Electroreduction of CO 2 /CO to C 2 Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis.

Direct electrochemical reduction of CO 2 to C 2 products such as ethylene is more efficient in alkaline media, but it suffers from parasitic loss of reactants due to (bi)carbonate formation. A two-step process where the CO 2 is first electrochemically reduced to CO and subsequently converted to desired C 2 products has the potential to overcome the limitations posed by direct CO 2 electroreduction. In this study, we investigated the technical and economic feasibility of the direct and indirect CO 2 conversion routes to C 2 products. For the indirect route, CO 2 to CO conversion in a high temperature solid oxide electrolysis cell (SOEC) or a low temperature electrolyzer has been considered. The product distribution, conversion, selectivities, current densities, and cell potentials are different for both CO 2 conversion routes, which affects the downstream processing and the economics. A detailed process design and techno-economic analysis of both CO 2 conversion pathways are presented, which includes CO 2 capture, CO 2 (and CO) conversion, CO 2 (and CO) recycling, and product separation. Our economic analysis shows that both conversion routes are not profitable under the base case scenario, but the economics can be improved significantly by reducing the cell voltage, the capital cost of the electrolyzers, and the electricity price. For both routes, a cell voltage of 2.5 V, a capital cost of $10,000/m 2 , and an electricity price of <$20/MWh will yield a positive net present value and payback times of less than 15 years. Overall, the high temperature (SOEC-based) two-step conversion process has a greater potential for scale-up than the direct electrochemical conversion route. Strategies for integrating the electrochemical CO 2 /CO conversion process into the existing gas and oil infrastructure are outlined. Current barriers for industrialization of CO 2 electrolyzers and possible solutions are discussed as well.