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Hydrogen production is usually the term for the industrial methods for generating hydrogen. Currently the dominant technology for direct production is steam reforming from hydrocarbons. Hydrogen is also produced as a byproduct of other processes and managed with hydrogen pinch[1]. Many other methods are known including electrolysis and thermolysis. The discovery and development of less expensive methods of production of bulk hydrogen is relevant to the establishment of a hydrogen economy.[2]

Contents

Hydrogen waste stream

Hydrogen is used for the creation of ammonia for fertilizer via the Haber process, converting heavy petroleum sources to lighter fractions via hydrocracking and petroleum fractions (dehydrocyclization and the aromatization process). It was common to vent the surplus of hydrogen, nowadays the plants are balanced with hydrogen pinch which creates the possibility of collecting the hydrogen for further use.

Hydrogen is also produced as a by-product of industrial chlorine production by electrolysis. It can be cooled, compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.

From hydrocarbons

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Steam reforming

Fossil fuel currently is the main source of hydrogen production[3]. Hydrogen can be generated from natural gas with approximately 80% efficiency, or from other hydrocarbons to a varying degree of efficiency. Specifically, bulk hydrogen is usually produced by the steam reforming of methane or natural gas[4] At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.

CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol[5]
Gasification

In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C:

CO + H2O → CO2 + H2 - 40.4 kJ/mol

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. Additional heat required to drive the process is generally supplied by burning some portion of the methane.

Steam reforming generates carbon dioxide (CO2). Since the production is concentrated in one facility, it is possible to separate the CO2 and dispose of it properly, for example by injecting it 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 a Norwegian company StatoilHydro in the North Sea, at the Sleipner field. However, even if the carbon dioxide is not sequestered, overall producing hydrogen from natural gas and using it for a hydrogen vehicle only emits half the carbon dioxide that a gasoline car would.[citation needed] (This is disputed in The Hype about Hydrogen: Fact and Fiction in the Race to Save the Climate, a book by Joseph J. Romm, published in 2004 by Island Press and updated in 2005. Romm says that directly burning fossil fuels generates less CO2 than hydrogen production.)

Integrated steam reforming / co-generation - It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants. Air Products recently built an integrated steam reforming / co-generation plant in Port Arthur, Texas. [6]

Partial oxidation

The partial oxidation reaction occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX).

  • General reaction equation: \mathrm{C_nH_m + \frac{n}{2} \ O_2 \rightarrow n \ CO + \frac{m}{2} \ H_2}
  • Possible reaction equation (heating oil): \mathrm{C_{12}H_{24} + 6 \ O_2 \rightarrow 12 \ CO + 12 \ H_2}
  • Possible reaction equation (coal): \mathrm{C_{24}H_{12} + 12 \ O_2 \rightarrow 24 \ CO + 6 \ H_2}

Plasma reforming

The Kværner-process or Kvaerner carbon black & hydrogen process (CB&H)[7] is a plasma reforming method, developed in the 1980s by a Norwegian company of the same name, for the production of hydrogen and carbon black from liquid hydrocarbons (CnHm). Of the available energy of the feed, approximately 48% is contained in the hydrogen, 40% is contained in activated carbon and 10% in superheated steam.[8] CO2 is not produced in the process.

A variation of this process is presented in 2009 using plasma arc waste disposal technology for the creation of hydrogen, heat and carbon from methane and natural gas in a plasma converter[9]

Coal

Coal can be converted into syngas and methane, also known as town gas, via coal gasification. Syngas consists of hydrogen and carbon monoxide.[10]. Another method for conversion is low temperature and high temperature coal carbonization[11].

From water

Hydrogen is produced on an industrial scale by the electrolysis of water. High-pressure and high-temperature systems improve the energy efficiency of electrolysis. Experimental processes include electrolysis at very high temperatures (800 C), so that much of the energy required to release hydrogen is supplied as heat instead of electricity. Various catalytic agents are being studied to improve the efficiency of high-temperature electrolysis.

Water spontaneously dissociates at around 2500 C, but this thermolysis occurs at temperatures too high for usual process piping and equipment. Catalysts are required to reduce the dissociation temperature.

From urine

Hydrogen can also be made from urine. Using urine, hydrogen production is 332% more energy efficient than using water.[12][13] The research was conducted by Geraldine Botte from the Ohio University.

Biohydrogen routes

Biomass and waste streams can be converted into biohydrogen with biomass gasification, steam reforming or biological conversion like biocatalysed electrolysis or fermentative hydrogen production:

Fermentative hydrogen production

Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. Photofermentation differs from dark fermentation because it only proceeds in the presence of light. For example photo-fermentation with Rhodobacter sphaeroides SH2C can be employed to convert small molecular fatty acids into hydrogen.[14]

Biohydrogen can be produced in bioreactors that utilize feedstocks, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO2. The CO2 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 (U.S.).

Biocatalysed electrolysis

Besides dark fermentation, electrohydrogenesis (electrolysis using microbes) is another possibility. Using microbial fuel cells, wastewater or plants can be used to generate power. Biocatalysed electrolysis should not be confused with biological hydrogen production, as the latter only uses algae and with the latter, the algae itself generates the hydrogen instantly, where with biocatalysed electrolysis, this happens after running through the microbial fuel cell and a variety of aquatic plants[15] can be used. These include reed sweetgrass, cordgrass, rice, tomatoes, lupines, algae [16]

Other methods

See also

References

External links


Hydrogen production is the industrial method for generating hydrogen. Currently the dominant technology for direct production is steam reforming from hydrocarbons. Hydrogen is also produced as a byproduct of other processes and managed with hydrogen pinch[1]. Many other methods are known including electrolysis and thermolysis. The discovery and development of less expensive methods of production of bulk hydrogen is relevant to the establishment of a hydrogen economy.[2]

Contents

Hydrogen waste stream

Hydrogen is used for the creation of ammonia for fertilizer via the Haber process, converting heavy petroleum sources to lighter fractions via hydrocracking and petroleum fractions (dehydrocyclization and the aromatization process). It was common to vent the surplus of hydrogen, nowadays the plants are balanced with hydrogen pinch which creates the possibility of collecting the hydrogen for further use.

Hydrogen is also produced as a by-product of industrial chlorine production by electrolysis. It can be cooled, compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.

From hydrocarbons

Steam reforming

Fossil fuel currently is the main source of hydrogen production[3]. Hydrogen can be generated from natural gas with approximately 80% efficiency, or from other hydrocarbons to a varying degree of efficiency. Specifically, bulk hydrogen is usually produced by the steam reforming of methane or natural gas[4] At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.

CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol[5]

In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C:

CO + H2O → CO2 + H2 - 40.4 kJ/mol

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. Additional heat required to drive the process is generally supplied by burning some portion of the methane.

Steam reforming generates carbon dioxide (CO2). Since the production is concentrated in one facility, it is possible to separate the CO2 and dispose of it properly, for example by injecting it 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 a Norwegian company StatoilHydro in the North Sea, at the Sleipner field. However, even if the carbon dioxide is not sequestered, overall producing hydrogen from natural gas and using it for a hydrogen vehicle only emits half the carbon dioxide that a gasoline car would.[citation needed] (This is disputed in The Hype about Hydrogen: Fact and Fiction in the Race to Save the Climate, a book by Joseph J. Romm, published in 2004 by Island Press and updated in 2005. Romm says that directly burning fossil fuels generates less CO2 than hydrogen production.)

Integrated steam reforming / co-generation - It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants. Air Products recently built an integrated steam reforming / co-generation plant in Port Arthur, Texas.[6]

Partial oxidation

The partial oxidation reaction occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX).

  • General reaction equation: \mathrm{C_nH_m + \frac{n}{2} \ O_2 \rightarrow n \ CO + \frac{m}{2} \ H_2}
  • Possible reaction equation (heating oil): \mathrm{C_{12}H_{24} + 6 \ O_2 \rightarrow 12 \ CO + 12 \ H_2}
  • Possible reaction equation (coal): \mathrm{C_{24}H_{12} + 12 \ O_2 \rightarrow 24 \ CO + 6 \ H_2}

Plasma reforming

The Kværner-process or Kvaerner carbon black & hydrogen process (CB&H)[3] is a plasma reforming method, developed in the 1980s by a Norwegian company of the same name, for the production of hydrogen and carbon black from liquid hydrocarbons (CnHm). Of the available energy of the feed, approximately 48% is contained in the hydrogen, 40% is contained in activated carbon and 10% in superheated steam.[7] CO2 is not produced in the process.

A variation of this process is presented in 2009 using plasma arc waste disposal technology for the creation of hydrogen, heat and carbon from methane and natural gas in a plasma converter[8]

Coal

Coal can be converted into syngas and methane, also known as town gas, via coal gasification. Syngas consists of hydrogen and carbon monoxide.[9]. Another method for conversion is low temperature and high temperature coal carbonization[10].

From water

Electrolysis and thermolysis

Hydrogen is produced on an industrial scale by the electrolysis of water. While this can be done with a few volts in a simple apparatus like a Hofmann voltameter,[11] larger scale production usually relies on high-pressure and high-temperature systems to improve the energy efficiency of electrolysis. Experimental processes include electrolysis at very high temperatures (800 C), so that much of the energy required to release hydrogen is supplied as heat instead of electricity. Various catalytic agents are being studied to improve the efficiency of high-temperature electrolysis.

Water spontaneously dissociates at around 2500 C, but this thermolysis occurs at temperatures too high for usual process piping and equipment. Catalysts are required to reduce the dissociation temperature.

Sulfur-Iodine Cycle

The sulfur-iodine cycle (S-I cycle) is a thermochemical process which generates hydrogen from water, but at a much higher efficiency than water splitting. The sulfur and iodine used in the process are recovered and reused, and not consumed by the process. It is well suited to production of hydrogen by high-temperature nuclear reactors.

From urine

Hydrogen can also be made from urine. Using urine, hydrogen production is 332% more energy efficient than using water.[12][13] The research was conducted by Geraldine Botte from the Ohio University.

Biohydrogen routes

Biomass and waste streams can be converted into biohydrogen with biomass gasification, steam reforming or biological conversion like biocatalysed electrolysis or fermentative hydrogen production:

Fermentative hydrogen production

Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. Photofermentation differs from dark fermentation because it only proceeds in the presence of light. For example photo-fermentation with Rhodobacter sphaeroides SH2C can be employed to convert small molecular fatty acids into hydrogen.[14]

Biohydrogen can be produced in bioreactors that utilize feedstocks, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO2. The CO2 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 (U.S.).

Enzymatic hydrogen generation

Due to the Thauer limit (four H2/glucose) for dark fermentation, the biochemical engineer -- Y-H Percival Zhang, associate professor at Virginia Tech -- designed a non-natural enzymatic pathway that can generate 12 moles of hydrogen per mole of glucose units of polysaccharides and water in 2007[15]. The stoichiometric reaction is C6H10O5+ 7 H2O --> 12 H2 + 6 CO2. The key technology is cell-free synthetic enzymatic pathway biotransformation (SyPaB)[16][17]. A biochemist can understand it as "glucose oxidation by using water as oxidant". A chemist can describe it as "water splitting by energy in carbohydrate". A thermodynamics scientist can describe it as the first entropy-driving chemical reaction that can produce hydrogen by absorbing waste heat. In 2009, cellulosic materials were first used to generate high-yield hydrogen[18]. Furthermore, Dr. Zhang proposed the use of carbohydrate as a high-density hydrogen carrier so to solve the largest obstacle to the hydrogen economy and propose the concept of sugar fuel cell vehicles[19].

Biocatalysed electrolysis

File:Microbial electrolysis
A microbial electrolysis cell

Besides dark fermentation, electrohydrogenesis (electrolysis using microbes) is another possibility. Using microbial fuel cells, wastewater or plants can be used to generate power. Biocatalysed electrolysis should not be confused with biological hydrogen production, as the latter only uses algae and with the latter, the algae itself generates the hydrogen instantly, where with biocatalysed electrolysis, this happens after running through the microbial fuel cell and a variety of aquatic plants[20] can be used. These include reed sweetgrass, cordgrass, rice, tomatoes, lupines, algae [21]

Other methods

Renewable (or "Green") Hydrogen Production

Currently there are several practical ways of producing hydrogen in a renewable industrial process. One is to use landfill gas to produce hydrogen in a steam reformer, and the other is to use renewable power to produce hydrogen from electrolysis. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is a renewable fuel [25].

See also

Sustainable development portal

References

  1. ^ Waste hydrogen purification and supply
  2. ^ Peter Häussinger1, Reiner Lohmüller2, Allan M. Watson “Hydrogen” Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. {{|10.1002/14356007.a13_297|date=May 2010}}
  3. ^ a b Bellona-HydrogenReport
  4. ^ Fossil fuel processor
  5. ^ "HFCIT Hydrogen Production: Natural Gas Reforming". U.S. Department of Energy. 2008-12-15. http://www1.eere.energy.gov/hydrogenandfuelcells/production/natural_gas.html. 
  6. ^ Port Arthur II Integrated Hydrogen/Cogeneration Facility, Port Arthur, Texas Power magazine, September 2007
  7. ^ https://www.hfpeurope.org/infotools/energyinfos__e/hydrogen/main03.html
  8. ^ Kværner-process with plasma arc waste disposal technology
  9. ^ "HFCIT Hydrogen Production: Coal Gasification". U.S. Department of Energy. 2008-12-12. http://www1.eere.energy.gov/hydrogenandfuelcells/production/coal_gasification.html. 
  10. ^ [pubs.acs.org/cgi-bin/jtext?enfuem/15/i03/abs/ef990178a Internal gas pressure characteristics generated during coal carbonization in a coke oven]
  11. ^ "Electrolysis of water and the concept of charge". http://www.practicalphysics.org/go/Experiment_677.html. 
  12. ^ Hydrogen from urine
  13. ^ 1,23V/0,37V
  14. ^ High hydrogen yield from a two-step process of dark-and photo-fermentation of sucrose
  15. ^ [1]
  16. ^ [2]
  17. ^ [3]
  18. ^ [4]
  19. ^ [5]
  20. ^ aquatic plants
  21. ^ Power from plants using microbial fuel cell
  22. ^ Synthetic biology and hydrogen
  23. ^ Synthetic biology to make hydrogen
  24. ^ Synthetic biology at Berkeley Lab
  25. ^ National Renewable Energy Laboratory 2003 Research Review: "New Horizons for Hydrogen."

External links


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