Electrochemically mediated separation for carbon capture

Abstract

Carbon capture technology has been proposed as an effective approach for the mitigation of anthropogenic CO[subscript 2] emissions. Thermal-swing separation technologies based on wet chemical scrubbing show potential for facilitating CO[subscript 2] capture at industrial-scale carbon emitters; however, the total operational and capital costs resulting from the high energy consumption are prohibitive for their implementation. Electrochemically mediated processes are proposed to be the next generation of CO[subscript 2] separation technology that can enable carbon capture to be a more viable option for carbon mitigation in the near future. This technology utilizes electrochemically active sorbents that undergo significant changes in their molecular affinity for CO[subscript 2] molecules as they progress through an electrochemical cycle. This nearly isothermal separation process consumes electrical energy to facilitate effective CO[subscript 2] capture and regeneration processes under more benign conditions of sorption and desorption than in traditional continuous wet-scrubber operations. This electrically driven separation process has the potential to significantly reduce the difficulty of retrofitting CO[subscript 2] capture units to existing fossil fuel-fired power generators. The ease of installing an electrically driven separation system would also allow its application to other industrial carbon emitters. The design of such a system, however, requires careful consideration since it involves both heterogeneous electrochemical activation/deactivation of sorbents and homogeneous complexation of the activated sorbents with CO[subscript 2] molecules. Optimization of the energy efficiency requires minimizing the irreversibility associated with these processes. In this study, we use a general exergy analysis to evaluate the minimum thermodynamic work based on the system design and the electrochemical parameters of quinodal redox-active molecules. Using this thermodynamic framework, our results suggest that the proposed technology could capture CO[subscript 2] from a dilute post-combustion flue gas and regenerate CO[subscript 2] at 1 bar with high efficiency, if a two-stage design is effectively implemented.