Experimental Study On Desulfurization And Denitrification By Fenton-like Advanced Oxidation Coupled With Liquid Phase Absorption

With the development of industry and economy,air pollution had become one of the problems faced by both developed and developing countries.The air pollutants emitted from power plant posed a serious threat to human health and ecosystem.Typical air pollutants in coal-fired flue gas include sulfur dioxide（SO₂）,nitric oxide（NO_x）,trace heavy metals,particulate matter（PM）,etc.SO₂and NO_x are the main precursors of acid rain and photochemical smog.Currently,selective catalytic reduction（SCR）and wet flue gas desulfurization（WFGD）are the most mature technologies to remove NO_xand SO₂in flue gas.Although these treatment strategies can achieve the deep removal of NO_x and SO₂,the system still has the disadvantages such as high construction and operation cost,large occupation,high complexity and low stability.Therefore,the development of an economical,efficient,and integrated method for removing SO₂ and NOx has very important engineering significance and research value.Based on the gas-phase Fenton reaction coupled with liquid-phase absorption solution integrated desulfurization and denitrification technology,the feasibility of attapulgite（ATP）as heterogeneous Fenton catalyst to remove flue gas pollutants was studied,and the effect of NO and SO₂ removal efficiency was further investigated by modified ATP.The reaction mechanism of SO₂ and NO in H₂O₂/ATP system under the different reaction conditions（different catalytic temperature,different H₂O₂feeding rate,humidity,different（NH₄）₂SO₃ and urea mass concentration）was discussed.The results showed that ATP with ordered layered structure had various surface groups,large specific surface area and abundant pore structure,which provided a place for the interaction between pollutants and H₂O₂.The increase of Fe OH content on the modified ATP surface was beneficial to the catalytic decomposition of H₂O₂.Magnetic carbon nanotube composites（RM-CNTs）were synthesized by dislocation pyrolysis of solid waste plastics and red mud（RM）.This material was used as a novel catalyst for gas-phase Fenton reaction to remove SO₂and NO from coal-fired flue gas.Under the optimal conditions（SO₂ inlet concentration was 2000 ppm,NO inlet concentration was 500 ppm,O₂ inlet concentration was 7 vol%,reaction temperature was 140℃,H₂O₂concentration was 5 mol/L,H₂O₂feeding rate was 1.5 ml/h,simulated flue gas flow rate was 1.5 L/min,catalyst dosage was 0.5 g,absorption liquid-solid ratio was 20:1）,desulfurization and denitrification efficiency were 98.6%and 91.5%respectively.The mechanism experiment and characterization results were analyzed,it was found that the active components of RM-CNTs include carbon nanotubes and metal nanoparticles（Fe₃O₄,Fe⁰ and Fe₃C）.The H₂O₂/RM-CNTs system showed a different catalytic pathway from the traditional Fenton-like reaction.It was confirmed that·OH and ¹O₂ both in the H₂O₂/RM-CNTs system.Furthermore,based on the free radical inhibition experiments,it was found that·O₂H is an important intermediate in the ¹O₂formation process.Bio-char with large surface area and various surface functional groups was obtained by thermochemical degradation of biomass.We studied the H₂O₂decomposition on Bio-char（made from rice husk,bamboo and pine）and conducted research on the oxidation process of NO.The experimental results showed that the type of biomass and pyrolysis temperature would affect the concentration and type of persistent free radicals（PFRs）in Bio-char.In this study,bio-char can be used as a good O₂ inducer,because PFRs can transfer electrons to molecular oxygen in the environment during the reaction to produce·O₂^-but PFRs could not promote the decomposition of H₂O₂.In order to further improve the oxidation efficiency of NO,magnetic Bio-char catalysts（MCs）was synthesized by one-step method.It was found that Fe Cl₃ and CO₂ promoted the pore development of MCS.Electron paramagnetic resonance and radical quenching experiments confirmed the PFRs,·OH and·O₂^-in H₂O₂/MBC system played a positive role in promoting NO oxidation.In addition,we studied the macro kinetics of NO oxidation reaction and found that the NO oxidation reaction conformed to the pseudo-first-order kinetic model.The reaction rate constant at 373-453 K conformed to the Arrhenius equation,and the apparent activation energy was 32.07 k J/mol.The oxidation mechanism of NO in H₂O₂/Fe₃O₄ system was studied by density functional theory.Firstly,we established the crystal structure of the catalyst,and studied the adsorption and decomposition of H₂O₂and NO on Fe₃O₄（111）surface.In addition,we used OH-Fe₃O₄（111）as the pre-adsorption surface to study the oxidation reaction of NO on the pre-adsorption surface.By analyzing the bond length,bond angle,Bader charge and electron differential density,the results showed that the decomposition reaction of H₂O₂followed the Haber-Weiss mechanism,and the combination of NO and·OH is an exothermic reaction,which was conducive to the spontaneous oxidation of NO.