Review on the Development of Sorbents for Calcium Looping

The calcium looping (CaL) process is a promising CO2 capture technology, which uses CaO-based sorbents by employing a reversible reaction between CaO and CO2 generally named carbonation and calcination for each direction of the reaction. Although CaO-based sorbents possess many advantages, including wide availability, relatively low cost, and high theoretical CO(2 )uptake (similar to 0.786 g of CO2/g of CaO), it mainly suffers from a rapid decline in CO(2 )capture performance during cyclic operation, which has remained an urgent issue required to be addressed for industrial applications of the CaL process. Extensive studies have been conducted thus far, attempting to prevent and/or alleviate the rapid performance decay of the sorbents. Thus, this paper reviews the recent development of the CaL process worldwide with an emphasis on its development in China, mainly focusing on the advancement in the design and reinforcement of CaO-based sorbents. These activation strategies mainly include doping, chemical pretreatment, incorporation of supports with high Tammann temperatures, and structural modification, which do enhance the cyclic performance of the sorbents. However, some challenges still exist in the development of the CaO-based sorbents, such as the cost of the synthesis route, the scale-up pathways of the sorbents, the assessment of cyclic performance under mild conditions, and the ignorance of mechanical strength and attrition resistance of the sorbents. Therefore, life cycle assessment together with techno-economic analysis is essential when synthesizing CaO-based sorbents. In addition, more work should be conducted under industrially relevant conditions in fluidized bed reactors and even pilot-scale reactors, which are much closer to industrial situations. In this case, mechanical strength and attrition resistance are also assessed during cyclic operation.