A Kinetic Model of CO2 Absorption in Molten CaO-CaF2-CaCl2

Abstract

Post-combustion CO2 capture is a promising method for removing CO2 from processes where emissions cannot be mitigated by renewable energy input and where the chemical reactions required for production emit CO2, e.g. calcination of calcium carbonate (CaCO3) for cement production. One promising capture method is carbon capture in molten salts (CCMS). CCMS is a thermal swing gas-liquid process that utilizes CaO carbonation to absorb CO2. The molten salt used in this work is 15 wt% CaO in eutectic CaCl2-CaF2 (86.2 : 13.8 wt%). The CaCl2-CaF2-CaO system has been found to have high cyclic absorption capacity (0.6 g CO2/g CaO), though reaction kinetics has yet to be studied. By utilizing a novel experimental setup, data is collected, and a kinetic model is developed, which can be used in a techno-economic evaluation. The model proposes a simplified description of the CaCl2-CaF2-CaO system, with the assumption that the reaction is a first order elementary reaction where CaO and CO2 react to form CaCO3 without any solubility of CO2 in the molten salt. CO2 concentration, temperature, wt% CaO and surface area of molten salt are parameters in the proposed kinetic model. The result is a kinetic model that accurately fits the experimental data with an R2 value above 0.98. It has been found that increasing the CO2 concentration and decreasing the temperature yield a higher CaO to CaCO3 equilibrium conversion.

Keywords

• carbon capture in molten salt
• kinetic study
• carbon capture
• gas-liquid reaction