CO 2 capture capacity of limestone and dolomite as CaO based sorbents in calcium looping cycle

Abstract Calcium oxide (CaO) based sorbents derived from natural minerals are promising materials for high temperature carbon dioxide (CO 2 ) capture, such as in the calcium looping cycle, due to their low cost and reactivity. Among common CaO sorbents, limestone and dolomite are abundant sources of CaO. However, their CO 2 capture performances differ significantly. Although dolomite typically shows higher porosity based on BJH analysis, limestone often exhibits superior CO 2 capture capacity. This discrepancy reveals a gap in understanding the relationship between pore structure and chemical reactivity in natural CaO sorbents under cyclic carbonation and calcination conditions. This study compares the CO 2 capture performance of calcined limestone and dolomite by evaluating their morphological and surface properties. Thermogravimetric analysis shows that limestone has higher CO 2 uptake over multiple calcium looping cycles. Scanning electron microscopy reveals differences in surface morphology that affect gas-solid interactions and sorbent stability. Surface modifications were performed using nitric acid and acetic acid to further enhance limestone performance. The nitric acid-treated limestone exhibited the highest CO 2 capture capacity due to enhanced surface reactivity and better accessibility of active sites after chemical activation. The results indicate that chemical properties are more critical than porosity alone in determining the CO 2 capture capacity and cyclic stability of natural CaO sorbents. Furthermore, simple acid treatments can significantly enhance sorbent ef iciency. These indings demonstrate that modified limestone is a promising, cost-effective, and scalable sorbent for industrial carbon capture applications.