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Co-precipitated manganese oxides- based sorbents for mercury and arsenic capture.

Co-precipitated manganese oxides- based sorbents for mercury and arsenic capture. Malgorzata Wiatros-Motyka EPSRC PhD project student

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Co-precipitated manganese oxides- based sorbents for mercury and arsenic capture.

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  1. Co-precipitated manganese oxides- based sorbents for mercury and arsenic capture. Malgorzata Wiatros-Motyka EPSRC PhD project student Grant: EPSRC China Cleaner fossil energy call: EP/G063176/1: Innovative Adsorbent Materials and Processes for Integrated Carbon Capture and Multi-pollutant Control for Fossil Fuel Power Generation Supervisors: Prof. Colin Snape and Dr Trevor Drage

  2. Hg and As – few facts • Naturallyoccurring elements, • In ppm in coals, but their emissions are growing environmental problem, • No legislation in EU setting legal limits for Hg, e.g. in Canada 70% must be removed, • The EU target value for As in ambient air (PM10) of 6 ng/m3 will be obligatory by the 31 December 2012, • UK’s emissions: Hg and As 6 t/year 13 t/year

  3. Why there is a problem? • Hg and As are highly toxic and tend to bio-accumulate in humans causing adverse health effects, including cancer, • Different oxidation states (As(0), As2O3; Hg(0),Hg (p),Hg(+2))and different forms, • Particulates forms can be removed by existing control device, while gaseous forms easily escape such systems, • As deactivatesSCR catalyst what affects NOx removal.

  4. Average removal efficiencies (%) of existing control devices * Gaseous forms & most toxic forms, data based on Pavlish et al., 2010.

  5. Existing sorbents • Activated carbons (sulphur, bromine, iodine impregnated), zeolites, calcium species (lime), fly ash, transition metals, and their oxides/sulfides – have been investigated, • Temperature restricted, • Usually low capacities, • Easily deactivated by flue gas • components (e.g. SOx,H2S).

  6. Challenge • An improved sorbent which: • can simultaneously capture multi-pollutant, • is not restricted by high temperatures and other operational conditions, • has high capacity for retaining pollutants as non-volatile compounds, • can be reused but does not require frequent reactivation, • is environmentally friendly, • is cheap and has ‘long life’.

  7. Previous use and preparation of MnOx-based sorbents • Main preparation methods: impregnation and precipitation, • Oxidative capture of Hg and As (III and V) in aqueous solutions and water1, • MnOx/Al2O3 used for removal of Hg from flue gas2,3, • Removal of elemental Hg, NOx and SO24. • 1Mohan and Pittman, 2007;2Granite et al., 2000; 3Qiao et al., 2009; • 4Palman and al., 2003.

  8. Preparation of MnOx-based sorbents by • co-precipitation* • Equal molar ratios of 28.7 g of Mn(NO3)2*6H20 and 33.9 g Zr0(N03)2*6H20 were dissolved in water and then mixed together, • Addition of concentrated ammonia solution, • Filtration, evaporation and drying at 105°C, • Activation of material using a continuous air stream at 450°C for 2 hours. • *Eguchi, K.; Hayashi, T. Catalyst Today 1998, 45, 109-115.

  9. Main aim • To continue testing of MnOx/ZrO2 sorbent for Hg capture in order to recognise the limiting factors and improve the operational conditions, • To investigate the potential of this sorbent for As capture.

  10. AFS DETECTOR LMVG at 30°C MFC Vent Thermostat at 40°C Sorbent bed Carrier gas MFC Dilution gas N2 Data acquisition system Figure 1. Schematic of Hg adsorption rig

  11. BET surface areas of MnO2, ZrO2 and MnOxZrO2 sorbents Patent PCT/GB2008/050056* MnOx/ZrO2 ZrO2 MnO2 The pore structure of the MnO2 obtained by precipitation without ZrO2 is dominated by macrospores, and therefore the surface area remains relatively small. * Colin Edward Snape,  Cheng-gong Sun,  Janos Lakatos,  Ron Earl Perry.

  12. Comparison between Activated Carbon and MnOx/ZrO2 sorbent performance Hg generation in the flow of 80 ml/min: 0.0028519 mg/min MnOx/ZrO2 AC

  13. Co-precipitated MnOx-based sorbents developed at the University of Nottingham Patent PCT/GB2008/050056* Capacity achieved for bed packed by sorbent at 50C and a N2 flow of 130 ml/min. * Colin Edward Snape,  Cheng-gong Sun,  Janos Lakatos,  Ron Earl Perry.

  14. Effect of temperatures and SO2 on the performance of the MnOx/ZrO2 sorbent Patent PCT/GB2008/050056 • Full capacity remains at 150oC and significant capacity still remains at 250oC. • Effect of SO2 in reducing capacity is greater at the higher temperatures. • 5% Oxygen increases capacity by ca. 1% at 250-350oC.

  15. Thermally regenerated MnOx/ZrO2 adsorbent Patent PCT/GB2008/050056

  16. Weight loss from MnOx/ZrO2 adsorbent Patent PCT/GB2008/050056 Most of Hg adsorption capacity retained until 300oC and then steady decrease to 500oC.

  17. MFC As2O3 Heating furnace 260°C Vent Diluent gas Sorbent bed N2 Carrier gas Nitric acid solution Figure 2. Schematic of As2O3 adsorption rig

  18. Conclusions • Present results indicate the significant promise of the MnOx-based sorbents for Hg capture. • Extensive testing required to recognise the limiting factors and improve the operational conditions. • A need of a more complete understanding of reaction mechanism and kinetics.

  19. Future work • Testing of MnOx- based sorbents sorbent for As removal in different atmospheres and operational conditions, • Testing of commercially available sorbents in same conditions as MnOx-based, • Evaluation of sorbents performance.

  20. Thank you for attention

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