Post on 13-Jul-2015
transcript
Contents
Introduction
Hydrogen properties
Hydrogen production methods
Bio hydrogen & its
History
production methods
Economics
Conclusion
Reference
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Understanding the hydrogen
Hydrogen is the first element on the periodic
table, making it the lightest element on earth.
0.00005% in air
It rises in the atmosphere and is therefore rarely
found.
pure hydrogen gas, burning in air, producing
water and heat.
Combustion heat enables hydrogen to act as a
fuel.
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Hydrogen properties
Colorless and odorless
Extremely reactive with oxygen and other
oxidizers.
Low ignition energy.
High flame temperature.
Invisible flame in daylight conditions.
Small molecular size promotes leaks and diffusion.
The cryogenic liquid at 20K is even colder than frozen nitrogen, oxygen or argon.
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Key facts about Hydrogen as a fuel
Highly combustible and can be used as a fuel.
1g of combustion provides 30000 cals as compared to gasoline
that gives only 11000 cals.
Can be produced from water using Biological agents.
Biologically produced hydrogen is known as Biohydrogen.
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Hydrogen Production
1. Electrolysis.
2. Steam-methane reforming process.
3. Biological process(bio-hydrogen).
Hydrogen production always requires more
energy than can be retrieved from the gas as
a fuel later on when they are produced by above
two process.
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Biological production
Biological hydrogen production stands out as
an environmentally harmless process carried
out under mild operating conditions, using
renewable resources.
Several types of microorganisms such as the
photosynthetic bacteria, cyano bacteria, algae
or fermentative bacteria are commonly utilized
for biological hydrogen production.
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Milestones
1939 Hans Gaffron discovered that algae can switch
between producing O2 and H2.
1997 prof. Anastasios Malis discovered that deprivation of
sulphur will cause the algae to switch from producing
H2.He found that enzyme hydrozenase responsible
for the reaction.
2006 Researcher from the University of Bielfeld have
genetically changed the single cell Chlamydomonas
reinhardtiiin in such a way that it produces an large
amount of hydrogen.
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2007 It was discovered that if cupper is added to
block O2 generation in algae.
2007 prof. Anastasios Malis studying solar to chemical
energy conversion efficiency in tax X mutants of
Chlamydomonas reinhardtiiin , achieved 15% efficiency .
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Methods of Bio hydrogen Production
1.Dark Fermentation
2.Photo Fermentation
3.Combined Fermentation
4.Direct Photolysis (algae)
5.Indirect Photolysis (cynobacteria)
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1. Dark Fermentation
Fermentative conversion of organic substrate to
biohydrogen.
This method doesn’t require light energy.
The Gram+ve bacteria of Clostridium genus is of
great potential in biohydrogen production.
Require wet carbohydrate rich biomass as a
substrate.
Produces fermentation end product as organic
acids, Co2 along with biohydrogen.
C6H12O6 + 2H2O 2CH3COOH + 4H2 +
2CO2
(Butyrate)
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Glu pyruvate acetylcoA fdH2
Carbohydrate mainly glucose is preffered.
Pyruvate the product of glucose catabolism is oxidized to
acetyl-coA requires ferrodoxin reduction.
Reduced ferrodoxin is oxidized by hydrogenase which
generates ferrodoxin and release electron as a molecular
hydrogen.
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Advantages
It produces valuable metabolites as a butyric acid,propionic acid.
It is an anaerobic process so no oxygen limitation.
It can produce carbon during day and night.
Variety of carbon sources can be used as a substrate.
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Drawbacks
Relatively lower achievable yield of H2, as a portionof substrate is used to produce organic acids.
Anaerobes are incapable of further breakdown ofacids.
Accumulation of this acids cause a sharp drop ofculture pH and subsequent inhibition of bacterialhydrogen production.
Product gas mixture contains Co2 which has to beseparated.
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Approaches to overcome
Metabolic shift of biochemical pathway to
arrest the formation of acid and alcohol.
To improve the techniques for the seperation of
the gases.
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2.Photo Fermentation
Purple non sulphur bacteria genus rhodobacter
holds significant promise for production of
hydrogen.
Photo fermentation where light is required as a
source of energy for the production of hydrogen
by photosynthetic bacteria.
Organic acids are preferred as a substrate.
The light energy required in this process is
upto the range of 400nm.
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MechanismCH3COOH + 2H2 + Light 4H2 + 2Co2
Production of hydrogen by photosynthetic
bacteria takes place under illumination and in
the presence of inert and anaerobic atmosphere
for the breakdown of organic substrate to
produce hydrogen molecules.
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Advantages
Relatively higher achievable yield of H2, as aportion of substrate is used to produce organicacids.
Anaerobes are capable of further breakdown ofacids in to biohydrogen.
Drawbacks
It can produce carbon during day only.
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Combined fermentation
The combination of dark and photo fermentation
provides an integrating system for maximization of an
hydrogen yield.
The idea of combined fermentation takes into an
consideration the very fact of relatively lower achievable
yield of H2 in dark fermentation.
The non utilization of acid produced in dark
fermentation.
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Mechanism
Stage 1 :- Dark fermentation:-
Anaerobic fermentation of carbohydrate
produces intermediates such as low molecular
weight organic acids and Co2 along with
hydrogen.
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Stage 2:- Light fermentation
The low mol wt organic acid in stage 1 are converted to hydrogen
by photosynthetic bacteria.
2CH3COOH + 4H2o CH3COOH + 2Co2 + 4H2
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Advantages
Two stage fermentation can improve the
overall yield of hydrogen and overcomes the
major limitation of dark fermentation.
Drawbacks:-
Relatively new approach techno economic
feasibility is yet to studied
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4.Direct Photolysis
Certain green algae produces H2 under anaerobic
condition.
Under deprived of S green algae Chlamydomonas reinhardtiiin
become anaerobic in light & commence to synthesis of
hydrogen.
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Molecular aspects
Light Absorption by Photo system II (PSII) Initiates thePhotosynthetic Pathway.
PSII is a large molecular complex that contains severalproteins and light-absorbing pigment molecules likecarotenoids, chlorophylls and phycobilins.
The reaction center strips electrons from two watermolecules, releasing four protons and an oxygen (O2)molecule into the thylakoid space.
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The electron carrier from PSII passes through thethylakoid membrane and transfers its electrons to thecytochrome complex, which consists of severalsubunits including cytochrome f and cytochrome b6.
A series of redox reactions within the complexultimately transfer the electrons to a second electroncarrier i.e. photo system I (PSI).
As electrons are transported through the complex,protons (H+) outside the thylakoid are carried to theinner thylakoid space.
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Light Absorption by PSI Excites Electrons and FacilitatesElectron Transfer to an Electron Acceptor Outside theThylakoid Membrane.
Light absorbed by the PSI reaction center energizes anelectron that is transferred to ferredoxin (Fd), a moleculethat carries electrons to other reaction pathways outside thethylakoid.
The reaction center replaces the electron transferred toferredoxin by accepting an electron from the electron-carriermolecule that moves between the cytochrome and the PS1
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Under Certain Conditions, Ferredoxin canCarry Electrons to Hydrogenase.
Normally, ferredoxin shuttles electrons to anenzyme that reduces NADP+ to NADPH, animportant source of electrons needed to convertCO2 to carbohydrates in the carbon-fixingreactions.
Under anaerobic conditions, hydrogenase canaccept electrons from reduced ferredoxinmolecules and use them to reduce protons tomolecular hydrogen (H2).
4H+ + ferredoxin(oxi) ――› ferredoxin(reduced) + 2H2
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Algae Recycle
Nutrient recycle
Sunlight
SunlightA LGAE
Hco2 o2
Algae production Bioreactor (Light Aerobic)
Algae Concentrator and adapter (Dark-Anaerobic)
H2 Photobioreactor(light anerobic)
Fig:- Schematic of Hydrogenase mediated Biophotolysis process
H2
H2
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Economics The US department of energy has targeted a selling price
of $2.60/kg as goal for making renewable hydrogen
economically viable.
1kg is approximately the energy equivalent to a gallon of gasoline.
To achieve this , the efficiency of light to hydrogen
conversion must reach 10% while current efficiency is only
1% and selling price is estimated at 13.53/kg.
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Reference
Hand book of bioenergy and biofuels – V K mutha
Journal on Bio hydrogen production aspotentialenergy resources by Kaushik & D Das.
Bio biohydrogen – Microbiological production of
hydrogen fuel by P C Hallebeck & J R Bennemen
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Conclusion Bio hydrogen is fuel of future
Areas of research to increase efficiency include developing
of oxygen tolerant hydrogenase and increased hydrogen
production rates.
Research on cost effective production of bio hydrogen for
commercialization is required.
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