Removal Of Elemental Mercury From Simulated Flue Gas By MnO_x-CeO_x Modified Activated Carbon

Mercury and its compounds are volatile,highly toxic,and persistent,etc,causing great harm to humans and environment.coal-fired power plants and coal-fired industrial boilers are the largest sources of atmospheric mercury emissions.Elemental mercury（Hg⁰）is characterized by its volatility and insolubility in water and has become the focus of mercury removal.Among many mercury synergistic control technologies,activated carbon injection（ACI）technology has been applied in some coal-fired power plants in the United States.However,the removal efficiency of ACI for Hg⁰ is affected by various components in the flue gas.Therefore,it is urgent to develop a highly efficient modified activated carbon for the removal of Hg⁰ in coal-fired flue gas.In this paper,activated carbon was prepared from Jincheng anthracite by KOH activation method.MnO_x modified activated carbon（MnO_x/AC）and MnO_x-CeO_x modified activated carbon（MnO_x-CeO_x/AC）were prepared by wet impregnation method using Mn（CH₃COO）₂·4H₂O and Ce（NO₃）₃·6H₂O as precursors.The mercury removal performance of MnO_x/AC and MnO_x-CeO_x/AC was evaluated on a mercury adsorption experimental system.The effect of preparation conditions of the adsorbent（Mn and Ce loading）and process conditions（adsorption temperature and flue gas composition）on mercury removal performance of MnO_x/AC and MnO_x-CeO_x/AC were investigated.The physicochemical properties of MnO_x/AC and MnO_x-CeO_x/AC were analyzed by means of nitrogen adsorption-desorption,TG/DTG,H₂-TPR,XRD,Raman and XPS,etc.For MnO_x/AC,the average Hg⁰ removal efficiency（η）on MnO_x/AC is 97.0%when Mn loading is 14%at 150 ^oC with 5%O₂ in simulated flue gas;Theηof 14Mn/AC is above90.0%at the sorption temperature between 125 and 200 ^oC.A small amount of O₂ and trace amounts of HCl and NO promoted the removal of Hg⁰ in gas phase,while trace amounts SO₂inhibited it.TG/DTG,XPS and Hg-TPD analyses of spent 14Mn/AC indicated that the inhibition of SO₂ on Hg⁰ removal of 14Mn/AC is due to the consumption of lattice oxygen in MnO_x by formation of MnSO₄ that occupies active sites on the surface of 14Mn/AC.This inhibition of SO₂ on removal of Hg⁰ could be effectively reduced by adding trace amount of NO.In order to improve SO₂ resistance of MnO_x/AC during Hg⁰ removal process,CeO_x modified MnO_x/AC（MnO_x-CeO_x/AC）was prepared by wet impregnation method.The optimum Ce loading is 8 wt.%andηof 14Mn8Ce is 73%under sorption temperature of 150^oC with with 200 ppm SO₂ in simulated flue gas,theηof 14Mn8Ce/AC was increased by35.6%compared with 14Mn/AC.O₂,HCl and NO in simulated flue gas promoted removal of Hg⁰ by 14Mn8Ce/AC,while SO₂ still inhibited removal of Hg⁰.When the presence of“SO₂+HCl”or“SO₂+NO”in the atmosphere,theηis close to 100%.The CeO_x modification of MnO_x/AC can not only increase the lattice oxygen content,but also supplement the lattice oxygen consumed by SO₂ during the sorption process,thus improving the SO₂ resistance of14Mn8Ce/AC.For long-term experiment on 14Mn8Ce/AC,when the sorption lasted to 24hours,the mercury removal efficiency of 14Mn8Ce/AC decreased to 91.4%;when the sorption lasted to 300 hours,the mercury removal efficiency decreased to 65.4%.