Hydrogen

STUDY OF HYDROGENAS AN INDUSTRIAL GAS

presented by :

KAMRAN ASHRAF &

Discovery of Hydrogen• In 1671, Robert Boyle described the reaction between iron

fillings and dilute acids which resultant produce the hydrogen gas.

• In 1766, Henery Cavendish was the 1st to recognise hydrogen as a discreate substance.

• He named the gas as “flammable air”.

• Cavendish studied the properties of hydrogen as an element.

Timeline and isotopes

• Lavoiser did the 1st preparation of H2 using steam flux on metallic iron.

• H2 was 1st liquefied by James Dewar in 1898 and solidified next year.

• Its isotope Deuterium was discovered in 1931 by Harold Urey.

• Heavy water which is deuterium oxide was also discovered by Urey’s group in 1932.

• Another isotope Tritium (which is radioactive) was prepared in 1934 by famous physicist Ernest Rutherford, Mark Oliphant and Paul Harteck.

HYDROGEN PRODUCTION METHODS

• Steam methane reforming

• Electrolysis of water

• Hydrogen from biomass

• High temperature fuel cells

• Other methods

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

STEAM METHANE REFORMING

• 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.

•  At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) in an endothermic reaction to yield syngas.

CH4 + H2O → CO + 3 H2

• In a second stage, additional hydrogen is generated through the lower-temperature, exothermic, water gas shift reaction, performed at about 360 °C:

CO + H2O → CO2 + H2

• 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.

What is shift reaction?

8

CH4 + H2O CO + 3H2 DH298 = 206 kJ/mol

Water gas shift reaction

CO + H2O CO2 + H2 DH298 = -41kJ/mol

Catalysts: Ni, or Au-Ni

SMR BLOCK DIAGRAM

Electrolysis of water

• Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current.

•   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.

• 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.

ELECTROLYSIS CONTD.

• In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e−) from the cathode being given to hydrogen cations to form hydrogen gas (the half reaction balanced with acid):

• Reduction at cathode: 2 H+(aq) + 2e− → H2(g)

• At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit:

• Oxidation at anode: 2 H2O(l) → O2(g) + 4 H+(aq) + 4e−

• To add half reactions they must both be balanced with either acid or base.

• Cathode (reduction): 2 H2O(l) + 2e− → H2(g) + 2 OH-(aq)

• Anode (oxidation): 4 OH- (aq) → O2(g) + 2 H2O(l) + 4 e−

• Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen:

• Overall reaction: 2 H2O(l) → 2 H2(g) + O2(g)

EFFICIENCY VS TEMP CURVE

Anaerobic Corrosion [Schikorr reaction]

• Under anaerobic condition iron alloys are slowly oxidised by protons of water

• Protons themselves get reduced to molecular hydrogen

• This process consist of following reactions-

Fe + 2H2O Fe(OH)2 + H2

3Fe(OH)2 Fe3O4 + 2H2O + H2

• Fe3O4 is thermodynamically more stable than Fe(OH)2

Gasification process

• 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).

• 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:

• 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:

• CO + H2O → CO2 + H2 C (i.e., coal) + O2 + H2O → H2 + 3CO

Coal gasification

Fuel oil Gasification

Above Ground Gasification

Fluid-bed reactor (Winkler, HTW, CFB – dry ash; KRW, U-Gas – Agglomerating)

Air fluidizes a bed and carbon containing particles addedProper mixing of fuel and oxidant provide good mass transfer and heat transferFine particle will escape with syngas and needs to be cleaned Very good heat/mass transfer so partially reacted carbon may settle with ashSlagging will reduce fluidization, so temp remains below softening point for ash

HYDROGEN FROM BIOMASS

• Biomass + O2 CO + H2 + CO2 + Energy

• Why Biomass to hydrogen?• Biomass has the potential to accelerate the realization of hydrogen as a

major fuel of the future.

• Biomass is renewable, consumes atmospheric CO2 during growth and is a CO2 neutral resource in life cycle

• It can have a small net CO2 impact compared to fossil fuels

• Gasification coupled with water-gas shift is the most widely practiced process route for biomass to H2.

Pyrolysis

Biofuel

Catalytic steam reforming

H2 and CO2

Separation

BIOMASS

H2O

CARBON

Co products

Phenolic intermediate

Resins

• 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.

• But generate pollution as burning is involved

• Alternate technologies developing rapidly involve-

• 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.

• 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.

• Use of thermo-nuclear device to vaporize waste organic materials in an underground large-scale plasma process

• Electrochemical oxidation of solid carbonaceous wastes.

OTHER METHODSHydrogen can also be produced via other methods means including-

• In 2007 it was discovered that an alloy of Al and Ga in pellet form when added to water generates H2

• This has imp potential implications on H2 economy as H2 can be produced in situ so transportation and storage costs can be cut short.

• From algae(C.reinhardtii)

• By direct solar electrochemical processes,

• From various nuclear-power-assisted pathways,

• From fossil fuels.

STEPS IN INDUSTRIAL PROCESSSING OF HYDROGEN

Production Delivery

Storage Conversion

End use application

CURRENT GLOBAL HYDROGEN PRODUCTION

• 48% from natural gas

• 30% from oil

• 18% from coal

• 4% from electrolysis of water

28

48%

30%

18%

4%

Natural Gas oil coalelectrolysis of water

INDUSTRIAL HYDROGEN APPLICATIONS

• Largest application of H2 is for processing of fossil fuels (hydrodealkylation, hydrodesulphurization & hydrocracking)

• Manufacture of Ammonia, Methanol

• Large amounts of H2 is used in oil industries for hydrogenation of unsaturated oils

• It is used shielding gas in welding.

• H2 is used as rotor coolant in electrical generators

INDUSTRIAL HYDROGEN APPLICATIONS contd.

• Liquid H2 is used in the Cryogenic studies including superconductivity studies.

• Earlier it was used as lifting gas lifting gas but after the incident of Hindenburg Disaster this practice was opted out.

• Recently, H2 is used pure or mixed with N2 as a tracer gas for minute leak detection in automobile, chemical plants, aerospace etc.

• Hydrogen is an authorised food additive ( E949) that allows food package leak testing among other anti-oxidizing properties

Hydrogen safety

• H2 safety covers safe production, use & handling of H2

• H2 posses unique challenges due to

• ease of leak – odourless, colourless & tasteless. Smell additives unsuccessful.

• low energy ignition- order of 0.02 mJ.

• buoyancy – once leaked rises rapidly, v difficult to control.

• its ability to embrittle materials- Enters pipe line and can follow them to their destination.

• Current ANSI/AIAA standards for H2 safety guidelines is G-095-2004, Guide to Safety of Hydrogen & Hydrogen Systems. These are adopted from NASA world’s largest user of H2.

Hydrogen Storage

Storage- A major difficulty with hydrogen

• H2 has low energy density per volume• Requires large tanks to store

• Ways of H2 storage• High-pressure storage in the gaseous form

• Very low temperature storage in the liquid form

• Hydride-based storage in the solid form

One way of storing hydrogen is at high pressure in tanksBut 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.

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

Environmental Concerns

• 48% of hydrogen made from natural gas

• Creates CO2 – a greenhouse gas

• Hydrogen H2 inevitably leaks from containers

• Creates free radicals (H) in stratosphere due to ultraviolet radiation

• Could act as catalysts for ozone depletion

ADVANTAGES OF HYDROGEN GAS

• Readily available- There is no other element in the entire universe as abundant as is H2

• No harmful emissions- As is apparent from the fact that NASA used exhaust from their shuttle as a source of drinking water for astronauts

• Fuel Efficient- H2 has very high calorific value as compared to other fuels(by mass)

• Very low viscosity makes it ideal as coolant

• Non-toxic- It has no benchmark effect on humans.

• Renewable- As we have more than ¾ portion of earth as water, there will be no shortage of H2, we just need to device a method to split it.

DISADVANTAGES

• Expensive- The available methods require a lot of energy hence capital input.

• Storage- Storage is one the main causes of reluctance of investors in this energy source.

• 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.

• Highly Flammable- It is a fire hazard, liquid H2 explodes with intensity comparable to TNT

• 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%).

REFRENCES

• www.google.com

• www.wikipedia.com

• www.sciencedirect.com

• http://hydrogen+productin.12:45/googlechrome.in