Kinetic and Thermodynamic Characterization of Enhanced Carbon Dioxide Absorption Process with Lithium...

Efficient and high-flux capture of CO₂ is the prerequisite of its utilization. Static absorption of CO₂ with solid Li₂O and molten salts (Li₂O-free and Li₂O-containing Li-Na-K carbonates) was investigated using a reactor with in situ pressure monitoring. The absorption capacity of dissolved Li₂O was 0.835 mol_CO/mol_Li at 723 K, larger than that of solid Li₂O. For the solid Li₂O absorbents, formation of solid Li₂CO₃ on the surface can retard the further reactions between Li₂O and CO₂, whereas the dissociation/dissolution effect of molten carbonate on Li₂O improved the mass-specific absorption capacity of liquid Li₂O. In Li₂O-containing Li-Na-K molten carbonate, CO₂ was mostly absorbed by alkaline oxide ions (O^2-). The chemical interactions between CO₂ and CO₃^2- contributed to CO₂ uptake via formation of multiple carbonate ions. The mass transfer of these absorbing ions was found as the dominating factor governing the rate of static absorption. Higher temperatures reduced the thermodynamic tendency of CO₂ absorption, but a lower viscosity at elevated temperature was conducive to absorption kinetics. Compared with the commonly used CaO absorbent, Li₂O was much more dissolvable in molten carbonate. The Li₂O-containing molten carbonate is potentially a promising medium for industrial carbon capture and electrochemical transformation process.