Study Of NO Absorption By Oxidation Of Persistent Free Radical-Activated Oxidants In Solid-Loaded Iron Oxide Biomass Charcoal

Coal is still the main source of consumption energy in China,and the massive use of coal will certainly cause serious air pollution,which will not only harm the environment but also harm the human body.Therefore,the treatment of coal-fired NOx is still of great relevance.At present,SCR and SNCR are the mainstream flue gas denitrification treatment methods in the traditional flue gas treatment,but the equipment is complex,ammonia escape is easy to cause secondary pollution,high energy consumption,large investment and other problems.Wet denitrification treatment,adaptable,simple equipment,good treatment effect,the NOx after absorption can be resourceful.Wet denitrification treatment,with strong adaptability,simple equipment,and good treatment effect,attracts a wide range of researchers to study it deeply.Among them,the advanced oxidation process has a very significant treatment effect because of the presence of oxidizing radicals,but some oxidants basically do not have the oxidizing ability in the original state and need certain activation means to activate their oxidizing performance.Common activation methods include thermal activation and ionic activation,among which the activation of substances containing persistent free radicals is more powerful.In addition,oxidative absorption of NO under low oxygen conditions was less studied.Therefore,in this paper,we have conducted a study on oxidative NO removal by activated H₂O₂ and Na2S2O8 from modified biomass char based on the ability of biomass char to produce persistent free radicals during pyrolysis.The main conclusions are as follows:Firstly,biomass char catalysts loaded with Fe₃O₄ with persistent free radicals were successfully prepared: Fe Cl3 was mixed with biomass and loaded with iron oxides by pyrolysis to prepare biomass char that could produce persistent free radicals.The SEM results showed that the surface of the iron oxide loaded biomass charcoal was rougher compared to the unloaded biomass charcoal.The EDS scans showed successful loading of Fe onto the biomass char surface.The BET results indicated that there was a high correlation between specific surface area and iron oxide loading and that both the specific surface area and pore volume of ferric chloride modified biomass charcoal increased more than threefold compared to pristine biomass charcoal,promoting the formation of biomass charcoal pore channels.The XRD analysis obtained showed that Fe3+ undergoed electron transfer with organic matter during biomass pyrolysis,and the main active component generated was Fe₃O₄.The stability of the catalyst was demonstrated by the XRD patterns,which revealed that the Fe₃O₄ crystal structure was still visible on the surface of the biomass after the reaction.The EPR results confirmed that the process of pyrolysis of biomass produced persistent free radicals,indicating the successful preparation of biomass carbon catalysts with persistent free radicals and iron oxides.Then,the modified biomass carbon was used to efficiently activate H₂O₂ to oxidise and absorb NO with a removal efficiency of up to 62.8%.On the oxidative absorption efficiency of NO in simulated flue gas,the effects of experimental conditions including pyrolysis temperature and residence time of biomass char,catalyst dosage,H₂O₂ concentration,solution temperature,initial p H of the solution,and initial NO concentration were investigated,and the mechanism of the NO oxidative absorption reaction in the biomass char/H₂O₂ system was verified by analyzing the liquid phase products after the reaction.The results demonstrated that as pyrolysis temperature and retention time increased,the efficiency of NO’s oxidative denitrification increased constantly,but the denitrification efficiency began to decrease when the pyrolysis temperature exceeded 500 ℃ and the retention time of pyrolysis was greater than 1 h.The rate of NO removal increased and stabilized with an increase in catalyst dosage.The concentration of H₂O₂ could be increased to increase the effectiveness of NO elimination,however,too much H₂O₂ could stifle the beneficial reaction.An increase in the temperature of the solution increased the rate of the reaction.However,too high a temperature led to inefficient decomposition of H₂O₂.Under acidic conditions,NO removal was favored.The increased inlet gas concentration of NO was not conducive to the oxidative absorption of NO.Under the optimal conditions（biomass char pyrolysis temperature of 500 ℃,pyrolysis residence time of 1 h,flue gas inlet flow rate of 200 ml/min,initial NO inlet concentration of 500 ppm,catalyst dosage of 2 g/L,solution temperature of 40 ℃,H₂O₂ concentration of 0.5 mol/L,and initial solution p H of 4）,the best NO removal efficiency in the simulated flue gas was achieved with the removal efficiency of 62.8%.Persistent free radicals in biochar activated H₂O₂,and iron oxides and H₂O₂ formed a Fenton-like system,which together promoted the decomposition of H₂O₂ to produce hydroxyl radicals for the oxidative absorption of NO.Using classical kinetics,the H₂O₂ reaction stage a = 0.147,the NO reaction stage b = 0.886,the finger front factor A0 was 0.011 L0.03/（mo10.03·s）,and the activation energy Ea was 5.16 k J/mol.Finally,oxidative absorption of NO using modified biomass charcoal activated Na2S2O8 achieved 66.3% removal.A comparative experiment of the Na2S2O8 system with modified biomass carbon was carried out,and the effects of experimental conditions,for example,the addition of biomass carbon,the concentration of Na2S2O8,the solution temperature,the initial p H,and the initial NO concentration,on the removal of NO from simulated flue gas were also investigated.The results indicated that the denitrification efficiency was as follows: Na2S2O8 & biomass carbon system> Na2S2O8 system> biomass carbon system,and the denitrification efficiency kept decreasing with the extension of oxidation and absorption time.The removal efficiency of NO was improved with the increase in biomass carbon dosage.The increased concentration of Na2S2O8 resulted in a larger improvement in NO removal efficiency.The efficiency of removing NO in an alkaline condition was superior to that of acid.When the temperature was higher,NO could be oxidized more easily,and it would be more slowly when the temperature was higher than 50 ℃.The increase in NO concentration in the inlet gas was unfavorable to the oxidation of NO.Under the optimal conditions,i.e.,biomass char pyrolysis temperature of 500 ℃,the pyrolysis residence time of 1 h,flue gas inlet flow rate of 200 ml/min,initial p H of the solution of 9,volume fraction of oxygen of 7%,volume of absorber liquid of 500 ml,solution temperature of 50 ℃,catalyst dosage of 2.5 g/L,Na2S2O8 of 0.12 mol/L,and initial NO inlet concentration of 500 ppm,the oxidation efficiency of NO reached the maximum of 66.3%.Na2S2O8 got electrons through persistent radicals and produced SO4-·for oxidative absorption of NO catalyzed by Fe2+.Classical kinetics yields Na2S2O8 reaction level a = 0.433,NO reaction level b = 0.981,a prefactor A0 of 0.039 L0.41/（mo10.41·s）,and an activation energy Ea of 5.38 k J/mol.