Alumina crack

Villet and Wilhelm Ind. Eng. Chem., 53 (837), 1961] have studied the Knudsen diffusion of hydrogen in porous silica-alumina cracking catalyst pellets. They used apparatus of the type depicted in Figure 12P.1. 

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... 

This paper identifies alumina, rare earths, platinum, and magnesia as important SOx capture materials. Alumina is either incorporated directly into the matrix of a cracking catalyst or added as a separate particle. Cerium is shown to promote the capture of SO2 on high alumina cracking catalyst, alumina, and magnesia. Other rare earths are ranked by their effectiveness. The promotional effect of platinum is shown between 1200 and 1400 F for SO2 capture on alumina. Silica, from free silica or silica-alumina in the matrix of cracking catalyst, acts as a poison by migrating to the additive. 

Rare Earths and Alumina. A much easier and cheaper way of getting the SO2 removal enhancement from rare earths that was observed with the well-exchanged rare earth Y zeolite was to add rare earths, especially cerium, by direct impregnation to high alumina cracking catalyst (24). 

The Mobility of Silica in Steam. The reactivity of silica and silica-containing materials to steam has been assumed in the literature to explain several phenomena, a few of which are the sintering of silica (35), the aging of amorphous silica alumina cracking catalysts (36) and the formation of ultrastable molecular sieves (37). The basis of all these explanations is the interaction of siliceous materials with water to form mobile, low molecular weight silicon compounds by hydrolysis (38) such as ... 

The rates of hydrolysis of siliceous materials will be affected by several factors. For instance, the rate will be directly related to surface area, explaining the low rates observed for silica deposition from the Vycor apparatus. Also, the composition of the siliceous material will Influence the rate of hydrolysis, explaining the differing amounts of silica transferred from pure silica, silica alumina, zeolite, and the high alumina cracking catalyst. 

Losses incurred in the non-interactive steamings, however, were lower than those found in the second set of experiments where the cerium/alumina additive was steamed together with a low alumina cracking catalyst at various temperatures. The results from this second set of experiments, shown in Figure 14, indicate that losses are important at temperatures above 1200 F. It should be noted that SO2 removal ability was measured under the same conditions in both sets of experiments. Also, these fixed bed steaming seem to be harsher than fluidized bed steamings because the losses incurred are greater. 

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%. 

Rare earths have also been included as desirable SOx catalyst components in early patents but the catalytic behavior of cerium, in particular, had not been clarified. This paper has presented evidence that cerium catalyzes the oxidative adsorption of SO2 on high alumina cracking catalyst, alumina, and magnesia. We also have shown the catalytic character of platinum. The details of the catalysis especially by cerium, however, remain unexplained. 

A West Texas gas oil is cracked in a tubular reactor packed with silica-alumina cracking catalyst. The liquid feed mw = 0.255) is vaporized, heated, enters the reactor at 630°C and 1 atm, and with adequate temperature control stays close to this temperature within the reactor. The cracking reaction follows first-order kinetics and gives a variety of products with mean molecular weight mw = 0.070. Half the feed is cracked for a feed rate of 60 m liquid/m reactor hr. In the industry this measure of feed rate is called the liquid hourly space velocity. Thus LHSV = 60 hr Find the first-order rate constants k and k " for this cracking reaction. 

Following their introduction to the refining industry in 1962, zeolite cracking catalysts, have virtually replaced the amorphous silica alumina cracking catalysts that had previously dominated the marketplace. To the rare earth industry the development of zeolite catalysts represented a new end use without precedent. Nearly all zeolite cracking... 

Several years ago, one of the authors found that nickel, platinum, and some other hydrogenating agents, when deposited on fresh synthetic silica-alumina cracking catalyst, made a new catalyst that would isomerize paraffin and naphthene hydrocarbons in the presence of hydrogen at elevated pressures and nominal temperatures. Table I shows some early typical results calculated from mass spectrometer analyses of the products obtained by passing methyl cyclopentane, cyclohexane, and n-hexane over a catalyst composed of 5% nickel in silica-alumina at the indicated reaction conditions. Isomerization of a number of other hydrocarbons has also been studied and reported elsewhere (2). 

During the 1940,s, much effort was made to elucidate the nature of the active sites in amorphous silica-alumina cracking catalysts (11). By... 

Figure 2. Synthesis of zeolite omega from silica-low-alumina cracking catalyst...

To explain the observed selectivity effect, consider the type of mechanism proposed by Matsumoto et al (9, 10) for reactions of o-ethyltoluene with H+A102 of amorphous silica-alumina cracking catalysts. 

The Octafining process (114—116) was developed and commercialized by Adantic Richfield and Engelhard in the eady 1960s. The first-generation catalyst was prepared by mixing equal amounts of a silica—alumina cracking catalyst with Pt on alumina. The Pt content of the mixture was about 0.5 wt %. The EB approach to equilibrium was 88%, with an 80% selectivity to xylenes. Reaction conditions consist of temperature of 425-480°C pressure of 1.14—2.51 MPa H2/hydrocarbon ratio < 10 1 (preferably 4—6 1) and LHSV = 0.6-1.6/h. An equilibrium mixture of xylenes is produced. To maintain... 

Results of three independent titration studies of silica-alumina cracking catalyst are compared in Fig. 2. Benesi (26) and Hirschler (24) used n-butylamine as the basic reagent and detected endpoints visually by means of Hammett and arylcarbinol indicators, respectively. Drushel and Sommers (21) used diethylamine as the basic reagent and measured end-... 

The spectrum of ammonia chemisorbed on a silica-alumina cracking catalyst was studied to determine whether the acidity of these catalysts is due to a Lewis (nonprotonic) or a Bronsted type of acid (28, 29). This work was based on the premise that ammonia chemisorbed on Lewis sites would retain a NH3 configuration while ammonia chemisorbed on a Bronsted site would form NHt. The NH3 configuration was expected to have bands near 3.0 and 6.1 p and the NHt near 3.2 and 7.0 p. 

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). 

Adsorption Equilibrium Constants for Various Inhibitors on Silica-Alumina Cracking Catalysts... 

Acid catalysts such as zeolites can be readily poisoned by basic organic compounds. One of the earlier studies of the deactivation of silica-alumina cracking catalysts by organic nitrogen compounds such as quinoline, quinaldine, pyrrole, piperidine, decylamine and aniline was done by Mills et al (6). The results of their partial poisoning studies showed an exponential dependence of the catalyst activity for cumene cracking reaction or... 

Simultaneous dehydrogenation and dehydration of cyclohexanol over silica-alumina cracking catalyst at 340-375° was reported (245) to give a 78 to 95% yield of hydrocarbons. Subsequent hydrogenation resulted in the formation of 45% methylcyclopent.ane (245). 

Figure 7.5 shows a comparison of the static and cyclic crack velocities for the alumina/SiC composite, similar to that illustrated in Fig. 7.2 for alumina. As seen for monolithic alumina, the ceramic composite undergoes slower rates of fracture when (1) fluctuations are introduced in the tensile loads and (2) the cyclic frequency is raised. The differences between static and cyclic crack growth rates are maximum at the lower Kmax levels. As in the case of unreinforced alumina, crack velocities estimated for cyclic loads on the basis of sustained load crack growth data (assuming identical failure mechanisms) are higher than those measured experimentally. 

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