Cyclic CO2 capture of CaO-based sorbent in the presence of metakaolin and aluminum (hydr)oxides

Metakaolin was added to CaO in an effort to improve the reversibility in carbonation cycles. The modified CaO-based sorbents were tested for their CO2 capture behavior through 25 carbonation/calcination cycles in a fixed bed reactor. Their morphology, pore structure and phase composition before and after carbonation/calcination cycles were determined by scanning electron microscopy, nitrogen adsorption, and X-ray diffraction. The metakaolin containing sorbents maintained the higher conversion only during the initial cycles. The reduced activity during carbonation/calcination cycles were explained by sintering processes and formation calcium silicate, mainly Ca2SiO4. To avoid this unfavorable effect, the silica of metakaolin was completely removed by acid-leaching and the remaining aluminum (hydr)oxides were mixed with CaO. This sorbent showed very promising results even under sever calciantion conditions. This improved performance was attributed to the formation of a stable framework of Ca12Al14O33 particles which inhibited the sintering of CaO.