Simultaneous absorption of SO2 and NO from flue gas using ultrasound/Fe2+/heat coactivated persulfate system

An experimental study on the simultaneous removal of NO and SO2 with a new wet recycling process based on the micro-nano bubble water system

The micronano bubble water system (MNBW) generated by a micronano bubble generator (MNBG) has the superior oxidation properties and can improve gas solubility. In the study, a new wet recycling process based on MNBW is proposed to simultaneously remove nitric oxide (NO) and sulfur dioxide (SO₂). The important experimental parameters such as initial water pH, initial water temperature, NO and SO₂ concentrations, and the presence of oxygen (O₂) were investigated to explore the feasibility of desulfurization and denitration with MNBW. The experimental results showed that decreasing initial water pH or increasing initial water temperature and NO and SO₂ concentrations were not conducive to the removal of NO or SO₂. O₂ could promote the removal of NO, but it had no effect on SO₂ removal. In addition, SO₂ removal efficiency always remained high and did not change obviously during the experimental period. However, NO removal efficiency gradually decreased in the first 50 min and then became stable.

A novel catalytic oxidation process for removing elemental mercury by using diperiodatoargentate(III) in the catalysis of trace ruthenium(III)

A series of experiments were conducted at a bench scale reactor to investigate the effects of key influencing factors on the Hg⁰ removal from flue gas using the prepared diperiodatoargentate (III) (DPA) as an oxidant, trace ruthenium(III) as a catalyst, respectively. The experimental results showed that the average Hg⁰ removal efficiency reached to 87.5% under the optimal conditions in which the DPA concentration was 1.03 mmol/L, catalyst concentration was 2.0 μmol/L, reaction temperature was 40 °C and solution pH was 8.5. Meanwhile, it was found from the experiments that the high concentrations of SO₂ and NO could inhibit the Hg⁰ removal due to the competition between Hg⁰ and SO₂/NO, while the lower NO concentration exhibited a slight promotion for Hg⁰ removal. The evolutions of DPA(III) and Ru(III) before and after the reaction were characterized by an ultraviolet visible spectrophotometer (UV-vis), from which, the promotional mechanism of Ru(III) on Hg⁰ removal was analyzed. The spent solution was analyzed by a cold vapor atomic fluorescence spectrometer (CVAFS), which verified that Hg⁰ was oxidized into Hg²⁺ by the catalytic system of DPA(III)-Ru(III), and DPA was converted into Ag⁺.

Degradation of ronidazole by electrochemically simultaneously generated persulfate and ferrous ions

Nitroimidazoles are found in pharmaceuticals and personal care products (PPCPs) and, when discharged into the environment, have adverse effects on human health and survival. Advanced oxidation technologies (AOTs) based on persulfate (PS) can rapidly and efficiently degrade organic pollutants via strong oxidizing radicals under activation conditions. This study investigated the degradation of ronidazole (RNZ) by indirect electrolytic generation of PS and its activator, ferrous ion (Fe²⁺). An electrochemical system was developed, with a high concentration of PS generated at the anode while the activator Fe²⁺ was produced at the cathode. It showed that ammonium polyphosphate (APP) could effectively promote the electrolysis of PS. A high current efficiency (88%) at the anode could be obtained after 180 min at a high current density (300 mA cm^-2). However, Fe²⁺ was inhibited at the cathode due to material control. The degradation of RNZ in the Fe²⁺/PS system generated from the electrochemical system was also explored. Increasing PS concentration and Fe²⁺/PS ratio were beneficial to the RNZ degradation. In homogeneous reactions, the degradation efficiency of RNZ could be improved by decreasing the Fe²⁺ addition rate through a peristaltic pump. Five intermediates were also detected and the degradation pathways were proposed. These findings provide a new method and mechanism for rapid and efficient degradation of RNZ.

Theoretical study on simultaneous removal of SO2, NO, and Hg0 over graphene: competitive adsorption and adsorption type change

In this work, the influence of competitive adsorption and the change of charge transfer for simultaneous adsorption removal of SO₂, NO, and Hg⁰ over graphene were investigated using density functional theory method. The results showed that all the adsorptive effect of SO₂, NO, and Hg⁰ were caused by physical interaction. The adsorptive energy of SO₂ was the highest, and the adsorptive energy of Hg⁰ was the lowest. SO₂ could be preferentially adsorbed and removed. NO/SO₂ and Hg⁰ had the mutual promotion effect for simultaneous adsorption over graphene surface. SO₂ and NO had the mutual inhibition effect for simultaneous adsorption over graphene surface. Compared with single molecular adsorption, the adsorption type of bi-molecular adsorption did not change. However, the simultaneous adsorption changed the adsorption type of Hg⁰ + SO₂ + NO to chemical adsorption due to the interaction among Hg⁰, SO₂, and NO. As such, this study provides a theoretical insight for future application and development. Graphical abstractNO/SO₂ and Hg⁰ had the mutual promotion effect for simultaneous adsorption. SO₂ and NO had the mutual inhibition effect for simultaneous adsorption.

Removal of Carbon Monoxide from Simulated Flue Gas Using Two New Fenton Systems: Mechanism and Kinetics

Two novel removal processes of carbon monoxide using two new Fenton systems (i.e., Cu²⁺/Fe²⁺ and Mn²⁺/Fe²⁺ coactivated H₂O₂ systems) were developed. The effect of several process parameters (concentrations of H₂O₂, Fe²⁺, Cu²⁺, and Mn²⁺, reagent pH value, solution temperature, and simulated flue gas components) on CO removal was studied in a bubbling reactor. The mechanism and kinetics of CO removal were also revealed. Results show that adding Cu²⁺ or Mn²⁺ obviously enhances the removal process of CO in new Fenton systems. The measured results of free radical yield demonstrate that the enhancing role is derived from producing more ·OH (they are produced due to the synergistic activation role of Cu²⁺/Fe²⁺ or Mn²⁺/Fe²⁺ in new Fenton systems. The removal efficiency of CO is raised by increasing concentrations of Fe²⁺, Cu²⁺, and Mn²⁺ and is reduced by raising concentrations of CO, NO, and SO₂. Increasing H₂O₂ concentration, reagent pH, and solution temperature demonstrates a dual impact on CO absorption. Three oxidation pathways are found to be responsible for CO removal in new Fenton systems. Results of mass-transfer reaction kinetics reveal that CO removal processes are located in a fast-speed reaction kinetics region (the CO removal process is controlled by the mass transfer rate).

An often-overestimated adverse effect of halides in heat/persulfate-based degradation of wastewater contaminants

Halides (X^-) in the industrial wastewater are usually thought to adversely affect the degradation kinetics and mineralization rates in several SO₄^--based advanced oxidation processes. However, their unfavorable effects might be overestimated, particularly the heat/persulfate (PS) system as tested in the present study. Here the degradation of phenol, benzoic acid, coumarin and acid orange 7 (AO7) was examined with the presence of chloride or bromide in a heat/PS process. Cl^- was found to have a dual effect (inhibition followed by enhancement) on the decomposition rates of organic pollutants, whereas the effects of Br^- are insignificant within the tested concentration (0-0.2 mM). However, some chlorinated or brominated compounds were still identified in this heat/PS system. Unexpectedly, the mineralization rates of AO7, phenol, benzoic acid and coumarin were not apparently inhibited. In addition, the formation of adsorbable organic halogen (AOX) in the heat/PS system was much less than those in the peroxymonosulfate (PMS)/Cl^- or PMS/Br^- systems. According to the results of kinetic modeling, SO₄^- was the dominating radical for AO7 degradation without Cl^- or Br^-, but Cl₂^- was the main oxidant in the presence of Cl^-, SO₄^-, Br and Br₂- were responsible for the oxidation of AO7 in the presence of Br^-. The present study assumes that X₂/HOX, rather than halogen radicals, is responsible for the enhanced formation of organohalogens. These findings are meaningful to evaluate the PS-based technologies for the high-salinity wastewater and to develop useful strategies for mitigating the negative effects of halides in advanced oxidation processes (AOPs).

Elemental Mercury Removal by a Method of Ultraviolet-Heat Synergistically Catalysis of H2O2-Halide Complex

A novel method of ultraviolet-heat synergistically catalyzing H₂O₂-X (X: NaCl, NaBr, HCl, and HBr) for removal of elemental mercury (Hg⁰) was developed. In terms of Hg⁰ removal efficiency and economy, HCl and HBr were the suitable additives. Hg⁰ removal efficiencies reached 93.6% for H₂O₂-HCl and 91.4% for H₂O₂-HBr, the concentrations of H₂O₂, HCl and HBr were 1 M, 4.2 mM and 0.5 mM. The doses of gaseous Cl and Br-oxidants were 6.27 and 0.75 ppm. The costs by using H₂O₂-HCl and H₂O₂-HBr were 1,180 USD/lb-Hg⁰ and 1,170 USD/lb-Hg⁰. The best temperature for heat catalysis was 413 K. Hg⁰ removal was enhanced by 500 mg/m³ SO₂ and 300 mg/m³ NO due to the formation of sulfuric and NO₂. Mercury distribution analyses indicated that 500 mg/m³ SO₂, 300 mg/m³ NO, and 6% O₂ favored KCl retaining Hg²⁺. When the H₂O₂ concentration was adjusted to 3 M, the simultaneous removal efficiencies of NO and Hg⁰ reached 83.7% and 99.2% for H₂O₂-HCl, and 82.8% and 98.8% for H₂O₂-HBr. Electron spin resonance demonstrated that ClOH•^-/BrOH•^- and Cl₂•^-/Br₂•^- played leading roles in Hg⁰ oxidation, besides Cl₂/Br₂. The mercury forms in spent KCl were HgCl₂, HgBr₂, and HgNO₃, according to X-ray photoelectron spectroscopy.

Use of cobalt(II) chelates of monothiol-containing ligands for the removal of nitric oxide

It is first reported herein that cobalt(II) complexes solution of monothiol-containing multidentate ligands are used to remove low concentration of nitric oxide (NO). These chelating ligands are water-soluble amines, alcohols or acids which containing at least one -SH group, include those of cysteine, mercaptosuccinic acid, mercaptoethanesulfonate, mercaptopropionic acid and the like. These -SH compounds when coordinated with cobalt ions, forming complexes are very effective for NO removal. The results indicate that the side group (methyl, carboxyl, carboxymethyl) on α-carbon atom of ligands contribute to the denitration of the chelate solution, whereas the substituents on sulfur atom of ligands deactivate the complexation system. In addition, we have found that several monothiol compounds with simple molecule structure and low cost exhibit good performance in denitration, and some of cobalt thiol complexes are more valuable in removing NO than ferrous thiol complexes.

Elemental mercury removal by a novel advanced oxidation process of ultraviolet/chlorite-ammonia: Mechanism and kinetics

A novel advanced oxidation process (AOP) of ultraviolet/chlorite-ammonia (UV/NaClO₂-NH₄OH) was developed to remove Hg⁰ from flue gas. The distribution of mercury concentration in three solutions of NaClO₂-NH₄OH, KCl, and H₂SO₄-KMnO₄ was determined by cold atom fluorescence spectrometry (AFS). The role of NH₄OH was to help NaClO₂ preserving and/or stabilizing Hg²⁺ meanwhile inhibiting the photo-production of ClO₂. In the absence of UV, decreasing pH promoted the release of Hg²⁺ from NaClO₂-NH₄OH; introducing NO, SO₂, O₂, Br^-, Cl^-, and HCO₃^- suppressed Hg⁰ oxidation. In the presence of UV, rising temperature accelerated the release of Hg²⁺ from NaClO₂-NH₄OH; while SO₂, Br^- and HCO₃^- facilitated Hg⁰ oxidation. In the absence and presence of UV, Hg⁰ oxidation was controlled by ClO₂^- and by ClO/Cl₂O₂/HO/ClO₂, respectively. The formations of ClO/HO/ClO₂ were confirmed by electron spin resonance (ESR). X-ray photoelectron spectroscopy (XPS) revealed that the products of Hg⁰ and ClO₂^- were HgCl₂, and ClO₂, Cl-, ClO₃-, Cl₂, and ClO₄-, respectively. Analysis of kinetics showed that the Hatta numbers were 23-133 and 69-305 without and with UV, respectively, thus, the gas-film mass transfer was the rate-determining step. This paper gives a new insight in radical behavior in Hg⁰ oxidation.

Gas-phase elemental mercury removal using ammonium chloride impregnated sargassum chars

In this article, pyrolyzed bio-chars derived from a kind of macroalgae, sargassum, were modified by ammonium chloride (NH4Cl) impregnation, and were applied to remove Hg0 from flue gas. The characteristics of sorbents were investigated by the Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, scanning electron microscopy and ultimate and proximate analysis. The key parameters (e.g. loading value, reaction temperature and concentration of O2, NO, SO2 and water vapor), kinetics analysis and reaction mechanism of Hg0 removal were investigated. The results show that increasing loading value, reaction temperature, O2 concentration and NO concentration enhance Hg0 removal. The increase in SO2 concentration or water vapor concentration has a dual effect on Hg0 removal. The C-Cl groups and C=O groups play an important role in the process of Hg0 removal. The Hg0 removal process of modified samples meets the pseudo-second-order kinetic model.

Peroxymonosulfate catalyzed by rGO assisted CoFe2O4 catalyst for removing Hg0 from flue gas in heterogeneous system

The cobalt ferrite-reduced oxidized graphene (CoFe₂O₄/rGO) catalyst was synthesized by hydrothermal method and characterized by Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Brunauere Emmette Teller (BET) and Hysteresis loop. For developing a new method of removing elemental mercury (Hg⁰) from flue gas, the effects of catalyst dosage, PMS concentration, solution pH and reaction temperature on the removal efficiency were investigated experimentally by using peroxymonosulfate (PMS) catalyzed by CoFe₂O₄/rGO at a self-made bubbling reactor. The average removal efficiency of Hg⁰ in a 30-min period reached 95.56%, when CoFe₂O₄/rGO dosage was 0.288 g/L, PMS concentration was 3.5 mmol/L, solution pH was 5.5 and reaction temperature was 55 °C. Meanwhile, based on the free radical quenching experiments, in which, ethyl alcohol and tert butyl alcohol were used as quenchers to prove indirectly the presence of ^•OH and SO₄^•-, the characterizations of catalysts and reaction products, and the existing results from other scholars. The reaction mechanism was proposed.

A novel method of ultraviolet/NaClO2-NH4OH for NO removal: Mechanism and kinetics

The key step for nitric oxide (NO) removal using oxidation method is to efficiently oxidize NO. This study developed a novel advanced oxidation process (AOP) of ultraviolet light (UV) catalysis of chlorite (NaClO₂) to oxidize NO. The production of nitric dioxide (NO₂) and photo-production of chlorine dioxide (ClO₂) were suppressed by adding ammonium hydroxide (NH₄OH). The NO conversion efficiency was 98.1% using UV/NaClO₂-NH₄OH. Electron spin resonance (ESR) tests confirmed the roles of hydroxyl radical (HO) and oxychloride radical (ClO/Cl₂O₂) in the oxidation of NO. Kinetics analyses showed that NO flux was significantly enhanced by radical-induced (HO/ClO) oxidation of NO. In the presence of UV, the overall reaction rates (k_ov1*) were 3-8 times higher than those without UV. The Hatta number, namely the enhanced factor, was calculated in the range of 229-403 and 730-780 corresponding to without and with UV light, suggesting that NO oxidation belonged to fast and/or instantaneous reaction. Thus, the gas-film mass transfer resistance was the rate-determining step. N-containing product was determined as NH₄⁺ and NO₃^- according to X-ray photoelectron spectroscopy (XPS).

Selective Catalytic Reduction of Nitric Oxide with Propylene over Fe/Beta Catalysts Under Lean-Burn Conditions

Fe/Beta catalysts were used for the selective catalytic reduction of nitric oxide with propylene (C3H6-SCR) under lean-burn conditions, which were prepared by liquid ion-exchange (LIE), solid-state ion-exchange (SIE), and incipient wet-impregnation (IWI) methods. The iron species on Fe/Beta were characterized and identified by a combination of several characterization techniques. The results showed preparation methods had a significant influence on the composition and distribution of iron species, LIE method inclined to produce more isolated Fe3+ ions at ion-exchanged sites than IWI and SIE method. C3H6-SCR activity tests demonstrated Fe/Beta(LIE) possessed remarkable catalytic activity and N2 selectivity at temperature 300–450 °C. Kinetic studies of C3H6-SCR reaction suggested that isolated Fe3+ species were more active for NO reduction, whereas Fe2O3 nanoparticles enhanced the hydrocarbon combustion in excess of oxygen. According to the results of in situ DRIFTS, more isolated Fe3+ sites on Fe/Beta(LIE) would promote the formation of the key intermediates, i.e., NO2 adspecies and formate species, then led to the superior C3H6-SCR activity. The slight decrease of SCR activity after hydrothermal aging of Fe/Beta(LIE) catalyst might be due to the migration of isolated Fe3+ ions into oligomeric clusters and/or Fe2O3 nanoparticles.

Removal of multi-pollutant from flue gas utilizing ammonium persulfate solution catalyzed by Fe/ZSM-5

A nano-sized iron loaded ZSM-5 zeolite (Fe/ZSM-5) catalyst was firstly used to activate (NH₄)₂S₂O₈ solution for the simultaneous removal of multi-pollutant from flue gas. The simultaneous removal efficiencies 100% of SO₂, 72.6% of NO and 93.4% of Hg° were achieved under the condition that the catalyst dose was 0.8 g/L, concentration, pH and temperature of (NH₄)₂S₂O₈ solution were 0.03 mol/L, 5 and 65 °C, respectively. The stability of catalyst was checked by a continuous test, proving that the catalytic activity was maintained for 4 h and the leached iron reached low levels. Based on the catalyst characterizations, product analysis and literatures, the removal mechanism was speculated preliminarily, during which, OH and SO₄^- played key roles for oxidizing NO and Hg° into NO₃^- and Hg²⁺.

Simultaneous Removal of NOx and SO2 through a Simple Process Using a Composite Absorbent

In this work, the feasibility of the simultaneous removal of NOx and SO2 through a simple process using a composite absorbent (NaClO2/Na2S2O8) was evaluated. Factors affecting the removal of NOx and SO2, such as NaClO2 and Na2S2O8 concentrations, solution temperature, the initial pH of solution, gas flow rate, and SO2, NO, and O2 concentrations were studied, with a special attention to NOx removal. Results indicate that a synergistic effect on NOx removal has been obtained through combination of NaClO2 and Na2S2O8. NaClO2 in the solution played a more important role than did Na2S2O8 for the removal of NOx. The above factors had an important impact on the removal of NOx, especially the solution temperature, the initial pH of the solution, and the oxidant concentrations. The optimum experimental conditions were established, and a highest efficiency of NOx removal of more than 80% was obtained. Meanwhile, tandem double column absorption experiments were conducted, and a NOx removal efficiency of more than 90% was reached, using NaOH solution as an absorbant in the second reactor. A preliminary reaction mechanism for NOx and SO2 removal was deduced, based on experimental results. The composite absorbent has the potential to be used in the wet desulfurization and denitration process, to realize the synergistic removal of multi-pollutants.

Low-temperature co-purification of NOx and Hg0 from simulated flue gas by CexZryMnzO2/r-Al2O3: the performance and its mechanism

In this study, series of Ce_xZr_yMn_zO₂/r-Al₂O₃ catalysts were prepared by impregnation method and explored to co-purification of NO_x and Hg⁰ at low temperature. The physical and chemical properties of the catalysts were investigated by XRD, BET, FTIR, NH₃-TPD, H₂-TPR, and XPS. The experimental results showed that 10% Ce_0.2Zr_0.3Mn_0.5O₂/r-Al₂O₃ yielded higher conversion on co-purification of NO_x and Hg⁰ than the other prepared catalysts at low temperature, especially at 200-300 °C. 91% and 97% convert rate of NO_x and Hg⁰ were obtained, respectively, when 10% Ce_0.2Zr_0.3Mn_0.5O₂/r-Al₂O₃ catalyst was used at 250 °C. Moreover, the presence of H₂O slightly decreased the removal of NO_x and Hg⁰ owing to the competitive adsorption of H₂O and Hg⁰. When SO₂ was added, the removal of Hg⁰ first increased slightly and then presented a decrease due to the generation of SO₃ and (NH₄)₂SO₄. The results of NH₃-TPD indicated that the strong acid of 10% Ce_0.2Zr_0.3Mn_0.5O₂/r-Al₂O₃ improved its high-temperature activity. XPS and H₂-TPR results showed there were high-valence Mn and Ce species in 10% Ce_0.2Zr_0.3Mn_0.5O₂/r-Al₂O₃, which could effectively promote the removal of NO_x and Hg⁰. Therefore, the mechanisms of Hg⁰ and NO_x removal were proposed as Hg (ad) + [O] → HgO (ad), and 2NH₃/NH₄⁺ (ad) + NO₂ (ad) + NO (g) → 2 N₂ + 3H₂O/2H⁺, respectively. Graphical abstract ᅟ.

Simultaneous purifying of Hg0, SO2, and NOx from flue gas by Fe3+/H2O2: the performance and purifying mechanism

Hg⁰, SO₂, and NOx result in heavily global environmental pollution and serious health hazards. Up to now, how to efficiently remove mercury with SO₂ and NOx from flue gas is still a tough task. In this study, series of high oxidizing Fenton systems were employed to purify the pollutants. The experimental results showed that Fe³⁺/H₂O₂ was more suitable to purify Hg⁰ than Fe²⁺/H₂O₂ and Cu²⁺/H₂O_2. The optimal condition includes Fe³⁺ concentration of 0.008 mol/L, Hg⁰ inlet concentration of 40 μg/m³, solution temperature of 50 °C, pH of 3, H₂O₂ concentration of 0.7 mol/L, and O₂ percentage of 6%. When SO₂ and NOx were taken into account under the optimal condition, Hg⁰ removal efficiency could be enhanced to 91.11% while the removal efficiency of both NOx and SO₂ was slightly declined, which was consistent to the analysis of purifying mechanism. The removal efficiency of Hg⁰ was stimulated by accelerating the conversion of Fe²⁺ to Fe³⁺, which resulted from the existence of SO₂ and NOx. The results of this study suggested that simultaneously purifying Hg⁰, SO₂, and NOx from flue gas is feasible.

Simultaneous removal of NO and SO2 using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS)

Simultaneous removal process of SO₂ and NO from flue gas using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS) in a VUV spraying reactor was proposed. The key influencing factors, active species, reaction products and mechanism of SO₂ and NO simultaneous removal were investigated. The results show that vacuum ultraviolet light (185 nm) achieves the highest NO removal efficiency and yield of and under the same test conditions. NO removal is enhanced at higher PMS concentration, light intensity and oxygen concentration, and is inhibited at higher NO concentration, SO₂ concentration and solution pH. Solution temperature has a double impact on NO removal. CO₂ concentration has no obvious effect on NO removal. and produced from VUV-activation of PMS play a leading role in NO removal. O₃ and ·O produced from VUV-activation of O₂ also play an important role in NO removal. SO₂ achieves complete removal under all experimental conditions due to its very high solubility in water and good reactivity. The highest simultaneous removal efficiency of SO₂ and NO reaches 100% and 91.3%, respectively.

Simultaneous absorption of NO and SO2 by combined urea and FeIIEDTA reaction systems

SO₂ and NO emitted from coal-fired power plants have caused serious air pollution in China. In this work, a novel mixed absorbent, Fe^IIEDTA/urea, was employed for simultaneous removal of SO₂ and NO in a packed tower, with a corresponding optimal ratio of 0.014 mol L⁻¹ : 5%. The effects of various factors, such as mixed absorbent constitutions, reaction temperature, pH, O₂ concentration, as well as concentrations of SO₂ and NO, on simultaneous removal were investigated. The desulfurization efficiency was 95–99% in all tests, whereas denitrification was affected significantly by various conditions. NO removal efficiency decreased increasing oxygen concentration as well as increasing NO concentration. With an increase in temperature, pH, or SO₂ concentration, NO removal efficiency increased first and then decreased. Under optimal conditions, SO₂ removal efficiency was 100% and NO removal efficiency could exceed 91% within 80 min. The reaction mechanism was speculated according to relevant literature.

SO₂ and NO emitted from coal-fired power plants have caused serious air pollution in China.

Mesoporous Mn–Ti amorphous oxides: a robust low-temperature NH3-SCR catalyst

Mn–Ti amorphous oxides prepared by the combinedin situdeposition and freeze-drying strategy exhibited excellent activities and stability in low-temperature NH₃-SCR.

Oxidation Removal of Nitric Oxide from Flue Gas Using UV Photolysis of Aqueous Hypochlorite

The oxidation removal of nitric oxide (NO) from flue gas using UV photolysis of aqueous hypochlorite (Ca(ClO)₂ and NaClO) in a photochemical spraying reactor was studied. The key parameters (e.g., light intensity, hypochlorite concentration, solution temperature, solution pH, and concentration of NO, SO₂, O₂, and CO₂), mechanism and kinetics of NO oxidation removal were investigated. The results demonstrate that UV and hypochlorite have a significant synergistic role for promoting the production of hydroxyl radicals (·OH) and enhancing NO removal. NO removal was enhanced with the increase of light intensity, hypochlorite concentration, or O₂ concentration but was inhibited with the increase of NO or CO₂ concentration. Solution temperature, solution pH, and SO₂ concentration have double the effect on NO removal. NO is oxidized by ·OH and hypochlorite, and ·OH plays a key role in NO oxidation removal. The rate equation and kinetic parameters of NO oxidation removal were also obtained, which can provide an important theoretical basis for studying the numerical simulation of NO absorption process and the amplification design of the reactor.