Preparation Of CaO/silicon Nitride CO₂ Adsorbent And Its Cyclic Adsorption Properties

Greenhouse effect due to excessive emissions of CO₂ in power plants has raised extensive concerns of the world's researchers in recent year.High temperature calcium-based sorbents become the most important research hotspots for their high theoretical adsorption capacity.However,CaO-based sorbents are easily sintered at high temperature,resulting in poor cyclic stability.In this paper,we synthesized resistant sintering adsorbents by adding inert silicon nitride dopant to the calcium source.The effects of different factors on the adsorption performance of CO₂ were investigated.The microstructure and the adsorption kinetics of as-prepared sorbents were also studied.The paper is divided into three parts:?1?The high purity silicon nitride was prepared by sol-gel carbothermal reduction one-step method at atmospheric pressure.The effects of nitriding temperature,C/Si ratio,nitrogen flow rate,nitriding time and carbon sorce on the nitridation products were investigated.The synthesis mechanism of silicon nitride was also studied in this paper.The results show that the optimum preparation of silicon nitride were as follows:the nitriding temperature was 1500 ?,the ratio of carbon to silicon was 3.5,the nitriding time was 6 h,and the nitrogen flow rate was 120 L/min.Under the same conditions,sucrose obtained the highest purity of silicon nitride products,followed by mahogany powder,and bagasse is the worst.?2?When sucrose based silicon nitride was used as additive,the effects of doping contents and calcium source on the cycling adsorption performance of CO₂ were investigated.When calcium gluconate was used as calcium source,the effects of doping contents,carbon source and precalcination condition on cycling performance were studied.The microstructures of the CaO-based sorbents were characterized by SEM,BET and XRD.The reasons for the different adsorption conversion of as-prepared adsorbents were discussed.The results show that the improved cyclic CO₂ capture performance was observed by doping silicon nitride;When calcium gluconate was choosed as calcium source,the adsorbent doped with 15 wt%silicon nitride shows better cyclic performance;The carbonation conversion order of three adsorbents during 15 cycles was mahogany powder>bagasse>sucrose,which was 60.36%,56.42%and 54.45%respectively.The increasing specific surface area of as-prepared adsorbents with cycles is the reason keeping durability cyclic performance,and the pore size of adsorbents affects its carbonation conversion.Finally,the pre-calcination temperature has an effect on the cycling performance.Too high or too low temperature is not conducive to the adsorption of CO₂.The optimum pre-calcination temperature is 900 ?,and the pre-calcination time has little effect on the cyclic absorption property.?3?The kinetic investigation results show that the three-dimensional diffusion moderl of Jander equation and Ginstling-Brounshtein equation,Avrami-Erofeev equation?n = 1/3?can be used to fit the experimental data well.The activation energy of the mahogany powder-based adsorbent is lower than that of the bagasse-based adsorbent,whether it is in the rapid stage or at the slow stage,which explains the reason why the former carbonation conversion rate is higher than the latter.