(406b) Electrochemical Reduction of CO2/CO to C2 Products: Process Design, Modeling, and Economic Analysis

Direct electrochemical reduction of CO2 to C2 products such as ethylene is more efficient in alkaline media, but suffers from parasitic loss of reactants due to (bi)carbonate formation. A two-step process where the CO2 is first electrochemically reduced to CO and subsequently converted to desired C2-products has the potential to overcome the limitations posed by direct CO2 electroreduction. We investigated the technical and economic feasibility of the direct and indirect CO2 conversion routes to C2 products. For the indirect route, CO2 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 CO2 conversion routes, which affect the downstream processing and the economics. A detailed process design and techno-economic analysis of both CO2 conversion pathways will be presented, which includes CO2 capture, CO2 (and CO) conversion, CO2 (and CO) recycling, and product (ethylene, ethanol, acetic acid, and hydrogen) 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 $10000/m2, 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.

1. Ramdin, M., De Mot, B., Morrison, A.R.T., Breugelmans, T., van den Broeke, L.J.P., Trusler, J.P.M., Kortlever, R., de Jong, W., Moultos, O.A., Xiao, P., Webley, P.A., Vlugt, T.J.H. Electroreduction of CO₂/CO to C₂ Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis. Ind. Eng. Chem. Res., 2021, 60, 17862-17880.