2. Discovery of Hydrogen
โข In 1671, Robert Boyle described the reaction between iron fillings and dilute
acids which resultant produce the hydrogen gas.
โข In 1766, Henery Cavendish was the 1st to recognise hydrogen as a discreate
substance.
โข He named the gas as โflammable airโ.
โข Cavendish studied the properties of hydrogen as an element.
3. Timeline and isotopes
โข Lavoiser did the 1st preparation of H2 using steam flux on metallic iron.
โข H2 was 1st liquefied by James Dewar in 1898 and solidified next year.
โข Its isotope Deuterium was discovered in 1931 by Harold Urey.
โข Heavy water which is deuterium oxide was also discovered by Ureyโs group in
1932.
โข Another isotope Tritium (which is radioactive) was prepared in 1934 by
famous physicist Ernest Rutherford, Mark Oliphant and Paul Harteck.
4. HYDROGEN PRODUCTION METHODS
โข Steam methane reforming
โข Electrolysis of water
โข Hydrogen from biomass
โข High temperature fuel cells
โข Other methods
5. 5
The First Question:
Where Does Hydrogen Come From?
95% of hydrogen is currently produced by steam reforming
Partial Oxidation
Steam Reforming
Electrolysis
Thermochemical
Fossil Fuels
Water
Biomass
HYDROGEN
6. STEAM METHANE REFORMING
โข It is the process by which natural gas or other methane stream, such as biogas or landfill gas, is
reacted with steam in the presence of a catalyst to produce hydrogen and carbon dioxide.
โข At high temperatures (700โ1100 ยฐC), steam (H2O) reacts with methane (CH4) in an endothermic
reaction to yield syngas.
CH4 + H2O โ CO + 3 H2
โข In a second stage, additional hydrogen is generated through the lower-temperature,
exothermic, water gas shift reaction, performed at about 360 ยฐC:
CO + H2O โ CO2 + H2
โข Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to
CO2. This oxidation also provides energy to maintain the reaction.
11. Electrolysis of water
โข Electrolysis of water is the decomposition of water (H2O) into oxygen (O2)
and hydrogen gas (H2) due to an electric current.
โข An electrical power source is connected to two electrodes, or two plates
(typically made from some inert metal such as platinum, stainless steel or
iridium) which are placed in the water.
โข Hydrogen will appear at the cathode (the negatively charged electrode,
where electrons enter the water), and oxygen will appear at the anode (the
positively charged electrode) being passed through the water.
12. ELECTROLYSIS CONTD.
โข In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (eโ) from the
cathode being given to hydrogen cations to form hydrogen gas (the half reaction balanced with acid):
โข Reduction at cathode: 2 H+(aq) + 2eโ โ H2(g)
โข At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the
anode to complete the circuit:
โข Oxidation at anode: 2 H2O(l) โ O2(g) + 4 H+(aq) + 4eโ
โข To add half reactions they must both be balanced with either acid or base.
โข Cathode (reduction): 2 H2O(l) + 2eโ โ H2(g) + 2 OH-(aq)
โข Anode (oxidation): 4 OH- (aq) โ O2(g) + 2 H2O(l) + 4 eโ
โข Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen:
โข Overall reaction: 2 H2O(l) โ 2 H2(g) + O2(g)
15. Anaerobic Corrosion [Schikorr reaction]
โข Under anaerobic condition iron alloys are slowly oxidised by protons of water
โข Protons themselves get reduced to molecular hydrogen
โข This process consist of following reactions-
Fe + 2H2O Fe(OH)2 + H2
3Fe(OH)2 Fe3O4 + 2H2O + H2
โข Fe3O4 is thermodynamically more stable than Fe(OH)2
16. Gasification process
โข Oxygen and water molecules oxidize the coal and produce a
gaseous mixture of carbon dioxide (CO2), carbon
monoxide (CO), water vapor (H2O), and molecular hydrogen (H2).
โข The desired end product is usually syngas (i.e., a combination of
H2 + CO), but the produced coal gas may also be further refined
to produce additional quantities of H2:
โข Hydrogen is the desired end-product, the coal gas (primarily the
CO product) undergoes the water gas shift reaction where more
hydrogen is produced by additional reaction with water vapor:
โข CO + H2O โ CO2 + H2 C (i.e., coal) + O2 + H2O โ H2 + 3CO
20. Above Ground Gasification
Fluid-bed reactor (Winkler, HTW, CFB โ
dry ash; KRW, U-Gas โ Agglomerating)
Air fluidizes a bed and carbon
containing particles added
Proper mixing of fuel and oxidant
provide good mass transfer and heat
transfer
Fine particle will escape with syngas and
needs to be cleaned
Very good heat/mass transfer so
partially reacted carbon may settle with
ash
Slagging will reduce fluidization, so
temp remains below softening point for
ash
21.
22. HYDROGEN FROM BIOMASS
โข Biomass + O2 CO + H2 + CO2 + Energy
โข Why Biomass to hydrogen?
โข Biomass has the potential to accelerate the realization of hydrogen as a major fuel of the future.
โข Biomass is renewable, consumes atmospheric CO2 during growth and is a CO2 neutral resource in
life cycle
โข It can have a small net CO2 impact compared to fossil fuels
โข Gasification coupled with water-gas shift is the most widely practiced process
route for biomass to H2.
24. โข Above shown method was a Thermo-chemical processes which is less
expensive because they can be operated at higher temperatures and therefore
obtain higher reaction rates.
โข But generate pollution as burning is involved
โข Alternate technologies developing rapidly involve-
โข Metabolic Processing of Biomass- H2 from biomass can also be produced by metabolic
processing to split water via photosynthesis or to perform the shift reaction by photo biological
organisms. The use of microorganisms to perform the shift reaction is of great relevance
to hydrogen production because of the potential to produce CO in the product gas far
below than in water gas shift catalysts.
25. โข Direct Solar Gasification- Several investigators have examined the use of solar process
heat for gasification or organic solid wastes such as carbonaceous materials such as
agricultural waste to produce syn-gas (a blend of hydrogen and carbon monoxide) for
producing H2.
โข Use of thermo-nuclear device to vaporize waste organic materials in an underground large-scale plasma
process
โข Electrochemical oxidation of solid carbonaceous wastes.
26. OTHER METHODS
Hydrogen can also be produced via other methods means including-
โข In 2007 it was discovered that an alloy of Al and Ga in pellet form when added
to water generates H2
โข This has imp potential implications on H2 economy as H2 can be produced in situ
so transportation and storage costs can be cut short.
โข From algae(C.reinhardtii)
โข By direct solar electrochemical processes,
โข From various nuclear-power-assisted pathways,
โข From fossil fuels.
27. STEPS IN INDUSTRIAL PROCESSSING OF
HYDROGEN
Production Delivery
Storage Conversion
End use application
28. CURRENT GLOBAL HYDROGEN
PRODUCTION
โข 48% from natural gas
โข 30% from oil
โข 18% from coal
โข 4% from electrolysis of water
28
48%
30%
18%
4%
Natural Gas
oil
coal
electrolysis of water
29. INDUSTRIAL HYDROGEN
APPLICATIONS
โข Largest application of H2 is for processing of fossil fuels (hydrodealkylation,
hydrodesulphurization & hydrocracking)
โข Manufacture of Ammonia, Methanol
โข Large amounts of H2 is used in oil industries for hydrogenation of
unsaturated oils
โข It is used shielding gas in welding.
โข H2 is used as rotor coolant in electrical generators
30. INDUSTRIAL HYDROGEN APPLICATIONS contd.
โข Liquid H2 is used in the Cryogenic studies including superconductivity
studies.
โข Earlier it was used as lifting gas lifting gas but after the incident of
Hindenburg Disaster this practice was opted out.
โข Recently, H2 is used pure or mixed with N2 as a tracer gas for minute leak
detection in automobile, chemical plants, aerospace etc.
โข Hydrogen is an authorised food additive ( E949) that allows food package
leak testing among other anti-oxidizing properties
31. Hydrogen safety
โข H2 safety covers safe production, use & handling of H2
โข H2 posses unique challenges due to
โข ease of leak โ odourless, colourless & tasteless. Smell additives unsuccessful.
โข low energy ignition- order of 0.02 mJ.
โข buoyancy โ once leaked rises rapidly, v difficult to control.
โข its ability to embrittle materials- Enters pipe line and can follow them to their destination.
โข Current ANSI/AIAA standards for H2 safety guidelines is G-095-2004, Guide to Safety of
Hydrogen & Hydrogen Systems. These are adopted from NASA worldโs largest user of H2.
32. Hydrogen Storage
Storage- A major difficulty with hydrogen
โข H2 has low energy density per volume
โข Requires large tanks to store
โข Ways of H2 storage
โข High-pressure storage in the gaseous form
โข Very low temperature storage in the liquid form
โข Hydride-based storage in the solid form
33. One way of storing hydrogen is
at high pressure in tanks
But requires large volume
(up to 700 bar);
Liquefied hydrogen is denser than
gaseous hydrogen and thus it contains
more energy in a given volume. Similar
sized liquid hydrogen tanks can store
more hydrogen than compressed gas
tanks, but it takes energy to liquefy
hydrogen.
34. Hydrogen atoms or molecules bound tightly
with other elements in a compound (or
potential storage material) may make it
possible to store larger quantities of hydrogen
in smaller volumes at conditions that are
within the practical operational boundaries of
a polymer electrolyte membrane (PEM) fuel
cell.
Material Based Storage
35. Environmental Concerns
โข 48% of hydrogen made from natural gas
โข Creates CO2 โ a greenhouse gas
โข Hydrogen H2 inevitably leaks from containers
โข Creates free radicals (H) in stratosphere due to ultraviolet radiation
โข Could act as catalysts for ozone depletion
36. ADVANTAGES OF HYDROGEN GAS
โข Readily available- There is no other element in the entire universe as abundant as is H2
โข No harmful emissions- As is apparent from the fact that NASA used exhaust from their shuttle as a
source of drinking water for astronauts
โข Fuel Efficient- H2 has very high calorific value as compared to other fuels(by mass)
โข Very low viscosity makes it ideal as coolant
โข Non-toxic- It has no benchmark effect on humans.
โข Renewable- As we have more than ยพ portion of earth as water, there will be no shortage of H2, we
just need to device a method to split it.
37. DISADVANTAGES
โข Expensive- The available methods require a lot of energy hence capital input.
โข Storage- Storage is one the main causes of reluctance of investors in this energy source.
โข Not easy to replace existing infrastructure- Currently all the machinery is designed to work
on the gasoline as fuel, it is said that replacing them to make compatible with H2 is far expensive
than its production.
โข Highly Flammable- It is a fire hazard, liquid H2 explodes with intensity comparable to TNT
โข Dependency on fossil fuels- It should not be overlooked that though H2 is never ending element,
but the energy required to separate it calls for dependency on natural fuels to a large extent(48%).
