Hydrogen storage

from Wikipedia, the free encyclopedia

The hydrogen storage is the reversible storage of hydrogen to obtain, with the aim of its chemical and physical properties for further use. Storage includes the processes of storage or storage loading, temporary storage and withdrawal or storage unloading. Conventional methods of storing hydrogen are:

Alternative forms of storing hydrogen use physical or chemical bonding to another substance:

  • Absorption in metal hydride storage (storage as a chemical compound between hydrogen and a metal or an alloy)
  • Adsorption storage (adsorptive storage of hydrogen in highly porous materials)
  • chemical bond in which the hydrogen is converted into another substance through a chemical reaction, which z. B. can be stored and transported without pressure and at room temperature (" chemically bound hydrogen "). The reverse reaction then takes place during withdrawal. Examples are the hydrogenation of organic substances or the formation of alcohols with CO.

Problem

Because of its chemical and physical properties, the handling of hydrogen differs from the previously used energy carriers .

  • When it escapes, hydrogen forms an inflammable mixture with the ambient air, with a proportion of 4% to 75%. Hydrogen only forms an explosive mixture ( oxyhydrogen ) with a proportion of 18%. Because hydrogen has a high tendency to diffuse and mixture clouds of hydrogen and air have a lower density than normal air, it usually evaporates in an open environment before it can form an explosive mixture, or in hot environments it burns at a concentration of 4 % off.
  • Compared to many hydrocarbons, hydrogen has a low combustion enthalpy and thus a low volume -related energy density (approx. 1/3 of natural gas). To store equivalent amounts of energy, this requires a tank three times as large or three times as high as for natural gas. Due to the low molar mass , however, there is a comparatively high mass -related energy density (e.g. more than twice the mass-related energy density of natural gas).
  • Due to its small molecule size , hydrogen diffuses relatively well through a large number of materials, so that many materials are unsuitable for the tank shell. The diffusion process is intensified by high temperatures and high internal pressure. Metallic tank casings are additionally stressed by hydrogen embrittlement . This effect does not occur with cases made of plastic.
  • In the case of cryogenic hydrogen liquefaction, unavoidable thermal insulation losses lead to evaporation / outgassing. To ensure that the pressure in the containers does not rise too high, the hydrogen gas is released using a pressure relief valve. If this hydrogen gas cannot be used, considerable losses occur. For example, the half-full liquid hydrogen tank of the BMW Hydrogen7 empties in 9 days if not used.
  • Large amounts of energy are required not only for the production of hydrogen, but also for storage (compression approx. 12%, liquefaction approx. 20%). Therefore, despite many advantages, hydrogen storage is currently (2012) often uneconomical.

Types of hydrogen storage

Compressed hydrogen storage

Net storage density as a function of pressure and temperature

The problems of storage in pressure vessels are now considered to have been solved. By using new materials, the effective shrinkage through diffusion is greatly reduced. While pressure tanks with 200 to 350 bar were still common in the motor vehicle sector around the year 2000, in 2011 it was already 700 and 800 bar tanks with a higher capacity. The complete hydrogen tank system for a car now weighs just 125 kg. The energy expenditure for the compression to 700 bar is approx. 12% of the energy content of the hydrogen. The pressure tanks that are in commercial use today meet all the safety requirements of vehicle manufacturers and have been approved by TÜV . Pressure tanks up to 1200 bar are technically possible.

A special case of pressurized hydrogen storage with a very high storage capacity is storage in underground gas storage facilities (e.g. salt cavern storage facilities) similar to storage facilities in the natural gas network. Specially created pipes can also serve as storage. → See: Hydrogen in pipelines

Liquid hydrogen storage

Linde tank for liquid hydrogen, Autovision Museum , Altlußheim

Liquid gas storage tanks are used for large quantities. Because above the critical point (−240 ° C, 1.3 MPa = 13.0 bar) no pressure liquefaction is possible, the hydrogen is strongly cooled and compressed (LH 2 ) for liquefaction .

The energy required for this can be broken down into the following proportions, each based on the stored energy content:

  • 28… 46% for the liquefaction depending on the quantity and the method used
  • 6% transport between liquefaction station and gas station (diesel and petrol 0.2%)
  • Up to 3% per day due to boil-off losses (see below)
  • Evaporation losses when decanting

The pressure is then no longer a problem for the design of the tank. However, a great deal of effort has to be made with the thermal insulation of the tank and the lines. The lower reactivity at low temperatures and the 800-fold higher density of liquid hydrogen compared to gaseous hydrogen at ambient pressure are advantageous. Nevertheless, liquid hydrogen requires a lot of space per unit weight. At 71 kg / m³, it has only a slightly higher density than small-pore foamed polystyrene (only 1.42 kg of liquid hydrogen fit into a 20-liter bucket, which is about a tenth of that of gasoline). The disadvantage is that due to the very low temperature inside the tank, even with good thermal insulation, a heat flow from the environment cannot be avoided. This leads to a partial evaporation of the hydrogen. In order to avoid a build-up of pressure, this hydrogen must be released if the hydrogen gas produced is unsteady or does not decrease (so-called boil-off losses). Further measures (boil off management) can minimize losses due to evaporation. B. by coupling with a combined heat and power unit (CHP).

For use in automobiles, tank robots have been developed that handle coupling and refueling. The energy required for liquefaction only occurs once, later decanting requires relatively little energy, but generates additional outgassing losses. Even the transport from the factory with tanker trucks to filling stations / storage tanks costs up to 6% of the energy used due to the large volume and the low energy density - a multiple compared to the distribution of liquid fuels (0.2%).

Transcritical storage (cryo compressed)

In confined spaces, the combination of the above variants enables significantly higher storage densities of up to 100 kg / m³. As with pressurized gas, storage takes place above the critical temperature and the critical pressure at up to 1000 bar. The storage pressure corresponds to that of compressed gas storage, but the storage temperature is −220 ° C (53 K) higher than that of liquid hydrogen. The advantage of the high storage density is offset by the effort required for the pressure tank and thermal insulation.

Metal hydride storage

Another possibility to reduce the pressure of the molecular hydrogen is the solution in other storage means. Because of its largely electrically and magnetically neutral properties, no liquid solvent is used, but solid storage materials such as metal hydrides . The hydrogen is stored in the gaps in the metal grid . This process is temperature-dependent, the storage capacity decreases at high temperatures, so that the hydrogen is released / stored again when the storage tank is heated. One cubic meter of metal hydride contains more hydrogen atoms than one cubic meter of liquefied hydrogen. A metal hydride storage system can store five times more electrical energy than a lead-acid battery of the same weight. But they turned out to be so expensive and heavy that they are only used in submarines, where neither factor plays a role. Critical for the selection of materials are the absorption and desorption temperature and pressure at which hydrogen is stored and released again, and the heavy weight of the tank.

In 2011, researchers from the Université Catholique de Louvain (Catholic University of Leuven) in Belgium and the University of Aarhus in Denmark presented a new, highly porous form of magnesium borohydride that can store hydrogen chemically bound and physically adsorbed. Magnesium borohydride (Mg (BH 4 ) 2 ) gives off hydrogen at relatively low temperatures and stores a high proportion of hydrogen by weight (approx. 15%).

Adsorptive storage

By accumulation on the surface of a highly porous material, the volume-related storage density can in principle be increased compared to compressed hydrogen at the same temperature and the same pressure. Possible materials for adsorptive hydrogen storage are, for example, zeolites , metal organic frameworks , carbon nanotubes or activated carbon . Since only very little hydrogen is adsorbed at room temperature , it is necessary for thermodynamic reasons to operate adsorption storage devices at lower temperatures. Much of the current work on this topic examines the absorption capacity at −196 ° C (the temperature of liquid nitrogen ). The cooling to −196 ° C entails a considerable energy requirement. As with liquid hydrogen, the very low temperatures also result in a permanent heat flow into the interior of the container, which leads to losses during storage. As a result, hydrogen storage by adsorption at low temperatures has very low energy efficiency. In order to reduce the losses, materials are currently being sought that can be used at higher temperatures (e.g. −78 ° C; the temperature of dry ice ). In these cases, however, the energy densities are significantly lower and even if higher efficiencies can be achieved, the losses are still considerable.

"Enhanced Amonia Borane" is a new development from NASA , whereby the carrier material consists of tiny polymer beads that behave like a liquid. The hydrogen is released by heating, and the discharged polymer beads are returned for recharging.

Metal Organic Framework
Metal-Organic Frameworks (engl. M etal- o rganic f rameworks, MOF) are porous materials with well-ordered crystalline structure. They consist of complexes with transition metals (mostly Cu, Zn, Ni or Co) as “nodes” and organic molecules ( ligands ) as connections (“linkers”) between the nodes. The MOF can be optimized for hydrogen storage by using suitable nodes and linkers, as well as by impregnation with other guest species. The MOF are an active field of research and are seen as one of the most promising technologies for hydrogen storage.

Zeolites
Zeolites are another class of potential carriers that have been proposed for adsorptive hydrogen storage. These are aluminosilicates with defined pore structures that have a large internal surface on which substances such as hydrogen can adsorb.

Carbon Carriers
Various high surface forms of carbon have also been investigated as carriers. However, the storage densities that can be achieved with activated carbon are very low, so that more work has been done on carbon nanotubes . Even on carbon nanotubes, the absorption capacity is probably still so low that the energy density is not sufficient for a technically sensible implementation.

Other adsorptive carrier materials
Other carrier materials such as TiO 2 nanotubes or SiC nanotubes are examined in the specialist literature for their suitability as hydrogen carriers. The absorption capacity is probably slightly higher than that of carbon-based carriers. Values ​​of about 2% by weight of hydrogen at 60 bar are given.

Chemically bound hydrogen

Main article: Chemical hydrogen storage

In addition to the options for storing molecular hydrogen, there are a number of options for transporting and storing it in chemically bound form. These possibilities do not count towards hydrogen storage in the narrower sense, which relates to the technical process of storing molecular hydrogen. In the context of a hydrogen economy , however, this possibility is counted as part of the productive process here, since the storage and extraction of hydrogen is the subject of the productive process .

Since the hydrogen carriers are mostly organic substances, they are also called "Liquid Organic Hydrogen Carriers" ( LOHC , liquid organic hydrogen carriers ).

Methanol

Particularly suitable hydrogen carriers are alcohols, e.g. B. methanol . Methanol can be obtained by reaction of hydrogen with CO and CO 2 are produced . By means of reforming can produce therefrom a hydrogen-rich gas mixture again. However, this contains considerable proportions of carbon monoxide or carbon dioxide . However, carbon monoxide in particular can cause problems when used in the fuel cell.

Liquid Organic Hydrogen Carrier (LOHC)

In liquid organic hydrogen carriers (LOHC), hydrogen is chemically bound to an unsaturated compound (hydrogenation) through a chemical reaction. To release it, the saturated compound formed during storage is dehydrated again, the unsaturated compound being re-formed and gaseous hydrogen being produced. A large number of substances can in principle be used for this. However, only aromatic compounds are suitable for industrial use.

toluene

The oldest researched LOHC system is based on the hydrogenation of toluene to methylcyclohexane (or the corresponding reverse reaction). This system was shown in a demonstration facility. However, due to partially unfavorable properties, other substances have been increasingly investigated for some years.

N-ethyl carbazole

Hydrogenation and dehydrogenation of N-ethylcarbazole

N-Ethylcarbazole is considered to be the most promising candidate among the hydrogenatable organic substances. For the recovery of the hydrogen for operating a hydrogen combustion engine or a fuel cell , the relatively low temperature required for the release is advantageous. The “discharged” carbazole can be exchanged for perhydro-N-ethylcarbazole (also known as perhydro-carbazole) that is “charged” with hydrogen at a filling station; the current gas station infrastructure could be retained with minor changes. The process is currently (2011) still in the development stage.

Dibenzyltoluene

After research had shown the reversible hydrogenation of dibenzyltoluene to be particularly promising for hydrogen storage, the world's first commercial LOHC plant for storing hydrogen in dibenzyltoluene was inaugurated in 2016. It was developed and created by Hydrogenious Technologies GmbH . With the help of solar power from a 98 kW p photovoltaic system, hydrogen is generated by means of PEM electrolysis . This is stored in dibenzyltoluene. The loaded dibenzyltoluene can then be stored in conventional tanks under ambient conditions or transported over long distances. If necessary, the stored hydrogen is released again. By connecting a fuel cell or a block-type thermal power station, the released hydrogen can be converted into electricity or usable heat. One liter of dibenzyltoluene (LOHC) absorbs about 660 liters of hydrogen.

commitment

Processes for the technical storage of hydrogen in elemental form require pressure vessels, for which a metallic outer shell is often used. This also applies to liquid gas storage facilities and metal hydride storage facilities, which have a temperature-dependent internal pressure. Carbon fiber reinforced plastics are also used for high-pressure storage at 700 bar in order to keep the weight of the tank low.

Liquid gas storage facilities are currently in use for large quantities in stationary systems. Pressure accumulators up to 700 bar are used for small quantities. Metal hydride storage systems are used where the storage weight does not play a major role, for example on ships. Due to their low weight, only pressure tanks are used today for vehicles and aircraft:

Toyota uses it in its fuel cell vehicle FCHV-adv and achieves a range of 830 km. The vehicle is already in commercial use and can be leased.

Volkswagen is installing a 700 bar hydrogen tank in the Tiguan HyMotion, Mercedes in the A-Class F-Cell "plus" and Opel in the HydroGen4.

Pressure tanks are now also used in buses, such as B. in the Citaro Fuel Cell Hybrid from Mercedes.

Companies involved in the research and production of hydrogen storage systems are e.g. B. in Germany Linde AG , in Norway and Iceland StatoilHydro and in the USA Quantum Fuel Technologies Worldwide .

Fuel cell rail vehicles

Planes

Risk of accident

The technology used industrially today takes into account the extremely flammable nature of hydrogen and its ability to form explosive oxyhydrogen. Lines and tanks are designed accordingly so that no greater risks arise in daily use than, for example, B. through the use of gasoline .

However, the hazards are still partly unknown due to the currently limited use. Oxygen / hydrogen mixtures with a proportion of less than 10.5 percent by volume of hydrogen, which is heavier than air, can sink to the ground when flowing out. The segregation does not take place immediately, so that the ignitability is maintained until the 4 volume percent limit is undershot. When handling hydrogen, safety regulations and ventilation systems must take this abnormal behavior into account.

Hydrogen vehicles with pressure tanks can easily be parked in multi-storey car parks and underground garages. There is no legal provision that restricts this. Vehicles with liquid hydrogen storage tanks must not be parked in closed rooms because of the inevitable outgassing.

Energy densities in comparison

Based on the mass (in kWh / kg):

  • Hydrogen: 33.3
  • Hydrogen storage with perhydro-N-ethylcarbazole : 1.9
  • Natural gas: 13.9
  • Gasoline: 11.1-11.6 (40.1-41.8 MJ / kg)
  • Diesel: 11.8–11.9 (42.8–43.1 MJ / kg)
  • Methanol: 6.2
  • LOHC (N-ethylcarbazole): 1.93
  • Li-ion battery: 0.2 (approx., Depending on the type)

Based on the volume (in kWh / l):

  • Hydrogen gas (normal pressure): 0.003
  • Hydrogen gas (20 MPa / 200 bar): 0.53
  • Hydrogen gas (70 MPa / 700 bar): 1.855
  • Hydrogen storage with perhydro-N-ethylcarbazole: 2.0
  • Hydrogen (liquid, −253 ° C): 2.36
  • Natural gas (20 MPa): 2.58
  • Gasoline: 8.2-8.6
  • Diesel: 9.7
  • LOHC (N-ethyl carbazole): 1.89
  • Li-ion battery: 0.25-0.675

See also

Web links

Commons : Hydrogen Storage  - Album with pictures, videos and audio files

References and comments

  1. ↑ Out and about in the hydrogen 7 Series. In: heise online , November 22, 2006, accessed on February 8, 2012
  2. ↑ Opel relies on hydrogen (as of April 6, 2011) ( Memento from February 22, 2012 in the Internet Archive )
  3. ↑ a b Peter Kurzweil, Otto K. Dietl Meier: Electrochemical storage . 2nd Edition. Springer Fachmedien, Wiesbaden 2018, ISBN 978-3-658-21828-7 , 8.2 Hydrogen storage.
  4. ↑ a b Source no longer available: Requirements for plastics for high pressure hydrogen tanks  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (Source: Adam Opel GmbH, as of June 30, 2002)@1@ 2Template: Toter Link / www.h2bz-hessen.de  
  5. ↑ a b High-performance hydrogen tank receives TÜV certificate ( Memento from June 26, 2012 in the Internet Archive ) (Source: Motor-Talk, as of June 30, 2002)
  6. ↑ a b Ulf Bossel: Hydrogen does not solve any energy problems. In: Technology Assessment - Theory and Practice. Karlsruhe Institute of Technology, April 1, 2006, accessed on February 3, 2019 .
  7. ↑ nano report from the HGW shipyard of submarines with fuel cell propulsion from metal hydride storage ( Memento from December 8, 2007 in the Internet Archive )
  8. ↑ Renate Hoer: Brimming with hydrogen. Gesellschaft Deutscher Chemiker, press release from September 29, 2011 from Informationsdienst Wissenschaft (idw-online.de), accessed on September 15, 2015.
  9. ↑ K. Müller, W. Arlt: Status and Development in Hydrogen Transport and Storage for Energy Applications , Energy Technology, 2013, 1, 9, 501-511, doi: 10.1002 / ente.201300055
  10. ↑ P. Adametz, K. Müller, W. Arlt: Efficiency of low-temperature adsorptive hydrogen storage systems , International Journal of Hydrogen Energy, 2014, 39, 28, 15604–15613, doi: 10.1016 / j.ijhydene.2014.07.157
  11. ↑ P. Adametz, K. Müller, W. Arlt: Energetic evaluation of adsorptive hydrogen storage , Chemie Ingenieur Technik, 2014, 86, 9, 1427, doi: 10.1002 / cite.201450249
  12. ^ J. Weitkamp , M. Fritz, S. Ernst: Zeolites as media for hydrogen storage , International Journal of Hydrogen Energy, 1995, 20, 12, 967-970, doi: 10.1016 / 0360-3199 (95) 00058-L
  13. ↑ AC Dillon, MJ Heben: Hydrogen storage using carbon adsorbents: past, present and future , Applied Physics A, 2001, 72, 2, 133-142, doi: 10.1007 / s003390100788
  14. ↑ C. Liu, Y. Chen, C.-Z. Wu, S.-T. Xu, H.-M. Cheng: Hydrogen storage in carbon nanotubes revisited , Carbon, 2010, 48, 2, 452–455, doi: 10.1016 / j.carbon.2009.09.060
  15. ↑ SH Lim, J. Luo, Z. Zhong, W. Ji, J. Li: Room-Temperature Hydrogen Uptake by TiO 2 - Nanotubes , Inorganic Chemistry, 2005, 44, 12, 4124-4126, doi: 10.1021 / ic0501723
  16. ↑ G. Mpourmpakis, G. Froudakis, GP Lithoxoos, J. Samios: SiC Nanotubes: A Novel Material for Hydrogen Storage , Nano Letters, 2006, 6, 8, 1581–1583, doi: 10.1021 / nl0603911
  17. ^ Daniel Teichmann, Wolfgang Arlt, Peter Wasserscheid and Raymond Freymann: A future energy supply based on Liquid Organic Hydrogen Carriers (LOHC). Energy Environ. Sci., 2011, 4, 2767-2773, July 8, 2011; doi: 10.1039 / C1EE01454D .
  18. ↑ Source: Chiyoda press release as of February 10, 2014
  19. ↑ Carbazole electric gasoline raises hope. ( Memento from July 5, 2011 in the Internet Archive ) In: Automobil Produktion , as of June 30, 2011
  20. ↑ VDI-Nachrichten, April 14, 2014: Transporting and storing hydrogen safely , accessed May 15, 2019
  21. ↑ Fuel cell: hydrogen in diesel form , report in Die Zeit dated May 31, 2019
  22. ↑ The Toyota FCHV-adv. ( Memento from August 10, 2009 in the Internet Archive ) In: Toyota.de
  23. ↑ Toyota optimizes fuel cell vehicles.  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. In: atzonline.de , June 16, 2008@1@ 2Template: Dead Link / www.atzonline.de  
  24. ↑ Japanese Ministry of the Environment leases FCHV-adv. ( Memento from September 16, 2009 in the Internet Archive ) In: auto.de , September 1, 2008
  25. ↑ Volkswagen Research: World premiere of the VW high-temperature fuel cell. In: innovations-report.de , November 1, 2006
  26. ↑ Opel HydroGen4 proves suitability for everyday use. In: auto.de , May 14, 2009
  27. ↑ Mercedes' new fuel cell bus. In: heise.de , November 17, 2009
  28. ^ Hydrogen. ( Memento of March 2, 2010 in the Internet Archive ) In: statoil.com , September 23, 2008
  29. ^ Hydrogen Refueling. ( Memento from September 16, 2008 in the Internet Archive ) In: quantum-technologies.com
  30. ↑ Spectacular test shows: Hydrogen in the car doesn't have to be more dangerous than gasoline. In: Wissenschaft.de. February 3, 2003, accessed September 8, 2019 .
  31. ↑ Safety aspects when using hydrogen. ( Memento from March 6, 2012 in the Internet Archive ) In: Hycar.de
  32. ↑ Video: University of Miami crash test
  33. ↑ BTE-Nachrichten 01/2007, Dr. Henry Portz: Combustible binary gas or vapor mixtures - an underestimated risk of explosion
  34. ↑ Energy content in comparison. In: Hydox.de , accessed March 11, 2012
  35. ↑ Wolfgang Arlt: Carbazol: The electric gasoline? ( Memento of March 30, 2012 in the Internet Archive ), Elektor , June 30, 2011.
  36. ↑ a b c d What is the calorific value of fuels? In: aral.de , accessed on March 11, 2012
  37. ↑ a b Benjamin Müller, Karsten Müller, Daniel Teichmann, Wolfgang Arlt: Energy storage using methane and energy-carrying substances - a thermodynamic comparison. Chemical Engineer Technology, 2011, 83, 2002–2013; doi: 10.1002 / cite.201100113 .

Remarks

  1. ↑ a b The mass-related energy content fluctuates depending on the composition and is almost the same for gasoline and diesel because of their different densities
  2. ↑ a b The volume-related energy contents fluctuate quite strongly depending on the temperature (ARAL: 15 ° C) and the mixing ratios of the components