Experimental Study On The Removal Of Elemental Mercury In Simulated Flue Gas By CoO_x-Fe₂O₃-modified ZSM-5

Mercury has a low melting point,volatility,persistence,mobility,etc.,and has strong neurotoxicity.It can spread in the atmosphere and cause great harm to humans and the ecological environment.The emission of mercury in the flue gas of coal-fired power plants is considered one of the main sources of atmospheric mercury pollution.China is rich in coal resources and is the world’s largest coal producer and user.Most of China’s electricity sources still come from coal-fired power plants,and its mercury emissions far exceed the world average.Therefore,developing technologies that have application prospects and can effectively control mercury emissions from coal-fired flue gas is the key to controlling mercury pollution in China.In this paper,the modified ZSM-5 molecular sieve adsorbent loaded with CoO_xand Ce O₂was synthesized by the impregnation method.Its mercury removal performance was investigated in a fixed bed reactor system.In the fixed bed reactor system,the mass ratio of cobalt-iron oxides on the adsorbent surface,the adsorption reaction temperature,the dispersion of metal oxides,and the influence of flue gas components（O₂,NO,SO₂）on the performance of mercury removal were investigated and explored The effect of high-temperature activation and regeneration on the stability of modified ZSM-5 adsorbent.Through FT-IR,XRD,BET,SEM,H₂-TPR,XPS characterization and experiments,the physical and chemical properties of modified ZSM-5molecular sieve adsorbent samples were analyzed,and the synergistic mechanism between CoO_xand Fe₂O₃and mercury removal were explored mechanism.In addition,the adsorption kinetic model and thermodynamic model are used to analyze the adsorption kinetics and thermodynamic process of Hg⁰by the adsorbent.The experimental results show that the optimal loading of the adsorbent is 8%,and the mercury removal efficiency of the ZSM-5 molecular sieve adsorbent loaded with CoO_xand Fe₂O₃is significantly improved.It is adsorbed with Co-ZSM-5 and Fe-ZSM-5.Compared with the catalyst,when the mass ratio of cobalt-iron metal oxide on the modified ZSM-5 surface is 4:1,the mercury removal efficiency is further increased by 5%,indicating a synergistic effect between CoO_xand Fe₂O₃.When the reaction temperature is 120^oC,the mercury removal efficiency reached the highest level at 98.17%.The mercury removal efficiency of the Co₄Fe₁-ZSM-5 adsorbent synthesized by the impregnation method is significantly higher than that of the mechanically mixed Co₄Fe₁-ZSM-5,indicating that the high dispersion of metal oxides on the surface of ZSM-5 is beneficial to improve the mercury removal of the adsorbent performance.The simulated flue gas mercury removal experiment shows that different flue gas components have different effects on the mercury removal performance of the adsorbent.O₂plays a key role in the Removal of Hg⁰;NO promotes the Removal of Hg⁰in the absence of O₂and the presence of O₂;SO₂has a significant inhibitory effect on the Removal of Hg⁰in the absence of O₂,When O₂is present,the inhibitory effect of SO₂on Hg⁰is weakened.XRD and H₂-TPR characterization results show that due to the synergistic effect of cobalt oxide and iron oxide,the surface of the Co₄Fe₁-ZSM-5 adsorbent has more active sites and better redox capacity.In the removal process of elemental mercury,chemical adsorption plays a dominant role,and the Removal of Hg0 obeys the Mars-Maessen mechanism.The adsorption kinetics results show that the mercury removal process of Co₄Fe₁-ZSM-5 adsorbent conforms to the quasi-second-order kinetic model.After multiple regenerations of the Co₄Fe₁-ZSM-5 adsorbent,the mercury removal efficiency of the adsorbent is not significantly different from that of the fresh adsorbent,which indicates that the Co₄Fe₁-ZSM-5 adsorbent has better regeneration performance and stability and might be a potential adsorbent to be utilized in practical applications.