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.