(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.