In situ and deactivation studies of the gasification of biomass in super-critical water over Ru/C catalysts

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In situ and deactivation studies of the gasification of biomass in super-critical water over Ru/C catalysts

G E N E R A L E N E R G Y D E P A R T M E N T G E N E R A L E N E R G Y D E P A R T M E N T

J. Wambach, M. Schubert*, M. Dreher, F. Vogel

Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

*Present address: Karlsruher Institut für Technologie (KIT), Institute for Chemical Technology and Polymer Chemistry, D-76131 Karlsruhe, Germany

Conclusions

Conclusions Acknowledgement Acknowledgement

Wet biomass, e.g. agricultural residues, and dry biomass (e.g. wood) are considered playing a major role in our future sustainable energy supply. Biogenic synthetic natural gas (Bio-SNG) is particularly interesting as it can be produced with a high efficiency from almost any kind of biomass applying a proper conversion technology. Hydrothermal processing under supercritical water (SCW) conditions does not require dry biomass and thus has a great potential for producing biofuels and bio-chemicals from various types of biomass.

At PSI a SCW process was developed, which is operated at temperatures of 400-450°C and pressures of 25-35 MPa. Presently we feed relatively simple model compounds of wet biomass, e.g. ethanol or glycerol mixtures for investigating supercritical water gasification (SCWG) [1]. The process efficiency was determined to be 66±5 %, and the residency time is < 10 min. The carbon gasification is in the order of > 99% and a yield of ~0.33 g CH4/g wood is obtained. As catalyst a commercial 2wt% Ru/C (activated char coal) proved to be efficient and relatively stable against the harsh reaction conditions.

Our research focuses on obtaining an improved insight on the catalyst as well as understanding of the processes and kinetics governing the catalytic reactions in the hydrothermal media and the occasionally observed deactivation.

The authors are very grateful to Sousan Abolhassani-Dadras(HR-TEM; PSI, NES), Erich De Boni(SEM/EDX; PSI, ENE), Max Döbeli(RBS/ERDA/PIXE; PSI + ETHZ), and Eszter Barthazy(HAADF-Stem/EDX; ETHZ, EMEZ) for having patiently measured our samples and the fruitful discussions, and all members of the CPE group.

This investigation was financially supported by AXPO Naturstom Fonds

Introduction

Introduction Setup‘ Setup ‘s and Analysis s and Analysis

XV. International Symposium on Relations between Homogeneous and Heterogeneous Catalysis; Berlin, Germany, September 11 - 16, 2011 References:

[1] M. Schubert, Ph.D. thesis, ETH Zurich, No. 19039 (2010).

[2] Z. Song, T. Cai, J.C. Hanson, J.A. Rodriguez, and J. Hrbek; J. AM. CHEM. SOC.126(2004) 8576.

[3] S. Rabe, M. Nachtegaal, T. Ulrich, F. Vogel; Angew. Chem. Int. Ed. 49 (2010) 1.

Results

• Catalyst is working; Ru metal identified as active species

• Deactivation sometimes observable, accompanied by:



Some Ru sintering + loss of surface area + loss of surface Ru



Contamination with minor amounts of corrosion products / other elements



Remarkable changes in the valence band region

Gasification experiments:

PSI’s SCW process:

•pre-heating + liquefaction / 300-370 °C:

break-up of cells, decomposition of large bio-polymers to smaller organic molecules, release of salts and organically bound hetero-atoms (N, P, S) as inorganic compounds

•super-heating + salt separation / ≤450 °C:

continuous precipitation and recovery of released salts

•catalytic gasification + methanation / ~ 400 °C:

final conversion to mainly CH4and CO2

• Max. 1 kg/h; Tmax= 773 K, pmax= 35 MPa

Applied analytical methods:

•at SLS: in situXAS / XES / EXAFS (super-XAS beamline)

•at ETHZ: RBS (2 and 5 MeV He)/ 13 MeV ¹²⁷I Heavy IonERDA / 5 MeV HePIXE HAADF-STEM / EDX

•at ENE: on lineQMS/GCMS BET / Chemisorption XPS (Al Kmono) SEM/EDX HR-TEM

RBS / EDX / ERDA:

Depth profiling + quantitative element analysis/ ~ top 100 nm

ERDA: EDX: ICP:

Fresh: 0.7 at% 0.87 at%

L-1: 0.5 at% 2.3 at%0.34 at%

L- 6: 2.2 at% 5.4 at%0.79 at%

Depletion / Dislocation of Ru to end of reactor

Surface enrichment:

Ru and corrosion products In situXANES [3]:

After initial in situ reduction, only Ru⁰ as catalytically active species during all states of the SCW reaction

0.2 Cr

0.9 Ni

-/-/- -/0.6/- 0.2/-/0.7 0.03/-/0.4 P, S, N

1.0 1.4 3.6 7.1 Ru

4.2 5.1 9.3 26.8 O

Level-6 Level-3 Level-1 Ref.

XPS at%

Surface area determination:

Tremendous loss of ASA and of pore volume

HAADF-STEM:

Heavy elements (e.g. Ru) appear as bright contrast

Ru cluster sintering:

from0.7 — 1 nm to 2 — 3 nm Total carbon fed 11.6 %

Salt Separation

Gasification

&

Methanation Gas

(0.02 %)

Total liquid: 17.4 %

• Total organic phase: 1.9 %

• Total aqueous phase: 15.5 %

Total liquid: 67.5 %

• Total organic phase: 3.1%

• Total aqueous phase: 64.3 % Gas (6.3 %) Total mass fed 100 %

(Crude glycerol, ~20 wt.% organics)

Total effluent: ~17.5 %

CH4: 5.3 % CO2: 7.7 % H2: 0.03 % C2-C4: 0.36 % CO: not detected Period of balancing: 262 min

Total gas: 13.3 % pH = 9.5

pH = 7.5 - 8

20 % Glycerol / + 0.05% K3PO4 T = 400 °C

350 360 370 380 390 400 410 420 430

0 20 40 60 80 100 120 140

Distance (from top inlet) [cm]

Fluid temperature [°C]

Glycerol _ T = 400°C Glycerol _ T off G + K3PO4 _ T = 400°C G + K3PO4 _T off Water Endo Exo

XPS:

Qualitative and quantitative surface analysis; analysis depth: ~2 – 3 nm

•Loss of surface Ru

•Ru⁰ + little RuO2

•VB:remarkable changes Literature knowledge [2]:

Ru⁰: -4.7%/ +9.8% mismatchwith HOPGlattice two possible Ru lattices rotated relatively by 30°

Lattice constants:

RuO2 = 0.449 nm Graphite = 0.246 nm Ru(0001) = 0.271 nm HOPG = 0.142 / 0.246 nm

CrudeGlycerol gasification:

Moving deactivation frontin direction of the mass flow, shift of the minimum of the fluid temperature inside the reactor.

Gasification of pureGlycerol / mixtures with salt(K₃PO₄):

Stable gasification, no shift of the minimum of the fluid temperature inside the reactor.

1400

1200 1000

800 600

400 200

0 Specific surface area (BET) [m2/g]

140 120 100 80 60 40 20 0

Distance from top inlet [cm]

3.5

3.0 2.5

2.0 1.5

1.0 0.5

0.0 Active metal surface area (ASA) [m2/g] BET, ASA of fresh catalyst

BET (N2 physisorption) ASA (H2 chemisorption)

0.25

0.20

0.15

0.10

0.05

0.00 Differential Pore Volume [cm3/A/g]

30 25 20 15 10 5

Pore Width [Å]

1.0x10^-3

0.8

0.6

0.4

0.2

0.0 Micro-pore Analysis:

Crude Glycerol Run fresh catalyst spent _ Level-1 spent _ Level-3 spent _ Level-6

Normalized Yield

400 350 300 250 200 150

100 Channel

1.8 1.6 1.4 1.2 1.0 0.8 0.6

Energy [MeV]

2 MeV He RBS Catalyst GRAINS:

fresh Ru/C spent Level-1 spent Level-6

ca. 1.4 m Ru

O

Ti, Cr, Fe, Ni K

Normalized Yield

500 400 300 200

100 Channel

4 3 2

1 Energy [MeV]

5 MeV He RBS Powderized catalyst fresh Ru/C spent Level-1 spent Level-6

Ru O

ca. 5.5 m

Fresh Catalyst

20 nm

200 nm (a)

Reduced Catalyst

20 nm 100 nm

(b)

Spent Level-1

200 nm 20 nm

(c)

Spent Level-6

500 nm

20 nm (d)

Intensity [a.u.]

295 290 285 280

Binding Energy [eV]

XPS Al K mono Ru3d + C1s

spent _ Level 1 spent _ Level 2 spent _ Level 3 spent _ Level 4 spent _ Level 5 spent _ Level 6 Ref.: "as delivered"

C1s

Ru metal Ru3d5/2

RuOx Ru3d3/2

RuOx Ru3d5/2 0

2 4 6 8 10 12

RefLevel-1Level-2Level-3Level-4Level-5Level-6

Ru content [at%]

Inte nsi ty [a.u .]

20 15 10 5 0

Binding Energy [eV]

spent - Level 6 spent - Level 3 spent - Level 1 "as delivered" cat / RuO2 reduced catalyst / Ru met Reference Ru metal Reference C support XPS Al K mono

Epass = 20 eV C1s shifted (284.45 eV) Valence Band Konti 2

Ni3d (Ni2O3)

Ni3d

shake up O2s

C2s