HighPressure 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
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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

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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

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Process Challenges

• Unfavorable H2 yield at thermodynamic equilibrium
  
• Higher tendency for coke formation
• Choice of material for high-temperature/
  high-pressure operation

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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

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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

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Background

• Hydrogen compression represents a significant
  power loss

Producing hydrogen at elevated pressures
represents a significant improvement in process
efficiency.
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High pressure increases CH4 formation at the
expense of H2 Ethanol steam reforming
reaction C2H5OH (l) 3H2O(l) 2CO2
6H2, ?H 348 kJ Eq. (1)
Effect of pressure on the equilibrium product gas
compositions from the steam reforming of ethanol.
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Tendency to form carbonaceous deposits (coke)
increases at higher pressures
COx selectivity as a function of pressure
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Potential remedies for adverse pressure effect

• 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

Effect of temperature and steam-to-carbon ratio
on the equilibrium product gas composition from
the steam reforming of ethanol.
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System Modeling

• Reformer efficiency achieves 89 at
  stoichiometric
• S/C ( 1.5), followed by a linear decline
  at higher S/C
• ?, LHV of H2 produced per Eq. (1)
  Heat of reaction of Eq.(1) ?
• 100/LHV of Ethanol
• where ? efficiency
• LHV lower heating value

Effect of S/C molar ratio on the efficiency of an
ideal reformer
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• Simulated process efficiency approaches 70 at a
  S/C 5

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The total moles of H2 recovered are insensitive
to reforming pressure in a two-stage
reforming/membrane separator system
Effect of the system pressure on the efficiency
of one- and two-stage reformer-separator systems
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• High-pressure ethanol steam-reforming experiments
  are
• conducted to maximize H2 yield with respect
  to temperature,
• pressure, S/C molar ratio, and space velocity
  

• Micro-reactor test facility
• Test conditions
• 600o-700oC
• 20-1000 psig

• The ethanol-water mixture is prevaporized before
  entering the reactor
• Sud-Chemie Ni catalyst in granules

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Ethanol decomposition as a function of
temperature
Gas composition of vaporized ethanol/water
mixture from vaporizer (Vaporizer temperatures
390o - 490oC)

• At vaporizer temp. lt 490oC, ethanol decomposed
• lt 12 for S/C 12 20 and 1000 psig
• lt 3 for S/C 20 and 500 psig

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Partially decomposed ethanol feed effectively
reformed by Ni catalyst bed

• Product yields as a
• function of time
• Feed S/C 20
• Catalyst bed
• temp. 620o-650oC
• Pressure 1000 psig

• The catalyst bed converted the decomposition
  products into reformate

• 3 times more H2 and CO2
• Twice the CH4
• 50 less CO, and undetectable ethane and
  ethylene
• 100 carbon conversion was achieved

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Ni catalyst slowly degraded with time

• Product yields and
• carbon conversion
• as 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

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Effect of pressure on product gas composition

• Effect of pressure on product gas composition
  agrees with equilibrium
• predicted trend

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Effect of gas hourly space velocity on product
yields

• Increasing GHSV decreases H2, CO2, and CO
  yields,
• but increases CH4 yield

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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

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Future Work

• Study kinetics and define operating parameters
  for maximizing H2 yield
• Evaluate system designs that take advantage of
  pressurized
• steam reforming

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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

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Argonne National Laboratory is managed by The
University of Chicago for the U.S. Department of
Energy