Self-Activation Mechanism Investigations on Large K 2 CO 3 -Doped Li 4 SiO 4 Sorbent Particles

This work investigated the self-activation behavior of large K 2 CO 3 -doped Li 4 SiO 4 sorbent particles. In this self-activation mechanism, the sorption ability increased as the number of cycles increased. After the sorption–desorption cycles occurred, the sorption ability of the K 2 CO 3 -doped Li 4 SiO 4 sorbent was remarkably enhanced from approximately 2.0 mmol CO 2 /g sorbent to approximately 5.0 mmol CO 2 /g sorbent at 565 °C in 10 vol % CO 2 atmosphere. The fresh and used sorbents were then characterized through N 2 adsorption and SEM methods. Results showed that the average pore size increased from 7 to 32 nm and the surface microstructure changed from dense to porous, because the molten eutectic mixture formed by Li 2 CO 3 and Li 2 SiO 3 can facilitate CO 2 diffusion. The formed CO 2 diffusion channel can provide more CO 2 accessibility; this channel can also reduce the CO 2 diffusion resistance through the product layer. Therefore, the sorption ability of the sorbent is enhanced. Meanwhile, the effects of the self-activation temperature were also investigated and the results revealed that the optimal self-activation temperature is 615 °C. Furthermore, under critical conditions, the self-activated sorbent performed more efficiently than the fresh sample. At 450 °C under 10 vol % CO 2 atmosphere, the sorption capacity of the self-activated sorbent was approximately 20 times higher than that of the fresh sample. Finally, a pore–core model was also proposed to illustrate the K 2 CO 3 -doped Li 4 SiO 4 self-activation mechanism.