Hydrogen production
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226000170
2008-07-16T11:35:13Z
Chem prof2000
1291593
/* Carbon monoxide */
{{Unreferenced|date=June 2008}}
'''Hydrogen''' is commonly produced by extraction from [[hydrocarbon]] [[fossil]] fuels via a chemical path. [[Hydrogen]] may also be extracted from water via [[Biological hydrogen production|biological production]] in an algae [[bioreactor]], or using [[electricity]] (by [[electrolysis]]) or [[heat]] (by [[thermolysis]]); these methods are less efficient for bulk generation in comparison to chemical paths derived from hydrocarbons. The discovery and development of less expensive methods of bulk production of hydrogen will accelerate the establishment of a [[hydrogen economy]].
== From hydrocarbons ==
Hydrogen can be generated from [[natural gas]] with approximately 80% efficiency, or from other [[hydrocarbon]]s to a varying degree of efficiency. The hydrocarbon conversion method releases [[greenhouse gas]]es. Since the production is concentrated in one facility, it is possible to separate the gases and dispose of them properly, for example by injecting them in an oil or gas reservoir (see [[carbon capture]]), although this is not currently done in most cases. A carbon dioxide injection project has been started by [[Norway|Norwegian]] company [[StatoilHydro]] in the [[North Sea]], at the [[Sleipner gas field|Sleipner field]].
==== Steam reforming ====
Commercial bulk hydrogen is usually produced by the [[steam reforming]] of [[natural gas]]. At high temperatures (700–1100 °C), steam (H<sub>2</sub>O) reacts with [[methane]] (CH<sub>4</sub>) to yield [[syngas]].
:[[methane|CH<sub>4</sub>]] + [[water|H<sub>2</sub>O]] → [[carbon monoxide|CO]] + 3 [[hydrogen|H<sub>2</sub>]] - 191.7 kJ/mol
The heat required to drive the process is generally supplied by burning some portion of the methane.
==== Carbon monoxide ====
[[Image:Hydrogen.from.Coal.gasification tampa.jpg|thumb|gasification]]
Additional hydrogen can be recovered by adding more water through the lower-temperature [[water gas shift reaction]], performed at about 130 °C:
:CO + H<sub>2</sub>O → CO<sub>2</sub> + H<sub>2</sub> + 40.4 kJ/mol
Essentially, the [[oxygen]] (O) atom is stripped from the additional water (steam) to oxidize CO to CO<sub>2</sub>.. This oxidation also provides energy to keep the reacction going.
==== Coal ====
[[Coal]] can be converted into [[syngas]] and [[methane]], also known as [[town gas]], via [[coal gasification]].
== From water ==
=== Biological production ===
{{main|Biological hydrogen production (Algae)}}
[[Biohydrogen]] can be produced in an [[algae]] [[bioreactor]]. In the late 1990s it was discovered that if the algae is deprived of [[sulfur]] it will switch from the production of [[oxygen]], i.e. normal [[photosynthesis]], to the production of hydrogen.
It seems that the production is now economically feasible by trespassing the 7-10 percent energy efficiency (the conversion of sunlight into hydrogen) barrier.
Biohydrogen can and is produced in bioreactors that utilize feedstocks other than algae, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO<sub>2</sub>. The CO<sub>2</sub> can be sequestered successfully by several methods, leaving hydrogen gas. A prototype hydrogen bioreactor using waste as a feedstock is in operation at Welch's grape juice factory in North East, Pennsylvania.
=== Electrolysis ===
{{main|Electrolysis of water}}
[[Image:Hydrogen-challenger hg.jpg|thumb|Electrolysis of water ship ''[[Hydrogen Challenger]]'']]
It is more efficient to produce hydrogen through a direct chemical path than by electrolysis, but the chemical feedsource will always produce pollution or toxic byproducts as hydrogen is extracted. With electrolysis, when the energy supply is mechanical (hydropower or wind turbines), or photovoltaic from sunlight, hydrogen can be made via [[electrolysis]] of [[water]]. Usually, the electricity consumed is more valuable than the hydrogen produced so this method has not been widely used in the past, but with electrolysis production of hydrogen, there is virtually no pollution or toxic byproducts, and the feed sources are fully renewable, so the importance of electrolysis is increasing as human population and pollution increase, and electrolysis will become more economically competitive as non-renewable resources (carbon-based compounds) dwindle and as governments remove subsidies on carbon-based energies.
[[Image:Electrolyser, front, B.jpg|left|thumb|Electrolyser front with electrical panel closest.]]
When the energy supply is in the form of heat (solar thermal or nuclear), the path to hydrogen is through high-temperature electrolysis. In contrast with low-temperature electrolysis, [[high-temperature electrolysis]] (HTE) electrolysis of water converts more of the initial [[heat]] energy into chemical energy (hydrogen), potentially doubling [[fuel efficiency|efficiency]], to about 50%. Because some of the energy in HTE is supplied in the form of heat, less of the energy must be converted twice (from heat to electricity, and then to chemical form), and so less energy is lost. HTE has been demonstrated in a laboratory, but not at a commercial scale.
Irrespective of efficiency, hydrogen production by electrolysis is a clean and renewable agent for storing electrical and mechanical energy for retrieval on demand.
==== Photoelectrochemical Water Splitting ====
Using electricity produced by photovoltaic systems offers the cleanest way to produce hydrogen. Water is broken into hydrogen and oxygen by electrolysis--a [[photoelectrochemical cell]] (PEC) process. Research aimed toward developing higher-efficiency multijunction cell technology is underway by the Photovoltaic industry.
====High-temperature electrolysis (HTE)====<!-- This section is linked from [[Nuclear power]] -->
{{main|High-temperature electrolysis}}
HTE processes are generally only considered in combination with a nuclear heat source, because the other non-chemical form of high-temperature heat (concentrating solar thermal) is not consistent enough to bring down the capital costs of the HTE equipment. Research into HTE and high-temperature nuclear reactors may eventually lead to a hydrogen supply that is cost-competitive with natural gas steam reforming.
Some prototype [[Generation IV reactor]]s operate at 850 to 1000 [[degrees Celsius]], considerably hotter than existing commercial [[nuclear power]] plants.
[[General Atomics]] predicts that hydrogen produced in a High Temperature Gas Cooled Reactor (HTGR) would cost $1.53/[[kilogram|kg]]. In 2003, steam reforming of natural gas yielded hydrogen at $1.40/kg. At [[As of 2005|2005]] gas prices, hydrogen cost $2.70/kg {{Fact|date=February 2007}}. Hence, just within the United States, a savings of tens of billions of dollars per year is possible with a nuclear-powered supply. Much of this savings would translate into reduced oil and natural gas imports.
One side benefit of a nuclear reactor that produces both [[electricity]] and hydrogen is that it can shift production between the two. For instance, the plant might produce electricity during the day and hydrogen at night, matching its electrical generation profile to the daily variation in demand. If the hydrogen can be produced economically, this scheme would compete favorably with existing [[grid energy storage]] schemes. What is more, there is sufficient hydrogen demand in the [[United States]] that all daily peak generation could be handled by such plants[http://www.dis.anl.gov/ceeesa/documents/NuclearHydrogen_ANL0530Final.pdf]. However, [[Generation IV reactor]]s are not expected until 2030 and it is uncertain if they can compete by then in safety and supply with the [[distributed generation]] concept.
=== Thermochemical production ===
Some thermochemical processes can produce hydrogen and oxygen from water and heat without using electricity. Since all the input energy for such processes is heat, they can be more efficient than high-temperature electrolysis. This is because the efficiency of electricity production is inherently limited. Thermochemical production of hydrogen using chemical energy from coal or natural gas is generally not considered, because the direct chemical path is more efficient.
Hundreds of thermochemical cycles have been pre-screened. Some of the most promising ones include:
* [[sulfur-iodine cycle]] (S-I)
* cerium-chlorine cycle (Ce-Cl)
* iron-chlorine cycle (Fe-Cl)
* magnesium-iodine cycle (Mg-Cl)
* vanadium-chlorine (V-Cl)
* copper-sulfate (Cu-SO<sub>4</sub>)
There are also "hybrid" variants, which are thermochemical cycles with an electrochemical step:
* [[hybrid sulfur cycle]]
* [[copper-chlorine cycle]] (Cu-Cl)
For all the thermochemical processes, the summary reaction is that of the decomposition of water:
:<math>H_2 O \text{ } \stackrel {Heat} {\rightleftharpoons} \text{ } H_2 + {1 \over 2} O_2</math>
All other chemicals used are recycled.
None of the thermochemical hydrogen production processes have been demonstrated at production levels, although several have been demonstrated in laboratories.
== Other methods ==
* [[Nanotechnology]] research on [[photosynthesis]] may lead to more efficient solar production of hydrogen, such as with [[photoelectrochemical cell]]s.
* The radical [[Hydridic Earth theory]] suggests that large quantities of hydrogen may exist in the Earth's mantle.
== See also ==
{{Portal|Sustainable development|Sustainable development.svg}}
{{Commons|Hydrogen production}}
* [[Ammonia production]]
* [[Hydrogen economy]]
* [[Hydrogen leak testing]]
* [[Hydrogen storage]]
* [[Hydrogen station]]
* [[Hydrogen technologies]]
* [[The Hype about Hydrogen]]
==External links==
* [http://www.hydrogen.energy.gov/annual_progress07_production.html U.S. DOE 2007-Technical progress in hydrogen production]
* [http://www.fe.doe.gov/programs/fuels/hydrogen/Hydrogen_from_Coal_R&D.html U.S. DOE Hydrogen from Coal Research]
* [http://www.nrel.gov/hydrogen/proj_production_delivery.html U.S. NREL article on hydrogen production]
* [http://www.world-nuclear.org/info/inf70.html Article advocating the use of nuclear power to produce hydrogen]
*[http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_1-12-2006-11-4-23?newsid=3016 Genetically engineered blood protein can be used to produce hydrogen gas from water]
*[http://www.greencarcongress.com/biohydrogen/index.html Biohydrogen]
[[Category:Peak oil]]
[[Category:Hydrogen production| ]]
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[[ru:Производство водорода]]