Preparation And Performance Study Of Modified Marble Powder Calcium-based CO₂ Adsorbent

The harm caused by carbon dioxide（CO₂）to the environment has seriously affected our life.At present,the technology of new energy resources is not proven yet.Fossil fuel is still the main source of energy.How to reduce carbon emissions efficiently is our urgent problem while ensuring the steady development of social processes.In the environment of high-temperature exhaust gas in large factories,CaO-based adsorbents have potential development prospects due to their high adsorption capacity and low cost.However,because of low Taman temperature,the conversion of adsorbent decreases fast after sintering,which has become a bottleneck for its current industrial application.Therefore,it is the most efficient and energy-saving method to modify the performance of CaO-based adsorbents by adding different dopants.Marble is a natural,pure,calcium-rich source of calcium.In this study,the modified marble powder CaO-based adsorbent was prepared by doping the pretreated Yunnan marble powder（YS）,which was mainly divided into the fo llowing four parts:（1）The YS adsorption pre-experiment was carried out in the thermogravimetric to explore the optimal react conditions,in which to investigate the cycle adsorpt performance.The results showed that the YS adsorption rate was the fastest at760°C,and the adsorption/desorption was completed at 15 min.Under this condition,the initial conversion of YS was 79.18%,and the conversion after 10cycles was 38.36%,a total decrease of 40.82%.（2）Taking YS as the calcium source,the effects of different silicon nitride（Si₃N₄）doping ratio,cement（C）doping ratio,precalcining time and temperature on the cycle performance of the adsorbent were investigated,and the adsorbents were characterized by XRD,SEM and BET.When the doping ratio of Si₃N₄ is 5wt%,the cement doping ratio is 10wt%,and precalcinated adsorbents at 850°C for 3h（ie5Si₃N₄-10C-850-3-D）,the prepared marble powder adsorbent has the best adsorpt performance and initial conversion.The initial conversion was 56.80%,the maximum conversion was 65.66%,the conversion rate after 20 cycles was 62.40%,and the conversion rate after 20 cycles was 59.62%.The cement mainly provides aluminium oxide（Al₂O₃）,which can combine with calcium（Ca）to synthesis calcium aluminum oxide(Ca₁₂Al₁₄O₃₃).The surface morphology of the hard skeleton modified adsorbent promotes the diffusion of CO₂ in the adsorbent,and improves the"self-activation"performance.The adsorbent exhibits stable long-circulating adsorption performance under the physical support of Si ₃N₄ and the chemical doping of cement.（3）Using YS as a calcium source,doping rare earth compound and waste rare earth polishing powder（RePP）,and investigating the effects of different dopants,preparation methods and preparation conditions on the adsorbent.By the wet mixing-calcination method,because of the abandent oxygen and higher thermostability of cerium oxide（CeO₂）,the modified adsorbent doped with cerous nitrate（Ce（NO₃）₃）can increase the self-activated conversion rate by 14.4%in the first 6 cycles,and remains stable at about 83%after 10 cycles.The conversion of adsorbent doped with RePP,has the same upward trend.But because it is waste,the initial cycle of conversion rate is reduced by 20%,and after 10 cycles,the difference is 7 percentage points.After single factor investigation,the optimum preparation conditions were 15wt%doping amount,precalcining at 800°C and 3h,which could reach 74.29%high conversion rate after 50 long cycles.The realization of cost reduction and resource reuse has great potential for development.（4）The 5Si₃N₄-10C-850-3-D and 15RePP-800-3-H were simulated by the Avrami-Erofeev equation.As 5Si₃N₄-10C-850-3-D,when n=1/3,the kinetic equation is?G（X）=[-ln?（1-x）]³,the fast stage activation energy is 55.23 kJ/mol,and the slow stage is 121.86 kJ/mol;As 15RePP-800-3-H,when n=1/2,the kinetic equation is?G（X）=[-ln?（1-x）]²,the fast stage activation energy is 77.55 kJ/mol,and the slow stage is 100.56 kJ/mol.The activation energy in the slow phase is greater than the fast phase,which is the key control process of the reaction.This is accord with the actual CO₂ adsorption process.