Potential Synergy of Chlorine and Potassium and Sodium Elements in Carbonation Enhancement of CaO-Based Sorbents

The calcium looping process is well regarded as one of the most prospective technologies for trapping CO2 from flue gas. However, the carbonation conversion of CaO derived from natural Ca precursors decayed drastically during the long-term cycles. Doping has been considered as a promising method to improve the cyclic carbonation performance. However, alkali salt, which derives from abundant natural sustainable resources such as seawater, saline, bittern deposit, and so on, is regarded as a low melting material that can hardly enhance the cyclic carbonation performance of the CaO-based sorbents. In this study, two common alkali salts, sodium and potassium, were doped to investigate the potential enhancing effect of alkali salt on CaO-based sorbents. The cyclic carbonation performance of those sorbents was tested in a simultaneous thermal analyzer (STA), and the enhancing mechanisms were illustrated by scanning electron microscope (SEM), X-ray powder diffraction (XRD), and N2 physical absorption methods. The results illustrated that KCl, NaCl, and K2CO3 boosted the carbonation property of CaO markedly, while KOH, NaOH, and Na2CO3 were detrimental to the sorbents. The synergistic effect of K+, Na+, and Cl– can improve the cyclic carbonation performance of CaO. After 50 cycles, the carbonation conversions of CaO modified by KCl or NaCl were about twice that of unmodified CaO. In general, the KCl and NaCl are promising dopants that can markedly enhance the carbonation property of CaO-based sorbents.