Study On The Adsorption Of Zero-Valent Mercury In Coal-Fired Flue Gas By Modified Manganese Oxides

Mercury is a toxic heavy metal with the characteristics of stability,bioaccumulation and long-range migration,which can cause irreversible harm to human body and the environment.Coal combustion flue gas emissions are the largest source of anthropogenic mercury emissions,of which Hg0 is difficult to be captured due to its stable nature and insoluble in water,so the preparation of efficient and stable Hg0 oxidation catalysts is the key to reduce Hg0 emissions from coal combustion flue gas.The main research of this thesis is the application of manganese cerium mixture-loaded activated carbon and polyaniline doped manganese dioxide for the removal of zero-valent mercury from coal-fired flue gas.Manganese cerium oxide loaded activated carbon(MnCe)x/AC and manganese dioxide doped polyaniline PANIx-MnO2 adsorbents with different mass fractions were prepared by high temperature impregnation method and in situ polymerization method,respectively.The optimum reaction conditions and mercury adsorption capacity were determined at different temperatures,different loadings and different The optimum reaction conditions and mercury adsorption capacity were determined under different temperatures,different loadings and different interfering gases,and the reaction mechanism of their ability to remove Hg0 efficiently was investigated by BET,XRD,SEM,XPS,Hg-TPD,adsorption kinetics and other characterization methods.According to the experimental results,it is known that among the(MnCe)s/AC adsorbents,MnCe6%with a loading of 6 wt%has the highest Hg0 removal efficiency at 200℃ and 6%O2 in 12h.The average Hg0 removal efficiency is 96%and the mercury adsorption capacity is 8.73 g/mg in 12 h,which is 58.20 times higher than that of activated carbon at room temperature.PANIx-MnO2 Among the adsorbents,PANI0.3-MnO2 with a loading of 30 wt%had the highest Hg0 removal efficiency at 150℃ and 6%O2 in 12 h.It could maintain more than 98%efficiency in 12 h.The mercury adsorption capacity was 4.94 g/mg,which was 40.92 times higher than that of MnO2 at room temperature.The removal efficiency of Hg0 by the adsorbent can be improved by increasing the temperature appropriately,and the temperature exceeding the threshold value will cause the desorption of mercury as well as the destruction of the adsorbent structure to reduce the removal efficiency of Hg0.The presence of SO2 will compete for the active sites of the adsorbent,consume O2,and inhibit the reaction,while the presence of O2 will promote the reaction,and NO has no effect on the overall removal efficiency of Hg0.The overall removal efficiency of Hg0 by NO was not affected by the presence of O2.The overall analysis of the adsorbent characterization showed that both physical and chemical oxidative adsorption existed for the removal of Hg0,with chemical oxidative adsorption being the dominant factor.The comparison of the studies in this thesis can prove that MnCe6%/AC and PANI0.3MnO2 adsorbents are more capable of removing Hg0 from coal combustion flue gas,which can be helpful in this field.