Synthesis And Characterization Of Nanosized Li₂ZrO₃and Li₄SiO₄Materials As Carbon Dioxide Sorbents

The capture of CO2at high temperatures, which is of utmost importance for the reduction of CO2emissions, is a key and common technology for the direct sequestrate of CO2from the high temperature flue gases as well as the in-situ removal of CO2from chemical processes to enhance the productivity of desired products. The key of the capture of CO2at high temperatures is to develop CO2sorbents. It has been reported that Li2ZrO3and Li4SiO4are promising candidates for CO2capture due to their excellent properties in terms of capacity, recyclability, mechanical strength etc. However, the reported Li2ZrO3and Li4SiO4materials encountered several problems involving of the slow capture rate and the low capture capacity. This thesis mainly deals with the synthesis of the nanosized K-doped Li2ZrO3materials and the Li4SiO4nanoparticles, leading to a great improvement of the CO2capture-regeneration properties. The main results are summarized as follows:1) K-doped Li2ZrO3sorbents with excellent CO2capture properties were synthesized via a citrate route. The effects of the K-doped amount of Li2ZrO3sorbents on their CO2sorption properties were investigated. The synthesized K-doped Li2ZrO3sorbents were characterized by nitrogen adsorption/desorption, XRD, SEM, and TEM techniques. The CO2capture-regeneration properties of the synthesized K-doped Li2ZrO3sorbents were investigated by thermogravimetric analysis (TGA) at different temperatures and CO2partial pressures. The effects of the composition, morphology, and particle size of the prepared samples on their CO2sorption properties were investigated and the sorption-desorption cycles of CO2on the sorbents were further studied. The sorbent with an optimized Li:Zr:K molar ratio of1.6:1:0.2shows the best CO2sorption properties, i.e., the sorption of CO2can reach23wt.%, which is more than90%of its stoichiometric sorption capacity, within15min at550℃and a CO2partial pressure of0.25bar. Furthermore, the sorbent shows a good stability, confirmed by CO2capture-regeneration cycles.2) A starch-assisted sol-gel method combined with the freeze-drying technique was developed to synthesize K-doped Li2ZrO3. The effects of different starch amounts on the CO2capture properties of the synthesized sorbents were investigated. The optimized sorbent shows excellent CO2adsorption properties, i.e., the uptake of CO2reaches23.2%within17min at550℃and a CO2partial pressure of0.25bar. Additionally, the sorbent shows a good stability, confirmed by five capture-regeneration cycles. Furthermore, the developed synthesis method can be easily reproduced and scaled up, and in the current work the sorbent was scaled up to batches of10g.3) Li4SiO4nanoparticles were synthesized by the developed starch-assisted sol-gel method combined with the freeze-drying technique. The effects of sorption temperature on the CO2capture properties of the synthesized sorbents were investigated. The phase structure, morphology, and particle size of the synthesized Li4SiO4sorbents were characterized by N2sorption, XRD, SEM, and TEM techniques. The CO2capture properties and the reusability of the sorbents were investigated by TGA. The synthesized Li4SiO4nanoparticles show a greatly improved CO2capture properties, i.e., the sorption of CO2can reach15.4wt.%within5min at550℃and a CO2partial pressure of0.1bar, compared to Li2ZrO3nanoparticles. After ten sorption-desorption cycles, the sorbent still shows the same CO2capture-regeneration properties as the fresh one, indicating a high stability of the prepared Li4SiO4nanoparticles.