Experimental Study On Simultaneous Desulfurization And Denitrification By Iron-based Heterogeneous Fenton-like Reaction

The conventional technologies of calcium-based wet flue gas desulfurization and selective catalytic reduction denitrification have been used to control the emission of SO2 and NO in coal-fired flue gas,which have the shortages of larger occupying area,higher costs of investment and operation,complexity of system and so on.Thus,it is necessary to develop simultaneous removal of SO2 and NO in flue gas with simple device and lower costs.Oxidation method is an important foundation for simultaneous removing SO2 and NO,with the key point of the oxidation of NO.As a representative of liquid advanced oxidation process,heterogeneous Fenton-like reaction has the advantages of wider pH window,no iron sludge and recyclability of catalyst comparing with traditional homogeneous Fenton reaction.Hence,the removal of SO2 and NO in heterogeneous Fenton-like process by using synthesized water insoluble iron-containing catalyst will be of great theory and practical values.In this paper,the water insoluble iron-containing polyoxometalates catalyst,denoted as Fe?AspPW,was synthesized by precipitation in aqueous solution.Then,the catalysts were used in three experimental systems for the removal of SO2 and NO in self-designed bench scale bubbling reactor platforms.The following experimental results were obtained.(1)The NO removal efficiency of 91.56%was obtained in Fe?AspPW and H2O2 system to remove NO under the reaction conditions,where catalyst dosage was 5g/L,H2O2 concentration was 4mol/L,reaction temperature was 50?,solution pH was 5.5,flue gas flow was 0.4L/min,NO concentration was 603mg/m3.(2)The removal efficiencies of 100%for SO2 and 84.27%for NO were obtained in Fe?AspPW heterogeneous catalytic UV-Fenton-like system to remove SO2 and NO under the reaction conditions,where catalyst dosage was 0.5g/L,H2O2 concentration was 9.0wt%,reaction temperature was 65?,solution pH was 5,the UV power was 18W,flue gas flow was 0.9L/min,NO concentration was 614mg/m3,SO2 concentration was 2094mg/m3,O2 concentration was 6.7%.(3)The optimal reaction conditions for Fe?AspPW heterogeneous catalytic Na2S2O8/H2O2 under UV radiation to remove SO2 and NO predicted by response surface method were that catalyst dosage was 0.69g/L,molar ratio of Na2S2O8/H2O2 was 0.01,reaction temperature was 70?,solution pH was 5.1,which were basically similar to the conditions established by single factor experiments.The predicted maximum removal efficiency for NO was 87.71%,which was closely to that of 87.06%obtained by experimental validation under the optimal conditions.Besides,SO2 was removed completely in the process.The catalyst was characterized by X-ray diffraction(XRD),Scanning electron microscope(SEM),Inductively coupled plasma mass spectrometer(ICP-MS),Thermal gravimetric analyzer(TG),Fourier transform infrared spectroscopy(FTIR),UV-vis diffuse reflection spectrometry(UV-vis DRS),Brunauer-Emmett-Teller(BET)method of the nitrogen adsorption-desorption isotherm.The molecular formula of synthesized Fe?AspPW was speculated to be[Fe(C4H5NO4)]3PW12o40·14H2O.The pore diameter,surface area and pore volume of spent catalyst were slightly smaller than those of fresh one,which suggested that the prepared catalyst was approximately stable in the experiments.The stability of the catalyst was further verified by the recycle experiments and the determination experiment of Fe leaching concentration.The products analysis and material balance summary of simultaneous removal of SO2 and NO in H2O2 system showed that the final oxidation product of NO was mainly NO3-,and a small quantity was NO2-,while that of SO2 was SO42-.Meanwhile,the XPS characteristic suggested that electron capture occurred for some of the Fe3+ on the surface of the spent catalyst,and Fe3+ was transformed partially to Fe2+,so the redox pair Fe3+/Fe2+ existed during the catalytic process.In combination with correlative references,the catalytic mechanism was proposed,which stemmed from the chemisorption of H2O2 by hydrogen bonding,the Fenton-like catalysis of?Fe?(?)?Fe? and photo-catalysis of ?POM(?)?POM-occurred on the surface of Fe?AspPW.According to the macrokinetics experiments,the reaction orders of removing NO by heterogeneous catalytic H2O2 and Na2S2O8/H2O2 systems were 2.09 and 1.07 respectively,and apparent activation energies were 14.05kJ/mol and 11.37kJ/mol respectively.The comparison of reaction rate constant and apparent activation energy reflected that the existence of Na2S2O8 accelerated the oxidation rate by the synergistic effect with H2O2.The experiments of the effect of reaction parameters on reaction rate constant indicated that existences of appropriate SO2,NO,O2,oxidant and catalyst could also accelerate reaction rate.The reaction rate constants of both systems especially for Na2S2O8/H2O2 complex oxidant were changed slightly in solution pH ranges of 2 to 7,which indicated that the reaction systems run well in a wider applicable pH range.