Electroreduction of CO2/CO to C2 Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis

Mahinder Ramdin; Bert De Mot; Andrew R T Morrison; Tom Breugelmans; Leo J P van den Broeke; J P Martin Trusler; Ruud Kortlever; Wiebren de Jong; Othonas A Moultos; Penny Xiao; Paul A Webley; Thijs J H Vlugt

doi:10.1021/acs.iecr.1c03592

Electroreduction of CO₂/CO to C₂ Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis

Ind Eng Chem Res. 2021 Dec 15;60(49):17862-17880. doi: 10.1021/acs.iecr.1c03592. Epub 2021 Nov 30.

Affiliations

¹ Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Leeghwaterstraat 39, 2628CB Delft, The Netherlands.
² Applied Electrochemistry & Catalysis, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
³ Large-Scale Energy Storage, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Leeghwaterstraat 39, 2628CB Delft, The Netherlands.
⁴ Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
⁵ Department of Chemical Engineering, The University of Melbourne, Victoria 3010, Australia.
⁶ Department of Chemical Engineering, Monash University, Victoria 3800, Australia.

Abstract

Direct electrochemical reduction of CO₂ to C₂ 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 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. In this study, 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 affects the downstream processing and the economics. A detailed process design and techno-economic analysis of both CO₂ conversion pathways are presented, which includes CO₂ capture, CO₂ (and CO) conversion, CO₂ (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/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. Strategies for integrating the electrochemical CO₂/CO conversion process into the existing gas and oil infrastructure are outlined. Current barriers for industrialization of CO₂ electrolyzers and possible solutions are discussed as well.