High-temperature CO2 sorption by Ca-doped Li4SiO4 sorbents

• Ca-doped Li4SiO4 exhibited enhanced CO2 absorption.
• The transformation of Ca species during reactions was identified.
• The influence of the transformation of Ca species was investigated.
• A possible CO2 absorption mechanism was proposed.

Ca-doped Li4SiO4 (LiCa) sorbent was synthesized using a solid-state reaction method. The CO2 sorption capacity of the sorbents was thermogravimetrically analyzed in the presence of a pure CO2 flux. The cyclic performances of the sorbents were investigated in a twin fixed-bed reactor with absorption and desorption temperatures of 700 °C and 800 °C, respectively. The results indicate that the surface area of Li4SiO4 increased from 0.064 m2 g−1 to 0.314 m2 g−1 as the Ca doping content increased to 32 mol%, which enabled the sufficient contact between CO2 and Li4SiO4, and enhanced its CO2 sorption. The transformation of the Ca species from Ca2SiO4 to Li2CaSiO4 during the absorption process was helpful for the transfer of CO2 to Li4SiO4, and the transformation of Li2CaSiO4 to Ca2SiO4 in the desorption process favors CO2 desorption. Due to the special composition and structure, Li4SiO4 doped with 6 mol% of Ca had a maximum CO2 sorption of 35.1 wt% at 700 °C for 1 h and exhibited an excellent cyclic performance for CO2 sorption/desorption.

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