CO 2 capture by Li 2 CaSiO 4 and enhancement with alkali carbonates.

Alkali and alkali earth oxides show good CO 2 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 SiO 2 to form oxysalts, the regeneration temperatures can be reduced, and the CO 2 adsorption capacity is maintained. In this study, the reaction between CO 2 and Li 2 CaSiO 4 , composed of stoichiometric CaO, Li 2 O, and SiO 2 , was evaluated thermodynamically by DFT. The synthesized Li 2 CaSiO 4 with and without alkali carbonates was used as CO 2 sorbents, and their CO 2 adsorption performances were examined using thermal analyses. The phase and morphology of Li 2 CaSiO 4 before and after CO 2 adsorption were characterized by XRD and SEM. According to the thermodynamic evaluation and the XRD results, Li 2 CaSiO 4 could adsorb CO 2 and form CaCO 3 and Li 2 SiO 3 . The thermal analyses showed that the regeneration of Li 2 CaSiO 4 started from 575 °C, at which it was difficult to realize the CO 2 diffusion through the solid CaCO 3 product layer. The mixed alkali carbonates can improve the kinetics and facilitate the CO 2 adsorption of Li 2 CaSiO 4 . Alkali carbonates were effective in reducing the activation energy of the reaction and CO 2 diffusion at low temperatures and improving the cyclic stability because of the dispersing carbonation products.