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

The increasing greenhouse effect has seriously threaten the survival and development of human beings. Development of the carbon dioxide (CO2) capture technology at high temperatures is of great significance for the control of CO2emissions and the mitigation of the greenhouse effect. As an efficient adsorbent material for CO2capture and separation at high temperatures, lithium silicate (Li4SiO4) has some advantages such as rapid uptake rates and large absorption capacities etc. In this thesis, Li4SiO4materials have been prepared by a solid-state method combined with multistep calcination. The effect of metallic dopant on the CO2absorption properties of Li4SiO4materials has also been investigated. This thesis mainly consists of two parts as follows:1) A solid-state milling method combined with multistep calcination was adopted to prepare Li4SiO4materials:The crystalline structure and morphology of Li4SiO4was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The investigations of CO2absorption properties of the Li4SiO4absorbents at different temperature and CO2partial pressure were performed on a thermogravimetric analysis instrument (TGA). The CO2capture-regeneration cycles on Li4SiO4absorbents were also studied. The results indicated that Li4SiO4materials with high crystallinity and homogeneous grain size distribution could be rapidly prepared in large scale by the solid-state milling method combined with multistep calcination. The prepared Li4SiO4materials show similar CO2absorption properties compared with those prepared by the starch assisted sol-gel method. At550℃and a CO2partial pressure of0.25bar, the absorption can reach a CO2amount absorbed of13.8wt.%within5min and an equilibrium amount of23.0wt.%within30min. Additionally, after five absorption-desorption cycles, a slight decay in the equilibrium absorption amount was observed. 2) Li4SiO4doped with metallic elements such as Fe, Mg, Ce, V were prepared by the above-mentioned solid-state method. The influence of element doping on the crystal structure and microscopic morphologies of lithium silicates was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The TGA technique was applied to investigate the CO2absorption properties of the doped LiSiO4adsorbents. The results indicated that doping with an appropriate amount of Ce or Fe could obviously improve the CO2absorption rate of Li4SiO4, while doping with Mg and V has not contribution to the CO2absorption uptake rate. The influence of the Ce or Fe amount doped on the CO2absorption properties was investigated and thereafter optimized. Trace Ce amount doped could significantly improve the CO2absorption properties. The introduction of Ce plays a role of dispersion of raw materials and thus promots the formation of Li4SiO4On the other hand, when doping Fe, a LiFeO2phase forms besides Li4SiO4.he synergistic effect of LiFeO2and Li4SiO4improves the CO2absorption properties. Specifically, on the Li4SiO4materials dopted with an optimized Fe amount (nFe/nSi=0.15), the CO2amount absorbed can reach16.7wt%within5min and the equillibium adsorption of27.3wt%can be achieved within30min. Additionally, after five absorption-desorption cycles, no decay of CO2absorption properties of the Fe doped Li4SiO4materials can be observed, revealing good recycling properties.