(120h) Liquid Metals As Robust Reaction Media for Intensified Ethane Dehydrogenation

Ethylene, a major building block in the chemical industry, is almost exclusively produced via steam cracking, a non-catalytic process in which ethane (or naphtha) is mixed with steam and thermally dehydrogenated at high temperature (~850°C). While this process is commercially widely deployed, it faces significant challenges including coking of the reactor and large CO₂ emissions due to the high-temperature operation and large steam co-feed.

The present work evaluated the use of liquid metals as an intensified, robust reaction media to address these challenges. Using bismuth-based liquid metal systems, we demonstrate via a combination of experimental studies and kinetic simulations that pure bismuth exhibits minimal catalytic activity but functions as a effective, integrated coke separator that enables ethylene yields exceeding those of commercial steam cracking. The system’s unique robustness against deactivation via coking is confirmed by alloying Bi with 5wt% Ni to intentionally increase coke formation and demonstrating stable operation for at least 100 hours time-on-stream. Remarkably, the liquid NiBi system shows five orders of magnitude reduction in deactivation rate compared to a conventional solid 5 wt% Ni/SiO₂ catalyst which deactivates within minutes. Most importantly, the robustness against coking entirely eliminates the need for steam co-feed, resulting in more than 30% decrease in energy intensity of the process, and the potential for up to 40 MMT/a reduction in global CO₂ emissions. Extension of the experimental studies onto other low-melting metals and concomittant life cycle assessment furthermore highlights the importance of the choice of the metal for the overall carbon footprint of the process.

Our results suggest new avenues for intensified, catalytic and non-catalytic ethane dehydrogenation and related hydrocarbon processing reactions with much reduced energy intensity and carbon footprints by exploiting the exceptional resilience of liquid metal systems in heavily coke-forming environments.