Preparation Of Ca-Al Layered Double Hydroxide And CO₂ Adsorption Capacity Of The Derived Sorbent

Nowadays,global warming has been considered as a global issue by the international society.As a consequence,it is urgent to reduce the excessive emission of CO₂ which stands for the major greenhouse gas.CO₂ capture technology is one of the most effective ways to reduce CO₂ emission.Structure characteristics and CO₂ adsorption performances of Ca-Al layered double hydroxides derived sorbents,using different preparation methods and different anions intercalated,were studied.Ca-Al mixed oxides were derived from Ca-Al-CO₃ layered double hydroxides（LDHs）,which were prepared using a low-saturated coprecipitation method at high constant pH.Compared to the high-saturated coprecipitation method,a better CO₂ adsorption capacity and stability were obtained.Acccording to the XRD and SEM characterization,it was attributed to the novel capsule-connected structure of LDHs nanoparticles,smaller particle size of CaO,and uniform distribution of CaO and Al2O3.The effect of the coprecipitation temperature,Ca/Al ratio and methanol modification on the CO₂ capture performance of Ca-Al mixed oxides was also investigated.The results indicated that different co-precipitation temperature influences the particle size and stack level,further affecting CO₂ adsorption capacity and stability.Different Ca/Al ratio influences the distribution of the sorbent particles,the reaction rate of the rapid reaction stage and the diffusion stage,which results in the differences in adsorption properties of the adsorbent.The modification by methonal had positive effect on the increase of CO₂ uptake and the improvement of sorbent stability.The 2:1 mixed oxides coprecipitated at room temperature and modified by methanol showed a much greater stability with carbonation capacity of about 56.7 wt% after 30 carbonation/calcination cycles.Citrate and stearate anions were chosen as the interlayer anions for the first time to investigate the effects of organic interlayer anions on the adsoption ability of sorbents derived from Ca-Al layered double hydroxides.The results showed that the sorbents（Ca/Al=5）with Ca-Al-citrate layered double hydroxides as precursors performed best and display remarkable CO₂ capture capacity of 52.0 wt% at the adsorption temperature of 600 °C without distinct recession during 17 carbonation-calcination tests.The excellent CO₂ adsorption performance of the sorbents was ascribed to the smaller crystallite size of calcinated particles,looser structure,optimizied pore size distribution as well as uniform distribution of Ca and Al in the sorbent.