Anti-coking materials and surfaces for hydrocarbon steam crackers
Bukhovko, Maxim P.
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Hydrocarbon steam cracking serves as the primary process for ethylene production. A major operating issue within steam cracking furnaces is the formation of solid carbon byproducts (i.e. coke) that deposit within the reactor tubes. The reactor must be periodically shut down to restore acceptable performance and production output. The overall aims of this work focused on exploring catalysts and a coating method that can prevent or limit coke deposition onto surfaces typically found in the cracker furnaces. Mn-Cr-O spinel oxides with varying Mn/Cr content were investigated to determine the differences in their reactivity for gasifying coke with steam and steam-hydrogen mixtures. The kinetics of coke gasification were determined from measured mass changes during thermogravimetric analysis. The Mn1.5Cr1.5O4 catalyst exhibited higher reactivity for coke gasification, and the hypothesized active Mn3+ species were mostly preserved or regenerated within the catalyst structure during simulated steam cracking conditions. Additionally, a Mn/MnO surface coating was successfully formed via electrodeposition on a Fe-Ni-Cr alloy (Incoloy 800H). Mn/MnO coated alloys show a considerable potential improvement compared to pre-oxidized alloy samples by reducing the amount of deposited coke and catalyzing its removal with air. The insights from these studies provide a deeper knowledge of the catalytic activity of various Mn-Cr-O oxides towards radically formed coke, with higher anti-coking performance when more Mn is present. The promising results of using manganese electrodeposition to form an anti-coking surface coating could be used in designing future approaches to optimize steam cracker operations and reduce time/energy expenditures from decoking shutdowns.