DLR’s Contribution to the Helmholtz Virtual Institute production...2017/09/13 · Characterisation by EDX and x-ray diffraction e.g. reduced Ce 0.85 Zr 0.15 O 2 (1683K (pO2=2,96E-9

$Page 1: DLR’s Contribution to the Helmholtz Virtual Institute production...2017/09/13 · Characterisation by EDX and x-ray diffraction e.g. reduced Ce 0.85 Zr 0.15 O 2 (1683K (pO2=2,96E-9$
DLR’s Contribution to the Helmholtz Virtual Institute Solar Syngas: Materials for solar-thermochemical fuelsproductionStefan Brendelberger, Josua Vieten, Nicole Knobloch, Sebastian Richter, Johannes Grobbel, Brendan Bulfin, Martin Roeb, Christian Sattler

International Workshop on Solar ThermochemistryJülich, Germany 13.09.2017

Overview

- Material characterization- Thermodynamic properties- Thermal expansion- Degradation

- Material development- Tailored perovskites

- Meso scale particle production- Drip casting

- Particle characterization- Heat transfer in particle bed at high T low p

www.DLR.de • Slide 2 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017

Ceria and Ceria Zirkonia: Statistical Thermodynamics


100µm

Material:Ce0.85Zr0.15O2(porous granules)

Vacancy concentration δ, the oxygen partial pressure pO2 and the temperature profile for a typical TGA experiment

B. Bulfin

Ceria and Ceria Zirkonia: Statistical Thermodynamics – Thermodynamic Model


B. Bulfin et al. Phys. Chem. Chem. Phys., 2016,18, 23147-23154

δ p O , Tδ ∙ ∙ p O ∙ exp ∆

1 ∙ p O ∙ exp ∆

0,000

0,010

0,020

0,030

1E-5 1E-4 1E-3 1E-2 1E-1

Red

uctio

nex

tentδ

p(O2) [bar]

1286°C

1237°C

1189°C

δmax ARed/AOx n ∆E R2

[barn] - [kJ/mol]

■ CeO2 0,5 12575 ±7550

0,2320 ±0,0079

206,7 ±8,2 0,9754

■ CeZr-S16

0,425 101 ± 11 0,2084 ±0,0019

121,6 ±1,4 0,9893

B. Bulfin

Redox tests of SrMnxFe1-xO3- in a thermobalance

12 °

Δ ° Δs°


Bulfin, B. et al. (2017). "Applications and Limitations of Two Step Metal Oxide Thermochemical Redox Cycles; A Review." Journal of Materials Chemistry A

B. Bulfin


oxyg

en lo

ss

..

Ce4+97pm

Ce3+114,3pm

polycrystallinesample rod

oxidized reduced

∆

Length variation:

Investigation of reduction by dilatometry[Thermal expansion]

[ Thermal expansion ] + [ (ΔV)↓ (oxygen vacancies) < (ΔV)↑ (Ce4+ →Ce3+) ]

reduction temperature

N. Knoblauch et.al., Solid state ionics,2017, 301, 43-52

N. Knoblauch


Thermal and chemical Expansion during reductionunder reduced atmosphere (pO2 = 2-7x10-9 atm )

Chemical expansion during isothermal segment

0 50 100 150 200 250 300-0,05

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

leng

th v

aria

tion

[%]

t [min]

1538 K 1588 K 1641 K

0 50 100 150 200 250 3000,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,10

1538 K 1588 K 1641 K

t [min]

200 400 600 800 1000 1200 1400 16008

9

10

11

12

13

14

15

16

this work Körner et al. Stecuura et al. Sata et al.

x

10-6 [1

/K]

temperature [K]

→ 2

Thermal expansion coefficient

Calculated nonstoichiometric value out of the chemical expansion by a given linear relationship

Temperatur [K]

N. Knoblauch et.al., Solid state ionics, 2017, 301, 43-52

N. Knoblauch

Degradation of (Ce,Zr)O2 Redox Ceramics by selective sublimation

In a previous study on redox characteristics of ceria data suggest sublimation of ceria at high temperature above 1660K and low pO2 (2–7×10−9 atm) [Knoblauch, N.; Simon, H.; Schmücker, M., Solid State Ionics

2017,301, 43–52, DOI10.1016/j.ssi.2017.01.003].

N. Knoblauch et.al., Inorganics, Special Issue "Cerium-based Materials for Energy Conversion“ coming soon

www.DLR.de • Slide 8 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017N. Knoblauch

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0,01

0,1

1

2,5x

10-4

3,0x

10-4

3,5x

10-4

4,0x

10-4

4,5x

10-4

5,0x

10-4

5,5x

10-4

6,0x

10-4

6,5x

10-4

CeO2 MgO ZrO2 La2O3

Vap

or p

ress

ure

[atm

]

1/T [1/°C]

Characterisation by SEMe.g. reduced Ce0.85Zr0.15O2 (1683K (pO2=2,96E-9 atm)

cross section top viewspongy surface zone

time [h] length [µm]1 2,5 2,992 5 3,873 15 6,44

Measured length of spongy surface zone after reduction at 1683K for various length of time

0 2 4 6 8 10 12 14 160

1

2

3

4

5

6

7

subl

imat

ion

zone

[µm

]

time [h]



Characterisation by EDX and x-ray diffractione.g. reduced Ce0.85Zr0.15O2 (1683K (pO2=2,96E-9 atm)

bulk

surface

Ce0.82Zr0.18O1.89

Ce0.47Zr0.53O1.83

Ce2Zr2O7 Pyrochlore formation at the surface!

-1 0 1 2 3 4 5 6 715

20

25

30

35

40

45

50

55

Zr Ce

depth [µm]

Zr [a

t%]

45

50

55

60

65

70

75

80

85

Ce

[at%

]bulksurface



Development of new materialsPerovskites for redox cycles

A2+M3+/4+O3-δ

∆HTiMnFeCoCu

Water splitting

CO2 splitting

Air separation

Oxygen pumps

A2+M3+/4+O3: Reaction enthalpy mainly goverenedby choice of transition metal M3+/4+

0 100 200 500 kJ/mol O

Bulfin, B. et al. (2017). "Applications and Limitations of Two Step Metal Oxide Thermochemical Redox Cycles; A Review." Journal of Materials Chemistry A

Reduction from perovskite to brownmillerite:4AMO 4AMO . O

gradual reduction possible -> non-stoichiometry δ

Image: Eames et al.

www.DLR.de • Slide 11 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017J. Vieten

Tailored thermodynamic propertiesMn-Fe solid solutions*in the fully oxidized state

SryCa(1-y)MnxFe(1-x)O3-δ

∆HTiMnFeCoCu

Water splitting

CO2 splitting

Air separation

Oxygen pumps

0 100 200 500 kJ/mol O

∆H per mol O

same crystal structure in oxidized state

Materials suitable for oxygen pumping, selection according to operation parameters

Vieten, J. et al. (2016). "Perovskite oxides for application in thermochemical air separation and oxygen storage." Journal of Materials Chemistry A 4(35): 13652-13659.Vieten et al. (2017), Redox thermodynamics and phase composition in the system SrFeO3 − δ — SrMnO3 − δ. Solid State Ionics, 308, 149-155

www.DLR.de • Slide 12 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017J. Vieten

Selection of redox material

- Low reduction temperatures1

- Non-stoichiometric redox characteristics

- Scalable synthesis

Tassel, Kageyama 2011: Square planar coordinate iron oxides

1Vieten et al. 2016, J. Mater. Chem. A

Strontium Iron OxideSrFeO3-δ

www.DLR.de • Slide 13 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017S. Richter

- High temperature solid statereaction

- Precursors: SrCO3 & Fe3O4

- Mesoscale synthesis

- Manual pestling of annealedmaterial

- Ball milling

SrFeO3-δ synthesis


- Drip casting

- Slurry dripped intocooled oil bath

- Separation from oil

Granulation


- Washing

- Drying

- Sintering

Granulation – post treatment


Heat transfer properties of Ceria particles at low pressures

2 cm

Thermocouples

483 kW/m²

1200 °C ceria particles 212-500 µm

p=25 Pa – 1 atm

J. Grobbelwww.DLR.de • Slide 17 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017

Fixed Bed Experiment with Ceria

Investigate effective conductivity as function of temperature and pressurekbed (p,T)

Comparison with Simulation

• Simulation withcontinuum model [1,2]

• Very low heat transfer particle mixing required

• How to model a moving bed?[1] P. Zehner and E. U. Schlünder, Chemie Ingenieur Technik, vol. 44, pp. 1303-1308, 1972.[2] R. Bauer, Düsseldorf: VDI-Verl., 1977.

,

J. Grobbelwww.DLR.de • Slide 18 > International Workshop on Solar Thermochemistry > Brendelberger et al. • SolarSynGas > 13.9.2017

Grobbel et al., Solar Energy, coming soon

Summary- Thermodynamic data from TGA measurements- Reduction extent from dilatometry experiments- Degradation by selective sublimation- Tailored perovskites for oxygen pumping- Production of spherical Strontium Iron Oxide particles- Pressure dependence of effective thermal conductivity in particle bed

- Other topics of DLR within SolarSynGas- Indirect particle based concept- Particle-particle heat exchanger- Indirect particle reactor- Sweep gas demand- Vacuum pumping requirements- Thermo-chemical pumping- Air separation- …


DLR.de • Chart 20

Thank you very much for your attention!

Our work was co-funded by the Initiative and Networking Fundof the Helmholtz Association of German Research Centres, by the Federal State of Northrhine-Westfalia, by the European Commission, by the FCH-JU and by the US DOE (via subcontract).

Documents

DLR’s Contribution to the Helmholtz Virtual Institute production...2017/09/13 · Characterisation by EDX and x-ray diffraction e.g. reduced Ce 0.85 Zr 0.15 O 2 (1683K (pO2=2,96E-9