Alkali Carbonate Molten Salt Coated Calcium Oxide with Highly Improved Carbon Dioxide Capture Capacity

CO2 reduction is crucial if the effects of this gas on global warming are to be alleviated. We report an alkali carbonate molten salt promoted CaO-based CO2 sorbent with superior CO2 capture performance over that of neat CaO for the first time. The influence of chemical composition, loading, and melting temperature of (Li‒Na‒K)2CO3 molten salts, and of the calcination and adsorption temperatures on CO2 capture was evaluated systematically. The microstructural and morphological evolution of samples during CO2 adsorption was studied by XRD, SEM, and FTIR. The (Li‒K)2CO3 molten salt coating not only promotes CO2 uptake, but also facilitates the CO2 desorption from CaO. In particular, at low temperatures of 500 and 600 oC, the CO2 capture capacity increased significantly from 1.19 and 3.26 mmol g-1 to 6.93 and 10.38 mmol g-1, respectively. The melting point of molten salts is also a crucial factor in the improvement of CO2 uptake. Kinetic studies based on fractal-like models indicate that the rate coefficients for (Li‒K)2CO3/CaO were about 3.3 to 3.8 times larger than those for neat CaO. The coating of alkali carbonate molten salts was believed to prevent the formation of a rigid CaCO3 layer on the surface of CaO particles and provide a continuous delivery of CO32‒ to promote CO2 capture. During the CO2 adsorption/desorption cycling tests, (Li‒K)2CO3/CaO resulted in a stable and reversible CO2 uptake of 6.0‒6.3 mmol g-1, which is much higher than that of neat CaO (2.0 mmol g-1).