Co-precipitated manganese oxides- based sorbents for mercury and arsenic capture. Malgorzata...
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![Page 1: Co-precipitated manganese oxides- based sorbents for mercury and arsenic capture. Malgorzata Wiatros-Motyka EPSRC PhD project student Grant: EPSRC China.](https://reader035.fdocuments.net/reader035/viewer/2022070407/56649e1b5503460f94b09a12/html5/thumbnails/1.jpg)
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
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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 (PM10) of 6 ng/m3 will be obligatory by the 31 December 2012,
UK’s emissions: Hg and As
Hg and As – few facts
13 t/year6 t/year
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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 deactivates SCR catalyst what affects NOx removal.
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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) * 0 0 0 0
>90Hg (p)
Hg(+2)
0-40 40-90 ≤ 90 ≤80
AsAs(0),As2O3
* 88 5 - - ?
* Gaseous forms & most toxic forms, data based on Pavlish et al., 2010.
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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).
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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’.
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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.
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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.
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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.
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AFS DETECTOR
Thermostat at 40°C
N2
VentMFC
MFC
Dilution gas
Carrier gas
LMVG at 30°C
Sorbent bed
Data acquisition system
Figure 1. Schematic of Hg adsorption rig
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0
20
40
60
80
100
120
140
160
180
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
p/p0
Vo
lum
e o
f so
rb
ed
nit
ro
gen
, cm
3g
-1 (
ST
P)
MnOyZrO
ZrO2
MnO2
BET surface areas of MnO2, ZrO2 and MnOxZrO2 sorbents
Patent PCT/GB2008/050056*
The pore structure of the MnO2 obtained by precipitation without ZrO2 is dominated by macrospores, and therefore the surface area remains relatively small.
MnOx/ZrO2
MnO2
ZrO2
Colin Edward Snape, Cheng-gong Sun, Janos Lakatos, Ron Earl Perry.
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AC
MnOx/ZrO2
Comparison between Activated Carbon and MnOx/ZrO2 sorbent performance
Hg generation in the flow of 80 ml/min: 0.0028519 mg/min
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Co-precipitated MnOx-based sorbents developed at the University of Nottingham
Patent PCT/GB2008/050056*
Capacity achieved for bed packed by sorbent at 50C and a N2 flow of 130 ml/min. * Colin Edward Snape, Cheng-gong Sun, Janos Lakatos, Ron Earl Perry.
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Effect of temperatures and SO2 on the performance of the MnOx/ZrO2 sorbent
0 50 100 150 200 250 300 350 400
0
5
10
15
20
Without SO2
With 300ppm SO2
Hg
brea
kthr
ough
cap
acity
, wt %
Temperature, oC
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.
Patent PCT/GB2008/050056
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Thermally regenerated MnOx/ZrO2 adsorbent Patent PCT/GB2008/050056
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Weight loss from MnOx/ZrO2 adsorbent Patent PCT/GB2008/050056
Most of Hg adsorption capacity retained until 300oC and then steady decrease to 500oC.
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N2
Vent
Nitric acid solution
Figure 2. Schematic of As2O3 adsorption rig
MFC
Heating furnace 260°C
As2O3
Diluent gas
Carrier gas
Sorbent bed
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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.
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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.
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Thank you for attention