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

• Main Authors: Igor Luisetto, Maria Rita Mancini, Livia Della Seta, Rosa Chierchia, Giuseppina Vanga, Maria Luisa Grilli, Stefano Stendardo
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Metals
• Subjects: CO₂ capture; calcium looping; nanometric CaZrO₃ particles
• Online Access: https://www.mdpi.com/2075-4701/10/6/750

Cycling high temperature CO₂ 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 gCO₂/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–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–ray diffraction (XRD), Brunauer–Emmett–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 °C and calcination (i.e., decomposition of CaCO₃ to CaO and CO₂) at 900 °C in pure Ar or with 85 vol% CO₂ using a thermogravimetric analyzer (thermogravimetric/differential thermal analysis (TG–DTA)). The most stable sorbent was with 40 wt% of CaO showing a CO₂ 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.