Exploring Performance and Cost Trade-Offs in Electrochemical CO2 Separation Processes

Abstract

Increasing global energy demand coupled with a continued reliance on carbon-intensive fuels has contributed to the rise in anthropogenic greenhouse gas emissions that are adversely impacting the global climate.1,2 While the expansion of low-cost renewable electricity (often coupled with energy storage) offsets fossil-fuel-based generation, complete mitigation of carbon emissions will likely require the capture, utilization, and/or storage of carbon dioxide (CO2) at scale. Today’s state-of-the-art separation technologies rely on thermochemical processes to extract CO2 from industrial waste streams, post-combustion flue gases, or directly from the atmosphere. Such approaches are energetically intensive and typically rely on fossil-fuel-derived heat to release CO2 and regenerate the sorbent, ultimately limiting process effectiveness.3 Electrochemical approaches to CO2 capture and concentration are increasingly seen as a viable pathway to reducing carbon emissions, as these processes enable several advantages including direct integration with renewables, modular deployment, operation near ambient conditions, and high energetic efficiencies.4 Despite this promise, these concepts are at an early-stage and the relationships between cost and performance are not well-understood at the molecular-, cell-, or system-level.In this presentation, we will discuss how techno-economic modeling can be used to inform design criteria for cost-competitive electrochemical CO2 separation systems. We will specifically focus on a 4-stage system with soluble redox-active species for direct binding / debinding with CO2. First, we describe and integrate all process units (i.e., electrochemical reactor, absorber, desorber) via thermodynamic, chemical, and electrochemical relationships and then estimate capital, fixed, and variable costs via a levelized cost of capture model. Second, we investigate key scaling correlations and cost sensitivities for the 4-stage system, including the role of resistive losses in the electrochemical reactor and binding affinity in the absorption column. Third and finally, we connect system-level performance and cost targets to molecular / system properties and operating envelopes. While our focus is on a particular system, the framework is generalizable and can be extended to different electrochemical and thermochemical approaches to CO2 separation, potentially enabling technology comparisons on a common basis. Acknowledgements This work was supported by the Alfred P. Sloan Foundation. K.M.R. gratefully acknowledges the support of the National Defense Science and Engineering Graduate (NDSEG) Fellowship. References Ritchie, H., Roser, M. & Rosado, P. CO2 and Greenhouse Gas Emissions. Our World in Data (2020). Annual Energy Outlook 2021. U.S. Energy Information Administration (2021).Khan, F. M., Krishnamoorthi, V. & Mahmud, T. Modelling reactive absorption of CO2 in packed columns for post-combustion carbon capture applications. Chemical Engineering Research and Design 89, 9, 1600–1608 (2011).Renfrew, S. E., Starr, D. E. & Strasser, P. Electrochemical Approaches toward CO2 Capture and Concentration. ACS Catal. 10, 21, 13058–13074 (2020).