Numerical Research On Removal Of Nitrogen Oxide From Flue Gas By Adsorption And Oxidation

In recent years,nitrogen oxides have become increasingly serious for environmental pollution.Based on the importance of controlling nitrogen oxides pollution,this paper studies the adsorption process of nitrogen oxides in molecular sieves by means of molecular simulation method and Materials simulation software Materials Studio.Monte carlo method was used to study the effect of Si/Al ratio,temperature and other conditions on the adsorption of NO_x by ZSM-5 molecular sieve.The diffusion process of NO_x in molecular sieve was studied by molecular dynamics method.The adsorption of NO_x on zeolite surface and the catalytic oxidation of NO on ZSM-5 zeolite cluster were studied by density functional method.The main conclusions are as follows:1.Monte-carlo method was used to study the adsorption efficiency of NO on the molecular sieves of ZSM-5.The adsorption efficiency of NO_x on the molecular sieves of ZSM-5 decreased with the increase of temperature.When the molecular sieve component contained Al,the adsorption of NO on ZSM-5 increased with the reduction of Si/Al ratio due to the introduction of H atom as a compensating charge,while the adsorption of NO on Na atom as a compensating charge atom had no obvious effect.The diffusion process of NO and NO₂ in ZSM-5 is transition zone diffusion,and the order of diffusion coefficient is 10^-8m²/s at 273k-313k.The presence of CO₂ and other gases significantly reduces the adsorption of NO_x on zeolites.Modified zeolites with transition metal oxides can significantly improve the adsorption selectivity for NO_x.The order of adsorption selectivity after modification is Ni>Cu>Mn>Zn?Co.Among them,the amount of NO_x adsorbed by modified zeolites can account for 57%of the total adsorption.The load distribution diagram shows that NiO as an active material distributes evenly in the channels of zeolites.2.Using density functional theory respectively to calculate the NO and NO₂ in ZSM-5 and Ni doped ZSM-5?100?surface adsorption behavior,the results show that the NO and NO₂ in the absence of Ni doped adsorption on the ZSM-5 for physical adsorption process,according to the frontier orbital theory and the analysis of the fukui function,N atom has stronger electrophilicity and nucleophilicity than O atom in NO molecule,The electrophilic nucleophilic properties of N and O atoms are similar in NO₂ molecule.When NO was adsorbed at Ni-top in the N-terminal mode at Ni-ZSM-5?100?,the bonding of N and Ni atoms was chemical adsorption,and the adsorption energy was-1.26ev.In this process,NO was transformed into nitryl ion NO⁺.The topmost adsorption position of NO₂ at Ni atom is still a physical adsorption process,while chemical adsorption takes place at the topmost adsorption position of O atom in the single coordination position.The adsorption energy is-1.37ev,and NO₂ is adsorbed on O atom and forms nitric ion NO₃^-.3.Based on the density functional theory,transition state search was conducted for the catalytic oxidation process of NO on the ZSM-5 molecular sieve,and the results showed that there were two catalytic pathways for NO catalyzed by the 4T ZSM-5 molecular sieve.Nitric ion NO₃^-and peroxynitrite ONOO^-are important intermediates in the catalytic process.At a low temperature,the reaction path of Ni-ZSM-5 catalytic oxidation of NO is:Z+O₂?Z-O₂,Z-O₂+NO?Z-ONOO,Z-ONOO?Z-O+NO₂,Z-O+NO?Z+NO₂.At high temperature,the reaction path of catalytic oxidation of NO by ZSM-5 doped with Fe or Cu is:Z+NO?Z-NO,Z-NO+O₂?Z-NO₃^-,Z-NO₃^-?Z-O+NO₂,Z-O+NO?Z+NO₂.