Removal of Elemental Mercury from Simulated Flue Gas by Combining Non-thermal Plasma with Calcium Oxide

Mercury emission from coal combustion has been the fourth biggest pollutant in China, following the dusts, SO₂ and NO_X. The technology of non-thermal plasma has been widely studied for oxidizing gaseous elemental mercury at low temperature. In this paper, a new method of combining non-thermal plasma with calcium oxide was proposed to remove elemental mercury from simulated flue gas. The effects of non-thermal plasma, input energy, combination mode of plasma and calcium oxide on Hg⁰ removal were investigated in a wire-cylinder non-thermal plasma reactor, whose energy was supplied by a high voltage alternating current power. The peak voltage and energy of the non-thermal plasma were measured by an oscilloscope and a high voltage probe (1000:1). The results showed that most of Hg⁰ was converted to oxidized mercury in simulated flue gas by non-thermal plasma treatment. The Hg⁰ removal efficiency of CaO was improved remarkably strengthened by the non-thermal plasma, which was closely related to input energy, and the maximum mercury removal efficiency was about 80 % at an optimal input energy. Through temperature-programmed decomposition and desorption and energy dispersive spectroscopy analysis, the majority of mercury species on CaO surface were Hg₂O and HgO₃ rather than HgO. Therefore, it can be concluded that O₃ plays an important role in Hg⁰ oxidation under the condition of non-thermal plasma.     

Enhanced activity and SO2 resistance of Co-modified CeO2-TiO2 catalyst prepared by facile co-precipitation for elemental mercury removal in flue gas

The Co-modified CeO₂-TiO₂ catalyst prepared by facile co-precipitation was used for efficient elemental mercury oxidation in flue gas. Results indicated that Co doping greatly enhanced the activity and SO₂ resistance of the CeO₂-TiO₂ catalyst. In the presence of 5% O₂, 500 ppm NO, 800 ppm SO₂ and 3% H₂O at 200 °C, the Hg⁰ removal efficiency of CeCo₃/Ti could maintain at about 87% for a relatively long time. Characterizations of catalysts (BET, XRD, Raman spectroscopy, TEM, H₂-TPR, O₂-TPD, XPS, TG-MS and SO₂-DRIFTS) were carried out to reveal the mechanism of Co modification on the redox ability, SO₂ resistance and resultant mercury oxidation removal performance of catalyst. It was found that an interaction of Ce with Co promoted the dispersion of CeO₂, increased chemisorbed oxygen concentration, and improved the oxygen storage capacity and the reducibility of catalyst, which was beneficial to the improvement of Hg⁰ oxidation removal. Hg⁰ would adsorb onto the catalyst and react with surface active oxygen species replenished by gas-phase O₂ to be oxidized via Mars-Maessen mechanism. SO₂ consumed the surface active oxygen species and resulted in the reduction of Ce⁴⁺ to Ce³⁺, which induced the deactivation of catalyst. The introduced Co in CeO₂-TiO₂ catalyst exerted the function of protecting Ce⁴⁺ from being poisoned by SO₂ and thus promoted the sulfur resistance and Hg⁰ removal performance of the catalyst in the presence of SO₂.     

Experimental Study on Demercurization Performance of Wet Flue Gas Desulfurization System

The demercurization performance of wet flue gas desulfurization (WFGD) system was investigated by measuring mercury concentrations at the inlet and outlet of WFGD system with a QM201H mercury analyzer. The selected desulfurizer included NH₃·H₂O, NaOH, Na₂CO₃, Ca(OH)₂ and CaCO₃. The influences of adding oxidant and coagulant such as KMnO₄, Fenton reagent, K₂S₂O₈/CuSO₄ and Na₂S into desulfurization solutions were also studied. The results show that elemental mercury is the main component of gaseous mercury in coal‐fired flue gas, and the proportion of oxidized mercury is less than 36%. Oxidized mercury could be removed by WFGD system efficiently, and the removal efficiency could amount to 81.1%–92.6%. However, the concentration of elemental mercury slightly increased at the outlet of WFGD as a result of its insolubility and re‐emission. Therefore, the removal efficiency of gaseous mercury is only 13.3%–18.3%. The mercury removal efficiency of WFGD system increased with increasing the liquid‐gas ratio. In addition, adding KMnO₄, Fenton reagent, K₂S₂O₈/CuSO₄ and Na₂S into desulfurization solutions could increase the mercury removal efficiency obviously. Various additives have different effects, and Na₂S is demonstrated to be the most efficient, in which a mercury removal efficiency of 67.2% can be reached.     

Oxidization of SO2 by Reactive Oxygen Species for Flue Gas Desulfurization and H2SO4 Production

A strong ionization dielectric barrier discharge was used to produce a high concentration of reactive oxygen species that were then injected into a simulated flue gas in a duct to remove SO₂ by oxidation. Sulfuric acid (H₂SO₄) was produced through the following two reactions: (1) O₃ oxidation of SO₂–SO₃, which then reacted with H₂O to produce H₂SO₄; and (2) reaction of O₂ ⁺ with H₂O to produce ·OH radicals, which then rapidly and non-selectively oxidized SO₂–H₂SO₄. When the molar ratio of reactive oxygen species to SO₂ was 4:1, the SO₂ removal efficiency was 94.6%, the energy consumption per cubic meter of flue gas was 13.3 Wh/m³, the concentration of recovered H₂SO₄ was 4.53 g/l, and the H₂SO₄ recovery efficiency was 28.8%. The H₂O volume fraction in the simulated flue gas affected the SO₂ removal efficiency, whereas the O₂ and CO₂ volume fractions did not. These results prove that oxidation by reactive oxygen species is a feasible method for flue gas desulfurization.     

Non-Thermal Plasma Assisted Regeneration of Acetone Adsorbed TiO2 Surface

Improvement of indoor air quality regarding volatile organic compounds (VOCs) requires the development of innovative oxidation processes. This paper investigates the coupling of a metal oxide sorbent with non-thermal plasma (NTP) in an especially designed reactor. TiO₂ was selected as model sorbent and acetone was used as model VOC. The analyses of gas phase species at the reactor downstream have been performed using FTIR spectroscopy. In a first step, acetone adsorption on TiO₂ surface under dry air was characterized in terms of total amount adsorbed, as well as reversibly and irreversibly adsorbed fractions. Obtained results were compared and discussed with literature in terms of acetone reactive adsorption on TiO₂ surface. Mesityloxide was proposed as the major compound in the irreversibly adsorbed fraction. In a second time, acetone saturated TiO₂ surface was exposed to NTP surface discharge. Irrespectively of the injected power, <30 % of the initially adsorbed acetone has been recovered as CO, CO₂ and desorbed acetone. Finally, thermal desorptions have been performed. They evidenced that (1) NTP treatment modifies the nature of the adsorbed organic species, (2) mineralization rate is considerably improved. Based on desorbed species temporal profile analysis, carboxylates and more especially formates are suggested as major adsorbed species after NTP treatment (P_inj > 0.2 W). This hypothesis has been evaluated and confirmed. This paper finally evidenced that NTP can be used as an efficient pretreatment technique to promote the mineralization of adsorbed acetone for further thermal treatment.     

柠檬烯和柠檬烯氧化物与硫酸的非均相反应动力学

主要对天然挥发性有机物柠檬烯和柠檬烯氧化物在30%-80% (w)硫酸表面的非均相吸收反应进行了研究, 借以评估天然挥发性有机物与大气环境中的酸性气溶胶的反应活性. 采用自行搭建的配以单光子激光电离飞行时间质谱的湿壁流动反应管的设备对柠檬烯及其氧化物在硫酸表面的非均相吸收动力学进行了测定,计算了稳态摄取系数(γ). 实验结果表明, 柠檬烯氧化物在硫酸表面比只含有双键的柠檬烯的反应活性高, 室温下柠檬烯氧化物在30%-50% (w)硫酸上对应的稳态摄取系数是(7.100±0.023)×10^-5-(8.150±0.162)×10^-3. 此外, 还利用气相色谱-质谱(GC-MS)联用和电喷雾电离质谱(ESI-MS)对柠檬烯氧化物与硫酸的体相反应产物进行了研究, 产物包括单萜烯、松油醇、水合萜二醇和水合萜二醇二硫酸酯. 其中, 水合萜二醇二硫酸酯作为有机硫酸酯的一种, 能够改变气溶胶的吸湿性, 增强云凝结核的活性, 对于大气中灰霾的形成可能有明显的促进作用.     

Thermal analysis of iron(II) sulphate heptahydrate in air

Iron(II) sulphate hydrates (hexa- through mono-) have been prepared and their thermal decomposition behaviours have been studied in air by isothermal and dynamic thermal analysis methods. The results show that their behaviours are similar to that of the heptahydrate. The stepwise loss of water molecules is accompanied by oxidation. Under a restricted supply of oxygen, the anhydrous sulphate is oxidized directly to Fe₂O(SO₄)₂ without the formation of Fe(OH)SO₄. When free exchange with oxygen is allowed, Fe(OH)SO₄ is formed, which in turn decomposes to Fe₂O(SO₄)₂. The decomposition of Fe₂(SO₄)₂ to iron(III) oxide and sulphur oxides appears to occur via two independent paths — one direct and other through iron(III) sulphate.     

Oxidation of SO2 to sulfate in sea salt aerosols

Summary In laboratory-scale experiments sea salt particles are exposed to SO₂ at a temperature of 22°C and relative humidities of 40, 60 and 80%; the SO₂ gas concentration is fixed to 0.2, 0.5 and 1.0 ppm (v), respectively. In further test series NO₂ is added to the gas phase. As kinetic data the capacity values of the sea salt particles (mg formed sulfate/g dry aerosol) are determined as function of time and from this the reaction rates (mg formed sulfate/g dry aerosol and minute) are calculated in dependence of the yield. The relative humidity (r.h.) has proved to be a decisive reaction parameter. For example, the rate (at a reaction time of one hour) increases at a SO₂ concentration of 0.5 ppm (v) from 0.01 to approx. 0.1 mg SO ₄ ^2– /g·min, if the r.h. will increase from 40 to 80%. However, the gas concentration has only an importance at high humidities (where the reaction takes place in droplets) for the sulfate formation in sea salt aerosols. If the SO₂ concentration is reduced from 1.0 to 0.2 ppm (v) at a r.h. of 80%, the rate will be decreased from 0.2 to about 0.07 mg SO ₄ ^2– /g·min; however, at a r.h. of 60% from 0.075 to 0.04 mg SO ₄ ^2– /g·min. As an increased sulfate formation but no nitrate formation can be detected when NO₂ is added to the gas phase, it can be assumed that SO₂ is oxidized in the electrolyte layer around the sea salt particles whereas NO₂ is reduced. If NO₂ (SO₂:NO₂=1:1) is added to the gas phase, the rate — for example at a r.h. of 40% — will be increased from 0.01 to 0.24 mg SO ₄ ^2– /g·min.     

Kinetics of Reactions between Some Compounds from the Three-Component Silver -Oxygen -Sulfur System

Reaction between Ag₂O and SO₂ gives silver and Ag₂SO₄. Heating Ag₂O/Ag₂S mixtures comprising between 66.67 to 100.00 mol % of oxide, at forced flow of inert gas, gives only silver.     

Sequestration of supercritical CO2 by mercury oxide

HgCO₃·2HgO (mercury oxide carbonate), along with partly unreacted reactants, was obtained by exploring the behaviour of the Hg₂Cl₂/HgO binary system in supercritical CO₂ (scCO₂) at 200°C, 22000 kPa in the presence and absence of water, using a self-made laboratory-scale system. The reaction of pure HgO with scCO₂ aimed at the synthesis of HgCO₃ (mercury carbonate), also yielded the same product. Meanwhile, with a small amount of water present in the Hg₂Cl₂/HgO-scCO₂ system, at 200°C, 22000 kPa, the mineral terlinguaite (Hg₄O₂Cl₂) was obtained instead of mercury oxide carbonate. Repeating this reaction under the same conditions, but in the absence of CO₂, again resulted in the synthesis of terlinguaite, leading to the assumption that the scCO₂ had no influence on the synthesis of terlinguaite. This study reveals a new moisture-free laboratory method and conditions for the permanent fixation of CO₂ by HgO. This method bears two benefits: 1) it can be introduced to reduce the Hg content in flue gas and fly ash emitted from coal-burning power plants and municipal waste incinerators; 2) it can contribute to CO₂ mineralisation in montroydite (HgO) geological formations as mercury oxide carbonate.     

Mechanistic insights into the reaction of CF3CCl3 with SO3: Theory and experiment

Reaction mechanism of 1,1,1-trifluorotrichloroethane (CF₃CCl₃) and sulphur trioxide (SO₃) in the presence of mercury salts (Hg₂SO₄ and HgSO₄) was studied applying the density functional theory (DFT) at the UB3LYP/6-31+G(d,p) level. It was found that this reaction occurs in the free radical chain path as follows: mercury(I) sulphate free radical is generated by heat, causing CF₃CCl₃ to produce the CF₃CCl₂ free radical which reacts with SO₃ leading to the formation of CF₃CCl₂OSO₂ decomposing into CF₃COCl and SO₂Cl. The SO₂Cl free radical triggers CF₃CCl₃ to regenerate CF₃CCl₂ which recycles the free radical growth reaction. This elementary reaction has the highest energy barrier and it is therefore the rate control step of the whole reaction path. Experiment data can confirm the existence of the mercury(I) salt free radical and the free radical initiation stage. So, mercury salts play the role of initiators not that of catalysts. The results agree well with our hypothesis.     

Reactions of CoS1.023 and Co3O4 with air and air/SO2 mixtures

It was reported in literature, that CoS_1+y oxidizes to CoO only, although it appears from Co-S-O predominance phase diagrams, that CoSO₄ is stable phase at partial pressures of SO₂ typical for sulfides oxidation. The experiments with CoS_1.023 oxidation with the air and the air/SO₂ gas mixture described in this paper, reveal that CoSO₄ phase is a product of such oxidation. However, the quantity of CoSO₄ is only of 1.4% of total cobalt content in the sample oxidized with the air and of 5.6-10.8% for oxidation with the air/SO₂ gas mixture. It is probably due to CoO layer, formed on CoS_1.023 grain's core, which results in hindering of oxidation after several minutes during the process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low Temperature Diesel Particulate Filter Regeneration by Atmospheric Air Non-thermal Plasma Injection System

An experimental study of the regeneration of diesel particulate filter (DPF) was conducted through the use of a self-designed Non-thermal plasma (NTP) injection system with an experimental temperature of 20–300 °C, with atmospheric air being used as the gas source. The results revealed that the PM could be broken down into CO and CO₂ by NTP, through a discharge reaction of the NTP reactor. As the temperature increases, the mass of C₁ (mass of C in CO) showed an overall declining trend. Interestingly, the mass of C₂ (mass of C in CO₂) and C₁₂ (the sum of C₁ and C₂) both showed an initial increase, followed by a decrease. The peak mass of C₁₂ appears at 150 °C, and both axial and radial temperature gradients are less than the limit of DPF temperature gradient at this temperature. In conclusion, DPF can be regenerated by the NTP technology at a lower temperature, which can aid in the avoidance of thermal damage of DPF. The technology boasts a great advantage in adopting atmospheric air as its gas source, which can not only reduce costs, but also is convenient.     

Applicability of microwave induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of mercury in flue gases

The applicability of microwave-induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of the environmentally hazardous element mercury in flue gases has been studied. Microwave induced plasmas have been sustained using both a TM₀₁₀ cavity (Beenakker resonator) and a so-called Surfatron. The analytical figures of merit for mercury in argon and helium discharges with both types of low-power micro-wave discharges have been examined. To determine mercury in artificial stack gases non-mixed argon/nitrogen discharges have been tested using a tangential flow torch design which allows to introduce a metal-loaded nitrogen gas flow as external gas and argon as internal gas. The addition of main flue gas components such as water vapour (concentration <6 g/m³), oxygen (<4% v/v) and carbon dioxide (<15% v/v) decrease the mercury line intensities to a considerable extent. Trace gases (CO, HCl, SO₂, NO) in concentrations typical to waste incineration processes have been found to have no effect on the mercury and the argon line intensities. The detection limit of mercury in nitrogen is 8 g/m³ using the TM₀₁₀ MIP and 10 g/m³ using the Surfatron. As such low detection limits are below the emission limit values of present-day environmental legislation MIP-OES is useful for on-line monitoring of mercury.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Studies on thermal decomposition of electrochemically oxidized glass-like carbon

Glass-like carbon (GC) tiles were electrochemically oxidized in 1 mol·dm^?3 H₂SO₄ solution at a potential of 2.3 V/SCE. The surfaces of the oxidized samples were examined by scanning electron microscopy (SEM). The solid oxidation products were studied by derivatographic (TG, DTG and DTA) and elemental analyses. The solid products of electrochemical oxidation of GC, with the general formula C₈O_4.2H_2.3 were thermolabile and revealed properties similar to those of graphite oxide. They are hydrophylic and their thermal decomposition proceeds in three steps: (i) evaporation of-chemisorbed water (320–400 K), (ii) exothermic decomposition of graphite oxide (370–430 K), and (iii) gradual decomposition of the oxidation products (>430 K).     

FTIR and GC as complementary tools for analysis of corrosive gases

The gas metrology laboratory of the National Metrology Institute of South Africa has developed methodology for the gravimetric preparation of corrosive gas mixtures such as nitric oxide (NO) in nitrogen, as well as sulphur dioxide (SO₂) in nitrogen or synthetic air. Fourier transform infrared (FTIR) spectroscopy has been used to analyse for trace and ultra trace levels of infrared active gaseous species, such as NO, nitrogen dioxide and SO₂ that are difficult to analyse by other means. These corrosive gas mixtures are also analysed using gas chromatography with pulsed helium ionisation detection to complement the work done using FTIR with infrared active impurities. A comparison between the techniques of FTIR, gas chromatography and non-dispersive infrared spectroscopy for corrosive gas analysis is also presented.     

Silanization and non-aqueous electrochemistry of two oxide states on platinum electrodes

When the surface of a Pt electrode is oxidized in aqueous 1 M H₂SO₄ at +0.8 to +2.0 V vs. SSCE for a few seconds to 10 min, disconnected, washed and dried, and placed in CH₃CN solvent, a negative potential scan shows that the surface oxide is reduced in two waves at potentials between?1.2 and?1.6 V vs. SSCE. The combined charge of the two waves amounts to 0.3–2.5 layers of oxide, depending on anodization potential and time. The more easily reduced oxide becomes non-reducible after reaction of the electrode with methyltrichlorosilane. The two oxide waves are interpreted as surface and subsurface oxide layers.     

Use of radiation sources with mercury isotopes for real-time highly sensitive and selective benzene determination in air and natural gas by differential absorption spectrometry with the direct Zeeman effect

A new analytical portable system is proposed for the direct determination of benzene vapor in the ambient air and natural gas, using differential absorption spectrometry with the direct Zeeman effect and innovative radiation sources: capillary mercury lamps with different isotopic compositions (¹⁹⁶Hg, ¹⁹⁸Hg, ²⁰²Hg, ²⁰⁴Hg, and natural isotopic mixture). Resonance emission of mercury at a wavelength of 254 nm is used as probing radiation. The differential cross section of benzene absorption in dependence on wavelength is determined by scanning of magnetic field. It is found that the sensitivity of benzene detection is enhanced three times using lamp with the mercury isotope ²⁰⁴Hg in comparison with lamp, filled with the natural isotopic mixture. It is experimentally demonstrated that, when benzene content is measured at the Occupational Exposure Limit (3.2 mg/m³ for benzene) level, the interference from SO₂, NO₂, O₃, H₂S and toluene can be neglected if concentration of these gases does not exceed corresponding Occupational Exposure Limits. To exclude the mercury effect, filters that absorb mercury and let benzene pass in the gas duct are proposed. Basing on the results of our study, a portable spectrometer is designed with a multipath cell of 960 cm total path length and detection limit 0.5 mg/m³ at 1 s averaging and 0.1 mg/m³ at 30 s averaging. The applications of the designed spectrometer to measuring the benzene concentration in the atmospheric air from a moving vehicle and in natural gas are exemplified.     

高选择性透过SO2气体分离膜研究 Ⅱ.丙基乙烯基亚砜改性聚乙烯醇功能高分子膜的分离性能

 丙基乙烯基亚砜改性聚乙醇功能高分子膜对SO₂,N₂及SO₂-N₂混合气体的渗透性能研究表明,该膜具有高选择透过SO₂的优良性能.透过SO₂的速率随着亚砜基含量的增加而增加,当亚砜基含量为25(mol)％时,经一次分离能使混合气体中SO₂的含量从1.54％提高到78.8％.     

Changes in Pt(111) Two-dimensional Long-range Order Induced by Slow Mercury Adsorption and Alloying

A long-term cyclic voltammetry study of Pt(111) electrode in dilute solutions of mercury sulfate (5 × 10^–8–5 × 10^–7 M Hg₂SO₄ + 0.5 M H₂SO₄) has shown that a slow transformation of Pt(111) surface takes place. This transformation leads to a decrease in the bi-dimensional long-range order of the surface. The interpretation of the process involves the increase in mobility of Pt atoms and surface alloying in the presence of mercury. Similar processes of Pt(111) surface disordering take place in acid solution of copper sulfate with the addition of Hg₂SO₄. The penetration of Hg atoms beneath the Pt(111) topmost layer proceeds when only a fraction of the mercury monolayer is deposited on the electrode surface.