The Preparation And Adsorption Kinetic Analysis Of Lithium Orthosilicate Based Adsorbents

Recently, the greenhouse effect has become the global problem, which is a great challenge for sustainable development of human society. And carbon dioxide?CO₂? is the main greenhouse gas. With the mass consumption of fossil fuels, high temperature flue gas has become the long-term stability source of CO₂. Therefore, the preparation of high temperature CO₂ adsorbents with high effective adsorption performance has becomed the research focus.The high temperature CO₂ adsorbents mainly include Ca O-based sorbents, hydrotalcite-like sorbents, lithium-containing sorbents. Among these sorbents, the regenerative temperature of Ca O-based sorbent is very high, and it's easy to sintering at high temperature. The adsorption capacity of hydrotalcite is very low. Among lithium-containing sorbents, lithium orthosilicate?Li4Si O4? is considered to be the most promising high temperature CO₂ adsorbents with high absorption capacity, fast absorption rate and good cyclic stability.On the basis of our previous work, we attempt to improve the adsorption performance of Li4 Si O4 at high temperature by changing the preparation methods and ion doping. In this paper, the specific works include the following three parts.?1? In this paper, we prepared Li4 Si O4 by impregnation-precipitation method and solid method with kaolin-Si O₂ as silicon source, lithium nitrate as lithium source. In the process of experiments, we discussed the optimum preparation conditions of impregnation-precipitation method and studied the influences of different preparation methods on the adsorption performances of Li4 Si O4. The morphologies, phase compositions and surface areas were analyzed by XRD, SEM and N2 adsorptiondesorption isotherm. And the CO₂ absorption performance was measured with a thermogravimetric analyzer. The optimum preparation conditions of impregnationprecipitation method were as follows: the impregnation temperature was 40 °C, the calcination temperature was 750 °C, the calcination time was 4 h. The CO₂ absorption performance of Li4 Si O4 made by impregnation-precipitation method was much better than Li4 Si O4 made by solid method, with smaller particles, more uniform particle size distribution and larger surface area.?2? On the basis of the above work, we attempted to reduce the adsorption temperature by doping modification and extended its application in the adsorption enhanced reactions. By doping different aluminum sources, we found that aluminum source had a great influence on the CO₂ adsorption performance of Li4 Si O4. The adsorbents doping with calcined halloysite nanotubes had better CO₂ adsorption performance. The optimal doping amount of halloysite nanotubes was x=1.04%??1-x?Li4Si O4·x Al2O3?.?3? In this paper, we discussed the influence of preparation methods and ion doping on the adsorption performance through kinetic analysis with the double exponentinal model.