Hydrogen Production

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Hydrogen Production
Hocking College
Nelsonville, Ohio
One Advantage of using hydrogen
1.
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.
Current global hydrogen production
 48%
from natural gas
 30%
from oil
 18%
from coal
 4%
from electrolysis of water
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.
Hydrogen Production Processes









Steam Methane Reforming
Coal Gasification
Partial Oxidation of Hydrocarbons
Biomass Gasification
Biomass Pyrolysis
Electrolysis
Thermochemical
Photochemical
Photobiological
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)
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
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.)
Schematic of the SMR Process
H 2O
Water
Methane
Gasoline
Ethanol
Methanol
10%
CO
REFOR MER
2,000 ppm
CO
WATER GAS SHIFT
REACTOR
<100 ppm
CO
REMOVAL OF CO
AND CO2
H2
FUEL CELL
STACK
O2
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.
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.
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)
Schematic of Partial Oxidation
Partial Oxidation Plant Diagram
Thermochemical Production of
Hydrogen
water is heated to above 2500 oC, it
separates into oxygen and hydrogen in a
process known as thermolysis.
 When
 However,
at such high temperatures, it is
difficult to prevent the oxygen and
hydrogen from recombining to form water.
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.
 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.
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.
There are three steps in the S-I
cycle
 Step
 I2
1:
+ SO2 + 2H2O
 The
 The
2HI + H2SO4
reaction is run at 120 degrees C.
hydrogen iodide and sulfuric acid are
separated, usually by distillation.
 Step
2:
 Generation
of oxygen and regeneration of
SO2.
 H2SO4
 This
H2O + SO2 + 1/2 O2
reaction is run at 850 degrees C.
 Step
3: Generation of hydrogen and
regeneration of I
 2HI
 This
H2 + I2
reaction is run at 450 degrees C.
Sulfur—Iodine 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
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:
>switchgrass
>plant scraps
>garbage
>human wastes
 Gasification of biomass could be a way of
extracting hydrogen from these organic sources.
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.
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
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.
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%.
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