Studies On The Synthsis Of Lithium Silicate Materials For High-temperature Adsorption Of CO₂ From Rice Husk Ash

Fossil fuels are widely used in daily life and industrial production, which increases CO2 emissions and leads to the greenhouse effect. With the greenhouse effect increasing, lithium-based sorbents become the focus of research in the field of high-temperature CO2 adsorbents, wherein the lithium silicate attracts more and more attention for its excellent adsorption performance.In this thesis, lithium silicate and Na doped lithium silicate materials have been prepared by solid-phase method and “two-step method” with rice husk ash, Li2CO3 and other compounds as raw materials, and the thesis discussed the influence of the source of lithium, roasting temperature and holding time on the preparation. The phase composition, microstructure and the performance of high temperature adsorption of CO2 in lithium silicate and Na doped lithium silicate materials have been studied by XRD, SEM, TG-DTA, TG and other testing technology. The results as following:(1) Rice husk ash was prepared at 600 ? for 1 h by the pretreated rice husk. The testing results of XRF, SEM, BET and XRD showed that rice husk ash was made of high purity(SiO2 content, 99.64 wt%), high specific surface area and poreous amorphous SiO2, and it was a kind of high quality silicon source which could be used to prepare lithium silicate.(2) Rice husk ash as silicon source, respectively by LiOH·H2O, Li2CO3, LiNO3, LiCl and C2H3LiO2 as lithium source, lithium silicate materials were prepared by solid-phase method, and the influence of the source of lithium, calcination temperature and holding time on the the product's phase composition and microstructure was discussed. The results showed that the suitable silicate source should be Li2CO3, calcination temperature should be more than 700 ?, and holding time should be more than 4 h. With these conditions, high purity and crystallinity lithium silicate could be prepared easily. The study of CO2 isothermal adsorption indicated that rice husk ash as silicon source, Li2CO3 as lithium source, calcined at 700 ? for 4 h, the lithium silicate could get better adsorption performance of CO2, the equilibrium absorbed amount of CO2 could reach to 32.2 wt% within 35 min at 680 ?.(3)Rice husk ash as silicon source, Li2SiO3 as lithium source, lithium silicate materials were prepared by “two-step method”. Firstly, The intermediate(Li2SiO3) was synthesized in the conditions of 70 ? for 4 h with LiOH·H2O as lithium source. Secondly, lithium silicate was prepared by mixing Li2SiO3 and Li2CO3. The results showed that the high purity and crystallinity lithium silicate materials were prepared on the conditions of calcination temperature above 800 ? and holding time over 4h. The study of CO2 isothermal adsorption indicated that lithium silicate calcined at 800 ? for 4 h could get better adsorption performance of CO2. The equilibrium absorbed amount of CO2 could reach to 35.3 wt% within 25 min at 680 ?. To some extent, it has better high-temperature adsorption performance than lithium silicate materials prepared by the solid-phase.(4)On the basis of the preparation of lithium silicate, Na doped lithium silicate materials were prepared. The results showed that the doped Na in lithium silicate was beneficial to improve the adsorption performance of high-temperature CO2. Lithium silicate was prepared by solid-phase method when the doping ratio of Na is 0.08, and it could reach equilibrium adsorption within 30 min at 680 ?, and the amount of adsorption was 38.1 wt%. Compared with the lithium silicate, the adsorption performance had a singnificant improvement. Lithium silicate was prepared by “two-step method” when the doping ratio of Na is 0.08, and it could reach equilibrium adsorption within 15 min at 680 ?, and the amount of adsorption was 38.7 wt%. Compared with the lithium silicate, the adsorption performance had a singnificant improvement. With the same conditions of Na doped amount, calcination temperature and holding time, it indicated that Na doped lithium silicate materials prepared by “two-step method” get faster CO2 adsorption rate than these materials prepared by solid-phase method.