Kinetic and Thermodynamic Characterization of Enhanced Carbon Dioxide Absorption Process with Lithium Oxide-Containing Ternary Molten Carbonate

Efficient and high-flux capture of CO 2 is the prerequisite of its utilization. Static absorption of CO 2 with solid Li 2 O and molten salts (Li 2 O-free and Li 2 O-containing Li–Na–K carbonates) was investigated using a reactor with in situ pressure monitoring. The absorption capacity of dissolved Li 2 O was 0.835 mol CO 2 /mol Li 2 O at 723 K, larger than that of solid Li 2 O. For the solid Li 2 O absorbents, formation of solid Li 2 CO 3 on the surface can retard the further reactions between Li 2 O and CO 2, whereas the dissociation/dissolution effect of molten carbonate on Li 2 O improved the mass-specific absorption capacity of liquid Li 2 O. In Li 2 O-containing Li–Na–K molten carbonate, CO 2 was mostly absorbed by alkaline oxide ions (O 2– ). The chemical interactions between CO 2 and CO 3 2– contributed to CO 2 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 CO 2 absorption, but a lower viscosity at elevated temperature was conducive to absorption kinetics. Compared with the commonly used CaO absorbent, Li 2 O was much more dissolvable in molten carbonate. The Li 2 O-containing molten carbonate is potentially a promising medium for industrial carbon capture and electrochemical transformation process.