cr02-containing amorphous silica-alumina (M) macroporous white catalyst. The weight (mg) of the bead tested is denoted by the numerals adjacent to the respective symbol. Dashed line represents intrinsic ratios from carbon combustion research. From Weisz (1966).

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... 

The catalyst used in these studies was a commercial type of bead silica-alumina cracking catalyst (Socony Mobil Oil Company, Inc.) containing 10% alumina by weight and having originally a bead diameter between 2 and 5 mm. This catalyst had a surface area of 350 m.2/g. and a CAT-A activity of 42 A.I. 13). 

Transhalogenation is also performed in the gas phase. The preferred catalysts are quaternary phosphonium salts supported on silica, alumina or glass beads which are applied in tubular reactor. At 140 °C, residence time of a few seconds is sufficient for 72-butyl bromide and -propyl chloride to equilibrate223. 

Weisz (2) carried experiments on silica- alumina beads (many times the size of an average FCC particle). Heobservedthattheintrinsic cokebuming rate was independent of the coke composition and the catalyst characteristics but dependent on initial coke level and the diffusivity. Weisz (3) inanotherstudy, found that the CO /CO ratio during intrinsic coke burning is only a function of temperature. He also observed that this ratio i s affected by the presence oftrace metals like iron and nickel etc. Even though this study was elaborate, it was limited to only silica-alumina catalysts in the form of beads. 

The ratio of CO2 to CO with Filtrol SR catalyst has been reported to be 1.2-1.3, closely resembling that obtained with synthetic silica-alumina (326). The ratio tends to increase with use for silica-alumina catalyst but not with silica-magnesia (355). The increase with silica-alumina is presumably due, at least in part, to accumulation of metal contaminants that promote complete combustion to CO2 total iron pick-up during commercial use was reported to be much less in the case of silica-magnesia than in a companion commercial run on silica-alumina (355). Intentional addition of a small amount of chromium to TCC bead catalyst is practiced commercially for the specific purpose of insuring complete combustion to CO2 and thereby avoiding afterburning (333). 

D = differential 7 = integral. The catalyst always used in the differential reactor was 42 A.I. (CAT-A), 349 m.Vg. white T.C.C. silica-alumina bead catalyst, crushed to 100-200 mesh, manufactured by the Socony Mobil Oil Co. 

Catalyst silica-alumina beads crushed to 8-14 mesh (Tyler), 35 A.I., 212 m.Vg. 

For example, consider the smallest particles of silica-alumina beads (14-mesh Tyler, r = 0.058 cm.) used in the styrene experiments at 800° F (426°). The initial rate dn /dt calculated as outlined above was 7 X 10 mole/cc. sec. The diffusivity of cumene in the pore structure of catalysts of this type having the same surface area was found by the porous plug method (5) to be 7 X 10 cm. /sec. The left side of Equation (22) yields the value 2. Thus the criterion for absence of significant diffusion transport is violated. Using the curves of Weisz and Prater (5) and the fact that (dur/dt) X (l/c)rVD ff = the value of 2 obtained above means that the observed rate in the front part of the catalyst bed was only 85 % of the rate in absence of diffusion transport effects. Since the addition of inhibitor reduces the rate and therefore reduces the diffusion transport effect, the value of Kp will be too small when it is determined under conditions in which either dn/dt for pure cumene or both dn/dt for pure cumene and inhibited cumene are affected by diffusion transport. 

Figure 7.26 Observed coke burning rates for a silica/alumina cracking catalyst with an initial coke content of 3.4 wt% big beads and fine powder. [From P.B. Weisz and R.D. Goodwin, Jr., J. Catal., 2, 397, with the permission of Academic Press, Inc., New York, NY, (1963).]...

Figure 1 Average observed burning rates of conventional silica-alumina cracking catalyst. Initial carbon content, 3.4 Beads dashed line), and ground-up catalyst (full curve) from Weisz and Goodwin [11 ]).

The synthetic silica-alumina bead catalyst developed at Socony-Vacuum had a distinct advantage because of its resistance to attrition. The bead also allowed for operating without the need of baffles in the reactor therefore, more reactor space was occupied by catalyst and the operation without baffles was much simpler. 

For HTCO analysis, manufacturers offer various combinations of instruments. Since it is difficult if not impossible to draw up an exhaustive list of all commercially available and laboratory-made apparatus, we only mention, with one example each, a few of the most frequently used configurations. Some instruments (e.g.. Ionics) use a combination of high temperature (900 °C) and pure platinum as catalyst. Others (e.g., Shimadzu), use platinised alumina catalysts at lower temperature (680 C). Analytik Jena sells an instrument working with a CuO catalyst at 950 °C. Antek produces a total nitrogen analyser based on the same principle (900 °C, on silica beads). The combination used by Sugimura and Suzuki (1988) which triggered the controversy on DOC concentrations was close to the Shimadzu design. The sample was injected vertically into a furnace filled with 3 % Pt on aluminium oxide, at 680 °C. 

Descending coke profiles were observed experimentally by Van Zoonen in the hydroisomerization of olefins [1965]. Hughes et al. [1987] observed a decreasing coke profile when xylenes reacted over a silica/alumina bead catalyst around 460°C. The profile was measured by a noninvasive technique neutron beam attenuation coupled with a BF3 counter. 

The desire to have catalysts that were uniform in composition and catalytic performance led to the development of synthetic catalysts. The first synthetic cracking catalyst, consisting of 87% silica (Si02) and 13% alumina (AI2O3), was used in pellet form and used in fixed-bed units in 1940. Catalysts of this composition were ground and sized for use in fluid catalytic cracking units. In 1944, catalysts in the form of beads about 2.5 to 5.0 mm in diameter were introduced and comprised about 90% silica and 10% alumina and were extremely durable. One version of these catalysts contained a minor amount of chromia (Cr203) to act as an oxidation promoter. 

Siantar compared the rates of reaction of DBCP on several 1% w/w Pd catalysts Pd/alumina powder, Pd/PEI/silica beads and powder, and Pd/PAC. The PEI/silica beads had the lowest first order reaction rate constant, followed by the PAC, the PEI/silica powder, and the alumina powder, which showed the highest activity. (Siantar et al. 1996)... 

The catalyst support impacts the rate of a catalyzed reaction, the reaction pathway (quantities and species of intermediates and products) and the resistance of the catalyst to deactivation. In DBCP reactions, powders had higher rate constants than beads, presumably due to reduced mass transfer limitations alumina yielded a faster rate than C, which had a faster rate than PEI/silica. Sorptive capabilities of the supports may also play an important role Kovenklioglu found that supports which sorbed 1,1,2-TCA more strongly had higher reaction rates, and Farrell concluded that TCE sorption to Fe cause higher reaction rates on Pd/Fe electrodes than on pure Pd electrodes. It is also clear that supports influence reaction products, but the correlation between a given support and pathways/products it promotes is not yet understood. The choice of support can also affect its resistance to deactivation this implies that catalyst supports may be tailored to maximize activity over the long term. 

In drop-coagulation to form beads of alumina hydroxide, the top of a column holding oil and 100°C is fed with a blend of a sol of aluminium oxychloride and hcxamcthylcnc tctraminc. Under the influence of the temperature, the amine is decomposed to liberate ammonia, which neutralizes the chloride ions. The product is then ripened, dried, calcined and can be used as a support for reforming catalysts or hydrodesulfurization catalysts [2], In the same way. a silica sol feeding the bottom of a column of trichloroethylene at around 75 °C permits obtaining silica beads at the top. 

Different inorganic materials have been used as supports in SAPC glass beads of controlled pore size [6,14—17, 24, 39—42,44,45, 53] porous [11,15,18,19, 21, 23, 28-32, 35, 36, 38, 39, 43, 48, 49] and nonporous [28, 33, 48] silica nanoparticles synthetic phosphate [27] carbon [39], and alumina [15,39]. It was shown that glass beads, siKca, and synthetic phosphate gave the best performance. All these supports have a high specific surface with an average diameter of the pores, in the case of porous supports, between 60 and 345 A. The use of chitosan as a natural polymeric support of SAP catalysts for the synthesis of fine chemicals has been reported recently [54]. 

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