Coke burning silica-alumina catalyst

In recent years, the process has been modified to increase the yield of lower olefines, too. Continually improved since then, especially in the mid-1960s with the replacement of the original silica-alumina catalyst by a zeolite. The catalyst is now typically a zeolite Y, bound in a clay matrix. The feed is vaporized and contacted in a pipeline reactor with concurrently flowing microspheroidal catalyst particles. The catalyst is then separated from the hydrocarbon products and is continuously regenerated by burning off the coke in a fluidized bed. The process is licensed by UOP several hundred units are in operation worldwide. See also HS-FCC. 

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. 

A variety of material could be used as the basis for cracking catalyst, including synthetic silica-alumina, natural clay, or silica-magnesia. If these materials did not contain significant amounts of metals such as chromium or platinum that catalyzed the burning of carbon, the burning rate of the coke is independent of the base as shown in Fig. 7. 

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).]...

An examination of this problem was provided by Weisz and Cktodwin [11,12]. The pellets were silica-alumina cracking catalyst, and the coke resulted from the cracking of light gas oil and naphtha. Measurements of the burning rate were followed by oxygen consumption rates, as shown in Fig. I. 

Figure 5.16P Coke burning rates of silica-alumina cracking catalyst. Initial carbon content is 3.4 wt%. (Weisz and Goodwin 1966. Reprinted with permission from Journal of Catalysis. Copyright by Academic Press.)...

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