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www.ecn.nl
Catalysts for Hydrogen Production in Membrane and Sorbent Reformers
Paul van Beurden, Eric van Dijk, Yvonne van Delft, Ruud van den Brink, Daan Jansen
Hydrogen Production with CO2 Capture
• Conventional CO2/H2 separation (PSA, scrubbers) involves many steps: Efficiency losses
GTCCGTCC
Air
O2, 79% N2
N2, H2O
LTS
Reformingor
Coal Gasification
Shift H2/CO2
separation CO2
H2
HTS
Natural gasor Coal
GTCCGTCCAir
N2, H2O
Reformingor
Coal Gasification
Separation-EnhancedWater Gas Shift
CO2
H2
Natural gasor Coal
Integration of shift- and CO2 capture steps
Separation-EnhancedReforming
Natural gas
One-step reforming and CO2 separation
GTCCGTCC
N2, H2O
Air
CO2
H2
Separation-enhanced Reforming
Steam reforming: CH4 + H2O 3 H2 + CO (H = 206 kJ/mol)
Water-gas shift: CO + H2O H2 + CO2 (H = – 41 kJ/mol)
Overall: CH4 + 2 H2O 4 H2 + CO2
CH4 + H2OCH4 + H2OCH4 + H2O
SMR-catalyst+
CO2 adsorbent
H2 (+ traces CO, CH4)
Sorption-
enhanced
reactors
CH4 + H2OCH4 + H2OCH4 + H2O
Pd-alloymembranecatalyst
Membrane
reactors
H2
H2
steamCO2 CO2 (+ traces CO, CH4, H2)
= Catalyst
The Water Gas Shift Equilibrium
CO + H2O H2 + CO2 (H = – 41 kJ/mol)
CO
con
vers
ion
Temperature
Water Gas Shift Catalysts
• Low-temperature shift catalysts‑ CuO /ZnO2 /Al2O3
‑ Operating Temperature: 185 – 275°C‑ Sulphur tolerance < 0.1 ppm
• High-temperature shift catalysts‑ Fe3O4 / Cr2O3
‑ Operating Temperature: 350 – 520°C‑ Sulphur tolerance 50 ppm
• Sulphur-tolerant shift catalysts‑ CoMoS‑ Operating Temperature: 250 – 500°C‑ > 100 ppm of sulphur is required in the feed
HTS catalyst in separation enhanced CO2 capture
H2 membranes CO2 sorbents
T > 520 °C In case of high CO concentration
Pre-shift necessary, high steam demand
Oxidation by steam May be an issue In regeneration mode:
Hydrogen co-feeding
Reduction because
CO2/CO ratio too low
- May be an issue at high temperature
Interaction with membrane / sorbent
Possible
Separate catalyst from membrane
Possible
Not observed in experiments
The Methane Steam Reforming Reaction
CH4 + 2 H2O 4H2 + CO2 (H = 165 kJ/mol)
CH
4 co
nver
sion
Temperature
Methane Steam Reforming Catalysts
• Ni-based catalysts‑ Used in industrial reforming at 800 – 1000 °C‑ Prone to oxidation and carbon formation
• Noble-metal based catalysts‑ Mainly Rhodium as active metal‑ Used/developed for low-temperature reforming
and more dynamic reforming
Activity at 400°C
• CeO2 and ZrO2 seem to promote activity at low temperature
0
5
10
15
20
25
Rh/LC
Z
Rh/CZA
Rh/ZrO
2
Rh/CeO
2
Rh/TiO
2
Rh/Al2O
3
Rh/M
gAl2O
4
Rh/M
orde
nite
Rh/La
CaCrO
x
Ac
tiv
ity
(a
.u.)
0
10
20
30
40
50
60
70
Dis
pe
rsio
n (
%)
CH4 2.9%
H2O 17.5%
N2 79.6%
Flow 25 sccm
T = 400 °C
P = 1 atm
Activity at higher temperatures
0
10
20
30
40
50
60
70
175 225 275 325 375 425 475 525
Temperature [C]
CH
4 C
onve
rsio
n [%
]
CH4 2.9%
H2O 17.5%
N2 79.6%
Flow 25 sccm
P = 1 atm
Dilution 1:5
Rh/CeZrO2
Rh/ZrO2
Rh/Al2O3
Rh/CeO2
Stability of commercial catalysts
0
10
20
30
40
50
60
70
0 20 40 60 80 100
Time [hr]
CH
4 C
onve
rsio
n [%
]
Ni-catalystVendor A
Noble Metal catalyst Vendor B
Noble metal catalyst Vendor C
Noble metal catalystVendor A
Noble metal catalystECN
CH4 2.9%
H2O 17.5%
N2 79.6%
Flow 25 sccm
T = 500 °C
P = 1 atm
Membrane reformer:Experimental
• ECN PdAg-membrane on ceramic support
• Catalyst: Nickel based reforming catalyst
• T = 650°C
• Feed pressure = 11 bar(a)
• Steam/CH4 ratio = 3
Membrane reformer
• Equilibrium is shifted at lower space velocities
0%
25%
50%
75%
100%
0,0 1,0 2,0 3,0 4,0 5,0
CH4 feed flow [nl/min]
CH
4 co
nver
sion
MR
FBR
Thermo
Coke formation !
Experimental conditions- 100 ml/min flows- 1 – 5 grams sample- 1 – 4 bar(a)- Sorbent only or
sorbent/catalyst mixture
Materials Research – Experimental Apparatus
Materials- Commercially available noble-metal
based catalyst
- 22 wt% K2CO3-Hydrotalcites
Sorption-enhanced reforming: three individual cycles
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 50 100 150 200 250Time [min]
conc
entr
atio
n [v
ol%
]
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%desorption desorption desorptionads ads ads ads
CH4
CO2
Conversion
Reaction conditions: 2.9% CH4, 17.5% H2O, 79.5% N2, 400°C Breakthrough of methane before CO2
CH
4 c
onv
ersi
on [
%]
Sorption-enhanced reforming
• Using a higher amount of catalyst suppresses methane breakthrough
• Amount of catalyst much higher than necessary to reach equilibrium
Reaction conditions: 2.9% CH4, 17.5% H2O, 79.5% N2, 400°C
0
0.2
0.4
0.6
0.8
0 10 20 30 40Elapsed time [min]
Con
cent
ratio
n [%
] adsorption desorptionsolid line: 3.0 g cat + 3.0 g ads
dashed line: 1.5 g cat + 3.0 g ads
CH4
CO2
Preliminary cost calculations for 400 MW NGCC
• For sorption-enhanced reformers, noble-metal catalyst costs are enormous.
• Rhodium-based catalyst costs are 5 times as high as Pd-membrane costs.
SESMR SESMR membraneCatalyst type 1wt% Rh Ni-based 1 wt% RhTemperature [°C] 400 400 650Sorbent/membrane [M Euro /yr] 2.7 2.7 0.9Catalyst [M Euro /yr] 138 8 4.6Natural gas [M Euro /yr] 96 96 97
Costs of Rhodium are very high at the moment…
Challenges for catalysts in separation enhanced reactions
• High activity at relatively low temperatures
• Resistant to carbon formation
Carbon formation
• Possible routes to carbon formation:
‑ Decomposition of CH4:
CH4 2H2 + C (high T)
‑ Boudouard:
2CO CO2 + C (low T)
0
2
4
6
8
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5O/C
H/C
400 °C500 °C600 °C700 °C
Carbon Formation
ATR
SR
H2 w
ithd
rawal
DR
Challenges for catalysts in separation enhanced reactions
• High activity at relatively low temperatures
• Resistant to carbon formation
• Stability under high carbon or strongly reducing conditions
• SERP: resistant to pure steam in sorbent regeneration step: Ni-based catalysts oxidise.
•Membrane: no negative interaction with PdAg-membrane
Conclusions
• The catalyst is an issue for both membrane and sorption-enhanced reforming!
• Nickel-based catalyst showed coking in membrane reactor experiment
• Rh-based catalysts are very active, but price is too high.‑ Ce and Zr promote low-temperature activity‑ Stability uncertain
Future work
• Continue study of (pre)commercial catalysts
• Study mechanism of low-temperature reforming and coke formation and development of low-cost catalysts.‑ Dutch CATHY-project with Technical University
of Eindhoven.
• Kinetics
Acknowledgement
CATO is the Dutch national research programme on CO2 Capture and Storage. CATO is financially supported by the Dutch Ministry of Economic Affairs (EZ) and the consortium partners. (www.co2-cato.nl)
GCEP: Global Climate and Energy Program:
‑ Stanford University
‑ ExxonMobil, GE, Toyota, Schlumberger