high-pressure steam reforming of ethanol
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High-Pressure Steam Reforming of Ethanol
Sheldon H.D. Lee, Rajesh Ahluwalia, and Shabbir Ahmed Argonne National Laboratory
Poster presented at 2005 Fuel Cell SeminarPalm Springs, CA, Nov. 13-17, 2005
Objective Study the pressurized steam reforming of hydrated ethanol for H2 production for a
refueling infrastructure
– Study reforming equilibria and kinetics at elevated pressures– Evaluate high-pressure reforming options, e.g. membrane reactors
Advantages Ethanol fuel
– Renewable liquid fuel– Easy to transport– High energy density (relative to compressed or liquefied gases)– Environmentally more benign (compared with petroleum-derived fuels)
High-pressure steam reforming– More options for H2 purification technique (membrane separation, PSA, etc.)– Energy cost saving for H2 compression
Process Challenges Unfavorable H2 yield at thermodynamic equilibrium
Higher tendency for coke formation
Choice of material for high-temperature/ high-pressure operation
Approach Study thermodynamic equilibria
– Effects of temperature, pressure, and steam-to-C ratio Evaluate system options with respect to efficiency and cost
– Compare high-pressure reforming, compressing reformate, compressing high-purity hydrogen
– Evaluate purification options with high-pressure reformate Establish reforming kinetics through experiments and models
– Set up a micro-reactor test facility for experimental testing– Use Chemcad to perform system modeling on efficiency and H2 yield associated
with alternative process designs
SR Reformer
MembraneSeparator Burner
HeatExchanger
AirHydrogen
Ethanol+Water
Exhaust
Approach Use membrane-reformer to shift the thermodynamic equilibrium back towards higher H2 yield
Use GCTool to perform system modeling on efficiency and H2 yield associated with alternative process designs
Conduct micro-reactor experiments to maximize H2 yield as a function of operating parameters: catalyst formulation, temperature, pressure, S/C molar ratio, and space velocity
Characterize potential membrane materials for their effectiveness, stabilities, and selectivities
Hydrogen compression represents a significant power loss
Background
18.519.8
21.3
23.5
31.5
27.5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8 9 10Initial Pressure of Hydrogen, atm
Com
pres
sion
Los
s / L
HV
(%)
5-Stage Intercooled Compressor Compressor Efficiency: 70%Mechanical Efficiency: 97%
Electric Motor Efficiency: 90%FinalPressure: 6000 psi
Producing hydrogen at elevated pressures represents asignificant improvement in process efficiency.
High pressure increases CH4 formation at the expense of H2
Ethanol steam reforming reaction: C2H5OH (l) + 3H2O(l) = 2CO2 + 6H2, ΔH = +348 kJ Eq. (1)
0
10
20
30
40
50
60
70
80
0 100 200 300Pressure, atm
Prod
uct,
%-w
et H2O
CH4
H2CO2
C2H5OH + 3H2O → ProductsT = 700°C
CO
Effect of pressure on the equilibrium product gas compositions from the steam reforming of ethanol.
Tendency to form carbonaceous deposits (coke) increases at higher pressures
0
20
40
60
80
100
120
0 1000 2000 3000 4000 5000Pressure, psia
CO
x Sel
ectiv
ity% COx
S/C = 6, T = 700°C
COx Selectivity, % =Mols of CO + CO2 Produced
G-Atoms of C in FeedX 100
COx selectivity as a function of pressure
0
1
2
3
4
5
6
600 700 800 900 1000Temperature, °C
Prod
uct Y
ield
, mol
/(mol
-EtO
H)
H2
CO2
CO CH4
S/C = 6, P = 2000 psia
0
1
1
2
2
3
3
1 2 3 4 5 6S/C Ratio
Prod
uct Y
ield
, mol
/(mol
-EtO
H)
H2
CO2
CO
CH4
T = 700°C, P = 2000 psia
• Remove H2 or CO2 to shift equilibrium
• High temperature and high S/C molar ratio in the feed increases H2 yield and reduces undesirable CH4
Potential remedies for adverse pressure effect
Effect of temperature and steam-to-carbon ratio on the equilibrium product gas composition from the steam reforming of ethanol.
System Modeling Reformer efficiency achieves 89% at stoichiometric S/C (= 1.5), followed by a linear decline at higher S/C
η, % = [LHV of H2 produced per Eq. (1) – Heat of reaction of Eq.(1)] 100/[LHV of Ethanol]
where η = efficiency LHV = lower heating value
0
20
40
60
80
100
1 2 3 4 5 6 7 8 9 10S/C Ratio
Theo
retic
al E
ffici
ency
% (L
HV) Effect of S/C molar ratio
on the efficiency of an ideal reformer
Simulated process efficiency approaches 70% at a S/C = 5
50
60
70
80
90
100
5 6 7 8 9 10Steam-to-C Ratio
Effic
ienc
y%
of L
HV
Ideal Reaction
Simulated Process
• C2H5OH + xH2O(l) CO2, CO, H2, H2O(g), CH4, CnHm, …• Chemcad simulated process based on
– Steam-reformer at equilibrium– Hydrogen separation with membrane
• 90% hydrogen recovery– Combustion of raffinate to generate heat – Heat exchange to reformer feeds– Exhaust at 200°C
• Efficiency decreases with increasing S/C
equilibrium
The total moles of H2 recovered are insensitive to reforming pressure in a two-stage reforming/membrane separator system
0
5
10
15
20
25
30
35
100 150 200 250 300 350 400
Reforming Pressure (atm)
H2 P
ress
ure
(atm
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
H2 R
ecov
ered
per
Mol
e of
Eth
anolH 2 Pressure (Stage 2)
H 2 Mols (Stage 2)
Two-Stage ReformingReforming T = 800 o C
H 2 Separation in Stage 1 = 90%S/C = 3.5
H 2 Mols (Stage 1)
H 2 Mols Total (Stage 1+2)
H 2 Pressure (Stage 1)
Effect of the system pressure on the efficiency of one- and two-stage reformer-separator systems
HPLC Pump Cooler Micro
Reactor
Micro-GC Analyzer
Back-Pressure Regulator
TC
TC
TC
TC
Gas-LiquidSeparator
Ethanol-WaterMixture
Ethanol-Water Vaporizer
SwitchingValve
Vent
Waste Container
Furn
ace
Chiller
Micro-reactor test facility
Test conditions:• 600o-700oC• 20-1000 psig
High-pressure ethanol steam-reforming experiments are conducted to maximize H2 yield with respect to temperature, pressure, S/C molar ratio, and space velocity
• The ethanol-water mixture is prevaporized before entering the reactor
• Sud-Chemie Ni catalyst in granules
Ethanol decomposition as a function of temperature
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250 300 350 400 450 500 550Time, min
CO
, CH
4, C
O2,
C2H
6, an
d C
2H4 G
as C
ompo
sitio
n (N
2-Fr
ee B
ase)
, %
(dry
)
80
85
90
95
100
105
H2 G
as C
ompo
sitio
n (N
2-Fr
ee B
ase)
,%
(dry
)
H2 H2
CO2CO2
CH4
CO
CO
CH4
1000 psigS/C = 20
1000 psigS/C = 12
1000 psigS/C = 20
500 psigS/C = 20
Ethylene
Ethane
TC5 = ~470oCStarted Acetaldehyde
decompostionC2H4O = CH4 + CO
Dehydrogenation occurredto form Acetaldehyde:C2H5OH = H2 + C2H4O
TC5 = ~440oCStarted Ethanol
dehydrationC2H5OH = C2H4 + H2O
Gas composition of vaporized ethanol/water mixture from vaporizer(Vaporizer temperatures = 390o - 490oC)
At vaporizer temp. < 490oC, ethanol decomposed < 12% for S/C = 12 & 20 and 1000 psig < 3% for S/C = 20 and 500 psig
Partially decomposed ethanol feed effectively reformed by Ni catalyst bed
0
1
2
3
4
0 50 100 150 200 250 300 350 400 450
Time, min
CO
, CH 4,
& C
O2,
Prod
uct Y
ield
s,
mol
/mol
of C
2H5O
H
0
1
2
3
4
5
6
H 2 Pro
duct
Yie
lds,
m
ol/m
ol o
f C2H
5OH
CO
H2
0.70 g/minBC
0.70 g/minAC
0.50 g/minAC
0.30 g/minAC
0.30 g/minBC
1.00 g/minBC
1.00 g/minAC
CO2
CO2
H2
H2
CO
CH4 CH4
CO
CH4
CO2
CH4
CO2H2
H2H2
H2
CO2
LegendFeed rateBC- Before catalyst bedAC- After catalyst bed
0
0.02
0.04
0.06
0.08
0.1
0 50 100 150 200 250 300 350 400 450
Time, min
Prod
uct Y
ield
, mol
/mol
of C
2H5O
H
Ethylene
Ethane
0.70 g/minBC
0.70 g/minAC
0.50 g/minAC
0.30 g/minAC
0.30 g/minBC
1.00 g/minBC
1.00 g/minAC
EthaneEthane
Ethylene
LegendFeed rateBC- Before catalyst bedAC- After catalyst bed
Product yields as afunction of time
• Feed: S/C =20• Catalyst bed temp. = 620o-650oC• Pressure = 1000 psig
3 times more H2 and CO2 Twice the CH4 50% less CO, and undetectable ethane and ethylene
100% carbon conversion was achieved
The catalyst bed converted the decomposition products into reformate
Ni catalyst slowly degraded with time
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 50 100 150 200 250 300 350 400
Time, min
CO
, CH 4,
& C
O2,
Prod
uct Y
ield
s,
mol
/mol
of C
2H5O
H
CO
CH4
CO2
2.37t = 50
t = 350
1.89
0.56
0.77
0.390.48
0.210.19
0
20
40
60
80
100
120
0 50 100 150 200 250 300 350 400
Time, min.
Gas
eous
Car
bon
Con
vers
ion,
% t = 50 t = 350
76.1
63.2
Product yields andcarbon conversionas a function of time
• Feed: S/C =12• GHSV = 85,600 h-1
• Catalyst bed temp. = 630o-660oC• Pressure = 1000 psig
Ni catalyst has been known* to deactivate as a result of coke formation The condensate collected from the test contained 4.53% ethanol,
0.84% acetaldehyde, and 0.06% acetic acid*Agus Haryanto, Sandun Fernando, Naveen Murali, and Sushil Adhikari, “Current Status of Hydrogen Production Techniques by Steam Reforming of Ethanol: A Review”, Energy & Fuel, 2005, 19, 2098-2106
Effect of pressure on product gas composition
0
20
40
60
80
H2 CO CH4 CO2 Ethylene Ethane
Prod
uct C
ompo
sitio
n, %
(dry
)
P = < 20 psig
P = 1000 psig
Effect of pressure on product gas composition agrees with equilibrium predicted trend
Feed: S/C = 12Temp. = 650oCGHSV = 85,600 h-1
Effect of gas hourly space velocity on product yields
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 20,000 40,000 60,000 80,000 100,000 120,000 140,000
GHSV, h-1
Avg
. CO
& C
H 4 Pro
duct
Yie
lds,
mol
/mol
0
1
2
3
4
5
6
Avg
. H2 &
CO
2 Pro
duct
Yie
lds,
mol
/mol
H2
CO2
Ethane & Ethylene
CO
CH4
Feed: S/C = 20Temp. = 620o-650oCP = 1000 psig
Increasing GHSV decreases H2, CO2, and CO yields, but increases CH4 yield
Conclusions Steam reforming of ethanol at elevated pressures can lead to better process
efficiencies. Elevated pressure process presents challenges in unfavorable thermodynamic
equilibrium, tendency for coke formation, and material choice. Homogeneous decomposition of ethanol occurred at temperatures close to boiling
point of ethanol-water solution at pressure. High pressure increases CH4 formation at the expense of H2 yield
Future Work Study kinetics and define operating parameters for maximizing H2 yield
Evaluate system designs that take advantage of pressurized steam reforming
Acknowledgements
This work is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen, Fuel Cells, & Infrastructure Technologies Program
Argonne National Laboratory is managed by The University of Chicago for the U.S. Department of Energy
The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
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