Effect Of Different Carbon Source Modified Calcium-based Sorbents For CO₂ Removal From Flue Gas

Carbon dioxide,one of the primary greenhouse gases blamed for global warming,comes from burning fossil fuels to produce electricity.As an effective way to cope with global warming and climate change,the capture and storage of CO₂ after fuel combustion has attracted more and more attention in recent years.Because of high adsorption speed,adsorption capacities and low cost,the natural calcium-based adsorbent?CaO?is the candidate of good adsorption of CO₂ in the flue gas of power plant.However,the heat stability of the CaO adsorbent is very low.After several adsorption-desorption cycles,the capture efficiency of CO₂ changes very quickly,it's not sustainable.This is because the sorbent get sintering in calcinations process.CaO particles tend to agglomerate in high temperature environment,the surface of adsorbent also becomes closed,the pores and specific surface area are reduced.In order to solve this phenomenon,sol-gel,carbonization and doping with inter metal elements were used in this paper to improve the adsorbent performance.The principle of structural modification of adsorbents was analyzed by comparison of XRD,SEM,and thermo gravimetric analysis.The main research contents are as follows:?1?Biomass not only has a wide range of sources,but also has advantages such as reproducibility and low pollution,and that contains a lot of carbon inside.Therefore,we use glucose,sucrose and starch as carbon sources,adopt sol-gel method to mix the biomass with the calcium base precursor,and then carbonized the adsorbent.The adsorption efficiency of the adsorbents prepared from sucrose and glucose as carbon templates reached 0.72 g/g for the first time.By observing the microscopic morphology of the sample,it was found that the CaO sorbent sample prepared with sucrose and glucose as the carbon template has small particle size and high pore density,which is favorable for the absorption of flue gas CO₂.?2?On the basis of the biomass carbon template,the citric acid carbon coating modification method was proposed.Experiments have shown that the citric acid carbon coating method has a better modification effect than the biomass modification.According to the representation results,citric acid mixed with the sample to form a complex colloidal compound,this colloid in the carbonization process has formed a rich surface pore structure,in which citric acid carbon coating in particles to form a protective film.The structure plays a solid role in maintaining the loose structure of the sample to a certain extent,which not only enhances the progress of the adsorption reaction,but also inhibits the phenomenon of sintering and aging to some extent.?3?Synthesize the former discussion,we mixed dolomite and limestone with a molar ratio of Ca²⁺ions to Mg²⁺ions of 9:1,and then modified them with different acids such as citric acid and gluconic acid,finally the adsorbent was prepared by combustion method.The cyclic desorption conditions are performed under difficult calcinations conditions?100%CO₂?,because of the partial pressure of CO₂,the adsorbent is more difficult to desorption.The prepared adsorbent has a sheet structure,MgO is uniformly dispersed in the adsorbent,so that the anti-sintering capability of the material is improved.On the other hand,the organic acid decomposes and releases a large amount of gas during the calcinations process,so that the crystal size of the adsorbent crystal get smaller,the structure is more bulky,and the adsorption efficiency and stability are obviously improved.