Yongfu Guo

Catalytic Oxidation of Elemental Mercury over the Modified Catalyst Mn/α-Al2O3 at Lower Temperatures

In order to facilitate the removal of elemental mercury (Hg(0)) from coal-fired flue gas, catalytic oxidation of Hg(0) with manganese oxides supported on inert alumina (alpha-Al2O3) was investigated at lower temperatures (373-473 K). To improve the catalytic activity and the sulfur-tolerance of the catalysts at lower temperatures, several metal elements were employed as dopants to modify the catalyst of Mn/alpha-Al2O3. The best performance among the tested elements was achieved with molybdenum (Mo) as the dopant in the catalysts. It can work even better than the noble metal catalyst Pd/alpha-Al2O3. Additionally, the Mo doped catalyst displayed excellent sulfur-tolerance performance at lower temperatures, and the catalytic oxidation efficiency for Mo(0.03)-Mn/alpha-Al2O3 was over 95% in the presence of 500 ppm SO2 versus only about 48% for the unmodified catalyst. The apparent catalytic reaction rate constant increased by approximately 5.5 times at 423 K. In addition, the possible mechanisms involved in Hg(0) oxidation and the reaction with the Mo modified catalyst have been discussed.

Capture of gaseous elemental mercury from flue gas using a magnetic and sulfur poisoning resistant sorbent Mn/γ-Fe2O3 at lower temperatures

A series of Mn/γ-Fe(2)O(3) were synthesized to capture elemental mercury from the flue gas. Mn(4+) cations and cation vacancies on the surface played important roles on elemental mercury capture by Mn/γ-Fe(2)O(3). Furthermore, the reaction route of elemental mercury oxidization was dependent on the ratio of Mn(4+) cations to cation vacancies. As a result, the capacities of 15%-Mn/γ-Fe(2)O(3)-250 for elemental mercury capture were generally higher than those of 30%-Mn/γ-Fe(2)O(3)-400. SO(2) mainly reacted with ≡Fe(III)-OH and only a small amount of ≡Mn(4+) reacted with SO(2), so the presence of a high concentration of SO(2) resulted in an insignificant effect on elemental mercury capture by 15%-Mn/γ-Fe(2)O(3)-250 at lower temperatures. The capacities of 15%-Mn/γ-Fe(2)O(3)-250 for elemental mercury capture in the presence of 2.8 g N m(-3) of SO(2) were more than 2.2 mg g(-1) at <200°C. Meanwhile, 15%-Mn/γ-Fe(2)O(3)-250 can be separated from the fly ash using magnetic separation, leaving the fly ash essentially free of sorbent and adsorbed HgO. Therefore, 15% Mn/γ-Fe(2)O(3)-250 may be a promising sorbent for elemental mercury capture.

Gaseous Elemental Mercury Capture from Flue Gas Using Magnetic Nanosized (Fe3-xMnx)1-δO4

A series of nanosized (Fe3-xMnx)1-δO4 (x = 0, 0.2, 0.5, and 0.8) were synthesized for elemental mercury capture from the flue gas. Cation vacancies on (Fe3-xMnx)1-δO4 can provide the active sites for elemental mercury adsorption, and Mn(4+) cations on (Fe3-xMnx)1-δO4 may be the oxidizing agents for elemental mercury oxidization. With the increase of Mn content in the spinel structure, the percents of Mn(4+) cations and cation vacancies on the surface increased. As a result, elemental mercury capture by (Fe3-xMnx)1-δO4 was obviously promoted with the increase of Mn content. (Fe2.2Mn0.8)1-δO4 showed an excellent capacity for elemental mercury capture (>1.5 mg g(-1) at 100-300 °C) in the presence of SO2 and HCl. Furthermore, (Fe2.2Mn0.8)1-δO4 with the saturation magnetization of 45.6 emu g(-1) can be separated from the fly ash using magnetic separation, leaving the fly ash essentially free of sorbent and adsorbed Hg. Therefore, nanosized (Fe2.2Mn0.8)1-δO4 may be a promising sorbent for the control of elemental mercury emission.

Significance of RuO2 Modified SCR Catalyst for Elemental Mercury Oxidation in Coal-fired Flue Gas

Catalytic conversion of elemental mercury (Hg(0)) to its oxidized form has been considered as an effective way to enhance mercury removal from coal-fired power plants. In order to make good use of the existing selective catalytic reduction of NO(x) (SCR) catalysts as a cobenefit of Hg(0) conversion at lower level HCl in flue gas, various catalysts supported on titanium dioxide (TiO(2)) and commercial SCR catalysts were investigated at various cases. Among the tested catalysts, ruthenium oxides (RuO(2)) not only showed rather high catalytic activity on Hg(0) oxidation by itself, but also appeared to be well cooperative with the commercial SCR catalyst for Hg(0) conversion. In addition, the modified SCR catalyst with RuO(2) displayed an excellent tolerance to SO(2) and ammonia without any distinct negative effects on NO(x) reduction and SO(2) conversion. The demanded HCl concentration for Hg(0) oxidation can be reduced dramatically, and Hg(0) oxidation efficiency over RuO(2) doped SCR catalyst was over 90% even at about 5 ppm HCl in the simulated gases. Ru modified SCR catalyst shows a promising prospect for the cobenefit of mercury emission control.

Nanosized Cation-Deficient Fe-Ti Spinel: A Novel Magnetic Sorbent for Elemental Mercury Capture from Flue Gas

Nonstoichiometric Fe-Ti spinel (Fe(3-x)Ti(x))(1-δ)O(4) has a large amount of cation vacancies on the surface, which may provide active sites for pollutant adsorption. Meanwhile, its magnetic property makes it separable from the complex multiphase system for recycling, and for safe disposal of the adsorbed toxin. Therefore, (Fe(3-x)Ti(x))(1-δ)O(4) may be a promising sorbent in environmental applications. Herein, (Fe(3-x)Ti(x))(1-δ)O(4) is used as a magnetically separable sorbent for elemental mercury capture from the flue gas of coal-fired power plants. (Fe(2)Ti)(0.8)O(4) shows a moderate capacity (about 1.0 mg g(-1) at 250 °C) for elemental mercury capture in the presence of 1000 ppmv of SO(2). Meanwhile, the sorbent can be readily separated from the fly ash using magnetic separation, leaving the fly ash essentially free of sorbent and adsorbed mercury.

Conversion of elemental mercury with a novel membrane catalytic system at low temperature.

A unique assembly, which integrated membrane delivery for oxidants with catalytic oxidation (MDCOs), was employed to convert elemental mercury (Hg(0)) to its oxidized form at low temperature (around 150 °C). MnO(x) was used as the main catalytic component in MDCOs with Mo and/or Ru to improve the catalytic activity. The MDCOs was proved to be very effective for the conversion of Hg(0) compared with the traditional catalytic oxidation mode (TCO). The analysis of speciation for Hg after catalytic oxidation showed that there was mainly mercury (II) chloride. The addition of transition metals of Mo and Ru obviously improved the conversion of Hg(0) to Hg(2+) and enhanced the activity of the MDCOs at low temperature, and the conversion efficiency of Hg(0) reached 95% with Mo-Ru-Mn catalyst and 8 ppmv HCl. The inhibition of SO(2) to Hg(0) conversion in the MDCOs was insignificant. The Hg(0) removal exceeded 80% even if the concentration of SO(2) reached 1000 ppmv. The results also indicated that the Deacon reaction with the yield of Cl(2) were significantly improved after modified, and MDCOs with Mo-Ru-Mn catalyst can work efficiently at low temperature.

Oxidation and Stabilization of Elemental Mercury from Coal-Fired Flue Gas by Sulfur Monobromide

Sulfur monobromide (S(2)Br(2)) was employed as a task-specific oxidant to capture and stabilize elemental mercury from coal-fired flue gas. Its performances on the removal of Hg(0) were investigated with respect to the gas-phase reaction and particle-involved reactions. It was found that the gas-phase reaction between Hg(0) and S(2)Br(2) was rapid, and the determined second-rate constant was about 1.2(+/-0.2) x 10(-17)cm(3) molecules(-1) s(-1) at 373 K, which was about 30 times higher than that with sulfur monochloride. The pilot tests showed that the presence of fly ash in flue gas can accelerate the removal of Hg(0) significantly. It was predicted that about 90% of Hg(0) removal efficiency can be obtained with 0.6 ppmv S(2)Br(2) and 30 g/m(3) fly ash in flue gas, and the unburned carbon in fly ash played an important role for Hg(0) removal. The fates of S(2)Br(2) and mercury in the process were evaluated, and the product analysis and leaching tests indicated that mercuric sulfide was the main product of the converted Hg(0) by the direct reaction and consequent series reactions, which is more stable and less toxic than other mercury species. Also, the surplus S(2)Br(2) in flue gas could be captured and neutralized effectively by the alkali components in fly ash or FGD liquor, and its hydrolysis products (elemental sulfur and sulfide) were also helpful to the stabilization of mercury. The result indicated that S(2)Br(2) is a promising oxidant for elemental mercury (Hg(0)) oxidation and stabilization for mercury emission control.

Conversion of Elemental Mercury with a Novel Membrane Delivery Catalytic Oxidation System (MDCOs)

In order to overcome the shortcomings of the traditional catalytic oxidation (TCO) mode for the conversion of the trace level of elemental mercury (Hg(0)) in flue gas, we put forward a novel and unique assembly that integrated membrane delivery with catalytic oxidation systems (MDCOs), which combined the controlled delivery of oxidants with the catalytic oxidation of Hg(0). The results show that the demanded HCl for Hg(0) conversion in the MDCOs was less than 5% of that in the TCO mode, and over 90% of Hg(0) removal efficiency can be obtained in the MDCOs with less than 0.5 mg m(-3) of HCl escaped. Meanwhile, the inhibition of SO(2) to Hg(0) catalytic conversion in the MDCOs was also less significant than in the TCO. The MDCOs have high retainability for HCl, which is quite favorable to Hg(0) conversion and HCl utilization. The reaction mechanism on mercury conversion in the MDCOs is discussed. The MDCOs appear to be a promising method for emission control of elemental mercury.

Removal of elemental mercury with Mn/Mo/Ru/Al2O3 membrane catalytic system

In this work, a catalytic membrane using Mn/Mo/Ru/Al2O3 as the catalyst was employed to remove elemental mercury (Hg0) from flue gas at low temperature. Compared with traditional catalytic oxidation (TCO) mode, Mn/Al2O3 membrane catalytic system had much higher removal efficiency of Hg0. After the incorporation of Mo and Ru, the production of Cl2 from the Deacon reaction and the retainability for oxidants over Mn/Al2O3 membrane were greatly enhanced. As a result, the oxidization of Hg0 over Mn/Al2O3 membrane was obviously promoted due to incorporation of Mo and Ru. In the presence of 8 ppmv HCl, the removal efficiency of Hg0 by Mn/Mo/Ru/Al2O3 membrane reached 95% at 423 K. The influence of NO and SO2 on Hg0 removal were insignificant even if 200 ppmv NO and 1000 ppmv SO2 were used. Moreover, compared with the TCO mode, the Mn/Mo/Ru/Al2O3 membrane catalytic system could remarkably reduce the demanded amount of oxidants for Hg0 removal. Therefore, the Mn/Mo/Ru/Al2O3 membrane catalytic system may be a promising technology for the control of Hg0 emission.