Downstream of the CO 2 Electrolyzer: Assessing the Energy Intensity of Product Separation

The electrochemical reduction of carbon dioxide (CO 2 RR) to chemical feedstocks, such as ethylene (C 2 H 4 ), is an attractive means to mitigate emissions and store intermittent renewable electricity. Much research has focused on improving CO 2 electrolysis cell efficiency; less attention has been paid to the downstream purification of outlet product streams. In this work, we model the use of mature downstream separation technologies as part of the overall production of polymer-grade C 2 H 4 from CO 2 . We find that CO 2 removal is the most energy-intensive downstream separation step. We identify opportunities to reduce separation energies to ∼22 GJ/tonne C 2 H 4 through necessary improvements in C 2 H 4 selectivity (>57%), cathodic CO 2 conversion (>80%), and CO 2 crossover (0 mol CO 2 /mol e – ). This work highlights the influence of cell performance parameters on downstream separation costs and motivates the development of new, efficient separation processes better suited to the distinctive outlet streams of CO 2 electrolyzers.