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 (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

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.

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.

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).

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 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.

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.

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.

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

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.

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

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.

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

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

Weight loss from MnOx/ZrO2 adsorbent Patent PCT/GB2008/050056

Most of Hg adsorption capacity retained until 300oC and then steady decrease to 500oC.

N2

Vent

Nitric acid solution

Figure 2. Schematic of As2O3 adsorption rig

MFC

Heating furnace 260°C

As2O3

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