CO2 capture by Li2CaSiO4 and enhancement with alkali carbonates

Abstract

Alkali and alkali earth oxides show good CO₂ capture performance for carbonation, while their regeneration occurs at high temperatures, leading to a high energy penalty. When alkali oxides and alkali earth oxides combine with SiO₂ to form oxysalts, the regeneration temperatures can be reduced, and the CO₂ adsorption capacity is maintained. In this study, the reaction between CO₂ and Li₂CaSiO₄, composed of stoichiometric CaO, Li₂O, and SiO₂, was evaluated thermodynamically by DFT. The synthesized Li₂CaSiO₄ with and without alkali carbonates was used as CO₂ sorbents, and their CO₂ adsorption performances were examined using thermal analyses. The phase and morphology of Li₂CaSiO₄ before and after CO₂ adsorption were characterized by XRD and SEM. According to the thermodynamic evaluation and the XRD results, Li₂CaSiO₄ could adsorb CO₂ and form CaCO₃ and Li₂SiO₃. The thermal analyses showed that the regeneration of Li₂CaSiO₄ started from 575 °C, at which it was difficult to realize the CO₂ diffusion through the solid CaCO₃ product layer. The mixed alkali carbonates can improve the kinetics and facilitate the CO₂ adsorption of Li₂CaSiO₄. Alkali carbonates were effective in reducing the activation energy of the reaction and CO₂ diffusion at low temperatures and improving the cyclic stability because of the dispersing carbonation products.