Preparation Of A High-temperature CO₂ Sorbent From Waste Brick And Exploration The Sorption Mechanism

Li₄SiO₄-based sorbents is one of the most promising high-temperature CO₂ sorbents,which has large theoretical sorption capacity,fast sorption rate,and excellent cycling stability.It is mainly used for the separation of CO₂ in high-temperature flue gas and sorption enhanced methane steaming reforming reaction for hydrogen production.However,as a high temperature CO₂ sorbent,Li₄SiO₄ exists some problems,such as high cost,sorption capacity and cycle stability need to be further improved.It is found that the preparation cost of Li₄SiO₄ can be reduced by using silicon-containing ore or solid waste as silicon source,and silicon source will affect the morphology of Li₄SiO₄,thus affect its sorption efficiency.Based on this,in this study,the waste brick was used as silicon resource to synthesize Li₄SiO₄-based sorbent directly for high-temperature CO₂ capture with a solid state method,and its CO₂ sorption performance and sorption mechanism were investigated.At the same time,doping Na₂CO₃ to further improve its CO₂ sorption performance,the main research contents and results are as follows:The waste brick was mixed with Li NO₃ in the molar ratio of Li:Si=6,calcined at 650℃for5h,under the concentration of 100,50,and 20vol%CO₂,sorption at 650,625,and 575℃,the CO₂ capture capacity reached 27.94,26.26,and 26.09wt%,respectively.With 20 cycles of sorption and desorption tests,the results shown that under three different CO₂ atmosphere,the sorbent exhibited high CO₂ sorption capacity and excellent cycling stability and regeneration performance.Although,the synthesized Li₄SiO₄ sorbent exhibited a high CO₂ sorption capacity at low CO₂ concentration,the sorption rate was slightly slower.In order to improve the sorption rate,the Li₄SiO₄ sorbent was modified by Na₂CO₃ doping.The results shown that when the sodium doping with 0.9 mol（molar ratio Si:Li:Na=1:5.1:0.9）,the sample synthesized by calcination at750℃for 5h,sorption at 550℃,which can reach the sorption equilibrium within 10min,and maximum CO₂ capacity of 28.04wt%at 20vol%CO₂ atmosphere.At 50vol%CO₂ atmosphere,when the sorption temperatures were 600℃and 625℃,the sorbent can reach the sorption equilibrium within 5min,the sorption capacity of CO₂ was 28.06 and 27.80wt%,respectively.The kinetic analysis of Li₄SiO₄ sorbent was carried out by using the double exponential model.The CO₂ capture performance and the influence of doping modification on the adsorption process were discussed.The results indicated that lithium diffusion controls the rate of the whole reaction process without Na-doped.In the case of Na-doped,the surface chemisorption reaction stage of CO₂ was more dominant.The sorption of CO₂ on Li₄SiO₄ was explained by the double-shell mechanism,and the molten eutectic carbonate was formed by doping Na₂CO₃,which improved the soption rate of Li₄SiO₄.