Design, Preparation And Absorption Properties Of Lithium-based High Temperature CO₂ Absorbents

To combat global warming,China has set a goal of peaking its carbon emissions by 2030 and reaching carbon neutrality and zero emissions by 2060.In this paper,according to the theory of industrial high temperature flue gas low concentration of carbon dioxide(15 vol%),developed a series of lithium silicate sorbents,research is focused on the following two aspects:silicon the effective use of natural resources and efficient molecular design and application of the high temperature lithium base absorbent,the composite absorbent can meet the application requirements of temperature swing absorption fluidized bed technology.I.A series of Li₄SiO₄ high temperature CO₂ absorbents were prepared by simple precipitation method using natural mineral bentonite as silicon source.The effects of pickling purification time of bentonite and the ratio of lithium to silicon on the absorbents were investigated.The absorption capacity,absorption rate and stability were measured by thermogravimetric analyzer(TGA).When bentonite is pickled for 1hour,most of the impurities can be removed effectively,which can be further used as absorbent for silicon synthesis.In addition,Li:Si=3.7 has the best absorption capacity,and the absorption capacity can reach 32.87 wt%under the atmosphere of 16.7 vol%CO₂.The impurity metal oxides in bentonite can reduce the particle size of the absorbent after pickling,and Li₂SiO₃ and other impurity also have a positive effect on the absorption stability.Using bentonite as a silicon source to prepare Li₄SiO₄ absorbent,which can reduce the production cost,provide a direction for the effective utilization of natural minerals and the industrial development of absorbent.2.A series of nano-sized Li₄SiO₄-Li₂ZrO₃ composite high-temperature CO₂absorbents SZ-x were prepared by sol-gel method at room temperature using cheap silicon and zirconium sources without adding any template,and the effect of Si-Zr ratio on the absorbents was investigated.The absorbents were characterized by SEM,XRD,BET and in situ XRD.The absorption capacity,absorption rate and cycling stability of the absorbents were evaluated by thermogravimetric analyzer.When Si:Zr=4:1,the nano-absorbent was uniformly dispersed(?50 nm).The absorption capacity of SZ-4reached the equilibrium of absorption-desorption at 580 ^oC for 7 min under 16.7 vol%CO₂ atmosphere.The absorption capacity of SZ-4 could reach 18.5 wt%,and the absorption capacity could still maintain 18 wt%in eight cycles of experiments.Due to the high dispersion of the two phases at the molecular level,Li₄SiO₄-Li₂ZrO₃ composites are separated by each other,which greatly reduces the particle size of the absorbent,thus reducing the diffusion resistance of Li⁺from the bulk phase to the surface,increasing the absorption rate,and maintaining good stability in several high temperature absorption-desorption cycle experiments.The absorption of Li₄SiO₄and Li₂ZrO₃ occurred at the operating range of 500-650 ^oC,and the uniform distribution of the two phases at the molecular level effectively reduced the absorption temperature of Li₂ZrO₃.The phase changes during the absorption process were studied in detail by using the in-situ XRD technology,and the synergistic mechanism of the two absorption phases Li₄SiO₄ and Li₂ZrO₃ was proposed.