Self-Activation Mechanism Investigations on Large K2CO3-Doped Li4SiO4 Sorbent Particles

Abstract

This work investigated the self-activation behavior of large K2CO3-doped Li4SiO4 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 K2CO3-doped Li4SiO4 sorbent was remarkably enhanced from approximately 2.0 mmol CO2/g sorbent to approximately 5.0 mmol CO2/g sorbent at 565 °C in 10 vol % CO2 atmosphere. The fresh and used sorbents were then characterized through N2 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 Li2CO3 and Li2SiO3 can facilitate CO2 diffusion. The formed CO2 diffusion channel can provide more CO2 accessibility; this channel can also reduce the CO2 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 % CO2 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 K2CO3-doped Li4SiO4 self-activation mechanism.