hydrogen separating membranes for coal gas reforming library/events/2003/materials... · hydrogen...

Tritium Science & Engineering/Materials Science & Technology

Hydrogen Separating Membranes for Coal Gas Reforming

Stephen N. Paglieri & Stephen A. BirdsellLos Alamos National Laboratory

Los Alamos, New Mexico, U.S.A.


Overview

■ Background– Hydrogen separating membranes

■ Coal-gas reforming in a PMR– Where membranes fit into Vision 21

■ Fabrication and testing of palladium composite membranes


What’s so special about palladium?

■ Palladium (Pd) can absorb many times its volume in hydrogen

■ Pd is catalytically active for hydrogen dissociation

■ Alloys of Pd are durable

*http://www.psc.edu/MetaCenter/MetaScience/Articles/Wolf/Wolf.html


Vision 21

■ Part of Vision 21 entails coal gasification to recover both H2 for fuel cell use and CO2 for sequestration

– http://www.netl.doe.gov

■ A PMR accomplishes this in a single unit operation

GasificationPyrolysis

Combustion

PalladiumMembrane

Reactor

Pure H2 Fuel CellReactor

ConversionCO2-richstreamSyngas

Products

TurbineSyngas

Conversion

ScrubbingSequestration

EnvironmentalControls

PowerHeat

Chemicals

ProductsEnergyConversion

FuelConditioning

CoalNatural gas

BiomassOxygenSteam

SulfurRemoval

ElectricityHeat

Chemicals


Scale-up issues for Pd membranes■ Cost

– price of Pd is ~$150/ounce (April, 2003)– thickness of Pd film will be < 2 µm for $50-100/ft2

■ Poisoning by process stream impurities– unsaturated hydrocarbons, H2S, carbon monoxide (CO)– should be regeneratable in steam or air

■ Embrittlement– resistance to thermal cycling– α → β (α’) phase transition

■ Leak-free sealing


How do we address these problems?

■ Cost– thin films of Pd on hydrogen-porous supports– minimize Pd film thickness

■ Poisoning– remove most H2S up front– PdCu40 is sulfur resistant

■ Embrittlement– Pd alloys reduce distortion upon hydriding/dehydriding


Types of composite configurations

■ Refractory metals have high hydrogen permeabilities– surfaces readily poisoned– must coat with Pd on both sides of metal foil or tube– ion-cleaning in-situ followed by sputter deposition of Pd

■ Pd on a porous support– porous metal supports

■ easier to weld into a module■ available pore sizes take thick Pd coatings (>20 µm) to plug

– porous ceramics■ possess high temperature stability■ commercially available tubes with well-defined pore sizes■ α and γ-alumina, titania, zirconia


Palladium alloys■ Increased hydrogen permeability and durability■ PdAg23 (weight %)

– tubes (100 µm thick) commonly used to purify hydrogen for semiconductor industry and hydrogen isotope recovery

– grain coarsening during operation at higher temperatures

■ PdRu6– higher melting point metal imparts high-temperature stability and

strength

■ PdCu40– sulfur resistance– D.L. McKinley, U.S. 3,439,474 (1969)– D.J. Edlund


Fabrication of a Pd-Cu Composite Membrane

■ Sequentially deposit Pd and then Cu■ Anneal to promote metallic interdiffusion

– > 350°C■ Characterization

– hydrogen flux and permselectivity– thickness: SEM, EPMA– composition: EDX, XRD– depth profiling: XPS, AES, Rutherford backscattering


Preparation of Pd/Ceramic Membraneclean ceramic

membrane

seal ends of ceramic membrane with high temp. glaze

Sensitize surface w/SnCl2 solution

activate or seed surface with Pd crystallites

plate in aqueous solution ofPd-amine complex andreducing agent (N2H4)

• Surface of GTC 998 0.2 µm symmetric Al2O3 Tube

»Scalebar is 2 µm


Sensitizing/Activating

■ Must catalyze surface of non-conductor to initiate deposition

■ Sensitization w/SnCl2

■ Activation w/PdCl2

■ Water rinse

Cl- Sn2+ Cl- Cl- Pd2+ Cl-

Al Al Al

O Oδ- δ-

Al Al Al

O Oδ-

Sn2+

Al Al Al

O O δ-

Sn4+

Clδ- PdClδ-

M. Charbonnier et al. J. Electrochem. Soc. 143(2) 472 (1996).


Membrane Preparation

■ Ends of porous tube are glazed to prevent gas bypass of selective layer

■ Electroless plating set-up enables solution circulation while membrane is immersed in sucrose solution


Pd-Cu/Alumina Composite Membrane

■ Image of a broken membrane showing copper layer

■ Membrane is sealed into the module using compression fittings with graphite ferrules


Test Module

■ 3 thermocouples on both the inside and outside of membrane

■ Catalyst packed inside the Pd-composite membrane

■ Max T = 550°C■ Max P = 250 psig

D = 0.39”

Pd/aluminamembrane

ID = 0.24”L = 2-10”

3/8”-1/4” Swagelokreducing unionw/graphite ferulles

catalyst

1/4” SS tubing

1/4” SS tubing

Feed (H2O, CO, H2S)Max P = 250 psig

Copper gasket

1/2” flange

2.75”

1/4” SS Swagelokbored through to enablepenetration of 1/4” tube

1/16” SS Swagelok forthermocouple penetration

1/4” SS Swagelokbored through to enablepenetration of 1/4” tube

1/4” SStube forpermeate

H2 Permeate

Tube 1.5”

Length of SSTube to weldedon flange L = 15”

1/4” SStube forpermeate

1/16” SS Swagelokfor thermocouplepenetration

Maximum system temperature = 550 CMaximum shell pressure = 30 psig

1/4” SS tube forconection to membrane (retentate)

Retentate


Hydrogen & Argon Flux vs. Time through Pd-Cu/Alumina Membrane

■ Hydrogen flux increases as Pd and Cu interdiffuse

■ ∆P = 100 psi■ αH2/Ar ≅ 68

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 5 10 15

Time (days)

Flux

[mol

(ST

P)/m

2s]

Hydrogen FluxArgon Flux

~335C ~355C


Pd/refractory foil/Pd Composite

HYDROGENMOLECULES

HYDROGENATOMS

HYDROGENMOLECULES

Pd

PALLADIUM

PALLADIUM

FEED GAS

ULTRA-PURE HYDROGEN

Group V Metal


Pd/V-alloy/Pd membrane■ Palladium coating is

very thin– 1000 Å

■ Alloy of vanadium reduces hydrogen embrittlement

■ Welded into the shape of a tube

– SS VCR fittings– Flux = 0.4 sccm/cm2•min @

∆P = 5 psi


AES Depth Profiles of Pd on V-CuAuger Depth Profile

0

500

1000

1500

2000

2500

3000

0 1000 2000 3000 4000 5000 6000 7000 8000

Time, sec.

Inte

nsity

, A

PPH

Pd

V

Cu

MPDVCU.A0

Auger Depth Profile

0

500

1000

1500

2000

2500

0 2000 4000 6000 8000 10000 12000

Time, sec.

Inte

nsity

, A

PPH

Pd

V

Cu

C

O

MCUVPD.ASpringer/LAN


Future Work

■ Membrane reactor■ Pack catalyst around membrane■ Low, medium, and high temperature water-

gas shift■ Fe-Cr-Cu oxide, Cu-ZnO catalysts■ Test sulfur resistance of membrane

materials


Acknowledgements

■ Membrane development work was funded by the US DOE, Office of Fossil Energy

■ Rob Dye, David Pesiri, Bob Springer, DonGettemy, John Moya, Stan Bennett, Stephen Cole, Jerry Schobert, Mike Brooks, Frank Smith, Ron Snow, Robert Barbero, Felix Garcia, Fino Armijo, John Valdez, Vincent Hesch, and Kevin Hubbard


Fuel Reforming for Fuel Cells

■ High efficiency■ High quality electricity■ Backup (UPS) ■ Decentralized power system■ Home, business, vehicle■ Liquid or gaseous fuel

– CnHm+nH2O ↔ nCO+[(m+2n)/2]H2

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