Molten?Carbonate-Mediated Oxidative Dehydrogenation of Ethane with in Situ CO2 Capture and Conversion

Ethylene is a cornerstone of the petrochemical industry, serving as a primary building block for polyethylene, polyvinyl chloride (PVC), and numerous other polymers. Industrially, it is produced predominantly through steam cracking of ethane, a process that is both energy- and carbon-intensive. Steam cracking requires high-temperature heat supplied by fossil fuel combustion, demands periodic reactor decoking, and is limited by thermodynamic equilibrium, all of which constrain ethylene yield and result in substantial CO₂ emissions. Our research investigates an alternative ethane-to-ethylene pathway that couples oxidative dehydrogenation with in situ CO₂ capture in a molten carbonate medium (MM-ODH). The MM-ODH cycle proceeds through two principal steps: (1) thermal cracking of ethane within gas bubbles dispersed through the molten medium, producing ethylene and hydrogen that concurrently reduces alkali metal carbonates to hydroxides and CO, and (2) regeneration of carbonates via reaction of the resulting hydroxides with CO₂ from flue gas, yielding H₂O and restoring the active medium.
Thus far, our research has focused on elucidating how the composition of molten carbonate mixtures influences MM-ODH product yields and CO₂ capture capacities. Systematic experiments performed in Li₂CO₃/Na₂CO₃/K₂CO₃/BaCO₃ media have examined the roles of mono- and divalent cations in governing the redox reactivity of the molten phase. In prior work, ternary Li₂CO₃–Na₂CO₃–K₂CO₃ (LNK) mixtures containing 40–80 mol% Li₂CO₃ achieved ethylene yields up to 62.6% and net CO₂ capture efficiencies of 76.3%. While enhanced H₂ conversion with increasing Li₂CO₃ content contributed to this performance, the observed improvements could not be fully explained by reverse water-gas shift thermodynamics alone, suggesting the presence of additional underlying composition–reactivity interactions. More recent testing of BaCO3-containing melts further underscores this complexity. Substituting Li₂CO₃ in LNK with an equivalent molar proportion of BaCO3 relative to Na₂CO₃ and K₂CO₃ only subtly impacted ethylene yield, despite substantial differences in their basicities, cation size, and cation charge. When combined in binary Li₂CO₃–BaCO₃ mixtures containing between 40–60 mol% BaCO₃, the two carbonates synergistically enhanced ethylene yield by up to 5.3% relative to the maximum observed in LNK mixtures.
To better understand these observed phenomena, ongoing work includes design-of-experiments (DOE)-based factor-response modeling and melt doping using conventional petrochemical ODH catalysts (e.g., vanadates, molybdates, tungstates, and ferrites) to systematically evaluate compositional and kinetic effects. In parallel, experiments varying the gas–melt interfacial area aim to assess the role of external mass transfer and multiphase reaction dynamics on overall performance.