Study On Manganese-cerium Binary Metal Mixed Oxides Modified Adsorbent For Hg~0 Removal

Mercury pollution caused a serious damage to human health.Coal-fired power plant is one of the largest sources of anthropogenic mercury emissions.At present,there is no effective mercury reduction measures for Hg⁰ in flue gas.The reduction of Hg⁰ in flue gas by the adsorbent is one of the most important ways to reduce mercury.However,active metal modified adsorbents have been extensively studied due to their good Hg⁰ removal performance and flexible work conditions.In addition,some active metals have good Hg⁰removal performance at low temperatures.Among them,manganese（Mn）-cerium（Ce）based composite adsorbent has attracted much attention for its good low temperature（below300℃）performance,good oxygen storage capacity and synergistic Hg⁰ removal ability.However,with the increase of Mn and Ce loading,the agglomeration and crystallization of active metal will occur,which limited the further improvement of Hg⁰ removal performance.So,this study intends to use a new type of support material to increase the loading of highly dispersed Mn and Ce to improve Hg⁰ removal performance.Meanwhile,the use of halides and sulfides modified adsorbent is also a way to improve Hg⁰ removal performance,but the cost is high.This study explored wether the use of cheap seawater modified adsorbent can further improve the Hg⁰ removal performance.In order to improve the loading of highly dispersed Mn-Ce,carbon nanofibers（CNFs）were employed as support.First,CNFs were placed in concentrated HNO₃ for surface modification.Then,MnCe/CNFs（OX）were prepared by wet chemical impregnation method.Experiments were carried out on a fixed-bed laboratory bench.The results showed that the optimal loading of individual highly dispersed Mn and Ce both reached 15%.Meanwhile,under N₂+6%O₂ atmosphere,the Hg⁰ removal efficiency was above 93%at120-220℃.Compared to traditional supported materials,the highly dispersed Mn and Ce loading increased.It provided more active components for Hg⁰ adsorption reactions,which help the adsorbent maintain a high Hg⁰ removal efficiency for a long time.Individual flue gas experiment results showed that O₂,NO and HCl promoted the removal of Hg⁰.O₂ in the flue gas can replenish the active oxygen.And the active components in adsorbent can promote the conversion of NO to NO_X to promote the catalytic adsorption of Hg⁰.The active Cl species in HCl can also greatly promote the catalytic adsorption of Hg⁰.CO₂ had a slight inhibitory effect on Hg⁰ removal.However,SO₂ will inhibit the adsorbent’s ability to remove Hg⁰ through competitive adsorption and the poisoning of active metals.H₂O has little effect on Hg⁰ removal efficiency.In summary,MnCe/CNFs（OX）possessed better Hg⁰removal performance at low temperature and less sulfur resistance,which is suitable for the removal of Hg⁰ in low-sulfur coal-fired flue gas.In addition,studies show that Cl can greatly promote the removal of Hg⁰.The low-cost sea water is rich in Cl and S.In this study,seawater modified Na[13X]molecular sieves were used for mercury removal.The results showed that the Hg⁰ removal performance have been improved by the modified adsorbents at 150-400°C.Meanwhile,it proved that Cl^-and SO₄^2-in seawater played a positive role in improving Hg⁰ removal.Then,seawater was used as dispersant to prepare seawater modified MnCe/Na[13X]S adsorbents.Compared with MnCe/Na[13X]D prepared with deionized water as dispersant,the Hg⁰ removal efficiency of the former was higher than the latter,especially at low temperatures.Compared with MnCe/CNFs（OX）,MnCe/Na[13X]S adsorbents are more stable for Hg⁰removal under simulated coal-fired flue gas.In summary,the study results of seawater modified molecular sieves is meaningful for developing low-cost efficient Hg⁰ removal adsorbent.