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Liquid hydrogen

Liquid hydrogen
Names
IUPAC name
Hydrogen
Systematic IUPAC name
Liquid hydrogen
Other names
Hydrogen (cryogenic liquid), Refrigerated hydrogen; LH2, para-hydrogen
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
KEGG
RTECS number
  • MW8900000
UNII
UN number 1966
  • InChI=1S/H2/h1H checkY
    Key: UFHFLCQGNIYNRP-UHFFFAOYSA-N checkY
  • InChI=1/H2/h1H
  • [H][H]
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]
GHS02: FlammableGHS04: Compressed Gas
Danger
H220, H280
P210, P377, P381, P403
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard CRYO: Cryogenic
3
4
0
CRYO
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).
checkY verify (what is checkY☒N ?)

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]

  1. ^ Thermophysical Properties of Hydrogen, nist.gov, accessed 2012-09-14
  2. ^ a b c d Information specific to liquid hydrogen Archived 2009-07-17 at the Wayback Machine, harvard.edu, accessed 2009-06-12
  3. ^ GHS: GESTIS 007010
  4. ^ "We've Got (Rocket) Chemistry, Part 1". NASA Blog. 15 April 2016. Retrieved 3 October 2021.
  5. ^ a b IPTS-1968, iupac.org, accessed 2020-01-01
  6. ^ "Liquid Hydrogen Delivery". Energy.gov. Retrieved 2022-07-30.
  7. ^ 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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