| In recent years,with the increase of tail gas emissions and the burning of fossil fuels,atmospheric pollution has become increasingly serious.SO2,H2S,NO2,and NO are the most common atmospheric pollutants,causing serious harm to human health and the environment.The adsorption and separation method can effectively control the pollution of toxic gases.The diffusion rate of gas in adsorbents restricts the utilization efficiency of adsorbents.Therefore,these four toxic gases are selected as the research object in this paper.The self-diffusivity of four pure toxic gases in nanoporous materials was studied from molecular dynamics simulation with changes of molecular concentrations.And we analyzed the effect of geometry of materials on the curve of self-diffusivities of four toxic gases.The results show that self-diffusivities of NO and NO2 gases increased firstly and then decreased with the NO and NO2 numbers increased in IRMOF series,open-metal sites series,ZIF series and zeolites.But the self-diffusivities of NO and NO2 gas only decreased with the NO and NO2 numbers increased in MIL series.And self-diffusivities of SO2 and H2S gases increased firstly and then decreased with the SO2 and H2S numbers increased in COFs,MOFs and zeolites.It is found that the behaviors of self-diffusivity of nitrogen oxides and sulfide are mainly influenced by PLD?Pore Limiting Diameter?and VF?Void Fraction?of nanoporous materials.The higher self-diffusivities of SO2,H2S,NO and NO2gas are obtained when the larger PLD and VF are contained in nanoporous materials.Through the analysis of the results of the self-diffusivity,nanoporous materials with larger self-diffusivities are selected,for example in IRMOF-9,MgMOF-74,MIL-47,MIL-53Crht,AFY,GME and LTA materials NO2 gas has better diffusion properties,and the value of self-diffusivity ranges from 0.637×10-9 m2·s-1,while in IRMOF-15,MOF-205,NU-108-Zn,COF-103,RWY and JSR materials SO2 gas has better diffusion properties,and the value of maximum self-diffusivity ranges from 0.117×10-9 m2·s-1.The diffusion rule was studied from the RDF and MD trajectory of gas in nanoporous materials.The results show that the curve of self-diffusivities of gas is affected by interaction of metal cluster of nanoporous materials.The activation energy of SO2,H2S,NO2 and NO in nanoporous was obtained through the fitting of simulated self-diffusivities at infinite dilution with various temperatures using Arrhenius equation.In addition,the diffusion performance of H2S/O2/N2 and SO2/O2/N2 mixture with increasing N2 concentration in MOFs was also studied.The results show that the diffusion rate of H2S in H2S/O2/N2 mixture is significantly lower than that of N2 and O2 gas.The diffusivities of H2S is the largest in UiO-66 material,of which the value ranges from0.250.32×10-9 m2·s-1,and the increase of N2 concentration is beneficial to the diffusion of H2S.The diffusion rate of SO2 in SO2/O2/N2 mixture is lower than that of N2 and O2 gas,but in MIL-100 material diffusion rate of SO2 gradually increases and then is larger than that of N2.The diffusivities of SO2 is larger in Zn-DOBDC and ZnBDC materials,of which the value ranges from 1.692.58×10-9 m2·s-1,and the change of N2 concentration has little effect on the diffusivities of SO2.The diffusion of H2S/O2/N2 and SO2/O2/N2mixture in MOFs material is influenced by PLD,and the diffusion rate of mixture approaches to zero,due to the much small PLD in COF-1,ZIF-20,ZIF-7 and ZIF-9materials. |
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