(240e) Establishing Product Purity and Recovery Benchmarks for Two Step CO2/CO to C2+ Products

Carbon dioxide electrolysis (CO₂R) is an emerging technology for the production of value-added molecules using renewable energy. Extensive research in the field during the past two decades has it made possible to produce a range of chemicals with high Faradaic efficiencies and current densities at relatively low overpotentials. The product concentration, which is an equally important parameter for the industrial scale-up of processes, has often been overlooked. The single-pass conversion (SPC) is commonly used as an additional performance indicator. However, a high SPC does not necessarily translate into a high product concentration. Low concentration products, low selectivities towards formation of a single major product, or loss of products (in the reactor or downstream separations) can have a detrimental effect on the process economics.

In this work, we considered at a tandem CO₂/CO to C₂₊ value added chemicals production process for ethylene production. CO₂ is first converted to CO in a Solid Oxide Electrolyzer Cell (SOEC) with high faradaic efficiencies to produce a mixture of CO₂ and CO. This mixture is fractionated, and CO₂ is recycled back to the SOEC while CO is fed to a low temperature electrolyzer to produce ethylene. We developed the adsorbents suitable for the two separations required in this refinery – CO/CO₂ and C₂H₄/syn gas. Then, performed a detailed process modeling to calculate the separation cost as a function of the feed concentration for a range of CO2R products (CO, formic acid, acetic acid, ethanol, ethylene, and propanol). From this analysis, we derived minimum concentration requirements and maximum acceptable loss ratios beyond which it is possible to have an economically feasible production of the CO2R reaction.