NATURAL GAS LIQUIDS (NGL)

Natural gas liquids (condensable hydrocarbons) are those hydrocarbons heavier than methane that are recovered from natural gas. The amount of NGL depends mainly on the percentage of the heavier hydrocarbons present in the gas and on the efficiency of the process used to recover them. (A high percentage is normally expected from associated gas.)  Natural gas liquids are normally fractionated to separate them into three streams:

1. An ethane-rich stream, which is used for producing ethylene.

2. Liquefied petroleum gas (LPG), which is a propane-butane mixture.

It is mainly used as a fuel or a chemical feedstock. Liquefied petroleum gas is evolving into an important feedstock for olefin production. It has been predicted that the world (LPG) market for chemicals will grow from 23.1 million tons consumed in 1988 to 36.0 million tons by the year 2000.

3. Natural gasoline (NG) is mainly constituted of C5+ hydrocarbons and is added to gasoline to raise its vapor pressure. Natural gasoline is usually sold according to its vapor pressure.

Natural gas liquids may contain significant amounts of cyclohexane, a precursor for nylon6. Recovery of cyclohexane from NGL by conventional distillation is difficult and not economical because heptane isomers are also present which boil at temperatures nearly identical to that of cyclohexane. An extractive distillation process has been recently developed by Phillips Petroleum Co. to separate cyclohexane.