Core-in-Shell, Cellulose-Templated CaO-Based Sorbent Pellets for CO2 Capture at Elevated Temperatures

Calcium looping is a promising postcombustion CO2 capture technology due to its low cost and widespread applicability. However, CaO-based sorbents are prone to encounter severe sintering and elutriation during practical carbonation/calcination cycles. To overcome the above issues, core-in-shell CaO-based pellets composed of a highly reactive CaO-based core and a hard cement-based outer shell were prepared. The highly reactive core contains 80 wt % Ca(OH)2 and 20 wt % cellulose, which was prepared via an extrusion–spheronization method. The cement-based outer shells were prepared via an approach of coating, and different amounts of cellulose (varying from 0 to 40 wt %) were added as a pore-forming template. It is found that the mechanical properties of the fresh, core-in-shell, cellulose-templated CaO-based pellets are gradually improved with the increased addition ratio of cellulose in the outer shell. It is mainly attributed to the adequately dispersed cellulose fibers reinforcing the cement-based outer shell. Although the high-temperature calcination causes the internal structure of the CaO-based pellets to become loose, they still exhibit relatively desirable compression strengths (0.95–1.80 MPa). Moreover, the porous outer shell contributes to promoting the accessibility of CO2 to the highly reactive core pellet, consequently obtaining superior CO2 capture performance. After 15 cycles, the core-in-shell, cellulose-templated CaO-based pellets containing 40 wt % of cellulose in the outer shell exhibit the highest CO2 capture capacity of 0.144 g/g, which is nearly 6.8 times that of the core-in-shell pellets with pure cement shell.