(453g) Ethane Dehydrogenation Using Liquid Metal Catalysts

Ethylene is a major building block in the chemical industry, with an annual production of 172 million tons in 2021. Due to the availability of abundant shale gas, ethylene is produced in the U.S. via steam cracking of ethane, i.e. via mixing ethane with steam at high temperature (~ 800) where it is dehydrogenated to ethylene. Although this process is widely used commercially, it suffers from multiple issues, including coking due to carbon deposition on the reactor walls and high emissions due to the required heating to high reaction temperature. Formation of the coke layer on the reactor walls results not only in reduced ethylene yields but also in further insulation of the reactor from the (external) heating source, and hence a further increase in the required energy input to maintain a steady reaction temperature. Reducing the impact of coke formation could hence have major impact on the energy intensity of this process. We are studying the use of liquid metals as an alternative reaction medium which has the potential to address this issue.

Liquid metals, i.e. metals with a low melting point, have recently emerged as an interesting novel reaction medium. Liquid metals combine a high heat capacity with excellent resistance to coking by separating the formed coke from the catalytically active molten metal due to density differences. Liquid metals hence have the ability to resist deactivation due to coke formation and thus offer the potential for continuous operation as well as continuous removal of coke without disrupting the production process, without need for steam, and without the CO_x emissions associated with the decoking process.

Here, we present initial data evaluating bismuth-based liquid metal systems for ethane dehydrogenation to ethylene. Molten Bi baths were doped with small amounts of catalytically active metals. While pure Bi showed no detectable activity, doping with Ni and In induced catalytic activity. Addition of Ni favored the formation of methane and coke, in agreement with the well-known carbon scission activity of solid Ni catalysts. In contrast, doping with In favored the desired ethylene production. In our presentation we will present characterization of the liquid metal systems, preliminary reactor design considerations for these novel reaction systems, as well as results from the catalytic studies.