(569dd) Liquid Metals As Robust Catalytic and Non-Catalytic Reaction Media for Ethane Dehydrogenation

Ethylene is a major building block in the chemical industry, with an annual production capacity of 228 million tons in 2023. Ethylene is produced, in the U.S., via steam cracking of ethane, i.e., via mixing ethane with steam at high temperature (~ 850^oC) where it is dehydrogenated to ethylene. This process suffers from coking due to carbon deposition on the reactor walls and high emissions due to the required high reaction temperature.

We are investigating the use of liquid metals as an alternative reaction medium which may help to mitigate these issues. Liquid metals show excellent resistance to coking by separating coke from the molten metal due to density differences. Liquid metals system offers the potential for catalytic ethane dehydrogenation via 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 are presenting results from an investigation of bismuth-based liquid metal systems for ethane dehydrogenation to ethylene. Our experimental results indicate that molten bismuth exhibits only minimal catalytic activity, which is further corroborated using conventional supported Bi/SiO₂ catalysts and via detailed homogeneous gas phase simulations. However, notably, at high space velocity (GHSV ≥ 1000 hr^-1), the liquid bismuth system functions as a non-catalytic coke filter. The addition of Ni, a well-known catalytically active metal, to a molten Bi bath enhances activity at the expense of ethylene selectivity. In contrast to conventional solid Ni catalyst, however, which deactivates within minutes under reaction conditions, liquid NiBi alloy shows stable operation for 100 hours time-on-stream. Kinetic fitting to a first-order deactivation model showed a reduction in deactivation rate by six orders of magnitude compared to the solid 5wt% Ni/SiO₂., emphasizing the exceptional robustness of these liquid metal catalyst systems against coking.