(677d) The Stability Performance of Synthetic Ca-Based Sorbents Doped By Zirconium-Based Ceramics in Cyclic CO2 capture Operations

Calcuim (Ca) based sorbents as an option for carbon dioxide (CO₂) capture process at high temperatures have displayed considerable activity loss during extended operation, due to sintering phenomena. Refractory zirconium-based ceramics have shown excellent performance as thermal barrier coatings in many high-tech applications; and, the recent doping of zirconia in Ca-based sorbents has exhibited improvement in the stability in cyclic CO₂ capture operations. In this work, sorbents were doped, at loadings of 10 wt%, with a zirconium-based ceramics, such as alkaline earth metal zirconate (MZrO₃, M= Mg, Ca and Ba) and aluminum zirconate (Al₂Zr₃O₉), which have the chemical structure of perovskite, and rare earth metal zirconates (Ln₂Zr₂O₇ and LnZrO₄, Ln = La, Ce and Sm), with the chemical structure of pyrochlore. These materials were prepared using the wet co-precipitation method. The results indicated significant sorbent stability and capacity improvement for mixed metal oxide zirconia-stabilized sorbents over those of pure CaO and natural Cadomin. Among the tested sorbents, the CaZrO₃-doped sorbents showed the best performance and remarkable stability due to their high resistance to sintering. The sorbent demonstrated a CO₂ capture capacity of 12 mole CO₂ / kg sorbent, with an activity loss of 19.6% through 30 cycles of carbonation at 675°C and calcination at 850°C. Among the rare earth metal zirconate ceramics, samarium zirconate (Sm₂Zr₂O₇) presented the best stability with an activity loss of 23.4 % loss, but at a lower uptake of 7.2 mole CO₂ / kg sorbent at the same conditions. In comparison, Cadomin (a natural calcium carbonate) at the same conditions resulted in a CO₂ capture capacity of 13 mole CO₂ / kg sorbent and an activity loss of 69%. Surface area measurements indicated that addition of the ceramics dopants to the Ca-based sorbents greatly inï¬?uenced both the surface area and pore volume of the sorbents. X-ray diffraction results showed that the improved resistance of the sorbent is due to the formation of structures such perovskite-type CaZrO₃, which provided a stable framework to the sorbent during the carbonation-calcination process.