Pd Alloy Membranes for Hydrogen Separation from Coal ...2 TDA R e s e a r c h Introduction zAdvanced...
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TDA Research Inc. • Wheat Ridge, CO 80033 • www.tda.com Pd Alloy Membranes for Hydrogen Separation from Coal-Derived Syngas Gökhan O. Alptekin, Ph.D., Sarah DeVoss, Bob Amalfitano TDA Research, Inc. Dr. Douglas Way, Dr. Paul Thoen, Dr. Mark Lusk Colorado School of Mines Pittsburgh Coal Conference Pittsburgh, PA September 26, 2006
Transcript of Pd Alloy Membranes for Hydrogen Separation from Coal ...2 TDA R e s e a r c h Introduction zAdvanced...
TDA Research Inc. • Wheat Ridge, CO 80033 • www.tda.com
Pd Alloy Membranes for Hydrogen Separation from Coal-Derived Syngas
Gökhan O. Alptekin, Ph.D., Sarah DeVoss, Bob AmalfitanoTDA Research, Inc.
Dr. Douglas Way, Dr. Paul Thoen, Dr. Mark LuskColorado School of Mines
Pittsburgh Coal ConferencePittsburgh, PA
September 26, 2006
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IntroductionAdvanced coal-to-hydrogen plants have the potential of co-generating power and a hydrogen in volumes sufficient to fuel the fuel cell-powered vehicles System studies show enhanced efficiency for coal-to-hydrogen plants if the WGS and H2 separation were combined into a single step
H2 can be produced at $3.98/MMBtu ($0.54/kg) in IGCC-based co-generation plantFurther cost reduction to $3.0/MMBtu if SOFCs were used to generate electricity
Source: Mitretek Report to NETL, Gray and Tomlinson, 2003.
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Membrane Requirements Requirements
High H2 flux High H2 purityRobustness and resistance to degradation by thermal cyclingOperation at the right temperature range (260-450oC)
– Above the dew point of the syngas but low enough to achieve effective contaminant control
Tolerance to all components of coal-derived synthesis gas– Particularly to sulfur
Potential Technologies for H2 SeparationPressure Swing Adsorption (PSA)Ceramic membranesDense ceramic membranes
Our approach is composite Pd alloy membranesCSM carries out film deposition and characterizationTDA carries out support development, membrane testing and module development
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• Potential for perfect H2 selectivity• The transport mechanism is
unique to hydrogen• Palladium catalyzes the
dissociation of molecular H2 into atomic H
• H atom is soluble in Pd metal and transports through a solution-diffusion mechanism
• H atoms recombine at the low pressure side and desorb from the surface
• Potential for high flux• Flux and permeability a function of
solubility and diffusion rate
Why Pd Membranes?
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Why Pd Alloy Membranes?Membranes based on pure Pd suffer from embrittlement and cracking due to the α→β Pd hydride phase transition (at ~300oC)
FCC to BCC phase change causes structural deformations in the film
Pd alloys avoids the α→β phase transition in pure Pd
Alloying eliminates swelling, warping, cracking due to phase transitionsEliminates the problems associated with thermal cycles
α phase is FCC
β phase is BCC
Some Pd alloys shows higher permeability than the pure Pd27% Ag, 6% Ru, 40% Cu, 5% Au alloys have shown to have much higher fluxes than pure Pd films
Additional benefits of alloyingReduced cost (depending on the selected component)Resistant to H2SDimensional stability (small degree of swelling)
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Why Pd Composite Membranes?
JH =
PH
l m
pH2 , feed − pH2 , permeate( )• Low cost when the alloys made into thin
alloy films5 µm PdCu (60/40) film
– Pd cost = $20/ft2 Cu Cost = 0.70/ft2
• 25 µm PdCu alloy will cost 5 times higher material cost and its flux will be much lower
• Pd alloys can be prepared into self supporting structures or can be prepared on porous supports (i.e., composite membranes) as thin films
• Thin films increases the H2 flux at a given pressure
• Flux equation in Pd membranes (Way, 1996)
The original idea is from the work of Uemiyaand Kikuchi, Chem. Lett., 1687, 1988
• The challenge is how to make them and operate them at high pressures
1 µm thick composite PdCu membrane
2 µm thick composite PdCu
membrane
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Why Electroless Plating?
AdvantagesNo expensive, complex equipment neededScale-up feasibleSimple technique with easy parameters to controlCan plate complex geometriesConsecutive plating followed by annealing to produce alloysProduces high flux membranes
DisadvantagesPossible contamination from carbonPd membrane thickness related to support surface roughness
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Porous Supports for Deposition of Pd FilmsPrevious work at CSM focused on preparing thin Pd or Pd alloy films on ceramic supports
Pd alloy film thickness ~1-5 µmSupports are commercially available by CoorsTek, and Pall originally developed for gas filtration
The substrates can be symmetric (constant pore size) or asymmetric (gradient in pore size)Symmetric ceramic supports
Low cost – Symmetric Supports ~ $25/ft2– Asymmetric Supports > $500/ft2
Higher strength, less defects
Membrane film is deposited either on the inside or outside diameter of the porous supports
Symmetric SupportAsymmetric Support
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Preparation of Pd Alloy Films on Steel Supports
Porous steel supports increases the robustness over the ceramic supportsIt is much easier to incorporate the metal supported membranes into modules
Welding or brazingElimination of ceramic/metal joints minimize leaks Issues need to be addressed:
Surface roughness– Thicker films are required
Inter-metallic diffusion– Cause formation of an undesired
alloyA diffusion barrier addresses all these problems:
An oxide layer diffusion barrier deposited on steel support prior to plating prevent diffusion of Pd membrane and support If the oxide layer diffusion barrier can be applied is in the form of small particles, surface roughness may be reduced
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Porous Stainless Steel Tube (ACCUSEP by Pall)
ACCUSEP tube with removable compression fittings
ACCUSEP tubes welded to the tubesheet
Module Construction The final membrane module or the membrane-WGS reactor will be similar to a shell-and-tube type heat exchanger
WeldjointWeldjoint
Porous steel tube
Non-porous steel tube
Tubular membranes
3 kWe
7 kWe
CO + H2O = CO2 + H2
Sulfur-rich Residue
H2 to fuel cell
H2
H2
CO-rich reformate
Nonporous wall of membrane reactor
Tubular symmetric stainless steel
membrane support
Pd/Cu film
Sulfur Tolerant WGS Catalyst
N2 , CO, CO2, H2O, H2S and some H2
Permeate
Permeate H2 to fuel cell
Steam Sweep
Steam Sweep High purity H2
To be burned with O2
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Outline
IntroductionBackground on Composite Pd Alloy MembranesResults
Sulfur Tolerant Composite PdAu MembranesMetal Supported PdAu Membrane
Future Work
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Molecular Modeling
Au25Pd75Au50Pd50
Polycrystalline arrangements
LROLRO
LRO
SROSROSRO SRO
All crystal structure in diagram are FCC
Focus:AuPd3 region
Atomistic studies were performed to measure rate of H atom diffusion through Au-Pd3 lattice at 300-400oC range
Molecular Dynamics Simulation is used to identify a promising Pdalloy composition that provides high flux and sulfur resistancePdCu and PdAu alloys were selected for initial considerations
Pd-rich alloys were examined both because of their lower cost and higher performance
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Diffusion of H through PdAu AlloyMolecular simulation results showed that H atom transport in thePd75Au25 matrix is slower than it is in the Pd60Cu40 at 400oC
Both lattices are dilated to the same extent lattice to increasediffusivity
Trap 1 Trap 2
Au atoms act as effective trap sites for H atom and slow the diffusion rate
Slower transport rates are correlated to higher activation energy for H diffusion
Pd Pd
Pd
Pd
Pd Pd
Au
Au AuAu
AuAu
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Impact of Sulfur on Pd Alloys
0
20
40
60
80
1000 ppm sulfur4 ppm Sulfur
Hyd
roge
n D
iffus
ion
(scf
h.m
il/ft2 )
Membrane Composition (weight. %)
Pd(100)
Pd/Ag(73/27)
Pd/Cu(60/40)
Pd/Au(60/40)(95/5)
Effect of Sulfur on H2 Permeation
Experimental evidence also confirms our model predictionsIn the presence of sulfur PdAu alloys show much higher stabilityPdAu alloy shows the a low binding energy for sulfur atom
Int. Conf. On Membranes (Way and Alptekin, 2006)
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Membrane Preparation
EDX analysis indicates that membrane consists of 87% Pd and 13% AuSmall number of spots or defects in the surface of the membrane
Nitrogen leak rate measurements show that the surface defects do not penetrate the entire thickness of the membrane
Several PdCu and PdAu composite membranes were developed for testing
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Membrane Testing System
Membrane module
Sub-ppm level sulfur detection capability with Sievers Chemiluminescence Detector
Feed In
Permeate
Residue
Thermocouple port
Shell (1.0 in)
Tube (0.25 in)
Membrane module
Thermocouple port
Test apparatus
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Baseline Performance of PdAu Membrane
A stable membrane performance (i.e., H2 permeation and selectivity) was observed for over 300 hrs in the presence of CO, CO2, H2O and H2 mix
0
50
100
150
200
250
300
350
Time
Per
mea
te (s
ccm
)
Hours 92-97 of the Test
Hours 140-147 of the Test
Hours 198-205 of the Test
Hours 315-331 of the Test
Per
mea
tion
Test
s, C
O2
test
, Air
Purg
e
Wat
er G
as S
hift
Test
ing
(400
°C,v
ario
us p
ress
ures
)
Wat
er G
as S
hift
Test
ing
(450
°C),
Air
Purg
e, H
2/N
2 te
st, W
ater
Gas
Shi
ft Te
stin
g (4
50°C
),
Wat
er G
as S
hift
Tem
pera
ture
Tes
ting,
Flo
w R
ate
Test
s, P
ress
ure
Test
s, C
O/C
O2
Test
H2/
N2
test
T=400oC, Pfeed= 100 psig, Pperm= 2 psig, Feed H2/H2O/CO/CO2 Conc. = 51/21/26/2
H2 permeation rate =32.5 sccm/cm2 or
64 scfh/ft2
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Effect of H2S on PdAu Membrane
With the introduction of sulfur to the syngas feed H2 permeation rate decreased (5 ppmv sulfur caused 40% decrease) When sulfur flow was stopped, membrane performance recovered
0
50
100
150
200
250
300
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Time (min)
Per
mea
te (s
ccm
), P
erm
eate
CO
(ppm
)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Per
mea
te C
O2 (
%)
Permeate
CO2
CO
1 pp
m H
2S in
R
efor
mat
e
1 pp
m H
2S in
R
efor
mat
e
5 pp
m H
2S in
R
efor
mat
e
Ref
orm
ate
Ref
orm
ate
T=400oC, Pfeed= 100 psig, Pperm= 2 psig, Feed H2/H2O/CO/CO2 Conc. = 51/21/2/26
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PdAu on Porous Steel Substrates
Treatment of the porous steel tubes (elimination of oils, grease etc for the application of coating)
Hermatic sealing of the ends of the porous steel tubes
Application of an oxide diffusion barrier
Deposition of Pd film (followed with deposition of gold and proper annealing
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Evaluation of PdAu on Porous Steel
0
25
50
75
100
125
150
175
200
225
0 50 100 150 200 250 300 350
Time (min)
Perm
eate
(scc
m),P
erm
eate
CO
(ppm
v)
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Perm
ate
CO
2 (%
)
CO averages less than 5 ppmv
Corresponds to a flux of 31 scc/cm2 min
The PdAu membrane prepared on porous steel support showed improved selectivity indicating non-selective transport is most likely due to the seals Even with a thicker film, H2 permeation rate of this membrane matched to that prepared on ceramic support
T=400oC, Pfeed= 100 psig, Pperm= 2 psig, Feed H2/H2O/CO/CO2 Conc. = 51/21/2/26
(61 scfh/ft2)
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Future Work
Work on reducing the thickness of the membrane film over the porous steel supported (PSS) membranesEvaluate performance of the PSS membranes in the presence of H2S
At sulfur concentrations up to 100 ppmv
Evaluate the potential problems associated with other coal gas contaminants
Arsenic, selenium, HCl …
Module design and developmentH2 separation moduleMembrane Water-Gas-Shift Reactor
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Acknowledgements
DOD SBIR Phase I (Contract No. W56HSV-06-C0077)
Contract Monitor: Mr. Dan Maslach
DOE SBIR Phase I Project Contract Monitor: Ms. Patricia Rawls
