CaO-CaZrO3Mixed Oxides Prepared by Auto-Combustion for High Temperature CO2Capture: The Effect of CaO Content on Cycle Stability

Cycling high temperature CO(2)capture using CaO-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 gCO(2)/gCaO), the low specific cost, and the negligible environmental impact of the employed materials. In this work, we investigated the self-combustion synthesis of CaO-CaZrO(3)sorbents with different CaO contents (40, 60, and 80 wt%) for use in the CaL process. CaZrO(3)was used as a spacer to avoid CaO grains sintering at high temperature and to reduce the diffusional resistances of CO(2)migrating towards the inner grains of the synthetic sorbent. Samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) analyses. The reaction between CO(2)and CaO (i.e., carbonation) was carried out in 20 vol% CO(2)at 650 degrees C and calcination (i.e., decomposition of CaCO(3)to CaO and CO2) at 900 degrees C in pure Ar or with 85 vol% CO(2)using a thermogravimetric analyzer (thermogravimetric/differential thermal analysis (TG-DTA)). The most stable sorbent was with 40 wt% of CaO showing a CO(2)uptake of up to 0.31 g CO2/g(sorbent)and 0.26 g CO2/g(sorbent)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 0.12-0.13 min(-1)was evaluated in the first cycle under mild and severe conditions of regeneration.