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LOGO
Production
Production from hydrocacbon
Steam methane reforming(SMR): • This is today's most efficient method for the production of
synthesis gas CO + H2. With raw material is natural gas should be
applied in the gas sources such as the U.S., Saudi Arabia. In addition, the source of naphtha is to be used in Europe.
• The reactions:
Besides natural gas, naphtas are also used as raw materials:
• Generally, a nickel catalyst is used for the reaction, loaded to an alumina base material at 10–15 wt%. Besides nickel, platinum and ruthenium are also used as catalysts.
Production from hydrocarbon
Partial Oxidation (POX):
This process can be used with diverse materials, from gases, liquids and even solids
such as coal.
The reactions:
POX can easily be performed without the presence of a catalyst. High temperatures
of 1200–1450°C and pressures of 3 –7.5 MPa (Texaco process) are needed to
ensure high conversion rates.
The catalytic partial oxidation (CPO) reaction, however, can take place at lower
temperatures and may lead to a significantly enhanced H2 yield from the fuel
Production from hydrocarbon
Coal Gasification
During World War II, the syngas is produced by this
method for the production of gasoline. At present,
hardly used due to its high price. However in some
coal-rich countries such as South Africa, it was
maintained. The reactions:
Then CO is converted to CO2 and H2:
Production from hydrocarbon
LOGO Water Electrolysis
Electrical energy input∆G = 237.13 kJ
Energy from environmentT∆S = 48.7 kJ
Energy exchange the processes for one mole of water ∆H = 285.83 kJ
Perry's Chemical Engineers' Handbook, Section 2.Physical and Chemical Data
Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current being passed through the water.
Alkaline electrolysis
- Alkaline electrolyte electrolyzers represent a
very mature technology that is the current
standard for large-scale electrolysis.
Common electrolyte: aqueous potassium
hydroxide (KOH) at 30% concentration
Operation Conditions: 70-100oC and 1- 30bar
Operational voltage: 1.7-2.2 V
Current density: 0.2-0.6 A/cm2
Electricity Consumption: 4.2 – 5.6 kWh/Nm3
Can utilize cost effective electrode
materialsDiaphragm often asbestos
Efficiency: 70-80% (based on hydrogen HHV) [1]
Russell H. Jones & George J. Thomas, “Materials for the Hydrogen economy”, 2008, p.40
PEM Electrolysis [1]
Polymer electrolyte water electrolysis (PEWE) uses a polymer electrolyte membrane as a medium of ion transfer instead of solution electrolyte in AWE. This method is often called polymer electrolyte membrane or proton exchange membrane (PEM) water electrolysis, too.
Operational principle The water flows from the plate to the
anode through the current collector, and reacts to make protons.
Current collectors are porous conductors that allow electrons to transfer from electrode to outer circuit and allow reactant gas from bipolar plate to electrode.
The protons are transported through the PEM to cathode side, and hydrogen is generated at the cathode.
The PEM also works as a separator of product gases.
[1] Seiji Kasahara et al., “Water electrolysis” in
“ Nuclear hydrogen production handbook”, 2011
Advantages
Corrosive liquid electrolyte is not required
Construction of facility is easy
No electric resistance by gas bubbles between electrodes can be made.
Purity of product gas is high
Disadvantages
Components should be corrosion resistant due to strong acidity of the PEM.
Uniform contact between the PEM and the electrodes should be achieved
Cost of the PEM, electrodes and current collectors is high
PEM Electrolysis
Steam electrolysis[1]
The process of the high-temperature electrolysis (HTE) of steam is a reverse reaction of the
solid-oxide fuel cell (SOFC): an oxygen ionic conductor is usually used as a solid-oxide
electrolyte.
The electrical energy demand, ΔG, decreases with increasing temperature. The ratio of ΔG to
ΔH is about 93% at 100°C and about 70% at 1000°C
An assembly unit consisting of 15 cells
Outer diameter: 12mm
Active area: 75 cm2
Hydrogen production rate: 100 NL/h.
Operation Conditions: 800oC
Operational voltage: 1.3 V
Current density: 0.45 A/cm2 [1] Seiji Kasahara et al., “Steam electrolysis” in
“ Nuclear hydrogen production handbook”,
2011
Photoelectrolysis
Photoelectrolysis involves splitting water directly into hydrogen (H2) and oxygen (O2) using the energy of sunlight.
The reactive decomposition occurs at 1.23 V, so the minimum bandgap for successful water splitting is 1.23 eV, corresponding to light of 1008nm. [2]
Operational principle [3]
TiO2 electrode electrowas irradiated with light consisting of wavelengths shorter than 415 nm (3.0 eV), photocurrent flowed from the Pt electrode to the TiO2 de through the external circuit.
The direction of the current revealed that the oxygen occurs at the TiO2 electrode and the hydrogen occurs at the Pt electrode.
This observation shows that water can be decomposed, using UV light, without the application of an external voltage.
Technical Target: Photoelectrochemical Hydrogen Production *Characteristics Unit 2003 Status 2006 Status 2013 Target 2018 Target
Usable semiconductor bandgap
eV 2.8 2.8 2.3 2.0
Chemical conversion process efficiency (EC)
% 4 4 10 12
Plant solar-to-hydrogen efficiency (STH)
% Not availble Not availble 8 10
Plant durability Hr Not availble Not availble 1000 5000
* Todd G. Deutsch & John A. Turner , Semiconductor Materials for Photoelectrolysis , May 16th, 2012 , p.3
Photoelectrolysis
Ad
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Disad
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• Small system size
• No moving parts
• Use in household
• Low efficiency
• Low capacity
• High cost materials
• Low durability
This GaInP2 /GaAs multiple-band-gap photoelectrochemical cell uses only illumination and can generate hydrogen at greater than 12% conversion efficiency.
Photobiological hydrogen
Microalgae and cyanobacteria are photoautotrophic organisms because they
can use light as the energy source and the carbon dioxide as carbon source
Under anaerobic conditions, microalgae can produce H2, by water photolysis,
using light as the energy source. The catalyst is a hydrogenase, an enzyme that
is extremely sensitive to oxygen, a by-product of photosynthesis.
Photobiological hydrogen
• The photosynthetically active radiation
(400–700 nm for green algae, and 400–
950 nm for purple bacteria) or on the full
solar irradiance (all wavelengths).
• In the Netherlands, 420 h would be
needed for the production of 1 GJ of
hydrogen per year. In southern Spain,
this would be 250h.
LOGO
An application-specific issue.
Hydrogen Storage
Physical storage of H2
Chemical storage of hydrogen
New emerging methods
Hydrogen Storage Overview
Compressed
•Volumetric and Gravimetric densities are inefficient, but the technology is simple, so by far the most common in small to medium sized applications.•3500, 5000, 10,000 psi variants.
Liquid (Cryogenic)
•Compressed, chilled, filtered, condensed•Boils at 22K (-251 C).•Slow “waste” evaporation•Kept at 1 atm or just slightly over.
•Gravimetrically and volumetrically efficient but very costly to compress
Metal Hydrides (sponge)
•Sold by “Interpower” in Germany•Filled with “HYDRALLOY” E60/0 (TiFeH2)•Technically a chemical reaction, but acts like a physical storage method•Hydrogen is absorbed like in a sponge.•Operates at 3-30 atm, much lower than 200-700 for compressed gas tanks•Comparatively very heavy, but with good volumetric efficiency, good for small storage, or where weight doesn’t matter
Carbon Nanofibers
Complex structure presents a large surface area for hydrogen to “dissolve” into
Early claim set the standard of 65 kgH2/m2
and 6.5 % by weight as a “goal to beat”
The claim turned out not to be repeatable
Research continues…
Methanol
Broken down by reformer, yields CO, CO2, and H2 gas.
Very common hydrogen transport method Distribution infrastructure exists – same as
gasoline
Ammonia
Slightly higher volumetric efficiency than methanol Must be catalyzed at 800-900 deg. C for hydrogen
release Toxic Usually transported as a liquid, at 8 atm. Some Ammonia remains in the catalyzed hydrogen
stream, forming salts in PEM cells that destroy the cells
Many drawbacks, thus Methanol considered to be a better solution
Alkali Metal Hydrides
“Powerball” company, makes small (3 mm) coated NaH spheres.
“Spheres cut and exposed to water as needed”
H2 gas released
Produces hydroxide solution waste
Sodium Borohydrate
Sodium Borohydrate is the most popular of many hydrate solutions
Solution passed through a catalyst to release H2
Commonly a one-way process (sodium metaborate must be returned if recycling is desired.)
Some alternative hydrates are too expensive or toxic The “Millennium Cell” company uses Sodium
Borohydrate technology
Amminex
•Essentially an Ammonia storage method•Ammonia stored in a salt matrix, very stable•Ammonia separated & catalyzed for use•Likely to have non-catalyzed ammonia in hydrogen stream •Ammonia poisoning contraindicates use with PEM fuel cells, but compatible with alkaline fuel cells.
Amminex
•High density, but relies on ammonia production for fuel.
•Represents an improvement on ammonia storage, which still must be catalyzed.
•Ammonia process still problematic.
Diammoniate of Diborane (DADB)
So far, just a computer simulation.
Compound discovered via exploration of Nitrogen/Boron/Hydrogen compounds (i.e. similar to Ammonia Borane)
Thermodynamic properties point towards spontaneous hydrogen re-uptake – would make DADB reusable (vs. other borohydrates)
Solar Zinc production
Isreli research effort utilizes solar furnace to produce pure Zinc
Zinc powder can be easily transported
Zinc can be combined with water to produce H2
Alternatively could be made into Zinc-Air batteries (at higher energy efficiency)
Alkaline metal hydride slurry
SafeHydrogen, LLC Concept proven with Lithium
Hydride, now working on magnesium hydride slurry
Like a “PowerBall” slurry Hydroxide slurry to be re-
collected to be “recycled” Competitive efficiency to Liquid
H2
Storage Method Comparison
Sodium Hydride slurry .9 1.0 Must reclaim used slurry
DADB .1 - .2 .09-.1 (numbers for plain “diborane”and sodium borohydride, should be similar)
Amminex 9.1 .081
Zinc powder unsure
US DOE goal 9.0 .081