Characteristics and performance of CaO-based high temperature CO2 sorbents derived from a sol-gel process with different supports

The calcium looping process with CaO-based sorbents is one of the most important technologies for high-temperature scrubbing of CO2. However, the CO2 uptake capacities of natural CaO-based sorbents decayed rapidly during cyclic reactions. Thus, sorbents featuring cyclic stability should be developed for repeated utilisation. In this work, different inert solid materials were used as effective metal skeletons to improve the CO2 uptake behaviour of the CaO-based sorbents. A dual fixed-bed reactor was used to investigate the CO2 uptake performance of the sorbents during long-term cycles. The microstructures of the calcined sorbents were analysed by XRD and SEM tests. Results showed that the melting point of the inert supports was a pivotal factor affecting the CO2 uptake behaviour. Zr-, Mg-, Y-, La- and Al-based supports were found to be outstanding supporting materials, whereas Co-, Zn-, Ba- and Fe-based supports were counteractive. Moreover, the calcination conditions significantly influenced the cyclic stability of the synthesised sorbents. After calcination at higher temperature in a pure CO2 atmosphere, most of them became more vulnerable to sintering. However, the 90% CaO-10% ZrO2 sorbent maintained a CO2 uptake capacity of 0.5311 g CO2 per g sorbent after 20 cycles. After 10 h of severe sintering stage, this material still demonstrated a capacity of 0.6493 g CO2 per g sorbent. The metal skeleton of the sorbent possibly prevented crystal boundary migration and the recrystallisation process.