Hydrogen - Overview
Hydrogen- future society
From International Society of Hydrogen Energy
Hydrogen
•Hydrogen is not a source of energy, while solar,
wind, natural gas and oil are.
•There are no naturally occurring sources or
reservoirs of hydrogen on earth.
•Hydrogen can be extracted from fossil fuels, or
can be produced by using the process of
electrolysis to split water into hydrogen and
ozxygen. Both these processes require energy. This
energy can be provided by fossil fuels or renewable
sources of energy like solar and wind.
Hydrogen- Usage
•Ammonia and methanol production as well petroleum
refining require huge amounts of hydrogen
•In the electronic industries, hydrogen is used to produce
silicon, which is needed for semiconductor processing
•In metallurgic industry, hydrogen is used to remove oxygen in
annealing, sintering and in furnace brazing
•Hydrogen and oxygen are the main propellants of rocketpowered spacecraft, missiles in the aerospace industry
Hydrogen-Properties
Symbol: H; gas H2
Oxidation number +1
Density: gas 0.090 kg/m3, (air 1.3 kg/m3)
liquid 70.8 kg/m3
solid: 70.6 kg/m3
Melting Point: -259.3 C
Boiling Point: - 252.9 C
Hydrogen-Properties
• Molar Mass
2.106 g/mol
• Electron binding (ionisation) energy in 1s ground state
2.18 aJ*
• Average distance between nucleons, H2
0.074 nm
• Dissociation energy, H2 to H at infinite separation
0.71 aJ*
• Ionic conductance at diluted H+ ions in water at 298 K
0.035 m2 /mol/Ω
• Specific heat at constant pressure and 298 K
14.3 kJ/kg/K
• Solubility in water at 1 bar, 298 K
0.019 m2 /m3
* aJ = attoJoule = 10-18 Joule
Hydrogen
•Hydrogen does not smell and is colorless and nontoxic.
•Hydrogen has a high caloric value, the lowest
molecular weight, the highest thermal conductivity
and the lowest density among all gases.
•0.324 g of hydrogen has the same energy content
as 1 kg gasoline but 1 kg gasoline corresponds to a
volume of 1.3 liters while 324 g hydrogen occupies
3.932 liters.
Hydrogen
• 1 kg hydrogen gas contains as much energy as
2.1 kg natural gas or 2.8 kg gasoline.
• The fraction of hydrogen in common water is
11.2 % of weight.
• Approximately 500 billions m3 hydrogen are
produced, stored and transported worldwide.
Mostly used in the chemical process
industries.
Hydrogen
•Air mixtures with hydrogen are explosive
in certain proportions. If the gas mixture
comprises two volume parts hydrogen and
one volume part oxygen the reaction is
very violent.
•The flame temperature of hydrogen is
2600 C, almost invisible but light blue.
Hydrogen – be careful
Hydrogen Production and Delivery
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Biological Water Splitting
Fermentation
Conversion of Biomass and Wastes
Photoelectrochemical Water Splitting
Solar Thermal Water Splitting
Renewable Electrolysis, e.g., wind energy
From Fossil fuels
Biological Water Splitting
• Certain photosynthetic microbes use light
energy to produce hydrogen from water as
part of their metabolic processes. Becuase
oxygen is produced along with the hydrogen,
photobiological hydrogen production
technology must overcome the inherent
oxygen sensitivty of hydrogen evolving
enzyme.
Fermentation
• Pretreatment to convert lignocellulosic
biomass into sugar-rich feedstocks that can be
directly fermentated to produce hydrogen,
ethanol and high value chemicals
• Fermentation of crystalline cellulose directly
to hydrogen means lower feedstock costs
Conversion of Biomass and Wastes
• Hydrogen can be produced by pyrolysis or
gasification of biomass resources, e.g.,
agricultural residues
Photoelectrochemical Water Splitting
• This is the cleanest way to produce hydrogen
by using the sunlight to directly split water
into hydrogen and oxygen
Solar Thermal Water Splitting
• Ultrahigh temperatures are required for
thermochemical reaction cycles to produce
hydrogen. High flux solar furnace reactors
concentrating the solar energy generate
temperatures between 1000 and 2000 C.
Renewable Electrolysis
• Renewable energy sources like photovoltaics,
wind, biomass, hydro and geothermal can
provide clean and sustainable electricity which
also can be used for electrolysis splitting of
water.
Illustration of Electrolysis of Water
by Electricity
From fossil fuels
• Industrial production dominated by using
methane (natural gas)
• Bad thing: Generation of CO2
From fossil fuels
• Steam reforming is commonly used today to produce
hydrogen from fuels based on hydrocarbons, like natural gas
or biogas.
• Industrial reforming of natural gas
• A high temperature (700° C – 1100° C) and presence of a
metal based catalyst makes steam to react with methane and
carbon monooxide and hydrogen are created. The reaction is
endothermal and requires a lot of energy,
• CH4 + H2O
CO + 3 H2
From fossil fuels
• The biproduct carbon monooxide can be used together with
water to produce additional hydrogen. This process occurs at
a lower temperature, The reaction is exothermal (energy is
released).
• CO + H2O
CO2 + H2
From fossil fuels
• Reforming of gases not being methane
• As oil is extracted, gases naturally present are exhausted. This
may create environmental problems for workers as well as
having negative effects on the climate. However, these gases
can be collected and be used as fuels.
• Hydrocarbons not being methane are first converted to
synthetic gas (H2 + CO) and then to methane (CH4), carbon
dioxide (CO2) and hydrogen (H2).
• Compared to the steam reforming process, this latter
reforming occurs at low temperature and less steam is
needed.
Storage of Hydrogen
Storage of Hydrogen
• In gaseous form at high pressure (700 bar) in
special high-pressure containers
Storage of Hydrogen in High Pressure
Vessels
• Cheap and most common in steel vessels
Typical pressure range: 200-700 bar
• Disadvantages: high weight and big volume
Storage of Hydrogen
• In liquid form. It needs to be chilled and
compressed. Very cold, below -423.2
Fahrenheit
Storage of Hydrogen in Zeolites
• A zeolite is a material consisting of silicon and
aluminum in crystalline and microporous form.
Pore size 0.3-1 nm.
• At pressure 30 bar, temperature 327 C, the
hydrogen molecules are forced into the material.
As temperature and pressure are reduced, the
hydrogen becomes bounded in the crystal.
• Disadvantage: low storage capacity, 0.7 % weight
is hydrogen.
Storage of Hydrogen in Iron
• In a vessel with corroded surfaces hydrogen
can be bounded in the corroded material and
the material is converted to iron. To extract
the hydrogen, water steam is supplied and the
corrosion process restarts.
• Storage capacity: 4.5 % weight is hydrogen
Storage of Hydrogen in Metal Hydrides
• A metal hydride is an alloy of a metal and
hydrogen.
• Magnesiumhydride has the best storage capacity,
7.6 % weight is hydrogen.
• The hydrogen is splitted up as it comes in contact
with magnesium which is pulverized. 30-55 bar
pressure during filling. Heat is released during the
process and as hydrogen should be extracted
heat has to be supplied.
Storage of Hydrogen in Metal Hydrides
• The metal hydrides are sensitive to poisoning
by water and oxygen but also by sulphur oxide
dihydrogensulphid, carbon monooxide and
carbon dioxide.
Metal hydride storage
Storage of hydrogen in sodiumboron-hydrides - Power balls
• Hydrogen can be stored by using sodium-boron-hydride
(NaBH4 ) which is produced by heating sodium-hydrooxide
(NaOH). As NaBH4 reacts with water, hydrogen is created. The
NaBH4 can be formed as balls or pellets.
• The rest product of the reaction of NaBH4 and H2O is called
Borax, NaBO2. The Borax can be exchanged and re-charged
with hydrogen. Borax is available to a large extent in out-dried
salty lakes.
• The NaBH4 is not explosive and not risky for fires. It can be
stored at atmospheric pressure. The storage capacity is
estimated to be 4.3 weight % hydrogen at a density of 47
kg/m3.
Storage in hydrogen pills
• In hydrogen pills, hydrogen is reacting with
nitrogen to form ammonia which is stored in
salt crystals of magnesium chlorine. Up to 9.1
% weight of the pills can be hydrogen. (1 litre
of hydrogen pills corresponds to 1 litre of
gasoline).
Properties of Some Fuels
Comparison of some properties of some fuels
Property
Min. Energy of Ignition,
10-3 J
Flame Temperature, C
Auto-Ignition
Temperature in Air, C
Max. Flame Velocity,
m/s
Range of Flammability
in Air, vol. %
Range of Explosivity in
Air, vol. %
Diffusion coefficient in
air, 10-4 m2/s
Hydrogen Methanol Methane Propane Gasoline
0.02
0.29
0.25
0.24
2045
585
385
3.46
4-75
7-36
13-65
0.61
1875
540
510
0.43
0.47
5-15
2.5-9.3
6.3-13.5
0.16
0.20
2200
230-500
1.0-7.6
1.1-3.3
0.10
0.05
Energy Density - Comparison
Storage form
Hydrogen, gas (100 kPa, 1
bar)
Hydrogen, gas (200 bar)
Hydrogen, gas (300 bar)
Hydrogen, liquid
Hydrogen in metal hydrides
Hydrogen in metal hydride,
typical
Methane (natural gas), (100
kPa)
Methanol
Ethanol
Energy Density
kJ/kg
120 000
Energy Density
MJ/m3
10
Density
kg/m3
0.090
120 000
120 000
120 000
2 000 - 9 000
2 100
1 900
2 700
8 700
5 000 - 15 000
11 450
15.9
22.5
71.9
5 480
56 000
37.4
0.668
21 000
28 000
17 000
22 000
0.79
0.79