Process and techno-economic analyses of ethylene production by electrochemical reduction of aqueous alkaline carbonates

Abstract

Electrolyzer architectures using bipolar membranes (BPMs) to convert alkaline aqueous carbonates into hydrocarbons are a potential solution to overcome limitations of conventional carbon dioxide (CO2) electrolyzers. We present comprehensive process designs, simulations and a techno-economic evaluation of integrated electrolysis-based systems (from CO2 capture to product separation and stream recycling) for the production of ethylene from carbonates. Using three different scenarios for an ethylene plant with a production capacity of 2 million metric tons per year, a set of key projected performance metrics has been determined. Carbonates for electrolysis sourced from direct air capture and flue gas capture scenarios showed equivalent economics in the optimistic scenario. Concentration of capture carbonates to at least 1.5 M by alkali-stable membranes upstream of the electrolyzer is needed to make the overall process feasible. Electrolyzer sizing, configuration and costing are examined in detail to better account for economies of scale. Emerging improvements in BPM-based processes—primarily in the electrolyzer design and BPM performance—can lead to a minimum selling price that is lower than for conventional CO2 electrolysis and approaching that achieved via naphtha-based processes. Future industrial processes for the electrolytic production of ethylene from aqueous carbonate feedstocks are not well understood. The authors develop unit operations and full process designs, evaluate the techno-economics at scale, identify key process requirements and barriers, and elucidate the minimum benchmarks needed for the future commercial viability of this technology.