| The combustion of fossil fuels produces large amounts of CO2,which is considered to be one of the major causes of global climate changes.Among them,coal-fired power plants are the main source of CO2 emissions.Therefore,CO2 capture of coal-fired power plants is one of the most important ways to mitigate the greenhouse effects.Calcium-based/magnesium-based sorbents have the advantages of large theoretical adsorption capacity,wide raw materials,and less secondary pollution to the environment.This type of adsorbent has become a potential high temperature/medium temperature CO2 capture material.This paper mainly focuses on the problem of the low reaction rate of common calcium-based sorbents and the degradation of cyclic adsorption performances with increasing number of cycles.The calcium-based sorbent was modified with a carbon template method to explore the modification principle and to prepare high-performance calcium-based sorbents.At the same time,with the help of carbon template method to obtain high-performance Mg-based medium temperature adsorbent.Firstly,various of high-efficiency pure calcium-based sorbents were prepared using the organic calcium in situ carbon template method.After the characterization of the sorbents and CO2 cyclic adsorption performance tests,it was found that:Calcium organic acid could produce carbon deposits during carbonization in N2 atmosphere.The coke deposit forms a sheet-like template that encloses the calcium source,prevents the agglomeration of the adsorbent and makes it more dispersed.The obtained sorbent has a smaller crystal grain size,a larger specific surface area and porosity,which makes positive effects on improving the CO2 adsorption capacity,rate,and stability.Adsorbent,prepared by the use of calcium gluconate as a carbon source,has the lowest initial carbonization temperature,the most complete package,the largest CO2 capacity,the fastest reaction rate,and the best cycle stability.The decarburization performance of the adsorbent was significantly improved by the carbonization final temperature in the range of 600-800?.In order to further improve the performance of calcium-based adsorbents and reduce the loss of calcium gluconate materials in the preparation process,an economic carbon template method was developed.The amount of carbon source(gluconic acid)employed in this process is only 1/4 of that of conventional calcium gluconate,and the adsorbent particles are all nanometer-sized,so the initial adsorption amount is as high as 0.71 g/g.After being doped with high-melting oxides during the preparation process,the adsorbent particles not only possess rich macroporous features,but also effectively inhibited the sintering phenomenon,and the adsorption performance of the adsorbent was also significantly improved.The initial adsorption amount of Mg O-doped sorbent was as high as 0.69 g/g.Under the condition of regeneration and calcination at 950?,the adsorption amount was still 0.65 g/g after ten cycles,showing good CO2 cycles adsorption performances.Sodium nitrate/sodium nitrite-coated magnesium-based sorbents were prepared by a simple wet mixing method.The CO2 adsorption of the coated sorbents were tested.The magnesium-based adsorbent with sodium nitrite as the coating agent has higher adsorption rate and adsorption capacity and better cycle stability.Further preparation of sodium nitrate and sodium nitrite mass ratio of 1:1 co-coated magnesium-based adsorbent,CO2 adsorption performance has been further improved.The carbon template method was introduced into the preparation process of magnesium-based adsorbents.Compared with the adsorbents prepared by the simple wet-mixing method,it was found that the adsorption performance of the Mg-based adsorbents prepared by the carbon template method were improved,and the maximum adsorption amout increase to 0.75g/g.The effects of preparation conditions were explored,and the best mass addition of sodium nitrate was 0.2,the optimum addition of gluconic acid was 1/8,and the optimum carbonization temperature was 400?. |
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