Elemental Mercury In Flue Gas Research Articles

Engineering single-atom Pd sites in ZIF-derived porous Co3O4 for enhanced elementary mercury removal

Engineering metal-based nanoarchitectures and their atomic-scale arrangement is a promising avenue for enhanced mercury adsorbent activities. Interactions between metal single atoms and substrates result in regulated transitions between distinct reaction processes that boost mercury adsorption activity. Herein, a novel sorbent of porous Co3O4 with Palladium atomic dispersed was successfully prepared by one-step pyrolysis of zeolitic imidazolate framework 67 (ZIF-67) precursors. Via engineering single Pd atoms into ZIF-derived Co3O4 (Pd1/Co3O4-ZIF), the strong metal-support interaction (SMSI) activated the reducibility of Co3+ in porous Co3O4 to efficiently adsorb and oxidize Hg0, enhancing its mercury removal efficiency. Specifically, Pd1/Co3O4-ZIF exhibited superior sorption performance for Hg0 over a broad range of temperatures (30–350 °C) and high gaseous hourly space velocity (about 555,500 hr−1) with the average Hg0 removal efficiency higher than 98%. The strategy of constructing atomic active sites on the surface of porous metal-oxide to convert adsorbed Hg0 into HgO is a promising approach to solve the problem that Hg0 in flue gas is challenging to remove. Density functional theory (DFT) calculation further proved that the existence of a single Pd site on the surface of Co3O4 significantly reduced the energy barrier of Hg0 to HgO at the atomic level. This work contributed to a thorough comprehension of the structural and adsorption properties of the ZIF-derived Co3O4 sorbent engineering with a single atom and enabled the efficient capture of elemental mercury in flue gas by such ZIF-derived sorbent.

Dual 2-dimensional CuSe/g-C3N4 nano-heterostructure for boosting immobilization of elemental mercury in flue gas

With the rapid development of Hg0 treatment methods in flue gas, the key challenge at the current stage is the trade-off between adsorbent performance, treatment cost and environmental friendliness. A series of dual 2-dimensional CuSe/g-C3N4 nano-heterostructures (CSCN) were successfully synthesized through an incipient wetness impregnation method followed by in-situ selenization, and further used for gaseous elemental mercury immobilization. The results had shown that the as-synthesized CSCN with CuSe loading ratio of 20% (20CSCN) achieved the maximum mercury removal performance. Up to 95.09% of Hg0 removal efficiency was achieved by 20CSCN under rigorous experimental conditions with the gas hourly space velocity and initial Hg0 concentration of 240000 h−1 and 180 ug/m3, respectively. After a 10 h adsorption test, the equilibrium adsorption capacity of 20CSCN reached 9.113 mg/g. Owing to the generation of dual 2-dimensional heterojunctions, the mercury removal performance of 20CSCN was superior to the contrast 20CSCN(mix) prepared by simply mechanically mixing. Besides, the acidic gases (NO and SO2) in the flue gas will adversely affect the Hg0 capture performance of CSCN, while O2 and CO2 exhibited a neutral effect on the Hg0 capture. Based on the analysis of XPS and TPD results, the chemical reaction rate was the main rate-controlling step and the chemisorption dominated the conversion of Hg0 on heterojunctions, which was in accordance with the Mars-Maessen mechanism. The active Se ligands on the surface of the heterojunction, as the main activity center of chemical reaction, could rapidly capture Hg0 in the flue gas to form stable HgSe. This can effectively avoid the secondary pollution caused by the re-release of Hg0 from Hg-containing waste exposed to the environment, because of its low Hg-leaching characteristic.

Rod-Shaped Bi2S3 Supported on Flaky Carbon Nitride for Effective Removal of Elemental Mercury in Flue Gas

Rod-Shaped Bi₂S₃ Supported on Flaky Carbon Nitride for Effective Removal of Elemental Mercury in Flue Gas

Conversion of 2H MoS2 to 1 T MoS2 via lithium ion doping: Effective removal of elemental mercury

In this work, a simple high-temperature calcination method was used to produce metallic molybdenum disulfide (1 T-LixMoS2). Experiments and simulations show that 1 T-MoS2 has stronger surface activity and enhances the adsorption capacity of Hg0, thereby effectively removing elemental mercury (Hg0) in coal-fired flue gas. Sample ML-100 could maintain a mercury removal efficiency of approximately 92% after 6-cycle experiments, and approximately 97% efficiency could be maintained throughout a long-term experiment. The proposed method converts the 2H phase to the 1 T phase by doping commercial MoS2 with lithium ions, thereby improving the removal efficiency of elemental mercury in the flue gas.

Adsorption of elemental mercury in flue gas using biomass porous carbons modified by microwave/hydrogen peroxide

In order to enhance the mercury adsorption capacity of bio-char and reduce the potential environmental damage caused by modification methods, a clean modification method combining microwave activation and H2O2 impregnation of bio-char was proposed in this paper. The effects of hydrogen peroxide concentration, reaction temperature and flue gas components (NO/O2/SO2/H2O) on Hg0 removal efficiency of the modified samples were studied. The physicochemical properties of the biomass porous carbons were analyzed by various characterization methods (i.e. BET, SEM, FTIR, XPS). The results show that the biomass porous carbons, WSW10 and RSW10, exhibit the best Hg0 adsorption performance at 130 ℃. Microwave activation and hydrogen peroxide modification can increase the specific surface area to improve the pore structure of biomass porous carbons. The number of surface functional groups of biomass porous carbons can be increased by the H2O2 impregnation, which can improve the Hg0 removal performance of biomass porous carbons. O2 and NO contribute to the removal of Hg0. With the increase of SO2 or H2O concentration, the Hg0 removal efficiency decreases. The results of kinetic simulation show that the pseudo-second-order model can well fit the mercury adsorption process of the modified biomass porous carbons, and chemisorption occurs on the surface of the adsorbent. The C-O functional groups and chemically adsorbed oxygen play an important role in the Hg0 removal.

Detection of elemental mercury in flue-gas by a chemiresistive SnS–SnO2 ccomposite ssensor

Due to bioaccumulation and globe atmosphere migration of elemental mercury, the source emission control of elemental mercury has attracted great attention. The elemental mercury sensor paves a new way for the detection of elemental mercury in the atmosphere. We introduced an elemental mercury sensor with high response and fast response-recovery features to elemental mercury based on the SnS–SnO2 composite. The mixed stacking SnS nanosheets and SnO2 nano-octahedrons composite were synthesized. The sensor showed a desired response of 14 to 3 mg/m3 elemental mercury with an ultra-fast response time of 40 s and a recovery time of 30 s. Besides, the sensor exhibits a high selectivity of various common interfering gases in the flue-gas like CO, SO2, NH3, and NO2. The detailed sensing mechanism was discussed at the molecular level by the energy band theory. The outstanding sensing properties of the SnS–SnO2 composite based elemental mercury sensor could be applied for the fast detection of elemental mercury in the flue gas.

Elimination of elemental mercury in flue gas by Arachis hypogaea Linn. shell generated activated carbon.

It is very necessary to produce bio-activated carbon for special use with easy procedure and low cost. One kind of huge surface area microporous bio-material was successfully prepared from agricultural residues (peanut shell, Arachis hypogaea Linn.) and beneficially applied to control elemental mercury (Hg0) in simulated coal-fired flue gas in this study. The possible effects of experimental factors including activator, reaction temperature, and flue components were investigated. The physicochemical properties of the prepared adsorbents were characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). The results indicated that the peanut shell activated carbon presented excellent Hg0 removal efficiency near 90% at 150°C. The characterization analysis indicated that the removal characteristics were governed by both physical adsorption and chemical adsorption. The chemisorbed mercury on the activated carbon was mainly distinguished into mercuric chloride (HgCl2) and mercuric oxide (HgO). The presence of C-Cl and O* promoted Hg0 into HgCl2 and HgO. Zinc chloride could not only improve the micropore quantity of activated carbon but also have remarkably positive effects on the elemental mercury removal. This study provided a practical and easy preparation method of bio-activated carbon for Hg0 removal with low cost. Graphical Abstract.

Removal of elemental mercury in flue gas by Cu-Fe modified magnetosphere from coal combustion fly ash

Magnetospheres (MF) obtained from fly ash by magnetic separation method has low mercury removal efficiency and weak magnetism in gas phase mercury removal. In this paper, magnetospheres were modified with Cu and Fe compounds by sol-gel method. The Hg0 removal performance of Cu-Fe modified MF were investigated in a fixed bed reactor, and the effect of calcination temperature and flue gas composition on magnetism of the modified MF were examined. The Hg0 removal efficiency of Cu(6)Fe-MF-400, which was obtained with 6 wt% Cu loading on MF, Cu:Fe atomic ratio being 1:2 and calcined at 400 °C, reaches 97% at 200 °C in the atmosphere of N2, CO2 and O2. Specific magnetic susceptibility of Cu(6)Fe-MF-400 enhances significantly from 41 to 52 cm3/g. The effect of flue gas composition on Hg0 removal indicated that HCl significantly shortens the required time to achieve 80% efficiency of Hg0 removal, while NO and SO2 prolong this required time. In the reaction temperature range of 100–350 °C, the required time decreases with the increase of temperature, and it is three seconds at temperature of 300 °C. The magnetism of Cu(6)Fe-MF is significantly weakened in atmosphere containing HCl or SO2, but strengthened in NO. Cu(6)Fe-MF still shows stable Hg0 removal efficiency and magnetism after reaction for 10 h. Cu-Fe modified not only make MF to be used for mercury control of coal-fired flue gas, but enables reuse of coal-fired waste-MF, which is in line with the principles of circular economics.

Recent developments on gas–solid heterogeneous oxidation removal of elemental mercury from flue gas

Mercury is a toxic and persistent environmental pollutant which has been recognized as a global threat to human health and our ecosystem because mercury bio-accumulates in the food chain and can be transformed into the more neurotoxic methylmercury. Among current and emerging abatement technologies for elemental mercury in flue gas, gas–solid heterogeneous oxidation is nowadays gaining increasing attention due to several inherent advantages. The catalysts and adsorbents are key materials that control the heterogeneous catalytic oxidation and adsorption of Hg0 from flue gas. Here we present a review of the recent developments on several catalysts and adsorbents, including noble metal-based catalysts, non-noble metal-based catalysts (transition metal oxides and selective catalytic reduction catalysts), activated carbon/coke-based sorbents, biochar-based sorbents, fly ash-based sorbents, mineral material-based sorbents and other novel catalysts. The key process parameters and kinetic reaction mechanisms and advantages and disadvantages of various emerging catalysts/adsorbents and technologies of Hg0 removal are described in detail.

Removal of Elemental Mercury in Flue Gas with H2O2 Solution Catalyzed by Zn-Doped BiFeO3

Magnetic Zn-doped BiFeO3 catalyst was synthesized by the tartaric acid sol–gel method, and its characteristics were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller technique, and vibration sample magnetometer. The catalytic activity of Zn-BiFeO3 was evaluated for activating H2O2 to oxidize elemental mercury in a self-designed bubbling reactor, and the effects of the Zn doped ratio in catalyst, catalyst dosage, H2O2 concentration, solution pH, and reaction temperature on the removal of Hg0 were also investigated systematically. The result indicated that the removal efficiency of Hg0 achieved 81% under the optimum conditions, in which the Zn doping ratio was 0.2, H2O2 concentration was 0.15 mol L–1, catalyst dosage was 0.3 g L–1, solution pH was 6, reaction temperature was 50 °C, and Hg0 concentration was 50 μg/m3. Moreover, it was demonstrated indirectly that •OH and HO2• were the active species when Hg0 was oxidized to oxidation state mercury using H2O2 ...

Promotional effect of Mo addition on CoOX/Ti-Ce catalyst for oxidation removal of elemental mercury in flue gas

To enhance the catalytic activity for elemental mercury (Hg0) oxidation and SO2 resistance of catalyst, Mo was applied to modify the CoOX/Ti-Ce (Co/TiCe) catalyst for better performance. The results showed that CoMo5/TiCe had the highest activity for Hg0 oxidation in the wide temperature window of 100–400 °C in the presence of 10 ppm HCl and 6% O2. NO exhibited insignificant effect on Hg0 oxidation. SO2 and H2O were found to inhibit Hg0 oxidation. Hg0 oxidation by HCl over CoMo5/TiCe catalyst mainly occurred through the Eley-Rideal mechanism, where gas-phase or weakly-bonded Hg0 reacted with surface chlorine species originated from adsorbed HCl to form Hg2+. SO2 could obstruct the generation of surface active chlorine species, thus inhibiting Hg0 oxidation. Compared with Co/TiCe, CoMo5/TiCe showed better resistance to SO2 and H2O for Hg0 oxidation. In the presence of 200 ppm SO2, CoMo5/TiCe achieved Hg0 oxidation efficiency of 96.1% and a simultaneous NO conversion efficiency of 42.9% at 300 °C, showing better performance than Co/TiCe. The physicochemical properties of the catalysts were examined by BET, XRD, Ranman spectroscopy, H2-TPR, XPS and EDS techniques to reveal the effect of Mo addition on the catalytic performances. It was found that an interaction of Mo with Co promoted the dispersion of Co3O4, increased the Co2+ and Oα concentration and enhanced the reducibility of catalyst, which contributed to the improvement of Hg0 oxidation activity. Moreover, the SO2 resistance of catalyst was enhanced by suppressing the reaction between the catalyst and SO2 due to Mo addition.

Removal of elemental mercury in flue gas at lower temperatures over Mn-Ce based materials prepared by co-precipitation

A series of Mn-Ce based materials were synthesized by co-precipitation method and were examined for mercury removal at lower temperatures (50–250°C) in the absence of HCl. The effect of preparation conditions (metal oxides and calcination temperature) and reaction conditions (reaction temperature and gas constituents) was investigated. Results showed that Mn0.1Ce0.2Al-400 was found to be the most active catalyst for mercury removal, achieving around 96% Hg0 removal efficiency in the presence of 6% O2 at 150°C. Higher calcination temperature could result in the grain growth and particle agglomeration, thus decreasing the activity. The optimum reaction temperature for mercury removal over Mn0.1Ce0.2Al-400 was about 150°C. NO was observed to promote mercury removal over Mn0.1Ce0.2-400 catalyst but SO2 generally suppressed it. Various techniques (BET, XRD, TEM, H2-TPR and XPS) were used to characterize the samples. The results substantiated the formation of a composite material consisted of high concentration of amorphous MnOX and nano-crystalline CeO2 supported by Al2O3, which might lead to an enhanced interaction of Ce with Mn. Moreover, the adsorbed Hg0 mainly interacted with the lattice oxygen in MnO2 to form HgO which was replenished by gas-phase O2. CeOx could facilitate the activation and transfer of oxygen and consequently improve the activity for oxidation removal of Hg0 over manganese oxides further.

Comparative study of Co/TiO2, Co–Mn/TiO2 and Co–Mn/Ti–Ce catalysts for oxidation of elemental mercury in flue gas

The Co–Mn/Ti–Ce catalyst prepared by sol–gel and impregnation method was evaluated for catalytic oxidation of Hg0 in the simulated flue gas compared with Co/TiO2 and Co–Mn/TiO2. The results showed that Co–Mn/Ti–Ce catalyst exhibited higher catalytic activity (around 93% Hg0 removal efficiency in the temperature of 150 °C with 6% O2, 400 ppm NO, 200 ppm SO2 and 3% H2O) than Co/TiO2 and Co–Mn/TiO2. Based on the characterization results of N2 adsorption–desorption, XRD, UV–Vis, XPS, H2-TPR and Hg-TPD, it could be concluded that the lower band gap, better reducibility and mercury adsorption capability and the presence of Co3+/Co2+, Mn4+/Mn3+ and Ce4+/Ce3+ redox couples as well as surface oxygen species contributed to the excellent Hg0 oxidation removal performance. In addition, well dispersion of active components and a synergetic effect among Co, Mn and Ce species might improve the activity further. A Mars–Maessen mechanism is thought to be involved in the Hg0 oxidation. The lattice oxygen derived from MnOx or CoOx would react with adsorbed Hg0 to form HgO and the consumption of lattice oxygen could be replenished by O2. For Co–Mn/Ti–Ce, MnOx−1 could be alternatively reoxidized by the lattice oxygen derived from adjacent CoOx and CeOx which is beneficial to the Hg0 oxidation.

Research on the effect of additives on mercury speciation in coal‐fired derived flue gas

In order to study the effect of additives on mercury speciation in coal‐fired derived flue gases, the additives experiment was conducted in one 110MW coal‐fired power plant, the additives including calcium bromide and iron oxide. Taking advantage of the Ontario Water Act (OHM) and sorbent tube method, mercury at the denitration (SCR) entrance and export and desulfurization (WFGD) entrance was sampled and the variation of mercury before and during adding the additives was analyzed. The results show that the additives of calcium bromide can oxidize elemental mercury and contribute to increasing the proportion of divalent mercury, and in denitration device, the ratio of divalent mercury in flue gas shows an increasing trend along with the increasing of calcium bromide. However, there is no such trend appearing at desulfurization entrance. In addition, the additives of iron oxide have no obvious effect on the oxidation of elemental mercury in flue gas. Adding a small amount of iron oxide has little effect on the form of mercury, and may even reduce the proportion of divalent mercury. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1566–1574, 2016

Catalytic oxidation removal of gaseous elemental mercury in flue gas over niobium‐loaded catalyst

Nb‐Co‐Ce/Al2O3 catalysts prepared by impregnation, sol‐gel method, and co‐precipitation were examined for elemental mercury (Hg0) oxidation in a simulated coal combustion flue gas. The catalysts were characterized by SEM‐EDS, BET, XRD, FTIR, and XPS techniques. The performances of different niobium‐loaded catalysts on Hg0 oxidation efficiency with regard to preparation method, assistant, reaction temperature, and typical individual flue gas were investigated. The results showed that the Hg0 oxidation efficiency performed at the highest value for niobium‐loaded catalysts at 523 K. SO2 was observed to have a negative effect on Hg0 oxidation. The niobium‐loaded catalysts prepared by the sol‐gel method and co‐precipitation exhibited higher Hg0 oxidation efficiency than that prepared by impregnation, due to higher specific surface area and more exposure of active sites. However, it also results in these catalysts being affected by SO2 more easily. An enhancing effect of O2 was observed and an addition of HCl would promote the Hg0 oxidation further. Results also indicated that synergistic effects between NbOx, CoOx, and CeOx could promote the sustainable capacity of Hg0 oxidation for Nb‐Co‐Ce/Al2O3 catalysts. Hg0 oxidation over Nb‐Co‐Ce/Al2O3 catalysts is thought to follow a Mars‐Maessen mechanism in which lattice oxygen derived from NbOx would react with absorbed Hg0.

Kinetics study on the capture of elemental mercury in flue gas by KI‐impregnated clays

AbstractTo understand the capture of elemental mercury (Hg0) on potassium iodide‐impregnated clays, a variety of kinetic models including pseudo‐first‐order, pseudo‐second‐order, Elovich, and intraparticle diffusion models were used to analyze the experimental data and discuss the mechanism. A strong correlation was observed between the pseudo‐second‐order kinetic model and the experimental data for a range of parameters (KI loading, adsorption temperatures, and O2 concentrations). This suggests that chemisorption may be a rate‐limiting mechanism during the adsorption process on KI clays. Further, the results of the pseudo‐first‐order model and the intraparticle diffusion model both indicate that mass transfer limitations should not be ignored during the initial stage of adsorption. Thermodynamic investigation shows that the adsorption reaction of Hg0 on the KI clays is inherently spontaneous and endothermic, corresponding to a process involving both physisorption and chemisorption, and the chemisorption is the dominant adsorption.

A study on removal of elemental mercury in flue gas using fenton solution

A novel technique on oxidation-separation of elemental mercury (Hg0) in flue gas using Fenton solution in a bubbling reactor was proposed. The effects of several process parameters (H2O2 concentration, Hg0 inlet concentration, Fe2+ concentration, solution temperature, solution pH, gas flow) and several flue gas components (NO, SO2, O2, CO2, inorganic ions and particulate matters on Hg0 removal were studied. The results indicate that H2O2 concentration, Fe2+ concentration, solution pH and gas flow have great effects on Hg0 removal. Solution temperature, Hg0, NO, SO2, CO32− and HCO3− concentrations also have significant effects on Hg0 removal. However, Cl−, SO42−, NO3−, O2 and CO2 concentrations only have slight effects on Hg0 removal. Furthermore, reaction mechanism of Hg0 removal and simultaneous removal process of Hg0, NO and SO2 were also studied. Hg0 is removed by oxidation of OH and oxidation of H2O2. The simultaneous removal efficiencies of 100% for SO2, 100% for Hg0 and 88.3% for NO were obtained under optimal test conditions. The results demonstrated the feasibility of Hg0 removal and simultaneous removal of Hg0, SO2 and NO using Fenton solution in a bubbling reactor.

Mercury emission characteristics from coal combustion by supplying oxygen and carbon dioxide with limestone injection

Coal combustion experiments at a lab-scale furnace with a capacity of 10,000kcal/h were conducted in order to investigate the speciation changes and mass distribution of mercury with limestone injection in conditions of air and oxy-fuel combustion. Mass distribution and concentration of mercury in flue gas at oxy-fuel combustion were higher than those at air combustion. With limestone injection, the reduction of mercury from flue gas by adsorption into limestone could be clearly observed at both air and oxy-fuel combustion conditions. In the speciation of mercury, the particulate mercury in flue-gas was dominant with around 50% and the portion of elemental mercury was higher than that of oxidized mercury as shown at other coal combustion cases. At oxy-fuel combustion, most of particulate mercury seemed to be bounded to limestone more easily in comparison to air combustion, so that the elemental mercury in flue gas resulted to be more dominant at oxy-fuel combustion.

Kinetic interpretation on mercury oxidation and transformation in simulated flue gases

The approach coupled with computation fluid dynamics (CFD) and complex chemical kinetic computation to predict the oxidation of the elemental mercury in flue gas was discussed in this paper. According to the oxidation mechanism of the elemental mercury, the reactions which were in close relationship with mercury oxidation were determined by the sensitivity analysis method. The mercury oxidation process was simulated under the atmospheric pressure condition with different flue-gas compositions. The three-dimensional concentration distribution of mercury within the cylindrical flue duct and the impact of the temperature, concentration of Cl2, HCl, NO, and O2 on the mercury oxidation were also obtained. The simulation results were compared with the experimental results of Mamani-Paco and Widmer. The results show that coupling computation solves the problem of the combination of the CFD with the complex kinetic mechanism. The promotion effect of Cl2 on the oxidation of elemental mercury is much better than that of HCl. The temperature window ranged from 950 to 1,150 K for the higher oxidizing rate of the elemental mercury was determined. The slight enhancement of NO on mercury oxidization was observed which was controlled by the competition between two reaction pathways. O2 weakly promotes homogeneous Hg oxidation, especially under the condition of high temperature. 1.1, 2.6 and 3.1 % of mercury was oxidized in the presence of 0, 4 and 16 % O2 at 600 K, respectively. However, 12.5, 22.5 and 26.0 % of Hg oxidation has been obtained at 1,200 K.

Oxidative Removal of Elemental Mercury in Flue Gas by DBD Discharge Plasma

Oxidation of gas phase elemental mercury (Hg0) in the simulated flue gas by DBD plasma under atmospheric pressure and ambient temperature (298 K) was conducted. Experimental results indicated that the oxidative efficiency of Hg0 increased with O2 content, the residence time of flue gas in reactor and the applied voltage. The oxidation efficiency of Hg0 reached over 96% under the applied voltage of 11 kV and the residence time of 0.24 s when the O2 content in flue gas was 20%, and the corresponding energy efficiency was at about 14.1 μg kJ-1. It was noted that the oxidation efficiency of Hg0 could still reach 80% when the O2 content in flue gas was only 4% (near the actual O2 content in flue gas of coal-fired boilers). The experimental results indicated that DBD plasma was one of the efficient technologies for purification of Hg0 vapor industrial flue gas.