Pore structure modified CaO-based sorbents with different sized templates for CO₂ capture

Porous structure is critical for CO₂ capture performance of CaO-based sorbents in Ca-looping. The sacrificial template method is an easy and effective way to alter the texture structure of sorbent pellets. To explore the optimal pore size distribution for CO₂ sorption, two micron templates, starch and cotton fiber, and two nano templates, carbon nanotubes and carbon nanofibers, were used to modify the pore structure on different scales for the first time. The CO₂ capture capacity of Ca-CNT in the 15th carbonation under severe calcination conditions was 86% more than that of the sorbent without templates. The enhanced CO₂ capture performance was attributed to the uniform small mesopores (2-10 nm) produced by nanosized templates. In this case, a large specific surface area is provided for carbonation. Micron templates would produce additional pores ranging from 10 to 100 nm and even large pores (>400 nm). The analysis results suggest that the pore volume (ranging from 2 to 10 nm) would have the linear relationship with CO₂ uptake at the reaction control stage; the pore volume of 10-100 nm was positively correlated with the CO₂ uptake at the diffusion control stage, and pores larger than 100 nm were ineffective in promoting CO₂ capture.