final.ppt em (1)

BY Muralidhar E(10PC16F)

Why hydrogen as a Fuel.?India will continue to experience an energy supply

shortfall in time to come. Govt subsidizes refined oil product prices, thus

compounding the to the overall monetary loss to the govt.

In fact rise in oil prices that has finally awakened professionals for the alternatives.

As a result we are looking forward for non-conventional energy sources like bioethanol, biodiesel, bio-oil, biohydrogen and the likes .

Hydrogen gas is seen as a future energy carrier because it is renewable and does not evolve the Co2 gas.

Economist and scientist believes that 21st century will be powered by hydrogen just as petroleum did it in 20th century and coal in 19th century.

It is believed that hydrogen will replace petroleum, driving the world economy from high carbon to no carbon fuel.

Hydrogen research still has a long way to go.

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.

Why Biohydrogen not hydrogen.?

Needs a primary energy source.

If source is fossils then hydrogen is not an clean energy carrier.

If gas is made from electrolysis of water, again an energy intensive process.

So thinking about production of hydrogen from biomass known as BIOHYDROGEN.

Methods of Biohydrogen Production

1. Dark Fermentation

2. Photo Fermentation

3. Combined Fermentation

4. Direct Photolysis (algae)

5. Indirect Photolysis (cynobacteria)

CH2OFd hyd

2H+

2

Dark Fermentation (Fermentative Bacteria)

Acetic acid, lactic acid, formic acid, Butyric acid etc

H2

Dark Fermentation

(3) 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.

Glu pyruvate acetyl coA fd H2

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.

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.

Drawbacks

Relatively lower achievable yield of H2, as a portion of substrate is used to produce organic acids.

Anaerobes are incapable of further breakdown of acids.

Accumulation of this acids cause a sharp drop of culture pH and subsequent inhibition of bacterial hydrogen production.

Product gas mixture contains Co2 which has to be separated.

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.

4. Photo Fermentation

Photo fermentation where light is required as a source of energy for the production of hydrogen by photosynthetic bacteria.

Purple non sulphur bacteria genus rhodobacter holds significant promise for production of hydrogen.

Organic acids are preffered as a substrate.The light energy required in this process is

upto the range of 400nm.

Mechanism

CH3COOH + 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.

Combined fermentation

The combination of dark and photo fermentation provides an integratin 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.

Mechamism

Stage 1 :- Dark fermentation:- Anaerobic fermentation of carbohydrate

produces intermediates such as low molecular weight organic acids and Co2

along with hydrogen.

Stage 2:- C6H12O6 +2H2O = CH3COOH + 2CO2 +4H2

The low mol wt organic acid in stage 1 are converted to hydrogen by photosynthetic bacteria.

2CH3COOH + 4H2o CH3COOH + 2Co2 + 4H2

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

FD hyd

2H+

02

H2o

PS

Direct Photolysis (Algae)

Direct Photolysis

1. Direct Photolysis(A)Light Absorption by Photosystem II (PSII)

Initiates the Photosynthetic Pathway. PSII is a large molecular complex that

contains several proteins and light-absorbing pigment molecules like carotenoids, chlorophylls and phycobilins.

The reaction center strips electrons from two water molecules, releasing four protons and an oxygen (O2) molecule into the thylakoid space.

(B)

The electron carrier from PSII passes through the thylakoid membrane and transfers its electrons to the cytochrome complex, which consists of several subunits including cytochrome f and cytochrome b6.

A series of redox reactions within the complex ultimately transfer the electrons to a second electron carrier i.e. photosystem I (PSI).

As electrons are transported through the complex, protons (H+) outside the thylakoid are carried to the inner thylakoid space.

(C)

Light Absorption by PSI Excites Electrons and Facilitates Electron Transfer to an Electron Acceptor Outside the Thylakoid Membrane.

Light absorbed by the PSI reaction center

energizes an electron that is transferred to ferredoxin (Fd), a molecule that carries electrons to other reaction pathways outside the thylakoid.

The reaction center replaces the electron transferred to ferredoxin by accepting an electron from the electron-carrier molecule that moves between the cytochrome complex and PSI.

(D)

Under Certain Conditions, Ferredoxin can Carry Electrons to Hydrogenase.

Normally, ferredoxin shuttles electrons to an enzyme that reduces NADP+ to NADPH, an important source of electrons needed to convert CO2 to carbohydrates in the carbon-fixing reactions.

Under anaerobic conditions, hydrogenase can accept electrons from reduced ferredoxin molecules and use them to reduce protons to molecular hydrogen (H2).

4H+ + ferredoxin(oxi) ――› ferredoxin(reduced) + 2H2

(E)Dissipation of Proton Gradient is Used to

Synthesize Adenosine Triphosphate (ATP).

ATP synthase couples the dissipation of the proton gradient generated in step 2 to the synthesis of ATP.

Translocation of protons from a region of high

concentration (thylakoid space) to a region of low concentration (outside thylakoid) releases energy that can be used to drive the synthesis of ATP from adenosine diphosphate (ADP) and phosphate (P).

ATP is a high-energy molecule used to convert CO2 to carbohydrates in the carbon-fixing reactions.

Algae Recycle

Nutrient recycle

Sunlight

Sunlight

A LGAE

H2co2 o2

Algae production Bioreactor (Light Aerobic)

Algae Concentrator and adapter (Dark- Anaerobic)

H2

Photobioreactor

(light aerobic)

Fig:- Schematic of Hydrogenase mediated Biophotolysis process

H2

H2

2. Indirect Biophotolysis

Cyanobacteria can also synthesis & evolve H2 through photosynthesis via the following process.

12H2o + 6Co2 C6H12O6 + 6O2

C6H12O6 + 12H2o 12H2 + 6Co2

Cynobacteria contains Photosynthetic pigments such as Chlorophyll & carotenoids and can perform oxygenic photosynthesis.

Within a bacteria vegetative cell may develop into structurally modified & functionally specialized cell (that perform nitrogen fixation).

CH2OFdhydnif

ATP

H2

oH2o

PSII

O2

CH2O

Co2Co2NADH

2H+

Vegitative cells

Indirect Photolysis (Cynobacteria)

2

Current position in India

MNRE, DST & DBT has initialize a basic research in our country.

Some Elite institutes like IIT-Kgp, BHU, MCRC, TERI, IICT, IIT-D and several other research groups working at national laboratories have taken a lead to develop biohydrogen as a potential alternative energy fuel.

A Group at IIT-Kgp has been involved for more than a decade its achievement till date is strains isolation, bioreactor design, bench & pilot scale studies on 20L & 800L capacity reactor producing about 90L of hydrogen from 180gm of Glucose.

Conclusion

There is a huge potential for improving hydrogen yield by metabolic engineering. The bacteria Clostridium could be improved for hydrogen production by disabling the uptake hydrogenase, or disabling the oxygen system. This will make the hydrogen production robust and increase the hydrogen yield in the dark-fermentation step.

The photo-fermentation step with Rhodobacter, is the step which is likely to gain the most from metabolic engineering. An option could be to disable the uptake-hydrogenase or to disable the photosynthetic membrane system II (PS-II). Another improvement could be to decrease the expression of pigments, which shields of the photo-system.

A important future application of hydrogen could be as an alternative for fossil fuels, once the oil deposits are depleted.This application is however dependent on the development of storage techniques to enable proper storage, distribution and combustion of hydrogen.

 If the cost of hydrogen production, distribution, and end-user technologies decreases, hydrogen as a fuel could be entering the market in 2020.

Industrial fermentation of hydrogen, or whole-cell catalysis, requires a limited amount of energy, since fission of water is achieved with whole cell catalysis, to lower the activation energy.

 This allows hydrogen to be produced from any organic material that can be derived through whole cell catalysis since this process does not depend on the energy of substrate.

References:

Ayhan Demirbas, "Biohydrogen: For Future Engine Fuel Demands (Green Energy and Technology)" 

WWW.Googlewikipedia.com Indian journal of BIOFUELS.

THANK YOU