Synthesis Of Lithium Silicate Materials And Their Carbon Dioxide Absorption Properties At High Temperatures

In recent years, the temperatures of earth’s atmosphere and ocean have been significantly increasing, ascribed for the aggravation of the greenhouse effect. The emission control of carbon dioxide (CO2), which is the main contributor to the greenhouse effect, has attracted the worldwide attention. The capture of CO2 at high temperatures and the corresponding CO2 capture materials are of significance for the reduction of CO2. Provious studies indicat that Li4SiO4 materials show an excellent application prospect in the high temperature CO2 capture technology due to the merits of high CO2 adsorption capacity, good mechanical strength and good recyclability. However, the Li4SiO4 materials usually have some problems, such as a slow capture rate and a low capture capacity. In this thesis, Li4SiO4 materials were synthesized by the liquid phase method combined with the freeze-drying technique. The synthesized Li4SiO4 materials show greatly improved CO2 capture properties in terms of both absorption rate and capacity. The thesis mainly consists two parts as follows:1) A liquid phase method combined with the freeze-drying technique was developed to synthesize Li4SiO4 sorbents. The phase structures and morphologies of Li4SiO4 materials were characterized by XRD and SEM, respectively. The CO2 capture-regeneration properties of prepared Li4SiO4 were investigated at different temperatures and different partial pressures of CO2 by thermal gravimetric analysis (TGA). The reusable stability was also tested by five sorption-desorption cycles. The results show that pure Li4SiO4 can be obtained by the liquid phase method combined with the freeze-drying technique. The obtained Li4SiO4 shows a better absorption property, compared with the Li4SiO4 sorbents prepared by solid-phase ball-milling method. At 550℃ and a partial pressure of 0.25 bar, the absorbed amount of CO2 on the optimized sorbent can reach to 24.1 wt.% within 5 min and an equilibrium amount of 29.9 wt.% can be achieved within 10 min. Additionally, after five absorption-desorption cycles, the sorbent still shows the same CO2 absorption properties as the fresh one. Moreover, the effect of lithium and silicon sources on the CO2 capture properties of the synthesized Li4SiO4 was investigated. Then Li4SiO4 materials were prepared by LiOH · H2O and silica sol show a better adsorption capacity. The absorbed amount of CO2 on the optimized sorbent can reach to 27.89 wt.% within 5 min and an equilibrium amount of 30 wt.% can be achieved within 7.5 min.(2) Attempts have been made to prepare porous Li4SiO4 materials by using carbon monospheres and polystyrene microspheres as templates. Their morphology and particle size of the synthesized Li4SiO4 sorbents were characterized by N2 sorption, SEM, and TEM. The CO2 capture-regeneration properties of prepared Li4SiO4 were investigated by thermal gravimetric analysis (TGA). The result shows that using carbon balls as templates, samples shows a good absorption property. The absorbed amount of CO2 on the optimized sorbent can reach to 21.8wt.% within 10 min, which is more than 89% of its stoichiometric sorption capacity, and to an equilibrium amount can be achieved within 20 min.