Study On Adsorption Behavior And Coadsorption Mechanism Of Modified MOF-74 For Sulfur,nitrate And Carbon In Coal-Fired Fiue Gas

Coal combustion flue gas pollutants SO_x,NO_x and CO_x have caused infinite harm to the environment.Extending the flue gas purification process from single pollutant control to the coordinated removal of multiple pollutants is a research hotspot in the field of environmental science and technology.Metal organic framework MOF-74material provides a new idea for simultaneous adsorption and removal of sulfur,nitrate and carbon because of its significant structural advantages,which has considerable competitive potentials and application prospects.However,at present,only a few scientific researchers have published relevant reports in this field,and the studies on the simultaneous removal of various flue gas pollutants were also rare.MOF-74 has poor antioxidant and water resistance properties,the co-adsorption mechanism is not clear.In response to the above problems,a series of Ni Mg-MOF-74 adsorbents were prepared in this paper,and their mono-adsorption,co-adsorption properties for sulfur,nitrate and carbon and regeneration capacity were determined;the physical and chemical properties of the adsorbents were analyzed by various characterization methods;Exploring the adsorption mechanism of sulfur,nitrate and carbon molecules on the surface of the adsorbent to reveal the adsorption mechanism.The main research conclusions are as follows:（1）Single metal MOF-74 adsorbents have certain effect on the simultaneous removal of SO₂,NO and CO due to the existence of micropores,but its saturated adsorption capacity and adsorption selectivity still need to be improved.（2）Among the bimetallic Ni_xMg_1-x-MOF-74 adsorbents prepared by solvothermal method,Ni_0.83Mg_0.17-MOF-74 has the optimal co-adsorption performance.The effects of temperature,O₂ and H₂O on the adsorbed gas of Ni_0.83Mg_0.17-MOF-74 were explored.It is manifested that high temperature inhibits the gas adsorption capacity of Ni_0.83Mg_0.17-MOF-74;While O₂ and H₂O promote the single adsorption capacity of gas,and in the co-adsorption system,which promote the adsorption of SO₂ and CO and inhibit the adsorption of NO.（3）Both the Thomas model and the Yoon-Nelson model can intuitively reflect the adsorption process of SO₂,NO and CO on MOF-74,and commendablly apply to the research of the adsorption characteristics of simulated gases.The fitting results of multi-component gas indicata that the MOF-74 adsorption bed has a fixed relationship between the outlet concentration and adsorption time of different gas components,which has practical guiding significance for industrial scale-up and production applications.（4）In situ infrared results reveal that SO₂ and NO are active on the surface of Ni_0.83Mg_0.17-MOF-74,with strong chemical adsorption,while CO is mainly physical adsorption.The introduction of O₂ and H₂O changes the adsorption species of SO₂,NO and CO on the adsorbent surface to promote co-adsorption.At low temperature,SO₂and NO interact on Ni_0.83Mg_0.17-MOF-74 to form an intermediate[SO₃NO_x],which is then decomposed into SO_x and NO_x.It is speculated that there are two pathways for the interaction between SO₂ and NO in the adsorption-desorption process.Path I is for NO promotes SO₂ adsorption,and path II is for SO₂ promotes NO adsorption,which both exist at the same time.（5）Ni_0.83Mg_0.17-MOF-74 was modified with ammonia by impregnation method.The results showed that the Ni_0.83Mg_0.17-MOF-74 modified with 0.2 mol/L ammonia water has the most outstanding effect on removal of SO₂,NO and CO in co-adsorption,and at the same time has more excellent antioxidant and water resistance.