Performance of Coal Fly Ash Stabilized, CaO-based Sorbents under Different Carbonation-Calcination Conditions

The rapid deactivation of CaO sorbents due to sintering currently presents a major barrier to calcium looping for CO₂ capture. In this work, we report an easy method for synthesizing highly stable CaO-based sorbents through mechanical mixing of a calcium precursor and coal fly ash (solid waste from coal-fired plants). To investigate the stable performance of as-synthesized sorbents, the effects of calcium precursors and carbonation–calcination conditions were studied and discussed. The synthetic sorbent derived from calcium oxalate (90%CaC₂O₄-FA-2h) showed the best performance and demonstrated a CO₂ uptake of 0.38 g(CO₂) g(CaO)⁻¹ after 30 cycles. Even under the most severe calcination condition (at 920 °C in pure CO₂), this sorbent maintained a stable capture capacity, with a final CO₂ uptake of 0.27 g(CO₂) g(CaO)⁻¹ and an average decay rate of only 0.29% per cycle. Characterization of the sorbents confirmed that the formation of dispersed inert phase (gehlenite, Ca₂Al₂SiO₇) was responsible for this high cyclic CO₂ uptake and strong sintering resistance. This strategy significantly enhances the high temperature stability of CaO-based sorbents through in situ reuse of coal fly ash, and is thus an effective approach to CO₂ capture from the large point source.