CO₂ Capture with Lithium Oxide in Molten Salt Media : A Case Study of CO₂ Capture via Electrochemically Produced Metal Oxide

Abstract

As the unprecedented temperature rise originating from anthropogenic carbon dioxide (CO₂) emission intensifies, the development of post-combustion carbon capture technologies has been urged. Although its maturity, conventional thermal swing processes using aqueous amines, suffer from significant limitations, including high energy requirements and sorbent degradation. Electrochemical CO₂ capture technologies, which use electrical energy instead of thermal energy, have emerged as an energy efficient way to capture CO₂. This shift not only improves energy efficiency but also reduces reliance on fossil fuels, further contributing to reduction in CO₂ emissions. This work explored the potential of electrochemical metal oxide formation for CO₂ capture, a promising alternative to amine-based systems due to its exceptional sorbent (i.e., metal oxide) stability. Li₂O in eutectic mixture of potassium nitrate (KNO₃) and lithium nitrate (LiNO₃) was chosen as a case study due to the relatively well-understood chemistry of the system and the potential synergistic effects between metal oxide and the molten salt. Primarily, we investigated the synergistic effect of Li₂O in nitrate molten salt via thermal gravimetric analysis. Next, electrochemically produced Li₂O by reduction of oxygen gas was tested as a CO₂ sorbent while investigating parameters affecting its conversion to lithium carbonate (Li₂CO₃). Through this study, we suggested dissolution model as a crucial pathway for conversion. Lastly, we explored the effect of adding nitrite ion (NO₂⁻) to the molten salt. Irreversible side reaction between NO₂⁻ and CO₂ was confirmed with X-ray diffraction and NOₓ measurement. This thesis demonstrates the feasibility of electrochemical metal oxide-based CO₂ capture, highlighting some considerations in the capture step.