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

 Naturally occurring 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 (PM 10 ) of 6 ng/m 3 will be obligatory by the 31 December 2012,  UK’s emissions: Hg and As Hg and As – few facts 13 t/year6 t/year

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), As 2 O 3; 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 deactivates SCR catalyst what affects NOx removal.

Average removal efficiencies (%) of existing control devices Electrostatic Precipitators (ESP) Fabric Filters (FF) Flue Gas Desulphurisation (FGD) Selective Catalytic Reduction (SCR) ACI Hg Hg (0) * 0000 >90 Hg (p) Hg (+2) ≤ 90≤80 As As (0), As 2 O 3 * ? * Gaseous forms & most toxic forms, data based on Pavlish et al., 2010.

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,H 2 S).

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’.

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 water 1,  MnOx/Al 2 O 3 used for removal of Hg from flue gas 2,3,  Removal of elemental Hg, NOx and SO Mohan and Pittman, 2007; 2 Granite et al., 2000; 3 Qiao et al., 2009; 4 Palman and al., 2003.

Preparation of MnOx-based sorbents by co-precipitation*  Equal molar ratios of 28.7 g of Mn (NO 3 ) 2 *6H 2 0 and 33.9 g Zr0(N0 3 ) 2 *6H 2 0 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,

Main aim  To continue testing of MnOx/ZrO 2 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.

AFS DETECTOR Thermostat at 40°C N2N2 VentMFC Dilution gas Carrier gas LMVG at 30 °C Sorbent bed Data acquisition system Figure 1. Schematic of Hg adsorption rig

BET surface areas of MnO 2, ZrO 2 and MnO x ZrO 2 sorbents Patent PCT/GB2008/050056* The pore structure of the MnO 2 obtained by precipitation without ZrO 2 is dominated by macrospores, and therefore the surface area remains relatively small. MnOx/ZrO 2 MnO 2 ZrO 2 * Colin Edward Snape* Colin Edward Snape, Cheng-gong Sun, Janos Lakatos, Ron Earl Perry.Cheng-gong SunJanos LakatosRon Earl Perry

AC MnOx/ZrO 2 Comparison between Activated Carbon and MnOx/ZrO 2 sorbent performance Hg generation in the flow of 80 ml/min: mg/min

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 N 2 flow of 130 ml/min. * Colin Edward Snape* Colin Edward Snape, Cheng-gong Sun, Janos Lakatos, Ron Earl Perry.Cheng-gong SunJanos LakatosRon Earl Perry

Effect of temperatures and SO 2 on the performance of the MnO x /ZrO 2 sorbent  Full capacity remains at 150 o C and significant capacity still remains at 250 o C.  Effect of SO 2 in reducing capacity is greater at the higher temperatures.  5% Oxygen increases capacity by ca. 1% at o C. Patent PCT/GB2008/050056

Thermally regenerated MnO x /ZrO 2 adsorbent Patent PCT/GB2008/050056

Weight loss from MnO x /ZrO 2 adsorbent Patent PCT/GB2008/ Most of Hg adsorption capacity retained until 300 o C and then steady decrease to 500 o C.

N2N2 Vent Nitric acid solution Figure 2. Schematic of As2O3 adsorption rig MFC Heating furnace 260°C As 2 O 3 Diluent gas Carrier gas Sorbent bed

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.

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.

Thank you for attention