Hydrogen Production

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Hydrogen Production

• Hocking College
• Nelsonville, Ohio

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One Advantage of using hydrogen

• One advantage is that it stores approximately 2.6
  times the energy per unit mass as gasoline, and
  the disadvantage is that it needs about 4 times
  the volume for a given amount of energy. A 15
  gallon automobile gasoline tank contains 90
  pounds of gasoline. The corresponding hydrogen
  tank would be 60 gallons, but the hydrogen would
  weigh only 34 pounds.

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Current global hydrogen production

• 48 from natural gas
• 30 from oil
• 18 from coal
• 4 from electrolysis of water

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Primary Uses for Hydrogen Today

• 1. About half is used to produce ammonia (NH3)
  fertilizer.
• 2. The other half of current hydrogen production
  is used to convert heavy petroleum sources into
  lighter fractions suitable for use as fuels.

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Hydrogen Production Processes

• Steam Methane Reforming
• Coal Gasification
• Partial Oxidation of Hydrocarbons
• Biomass Gasification
• Biomass Pyrolysis
• Electrolysis
• Thermochemical
• Photochemical
• Photobiological

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Steam Methane Reforming

• most common method of producing commercial bulk
  hydrogen.
• Most common method of producing hydrogen used in
  the industrial synthesis of ammonia.
• It is the least expensive method.
• High temperature process (700 1100 C.
• Nickel based catalyst (Ni)

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The Steam Methane Reforming Process

• At 700 1100 C and in the presence of a nickel
  based catalyst (Ni), steam reacts with methane to
  yield carbon monoxide and hydrogen.
• CH4 H2O ? CO 3 H2
• Additional hydrogen can be recovered by a
  lower-temperature gas-shift reaction with the
  carbon monoxide produced. The reaction is
  summarized by
• CO H2O ? CO2 H2

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Purification of Hydrogen

• Carbon dioxide and other impurities are removed
  from the gas stream, leaving essentially pure
  hydrogen.
• Endothermic reaction (Heat must be added to the
  reactants for the reaction to occur.)

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Schematic of the SMR Process
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Coal Gasification

• well-established commercial technology
• competitive with SMR only where oil and/or
  natural gas are expensive.
• coal could replace natural gas and oil as the
  primary feedstock for hydrogen production, since
  it is so plentiful in the world.

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Partial Oxidation Hydrocarbons

• process can be used to produce hydrogen from
  heavy hydrocarbons such as diesel fuel and
  residual oil.
• Any hydrocarbon feedstock that can be compressed
  or pumped may be used in this technology.

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Partial Oxidation

• methane and other hydrocarbons in natural gas are
  reacted with a limited amount of oxygen
  (typically, from air) that is not enough to
  completely oxidize the hydrocarbons to carbon
  dioxide and water.
• CH4 ½O2 ? CO 2H2 (heat)
• Exothermic reaction (heat is evolved)

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Schematic of Partial Oxidation
Partial Oxidation Plant Diagram
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Thermochemical Production of Hydrogen

• When water is heated to above 2500 oC, it
  separates into oxygen and hydrogen in a process
  known as thermolysis.
• However, at such high temperatures, it is
  difficult to prevent the oxygen and hydrogen from
  recombining to form water.

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Thermochemical Production of Hydrogen

• Thermochemical water-splitting cycles can lower
  the temperature and help separate oxygen and
  hydrogen products to produce pure hydrogen gas.
• These cycles can improve the efficiency of
  hydrogen production from 30 for conventional
  electrolysis to around 50 efficiency
• One of the most promising cycles so far is the
  sulfur-iodine (S-I) cycle.

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• Sulfur dioxide (SO2 ) and iodine (I2) are fed
  into the cycle as chemical catalysts..
• A catalyst lowers the activation energy of a
  reaction without being used up by the reaction.

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Sulfur-Iodine Thermochemical Cycle

• In this cycle, sulfur dioxide (SO2) and iodine
  (I2) are feed into the cycle as a chemical
  catalyst.
• A catalyst lowers the temperature at which the
  reaction will occur without being used up by the
  reaction.

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There are three steps in the S-I cycle

• Step 1
• I2 SO2 2H2O 2HI H2SO4
• The reaction is run at 120 degrees C.
• The hydrogen iodide and sulfuric acid are
  separated, usually by distillation.

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• Step 2
• Generation of oxygen and regeneration of SO2.
• H2SO4 H2O SO2 1/2 O2
• This reaction is run at 850 degrees C.

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• Step 3 Generation of hydrogen and regeneration
  of I
• 2HI H2 I2
• This reaction is run at 450 degrees C.

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SulfurIodine Cycle

• These reactions can reduce the high temperature
  demands of the thermolysis of water for the
  production of hydrogen gas and can provide a
  mechanism for the separation of oxygen and
  hydrogen products to prevent recombination.

Source Office of Nuclear Energy, Science and
Technology
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Biomass Production of Hydrogen

• Hydrogen can be produced numerous ways from
  biomass.
• Biomass is defined as a renewable resource made
  from renewable materials. Examples of biomass
  sources include
• gtswitchgrass
• gtplant scraps
• gtgarbage
• gthuman wastes
• Gasification of biomass could be a way of
  extracting hydrogen from these organic sources.

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Biomass Production of Hydrogen

• The biomass is first converted into a gas through
  high-temperature gasifying.
• The hydrogen rich vapor is condensed in pyrolysis
  oils.
• These oils can be steam reformed to generate
  hydrogen.
• This process has resulted in hydrogen yields of
  12 - 17 hydrogen by weight of the dry biomass.
• When biological waste material is used as a
  feedstock, this process becomes a completely
  renewable, sustainable method of hydrogen
  generation.

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Electrolysis

• Electrolysis is the technical name for using
  electricity to split water into its constituent
  elements, hydrogen and oxygen.
• The splitting of water is accomplished by passing
  a DC electric current through water.
• The electricity enters the water at the cathode,
  a negatively charged terminal, passes through the
  water and exists via the anode, the positively
  charged terminal.
• The hydrogen is collected at the cathode and the
  oxygen is collected at the anode. Electrolysis
  produces very pure hydrogen for use in the
  electronics, pharmaceutical and food industries

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Electrolysis

• The hydrogen is collected at the cathode and the
  oxygen is collected at the anode.
• Electrolysis produces very pure hydrogen for use
  in the electronics, pharmaceutical and food
  industries.

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Photobiological

• This method involves using sunlight, a biological
  component, catalysts and an engineered system.
• Specific organisms, algae and bacteria, produce
  hydrogen as a byproduct of their metabolic
  processes.
• These organisms generally live in water and
  therefore are biologically splitting the water
  into its component elements.
• Currently, this technology is still in the
  research and development stage and the
  theoretical sunlight conversion efficiencies have
  been estimated up to 24.