Experimental Study On The Cyclic Absorption/separation Of Carbon Dioxide From Acidified Modified Eggshells

As a typical greenhouse gas,carbon dioxide has attracted the attention of the international community.As the most important carbon dioxide emission source in the world,the thermal power plant using calcium cycle technology to decarbonize flue gas is the most economical and feasible carbon dioxide emission reduction technology.Considering the serious degradation of natural calcium based adsorbents,egg shell,boiled egg shell and analytical pure calcium carbonate were used as calcium based precursors.The effects of precursor types,organic acid types,calcination temperature and cycle times on the adsorption were investigated by thermogravimetric analysis,X-ray diffraction analysis,X-ray fluorescence analysis,scanning electron microscopy analysis,specific surface area and pore structure analysis The attenuation characteristics of adsorbent after long cycle were predicted.The main research contents are as followsCalcium based adsorbents were prepared with different precursors and the cyclic absorption / separation characteristics of carbon dioxide were tested.The results show that although the initial carbonation conversion of each sample is similar,the cyclic stability of the adsorbent prepared from analytical pure calcium carbonate precursor is higher because of its smaller crystal size and more mesoporous and macroporous;the eggshell needs to be modified to improve the cyclic stability.Different precursors are selective to the calcination temperature.Higher pre calcination temperature(900 ?)is beneficial to increase the maximum carbonation conversion and reaction rate of chemical reaction control stage of eggshell,while the pre calcination temperatures of boiled eggshell and analytical pure calcium carbonate are 700 ? and 800 ?,respectively,showing higher CO2 adsorption performance.Four kinds of organic acids were used to modify the eggshell,and the cyclic absorption / separation experiments of carbon dioxide were carried out.The results showed that the performance of the modified adsorbent was improved to a certain extent.In the 20 cycles,the maximum carbonation conversion of cies900 is 90.7%,and the cycle stability of malic acid modified adsorbent is the best,which is 93%.This is due to the formation of rich pore structure in the calcination process of organic acid salts,which reduces the diffusion resistance of carbon dioxide and slows down the sintering process to a certain extent.Different acids are selective to calcination temperature.In terms of maximum carbonation conversion,except glacial acetic acid modified adsorbent,the maximum carbonation conversion of adsorbent prepared at 900 ? is higher than 700 ? and 800 ?;in terms of cycle stability,the cycle stability of four acid modified adsorbents at 900 ? is higher than 700 ? and 800 ?.The citric acid modified adsorbent with smaller crystal size and larger specific surface area showed higher cycle stability and carbonation conversion rate in 20 cycles.The modified decay model was used to predict the decay of carbonation conversion of each adsorbent in 100 cycles.It was found that the lowest conversion of ES900 was 15.2% and the cycle stability was 17.8% after 100 cycles.After 100 cycles,the conversion of citric acid modified adsorbent was 74.7%,and the cycle stability was 82.4%.