Anti-coking materials for steam crackers
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Catalysts that have the potential to minimize coke formation in steam crackers as well as help in the oxidation of these deposits at low temperatures, were developed. A specialized thermo-gravimetric analyzer was used for generation of in-situ coke to simulate coke formed in steam cracking furnaces. Thermally aging the coke generated in-situ in an inert atmosphere increased the graphitic nature of coke and was supported by temperature programmed oxidation studies and Raman analysis. The reaction rate constants for oxidation of coke were determined by fitting a first order rate equation to the mass loss data. Ceria catalyzed oxidation was faster than un-catalyzed oxidation. In addition, α-alumina supported ceria catalysts demonstrated faster kinetics than bulk ceria. The activity of these oxides was related to the availability of these surface oxygen atoms. Gd doped ceria was found to be the best for steam gasification studies and was able to reduce the coke gasification temperature by 65 °C. In addition to steam, Gd, and Mn doped ceria catalysts also showed improved activity for oxidation. In the presence of steam – air mixtures, oxidation due to air dominated the process and Gd showed the best activity by reducing the gasification temperature by 125 °C. Catalytic ceria coatings synthesized in lab, not only reduced catalytic coking by acting like a barrier between the gaseous hydrocarbons and the metallic species on the Incoloy substrate, but also reduced the coke oxidation temperature by ~ 160 °C. Synthesis of catalytic powders and coatings, their characterization, activity towards coke resistance, coke oxidation and gasification are discussed in detail in this work.