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-N-2) 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 degrees C. Desorption of CO2, performed by a thermal swing technique, proceeded rapidly and completely at 927-946 degrees C. The CaO activity dropped significantly when the inlet gas contained less than 5.6 vol % CO2 in N-2. 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.