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Liquid hydrogen
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| Names | |||
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| IUPAC name
Hydrogen
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| Systematic IUPAC name
Liquid hydrogen | |||
| Other names
Hydrogen (cryogenic liquid), Refrigerated hydrogen; LH2, para-hydrogen
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| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
| ChemSpider | |||
| KEGG | |||
PubChem CID
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| RTECS number |
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| UNII | |||
| UN number | 1966 | ||
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| Properties | |||
| H2(l) | |||
| Molar mass | 2.016 g·mol−1 | ||
| Appearance | Colorless liquid | ||
| Density | 0.07085 g/cm3 (4.423 lb/cu ft)[1] | ||
| Melting point | −259.14 °C (−434.45 °F; 14.01 K)[2] | ||
| Boiling point | −252.87 °C (−423.17 °F; 20.28 K)[2] | ||
| Hazards | |||
| GHS labelling:[3] | |||
 
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| Danger | |||
| H220, H280 | |||
| P210, P377, P381, P403 | |||
| NFPA 704 (fire diamond) | |||
| 571 °C (1,060 °F; 844 K)[2] | |||
| Explosive limits | LEL 4.0%; UEL 74.2% (in air)[2] | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Liquid hydrogen (H2(l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.[4]
To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F).[5] A common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage. Storing it as liquid takes less space than storing it as a gas at normal temperature and pressure. However, the liquid density is very low compared to other common fuels. Once liquefied, it can be maintained as a liquid for some time in thermally insulated containers.[6]
There are two spin isomers of hydrogen; whereas room temperature hydrogen is mostly orthohydrogen, liquid hydrogen consists of 99.79% parahydrogen and 0.21% orthohydrogen.[5]
Hydrogen requires a theoretical minimum of 3.3 kWh/kg (12 MJ/kg) to liquefy, and 3.9 kWh/kg (14 MJ/kg) including converting the hydrogen to the para isomer, but practically generally takes 10–13 kWh/kg (36–47 MJ/kg) compared to a 33 kWh/kg (119 MJ/kg) heating value of hydrogen.[7]
- ^ Thermophysical Properties of Hydrogen, nist.gov, accessed 2012-09-14
- ^ a b c d Information specific to liquid hydrogen Archived 2009-07-17 at the Wayback Machine, harvard.edu, accessed 2009-06-12
- ^ GHS: GESTIS 007010
- ^ "We've Got (Rocket) Chemistry, Part 1". NASA Blog. 15 April 2016. Retrieved 3 October 2021.
- ^ a b IPTS-1968, iupac.org, accessed 2020-01-01
- ^ "Liquid Hydrogen Delivery". Energy.gov. Retrieved 2022-07-30.
- ^ Gardiner, Monterey (2009-10-26). DOE Hydrogen and Fuel Cells Program Record: Energy requirements for hydrogen gas compression and liquefaction as related to vehicle storage needs (PDF) (Report). United States Department of Energy.
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