Modification Of Ca-based Sorbents For Efficient CO₂Mitigation

Ca-based sorbents are an excellent kind of materials for high-temperature CO2capture. However, their weak thermal stability prevents them from large-scaleapplication. Aiming at solving this problem, Y2O3was doped into Ca-based sorbents inthis study. Meanwhile, the CO2capture performance, physical and chemical structuresof the modified sorbents were systematically tested and analyzed. Our achievements areas follows:Four preparation methods were applied to achieve CaO-Y2O3sorbents with Y2O3concentration of20wt%. Characterization measures such as XRD, SEM and N2adsorption were taken to analyze the physical and chemical structures of the sorbents.Afterwards, the sorbents were tested under simulated coal-fire flue gas conditions tounderstand their cyclic CO2capture performance. Our study reveals that the degree ofY2O3dispersion significantly affects the degree of sintering and anti-sintering propertiesof the sorbents. The microstructures of sorbents prepared by different methods variedand these sorbents presented different CO2capture capacities. Y2O3washomogeneously dispersed as nanoparticles in the sorbent prepared by sol-gelcombustion method. Therefore, the BET surface area and total pore volume of thissorbent reached24.8m2/g and0.115cm3/g. It also presented the highest CO2uptake and the best cyclic stability. At the end of the10th cycle, it can stillcapture0.57g CO2/g sorbent.The structure and CO2capture performance of CaO-Y2O3sorbents prepared bysol-gel combustion method were systematically studied. Our study revealed that Y2O3did not react with either CaO or CO2. Its doping could effectively prevent Ca-basedsorbents from sintering, which consequently enhanced the BET surface area andenlarged the number of pores less than220nm in diameter. CaO-Y2O3sorbentsprepared by sol-gel combustion method possessed fast carbonation rates. The maximumcarbonation rate of the sorbent with20wt%Y2O3amount reached1.42/min. Duringten cycles, the CO2uptakes of CaO-Y2O3sorbents with different Y2O3amounts rangedbetween a high level of0.43~0.64g CO2/g sorbent. In consideration of thecost-effective factors, sorbents with an Y2O3amount of20wt%was selected as the optimum sorbent. The influences of different reaction parameters on cyclic CO2captureperformance were critically analyzed. Combined with pore structure analysis, twocounteractive effects of CO2were elucidated under different regeneration temperatures.Thus, the significance of the stability of pores smaller than220nm in diameter on thecyclic CO2capture performance of Ca-based sorbents was affirmed.Carbon sphere templates with an average diameter of4.56μm were obtained bytuning reaction parameters such as glucose concentration, temperature and time.Through wet impregnation method, CaO-Y2O3sorbents with carbon to saltratios of0.09~1.17were prepared. The BET surface area and total pore volumeof the obtained sorbents were20m2/g and0.144~0.170cm3/g. Under simulatedcoal-fire flue gas conditions, all sorbents presented high cyclic CO2uptake andcomparatively good carbonation kinetics. The optimum sorbent could stillcapture0.55g CO2/g sorbent after being subjected to severe reaction conditions(regeneration:950°C,100%CO2,5min).