Natural gas liquids
From Wikimarcellus
Natural gas liquids (aka NGLs) are hydrocarbons such as propane, ethane, butane, and pentanes that are mingled with methane in wet gas areas of the Marcellus shale such as southwestern Pennsylvania and northern West Virginia. These must be separated from the methane before it can be transported by gas pipelines. Wet gas, or condensate, develops in lower pressure areas of the Marcellus play. "Dry gas" occurs in higher pressure areas that tend to be more mountainous.
A type number such as “(C2)” next to each NGL denotes how many carbon atoms a molecule the NGL contains. The name and type number can be used interchangeably; for example, Ethane and C2, Propane and C3., etc.)
Ethane (C2) – heavily used as a feedstock to produce ethylene.
Propane (C3) – heating and petrochemical applications.
Butane (C4) – industrial and residential uses. It's often blended with propane to produce liquid petroleum gas (LPG)
Pentanes or Natural gasoline (C5-C9) – used as a fuel additive and blended with regular gasoline as well as a petrochemical feedstock.
Condensates (C10+) - equivalent to crude oil and has many of the same end markets.
NGLs can be separated from methane in a cryogenic processing plant.