Experiment Investigation On Simultaneous Removal Of O-xylene And NO_x From Flue Gas By Ozone Coupled With Catalyst

The industrial structure is dominated by the heavy chemical industry,the energy structure is dominated by coal,and the transportation structure is dominated by roads in China.It is difficult to change fundamentally in a short time.The long-term,complex and arduous nature of atmospheric environmental problems still exists.Winning the blue sky defense war is the top priority in fighting the tough battle of pollution prevention and control.At present,the main contradiction in the prevention and control of air pollution lies in PM and ozone pollution.As the precursors of PM and near-ground ozone,VOCs and NO_x seriously endanger the ecological environment and human health.It is urgent to carry out VOCs degradation and NO_x removal.The concentration of organic pollutants in coal-fired flue gas is low,the composition is complex and the amount of flue gas is large.It belongs to the high SO₂and H₂O content atmosphere,and the existing industrial source VOCs adsorption technology and catalytic oxidation technology cannot be directly applied.It is urgent to carry out research on the efficient control technology of VOCs in the coal-fired flue gas.Based on the integrated ozone multi-pollutant removal technology,this paper selects o-xylene(o-C₈H₁₀),which is the representative of aromatic VOCs with high content and harmful in coal-fired flue gas,and carries out the research on the oxidation of VOCs and NO_xby ozone coupling catalyst,which mainly includes the following two parts:（1）The part of decomposition of o-xylene.A series of MO_x/γ-Al₂O₃ catalysts（M=Cu,Co,Mn,Ni,Cr）were synthesized by the isometric impregnation method for the oxidation of o-xylene and concluded that Mn-based catalysts perform best and 1.5 wt.%Mn loadings show the highest catalytic oxidation activity.The 1.5%Mn has the best catalytic activity and stability,which can achieve about 97%conversion of o-xylene at 80°C when the molar ratio of O₃/o-C₈H₁₀ is 10.In addition,this paper found that the best temperature range of the reaction is 80°C to 120°C,and the suggested molar ratio of O₃/o-C₈H₁₀ is 10 to 12.The higher the molar ratio,the higher the CO_xselectivity in outlet gas.The catalyst adapts well to different concentrations of o-xylene.In the SO₂ and water resistance test,the catalyst performs well with SO₂ and H₂O resistance:a low concentration of SO₂（100 ppm）hardly affected the performance of the catalyst;a high concentration of SO₂（200 ppm）and H₂O will cause the catalyst deactivation,in which the effect of H₂O is reversible and SO₂ is irreversible.Even in the atmosphere of SO₂（200 ppm）+H₂O（60%RH）,the degradation efficiency of o-C₈H₁₀ can still be maintained above 85%.When SO₂ and H₂O exist at the same time,H₂O can alleviate the impact of SO₂ on the catalyst.Finally,the in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy（in-situ DRIFTS）test was used to reveal the mechanism of ozone oxidation mechanism.（2）The part of co-oxidation of NO and o-xylene.A series of bimetallic supported catalysts,M-Mn O_x/γ-Al₂O₃（M=Ce,Co,Cr,Fe）were synthesized by isometric impregnation,which is used for NO and o-xylene catalytic oxidation with ozone at low temperature.All the improved catalysts haven’t shown deactivation,and the stability improved significantly.Fe/Mn catalyst shows the highest catalytic oxidation activity and the best temperature range is 60～100°C.It is found that when NO and o-xylene exist at the same time,ozone oxidizes NO to NO₂ preferentially,then the deep oxidation of NO₂ and the preliminary oxidation of o-xylene are carried out at the same time,and finally,the excess ozone oxidizes the small molecular organics generated by the preliminary oxidation of o-xylene to CO and CO₂.The tolerance of Fe/Mn to SO₂ is improved,even the high concentration of SO₂ will not affect the catalytic performance.H₂O still causes reversible deactivation,and the simultaneous presence of SO₂ and H₂O will lead to irreversible deactivation,but the catalyst can still realize about 90%deep oxidation of NO and 80%degradation efficiency of o-xylene.In addition,the catalyst adapts well to different initial pollutant concentrations and has great significance for industrial applicate promotion.