Simultaneous Removal of NO and SO2 from Flue Gas by UV/H2O2/CaO

The effects of several influencing factors (CaO and H₂O₂ concentration, gas flow, solution temperature, NO, SO₂, O₂ and CO₂ concentration) on the simultaneous removal of NO and SO₂ from flue gas by using a UV/H₂O₂/CaO process were studied. In addition, the anions in the liquid phase were measured by ion chromatography and the material balances for NO and SO₂ were calculated. It was found that, under all experimental conditions, this process achieved a SO₂ removal efficiency of 100 %. With the increase in CaO concentration, NO removal efficiency first increased and then remained almost unchanged. With the increase in H₂O₂ concentration, NO removal efficiency increased but the changes gradually became smaller. NO removal efficiency greatly decreased with increasing gas flow, NO concentration and CO₂ concentration. Slightly increasing the solution temperature and SO₂ concentration reduced NO removal efficiency. Increasing O₂ concentration can promote the removal of NO. The anions in the liquid phase were mainly SO₄^2– and NO₃^–. Most of the low valence nitrogen elements in NO and the low valence sulfur elements in SO₂ transformed into the high valence nitrogen element in NO₃^– and the high sulfur element in SO₄^2–.     

Simulation of SO2 absorption by falling water drops

The experimental data of Walcek et al. (1981) for SO₂ absorption by falling water drops of 600 μm dia. at 13-15°C and 1-50 vol% SO₂ in air can be well predicted by a model which ignores the effect of internal circulation and considers the diffusion of both SO₂H₂O and HSO₃ and the accompanying equilibrium dissociation reaction of SO₂.H₂O within the drop. The data can also be described by the analytical solution obtained by simplifying the rigorous model with the assumption that the gas phase mass transfer resistance is negligible and that the difhtsivities of sulfur species are equal.     

Removal of Hg0 from containing‐SO2/NO flue gas by ultraviolet/H2O2 process in a novel photochemical reactor

A novel photochemical spray reactor is first developed and is used to remove Hg⁰ and simultaneously remove Hg⁰/SO₂/NO from flue gas by ultraviolet (UV)/H₂O₂ process. The effects of several parameters (UV wavelength, UV power, H₂O₂ concentration, Hg⁰ inlet concentration, solution temperature, liquid–gas ratio, solution pH, SO₂ concentration, NO concentration, and O₂ concentration) on removal of Hg⁰ by UV/H₂O₂ process were investigated. Removal mechanism of Hg⁰ is proposed and simultaneous removal of Hg⁰, NO, and SO₂ is also studied. The results show that the parameters, UV wavelength, UV power, H₂O₂ concentration, liquid–gas ratio, solution pH, and O₂ concentration, have significant impact on removal of Hg⁰. However, the parameters, Hg⁰ inlet concentration, solution temperature, SO₂ concentration, and NO concentration, only have small effect on removal of Hg⁰. Hg²⁺ is the final product of Hg⁰ removal, and Hg⁰ is mainly removed by oxidations of H₂O₂, ·OH, · O, O₃, and photoexcitation of UV. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2275–2285, 2014     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

The absorption rate of CO2/SO2/NO2 into a blended aqueous AMP/ammonia solution

The Inter-governmental Panel on Climate Change (IPCC) reported that human activities result in the production of greenhouse gases (CO₂, CH₄, N₂O and CFCs), which significantly contribute to global warming, one of the most serious environmental problems. Under these circumstances, most nations have shown a willingness to suffer economic burdens by signing the Kyoto Protocol, which took effect from February 2005. Therefore, an innovative technology for the simultaneously removal carbon dioxide (CO₂) and nitrogen dioxide (NO₂), which are discharged in great quantities from fossil fuel-fired power plants and incineration facilities, must be developed to reduce these economical burdens. In this study, a blend of AMP and NH₃ was used to achieve high absorption rates for CO₂, as suggested in several publications. The absorption rates of CO₂, SO₂ and NO₂ into aqueous AMP and blended AMP+NH₃ solutions were measured using a stirred-cell reactor at 293, 303 and 313 K. The reaction rate constants were determined from the measured absorption rates. The effect of adding NH₃ to enhance the absorption characteristics of AMP was also studied. The performance of the reactions was evaluated under various operating conditions. From the results, the reactions with SO₂ and NO₂ into aqueous AMP and AMP+NH₃ solutions were classified as instantaneous reactions. The absorption rates increased with increasing reaction temperature and NH₃ concentration. The reaction rates of 1, 3 and 5 wt% NH₃ blended with 30 wt% AMP solution with respect to CO₂/SO₂/NO₂ at 313 K were 6.05～8.49×10^?6, 7.16–10.41×10^?6 and 8.02～12.0×10^?6 kmol m^?2s^?1, respectively. These values were approximately 32.3–38.7% higher than with aqueous AMP solution alone. The rate of the simultaneous absorption of CO₂/SO₂/NO₂ into aqueous AMP+NH₃ solution was 3.83–4.87×10^?6 kmol m^?2s^?1 at 15 kPa, which was an increase of 15.0–16.9% compared to 30 wt% AMP solution alone. This may have been caused by the NH₃ solution acting as an alternative for CO₂/SO₂/NO₂ controls from flue gas due to its high absorption capacity and fast absorption rate.     

Dissolution mechanism of colemanite in sulphuric acid solutions

Boron compounds are very important raw materials in many branches of industry and their uses have been increasing and expanding continuously. Colemanite, one of the most common boron minerals, has a monoclinic crystal structure with a chemical formula of 2CaO·3B₂O₃·5H₂O and is used usually in the production of boric acid. The present study concerns and investigation of the dissolution mechanism of colemanite in H₂SO₄ solution and the effect of acid concentration, the effect of SO₄⁻² ion on the dissolution process, using H₂SO₄, HCI+H₂SO₄ and H₂SO₄+Na₂SO₄ solutions. The analysis of the experimental data shows that increasing H₃O⁺ acid concentration increased the dissolution rate, but increasing SO₄⁻² concentration reduced dissolution rate because of the precipitation of a solid film of CaSO₄ and CaSO₄·H₂O.     

Study and Characterisation of Activated Carbon Treated with H2SO4 Solutions

Several samples of activated carbon (AC), previously outgassed and treated with H₂SO₄ solutions of varying concentration, were prepared. The contact between the phases and the outgassing of AC were carried out under controlled conditions. The chemical composition and the thermal behaviour as well as the texture of the samples were studied. Techniques used were chemical analysis, FT-IR spectroscopy, thermogravimetric analysis, gas adsorption, mercury porosimetry and density measurements. After the contact of H₂SO₄ solutions with AC, the mass of samples increased greatly. It was associated with the uptake by AC of components of the solution, especially H₂SO₄. The presence in the samples of HSO₄⁻ and SO₄²⁻ ions was shown by the FT-IR spectra. The mass increase was strongly dependent on the method of preparation of the samples. In the heat treatment of the samples between 30 and 800°C a great mass loss occurred below 400°C. However, it was small at higher temperatures and when the samples were outgassed at 120°C for 12 h, at 133×10⁻³ Pa. The introduction of H₂SO₄ solution in AC pores produced a drastic reduction in the surface area and in the microporosity of the material. It also affected the pore-size distribution in the mesopore and macropore ranges. © 1997 SCI.     

SO2 Oxidation and H2O-H2SO4 Binary Nucleation by Radon Decay

The oxidation of SO₂ by ·OH radical produced by radon decay and binary nucleation of H₂SO₄-H₂O were studied using a thermal diffusion cloud chamber. A kinetic model was developed to examine the oxidation of SO₂ by ·OH to H₂SO₄ to estimate airborne concentration of the critical species. The kinetic modelling calculations suggested that ·OH radical production is the rate control step among the gas-phase reactions proposed. The experimental results showed that nucleation rates increase with increasing radon and SO₂ concentrations. Two distinct types of nucleation, mist and rain, were observed at different super-saturation in the thermal diffusion cloud chamber. The experimental observations suggest that both SO₂ and H₂SO₄ can cause binary nucleation with water vapor. It is necessary to further distinguish between these two nucleation mechanisms in the future in order to obtain a better understanding of this combined oxidation and nucleation mechanism.     

Citrate process for SO2 recovery: Vapour-liquid data and correlation

Precise knowledge of the quantitative data of equilibrium vapour pressure of SO₂ over aqueous sodium citrate solution is of considerable technological importance for the design of both absorber and regenerator. The absence of such data prompted a series of measurements to determine them. The ranges of experimental conditions used for measurements of vapour-liquid equilibrium data were: gas flow rate, 1.60–1.701 min⁻¹; SO₂ concentration in inlet gases, 0.50–6.00 vol%; temperature, 40–70°C at atmospheric pressure and citrate buffer with the molar ratio C_NaOH/C_H3Ci of 0.50/1 .00, 1 .00/1 .00 and 2.00/1.00. The equilibrium vapour-liquid data were correlated by the extended two-parameter model. Good agreement between experimental results and those predicted by the suggested model was obtained for the whole investigated region of interest for SO₂ absorption.     

SO2-removal using ammonia solution in a packed column

The effect of variables on efficiency of SO₂ removal from a simulated waste gas by use of ammonia solution was studied. The variables were gas, feed solution and recirculation flow rate, SO₂ concentration in the gas phase, NH₃ concentration in the ammonia solution, and pH in scrubber effluent solutions. The scrubber was 3“ — OD methyl metacrylate column packed with 1 •4” — plastic Rasching rings in 90 cm packed height. Solution analysis was performed by Palmrose method and pH meter. The following empirical equations were obtained by regression analysis; EFF = 33.52 G^0.0552 F^0.118 R^0.772 EFF = 64.10 S^0.143 N^0.0153 k_G = 3.51 x 10^-6 G^1.160 L_0.647     

Kinetic Studies on NO2 Absorption into Ammonium Sulfite Solutions

The absorption reactions of NO₂ into (NH₄)₂SO₃ solution were investigated in a stirred tank reactor. The kinetic regime of the absorption reaction was identified and the effects of various experimental parameters were studied. The experimental results indicated that the absorption of NO₂ into (NH₄)₂SO₃ solution is accompanied by a fast pseudo-first-order reaction. It was found that the NO₂ absorption rates were enhanced by the increasing concentration of (NH₄)₂SO₃ but nearly remained constant if the concentration is greater than 0.1 mol/L. The absorption rates also increased with increasing the reaction temperature and the concentration of NO₂ in inlet gas, but decreased as the oxygen concentration increased.     

Acidic protic ionic liquid-based deep eutectic solvents capturing SO2 with low enthalpy changes

With the aim of lowering energy consumption for gas regeneration, rational design of absorbents with low absorption enthalpy changes while retaining good gas solubility is of both scientific and practical significance. Herein, we demonstrated that acidic protic ionic liquid (APIL)-based deep eutectic solvents (DESs), which comprise N-ethylimidazole hydrochloride ([EimH]Cl) and ethylene glycol (EG), were able to reversibly absorb SO₂ with high solubility (11.60 mol kg⁻¹) and SO₂/CO₂ selectivity (655) at 293.2 K and 101.3 kPa. Meanwhile, [EimH]Cl/EG DESs exhibit very low enthalpy changes (Δ_rH_m) ranging from −27.1 to −25.6 kJ mol⁻¹, and thus ease of desorption at very mild temperature conditions (303.2 K) with desorption ratios up to 99.6%. Recycling experiments showed that no obvious loss in capacity was found after six absorption–desorption cycles, suggesting good regeneration performance of [EimH]Cl/EG DESs. Moreover, spectroscopic analysis revealed the charge-transfer interaction between [EimH]Cl/EG and SO₂.     

Absorption of NO by Aqueous Solutions of KMnO4/H2SO4

The absorption of NO in aqueous solutions of KMnO₄ and H₂SO₄ was carried out in a stirred tank reactor under atmosphere pressure. The results indicated that the absorption process was under a fast pseudo-m th reaction regime. The reaction between NO and aqueous solutions of KMnO₄/H₂SO₄ was found to be first-order with respect both to NO and to KMnO₄. The addition of H₂SO₄ to KMnO₄ solutions increased the absorption rate of NO and increasing reaction temperature was also favorable to the absorption of NO.     

Simultaneous removal of NO and SO2 using aqueous peroxymonosulfate with coactivation of Cu2+/Fe3+ and high temperature

A novel process on simultaneous removal of NO and SO₂ using aqueous peroxymonosulfate (PMS) with synergic activation of Cu²⁺/Fe³⁺ and high temperature in an impinging stream reactor is developed for the first time. Effects of PMS concentration, Cu²⁺/Fe³⁺ concentration, reaction temperature, solution pH, flue gas flow, liquid–gas ratio, gas components, and inorganic ions on NO/SO₂ removals were investigated. Active species and products were determined by electron spin resonance spectroscopy and ion chromatography. Removal pathways of NO/SO₂ were revealed, and mass transfer‐reaction kinetics of NO removal was studied. The optimal experimental conditions are obtained. H₂SO₄ and HNO₃ are the main products. It is found that there is a clear synergy between Cu²⁺/Fe³⁺ and high temperature for activating PMS. and ·OH are found to be the main oxidants for NO removal. NO removals belong to pseudo‐first fast reactions in the two investigated oxidation systems. Besides, the kinetic parameters are also measured. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1287–1302, 2017     

Spectroscopic study on the intermolecular interaction of SO2 absorption in poly-ethylene glycol+H2O systems

Poly-Ethylene Glycol (PEG) 300+H₂O solutions (PEGWs) has been used as a promising medium for the absorption of SO₂. We investigated the UV, FTIR, ¹H-NMR, and fluorescence spectra in the absorption processes of SO₂ in PEGWs to present an important absorption mechanism. Based on the spectral results, the possibility of intermolecular hydrogen bond formation by hydroxyl oxygen atom in the PEG molecule with hydrogen atom in H₂O and S…O interaction formation by the oxygen atoms in PEG with the sulfur atom in SO₂ are discussed. This shows that the spectral changes may be due to the formation of -CH₂CH₂O(H)…HOH… and -CH₂-CH₂-O(CH₂-CH₂-)…HOH… in PEGWs and the formation of -CH₂CH₂OH…OSO…, and intermolecular S…O interaction between PEG and SO₂ as the formation of -CH₂CH₂OCH₂CH₂O(H)…(O)S(O)… and -CH₂-CH₂-O(CH₂-CH₂-)…(O)S(O)…. The existence of these bonds benefits the absorption and desorption processes of SO₂ in PEGWs.     

五元体系KCl-KBr-K2SO4-K2B4O7-H2O 323 K和348 K的相平衡

用等温溶解平衡法研究了五元体系KCl-KBr-K₂SO₄-K₂B₄O₇-H₂O在323 K和348 K时的相平衡关系,测定了该五元体系在相应温度条件下平衡溶液的溶解度和密度,根据相平衡实验数据绘制相应的相图(K₂SO₄饱和)。研究结果表明:该五元体系在323 K和348 K条件下均属于固溶体型,相图中均有2个平衡固相结晶区,其平衡固相分别为固溶体K(Cl,Br)和K₂B₄O₇·4H₂O,1条单变量曲线。该五元体系323 K和348 K的相图相比,348 K时K₂ B₄O₇·4H₂O结晶区变小,而固溶体K(Cl,Br)结晶区变大。     

Effect of SO2 on NOx reduction by ethanol over Ag/Al2O3 catalyst

A new Ag/Al₂O₃ catalyst for removing NO_x in diesel engine exhaust gas was developed. The influence of SO₂ on the reduction of lean NO_x by ethanol over the Ag/Al₂O₃ catalyst was evaluated in simulated diesel exhaust and characterized using TPD, XRD, XPS, SEM and BET measurements. The Ag/Al₂O₃ catalyst was highly active for the reduction of NO_x with ethanol in the presence of SO₂ although the reduction of NO_x is suppressed at lower temperatures. The activity for NO_x reduction is high even on the Ag/Al₂O₃ catalyst exposed to a SO₂ (200 ppm)/O₂ (10%)/H₂O (10%) flow for 20 h at 723 K and comparable to that on the fresh Ag/Al₂O₃ catalyst. No crystallized Ag metal and Ag compounds were formed by the SO₂/O₂/H₂O exposure. On the other hand, crystallized Ag₂SO₄ was easily formed when the Ag/Al₂O₃ catalyst was exposed to a SO₂ (200 ppm)/O₂ (10%)/NO (800 ppm)/H₂O (10%) flow for 10 h at 723 K. XRD, SEM and XPS studies showed that the formation of crystallized Ag₂SO₄ results in growing of Ag particles in larger size and lowering the surface content of Ag particles. In addition, the specific surface area of the Ag/Al₂O₃ catalyst decreases from 221 to 193 m²/g. Although the dispersion of Ag particles was decreased by the formation of Ag₂SO₄, the activity for the reduction of lean NO_x was, remarkably, not affected. This suggests that the Ag–alumina sites created by the Ag₂SO₄ formation are still active for the lean catalytic reduction of NO_x. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogen-ion transport numbers in cation exchange membrane determined by emf method

The electromotive force of the membrane cells /Hg/Hg₂SO₄/H₂SO₄, a′/ lon exchange Nafion membrane /H₂SO₄ a″/Hg₂SO₄/Hg/ with different solution concentrations from 0.01 to 2 mol kg^?1 H₂O were measured. On that basis the apparent transport number of H⁺-ions and its dependence on external electrolyte concentration were determined. The dependence was then used for the calculation of both the transport number of H⁺-ions and the water transference numbers. It was found that the apparent transport number of H⁺-ions decreases with increasing external concentration while the transport number of H⁺-ions and the transference number of water remain constant up to concentrations of 1.2 moles kg^?1 h₂O.     

Removal of CO2 and/or SO2 from gas streams by a membrane absorption method

Studies were made on the membrane absorption of CO₂ and/or SO₂ using hydrophobic microporous hollow-fibre (HF) membrane modules. The absorbent liquids used were aqueous solutions of NaOH, K₂CO₃, alkanolamines and Na₂SO₃, flowing on the lumen side of the HF in laminar flow. A semi-empirical correlation was derived for the gas-phase mass-transfer coefficient on the shell side, by including geometrical factors of the HFs and the shell tube in the general correlation for mass transfer. It was found that the CO₂ absorption rate in various aqueous solutions of alkalis and alkanolamines is successfully described by a model based on gas diffusion through the membrane pores subsequent to gas absorption accompanied by chemical reaction. The simultaneous membrane absorption of SO₂ and CO₂ was also studied using aqueous Na₂SO₃ solution, the selective removal of SO₂ to CO₂ being successfully achieved when both the liquid flow rate and solute concentration are low. This suggests that this membrane absorption method provides an energy saving process for SO₂ removal from flue gases.