CaO–CaZrO3 Mixed Oxides Prepared by Auto–Combustion for High Temperature CO2 Capture: The Effect of CaO Content on Cycle Stability

Cycling high temperature CO2 capture using CaO&ndash
based solid sorbents, known as the calcium looping (CaL) process, is gaining considerable scientific and industrial interest due to the high theoretical sorbent capacity (0.78 gCO2/gCaO), the low specific cost, and the negligible environmental impact of the employed materials. In this work, we investigated the self&ndash
combustion synthesis of CaO&ndash
CaZrO3 sorbents with different CaO contents (40, 60, and 80 wt%) for use in the CaL process. CaZrO3 was used as a spacer to avoid CaO grains sintering at high temperature and to reduce the diffusional resistances of CO2 migrating towards the inner grains of the synthetic sorbent. Samples were characterized by X&ndash
ray diffraction (XRD), Brunauer&ndash
Emmett&ndash
Teller (BET), and scanning electron microscopy (SEM) analyses. The reaction between CO2 and CaO (i.e., carbonation) was carried out in 20 vol% CO2 at 650 &deg
C and calcination (i.e., decomposition of CaCO3 to CaO and CO2) at 900 &deg
C in pure Ar or with 85 vol% CO2 using a thermogravimetric analyzer (thermogravimetric/differential thermal analysis (TG&ndash
DTA)). The most stable sorbent was with 40 wt% of CaO showing a CO2 uptake of up to 0.31 g CO2/gsorbent and 0.26 g CO2/gsorbent operating under mild and severe conditions, respectively. The experimental data corroborated the prediction of the shrinking core spherical model in the first phase of the carbonation. A maximum reaction rate of 0.12&ndash
0.13 min-1 was evaluated in the first cycle under mild and severe conditions of regeneration.