Hydrotalcite-like Derived Calcium-based Oxides Using For CO₂ Capture

Nowadays,the Greenhouse Effect has become an environmental problem concerned by the whole world.Therefore the scientists all over the world are focusing on reducing CO₂ in the atmosphere which is the major greenhouse gas.CO₂ is also a by-product of coal-to-SNG process which reacts at temperatures ranges from 350-600 ?.In this paper,CO₂ adsorption performances of hydrotalcite-like derived mixed oxides were investigated.CO₂ absorption performances of hydrotalcite-like derived mixed oxides were tested on TGA at adsorption temperatures of 500 ?,600 ? and desorption temperatures of 600 ?,700 ?,respevtively.The results showed that the CO₂ adsorption performances of Ca_1-xAl_x?OH?₂?CO₃?_x/2 derived mixed oxides is better than that of Ca_1-xAl_x?OH?₂ClO₄,Ca-Mg-Al-CO₃ hydrotalcite-like derived mixed oxides.Ca-Al-CO₃ derived mixed oxides with Ca/Al=2.5 performed better than other ratio of Ca/Al.The best preparation conditions were 70 ? of coprecipitation preparation temperature,120 ? of crystallization temperature and 15 h of crystallization time.From XRD,it confirmed that the layered structure of the hydrotalcite-like compounds was completely collapsed after calcinations at 600 ?.The materials after calcination include CaO and CaCO₃.It performed better when the particle size of CaO in the hydrotalcite-like derived mixed oxides was small and the CaCO₃ content was high.The formation of the particle of Ca₃Al₂?OH?₁₂ was favorable for the dispersion of CaO with little particle size.The results of SEM-EDX showed that CaO was well dispersion,resulting in the improvement of the cyclic stability of the mixed oxides.The influence of CO₂ adsorption and desorption temperatures,the flux and concentration of CO₂ on the adsorption performances of CaAl-CO₃?Ca/Al=2.5?derived mixed oxides were studied.The result showed that the appropriate adsorption and desorption temperatures were 600 ? and 700 ? respectively.The concentration of CO₂ makes no difference to the CO₂ adsorption performances of this mixed oxides.The influence of water vapor on CO₂ adsorption performances of the mixed oxides are also studied in this work.The water vapor enhances CO₂ adsorption capacities and stabilities of the mixed oxides greatly.The stability of CaAl-CO₃?Ca/Al=2.5?derived mixed oxides was investigated under the adsorption temperature of 600 ? and desorption temperature of 700 ? with 1% steam vapor and 220 cycles.The CO₂ adsorption capacity retained 56.1% after 220 cycles,indicating that it had excellent stability.The water vapor has positive effect on both carbonation and decarbonation.The reason for the improved stability of the mixed oxides in the presence of water vapor may be that the water vapor enhances solid state diffusion during diffusion control stage in the carbonation stage and the rate and degree of decomposition in the calcination stage,and loose porous structure is made in the presence of water vapor which is favorable for the subsequent carbonation of CaO.