CO2 sorption/desorption performance study on K2CO3-doped Li4SiO4-based pellets

This study focuses on the preparation and characterization of macroporous pellets based on K2CO3-doped Li4SiO4 for the CO2 capture from the hot exhaust gas of gas-turbines. In view of this application, the CO2 sorption properties of the starting powders and produced pellets were investigated under low CO2 partial pressure (0.04 atm) and high temperature (580 °C). The desorption mechanism of the sorbents was investigated at different temperatures (580-700 °C) and by multiple CO2 sorption/desorption cycles. Results showed that the chemisorption kinetics of the starting powders and pellets was adequately fitted to the double exponential model, revealing that the diffusive processes through the molten product layer were the controlling steps for the overall process and the CO2 diffusion resistance in the macro-pores of the pellet resulted negligible. The temperature of 660 °C resulted to be the optimal regeneration temperature with adequate regeneration rate/time and less potential of sintering phenomena compared to 700 °C. In order to guarantee an excellent cyclic stability of the sorbent pellets over 250 sorption/desorption cycles, it was necessary to operate at Li4SiO4 conversions below 50% during the sorption run to avoid an excessive formation of molten eutectic mixture that, reducing the porosity of the pellet, led to reduce the long-term sorbent performance.