CO₂ Capture by CaO in Molten CaF2–CaCl2: Optimization of the Process and Cyclability of CO₂ Capture

CO₂ capture by CaO dissolved or partly dissolved in a molten salt shows high, reversible CO₂ sorption because of rapid gas–liquid interactions. Using previously obtained data on CaO reactivity with CO₂ in a CaCl2 melt, we describe here the application of the CaF2–CaCl2 molten salt for CaO dissolution or partly dissolution in a CO₂ capture process. The effects of the CaO concentration in CaF2–CaCl2 (ratio fixed to the eutectic composition), temperature, and gas composition (CO₂–N2) on the carbonation/decarbonation reactions in a one-chamber atmospheric pressure reactor were established by means of a Fourier transform infrared (FTIR) gas detector and gravimetric analysis. The CO₂ uptake efficiency by CaO dissolved or partly dissolved in the metal halides was found to enhance and stabilize with concentrations of CaO exceeding 10 wt % in CaF2–CaCl2 in the temperature range of 670–710 °C. Desorption of CO₂, performed by a thermal swing technique, proceeded rapidly and completely at 927–946 °C. The CaO activity dropped significantly when the inlet gas contained less than 5.6 vol % CO₂ in N2. In addition, 15 wt % CaO in CaF2–CaCl2 (13.8/86.2 wt %) exhibited efficient and constant CO₂ carrying capacity of 0.667 g of CO₂/g of CaO after 12 carbonation/decarbonation cycles.