Product concentration benchmarks for tandem electrochemical conversion of CO₂ to C₂H₄

Despite the strong focus on developing electrochemical conversion systems for upgrading CO₂ to C₂₊ hydrocarbons, the downstream separations required to complement reactors have received relatively less attention. Here we develop materials for the separation of two critical binary gas mixtures, CO₂/CO and C₂H₄/CO. These mixtures are produced in a tandem reaction system that first upgrades CO₂ to CO in a solid oxide fuel cell, followed by reduction of CO in a separate electrolyzer that produces ethylene. We then model the entire plant, including the gas and liquid separation systems, to determine how reactor product concentrations affect the overall process economics. Our analysis shows that effective gas separations via temperature/vacuum swing adsorption processes, using the materials developed in this work, significantly enhance the net present value of the plant, rendering gas separation no longer a limiting factor in process economics. However, liquid product concentrations of ~1 wt% (typical of current literature reports) and high CO₂ capture costs (>US$50 per tonne) can make the process economically unviable.