Unveiling the Potential of Ca/Cu Composite Sorbents for CO2 Capture: A Precursor Perspective

The combined Ca/Cu process holds promise as a CO₂ capture technique utilizing chemical looping combustion to provide heat for regenerating CaO-based sorbents in a calcium looping configuration through the Ca/Cu composite sorbents. Developing Ca/Cu composite sorbents with high reactivity is crucial for advancing combined Ca/Cu technology. However, these sorbents encounter a rapid decline in the CO₂ capture performance, remaining a significant problem to be addressed. Herein, various calcium/copper precursors, comprising copper acetate, copper nitrate, calcium propionate, calcium acetate, calcium formate, and calcium nitrate, were utilized to synthesize Ca/Cu composite sorbents using a Pechini method. The results reveal that the selection of calcium and copper precursors significantly affected the CO₂ capture performance. Utilizing organic salts as calcium and/or copper precursors proved beneficial in enhancing the CO₂ capture performance, particularly when employing organic salts with high molecular weights (e.g., copper acetate, calcium propionate, and calcium acetate). The sorbent synthesized using calcium propionate and copper acetate possessed the highest CO₂ capture performance, achieving a final CO₂ uptake capacity of 0.22 g_CO2/g_material in the 10th cycle while retaining 80% of its initial reactivity. In contrast, the sorbent synthesized using calcium nitrate and copper nitrate showed the poorest CO₂ capture performance, with an initial capacity of 0.18 g_CO2/g_material and a final capacity of 0.08 g_CO2/g_material in the 10th cycle. In comparison to the significant impact on the CO₂ capture performance, the selection of precursors had a minimal effect on oxidation performance. Regardless of the precursors used, all the sorbents exhibited commendable oxidation performance, achieving oxidation conversions exceeding 90%. Additionally, systematic investigations were conducted on process conditions encompassing the reaction atmosphere and temperature during the oxidation and carbonation stages. The findings indicate that process conditions had a greater impact on the CO₂ capture performance than on the oxidation performance.