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Hydrocarbon gas liquids explained  

What are hydrocarbon gas liquids?

Natural gas and crude oil are mixtures of different hydrocarbons. Hydrocarbons are molecules of carbon and hydrogen in various combinations. Hydrocarbon gas liquids (HGL) are hydrocarbons that occur as gases at atmospheric pressure and as liquids under higher pressures. HGLs can also be liquefied by cooling. The specific pressures and temperatures at which the gases liquefy vary by type of HGL. HGLs may be described as being light or heavy according to the number of carbon atoms and hydrogen atoms in an HGL molecule.

HGLs are categorized chemically as:

  • Alkanes, or paraffins
    • Ethane—C2H6
    • Propane—C3H8
    • Butanes: normal butane and isobutane—C4H10
    • Natural gasoline or pentanes plus—C5H12 and heavier
  • Alkenes, or olefins
    • Ethylene—C2H44
    • Propylene—C3H6
    • Normal butylene and isobutylene—C4H8

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Propane and butane were discovered in 1912 by Dr. Walter Snelling, a U.S. scientist. He identified these gases in gasoline, and he found that cooling and pressuring these gases changed them to liquid. He also learned that the liquefied gases could be stored and transported in pressurized containers.

Hydrocarbon gas liquids are from natural gas and crude oil

HGLs are found in raw natural gas and crude oil. HGLs are extracted from natural gas at natural gas processing plants and from crude oil when it is refined into petroleum products. Natural gas plant liquids, which account for most HGL production in the United States, fall solely into the alkanes category. Refinery production accounts for the remainder of U.S. alkanes production, and it accounts for all olefins production data the U.S. Energy Information Administration (EIA) publishes. Greater volumes of olefins are produced at petrochemical plants from HGL and heavier feedstock. EIA does not collect or report petrochemical production data.

Hydrocarbon gas liquids have many uses

Because HGLs straddle the gas/liquid boundary, their versatility and high energy density in liquid form make them useful for many purposes:

  • Feedstock in petrochemical plants to make chemicals, plastics, and synthetic rubber
  • Fuels for heating, cooking, and drying
  • Fuels for transportation
  • Additives for motor gasoline production
  • Diluent (a diluting or thinning agent) for transporting heavy crude oil

In 2022, total HGL consumption accounted for about 17% of total U.S. petroleum consumption.

Image of sources, production, and types of hydrocarbon gas liquids

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HGLs were initially considered a nuisance, but they are now high-value products. Shortly before World War I, a problem in a natural gas pipeline occurred where a section of pipeline in a natural gas field ran under a cold stream. The low temperature caused liquids to form and sometimes block the flow of natural gas in the pipeline. As a result of this discovery, natural gas processing facilities were built to cool and compress natural gas, which separated the liquid form of hydrocarbon gas from the natural gas. The HGLs then became marketable commodities as fuels and as feedstock for making other petroleum products and petrochemicals.

Last updated: December 26, 2023.