Hydrophobic layer assisting-casted dark Ca-based CO2 sorbent pellets for solar-driven calcium looping: Insights into pellet configuration and properties

Abstract

Solar radiation heat replaces pulverized coal as the heat source in the calcination reactor of the direct solar-driven Calcium Looping (CaL) system, eliminating the adverse impact of in-situ coal combustion on Ca-based sorbents. To ensure the system’s efficiency, the Ca-based sorbents must exhibit strong light absorption capabilities, with manganese incorporation being an effective strategy to enhance this characteristic. The integration of impregnated layer solution combustion with hydrophobic layer-assisted casting is a promising approach for fabricating highly efficient Mn-incorporated Ca-based sorbent pellets. Constructing Mn-incorporated Ca-based sorbent pellets with a graphite hydrophobic layer results in better performance compared to using a Nano-TiO₂ hydrophobic layer. The latter is prone to forming a white shell on the sorbent pellets’ surface, which seriously affects the light absorption features. High levels of Mn loading work to increase the optical absorbance of hydrophobic graphite layer assisting-casted Ca-based sorbent pellets, but this inevitably leads to a sacrifice in their CO₂ sorption capacity. Therefore, the core–shell structured Ca-based sorbent pellets, comprising a highly active Al-stabilized CaO pristine core and a dark Mn-based outer shell, fabricated with a graphite/MnO₂ mixture as the hydrophobic layer, exhibit exceptional optical absorbance (88.4 %) alongside excellent CO₂ sorption capabilities (maintaining average CO₂ uptake of 0.39 g/g during 20 cycles), making them optimal candidates for direct solar-driven CaL.