(747c) Redox-Responsive Sorbents for Energy Efficient CO2 Separation

Carbon capture and sequestration (CCS) has been proposed as an effective approach for the mitigation of the contribution of anthropogenic CO2 emissions to climate change. Implementing this technology is a challenging task due to the scale at which CO2 is produced and the energy requirement to drive the separation process. Thermal-swing separation processes based on chemical sorbents show potential for facilitating large-scale CO2 capture; however, the energy efficiency in the current thermal-swing processes is unacceptable for their implementation. To overcome this problem, new approaches to gas separation have to be developed. Electrochemically mediated processes are proposed to facilitate CO2 capture from a dilute gas mixture by exploiting the significant changes in molecular affinity of certain sorbents for CO2 molecules when they undergo a redox cycle. The proposed process has the potential for reducing the parasitic energy of the current solvent-based absorption processes since it does not require significant temperature swings to regenerate the sorbents. Molecular optimization of the sorbent structure is achieved through a combination of electrochemical experiments and quantum chemical simulations. The results from the potentiostatic study of the promising sorbent candidates are used to elucidate the energy required for CO2 separation from a dilute gas mixture using the proposed technology. We have explored the use of both molecularly dispersed redox absorbents, and of redox active moieties conjugated molecularly to a polymeric backbone to provide a redox-responsive adsorbent. Results on a small laboratory scale CO2 capture unit demonstrate the feasibility of the process for CO2 capture from dilute gas streams.