Research On The Preparation Of Lithium Silicate Materials And Its Carbon Dioxide Adsorption Performance At High Temperature

Coal fired power plant is the main emission source of CO₂,and post-combustion CO₂ capture and storage（CCS）technology is considered to be the most direct and effective options to reduce CO₂ emissions.Lithium orthosilicate（Li₄SiO₄）have been considered as one of the most promising sorbent for capturing CO₂ at high temperature since its large absorption capacity,stable cyclability and reasonable material costs.The synthesis of lithium silicate adsorbent prepared by conventional solid state method has the disadvantages of low CO₂ adsorption capacity and slow reaction rate,which is difficult to meet the needs of practical application.To overcome the above disadvantages,this paper mainly adopt different methods to prepare excellent adsorbent.Various characterization methods,such as X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,N2 adsorption analyzer and thermogravimetric analyzer（TG）and so on,were used to characterize the phase composition,structural characteristics and adsorption properties of the synthesized samples.The main research contents are as follows:（1）A highly efficient lithium orthosilicate（CSG-Li₄SiO₄）was synthesized using a sol-gel method combined with carbon coating.The presence of citric acid played dual roles,serving as a complexing agent that homogeneously mixed the precursors and as a carbon source,which effectively prevented the Li₄SiO₄ crystallite from growing.Compared with two reference sorbents synthesized using the solid-state method and a simple sol-gel without carbon coating,CSG-Li₄SiO₄ presented a loose shell-connected structure with higher purity,smaller grain size and larger specific surface area.This favorable structure was responsible for the sorbent’s improved performance,as indicated by a higher capacity（a maximum absorption of 34.2 wt.%）,faster absorption kinetics and better stability.（2）Lithium orthosilicate（Li₄SiO₄）doped with different metallic elements,K,Mg,Cr,or Ce,was prepared by a sol-gel method for high-temperature CO₂ capture.The doped sorbents were systematically studied and compared with non-doped Li₄SiO₄.All the metallic elements could insert into the crystal lattice.In particular,Ce doping effectively inhibited the growth of crystal aggregation,resulting in a foam-like morphology with small particle size.Thus,significantly improved CO₂ chemisorption properties were achieved with higher capacity and faster absorption kinetics.The optimal doping molar content of Ce/Li₄SiO₄ was 0.02,with a maximum absorption capacity of 34.57 wt.%.Moreover,this improved performance was maintained for 10 sorption/desorption cycles.（3）A sodium chloride（NaCl）doping-hydration technique was used to modify the structure of Li₄SiO₄ to improve its sorption properties at low CO₂ concentration.The hydration products of Li₄SiO₄ materials are mainly LiOH and Li₂SiO₃,and the particle size of HC sample obtained after hydration and calcination treatment was reduced,which would be helpful to the adsorption of CO₂,and the corresponding CO₂ adsorption capacity was 13.7 wt.%,which was more than two times of that of SS.The effects of NaCl doping mainly include two aspects.On one hand,a small particle size and large specific surface area were obtained,significantly facilitating chemisorption processes.On the other hand,co-doped sodium and chlorine induced molten phases when absorbing CO₂,noticeably decreasing CO₂ diffusion resistance.Thus,the CO₂ absorption rate and uptake were remarkably improved.Different amounts of NaCl also greatly affected the morphology and chemisorption properties of the sorbents,the larger the doping amount,the faster the absorption rate of the adsorbent,but the excessive NaCl（5 wt.%）will lead to the formation of impurities,thus reducing the adsorption capacity.At the optimized NaCl concentration,the sorbent only required 3 wt.% doping to attain a maximum sorption capacity of up to 34.2 wt.%.Moreover,the high capacity was maintained after 10 sorption/desorption cycles.